In Cohort 2, new FOP subjects meeting all inclusion/exclusion criteria will be randomly assigned 3:3:2 to two dose regimens of palovarotene (10 mg for 14 days and 5 mg for 28 days; 5 mg for 14 days and 2.5 mg for 28 days) or placebo daily for 42 days. Doses will be weight-adjusted and subjects randomized within three weight-range categories (20 to <40 kg, 40 to <60 kg, and ≥60 kg).