BMP Signaling in Fibrodysplasia Ossificans Progressiva, a Rare Genetic Disorder of Heterotopic Ossification

Abstract

Heterotopic ossification (HO), the formation of extraskeletal bone, is most frequently associated with severe tissue injury. However, predicting who will be susceptible to HO and when HO will form has been challenging, resulting in a paucity of information about the causes and progression of this heterotopic bone formation. Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder in which heterotopic bone forms in soft connective tissues during childhood and throughout adult life, frequently in response to tissue trauma. The discovery that FOP is caused by gain-of-function mutations in ACVR1, the gene encoding the ALK2 BMP type I receptor, established that perturbation in the bone morphogenetic protein (BMP) signaling pathway is an underlying cellular mechanism for HO. The identification of the responsible gene for FOP, together with the development of animal models for HO and FOP, is now leading to advances in understanding the cellular and molecular mechanisms of bone formation and the induction of HO.