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.