Fibrodysplasia ossificans progressiva (FOP) 

It is a disorder in which skeletal muscle and connective tissue, such as tendons and ligaments, are gradually replaced by bone (ossified). This condition leads to bone formation outside the skeleton (extra-skeletal or heterotopic bone) that restricts movement.

This process generally becomes noticeable in early childhood, starting with the neck and shoulders and moving down the body and into the limbs. People with FOP are born with abnormal big toes (hallux valgus) which can be helpful in making the diagnosis. Trauma, such as a fall or invasive medical procedure, or a viral illness may trigger episodes of muscle swelling and inflammation (myositis). These flareups lasts for several days to months and often result in permanent bone growth in the injured area.

FOP is almost always caused by a mutation at the same place in the ACVR1 gene (The ACVR1 gene provides instructions for making the activin receptor type-1 (ACVR1) protein, which is a member of a protein family called bone morphogenetic protein (BMP) type I receptors.)  and is inherited in an autosomal dominant manner. This condition occurs in about 1 in 1,600,000 newborns and about 800 people worldwide are known to have FOP.

SIGNS AND SYMPTOMS

-Fibrodysplasia ossificans progressiva (FOP) is characterized by the gradual replacement of muscle tissue and connective tissue (such as tendons and ligaments) by bone, restricting movement. This process generally becomes noticeable in early childhood, starting with the neck and shoulders and proceeding down the body and into the limbs.

-The formation of extra-skeletal bone causes progressive loss of mobility as the joints become affected. Speaking and eating may also become difficult as the mouth becomes affected. Over time, people with FOP may become malnourished because of the inability to eat. They may also develop breathing difficulties as a result of extra bone formation around the rib cage that restricts expansion of the lungs.

-Any trauma to the muscles of an individual with FOP (a fall or an invasive medical procedure) may trigger episodes of muscle swelling and inflammation followed by more rapid ossification in the injured area. Flare-ups may also be caused by viral illnesses such as the flu.

-Affected individuals may also have short thumbs and other skeletal abnormalities.

Inheritance

-Fibrodysplasia ossificans progressiva is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

-Most cases of fibrodysplasia ossificans progressiva result from new mutations in the gene. These cases occur in people with no history of the disorder in their family. In only a small number of cases, an affected person has inherited the mutation from one affected parent.

How this disease is diagnosed:

-Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

-The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

TREATMENT:

There is currently no definitive treatment.  However, a brief course of high-dose corticosteroids, such as Prednisone, started within the first 24 hours of a flare-up, may help reduce the intense inflammation and tissue swelling seen in the early stages of fibrodysplasia ossificans progressiva.  Other medications, such as muscle relaxants, mast cell inhibitors, and aminobisphosphonates, if appropriate, should be closely monitored by a physician.  Surgery to remove heterotopic and extra-skeletal bone is risky and can potentially cause painful new bone growth.

References:

 

• Fibrodysplasia ossificans progressiva. Genetics Home Reference (GHR). August 2007; http://ghr.nlm.nih.gov/condition/fibrodysplasia-ossificans-progressiva.
• FOP Fact Sheet. International Fibrodysplasia Ossificans Progressiva Association. http://www.ifopa.org/what-is-fop/overview.html. Accessed 6/5/2014.
• Pignolo R, Kaplan F. Pediatric Fibrodysplasia Ossificans Progressiva. E-medicine. July 30, 2009; http://emedicine.medscape.com/article/1007104-overview. Accessed 3/17/2011