Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder that occurs when muscle and supportive tissues of the body, such as the tendons, ligaments, and cartilage, are gradually replaced with bone. As a result, movement becomes limited in the affected areas of the body, usually starting with the neck and shoulders and progressing down the body. Commonly affected areas include the neck, spine, chest, shoulders, elbows, wrists, hips, knees, ankles, and jaw.
Although symptoms do not typically develop until a child is a few months or years old, the disorder may be indicated at birth by the presence of malformed big toes. The big toes may be short and abnormally turned outward in a position called a valgus deviation. This abnormality helps distinguish FOP from other types of bone and muscle disorders. People with FOP may also have short limbs and other bone abnormalities.
There are many complications associated with FOP. The condition leads to progressive loss of mobility as more and more tissues become affected. For example, if extra bone develops in the jaw joints, a person may have difficulty talking or eating. If extra bone develops in the tissues over the rib cage, people may have difficulty breathing. The rates at which new bone forms and the disease progresses vary among patients.
People with FOP may experience a flare-up, or a sudden worsening of symptoms, if they experience any trauma to the muscles or connective tissues. For instance, if a person with FOP falls down, it may trigger episodes of muscle swelling (called myositis), followed by rapid development of bone (ossification) in the injured area. Illnesses, such as the flu, may also trigger flare-ups.
Researchers estimate that FOP affects one out of two million people worldwide.
The life expectancy for patients with FOP is generally poor because there is no cure for the disorder. Most patients die before age 40.
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