A Phase 3 Randomized, Double-Blind, Placebo Controlled, Parallel Group, Multicenter Study With Open-Label Extension to Evaluate the Efficacy And Safety of Fenfluramine Hydrochloride in Study Participants With Rett Syndrome

Inclusion Criteria: * Participant has typical or classic Rett Syndrome (RTT) according to the RettSearch Consortium 2010 revised criteria * Participant has a documented disease-causing mutation or deletion in the methyl-CpG-binding protein 2 (MECP2) gene * Participant meets criteria for postregression for at least 6 months prior to Screening, defined as: * No loss or degradation of ambulation (including gait, coordination, or independence of walking/standing); * No loss or degradation of hand function; no loss or degradation of speech (including babbling, words, or previously developed commun…