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 pathogenicSCN1A variant.

• Participant must have experienced their first seizure between the ages of 3 and 15months.

• Participant must have a clinical diagnosis of Dravet syndrome or the treatingclinician 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 couldpotentially confound the typical Dravet phenotype.

• Participant has a known central nervous system structural and/or vascularabnormality (indicated by an MRI or CT scan of the brain).

• Participant has an abnormality that may interfere with CSF distribution and/or hasan existing ventriculoperitoneal shunt.

• Participant has received sodium channel blockers during the Pre-Dosing SeizurePeriod.

• Participant has experienced seizure freedom for a period of 4 consecutive weekswithin 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 aninvestigational therapy.

• Participant has clinically significant underlying liver disease.