Fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva
Other namesFOP, Stoneman disease
Fibrodysplasia ossificans progressiva.jpg
The effects of fibrodysplasia ossificans progressiva, a disease which causes damaged soft tissue to regrow as bone.
SpecialtyMedical genetics, rheumatology
Usual onsetBefore age 10
Differential diagnosisFibrous dysplasia
PrognosisMedian life expectancy ≈ 40 years old (if properly managed)
Frequency800 confirmed cases worldwide (2017); incidence rate estimated to be 0.5 cases per million people

Fibrodysplasia ossificans progressiva (/ˌfaɪbroʊdɪˈspleɪʒə ɑˈsɪfəˌkænz prəˈgrɛsəvə/,[1] FOP) is an extremely rare connective tissue disease. It is a severe, disabling disease with no cure or treatment and is the only known medical condition where one organ system changes into another.

The disease is caused by a mutation of the body's repair mechanism, which causes fibrous tissue (including muscle, tendon, and ligament) to be ossified spontaneously or when damaged. In many cases, otherwise minor injuries can cause joints to become permanently frozen in place, as new bone forms and replaces the damaged muscle tissue. This new bone eventually forms a secondary skeleton and progressively restricts the patient's ability to move. Circumstantial evidence suggests that the disease can cause joint degradation separate from its characteristic bone growth.[2]

Surgical removal of the extra bone growths has been shown to cause the body to "repair" the affected area with even more bone. Although the rate of bone growth develops differently depending on the patient, the condition ultimately leaves those affected in a "frozen" position as new bone replaces musculature and fuses with the skeleton. If possible, adult patients eventually have to decide on a position they wish to predominantly assume for the rest of their lives.

Signs and symptoms

For unknown reasons, children born with FOP have deformed big toes, sometimes missing a joint or, in other cases, simply presenting with a notable lump at the minor joint. The first "flare-up" that leads to the formation of FOP bones usually occurs before the age of 10. The bone growth progresses from the top of the body downward, just as bones grow in fetuses. A child with FOP will typically develop additional bones starting at the neck, then at the shoulders, arms, chest area, and finally at the feet.

Specifically, ossification is typically first seen in the dorsal, axial, cranial and proximal regions of the body. Later the disease progresses in the ventral, appendicular, caudal and distal regions of the body.[3] However, it does not necessarily occur in this order due to injury-caused flare-ups. Often, the tumor-like lumps that characterize the disease appear suddenly. This condition causes loss of mobility to affected joints, including the inability to fully open the mouth, limiting speech and eating; a specific occurrence of this condition to the foot joints can result in limited ability of the FOP patient to put a foot flat on the ground. Bone growth can also result in the immobilization of the hip or knee, also limiting the individual's ability to walk. Extra bone formation around the rib cage restricts the expansion of lungs and diaphragm causing respiratory complications.

Since the disease is so rare, the condition may be misdiagnosed as cancer or fibrosis. This leads physicians to order biopsies, which can exacerbate the growth of the FOP bone.[4] The presence of malformed toes or thumbs in those born with FOP help distinguish this disorder from other skeletal problems.[5]

The median age of survival is 40 years with proper management. However, delayed diagnosis, trauma, and infections can decrease life expectancy.[6]

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