A Phase 3 Study to Examine the Efficacy and Safety of ZX008 in Subjects With CDKL5 Deficiency Disorder.

This is an up to 3-part multicenter study: a double-blind, placebo-controlled part (Part 1) which includes Baseline Period (4 weeks), Titration Period (2 weeks), Maintenance Period (12 weeks) and Transition Period (2 weeks), followed by up to 2 open-label extension (OLE) parts: Part 2 of 54 weeks \[Treatment Period (52 weeks), Taper Period (2 weeks)\] and Part 3, i.e., OLE1 and OLE2, respectively, with the addition of the second OLE part (Part 3/OLE2) only for participants who will continue on fenfluramine and have no alternative treatment access from another source (e.g., a managed access program \[MAP\]). Participants can remain in Part 3 until MAP access or approval of fenfluramine (ZX008) has been obtained from regulatory authorities for CDD in the participant's country of residence, or until the investigational product development for CDD is stopped by the Sponsor, whichever comes first. Participants who discontinue early from Part 1, Part 2, or Part 3 will attend a Cardiac Follow-Up Visit 6 months after their last dose of study drug.