Inclusion Criteria:

• Patients meeting the following criteria will be considered eligible for this study:
  • Patient and/or legally authorized; representative must be willing and able to give informed consent/assent for participation in the study;
  • Patient and their caregiver must be willing and able (in the Investigator’s opinion) to comply with all study requirements;
  • Patient must be between 2 and 18 years of age (inclusive) at Screening.
  • Patient must have a diagnosis of DS as defined by:
    • Onset prior to 12 months of age with recurrent focal motor or hemiconvulsive or generalized tonic-clonic seizures, which are often prolonged and triggered by hyperthermia;
    • No history of causal magnetic resonance imaging (MRI) lesion (MRI not required to confirm absence of lesion);
    • No other known etiology;
    • Normal development at seizure onset;
    • Patient must have a documented pathogenic or likely pathogenic genetic mutation in the SCN1A gene associated with DS. Patients with SCN1a testing results only of Variant(s) of Uncertain Significance identified or Negative (no variants of clinical significance identified) cannot be enrolled;
    • Patient has had in the past at least two treatments for epilepsy that either had lack of adequate seizure control (requiring an additional AED) or had to be discontinued due to an adverse event(s);
    • Patient must have experienced 4 or more convulsive seizures (all countable atonic, tonic, clonic, and tonic-clonic seizures) in the past 4 weeks prior to Screening;
    • Patient must currently be taking at least one AED at a dose which has been stable for at least 4 weeks prior to Screening;
    • All medications or interventions for epilepsy (including ketogenic diet) must have been stable for 4 weeks prior to Screening;
    • Patient and/or family (or caretaker) must be sufficiently fluent in English or Spanish to be able to complete questionnaires relevant to this study.

Exclusion Criteria:

The patient may not enter the study if ANY of the following apply:

• Patient has one of the following mutations in the SCN1A gene:
  • Thr226Met, Val422Leu, Q1489K, L1624P, L1649Q, or L1670W.
• Patient is currently being treated with a sodium channel blocker including:
  • phenytoin (Dilantin), carbamazepine (Tegretol), oxcarbazepine (Trileptal), lamotrigine (Lamictal), or lacosamide (Vimpat).