An Efficacy and Safety Study of Palovarotene for the Treatment of Fibrodysplasia Ossificans Progressiva.

One of the primary objectives was to evaluate the efficacy of palovarotene in decreasing new HO in participants with FOP as assessed by low-dose, whole body computed tomography (WBCT), excluding head, compared to untreated participants from Clementia's FOP natural history study (Study PVO-1A-001, NHS). The other primary objective was to evaluate the safety of palovarotene in participants with FOP. This study was conducted in three parts. Part A was the main part of the study, Part B, the 2-year (24-month) extension and Part C was an up-to-2-year post last dose of study treatment follow-up for skeletally immature participants. Participants in Part A and B received a chronic/flare-up dosing regimen of palovarotene for up to 4 years (48 months) as follows: * Chronic treatment: orally administered 5 mg palovarotene once daily. * Flare-up treatment: orally administered 20 mg palovarotene once daily for 4 weeks (28 days) followed by orally administered 10 mg palovarotene once daily for 8 weeks (56 days). Flare-up treatment may be extended until the Investigator determines that the flare-up has resolved. Note that all dosing was weight-adjusted in skeletally immature participants (those under the age of 18 years with less than 90% skeletal maturity on hand/wrist x-rays performed at Screening). In part C, participants who were enrolled in Parts A or B who discontinued the study and were skeletally immature were invited back to participate in the off-treatment safety follow-up. No new participants were enrolled into Part C.