FOP; Myositis Ossificans Progressiva; Progressive Myositis Ossificans; Progressive Ossifying Myositis; Munchmeyer Disease

Fibrodysplasia Ossificans Progressiva (FOP) is an inherited disorder in which muscle tissue and connective tissue such as tendons, muscles and ligaments are gradually replaced by bone (ossified), forming bone outside the skeleton (extra-skeletal or heterotopic bone) that progressively locks joints in place and makes movement difficult or impossible.

This process generally becomes noticeable in early childhood, starting with the neck and shoulders and proceeding down the body and into the limbs, rendering them permanently unable to bend or move. Any small injury to connective tissue (muscles, ligaments, and tendons) can result in the formation of hard bone around the damaged site. The extra bone that develops is normal, but grows in the wrong place.

Surgical attempts to remove the extra, unwanted bone results in an explosive growth of more bone. Inability to open the mouth may cause difficulty speaking or eating.

Over time, individuals with this disorder may experience malnutrition due to their eating problems. These individuals may also have breathing difficulties because of extra bone formation around the rib cage that restricts expansion of the lungs.

FOP is caused by mutations in the ACVR1 gene related to the “BMP pathway”, which is associated with the formation of the skeleton in the embryo and the repair of the skeleton following birth.

FOP is a very rare genetic disease affecting approximately 1 in 2 million people worldwide.

Physical findings:

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  Malformations of the big (great) toes;

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  Short thumbs; curved fifth finger;

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  Diminished range of motion (ROM) of the joints, especially the neck, spine, shoulder girdle and arms;

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  Tall narrow vertebral bodies;

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  Fusion of the facet joints between C2 and C7;

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  Decreased oral aperture (opening of the mouth); and

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  Diminished chest expansion.

ICD-9: 728.11

Currently there are no known effective treatments. Medication is only helpful to manage symptoms of pain, inflammation, etc. during acute flare-ups. Surgical attempts to remove the extra, unwanted bone may result in growth of more bone.

FOP usually begins during early childhood and progresses throughout life. Most children with FOP develop episodic, painful inflammatory soft tissue swellings (or flare-ups) during the first decade of life. Life expectancy is variable and usually related to the extent of calcification and the organ systems affected.

SUGGESTED PROGRAMMATIC ASSESSMENT*

Suggested MER for Evaluation:

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  Clinical history and examination that describes the diagnostic features of the impairment;

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  MRI/CT of muscles and joints; and

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  Laboratory tests results documenting mutations in the ACVR1 gene.

Suggested Listings for Evaluation:

REMARKS