Zorevunersen: a defined EMPEROR analysis after FDA dialogue

October 5, 2026: meeting outcome, not an NDA

Stoke reported completion of an FDA meeting addressing its planned U.S. application and the EMPEROR analysis. The milestone is the disclosed meeting outcome; its exact meeting date was not provided. The company plans to begin submitting application material in the first half of 2027 and complete the package after a third-quarter-2027 readout, in the second half of 2027. A possible early-2028 approval remains management’s aspiration, not an FDA action date. Neither an accepted NDA nor approval was announced. [1]

SCN1A haploinsufficiency and intrathecal delivery

Many cases of Dravet syndrome arise from loss of function in one SCN1A copy, reducing the NaV1.1 sodium-channel protein needed for neuronal signaling. Zorevunersen, formerly STK-001, is an antisense oligonucleotide intended to increase productive expression from the unaffected copy through Stoke’s TANGO approach. The biological proposition extends beyond acute seizure suppression, but a mechanism directed at a disease cause does not itself establish disease modification. Gain-of-function variants are excluded from the pivotal population because increasing their activity would address a different biological problem. [2] [7]

Intrathecal delivery bypasses poor systemic access to the central nervous system. Early studies assessed plasma pharmacokinetics and CSF exposure as primary objectives, alongside safety. Slow bolus administration took one to three minutes. The pivotal program uses two 70 mg loading doses followed by two 45 mg maintenance doses across 52 weeks. No quantitative human brain target-engagement threshold or individual concentration–response rule is established by the retrieved materials. Repeated lumbar punctures also introduce procedural events that must be separated from drug-related toxicity.

Early trials and the later extension are different datasets

MONARCH (NCT04442295) and ADMIRAL (ISRCTN99651026) enrolled 62 and 19 patients, respectively, aged two to 18, on background antiseizure medicines. They were open-label, without concurrent placebo. Single doses ranged from 10 to 70 mg; repeated-dose cohorts received 20–70 mg. Eighty-five percent used at least three background medicines. The December 12, 2023 data cut in the AES poster includes 81 treated patients but 77 seizure-evaluable participants, excluding an incorrect dose and three patients with fewer than four baseline seizures. [2] [3] [4]

The 2026 NEJM report separately follows 75 extension entrants as of May 30, 2025. Among patients initially receiving 70 mg and then up to 45 mg every four months, median convulsive-seizure changes ranged from −58.82% to −90.91% across monthly intervals in the first 20 extension months. These are changing longitudinal observations, not a single responder rate or randomized treatment effect. The September 2026 four-year update reported 58/75 remaining in extension studies; attrition and survivor selection limit causal interpretation of sustained gains.

EMPEROR design and revised analysis detail

NCT06872125 is double-blind and sham-controlled, randomizing children aged two to under 18 with a qualifying non-gain-of-function SCN1A variant 1:1 after an eight-week baseline. Treatment lasts 52 weeks. The planned primary analysis population comprises 162 patients enrolled in the United States, United Kingdom and Japan by June 2026; 34 additional European participants enrolled by August. China enrollment is separate and ongoing. These regional numbers must not be treated as published efficacy or safety denominators before the analysis sets are available. [1] [6]

The primary seizure endpoint concerns Week 28, using the Week 24–28 interval, with a repeated-measures model incorporating observations through Week 52. The key secondary sequence assesses seizure durability at Week 52 and adaptive behavior. The October meeting disclosure specifies a multivariate MMRM jointly modeling four prespecified Vineland-3 subdomains: expressive communication, receptive communication, interpersonal relationships and personal skills. Earlier public descriptions included coping skills; that older description is not substituted for the October four-domain plan.

Analysis: jointly modeling correlated domains may improve precision and address a broad functional claim, but does not create four independent positive trials. Success still depends on the specified hierarchy, missing-data assumptions and a clinically interpretable magnitude. Public material does not supply the complete SAP, power assumptions, imputation details or sensitivity-analysis results. Reaching Week 28 alone will not trigger the stated full readout: participants are followed through Week 52 before the planned package is analyzed.

Safety by study and data version

In the original Phase 1/2a dataset, 78/81 experienced TEAEs and 18/81 serious TEAEs; one MONARCH death from SUDEP was considered unrelated. No early-study withdrawal was attributed to TEAEs. The later NEJM dataset reports two SUDEP deaths and one malnutrition death, one suspected unexpected serious adverse reaction case and one adverse-event withdrawal. These are later cumulative observations, not additional events that can simply be added to the earlier table. [2] [3] [4] [6]

The March 2026 sponsor report identified CSF-protein adverse events in 33/75 extension participants and one resulting discontinuation. By the September update, after more than 930 doses through July 31, approximately 94% had elevated CSF laboratory values and 59% were classified as TEAEs, without serious or severe clinical manifestations or reported hydrocephalus. Laboratory abnormalities and coded adverse events use different definitions; the disclosure does not supply the exact denominator behind the later percentages. Long-term surveillance remains necessary despite the absence of severe clinical manifestations.

Execution, partnership and funding

Stoke retains U.S., Canadian and Mexican rights while Biogen holds the rest-of-world commercialization rights. Biogen is a partner in the same development program, not a second independent clinical replication. The August financial update reports $354.3 million in cash, equivalents and marketable securities at June 30 plus $65.7 million net from a subsequent ATM sale, totaling $420.0 million on that stated basis. Management projected funding through potential early-2028 U.S. commercialization. The dated balance and subsequent financing should remain separate, and the projection does not ensure a positive EMPEROR result or an acceptable application. [1] [5]

Sources / References

1. Stoke · FDA meeting · October 5, 2026
2. Laux et al. · AES 2024 original MONARCH/ADMIRAL poster
3. Laux et al. · NEJM · March 4, 2026
4. Stoke/Biogen · four-year EEC disclosure · September 3, 2026
5. Stoke · Q2 financial results · August 3, 2026
6. Stoke · NEJM data announcement · March 4, 2026
7. Stoke · 2025 annual report / EMPEROR dosing