Fibrodysplasia ossificans progressiva-When bone suddenly forms within muscle

Fibrodysplasia ossificans progressiva (FOP) is a very rare genetic condition caused by a point mutation in the ACVR1 gene. There are two clinical features indicative of FOP: 1) a congenital malformation of the great toe(s), similar to a hallux valgus and 2) unexplained soft tissue swelling usually resulting in heterotopic ossifications (HO). Early recognition of these two features is very important to avoid misdiagnosis and incorrect treatment and to ensure the correct diagnosis as early as possible by genetic testing of the ACVR1 gene. As soon as this diagnosis is available it is advisable for the affected person to see a FOP specialist and to establish contact with the German patient organization "FOP e. V.".All invasive interventions should be strictly avoided, as they can trigger irreversible HO. The complexity and systemic course of FOP requires the establishment and collaboration of an interdisciplinary team for optimal care of affected individuals. Treatment of FOP flare-ups and subsequent ossification is currently symptomatic according to the international guidelines of the ICC on FOP (www.iccfop.org). Targeted treatment approaches in current clinical trials aim to influence the bone morphogenetic protein (BMP) signalling pathway at multiple levels to halt or slow disease progression.While more than 95% of all affected individuals have the classical point mutation, a small number of affected individuals have variant mutations. Each of these mutations leads to hypersensitivity and overactivation of the ACVR1 receptor and results in an increased BMP signalling response.