Mona Al Mukaddam, MD, Associate Professor of Clinical Medicine and Orthopaedic Surgery at Penn Medicine, describes fibrodysplasia ossificans progressiva (FOP).



FOP is genetic disorder characterized by new bone formation outside of the normal skeletal system, like in soft connective tissues, a process known as heterotopic ossification, which can be preceded by painful soft-tissue swelling or “flare-ups”. Heterotopic ossification, once formed, is irreversible and leads to loss of mobility and shortened life expectancy. FOP is a particularly painful and deliberating condition. Often, early death can be the result of bone forming around the ribcage leading to breathing problems and cardiorespiratory failure.

FOP is an ultra-rare condition that afflicts about 400 people in the US and 900 people globally.

As noted by Dr. Al Mukaddam, FOP is a genetic disease. That means that children are born with the condition. However, the slow progressive nature of the second skeleton developing means it is not always diagnosed quickly. A common symptom observed at birth is a curved big toe. That, along with children often showing symptoms of joint stiffening or pain, should alert the physician to consider FOP as a possibility. Recently, the orphan drug palocarotene, was approved to treat patients.

To learn more about FOP and other skeletal disorders, visit