Illuminating fibrodysplasia ossificans progressiva

By Dr Nicola Davies

Fibrodysplasia ossificans progressiva (FOP) is a rare connective tissue disease characterized by heterotopic ossification, where bone growth occurs in areas where bone typically should not be present.1 Ligaments, tendons and skeletal muscles are often affected, eventually locking joints in place and constricting movement. FOP is caused by mutations on the ACVR1 gene, which codes for the activin receptor-like kinase-2 (ALK2), a crucial receptor on the bone morphogenetic protein. These mutations are often spontaneous, although the disease can be inherited as an autosomal dominant trait.2

FOP is a very rare disease, with a frequency of 1 in 2 million people and approximately 900 cases confirmed worldwide.1,2 It affects both genders and all ethnicities. Malformations in the big toes are a tell-tale sign of the disease, a characteristic that is present in all patients. Approximately 50% of patients also present with malformations in the thumbs, and some patients can have malformations of the spinal column and thigh bone. These are usually accompanied by flare-ups in the form of swellings, pain, stiffness, and fevers.1,2,3