In-Home Evaluation of Episodic Administration of Palovarotene in Fibrodysplasia Ossificans Progressiva (FOP) Subjects

The primary objective of this Phase 2, open-label, multicenter, single-arm, extension study is to investigate the safety and efficacy of episodic treatment with palovarotene in FOP subjects with flare-ups. Secondary objectives are: The effect of episodic treatment of flare-ups with palovarotene on range of motion (ROM) as assessed by the subject global assessment of movement. * The effect of episodic treatment of flare-ups with palovarotene on ROM as assessed by the Cumulative Analogue Joint Involvement Scale for FOP (CAJIS) for subjects with video-conferencing capability. * The effect of episodic treatment of flare-ups with palovarotene on the total burden of heterotopic ossification (HO) as assessed by low-dose whole body computerized tomography (WBCT), excluding the head; and whole body dual energy x-ray absorptiometry (DEXA). * The effect of episodic treatment of flare-ups with palovarotene on physical function using age-appropriate forms of the FOP-Physical Function Questionnaire (FOP-PFQ). * The effect of episodic treatment of flare-ups with palovarotene on physical and mental health using age appropriate forms of the Patient Reported Outcomes Measurement Information System (PROMIS) Global Health Scale. * The effects of episodic treatment of flare-ups with palovarotene on pain and swelling associated with the flare-up using numeric rating scales (NRS) or the Faces Pain Scale-Revised (FPS-R) in subjects under 8 years of age. * The use of assistive devices and adaptations for daily living by FOP subjects. The follow-up portion of the study will consist of a Screening visit that will correspond to the last day (Study Day 84) of Study PVO-1A-202 and bi-annual assessments at Months 6, 12, 18, 24, 30, and 36. Subjects experiencing a new, distinct flare-up during the 36-month follow-up will be evaluated and if eligible, receive palovarotene at the weight-adjusted equivalent of 10 mg for 14 days followed by 5 mg for at least 28 days. Any subject who received a lower dosing regimen due to tolerability issues during Study PVO-1A-202 will receive that tolerated dose. For each flare-up there will be two periods: 1. A Screening period to occur within 7 days of the start of a new, distinct flare-up. The first dose of palovarotene will be taken within 10 days of the flare-up onset to allow for shipment of study medication to the subject's home. 2. A treatment period of at least 6 weeks duration. Subjects experiencing a new, distinct flare-up will be evaluated