Fibrodysplasia ossificans progressiva (FOP), a hereditary form of HO, is caused by gain of function mutations in the BMP type 1 receptor ACVR1 (ALK2) with R206H being the most common point mutation located in the intracellular glycine-serine (GS) rich domain [9]. Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.