Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder in which normal bone forms in abnormal locations, such as in muscles, tendons, ligaments and other connective tissues. The body produces not just too much bone, but an extra skeleton that immobilizes the joints of the body. These lesions slowly replace the body's muscles with normal appearing bone. Any attempt to remove the extra bone results in even more robust bone formation. There is no effective treatment.
FOP has a prevalence of approximately one in two million, affecting approximately 2,500 people worldwide.