FOP (Fibrodysplasia Ossificans Progressiva)

What is FOP?

FOP is short for Fibrodysplasia Ossificans Progressiva. The disease is also known as Myositis Ossificans Progressiva; the name was modified in the 1970s to acknowledge the involvement of other soft, or fibrous, tissues in addition to muscle. FOP is a rare genetic disorder in which bone forms in muscles, tendons, ligaments, and other connective tissues. Bridges of extra bone form across the joints in characteristic patterns, progressively restricting movement. FOP is a disease in which the body produces not just too much bone, but an extra skeleton that immobilizes the joints of the body.

What are the Symptoms of FOP?

Children with FOP appear normal at birth except for congenital malformations of the great toe. During the first or second decade of life, children form painful fibrous nodules over the neck, back, and shoulders which mature into bone in a process known as heterotopic ossification. FOP then progresses along the trunk and limbs 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. People who have FOP experience different rates of new bone formation; in some the progress is rapid, while in others it is more gradual. In each case, the exact rate of progression is unpredictable, although there does appear to be a characteristic pattern to the progression. For example, FOP involvement of the upper regions of the body, such as the back and shoulder areas, almost always precedes the development of FOP in the lower portion of the body, i.e. the hips and knees.

When was FOP first documented?

The earliest documented cases date back to the 17th and 18th centuries.

How many people have FOP?

It is estimated that FOP affects about 2,500 people worldwide, or approximately one in two million people. Such statistics may be better grasped by the following example: if a large football stadium holds 100,000 fans, one would need to fill nearly 20 football stadiums to find one person who has FOP. At the present time, researchers are aware of approximately 600 people throughout the world who have FOP.

Can the extra bone be removed?

The technical answer is surprisingly "yes," but that does not tell the whole story. Surgical intervention often results in a worsening of the condition. New bone will grow back and further impair mobility.

How is the extra bone in FOP different from normal bone?

The extra bone in FOP forms by a progressive transformation of soft tissue into cartilage and bone. This is the same process by which bone regenerates (heals) after a fracture (break) occurs and is nearly identical to the process by which bone forms normally in an embryo. The abnormality in FOP occurs not in the manner of bone formation but rather in its timing and location.

What is a flare-up and is it painful?

A flare-up occurs when the body starts to generate new bone. No one knows what initiates this process, but once it begins, it leads to tissue swelling and much discomfort. Flare-ups are usually painful. Sometimes the individual will not feel well and may develop a low-grade fever. While there is no medication or therapy that can stop the process of bone formation once it has begun, a physician can prescribe medicine to help relieve the pain. A single flare-up may continue for as long as 6-8 weeks. However, major overlapping flare-ups may occur in which pain does not subside as quickly. When a flare-up is in progress, joint stiffness may occur overnight. The stiffness comes from swelling and pressure inside the muscle during the earliest stages of new bone formation.

Most people find that the pain subsides when a flare-up is over; it appears that it is the process of extra bone formation, rather than the extra bone itself, that usually leads to pain. FOP is not always painful.

Will FOP get worse? Does it ever stop or go away?

Unfortunately, FOP does not improve over time. The "P" in FOP stands for "Progressiva." That means that FOP will progress, or get worse, as a person ages. As FOP is part of a person's genetic make-up, people with FOP are born with the condition, even though the extra bone may not have appeared at birth. So people with FOP will not outgrow the condition. Nor can the extra bone that has been produced by FOP disappear. The body of a person with FOP does not make extra bone all of the time; a person with FOP may go months or years without a flare-up. Nevertheless, there is always a chance that extra bone can form, either without any warning, or as a result of trauma (injury), such as a bump or a fall. There are also times when, in spite of obvious trauma, FOP does not manifest itself. It is unclear why the disease is active some times and quiet or dormant at other times.

What parts of the body are involved in FOP? How does FOP affect mobility?

FOP affects the neck, spine, chest, shoulders, elbows, wrists, hips, knees, ankles, jaw, and many areas in between. The progression of ossification follows a characteristic pattern. Usually extra bone forms in the neck, spine, and shoulders before developing in the elbows, hips and knees. The muscles of the diaphragm, tongue, eyes, face, and heart are characteristically spared. The well-documented and characteristic progression of FOP, as well as the regions not affected, likely hold important clues to the cause and development of the disease.

FOP affects mobility because the body's joints, such as the knees or the elbows, connect the bones and aid in movement. In FOP, extra bone replaces the ligaments (which cover the joints), as well as muscles and tendons (which move the joints). Consequently, movement in areas affected by FOP becomes difficult or impossible.

What physical variations are seen from person to person?

The largest variation seen is the timing and rate of extra bone formation. Another common variation includes the severity of movement restriction. For example, an elbow could be fixed in a closed position, putting the hand permanently across the chest, or the elbow may be left with some range of motion.

Is there any treatment for FOP?

At this time, there is no treatment for FOP. There is a drug currently under development which may one day be used to help control extra bone growth. For now, medication is only helpful to manage the symptoms of FOP (pain, inflammation, etc.) Read our treatment considerations for more information.

More information available at http://www.ifopa.org

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