A mutation (c.G617A, p.R206H) in the glycine-serine (GS) activation domain of activin receptor type I (ACVR1, also called activin-like kinase 2 (ALK2)) was found through a linkage and sequencing analysis, and was reported in all sporadic and familial cases of classic FOP [2–6]. This evidence concerns the gene ACVR1 and fibrodysplasia ossificans progressiva.