ACVR1 and hereditary disease: Fibrodysplasia ossificans progressiva (FOP, MIM 135100) is a rare genetic disorder most commonly caused by a heterozygous c.617G>A (Arg206His) germline missense mutation in the ACVR1 (human activin receptor type I) gene, leading to specific anatomical patterns of progressive heterotopic ossification (HO) and cumulative immobility [1].