Most FOP patients harbor the c.617G>A (R206H) mutation in the ACVR1/ALK2 gene (FOP-ACVR1) (Shore et al, 2006; Kaplan et al, 2009; Zhang et al, 2013), which encodes one of the type I transmembrane receptors of bone morphogenetic proteins (BMPs), suggesting the involvement of BMP signaling in HO development. This evidence concerns the gene CLN5 and fibrodysplasia ossificans progressiva.