A Clinical Study to Evaluate the Safety and Efficacy of ETX101, an AAV9-Delivered Gene Therapy in Children With SCN1A-positive Dravet Syndrome

Inclusion Criteria:

• Participant has a predicted loss of function pathogenic or likely pathogenic SCN1Avariant

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

• Participant must have a clinical diagnosis of Dravet syndrome or the treatingclinician must have 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 is currently taking or has taken antiseizure medications (ASMs) at atherapeutic dose that are contraindicated in Dravet syndrome, including sodiumchannel blockers.

• 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.