Fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare disorder of the connective tissue, in which fibrous tissue (including muscle, tendon, and ligament) is ossified and slowly turned into bone. This occurs when the fibrous tissue is damaged and is replaced with bone tissue, because the body's repair mechanism is mutated. These bony growths occur painfully and slowly over a period of weeks or months, and usually begin in the upper back and shoulders. FOP bones are not usually removed with surgery because that causes the body to "repair" the area of surgery with more bones. Over time, as more FOP bones grow and joints get stiffer, it becomes more difficult to walk, eat, and even breathe. more...

Children born with FOP have a characteristic shortening of the great toe. Their first "flare-up" that leads to the formation of FOP bones is usually before the age of 10. Sometimes after a flare-up is over there is no new noticeable FOP bone. It is important that people with FOP do not participate in strenuous activity, and they should try to avoid falling or getting bruises, because those things can cause more FOP bones to grow. People with FOP should never allow anyone to try to stretch out their joints or bend them more than they can go on their own. However, sometimes flare-ups happen for no apparent reason, so being careful is not a guarantee of health.

FOP is caused by an autosomal dominant allele on chromosome 4. There have been fewer than 200 cases reported, but a study found that it affects approximately 1 in 1.64 million people. Most cases are caused by spontaneous mutation in the gametes, because most people with FOP cannot have children. However, the allele has varying expressivity, but complete penetrance (i.e. it always affects the bearer, but its effects are variable). A similar, but less catastrophic disease is Fibrous dysplasia, which is caused by a postzygotic mutation.

Sources

• The International FOP Association
• "Fibrodysplasia ossificans progressiva" eMedicine
• "Fibrodysplasia ossificans progressiva" WebMDHealth

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