ACVR1 and fibrodysplasia ossificans progressiva: A single common heterozygous mutation (617G>A; R206H) has been identified in the cytoplasmic domain of activin receptor IA/activin-like kinase 2 (ACVR1/ALK2), a BMP type I receptor, in affected individuals of five small multigenerational families and in all sporadically affected individuals with the features of classic FOP [14].