Treatment of Sunflower Syndrome With ZX008 (Fenfluramine Hydrochloride) in Children and Young Adults (Ages 4-25).

Fenfluramine Hydrochloride will be supplied to the treatment group as an oral solution in a concentration of 2.5 mg/mL. Subjects will receive their daily dose of Fenfluramine Hydrochloride in two doses (one in the morning and one in the evening). After a four week baseline, subjects that meet enrollment criteria will enter a titration period. The starting dose will be 0.2 mg/kg/day for the first 14 days. The dose will be increased every 2 weeks as tolerated by 0.2 mg/kg/day, to a maximum dose of 0.7 mg/kg/day, or a total maximum dose of 26 mg/day. The subject will remain on a dose of 0.7 mg/kg/day, 26 mg/day, or maximum tolerated daily dose through the end of the core study period.