STOK 10-K & 10-Q changes, risk factors and insider trading

An investment in our common stock involves various risks, and prospective investors are urged to carefully consider the matters discussed in thethis section titled “Risk Factors” prior to making an investment in our common stock. These risks include, but are not limited to, the following:

We are early in our development efforts. If we or our collaborators are unable to develop, obtain regulatory approval for and commercialize zorevunersen (STK-001), STK-002 and our future product candidates, or if we experience significant delays in doing so, our business will be materially harmed.

We may not be successful in our efforts to use our Targeted Augmentation of Nuclear Gene Output (“TANGO”) technology to expand our pipeline of product candidates and develop marketable products.

A Fast Track Designation by the FDA, even if granted for zorevunersen, STK-002 or any of our future product candidates,FDA or any use of the accelerated approval pathway, may not lead to a faster development or regulatory review or approval process, and would not increase the likelihood that zorevunersen, STK-002 or any of our future product candidates will receive marketing approval.

A Breakthrough Therapy Designation by the FDA, even if granted for zorevunersen, STK-002 or any of our future product candidatesFDA may not lead to a faster development or regulatory review or approval process, and it would not increase the likelihood that thezorevunersen, STK-002 or any of our future product candidates will receive marketing approval.

We are early in our development efforts. If we or our collaborators are unable to develop, obtain regulatory approval for and commercialize zorevunersen (STK-001), STK-002 and our future product candidates, or if we experience significant delays in doing so, our business will be materially harmed.

We have invested substantially all of our efforts and financial resources in the development of TANGO and our current lead product candidate, zorevunersen, for the treatment of Dravet syndrome. We submitted an investigational new drug application (“IND”) for zorevunersen to the FDA in late 2019. In August 2020, we dosed the first patient with zorevunersen in the single ascending dose portion of the MONARCH Phase 1/2a Study at the 10mg dose level, and in JanuaryAugust 2025 we announceddosed plansthe tofirst initiatepatient with zorevunersen in the EMPEROR Phase 3 study.

In addition, in November 2020, we announced the nomination of OPA1 as our next target for preclinical development to treat ADOA. In November 2021, we announced the nomination of STK-002 as the lead product candidate for the treatment of ADOA and intend to invest significant efforts and financial resources in its development. We submitted a Clinical Trial Authorization (“CTA”) application for STK-002 to the United Kingdom Medicines and Healthcare Products Regulatory Agency (the “MHRA”) in early 2023, and in February 2026 we dosed the MHRAfirst authorizedpatient suchwith CTASTK-002 in Aprilthe 2023,OSPREY butPhase enrollment1 and dosing of patients has not yet commenced.Study. Our ability to generate product revenue, which we do not expect will occur for many years, if ever, will depend heavily on the successful development and eventual commercialization of TANGO and our product candidates, which may never occur. We currently generate no revenue from sales of any product, and we may never be able to develop or commercialize a marketable product.

the direct and indirect impact of general economic, industry and market conditions, including fluctuating interest rates, inflation, market volatility, tariffs, potential recessions, a potential federal government shutdown, and any health pandemic on our business and operations, third party vendors, supply chain, and regulatory approvals;

Zorevunersen is currently being evaluated in human clinical trials, and we may experience unexpected or negative results in the future. We will be required to demonstrate through adequate and well-controlled clinical trials that our product candidates are safe and effective, with a favorable benefit-risk profile, for use in their target indications before we can seek regulatory approvals for their commercial sale. The positive results we have observed for our product candidates in preclinical animal models may not be predictive of our future clinical trials in humans, as mouse models carry inherent limitations relevant to all preclinical studies. In particular, the Dravet syndrome mouse model is more severe than the human disease and provides a shorter post-symptomatic observation period. Trial designs and results from early-phase trials are not necessarily predictive of future clinical trial designs or results, and initial positive results we may observe may not be confirmed in later-phase clinical trials. For example, although we reported end of study data from our Phase 1/2a open-label studies of zorevunersen demonstrating a reduction in median convulsive seizure frequency compared to baseline, these results were based on pooling data from the Phase 1/2a open-label studies of zorevunersen in the United States (MONARCH) and in the United Kingdom (ADMIRAL) and additional trialstrials, including the Phase 3 EMPEROR study, may not confirm these results. Our product candidates may also fail to show the desired safety and efficacy in later stages of clinical development even if they successfully advance through initial clinical trials, and preliminary interim data readouts of ongoing trials may show results that change when such trials are completed. We may not be able to demonstrate a disease-modifying effect of zorevunersen in our clinical trials in Dravet syndrome patients, even if we are able to demonstrate efficacy on seizure reduction, and we may be similarly unable to demonstrate the efficacy of STK-002 in our ADOA program or other future programs. In addition, our clinical trials to date have necessarily involved relatively small numbers of participants. Therefore, conclusions we draw based upon trial results to date may not be repeatable across larger cohorts of participants or patients with different characteristics. Moreover, even if our clinical trials demonstrate acceptable safety and efficacy of zorevunersen, STK-002 or our future product candidates, the labeling we obtain through negotiations with the FDA or foreign regulatory authorities may not include data on secondary endpoints and may not provide us with a competitive advantage over other products approved for the same or similar indications.

In addition, we, the FDA, foreign regulatory authorities, or an IRB or similar foreign review board or committee, may delay initiation of, suspend or limit dose escalation of clinical trials of a product candidate at any time for various reasons, including if we or they believe the healthy volunteer subjects or patients participating in such trials are being exposed to unacceptable health risks. Among other reasons, adverse side effects of a product candidate or a related product in preclinical trials or on healthy volunteer subjects or patients in a clinical trial could result in such a decision. For example, in November 2022, we announced our decision to limit chronic dosing in the open-label extensionOLE studies to 30mg in SWALLOWTAIL in the U.S. and 45mg in LONGWING in the U.K. Our decision at that time was based on interactions with regulatory agencies and a review of interim chronic toxicology data from a study in non-human primates (“NHPs”) in which the total drug administered to NHPs over a 1-year period was substantially higher than what we would anticipate giving to participants in clinical trials.

the facilities of third-party manufacturers with which we contract or procure certain serviceservices or raw materials may not be adequate to support approval of our product candidates;

Even if our product candidates meet their safety and efficacy endpoints in clinical trials, the regulatory authorities may not complete their review processes in a timely manner, or we may not be able to obtain regulatory approval. Additional delays may result if an FDA Advisory Committee or othera regulatory authority recommends non-approval or restrictions on approval. In addition, we may experience delays or rejections based upon additional government regulation from future legislation or administrative action, or changes in regulatory authority policy during the period of product development, clinical trials, a potential temporary federal government shutdown and the review process.

Further, in June 2024, the U.S. Supreme Court reversed its longstanding approach under the Chevron doctrine, which provided for judicial deference to regulatory agencies, including the FDA. AsIn athe result of this decision,future, we cannot be sure whether there will be increased challenges to existing agency regulations or how lower courts will apply the decision in the context of other regulatory schemes without more specific guidance from the U.S. Supreme Court. For example, this decision may result in more companies bringing lawsuits against the FDA to challenge longstanding decisions and policies of the FDA, which could undermine the FDA’s authority, lead to uncertainties in the industry, and disrupt the FDA’s normal operations, which could impact the timely review of any regulatory filings or applications we submit to the FDA.

We may not be successful in our efforts to use TANGO to expand our pipeline of product candidates and develop marketable products.

Because we have limited financial and managerial resources, we focus on research programs and product candidates that we identify for specific indications. Our business depends on our successful development and commercialization of the limited number of internal product candidates we are researching or have in preclinical development. Even if we are successful in continuing to build our pipeline, development of the potential product candidates that we identify will require substantial investment in additional clinical development, management of clinical, preclinical and manufacturing activities, regulatory approval in multiple jurisdictions, obtaining manufacturing supply capability, building a commercial organization, and significant marketing efforts before we generate any revenue from product sales. Furthermore, such product candidates may not be suitable for clinical development, including as a result of their harmful side effects, limited efficacy or other characteristics that indicate that they are unlikely to be products that will receive marketing approval and achieve market acceptance. If we cannot validate TANGOour approach to protein upregulation by successfully developing and commercializing product candidates based upon our technological approach, we may not be able to obtain product revenue in future periods, which would adversely affect our business, prospects, financial condition and results of operations.

In NovemberFebruary 2021,2026, we announceddosed the nominationfirst ofpatient with STK-002 asin ourthe leadOSPREY productPhase candidate1 Study for in the treatment of ADOA; however, we are primarily focused on our lead product candidate for Dravet syndrome, zorevunersen, and we may forego or delay pursuit of opportunities with other product candidates or for other indications that later prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. Our spending on current and future research and development programs and product candidates for specific indications may not yield any commercially viable products. Our understanding and evaluation of biological targets for the discovery and development of new product candidates may fail to identify challenges encountered in subsequent preclinical and clinical development. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through collaboration, licensing or other royalty arrangements in cases in which it would have been more advantageous for us to retain sole development and commercialization rights.

Under the Rare Pediatric Disease Priority Review Voucher program, upon the approval of a qualifying NDA for the treatment of a rare pediatric disease, the sponsor of such an application would be eligible for a rare pediatric disease priority review voucher that can be used to obtain priority review for a subsequent Biologics License Application or NDA. As part of our business strategy for zorevunersen, we received Rare Pediatric Disease Designation in October 2022. If the law is extended, weWe may also seek Rare Pediatric Disease designations for any other future product candidates. IfUnder the current sunset provisions, a product candidate is designated before December 20, 2024, it isnot eligible to receive a voucher if it is not approved before September 30, 2026.2029. However, there is no expectation that zorevunersen, STK-002 or our future product candidates will be designated, other than zorevunersen, or approved by those dates, or at all,designated or that theany programother product candidates will bebe, further extended,approved, and, therefore, we may not be in a position to obtain any priority review vouchers. Additionally, designation of a drug for a rare pediatric disease does not guarantee that an NDA will meet the eligibility criteria for a rare pediatric disease priority review voucher at the time the application is approved. Finally, a Rare Pediatric Disease Designation does not lead to faster development or regulatory review of the product or increase the likelihood that it will receive marketing approval.

A Fast Track Designation by the FDA, even if granted for zorevunersen, STK-002 or any of our future product candidates,FDA or any use of the accelerated approval pathway, may not lead to a faster development or regulatory review or approval process, and would not increase the likelihood that zorevunersen, STK-002 or our future product candidates will receive marketing approval.

We may also seek accelerated approval for our product candidates. Under the FDA’s accelerated approval program, the FDA may approve a drug for a serious or life-threatening illness that provides meaningful therapeutic benefit to patients over existing treatments based upon a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the availability or lack of alternative treatments. Full approval of another product for the same indication as any of our product candidates for which we are seeking accelerated approval may make accelerated approval of our product candidates more difficult. For drugs granted accelerated approval, post-marketing confirmatory trials are required to describe the anticipated effect on irreversible morbidity or mortality or other clinical benefit. These confirmatory trials must be completed with due diligence and in general the FDA may require that the trial be designed and/or initiated prior to approval. The Food and Drug Omnibus Reform Act (“FDORA”) was recently enacted, which included provisions related to the accelerated approval pathway. Pursuant to FDORA, the FDA is authorized to require a post-approval study to be underway prior to approval or within a specified time period following approval. FDORAThe FDA is also requires the FDArequired to specify conditions of any required post-approval study, which may include milestones and requires sponsors to submit progress reports for required post-approval studies and any conditions required by the FDA. FDORA enables theThe FDA tomay initiate enforcement action for the failure to conduct with due diligence a required post-approval study, including a failure to meet any required conditions specified by the FDA or to submit timely reports. All promotional materials for product candidates approved via accelerated approval are subject to prior review by the FDA. Moreover, the FDA may withdraw approval of any product candidate or indication approved under the accelerated approval pathway if, for example:

A Breakthrough Therapy Designation by the FDA, even if granted for zorevunersen, STK-002 or any of our future product candidates,FDA may not lead to a faster development or regulatory review or approval process, and it would not increase the likelihood that thezorevunersen, STK-002 or any of our future product candidates will receive marketing approval.

Healthcare reform initiatives culminated in the enactment of the Inflation Reduction Act (“IRA”) in August 2022, which, among other things, allowsrequires the U.S. Department of Health and Human Services (“HHS”) to directly negotiate the selling price of a statutorily specified number of drugs and biologics each year that the Centers for Medicare & Medicaid Services (“CMS”) reimburses under Medicare Part B and Part D. The negotiated price may not exceed a statutory ceiling price. Only high-expenditure single-source drugs that have been approved for at least 7 years (11 years for single-source biologics) are eligible be selected by CMS for negotiation, with the negotiated price taking effect two years after the selection year. For 2026, the first year in which negotiated prices become effective, CMS selected 10 high-cost Medicare Part D products in 2023, negotiations began in 2024, and the negotiated maximum fair price for each product has been announced. In addition, CMS has selected and announced the negotiated maximum fair price for 15 additional Medicare Part D drugs forwhich negotiatedwill maximumbecome fair pricingeffective in 2027. For 2028, CMS selected an additional 15 drugs,drugs whichcomprised mayof bedrugs covered under eitherMedicare Part D and, for the first time, drugs payable under Medicare Part BB. or Part D, will be selected, and forFor 2029 and subsequent years, 20 Part B or Part D drugs will be selected. AThe negotiated prices will represent a significant discount from average prices to wholesalers and direct purchasers. Currently, a drug or biological product that has an orphan drug designation for only one rare disease or condition will be excluded from the IRA’s price negotiation requirements, but will lose that exclusion if it receives designations for more than one rare disease or condition, or if is approved for an indication that is not within that single designated rare disease or condition, unless such additional designation or such disqualifying approvals are withdrawn by the time CMS evaluates the drug for selection for negotiation. TheHowever, as a result of a statutory amendment enacted in July 2025, beginning with the 2028 negotiated pricesprice willapplicability representyear, a significantdrug discountmay be designated for more than one rare disease or condition and still be excluded from averageprice pricesnegotiation, toas wholesalerslong andas directthe purchasers.only approved indications are for such rare diseases or conditions. The law also imposes rebates on Medicare Part D and Part B drugs whose prices have increased at a rate greater than the rate of inflation, and in November 2024, CMS finalized regulations pertaining to these inflation rebates. In addition, the law eliminates the “donut hole” under Medicare Part D beginning in 2025 by significantly lowering the beneficiary maximum out-of-pocket cost through a newly established manufacturer discount program which requires manufacturers, in order for their brand drugs to be reimbursed, to subsidize 10% of Part D enrollees’ prescription costs for brand drugs below the out-of-pocket limit, and 20% once the out-of-pocket limit has been reached. The IRA also extends enhanced subsidies for individuals purchasing health insurance coverage in ACA marketplaces through plan year 2025. The IRA permits the Secretary of HHS to implement many of these provisions through guidance, as opposed to regulation, for the initial years. Manufacturers that fail to comply with the IRA may be subject to various penalties, including civil monetary penalties. These provisions may be subject to legal challenges. For example, the provisions related to the negotiation of selling prices of high-expenditure single-source drugs and biologics have been challenged in multiple lawsuits brought by pharmaceutical manufacturers. Thus, while it is unclear how the IRA will be implemented, it will likely have a significant impact on the pharmaceutical industry.

In addition, other legislative changes have been proposed and adopted. These changes have included statutory aggregate reductions of Medicare payments to providers. More recently, in November 2024, CMS issued a final rule that decreased Medicare reimbursement for physician services by 2.8%, effective January 1, 2025. In July 2025, Congress enacted legislation providing for a one-time 2.5% increase to physician payment rates from January 1, 2026 through December 31, 2026, but this increase does not retroactively adjust payments to compensate for the 2025 payment cut. In January 2013, the American Taxpayer Relief Act of 2012 was signed into law, which, among other things, increased the statute of limitations period for the government to recover overpayments to providers from three to five years. Other laws or regulations may result in additional reductions in Medicare and other healthcare funding, which could have a material adverse effect on customers for our drugs, if approved, and accordingly, our financial operations. Additionally, on May 30, 2018, the Trickett Wendler, Frank Mongiello, Jordan McLinn, and Matthew Bellina Right to Try Act of 2017 was signed into law. The law, among other things, provides a federal framework for certain patients to access certain investigational new drug products that have completed a Phase 1 clinical trial and that are undergoing investigation for FDA approval. Under certain circumstances, eligible patients can seek treatment without enrolling in clinical trials and without obtaining FDA authorization under an FDA expanded access program; however, manufacturers are not obligated to provide investigational new drug products under the current federal right to try law. We may choose to seek an expanded access program for our product candidates, or to utilize comparable rules in other countries that allow the use of a drug, on a named patient basis or under a compassionate use program.

Furthermore, there have been, and continue to be, a number of other initiatives at the United States federal and state levels that seek to reduce healthcare costs. For example, in December 2020, CMS issued a final rule implementing significant manufacturer price reporting changes under the Medicaid Drug Rebate Program, including an alternative rebate calculation for line extensions that is tied to the price increases of the original drug, and Best Price reporting related to certain value-based purchasing arrangements. Additionally, under the American Rescue Plan Act of 2021 eliminated the statutory cap on Medicaid Drug Rebate Program rebates that manufacturers pay to state Medicaid programs on a unit of drug was eliminated.drug. Elimination of this cap may,has, in some cases, requirerequired pharmaceutical manufacturers to pay more in rebates than they receive on the sale of products. Further, the Infrastructure Investment and Jobs Act added a requirement, effective January 1, 2023, for manufacturers of certain single-source drugs separately paid for under Medicare Part B for at least 18 months and marketed in single-dose containers or packages (known as refundable single-dose containers or single-use package drugs) to provide annual refunds for any portions of the dispensed drug that are unused and discarded if those unused or discarded portions exceed an applicable percentage defined by statute or regulation. Manufacturers are subject to periodic audits and those that fail to pay refunds for their refundable single-dose containers or single-use package drugs shall be subject to civil monetary penalties. Healthcare reforms that have been adopted, and that may be adopted in the future, could result in further reductions in coverage and levels of reimbursement for pharmaceutical products, increases in rebates payable under U.S. government rebate programs and additional downward pressure on pharmaceutical product prices.

At the state level in the United States, legislatures are increasingly enacting laws and implementing regulations designed to control pharmaceutical and biologic product pricing, including price constraints, restrictions on certain product access, reporting on price increases and the introduction of high-cost drugs.drugs, and, in some cases, designed to encourage importation from other countries and bulk purchasing. For example, the FDA released a final rule in September 2020 providing guidance for states to build and submit importation plans for certain prescription drugs from Canada into the United States, and the FDA authorized the first such plan in Florida in January 2024. This plan has been granted extensions until May 6, 2026. It is unclear how this program will be implemented, if at all, including which drugs will be chosen, and whether it will be subject to legal challenges in the United States or Canada.

Moreover, increasing efforts by governmental and third-party payors, in the United States and internationally, to cap or reduce healthcare costs may cause such organizations to limit both coverage and level of reimbursement for new products approved and, as a result, they may not cover or provide adequate payment for our product candidates. We expect to experience pricing pressures in connection with the sale of any of our product candidates due to the trend toward managed healthcare, the increasing influence of certain third-party payors, such as health maintenance organizations, and additional legislative changes. The downward pressure on healthcare costs in general, particularly prescription drugs and surgical procedures and other treatments, has become very intense. As a result, increasingly high barriers are being erected to the entry of new products into the healthcare market. Recently there have been instances in which third-party payors have refused to reimburse treatments for patients for whom the treatment is indicated in the FDA-approved product label. Furthermore, the legislation commonly referred to as the “One Big Beautiful Bill Act”) (the “OBBBA”) was recently signed into law in the U.S., which reduces funding to federal healthcare programs and imposes additional requirements to be eligible for healthcare, which may result in decreased access to healthcare, particularly for Medicaid programs. Even if we are successful in obtaining FDA approvals to commercialize our product candidates, we cannot guarantee that we will be able to secure reimbursement for all patients for whom treatment with our product candidates is indicated.

Numerous treatments for epilepsy exist, including 5-HT agonists, such as UCB’s Fintepla, cannabidiols, such as Jazz Pharmaceuticals’ Epidiolex, GABA receptor agonists, such as clobazam and stiripentol, and glutamate blockers, which is one of the mechanisms of action of topiramate. In addition, numerous compounds are in clinical development for treatment of epilepsy. We believe the clinical development pipeline includes cannabinoids, 5-HT release stimulants, cholesterol 24-hydroxylase inhibitors, potassium channel openers, and sodium channel agonists from a variety of companies. In addition to competition from these small molecule drugs, any products we may develop may also face competition from other types of therapies, such as gene therapy, gene editing, tRNA therapies, modified mRNA therapies or other ASO approaches. For example, one company (Encoded Therapeutics) has initiated astarted clinical developmenttesting planof its program for a gene regulation therapy in Dravet syndrome that may address the underlying genetic cause of the disease.

Although there are no approved treatments for ADOA at this time, we may also face potential competition in our ADOA program. For example, one company (PYC Therapeutics) has announcedinitiated a clinicaldose developmentescalation planstudy for an RNA-based therapy in ADOA.

We currently have a limited marketing organization in the U.S., and we do not yet have anany organization for the sales,sales marketing andor distribution of zorevunersen, STK-002 andor our future product candidates and the cost of establishing and maintaining such an organization may exceed the cost-effectiveness of doing so.candidates. To market any products that may be approved, we must build our sales, marketing, managerial and other non-technical capabilities or make arrangements with third parties to perform these services. With respect to certain of our current programs as well as future programs, we may rely completely on an alliance partner for sales and marketing. In addition, although we intend to establish a sales organization if we are able to obtain approval to market any product candidates, we have entered into a strategic alliance with Biogen to develop and commercialize zorevunersen,zorevunersen outside of North America (the U.S., Canada and Mexico), and we may enter into strategic alliances with third parties, such as Acadia Pharmaceuticals, to develop and commercialize STK-002 and other future product candidates, including in markets outside of the United States or for other large markets that are beyond our resources. This will reduce the revenue generated from the sales of these products.

We have entered into a collaborationcollaborations with Acadia Pharmaceuticals and Biogen and may, in the future, seek to enter into collaborations with other third parties for the discovery, development and commercialization of our product candidates. If our collaborators cease development efforts under our collaboration agreements, or if any of those agreements are terminated, these collaborations may fail to lead to commercial products and we may never receive milestone payments or future royalties under these agreements.

We may derive a significant portion of our future revenue from these agreements or other similar agreements into which we may enter in the future. Revenue from research and development collaborations depends upon continuation of the collaborations, payments for research and development services and resulting options to acquire any licenses of successful product candidates, and the achievement of milestones, contingent payments and royalties, if any, derived from future products developed from our research.

We have incurred net losses in each year since our inception. We incurred net losses of $89.0$6.9 million and $104.7$89.0 million, for the years ended December 31, 2024and2025 2023,and 2024, respectively. As of December 31, 2024,2025, we had accumulated deficitsdeficit of $490.8$497.7 million. Substantially all of our operating losses have resulted from costs incurred in connection with our research and development programs and from sales, general and administrative costs associated with our operations. We expect to continue to incur significant expenses and operating losses over the next several years and for the foreseeable future as we intend to continue to conduct research and development, clinical testing, regulatory compliance activities, manufacturing activities, and, if any of our product candidates is approved, sales and marketing activities that, together with anticipated sales, general and administrative expenses, will likely result in us incurring significant losses for the foreseeable future. Our prior losses, combined with expected future losses, have had and will continue to have an adverse effect on our stockholders’ equity and working capital.

We will require substantial future capital in order to complete planned and future preclinical and clinical development for zorevunersen, STK-002 and other future product candidates, if any, and potentially commercialize these product candidates. Based upon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of $246.7approximately $390.9 million as of December 31, 2024, which, along with the $165 million upfront payment received in March 2025 and other eligible cash flows from the Biogen collaboration, we anticipate2025, will fund operations tointo mid-2028.2028. We expect our spending levels to increase in connection with our preclinical studies and clinical trials of our product candidates. In addition, if we obtain marketing approval for any of our product candidates, we expect to incur significant expenses related to commercial launch, product sales, medical affairs, marketing, manufacturing and distribution. Furthermore, we incur significant costs associated with operating as a public company. Accordingly, we will need to obtain substantial additional funding in connection with our continuing operations. If we are unable to raise capital when needed or on attractive terms, we would be forced to delay, reduce or eliminate certain of our licensing activities, our research and development programs or other operations.

In December 2017, U.S. federal tax legislation, commonly referred to as the Tax Cuts and Jobs Act (the “TCJA”) was signed into law, significantly reforming the Code.IRC The TCJA, among other things, includes changes to U.S. federal tax rates, imposes significant additional limitations on the deductibility of business interest, allows for the expensing of capital expenditures, puts into effect the migration from a “worldwide” system of taxation to a partial “territorial” system, and modifies or repeals many business deductions and credits. BeginningFor inour 2022,2022 through 2024 tax years, the TCJA also eliminated the option to immediately deduct research and development expenditures and required taxpayers to amortize domestic expenditures over five years and foreign expenditures over fifteen years. Beginning with our 2025 tax year, the OBBBA restored immediate deductibility of domestic expenditures, while foreign expenditures will continue to be capitalized and amortized over fifteen years.

We continuehave toexamined examineand incorporated into our financial results the impactimpacts the TCJA and OBBBA may have on our business. The TCJA isand aOBBBA are far-reaching and complex revisionrevisions to the U.S. federal income tax laws with disparate and, in some cases, countervailing impacts on different categories of taxpayers and industries, and will require subsequent rulemaking and interpretation in a number of areas. The long-term impact of the TCJA and OBBBA on the overall economy, the industries in which we operate and our and our partners’ businesses cannot be reliably predicted at this early stage of the new law’s implementation. There can be no assurance that the TCJA and OBBBA will not negatively impact our operating results, financial condition, and future business operations. The estimated impact of the TCJA and OBBBA is based on our management’s current knowledge and assumptions, following consultation with our tax advisors.

Because of our valuation allowance in the U.S., ongoing tax effects of the TCJA and OBBBA are not expected to materially change our effective tax rate in future periods.

Our commercial success will depend in large part on obtaining and maintaining patent, trademark, trade secret and other intellectual property protection of our proprietary technologies and product candidates, which include TANGO, zorevunersen, STK-002 and the additional gene targets identified by TANGO, their respective components, formulations, combination therapies, methods used to manufacture them and methods of treatment, as well as successfully defending our patents and other intellectual property rights against third-party challenges. Our ability to stop unauthorized third parties from making, using, selling, offering to sell, importing or otherwise commercializing our product candidates is dependent upon the extent to which we have rights under valid and enforceable patents or trade secrets that cover these activities. If we are unable to secure and maintain patent protection for any product or technology we develop, or if the scope of the patent protection secured is not sufficiently broad, our competitors could develop and commercialize products and technology similar or identical to ours, and our ability to commercialize any product candidates we may develop may be adversely affected. The patenting process is expensive and time-consuming, and we may not be able to file and prosecute all necessary or desirable patent applications at a reasonable cost or in a timely manner. In addition, we may not pursue or obtain patent protection in all relevant markets. It is also possible that we will fail to identify patentable aspects of our research and development output before it is too late to obtain patent protection. Moreover, in some circumstances, we may not have the right to control the preparation, filing and prosecution of patent applications, or to maintain the patents, covering technology that we license from or license to third parties and are reliant on our licensors or licensees to do so. For instance, pursuant to the AgreementBiogen with Biogen,Agreement, Biogen has certain rights to prepare, file, prosecute, and maintain certain patents and patent applications licensed to Biogen in the Biogen Territory. Our pending and future patent applications may not result in issued patents. Even if patent applications we license or own currently or in the future issue as patents, they may not issue in a form that will provide us with any meaningful protection, prevent competitors or other third parties from competing with us, or otherwise provide us with any competitive advantage. Any patents that we hold or in-license may be challenged, narrowed, circumvented, or invalidated by third parties. Consequently, we do not know whether any of our platform advances and product candidates will be protectable or remain protected by valid and enforceable patents. In addition, our existing patents and any future patents we obtain may not be sufficiently broad to prevent others from using our technology or from developing competing products and technologies.

In addition to patent protection, we rely upon know-how and trade secret protection, as well as non-disclosure agreements and invention assignment agreements with our employees, consultants and third-parties,third parties, to protect our confidential and proprietary information, especially where we do not believe patent protection is appropriate or obtainable.

It is our policy to require our employees, consultants, outside scientific collaborators, sponsored researchers and other advisors to execute confidentiality agreements upon the commencement of employment or consulting relationships with us. These agreements provide that all confidential information concerning our business or financial affairs developed or made known to the individual or entity during the course of the party’s relationship with us is to be kept confidential and not disclosed to third parties, except in certain specified circumstances. In the case of employees, the agreements provide that all inventions conceived by the individual, and that are related to our current or planned business or research and development or made during normal working hours, on our premises or using our equipment or proprietary information, are our exclusive property. In the case of consultants and other third parties, the agreements provide that all inventions conceived in connection with the services provided are our exclusive property. However, we cannot guarantee that we have entered into such agreements with each party that may have or have had access to our trade secrets or proprietary technology and processes. We have also adopted policies and conduct trainingtrainings that providesprovide guidance on our expectations, and our advice for best practices, in protecting our trade secrets. Despite these efforts, any of these parties may breach the agreements and disclose our proprietary information, including our trade secrets, and we may not be able to obtain adequate remedies for such breaches.

To succeed, we must recruit, retain, manage and motivate qualified clinical, scientific, technical and management personnel, and we face significant competition for experienced personnel. If we do not succeed in attracting and retaining qualified personnel, particularly at the management level, it could adversely affect our ability to execute our business plan, harm our results of operations and increase our capabilities to successfully commercialize zorevunersen, STK-002 and our future product candidates. In particular, we believe that our future success is highly dependent upon the contributions of our senior managementmanagement, including Ian F. Smith, our Chief Executive Officer, as well as our senior scientists and other members of our management team. The loss of services of one or more of these individuals, who all have at-will employment arrangements with us, could delay or prevent the successful development of our product pipeline, completion of our planned clinical trials or the commercialization of our product candidates, if approved. The competition for qualified personnel in the biotechnology field is intense and as a result, we may be unable to continue to attract and retain qualified personnel necessary for the development of our business or to recruit suitable replacement personnel.

Our results of operations could be adversely affected by general conditions in the global economy and in the global financial markets. For example, the global financial crisis of 2008 caused extreme volatility and disruptions in the capital and credit markets. Similarly, the global economy has been impacted by fluctuating interest rates, inflation and actual and threatened tariffs, as well as the possibility of a recession or further economic downturn. Moreover, adverse developments that affect financial institutions, such as events involving liquidity that are rumored or actual, have in the past and may in the future lead to market-wide liquidity problems. For example, on March 10, 2023, Silicon Valley Bank (“SVB”), one of our banking partners, was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation (the “FDIC”) as receiver. While we only had a minimal amount of our cash directly at SVB and, since that date, the FDIC has stated that all depositors of SVB will be made whole, there is no guarantee that the federal government would guarantee all depositors in the event of future bank closures, and continued instability in the banking system may adversely impact our business and financial condition. Likewise, the capital and credit markets may be adversely affected by the ongoing conflicts in IsraelIsrael, Ukraine and Ukraine,Venezuela, and the possibility of a wider Middle Eastern, European or global conflict, global sanctions imposed in response thereto, an energy crisis and potential recessions. A weak or declining economy and actual or threatened tariffs could also strain our suppliers, possibly resulting in supply disruption, or cause our customers to delay making payments for our services. If the current equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult, more costly, and more dilutive. Failure to secure any necessary financing in a timely manner and on favorable terms could have a material adverse effect on our growth strategy, financial performance and stock price and could require us to delay or abandon clinical development plans. In addition, there is a risk that one or more of our current service providers, manufacturers and other partners may not survive such difficult economic times, which could directly affect our ability to attain our operating goals on schedule and on budget. Also, hospitals and other medical facilitates face staffing shortages, whether due to labor relations or otherwise, which could potentially cause delays in enrollment, site visits, evaluations or other activities important to our research and development efforts. Any of the foregoing could harm our business and we cannot anticipate all of the ways in which the current economic climate and financial market conditions could adversely impact our business. Furthermore, our stock price may decline due in part to the volatility of the stock market and any general economic downturn.

terrorist acts, acts of war or periods of widespread civil unrest, including the conflictconflicts in UkraineUkraine, Israel and Venezuela and actions taken by third parties in response to such conflict;

We are a “smaller reporting company,” meaning that our annual revenue is less than $100.0 million during the last completed fiscal year or the market value of our stock held by non-affiliates was less than $700.0 million and our annual revenue was less than $100.0 million as of the last business dayend of our most recently completedthat fiscal year.year’s second fiscal quarter. We maywill continue to be a smaller reporting company as long as either (i)until the marketfirst valuequarter of our2027. stock held by non-affiliates is less than $250.0 million or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and the market value of our stock held by non-affiliates is less than $700.0 million. In addition, asAs a smaller reporting company we may choose to present only the two most recent fiscal years of audited financial statements in our Annual Report on Form 10-K and smaller reporting companies have reduced disclosure obligations regarding executive compensation. We cannot predict if investors will find our common stock less attractive because we may rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stock and our share price may be more volatile.

We previously were not required to independently comply with Section 404(a) of the Sarbanes-Oxley Act. Section 404(a) of the Sarbanes-Oxley Act requires annual management assessments of the effectiveness of our internal control over financial reporting, starting with the second annual report that we file with the SEC. We were required to meet these standards in the course of preparing our financial statements as of and for the year ended December 31, 2024,2025, and our management iswas required to report on the effectiveness of our internal control over financial reporting for such year and has been annually thereafter. Additionally, once we are no longer a “smaller reporting company,” our independent registered public accounting firm will be required pursuant to Section 404(b) of the Sarbanes-Oxley Act to attest to the effectiveness of our internal control over financial reporting on an annual basis. The rules governing the standards that must be met for our management to assess our internal control over financial reporting are complex and require significant documentation, testing, and possible remediation.

We are a late-stage clinical-stageclinical company dedicated to addressing the underlying causes of severe diseases by upregulating protein expression with RNA-based medicines. Using our proprietary TANGO (Targeted Augmentation of Nuclear Gene Output) approach, we are developing antisense oligonucleotides (“ASOs”) to selectively restore protein levels.

Our first compound,investigational new medicine in development, zorevunersen (STK-001), is a potential disease modifying medicine that is in late-stage clinical testing for the treatment of Dravet syndrome, a severe and progressive genetic epilepsy.syndrome. Dravet syndrome is characterized by frequent, prolonged and refractory seizures beginning within the first year of life. The disease is classified as a developmental and epileptic encephalopathy (DEE) due to the developmental delays and cognitive impairment associated with it. Dravet syndrome is one of many diseases caused by a haploinsufficiency, in which a loss of approximately 50% of normal protein levels leads to disease. We have completed two Phase 1/2a open-label studies of zorevunersen, MONARCH in the United States and ADMIRAL in the United Kingdom, and we have announced plans to initiate the EMPEROR Phase 3 study of zorevunersen in the second quarter of 2025. We also have two ongoing Open Label Extension (“OLE”) studies of zorevunersen for children and adolescents with Dravet syndrome, SWALLOWTAIL in the U.S. and LONGWING in the United Kingdom. Patients who participated in the MONARCH study in the United States or the ADMIRAL study in the United Kingdom and met study entry criteria were eligible to continue treatment in SWALLOWTAIL or LONGWING, respectively, both of which are designed to evaluate the long-term safety and tolerability of repeat doses of zorevunersen.

WeIn addition to our Dravet program, we are also pursuing treatment for a second haploinsufficient disease, autosomal dominant optic atrophy (“ADOA”), the most common inherited optic nerve disorder.disorder for which there are currently no approved treatments. STK-002 is our lead clinical candidate for the treatment of ADOA. STK-002 is designed to upregulate OPA1 protein expression by leveraging the non-mutant (wild-type) copy of the OPA1 gene to restore OPA1 protein expression with the aim to stop or slow vision loss in patients with ADOA. In a non-human primate (NHP) model of ADOA conducted in collaboration with UC Davis, treatment with STK-002 was well tolerated and helped protect, and possibly improve, eye health. The data suggest that STK-002 may help preserve the function of important vision-related nerve cells, which could potentially improve or maintain vision. We have received authorization in the United KingdomUK to proceed with a Phase 1 open-label study (OSPREY) of children and adults ages 6 to 55 who have an established diagnosis of ADOA and have evidence of a genetic mutation in the OPA1 gene. However,In February 2026, we havedosed alsothe identifiedfirst additionalpatient importantwith pre-clinicalSTK-002 activitiesin tothe supportOSPREY ourPhase understanding1 of dosingstudy for the Phase 1 OSPREY study and other OPA1 indications as we seek to optimize our clinical plans and better understand the potential for targeting OPA1 beyond ADOA. We anticipate that these data, along with further research on the commercial opportunity, will provide a more complete picturetreatment of the opportunity and support for the clinical studies prior to initiating the Phase 1 OSPREY study.ADOA.

In terms of our liquidity and capital resources, in May 2022, we filed a universal Shelf Registration statement on Form S-3 (the “2022 Registration Statement”) with the SEC. The 2022 Registration Statement was declared effective by the SEC on May 31, 2022, and containscontained two prospectuses: a base prospectus, which coverscovered the offering, issuance and sale by us of up to a maximum aggregate offering price of $400.0 million of our common stock, preferred stock, debt securities, warrants to purchase common stock, preferred stock or debt securities, subscription rights to purchase common stock, preferred stock or debt securities and/or units consisting of some or all of these securities; and a sales agreement prospectus covering the offering, issuance and sale by us of up to a maximum aggregate offering price of $150.0 million of common stock that may be issued and sold under a Controlled Equity Offering Sales Agreement (the “Sales Agreement”).

On April 2, 2024, we completed an underwritten public offering, pursuant to the 2022 Registration Statement, of 5,555,557 shares of common stock at a public offering price of $13.50 per share and issued pre-funded warrants to purchase 3,703,730 shares of common stock at a public offering price of $13.499 per share subject to an exercise price equal to $0.0001. The common stock and pre-funded warrants sold resulted in net proceeds of approximately $119.9 million after deducting underwriting discounts, commissions and offering costs. No pre-funded warrants have been exercised as of December 31, 2024.2025.

In OctoberJuly 2024,2025, we filed an automatica universal Shelf Registration statementStatement on Form S-3 (the “20242025 Registration Statement”) with the SEC. The 20242025 Registration Statement was declared effective by the SEC on July 11, 2025, and contains two prospectuses: a base prospectus, which covers the offering, issuance and sale by us of itsup to a maximum aggregate offering price of $400.0 million of our common stock, preferred stock, debt securities, warrants to purchase common stock, preferred stock or debt securities, subscription rights to purchase common stock, preferred stock or debt securities and/or units consisting of some or all of these securities; and a sales agreement prospectus covering the offering, issuance and sale by us of up to a maximum aggregate offering price of $150.0 million of common stock that may be issued and sold under the Sales Agreement. The specific terms of any securities to be offered pursuant to the base prospectus will be specified in a prospectus supplement to the base prospectus.

As of December 31, 2024,2025, we had issued approximately 7.0 million shares of common stock pursuant to the Sales Agreement for net proceeds of $61.0 million pursuant to the 2022 Registration Statement. As of December 31, 2024,2025, we had not issued orapproximately sold3.2 anymillion shares of common stock pursuant to the 20242025 Registration Statement.Statement for net proceeds of $87.8 million. We may terminate this at-the-market program under the Sales Agreement at any time, pursuant to its terms.

Since inception, we have had operating losses, the majority of which are attributable to research and development activities. Our net losses were $89.0$6.9 million and $104.7$89.0 million for the years months ended December 31, 20242025 and 2023,2024, respectively. As of December 31, 2024,2025, we had an accumulated deficit of $490.8$497.7 million.

Our primary use of cash is to fund operating expenses, which consist primarily of research and development expenditures,activities, andincluding tomedical aaffairs, lesseras extent,well as sales, general and administrative expenditures.expenses, including commercial operations. Cash used to fund operating expenses is impacted by the timing of when we pay these expenses, as reflected in the change in our outstanding accounts payable and accrued expenses. We expect to continue to incur net losses for the foreseeable future, and we expect our research and development expenses, sales, general and administrative expenses, and capital expendituresexpenses will continue to increase. In particular, we expect our expenses and losses to increase as we continue our development of, and seek regulatory approvals for, our product candidates, and begin to commercialize any approved products, as well as hire additional personnel, develop commercial infrastructure, pay fees to outside consultants, lawyers and accountants, and incur increased costs associated with being a public company such as expenses related to services associated with maintaining compliance with Nasdaq listing rules and SEC requirements, insurance and investor relations costs.products. Our net losses may fluctuate significantly from quarter-to-quarter and year-to-year, depending on the timing of our clinical trials and our expenditures on other research and development activities.

Based upon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of $246.7approximately $390.9 million as of December 31, 2024, which, along with the $165 million upfront payment received in March 2025 and other eligible cash flows from the Biogen collaboration, we anticipate2025, will fund operations tointo mid-2028.2028. To date, we have not had any products approved for sale and have not generated any product sales. We do not expect to generate any revenues from product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates, which we expect will take a number of years.candidates. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution. As a result, until such time, if ever, as we can generate substantial product revenue, we expect to finance our cash needs through equity offerings, debt financings or other capital sources, including potentially collaborations, licenses and other similar arrangements. However, we may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all. Any failure to raise capital as and when needed could have a negative impact on our financial condition and on our ability to pursue our business plans and strategies. If we are unable to raise capital, we will need to delay, reduce or terminate planned activities to reduce costs.

In January 2022, we entered into a licenseLicense and collaborationCollaboration agreementAgreement (the “Acadia Agreement”) with Acadia Pharmaceuticals Inc. (“Acadia”) for the discovery, development and commercialization of novel RNA-based medicines for the treatment of severe and rare genetic neurodevelopmental diseases of the central nervous system (the “CNS”).system. The agreementAcadia focusesAgreement focused on the targets SYNGAP1, MECP2 (Rett syndrome), and an undisclosed neurodevelopmental target of mutual interest. In connection with each target, we willagreed to collaborate with Acadia to identify potential treatments for further development and commercialization as licensed products. With respect to SYNGAP1, we haveagreed with Acadia to co-develop and co-commercialize licensed products for such target globally, and in connection therewith we granted to Acadia worldwide, co-exclusive (with us) licenses for such licensed products. With respect to SYNGAP1, we agreed with Acadia to co-develop and co-commercialize licensed products for such target globally, and in connection therewith we granted to Acadia worldwide, co-exclusive (with us) licenses for such licensed products. With respect to MECP2 and the neurodevelopmental target, we granted to Acadia worldwide, exclusive licenses to develop and commercialize licensed products for such targets. Effective as of September 3, 2025, Acadia terminated the MECP2 and the undisclosed neurodevelopmental programs under the Acadia Agreement (the “Discontinued Acadia Programs”) and rights to these targets returned to us. The collaboration with Acadia with respect to SYNGAP1 remains ongoing.

Pursuant to the terms of the agreement,Acadia Agreement, we received an upfront payment of $60.0 million from Acadia. Acadia agreed to fund the research to identify potential licensed products for MECP2 and the neurodevelopmentalDiscontinued target,Acadia Programs, and we will equally fund with Acadia the research to identify potential licensed products for SYNGAP1. We are eligible to receive up to $907.5$245.0 million in potential total milestone payments based upon the achievement of certain development, regulatory, first commercial sales and sales milestone events across the programs for the threeSYNGAP1 targets,program, assuming each milestone were achieved at least once. With respect to licensed products for MECP2 and the neurodevelopmental target, we are also eligible to receive tiered royalties at percentages ranging from the mid-single digits to the mid-teens on future net sales by Acadia of licensed products worldwide. Royalties payable under the agreement are subject to standard royalty reductions. For SYNGAP1 licensed products that we are co-developing and co-commercializing, we will be responsible for 50% of the development and commercialization costs and will receive 50% of the profits from global commercialization. We are provided with a co-development and co-commercialization opt out option relating to the SYNGAP1 target indication at our discretion. Such opt-out would reduce development and commercialization milestones but would provide us with royalties on an escalating basis attributable to net sales milestones. As a result of the termination of the Discontinued Acadia Programs, we are no longer eligible to receive the milestones for those programs of up to $662.5 million or any royalties related thereto.

For the year ended, December 31, 2024,2025, we recognized revenue related to the AcadiaBiogen collaboration of $36.6$168.3 million; andthere forwas the year ended, December 31, 2023, we recognizedno revenue prior to 2025 related to the AcadiaBiogen collaboration of $8.8 million.collaboration.

See Note 8—License and Collaboration Agreement with Acadia Pharmaceuticals, Inc.Agreements of the notes to our consolidated financial statements included elsewhere in this Annual Report on Form 10-K.

laboratory equipment and supplies; and facilities costs, depreciation and other expenses related to internal research and development activities.

GeneralSales, general and administrative expenses

GeneralSales, general and administrative expenses consist primarily of personnel costs, costs related to maintenance and filing of intellectual property, expenses for outside professional services, including legal, human resources, information technology, audit and accounting services, and facilities and other expenses. Personnel costs consist of salaries, benefits and stock-based compensation expense. We expect our sales, general and administrative expenses to increase over the next several years to support our continued research and development activities, manufacturing activities, increased costs of operating as a public company and the potential commercialization of our product candidates. These increases are anticipated to include increased costs related to the hiring of additional personnel, developing commercial infrastructure, fees to outside consultants, lawyers and accountants, and costs associated with being a public company such as expenses related to services associated with maintaining compliance with Nasdaq listing rules and SEC requirements, insurance and investor relations costs.

The increase in research and development expenses werewas driven primarily attributableby toa an increase of $4.7$33.8 million in personnel costs resulting from annual compensation increases and increases in stock-based compensation expense, $2.9 millionincrease in expenses related to our zorevunersen program, which is comprisedconsisted of third-partythird‑party services and scientific consulting fees, $13.8 million increase in personnel‑related costs, a $1.8 million increase in external third‑party expenses related to non–program-specific expenses and $1.1 million in facilities and other research and development costs, and an increase of $0.7 million in external third-party expenses related to SYNGAP1 and MECP2, both of which consisted of third‑party services and scientific consulting fees. These increases were partially offset by a decrease of $2.2$0.7 million decrease in expenses related to our STK-002ADOA program, which is comprised of third-party servicesprogram and scientifica consulting$1.0 feesmillion decrease in facilities and $0.3other millionnon–program-related of non-project specific consulting and third-party services. The increase in expenses reflects the accelerating pace of research and development activities and the increases in personnel needed to support those activities.expenses.

GeneralSales, general and administrative expenses

GeneralSales, general and administrative expenses were $67.1 million for the year ended December 31, 2025 as compared to $48.8 million for the year ended December 31, 2024 as compared to $41.3 million for the year ended December 31, 2023,2024, an increase of $7.5$18.3 million.

The increases in sales, general and administrative expenses werewas primarily attributable to an increase of $4.4$7.4 million in personnel‑related costs, including increases in stock-based compensation expense, from increases in headcount and the annual options awardawarded and an increase of $3.1$10.9 million in third-party services to support our in-house personnel in various aspects of developing and supporting the business including commercialization efforts, human resources, information technology, audit, tax, public relations, communications and other sales, general and administrative activities.

Since our inception through December 31, 2024,2025, our operations have been financed by net proceeds of $671.6$926.6 million from the sale of convertible notes payable and our convertible preferred stock, our initial public offering, follow-on offering, proceeds from the controlled equity offering sales agreements and the upfront paymentpayments from Acadia.Acadia and Biogen. As of December 31, 2024,2025, we had $246.7$390.9 million in cash, cash equivalents and marketable securities. Cash in excess of immediate requirements is invested in accordance with our investment policy, primarily with a view to liquidity and capital preservation.

We have incurred losses since our inception in June 2014 and, as of December 31, 2024 and 2023, we had accumulated deficits of $490.8 million and $401.8 million, respectively. Our primary use of cash is to fund operating expenses, which consist primarily of research and development expenditures,activities, andincluding tomedical aaffairs, lesseras extent,well as sales, general and administrative expenditures.expenses, including commercial operations. Cash used to fund operating expenses is impacted by the timing of when we pay these expenses, as reflected in the change in our outstanding accounts payable and accrued expenses.

Our product candidates may never achieve commercialization and we anticipate that we will continue to incur losses for the foreseeable future. We expect that our research and development expenses, sales, general and administrative expenses, and capital expenditures will continue to increase. As a result, until such time, if ever, as we can generate substantial product revenue, we expect to finance our cash needs through a combination of equity offerings, debt financings orand other capital sources, including potentially collaborations, licenses and other similar arrangements. Our primary uses of capital are, and we expect will continue to be, compensation and related expenses, third-party clinical research and development services, costs relating to the build-out of our headquarters and manufacturing facility, license payments or milestone obligations that may arise, laboratory and related supplies, clinical costs, manufacturing costs, legal and other regulatory expenses and general overhead costs.

Based upon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of $246.7approximately $390.9 million as of December 31, 2024, which, along with the $165 million upfront payment received in March 2025 and other eligible cash flows from the Biogen collaboration, we anticipate2025, will fund operations tointo mid-2028.2028. We have based this estimate on assumptions that may prove to be wrong, and we could utilize our available capital resources sooner than we currently expect. We will continue to require additional financing to advance our current product candidates through clinical development, to develop, acquire or in-license other potential product candidates and to fund operations for the foreseeable future. We will continue to seek funds through equity offerings, debt financings or other capital sources, including potentially collaborations, licenses and other similar arrangements. However, we may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all. Our ability to raise additional funds may be adversely impacted by potential worsening global macroeconomic conditions, including inflation, changing interest rates and instability in the global banking system, tariffs, and disruptions to and volatility in the credit and financial markets in the United States and worldwide. If we do raise additional capital through public or private equity offerings, the ownership interest of our existing stockholders will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect our stockholders’ rights. If we raise additional capital through debt financing, we may be subject to covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends. Any failure to raise capital as and when needed could have a negative impact on our financial condition and on our ability to pursue our business plans and strategies. If we are unable to raise capital, we will need to delay, reduce or terminate planned activities to reduce costs.

Our financing activities during year ended December 31, 20232025 consisted of $0.4$8.6 million from the exercise of stock options, $0.6$1.0 million in proceeds from our Employee Stock Purchase Plan and $52.1$87.8 million of net proceeds from the controlledSales equity offering sales agreements.Agreement.

In September 2021, we entered into an agreement to extend the initial term of the 23,000 square foot lease for a period of three years ending December 31, 2024.years. In addition, this agreement provides for the lease of an additional 15,000 square feet of rentable space beginning on April 1, 2022 and ending on December 31, 2024.2022. Initial monthly lease payments are approximately $0.1 million with respect to the 23,000 square feet space, and $0.1 million with respect to the 15,000 square feet space, and in each case subject to annual rent escalations.

Our management’s discussion and analysis of our financial condition and results of operations is based on our consolidated financial statements, which have been prepared in accordance with generally accepted accounting principles,principles or GAAP.(“GAAP”). The preparation of these consolidated financial statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, as well as the reported expenses incurred during the reporting periods. Our estimates are based on our historical experience and on various other factors that we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions. We believe that the accounting policies discussed below are critical to understanding our historical and future performance, as these policies relate to the more significant areas involving management’s judgments and estimates.

WeFor revenue arrangements accounted for under ASC 606, we recognize revenue in accordance with Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”). This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, and financial instruments. Under ASC 606, an entity recognizes revenue when itsa customer obtains control of promised goods or services, in an amount that reflects the consideration thatwhich the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue recognitionto be recognized for arrangements thatdetermined anto entity determines arebe within the scope of ASC 606, thewe entity performsperform the following five-stepfive analysissteps: (i) identifyidentification the contract(s) with a customer; (ii) identify the performance obligations inof the contract; (ii) determination of whether the promised goods or services are performance obligations; (iii) determinemeasurement of the transaction priceprice, including evaluating the constraint on variable consideration; (iv) allocateallocation of the transaction price to the performance obligations in the contract; and (v) recognizerecognition of revenue when (or as) thewe entitysatisfy satisfies aeach performance obligation. We only apply the five-step analysismodel to contractsall whencontracts, itincluding istransactions probablewith that the entity will collect the consideration to which it is entitled in exchange for the goodscollaborators or servicespartners, itif transfersthey toare the customer. As part of the accounting for these arrangements, we must use significant judgment to determine: (a) the number of performance obligations based on the determination under step (ii) above; (b) the transaction price under step (iii) above; and (c) the timing of satisfaction of performance obligations aswith a measure of progress in step (v) above.customer.

We have invested substantially all of our efforts and financial resources in the development of our proprietary protein upregulation platform and our current lead product candidate, zorevunersen, for the treatment of Dravet syndrome. We submitted an investigational new drug application (“IND”) for zorevunersen to the FDA in late 2019. In August 2020, we dosed the first patient with zorevunersen in the single ascending dose portion of the MONARCH Phase 1/2a Study at the 10mg dose level,Study, and in August 2025 we dosed the first patient with zorevunersen in the EMPEROR Phase 3 study.

In addition, in November 2020, we announced the nomination of OPA1 as our next target for preclinical development to treat ADOA. In November 2021, we announced the nomination of STK-002 as the lead product candidate for the treatment of ADOA and intend to invest significant efforts and financial resources in its development. We submitted a Clinical Trial Authorization (“CTA”) application for STK-002 to the United Kingdom Medicines and Healthcare Products Regulatory Agency (the “MHRA”) in early 2023, and in February 2026 we dosed the first patient with STK-002 in the OSPREY Phase 1 Study. Our ability to generate any future product revenue will depend heavily on the successful development and eventual commercialization of our product candidates, which may never occur. We currently generate no revenue from sales of any product, and we may never be able to develop or commercialize a marketable product.

effectiveour INDsability to obtain IND and CTAsCTA approvals that allow commencement of our planned clinical trials or future clinical trials for our product candidates in relevant territories;

potential delays in enrollment, site visits, evaluations, or dosing of patients participating in clinical trials as hospitals face staffing shortages, whether due to labor relations or otherwise, or patients decide not to enroll in the study as a result of such staffing shortages;

the direct and indirect impact ofconducive general economic, industry and market conditions, including fluctuating interest rates, inflation, market volatility, tariffs, potential recessions, a potential federal government shutdown,volatility and any health pandemic on our business and operations, third party vendors, supply chain, and regulatory approvalstariffs;

Zorevunersen is currently being evaluated in human clinical trials, and we may experience unexpected or negative results in the future. We will be required to demonstrate through adequate and well-controlled clinical trials that our product candidates are safe and effective, with a favorable benefit-risk profile, for use in their target indications before we can seek regulatory approvals for their commercial sale. The positive results we have observed for our product candidates in preclinical animal models may not be predictive of our current or future clinical trials in humans, as mouse models carry inherent limitations relevant to all preclinical studies. In particular, the Dravet syndrome mouse model is more severe than the human disease and provides a shorter post-symptomatic observation period. Trial designs and results from early-phase trials are not necessarily predictive of future clinical trial designs or results, and initial positive results we may observe may not be confirmed in later-phase clinical trials. For example, although we reported end of study data from our Phase 1/2a open-label studies of zorevunersen demonstrating a reduction in median convulsive seizure frequency compared to baseline, these results were based on pooling data from the Phase 1/2a open-label studies of zorevunersen in the United States (MONARCH) and in the United Kingdom (ADMIRAL) and additional trials, including the Phase 3 EMPEROR study, may not confirm these results. Our product candidates may also fail to show the desired safety and efficacy in later stages of clinical development even if they successfully advance through initial clinical trials, and preliminary interim data readouts of ongoing trials may show results that change when such trials are completed. We may not be able to demonstrate a disease-modifying effect of zorevunersen in our clinical trials in Dravet syndrome patients, even if we are able to demonstrate efficacy on seizure reduction, and we may be similarly unable to demonstrate the efficacy of STK-002 in our ADOA program or other future programs. In addition, our clinical trials to date have necessarily involved relatively small numbers of participants. Therefore, conclusions we draw based upon trial results to date may not be repeatable across larger cohorts of participants or patients with different characteristics. Moreover, even if our clinical trials demonstrate acceptable safety and efficacy of zorevunersen, STK-002 or our future product candidates, the labeling we obtain through negotiations with the FDA or foreign regulatory authorities may not include data on secondary endpoints and may not provide us with a competitive advantage over other products approved for the same or similar indications.

Many companies in the biotechnology industry have suffered significant setbacks in late-stage clinical trials after achieving positive results in early-stage development and there is a high failure rate for product candidates proceeding through clinical trials. We cannot be certain that we will not face similar setbacks. In addition, different methodologies, assumptions and applications we utilize to assess particular safety or efficacy parameters may yield different statistical results. Even if we believe the data collected from clinical trials of our product candidates are promising, these data may not be sufficient to support approval by the FDA or foreign regulatory authorities. Preclinical and clinical data can be interpreted in different ways. Accordingly, the FDA or foreign regulatory authorities could interpret these data in different ways from us or our partners, which could delay, limit or prevent regulatory approval. If our study data do not consistently or sufficiently demonstrate the safety or efficacy of any of our product candidates, including zorevunersen for Dravet syndrome or STK-002 for ADOA, then the regulatory approvals for such product candidates could be significantly delayed as we work to meet approval requirements, or, if we are not able to meet these requirements, such approvals could be withheld or withdrawn. Regulatory delays or rejections may be encountered as a result of many factors, including changes in regulatory policy during the period of product development. We cannot be certain that we will not face similar setbacks.

the approval policies or regulations of the FDA or comparable foreign regulatory authorities may significantly change in a manner rendering our clinical data insufficient for approval; and potential delays in enrollment, site visits, evaluations, or dosing of patients participating in the clinical trial as hospitals face staffing shortages, whether due to labor relations or otherwise, or patients decide to not enroll in the study as a result of or such staffing shortages.study.

Under the Rare Pediatric Disease Priority Review Voucher program, upon the approval of a qualifying NDA for the treatment of a rare pediatric disease, the sponsor of such an application would be eligible for a rare pediatric disease priority review voucher that can be used to obtain priority review for a subsequent Biologics License Application or NDA. As part of our business strategy for zorevunersen, we received Rare Pediatric Disease Designation in October 2022. We may also seek Rare Pediatric Disease designations for any other future product candidates. Under the current sunset provisions, a product candidate is not eligible to receive a voucher if it is not approved before September 30, 2029. However, there iscan be no expectationassurance that STK-002 or ourany other future product candidates will be designated or that any other product candidates will be, approved, and, therefore, we may not be in a position to obtain any priority review vouchers. Additionally, designation of a drug for a rare pediatric disease does not guarantee that an NDA will meet the eligibility criteria for a rare pediatric disease priority review voucher at the time the application is approved. Finally, a Rare Pediatric Disease Designation does not lead to faster development or regulatory review of the product or increase the likelihood that it will receive marketing approval.

Healthcare reform initiatives culminated in the enactment of the Inflation Reduction Act (“IRA”) in August 2022, which, among other things, requires the U.S. Department of Health and Human Services (“HHS”) to directly negotiate the selling price of a statutorily specified number of drugs and biologics each year that the Centers for Medicare & Medicaid Services (“CMS”) reimburses under Medicare Part B and Part D. The negotiated price may not exceed a statutory ceiling price. Only high-expenditure single-source drugs that have been approved for at least 7 years (11 years for single-source biologics) are eligible to be selected by CMS for negotiation, with the negotiated price taking effect two years after the selection year. For 2026, the first year in which negotiated prices become effective, CMS selected 10 high-cost Medicare Part D products in 2023, negotiations began in 2024, and the negotiated maximum fair price for each product has been announced. In addition, CMS has selected and announced the negotiated maximum fair price for 15 additional Medicare Part D drugs which will become effective in 2027. For 2028, CMS selected an additional 15 drugs comprised of drugs covered under Medicare Part D and, for the first time, drugs payable under Medicare Part B. For 2029 and subsequent years, 20 Part B or Part D drugs will be selected. The negotiated prices will represent a significant discount from average prices to wholesalers and direct purchasers. Currently, a drug or biological product that has an orphan drug designation for only one rare disease or condition will be excluded from the IRA’s price negotiation requirements, but will lose that exclusion if it receives designations for more than one rare disease or condition, or if it is approved for an indication that is not within that single designated rare disease or condition, unless such additional designation or such disqualifying approvals are withdrawn by the time CMS evaluates the drug for selection for negotiation. However, as a result of a statutory amendment enacted in July 2025, beginning with the 2028 negotiated price applicability year, a drug may be designated for more than one rare disease or condition and still be excluded from price negotiation, as long as the only approved indications are for such rare diseases or conditions. The law also imposes rebates on Medicare Part D and Part B drugs whose prices have increased at a rate greater than the rate of inflation, and in November 2024, CMS finalized regulations pertaining to these inflation rebates. In addition, the law eliminates the “donut hole” under Medicare Part D beginning in 2025 by significantly lowering the beneficiary maximum out-of-pocket cost through a newly established manufacturer discount program which requires manufacturers, in order for their brand drugs to be reimbursed, to subsidize 10% of Part D enrollees’ prescription costs for brand drugs below the out-of-pocket limit, and 20% once the out-of-pocket limit has been reached. The IRA permits the Secretary of HHS to implement many of these provisions through guidance, as opposed to regulation, for the initial years. Manufacturers that fail to comply with the IRA may be subject to various penalties, including civil monetary penalties. These provisions may be subject to legal challenges. For example, the provisions related to the negotiation of selling prices of high-expenditure single-source drugs and biologics have been challenged in multiple lawsuits brought by pharmaceutical manufacturers. Thus, while it is unclear how the IRA will be implemented, it will likely have a significant impact on the pharmaceutical industry.

In addition, in May 2025, the administration published an executive order regarding most favored nation (“MFN”) drug pricing, which is sometimes referred to as international reference pricing. This executive order directs the Secretary of HHS to communicate MFN price targets to pharmaceutical manufacturers, and if significant progress towards MFN pricing is not delivered, to propose a rulemaking plan to implement MFN pricing. Recently, onOn December 23, 2025, CMS issued proposed regulations to establish, under the Center for Medicare and Medicaid Innovation, two mandatory MFN demonstration models under Medicare Parts B and D, respectively. If these rules or other MFN pricing rules are finalized, they are likely to mandate reduced prices of at least some drugs in the United States, if they are also sold in comparator countries.

At the state level in the United States, legislatures are increasingly enacting laws and implementing regulations designed to control pharmaceutical and biologic product pricing, including price constraints, restrictions on certain product access, reporting on price increases and the introduction of high-cost drugs, and, in some cases, designed to encourage importation from other countries and bulk purchasing. For example, the FDA released a final rule in September 2020 providing guidance for states to build and submit importation plans for certain prescription drugs from Canada into the United States, and the FDA authorized the first such plan in Florida in January 2024. This plan has beenwas granted extensions until May 6, 2026. It is unclear how this program will be implemented, if at all, including which drugs will be chosen, and whether it will be subject to legal challenges in the United States or Canada.

Regulatory authorities in some jurisdictions, including the United States and Europe, may designate drugs intended to treat relatively small patient populations as orphan drugs. Under the Orphan Drug Act, the FDA may designate a drug as an orphan drug if it is intended to treat a rare disease or condition, which is defined as a patient population of fewer than 200,000 individuals in the United States. In the United States, Orphan Drug Designation entitles a party to financial incentives such as opportunities for tax credits for qualified clinical research costs and exemption from prescription drug user fees. Similarly, in the EU, the European Commission grants Orphan Drug Designation after receiving the opinion of the EMA’s Committee for Orphan Medicinal Products on an Orphan Drug Designation application. In the EU, Orphan Drug Designation is intended to promote the development of drugdrugs that are intended for the diagnosis, prevention or treatment of life-threatening or chronically debilitating conditions affecting not more than five in 10,000 persons in the EU and for which no satisfactory method of diagnosis, prevention or treatment has been authorized (or the product would be a significant benefit to those affected). In the EU, Orphan Drug Designation entitles a party to financial incentives such as reduction of fees or fee waivers.

FDA-regulated industries, such as ours, face uncertainty with regard to the regulatory environment we will face under the current administration as we proceed with research and development and potential future commercialization. Some of these efforts have manifested to date as efforts to reduce the size of the federal government, including large-scale reductions in force at FDA. The loss of key personnel at FDA, including those in leadership positions, is likely to impact operations at FDA, which could result in, among other things, delays or limitations on our ability to obtain guidance from FDA on our product candidates in development, longer review times, and delays in obtaining regulatory approvals for our product candidates. Moreover, the current administration has recently proposed action to freeze or reduce the budget of the National Institutes of Health (the “NIH”) as related to its funding for medical research, which could decrease the ability of facilities that rely on NIH funding to enroll and conduct clinical trials or increase the costs to us of conducting clinical trials. There remains general uncertainty around future activities. New executive orders, regulations, policies or guidance could be issued or promulgated that adversely affects us or creates a more challenging or costly environment to pursue the development of new therapeutic products. Alternatively, state governments may attempt to address or react to changes at the federal level with changes to their own regulatory frameworks in a manner that is adverse to our operations. If we become negatively impacted by future government orders, regulations, policies or guidance, there could be a material adverse effect on us and our businessbusiness.

Moreover, increasing efforts by governmental and third-party payors, in the United States and internationally, to cap or reduce healthcare costs may cause such organizations to limit both coverage and level of reimbursement for new products approved and, as a result, they may not cover or provide adequate payment for our product candidates. We expect to experience pricing pressures in connection with the sale of any of our product candidates due to the trend toward managed healthcare, the increasing influence of certain third-party payors, such as health maintenance organizations, and additional legislative changes. The downward pressure on healthcare costs in general, particularly prescription drugs and surgical procedures and other treatments, has become very intense. As a result, increasingly high barriers are being erected to the entry of new products into the healthcare market. Recently there have been instances in which third-party payors have refused to reimburse treatments for patients for whom the treatment is indicated in the FDA-approved product label. Furthermore, the legislation commonly referred to as the “One Big Beautiful Bill Act”) (the “OBBBA”) was recently signed into law in the U.S., which reduces funding to federal healthcare programs and imposes additional requirements to be eligible for healthcare, which may result in decreased access to healthcare, particularly for Medicaid programs. Even if we are successful in obtaining FDA approvals to commercialize our product candidates, we cannot guarantee that we will be able to secure reimbursement for all patients for whom treatment with our product candidates is indicated.

We have incurred net losses in each year since our inception. We incurredhad net losses of $50.0$61.6 million for the three months ended MarchJune 31,30, 2026 and net income of $112.9$23.5 million for the three months ended MarchJune 31,30, 2025. We had a net loss of $111.6 million for the six months ended June 30, 2026 and a net income of $89.4 million for the six months ended June 30, 2025. As of MarchJune 31,30, 2026, we had an accumulated deficitdeficits of $547.7$609.3 million. Substantially all of our operating losses have resulted from costs incurred in connection with our research and development programs and from sales, general and administrative costs associated with our operations. We expect to continue to incur significant expenses and operating losses over the next several years and for the foreseeable future as we intend to continue to conduct research and development, clinical testing, regulatory compliance activities, manufacturing activities, and, if any of our product candidates is approved, sales and marketing activities that, together with anticipated sales, general and administrative expenses, will likely result in us incurring significant losses for the foreseeable future. Our prior losses, combined with expected future losses, have had and will continue to have an adverse effect on our stockholders’ equity and working capital.

We will require substantial future capital in order to complete planned and future preclinical and clinical development for zorevunersen, STK-002 and other future product candidates, if any, and potentially commercialize these product candidates. Based uponon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of approximately $411.0$354.3 million as of MarchJune 31,30, 2026,2026 and additional proceeds from the ATM sale of $65.7 million, will fund operations intothrough to potential U.S. commercialization of zorevunersen in early 2028. We expect our spending levels to increase in connection with our preclinical studies and clinical trials of our product candidates. In addition, if we obtain marketing approval for any of our product candidates, we expect to incur significant expenses related to commercial launch, product sales, medical affairs, marketing, manufacturing and distribution. Furthermore, we incur significant costs associated with operating as a public company. Accordingly, we will need to obtain substantial additional funding in connection with our continuing operations. If we are unable to raise capital when needed or on attractive terms, we would be forced to delay, reduce or eliminate certain of our licensing activities, our research and development programs or other operations.

We depend on intellectual property licensed to us from third parties, and our licensors may not always act in our best interest. If we fail to comply with our obligations under our intellectual property licenses, if the licenses are terminated, or if disputes regarding these licenses arise, we could lose significant rights that are important to our business.

For example, we are a party to a license agreement with the University of Southampton, pursuant to which we in-license key patents and patent applications for our proprietary protein upregulation platform, zorevunersen, STK-002 and our future product candidates. For more information regarding the agreement, please see “BusinessNote 6—LicenseCommitments and researchcontingencies agreements.”of the notes to the condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q. The agreement imposes various diligence, milestone payment, royalty, insurance and other obligations on us. If we fail to comply with these obligations, our licensor may have the right to terminate our license, in which event we would not be able to develop or market our proprietary protein upregulation platform, zorevunersen, STK-002 or any other technology or product candidates covered by the intellectual property licensed under the agreement. In addition, we may need to obtain additional licenses from our existing licensor and others to advance our research or allow commercialization of product candidates we may develop. It is possible that we may be unable to obtain any additional licenses at a reasonable cost or on reasonable terms, if at all. In either event, we may be required to expend significant time and resources to redesign our technology, product candidates, or the methods for manufacturing them or to develop or license replacement technology, all of which may not be feasible on a technical or commercial basis. If we are unable to do so, we may be unable to develop or commercialize the affected technology or product candidates.

Furthermore, inventions contained within some of our existing or future in-licensed patents and patent applications may be made using U.S. government funding or other non-governmental funding. We rely on our existing or future licensors to ensure compliance with applicable obligations arising from such funding, such as timely reporting, an obligation associated with in-licensed patents and patent applications. The failure of our existing or future licensors to meet their obligations may lead to a loss of rights or the unenforceability of relevant patents. For example, the government could have certain rights in such in-licensed patents, including a non-exclusive license authorizing the government to use the invention or to have others use the invention on its behalf for non-commercial purposes. If the U.S. government then decides to exercise these rights, it is not required to engage us as its contractor in connection with doing so. These rights may also permit the government to exercise march-in rights to use or allow third parties to use the technology covered by such in-licensed patents. The government may also exercise its march-in rights if it determines that action is necessary because we or our licensors failed to achieve practical application of the government-funded technology, because action is necessary to alleviate health or safety needs, to meet requirements of federal regulations, or to give preference to U.S. industry. In addition, our rights in such in-licensed government-funded inventions may be subject to certain requirements to manufacture products embodying such inventions in the United States. Any of the foregoing could harm our business, financial condition, results of operations, and prospects significantly.

We dependalso onlicense intellectual property licensed to third parties, and our licensees may not always act in our best interest. If these third parties fail to comply with their obligations under their respective licenses with us, if these licenses are terminated, or if disputes regarding these licenses arise, we could lose significant revenue or rights that are important to our business.

Furthermore, because of the substantial amount of discovery required in connection with intellectual property litigation, there is a risk that some of our confidential information could be compromised by disclosure during this type of litigation. In addition, there could be public announcements of the results of hearings, motions or other interim proceedings or developments. If securities analysts or investors perceive these results to be negative, that perception could have a substantial adverse effect on the price of our common stock. Any of the foregoing could have a material adverse effect on our businessbusiness, financial condition, results of operations and prospects.

The licensing and acquisition of third-party intellectual property rights is a competitive area, and companies that may be more established or have greater resources than we do may also be pursuing strategies to license or acquire third-party intellectual property rights that we may consider necessary or attractive in order to commercialize our product candidates. More established companies may have a competitive advantage over us due to their size, cash resources and greater clinical development and commercialization capabilities. In addition, companies that perceive us to be a competitor may be unwilling to assign or license rights to us. There can be no assurance that we will be able to successfully complete these types of negotiations and ultimately acquire the rights to the intellectual property surrounding the additional product candidates that we may seek to develop or market. If we are unable to successfully obtain rights to required third-party intellectual property or to maintain the existing intellectual property rights we have, we may have to abandon development of certain programs and our businessbusiness, financial condition, results of operations and prospects could suffer.

Periodic maintenance fees on any issued patent are due to be paid to the USPTO and foreign patent agencies in several stages over the lifetime of the patent. The USPTO and various foreign patent agencies also require compliance with a number of procedural, documentary, fee payment and other provisions during the patent application process and following the issuance of a patent. While an inadvertent lapse can in many cases be cured by payment of a late fee or by other means in accordance with the applicable rules, there are situations in which noncompliance can result in abandonment or lapse of the patent or patent application, resulting in partial or complete loss of patent rights in the relevant jurisdiction. Noncompliance events that could result in abandonment or lapse of a patent or patent application include, but are not limited to, failure to respond to official actions within prescribed time limits, non-payment of fees and failure to properly legalize and submit formal documents. Were a noncompliance event to occur, our competitors might be able to enter the market, which would have a material adverse effect on our businessbusiness, financial condition, results of operations and prospects.

To succeed, we must recruit, retain, manage and motivate qualified clinical, scientific, technical and management personnel, and we face significant competition for experienced personnel. If we do not succeed in attracting and retaining qualified personnel, particularly at the management level, it could adversely affect our ability to execute our business plan, harm our results of operations and increaseimpair our capabilitiesability to successfully commercialize zorevunersen, STK-002 and our future product candidates. In particular, we believe that our future success is highly dependent upon the contributions of our senior management, including Ian F. Smith, our Chief Executive Officer, as well as our senior scientists and other members of our management team. The loss of services of one or more of these individuals, who all have at-will employment arrangements with us, could delay or prevent the successful development of our product pipeline, completion of our planned clinical trials or the commercialization of our product candidates, if approved. The competition for qualified personnel in the biotechnology field is intense and as a result, we may be unable to continue to attract and retain qualified personnel necessary for the development of our business or to recruit suitable replacement personnel.

Moreover, adverse developments that affect financial institutions, such as events involving liquidity that are rumored or actual, have in the past and may in the future lead to market-wide liquidity problems. For example, on March 10, 2023, Silicon Valley Bank (“SVB”), one of our banking partners, was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation (the “FDIC”) as receiver. While we only had a minimal amount of our cash directly at SVB and, since that date, the FDIC has stated that all depositors of SVB will be made whole, there is no guarantee that the federal government would guarantee all depositors in the event of future bank closures, and continued instability in the banking system may adversely impact our business and financial condition. Likewise, the capital and credit markets may be adversely affected by the ongoing conflicts in Israel, Ukraine, Venezuela and Iran, and the possibility of a wider Middle Eastern, European or global conflict, global sanctions imposed in response thereto, an energy crisis and potential recessions. Any further escalation or expansion of hostilities involving Iran, including retaliatory actions, heightened regional instability, disruption to transportation or logistics, volatility in energy markets, or additional sanctions or other governmental actions, could further adversely affect global markets and macroeconomic conditions and, in turn, our businessbusiness, financial condition and results of operations. A weak or declining economy and actual or threatened tariffs could also strain our suppliers, possibly resulting in supply disruption, or cause our customers to delay making payments for our services. If the current equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult, more costly, and more dilutive. Failure to secure any necessary financing in a timely manner and on favorable terms could have a material adverse effect on our growth strategy, financial performance and stock price and could require us to delay or abandon clinical development plans. In addition, there is a risk that one or more of our current service providers, manufacturers and other partners may not survive such difficult economic times, which could directly affect our ability to attain our operating goals on schedule and on budget. Also, hospitals and other medical facilities face staffing shortages, whether due to labor relations or otherwise, which could potentially cause delays in enrollment, site visits, evaluations or other activities important to our research and development efforts. Any of the foregoing could harm our business and we cannot anticipate all of the ways in which the current economic climate and financial market conditions could adversely impact our business. Furthermore, our stock price may decline due in part to the volatility of the stock market and any general economic downturn.

terrorist acts, acts of war or periods of widespread civil unrest, including conflicts in Ukraine, Israel, Venezuela and Iran, including any further escalation or expansion of hostilities involving Iran, and actions taken by third parties in response to such conflict;

We are a “smaller reporting company,” meaning that our annual revenue is less than $100.0 million during the last completed fiscal year or the market value of our stock held by non-affiliates was less than $700.0 million as of the end of that fiscal year’s second fiscal quarter. We will continueexpect to be a smaller reporting company until the first quarter of 2027. As a smaller reporting company we may choose to present only the two most recent fiscal years of audited financial statements in our Annual Report on Form 10-K and smaller reporting companies have reduced disclosure obligations regarding executive compensation. We cannot predict if investors will find our common stock less attractive because we may rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stock and our share price may be more volatile.

In addition to the MONARCH and ADMIRAL studies, we continue to run open-label extension (“OLE”) studies in patients who completed the Phase 1/2a studies and met study entry criteria. The four studies have shown substantial and durable reductions in convulsivemajor motor seizure frequency when administered on top of standard of care anti-seizure medicines. In the Phase 1/2a studies, 85% of patients were taking at least three and 54% were taking at least four medicines to control seizures. Half the patients in the studies were taking concomitant fenfluramine. Ongoing treatment has led to continuous improvements in cognition and behavior through threefour years. Additional improvements were indicated within the first nine months of treatment among patients in the Phase 1/2a study. These improvements were observed across multiple domains of the Vineland-3 (Vineland Adaptive Behavior Scale, Third Edition), a standardized assessment of behavioral outcomes that is a key secondary endpoint for the Phase 3 study. Zorevunersen has been generally well tolerated across the studies.

In addition to our Dravet program, we are also pursuing treatment for a second haploinsufficient disease, autosomal dominant optic atrophy (“ADOA”), the most common inherited optic nerve disorder for which there are currently no approved treatments. STK-002 is our clinical candidate for the treatment of ADOA. STK-002 is designed to upregulate OPA1 protein expression by leveraging the non-mutant (wild-type) copy of the OPA1 gene to restore OPA1 protein expression with the aim to stop or slow vision loss in patients with ADOA. In a non-human primate (NHP) model of ADOA conducted in collaboration with UC Davis, treatment with STK-002 was well tolerated and helped protect, and possibly improve, eye health. The data suggest that STK-002 may help preserve the function of important vision-related nerve cells, which could potentially improve or maintain vision. We receivedare authorizationstudying STK-002 in the UK to proceed with a Phase 1 open-label study (OSPREY) of children and adults ages 6 to 55 who have an established diagnosis of ADOA and have evidence of a genetic mutation in the OPA1 gene. In February 2026, we dosed the first patient with STK-002 in the OSPREY Phase 1 study for the treatment of ADOA. Dose escalation is continuing, and the study is actively recruiting in the United Kingdom and the European Union.

As of MarchDecember 31, 2026,2025, we had issued approximately 3.2 million shares of common stock pursuant to the 2025 Registration Statement for net proceeds of $87.8 million. In addition, as of MarchJune 31,30, 2026, we had issued approximately 2.6 million shares of common stock pursuant to the Sales Agreement and the 2026 Registration Statement for net proceeds of $80.7 million. Since June 30, 2026, through the issuance of these condensed consolidated financial statements, we sold approximately 2.1 million shares of our common stock pursuant to the Sales Agreement and the 2026 Registration Statement for net proceeds of $65.7 million after deducting commissions. We may terminate this at-the-market program under the Sales Agreement at any time, pursuant to its terms.

As of MarchJune 31,30, 2026 and December 31, 2025 we had $411.0$354.3 million and $390.9 million, respectively, in cash, cash equivalents and marketable securities.

Since inception, we have had operating losses, the majority of which are attributable to research and development activities. Our net losses were $50.0$61.6 million and $23.5 million for the three months ended MarchJune 31,30, 2026 and our2025, respectively. For the six months ended June 30, 2026 we had a net loss of $111.6 million and for the six months ended June 30, 2025 we had net income forof the three months ended March 31, 2025 was $112.9$89.4 million. As of MarchJune 31,30, 2026, we had an accumulated deficit of $547.7$609.3 million.

Based uponon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of approximately $411.0$354.3 million as of MarchJune 31,30, 2026,2026 and additional proceeds from the ATM sale of $65.7 million, will fund operations intothrough to potential U.S. commercialization of zorevunersen in early 2028. To date, we have not had any products approved for sale and have not generated any product sales. We do not expect to generate any revenues from product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution. As a result, until such time, if ever, as we can generate substantial product revenue, we expect to finance our cash needs through equity offerings, debt financings or other capital sources, including potentially collaborations, licenses and other similar arrangements. However, we may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all. Any failure to raise capital as and when needed could have a negative impact on our financial condition and on our ability to pursue our business plans and strategies. If we are unable to raise capital, we will need to delay, reduce or terminate planned activities to reduce costs.

Presentations of new clinical data for zorevunersen at medical congresses have contributed to greater understanding of its disease-modifying potential that is highly differentiated from any currently available treatments. InThe MayCompany 2026,will wecontinue announcedits neweducational findingsefforts fromat four-yearmajor longitudinalneurology and epilepsy congresses during the second half of 2026. Analyses of data from the ongoing PhaseOLEs 1/2will open-labelsupport extensionefforts (OLE)to studiesincrease clinician understanding of zorevunersen inwhile childrenthe Phase 3 EMPEROR study advances toward completion and adolescentsthe Company prepares for a potential U.S. approval and launch. The Company will also continue discussions with Dravetthe syndrome.FDA 93%to (75/81) of eligible patients continued treatment inupdate the OLEAgency studies,on providing a longitudinal dataset to assessits long-term outcomes.data Asfor of February 2026, 77% (58/75) of patients remain in these studies.zorevunersen.

EMPEROR is a global, pivotal Phase 3 study. NewIn patientJune entry2026, intowe screeningannounced forcompletion of enrollment of 162 patients in the U.S., UK, and JapanJapan, cohort is closed andwhere patients currently in screening are progressing through the 8-week screening period. Following successful completion of screening, these patients will be randomized to treatment with zorevunersen or a sham control administered via lumbar puncture (LP). TheA finalPhase patient3 data readout is expected to be randomized in June 2026. Data from this LP cohort of approximately 150 patients are anticipated in mid-2027the andthird arequarter expectedof 2027 to be the final data required for completion ofcomplete the planned rolling U.S. NDA submission.submission in the second half of 2027. Commercial preparation is underway to support a potential U.S. commercial launch asof zorevunersen in early as late 2027.2028.

We are also pursuing treatment for Autosomal Dominant Optic Atrophy (ADOA), the most common inherited optic nerve disorder, with STK-002. In February 2026, the first patient was dosed in the Phase 1 OSPREY study of STK-002. As of MayAugust 2026, twoall patientseight haveplanned beenclinical dosed and recruitment is ongoing attrial sites are active in the United Kingdom, Germany, AustriaAustria, Italy and Denmark.Denmark, Doseand escalationdosing acrossof initialthe fourfirst cohortscohort of patients (n=3) is complete with no serious safety events observed to date. Dosing of the second cohort is expected to continuebegin throughin 2026August 2026. Subject to ongoing safety assessments, dosing in the third and intofourth earlydose 2027,cohorts pendingare expected to follow with a readout of safety and tolerabilityefficacy assessments.results anticipated in the first half of 2027.

We are comprised of one reportable segment and as of MarchJune 31,30, 2026 and 2025, have not generated any product revenue since inception, as we do not yet have approved products for sale. If we are able to successfully develop, receive regulatory approval for and commercialize any of our current or future product candidates alone or in collaboration with third parties, we may generate revenue from the sales of these product candidates.

On February 14, 2025, we entered into a License and Collaboration Agreement (the “Biogen Agreement”) with Biogen International GmbH (“Biogen”) for the joint development and commercialization of zorevunersen and other compounds targeting the SCN1A gene (the “Licensed Product”). Under the terms of the Biogen Agreement, we granted Biogen an exclusive, royalty-bearingroyalty bearing license to develop, manufacture,manufacture and exportcommercialize licensed products in all territories outside the U.S.,United Canada,States, Canada and Mexico (the “Biogen Territory”). InBiogen addition, Biogenalso has thean option to exercise an exclusive, royalty-bearing, sublicensable and transferable license forto certain future follow-onfollow on antisense oligonucleotides (“ASOs”) directed to SCN1A controlled by us. Under the BiogenCompany. Agreement, theThe parties are jointly developing zorevunersen, andwith we areus leading global development. Wedevelopment, and Biogen share global development costs basedare onshared pursuant to an agreed budget.budget, Wewith areus responsible for 70% of these development costs and Biogen is responsible for the remaining 30% of these development costs.30%.

In connection with the closing of this transaction in February 2025, weWe received an upfront payment of $165.0 million and are eligible to receive development and commercial milestone paymentsmilestones that could total up to approximately $50.0 million and $335.0 million, respectively,respectively if all the specified milestones set forth in thisthe collaboration arrangement are achieved. In addition, weWe are also eligible to receive tiered, double-digit royalties ranging from the low double-digitdouble digits to the high teen percentages ofon future net sales onin the licensedLicensed products.Product territory. As of MarchJune 31,30, 2026, no milestones have been met. Royalties payable under the Biogen Agreement are subject to standard royalty reductions.achieved.

SeeFor more information see Note 7—License and Collaboration Agreements of the notes to our unaudited condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q.

Results of operations for the three months ended MarchJune 31,30, 2026 and 2025

Revenue for the three months ended MarchJune 31,30, 2026 was $6.2$9.3 million compared to $158.6$13.8 million for the three months ended MarchJune 31,30, 2025, a decrease of $152.4$4.5 million. Revenue is generated from satisfying contractual obligations of the collaboration and licensing agreements with Acadia and Biogen. The decrease in revenue is primarily driven by the recognition of $150.8 million related to the IP license performance obligation during the year ended December 31, 2025.

Research and development expenses were $39.7$49.5 million for the three months ended MarchJune 31,30, 2026 as compared to $32.7$25.9 million for the three months ended MarchJune 31,30, 2025, an increase of $7.0$23.6 million. The table below summarizes our research and development expenses (in thousands):

The increase in research and development expenses was attributable to an increase of $5.1$12.8 million of expenses related to zorevunersen, which are comprised of third-party services and scientific consulting fees, $6.6 million in personnel-related expenses, $0.7$3.4 million in other external program costs, $1.5 million in expenses related to our ADOA program, which are comprised of third-party services and scientific consulting fees, and an increase of $0.4$0.3 million related to SYNGAP1 offset by a decrease of $0.1 million related to MECP2 in external third-party expenses related to SYNGAP1 and MECP2, and an increase of $1.4 million in other non-program related costsSYNGAP1, offset by a decrease of $0.5$1.2 million related to other non-program costs, and $0.2 million in external third-party expenses related to our zorevunersen program.MECP2.

Sales, general and administrative expenses were $20.0$25.3 million for the three months ended MarchJune 31,30, 2026 as compared to $14.7$15.3 million for the three months ended MarchJune 31,30, 2025. The increase of $5.3$10.0 million in sales, general and administrative expenses was attributable to an increase of $3.4$6.6 million in facilities and other sales, general and administrative costs for commercial readiness, and $1.9$3.4 million in personnel-related expenses.

Other income (expense) was $3.4$3.8 million for the three months ended MarchJune 31,30, 2026 as compared to $2.9$3.8 million for the three months ended MarchJune 31,30, 2025.

Since our inception through MarchJune 31,30, 2026, our operations have been financed by net proceeds of $1.0 billion from the sale of convertible notes payable and our convertible preferred stock, our initial public offering, public offerings of common stock and pre-funded warrants, proceeds from the Sales Agreement and the upfront payments from Acadia and Biogen. As of MarchJune 31,30, 2026, we had $411.0$354.3 million in cash, cash equivalents and marketable securities. Cash in excess of immediate requirements is invested in accordance with our investment policy, primarily with a view to liquidity and capital preservation. On April 2, 2024, we completed an underwritten public offering of our common stock and issued and sold 5,555,557 shares of common stock at a public offering price of $13.50 per share and issued pre-funded warrants to purchase 3,703,730 shares of common stock at a public offering price of $13.499 per share subject to an exercise price equal to $0.0001. The common stock and warrants sold resulted in net proceeds of $119.9 million after deducting underwriting discounts, commissions and offering costs. No pre-funded warrants have been exercised.

We have primarily incurred losses since our inception in June 2014 and, as of MarchJune 31,30, 2026, we had an accumulated deficit of $547.7$609.3 million. Our primary use of cash is to fund operating expenses, which consist primarily of research and development expenditures, and to a lesser extent, sales, general and administrative expenditures. Cash used to fund operating expenses is impacted by the timing of when we pay these expenses, as reflected in the change in our outstanding accounts payable and accrued expenses.

Based uponon our current operating plan, we believe that our cash, cash equivalents, and marketable securities of approximately $411.0$354.3 million as of MarchJune 31,30, 2026,2026 and additional proceeds from the ATM sale of $65.7 million, will fund operations intothrough to potential U.S. commercialization of zorevunersen in early 2028. We have based this estimate on assumptions that may prove to be wrong, and we could utilize our available capital resources sooner than we currently expect. We will continue to require additional financing to advance our current product candidates through clinical development, to develop, acquire or in-license other potential product candidates and to fund operations for the foreseeable future. We will continue to seek funds through equity offerings, debt financings or other capital sources, including potentially collaborations, licenses and other similar arrangements. However, we may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all. Our ability to raise additional funds may be adversely impacted by potential worsening global macroeconomic conditions, including inflation, changing interest rates and instability in the global banking system, tariffs, military conflicts and disruptions to and volatility in the credit and financial markets in the United States and worldwide. If we do raise additional capital through public or private equity offerings, the ownership interest of our existing stockholders will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect our stockholders’ rights. If we raise additional capital through debt financing, we may be subject to covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends. Any failure to raise capital as and when needed could have a negative impact on our financial condition and on our ability to pursue our business plans and strategies. If we are unable to raise capital, we will need to delay, reduce or terminate planned activities to reduce costs.

During the threesix months ended MarchJune 31,30, 2026, cash used in operating activities was $60.6$117.1 million. This was attributable to a net loss of $50.0$111.6 million, a net change of $20.1$26.6 million in our net operating assets and liabilities offset by non-cash charges of $9.5$21.0 million for stock-based compensation, depreciation, amortization and accretion of marketable securities, and a reduction in the carrying amount of right of use assets.

During the threesix months ended MarchJune 31,30, 2025, cash provided by operating activities was $131.8$106.4 million. This was primarily attributable to a net income of $112.9$89.4 million, a net change of $11.5$0.5 million in our net operating assets and liabilities and non-cash charges of $7.3$16.5 million for stock-based compensation, depreciation, amortization and accretion of marketable securities, and a reduction in the carrying amount of right of use assets.

Our investing activities during the threesix months ended MarchJune 31,30, 2026 consisted primarily of $60.9$108.0 million from the maturity of marketable securities offset by $9.9$46.0 million of purchases of marketable securities and $0.4$2.3 million of purchases of property plant and equipment.

Our investing activities during the threesix months ended MarchJune 31,30, 2025 consisted primarily of $32.8 million from the maturity of marketable securities offset by $19.0$200.6 million of purchases of marketable securities and $0.3 million of purchases of property plant and equipment offset by $66.0 million from the sales of marketable securities.

Our financing activities during the threesix months ended MarchJune 31,30, 2026 consisted primarily of $80.7 million in proceeds from the controlled equity offering sales agreement, $3.2$5.1 million from the exercise of stock options and $0.5 million in proceeds from our Employee Stock Purchase Plan (the “ESPP”).

Our financing activities during the threesix months ended MarchJune 31,30, 2025 consisted of $1.0$1.6 million from the exercise of stock options and $0.4 million in proceeds from theour ESPP.

The following table summarizes our contractual obligations as of MarchJune 31,30, 2026 and the effects that such obligations are expected to have on our liquidity and cash flows in future fiscal periods:

On January 21, 2026, we entered into a new lease for our corporate headquarters and laboratory space with NWALP PHOP Property Owner LLC, located at 245 Fifth Avenue, Waltham, Massachusetts (the “Lease Agreement”), in order to expand our office and laboratory space. The Lease Agreement premises include approximately 98,500 square feet. The Lease Agreement will expire on March 31, 2038, and includes two options to further extend the Lease Agreement for an additional five years at the then-prevailing market rate. The aggregate estimated base rent payments due over the term of the Lease Agreement is approximately $86.6 million. We paid a security deposit of $3.0 million in the form of an irrevocable standby letter of credit, which may be reduced over time in accordance with the terms of the Lease Agreement. We expect to occupy the space late in 2026.

Our commitments primarily consist of obligations under our agreement with the University of Southampton. As of MarchJune 31,30, 2026, we were unable to estimate the timing or likelihood of achieving the milestones or making future product sales. For additional information regarding our agreements, see Note 6—Commitments and Contingencies of the notes to our condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q.

We are a “smaller reporting company,” meaning that our annual revenue is less than $100.0 million during the last completed fiscal year or the market value of our stock held by non-affiliates was less than $700.0 million as of the end of that fiscal year’s second fiscal quarter. We willexpect to continue to be a smaller reporting company until the first quarter of 2027. As a smaller reporting company we may choose to present only the two most recent fiscal years of audited financial statements in our Annual Report on Form 10-K and smaller reporting companies have reduced disclosure obligations regarding executive compensation.