Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disorder caused by abnormal BMP signaling activated by a mutant BMP receptor [activin receptor-like kinase-2 (ALK2)], leading to progressive heterotopic ossification (HO) in soft tissues [115, 116]. This evidence concerns the gene ACVR1 and fibrodysplasia ossificans progressiva.