ACVR1 and fibrodysplasia ossificans progressiva: For example, fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder characteristic of progressive HO formation, arises from mutations of the BMP type I receptor ALK2, 95% of which are R206 to H mutation resulting in a constitutive activation of the receptor and Smad1/5‐mediated signalling events essential for osteogenesis.24