This is a multi-center, natural history, non-interventional, longitudinal study in subjects with classic FOP. A thorough baseline examination will be performed to determine the current status of disease in each subject. In Part A, two imaging modalities assessed total body HO at baseline, and the optimal method (low-dose whole body CT scan \[excluding head\]) will be employed in Part B for the balance of the study. Progression will be assessed at annual in-clinic visits (ie, at Months 12, 24, and 36) at which time the procedures conducted at the baseline visit will be repeated. In addition, site personnel will telephone subjects midway between the annual visits (ie, at Months 6, 18, and 30).
During the 36-month follow-up period, at least one new flare-up (with a maximum of one per year) will be carefully studied. An in-clinic visit will be performed within 14 days following the subject's identification of his/her flare-up. Additional visits at Day 42 and Day 84 (after the initial flare-up clinic visit) will be performed. An additional future visit may be scheduled after Day 84 at the discretion of the Principal Investigator (PI) for prolonged flare-ups. However, subjects with an eligible flare-up may elect to participate in an ongoing Clementia interventional study rather than continue in this natural history study.