An Efficacy and Safety Study of Palovarotene to Treat Preosseous Flare-ups in FOP Subjects

Inclusion Criteria: * Written, signed, and dated informed subject/parent consent or age-appropriate assent. * Subjects clinically diagnosed with classic Fibrodysplasia Ossificans Progressiva (FOP). * Symptomatic onset of a distinct flare-up within 7 days of Study Day 1 (start of study drug) and defined by the presence of at least two of six of the following symptoms: pain, soft tissue swelling, decreased range of motion, stiffness, redness, and warmth. Flare-up must be confirmed by the physician at the Screening visit. * Flare-up is at an appendicular area (upper or lower extremity), abdomen, or chest; and subject has received, is receiving, or is willing to receive treatment per standard of care, which may or may not include oral prednisone (2 mg/kg PO to a maximum dose of 100 mg daily) for 4 days. * Abstinent or using two highly effective forms of birth control. * Subjects must be accessible for treatment and follow-up. Subjects living at distant locations from the investigational site must be able and willing to travel to a site for the initial and all follow-up visits. Exclusion Criteria: * Weight \<20 kg. * Intercurrent non-healed fracture at any location. * Complete immobilization of joint at site of flare-up. * The inability of the subject to undergo imaging assessments using plain radiographs. * If currently using vitamin A or beta carotene, multivitamins containing vitamin A or beta carotene, or herbal preparations, fish oil, and unable or unwilling to discontinue…