Fibrodysplasia ossificans progressiva is a genetic disorder that affects connective tissue. The main consequence of this disorder is heterotopic ossification, the development of bony tissue in locations where bone is not present in a healthy body. Such locations include the muscles, tendons and ligaments. The first symptoms of fibrodysplasia ossificans progressiva usually develop in childhood, and the disease progresses throughout the life of the individual. This is an extremely rare disorder with a global frequency of one person out of 2 million.
Children who are born with fibrodysplasia ossificans progressiva appear normal in almost all respects. The single abnormality present in almost all cases is a deformity of the big toes, in which the toes are much shorter than normal and have a bunion-like bony lump near the base of the toe. The presence of this toe abnormality at birth is considered a defining diagnostic characteristic of the disorder.
Generally, progressive symptoms begin to appear as the child approaches adolescence. The first symptoms are painful soft tissue swellings that are exacerbated by injury or viral illnesses. Over time, swellings become more numerous, and existing swellings become harder as soft tissues gradually transform into bone. Joints stiffen, and movement becomes difficult and painful. People with this condition gradually lose mobility as the disease progresses, and most require a wheelchair or other mobility aids by the third decade of life.
Loss of mobility is not necessarily the most debilitating consequence of this disorder, because of the involvement of soft tissue in all parts of the body in addition to those involved in movement. For example, muscles and connective tissue in the chest wall can be disrupted as a result of bony growths. This can lead to acute or chronic pneumonia and heart failure.
The underlying cause of fibrodysplasia ossificans progressiva is a mutation in a gene called ACVR1, which codes for a protein known as activin receptor type-1. This mutation changes the shape of the receptor and causes it to malfunction. As a result, injury to soft tissue causes bone to be deposited during the body’s repair process. This is why injury can not only cause the formation of new swellings but also exacerbate existing ones. Viral illness plays a role in the development of abnormal bone tissue because the immune system causes inflammatory reactions that also can cause tissue damage.
Fibrodysplasia ossificans progressiva is an incurable disorder, but certain medications can help reduce the rate of bone deposition in the body. The main medication used to achieve this is corticosteroids. A short course of high-dose corticosteroids can be administered when symptoms of the disorder flare up. By reducing inflammation in the body, this treatment can reduce the amount of bone deposition that occurs. Other medications that might be used include painkillers and muscle relaxants, to reduce pain and muscle spasms.