ACVR1 and progressive osseous heteroplasia: Osteogenesis induction in FOP is caused by a mutation of the activin A receptor type 1/activin receptor-like kinase 2 gene (ACVR1/ALK2; in most cases R206H), which encodes the bone morphogenetic protein (BMP) receptor, type I. POH and AHO are caused by mutations in the GNAS1 gene, influencing Wingless-related integration site (WNT) and Hedgehog signaling (HH), the key controllers of skeletal maturation and regeneration [31–33].