FOP Awareness Day Date in the current year: April 23, 2025

Fibrodysplasia ossificans progressiva (FOP), also known as Münchmeyer’s disease or stone man disease, is an extremely rare congenital disorder in which muscles, tendons, and ligaments gradually ossify (turn into bone tissue), eventually rendering patients immobile. It is one of the rarest diseases in the world: fewer then 1,000 cases of FOP have been confirmed worldwide.

The disease has been known since at least the 17th century: a patient with FOP is described in the writings of the French physician Guy Patin. It was originally called myositis ossificans progressiva because it was thought to be caused by inflammation of the muscles. In 1970, American physician Victor A. McKusick discovered that it affected ligaments and tendons as well as muscles, and gave the disease its current name.

FOP is most often caused by a de novo (new) mutation on chromosome 2q23-24 that affects the body’s bone repair mechanism. The only sign of the disease in newborns is deformed big toes, which may have a lump at the minor joint or even miss a joint. The onset of FOP usually occurs before the age of 10; ossification generally begins at the neck and progresses downward to the shoulders, arms, chest, and finally the feet. The disease can affect any part of the body that has muscle or other soft tissue, except for the heart, diaphragm, tongue, face, and eyes.

Bone growth usually occurs in spurts called flare-ups. They can be spontaneous or triggered by trauma (bumps, falls, injuries, overexertion, or even intramuscular injections) and last from a few days to a year or more. During flare-ups, painful tumor-like swellings appear in areas of new bone growth. These swellings usually subside as the flare-up passes and the new bone matures. The new bones eventually form a secondary skeleton that fuses with the existing skeleton, immobilizing the patient.

FOP is an incurable disease that inevitably progresses over time. The average life expectancy of a patient with FOP is 56 years; the most common cause of death is cardiorespiratory failure due to chest wall deformities.

FOP cannot be treated by surgically removing the extra bone, because bone growth is often triggered by trauma; after the new bone is removed, the body tries to “repair” the affected area by growing even more bone. The only approved treatment for FOP is palovarotene (Sohonos), which helps inhibit abnormal bone growth; as of 2025, it has been approved in Canada and the United States, but not in the EU.

FOP Awareness Day was created to educate the public about this rare disease and to highlight the importance of finding a cure. The date, April 23, was chosen to commemorate the anniversary of the discovery of the gene responsible for FOP. You can get involved by learning more about the disease and sharing what you’ve learned with others, donating to an organization that supports FOP patients and their families or funds research, and spreading the word on social media using the hashtag #FOPAwarenessDay.