Key Inclusion Criteria:
- Age: 2 Years to 22 Years
- Ability to swallow capsules unless enrolled in Part E
- Body surface area (BSA): Subjects must have a body surface area ≥ 0.45 m2 at the time of the study enrollment, unless enrolled in Part E
- Adequate organ and neurologic function
Key Exclusion Criteria:
- Known congenital long QT syndrome
- Receiving Enzyme Inducing Antiepileptic Drugs (EIAEDs) within 14 days of first dose.
- Incomplete recovery from acute effects of any surgery prior to treatment.
- Active gastrointestinal disease or other malabsorption syndromes that would impact drug absorption.