A Phase 2, Multicenter, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy, Safety, and Tolerability of TAK-935 (OV935) as an Adjunctive Therapy in Pediatric Patients With Developmental and/or Epileptic Encephalopathies

The drug being tested in this study is called TAK-935 (OV935). This randomized, double-blind
study will assess the effects of TAK-935 (OV935), compared to placebo, on efficacy, safety,
and tolerability in pediatric patients with Dravet syndrome or LGS. This multi-center trial
will be conducted worldwide and will enroll approximately 126 participants.

Participants will be randomized based on their diagnosis in 2 categories; Dravet syndrome and
LGS. The study will consist of 2 periods: Screening Period and Treatment Period. The overall
duration of Treatment Period is 14 weeks including 2-week Titration Period and 12-week
Maintenance Period. The overall time to participate in this study is approximately 24 weeks.

Participants completing this study will have an option to enroll in the open-label extension
study, under a separate protocol.

Inclusion Criteria:

1. Male and female patients aged ≥2 and ≤17 years

2. Clinical diagnosis of Dravet Syndrome or LGS

3. Weight of ≥10 kg at the Screening visit

4. Currently taking 1 to 4 anti-epileptic drugs (AED) at a stable dose

5. Failed to become and remain seizure free with trials of at least 2 AEDs

Exclusion Criteria:

1. On average 1 or more episodes of convulsive status epilepticus requiring
hospitalization per week in the 3 months immediately prior to the screening visit

2. Non-epileptic events that cannot be reliably distinguished from epileptic seizures

3. Participation in a clinical study involving another study drug in the previous month