Fibrodysplasia ossificans progressiva
| Fibrodysplasia ossificans progressiva | |
|---|---|
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| The effects of fibrodysplasia ossificans progressiva, a disease which causes damaged soft tissue to regrow as bone. | |
| Classification and external resources | |
| Specialty | Medical genetics |
| ICD-10 | M61.1 |
| ICD-9-CM | 728.11 |
| OMIM | 135100 |
| DiseasesDB | 8732 |
| eMedicine | derm/609 |
| MeSH | D009221 |
Fibrodysplasia ossificans progressiva (FOP) is an extremely rare connective tissue disease. 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, injuries can cause joints to become permanently frozen in place. Surgical removal of the extra bone growths has been shown to cause the body to "repair" the affected area with even more bone.
For unknown reasons, children born with FOP have deformed big toes, possibly missing a joint or 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 downward, just as bones grow in fetuses. A child with FOP will typically develop bones starting at the neck, then on the shoulders, arms, chest area and finally on 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. 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 inability to fully open the mouth limiting speech and eating. Extra bone formation around the rib cage restricts the expansion of lungs and diaphragm causing breathing complications.
Since the disease is so rare, the symptoms are often misdiagnosed as cancer or fibrosis. This leads physicians to order biopsies, which can exacerbate the growth of these lumps. However, those born with FOP tend to have malformed toes or thumbs which help distinguish this disorder from other skeletal problems.
The median age of survival is 40 years with proper management. However, delayed diagnosis, trauma and infections can decrease life expectancy.
FOP is caused by an autosomal dominant allele on chromosome 2q23-24. The allele has variable expressivity, but complete penetrance. Most cases are caused by spontaneous mutation in the gametes; most people with FOP cannot or choose not to have children. A similar but less catastrophic disease is fibrous dysplasia, which is caused by a post-zygotic mutation.
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