A Clinical Study to Evaluate the Safety and Efficacy of ETX101 in Infants and Children With SCN1A-Positive Dravet Syndrome

Inclusion Criteria:

* Participant must be aged between ≥6 months and \<36 months in Part 1A, ≥48 months and \<18 years in Part 1B, ≥6 months and \<48 months in Part 2.
* Participant must have a predicted loss of function pathogenic or likely pathogenic SCN1A variant.
* Participant must have experienced their first seizure between the ages of 3 and 15 months.
* Participant must have a clinical diagnosis of Dravet syndrome or the treating clinician must have a high clinical suspicion of a diagnosis of Dravet syndrome.
* Participant is receiving at least one prophylactic antiseizure medication.

Exclusion Criteria:

* Participant has another genetic mutation or clinical comorbidity which could potentially confound the typical Dravet phenotype.
* Participant has a known central nervous system structural and/or vascular abnormality (indicated by an MRI or CT scan of the brain).
* Participant has an abnormality that may interfere with CSF distribution and/or has an existing ventriculoperitoneal shunt.
* Participant has received sodium channel blockers during the Pre-Dosing Seizure Period.
* Participant has experienced seizure freedom for a period of 4 consecutive weeks within the 90-day period prior to informed consent.
* Participant has previously received gene or cell therapy.
* Participant is currently enrolled in a clinical trial or receiving an investigational therapy.
* Participant has clinically significant underlying liver disease.