In 2006, it was discovered that a single nucleotide substitution encoding the activin receptor type 1 (ACVR1)/activin receptor-like kinase 2 (ALK2) was the cause of FOP, and further genetic analyses revealed that nearly 97% of FOP cases are caused by the same mutation (c.617G>A, R206H), although other mutations have been described (3). Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.