The purpose of the study is to evaluate the efficacy, safety, and tolerability of zorevunersen in Patients with Dravet syndrome.

Zorevunersen is an investigational new medicine for the treatment of Dravet syndrome. It is an antisense oligonucleotide (ASO) that is intended to increase the level of productive SCN1A messenger RNA (mRNA) and consequently increase the expression of the sodium channel Nav1.1 protein. This RNA-based approach is not gene therapy, but rather RNA modulation, as it does not manipulate nor insert genetic deoxyribonucleic acid (DNA).

Zorevunersen is designed to upregulate Nav1.1 protein expression from the nonmutant (wild-type) copy of the SCN1A gene to restore physiological Nav1.1 levels. Nav1.1 levels are reduced in people with Dravet syndrome.

This is a global, multicenter, randomized, double-blind, sham-controlled, parallel group Phase 3 study to assess the efficacy, safety, and tolerability of zorevunersen in patients with Dravet syndrome. The study duration and endpoints are designed to evaluate the potential of zorevunersen for disease modification. The study consists of two parts, Treatment Period 1 and Treatment Period 2. The primary and secondary endpoints will be assessed at the conclusion of Treatment Period 1. These endpoints will be assessed again at the end of Treatment Period 2. The primary endpoint is the change from baseline in major motor seizure frequency. Secondary endpoints include the change in behavior and cognition, clinical status, and health-related quality of life in patients with Dravet syndrome.

Patients will have the opportunity to enroll in an open label extension study and receive zorevunersen if they meet eligibility criteria at the end of the study.

Key Inclusion Criteria:

1. Patients must be ≥2 and <18 years of age.

2. Patients must have a clinical diagnosis of DS confirmed by the Epilepsy Study Consortium, Inc. (ESCI) and as defined by:

   Onset, prior to 12 months (inclusive, <13 months), of age, of recurrent focal with motor signs, hemiclonic, or generalized tonic-clonic seizures. No other known etiology causing clinical DS manifestations..

3. Patient must have a documented pathogenic, likely pathogenic variant, or variant of uncertain significance in the sodium voltage-gated channel type 1 alpha subunit (SCN1A) gene. Patients who have SCN1A testing results of Negative (no variants identified) cannot be randomized.

4. Patient must experience the required number of major motor seizures during the 6-week Observation Period. Major motor seizure types included are Seizure types included in counts are Hemiclonic, Focal with Motor Signs, Focal to Bilateral Tonic-Clonic, Generalized Tonic-Clonic, Tonic, Tonic/Atonic (Drop Attacks with fall or risk of fall), and Bilateral Clonic.

5. Patient must have used at least 2 prior interventions for seizures. These can include anti-seizure medications (ASMs), ketogenic diet and/or vagus nerve stimulation (VNS) with either lack of adequate seizure control or discontinued due to an AE(s). These interventions can be ongoing therapies.

6. Patient must be taking at least one ASM. Benzodiazepines or ASMs used on a standing basis (i.e., not as needed [PRN]) for any indication will be considered an ASM.

7. Patients' maintenance ASMs and interventions for seizures (i.e., ketogenic diet or VNS), as well as any marijuana- or cannabinoid-based products, must have been stable (unless adjusted for weight) during the Baseline Period.

Key Exclusion Criteria:

1. Patient has documented variant in the SCN1A gene associated with gain-of-function
2. Patient is currently treated with a maintenance ASM acting primarily as a sodium channel blocker, including but not limited to phenytoin, carbamazepine, oxcarbazepine, lamotrigine, lacosamide, rufinamide, or cenobamate, given the mechanism of action of zorevunersen.
3. Patient is currently treated with neuromodulation techniques (e.g., responsive neurostimulation, deep brain stimulation, or transcranial magnetic stimulation), with the exception of VNS.
4. Patient has emergence of a new seizure type or reemergence of a past seizure type (seizure types that last occurred more than 12 months before Screening Visit A) during the Baseline Period, or has more than 1 hospitalization for seizures during the Baseline Period.