ACVR1 and fibrodysplasia ossificans progressiva: The molecular basis of FOP was identified in 2006, when activating mutations in activin receptor A type I gene (ACVR1, also referred to as activin receptor-like kinase 2, ALK2), which codes for a bone morphogenetic protein (BMP) type I receptor, were recognized as the proximate genetic cause of FOP in all affected individuals [2].