Progressive myositis ossificans

Progressive Myositis Ossificans (PMO), also known as Fibrodysplasia Ossificans Progressiva (FOP), is a rare and disabling genetic condition characterized by the abnormal development of bone in muscles, tendons, and other soft tissues. This process, called ossification, occurs progressively over time, leading to significant restrictions in movement due to the extra-skeletal bone formation.

Etiology

The primary cause of PMO/FOP is a mutation in the ACVR1 gene, which is involved in the bone morphogenetic protein (BMP) pathway, a critical pathway for bone growth and development. This mutation leads to the BMP pathway's abnormal activation, causing bone to form in soft tissues.

Symptoms

Symptoms of PMO/FOP usually begin in childhood and are characterized by two main features: malformed big toes (hallux valgus) present at birth and progressive heterotopic ossification. The latter typically starts in the neck and shoulders and progresses down the body. Flare-ups, which can lead to new bone formation, may be triggered by soft tissue injuries, vaccinations, or viral infections.

Diagnosis

Diagnosis of PMO/FOP is primarily clinical, based on the characteristic malformations of the big toe and the pattern of heterotopic ossification. Genetic testing can confirm the diagnosis by identifying mutations in the ACVR1 gene.

Treatment

There is currently no cure for PMO/FOP. Treatment focuses on managing symptoms, preventing flare-ups, and maintaining mobility for as long as possible. This may include the use of corticosteroids to manage flare-ups, careful management of injuries and infections to prevent unnecessary bone formation, and physical therapy to maintain movement.

Prognosis

The prognosis for individuals with PMO/FOP is variable and depends on the rate and extent of heterotopic ossification. Life expectancy can be shortened due to complications related to extra-skeletal bone formation, such as respiratory failure.

Research

Research into PMO/FOP is ongoing, with efforts focused on understanding the mechanisms of the disease and developing treatments that can prevent or reverse the process of heterotopic ossification. Clinical trials for potential treatments, including drugs that target the BMP pathway, are in various stages of development.

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