ACVR1 and fibrodysplasia ossificans progressiva: Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disease caused by one of several point mutations in the BMP type I receptor, ALK2 [1,2] and results in episodes of hyperinflammatory, fibroproliferative, and edematous soft tissue lesions, termed “flares”, that frequently progress to intramuscular endochondral heterotopic ossification (EHO) [3,4,5,6].