What is FOP?

Home / What is FOP?

Fibrodysplasia Ossificans Progressiva, or FOP, is one of the rarest and most disabling genetic conditions known to medicine. It causes bone to form in muscles and other connective tissues such as tendons and ligaments.

Most cases of FOP are new.  This means that no-one else in the family has FOP.  This happens because unexpected changes (mutations) happen as the genes are passed along from each parent.  Many of these changes, such as the change that leads to FOP, are accidents of nature that happen for no apparent reason.  If one parent has FOP, then there is a 50% chance that the FOP gene will be passed on to their child.

FOP is extremely variable and unpredictable.  It affects every person differently, and at different rates.  Disease progression is rapid in some individuals, while in others it is gradual.  There can be no way to predict how FOP will affect a person.

If the person with FOP suffers a trauma to the body such as a knock, bump or fall, then it can exacerbate the progression.  However, FOP flare-ups can and will occur without warning or explanation.

Children with FOP usually appear normal at birth, except for congenital malformation of the great toes.  However, some rarer atypical cases may not display such malformation.

A baby with FOP may have restricted movement in their neck and shoulders from as early as birth.  Babies with FOP typically don’t crawl due to fused vertebrae in the neck.

During the first two decades of their life, a child with FOP may experience unusual swellings across their body.  This can sometimes be misdiagnosed as tumours resulting in potentially harmful biopsies or invasive treatments.

Worldwide, FOP affects around one in 1.4 million births, with just over 800 confirmed cases worldwide. In the UK there are around 80 known cases.  This makes FOP an ultra-rare condition.

FOP Friends works closely with the other patient organisations around the world.  Chris serves on the board of the IFOPA, and is also Chair of the International President’s Council.


Unfortunately, the P in FOP means the condition is progressive: it won’t get better over time.  As the person with FOP gets older, it is likely that the condition will worsen too.  Once the extra bone has developed in a person’s body, there is no way to remove it, as surgery would only trigger further FOP flare-ups and bone growth.

A person with FOP may go months or years without experiencing a flare-up.  Other people may find they are locked in a flare-cycle for months.  The flare-ups can occur after ‘trauma’ to the body, such as a knock, bump, fall, impact to the muscle, overexertion, intramuscular injections or even some viruses.  However, there is also the chance that the extra bone growth may occur spontaneously without any reason or warning.

The reasons for why the disease behaves in this way are still unclear at this time.  However, there are currently 16 research programmes into underway.  Although most of these won’t lead to a treatment for FOP, they all have the potential to increase scientists’ understanding of the condition which will ultimately give us a treatment and cure.

The research into rare diseases such has FOP has a massive implication for doctors’ understanding of other more common medical conditions.  Research into treatments for FOP has the potential to advance the treatment for other diseases such as osteoporosis, childhood brain cancer, heart disease, burns, heterotopic ossification following military injuries or surgeries, sporting injuries, chronic anaemia, and atherosclerosis.

Supporting the research into FOP could help change the lives of millions of people.

There are currently 16 FOP drugs in research or development.

Ipsen Pharmaceuticals are coming to the end of their Phase 3 clinical trial for palovaretene (Clementia previously owned this drug but the company was taken over by Ipsen in 2019).  In December 2019, paediatric trials for palovaretene were put on hold.

In January 2020, Regeneron released promising Phase 2 results.

Kyoto University and VUmc/Oxford/Harvard have drugs in Phase 2 clinical trials.