Major breakthrough in treatment for ultra-rare 'second skeleton' disease

A “life changing” new therapy for an extremely rare medical condition which causes patients to grow a second skeleton has been proven successful in a key clinical trial.

Relatives of people living with fibrodysplasia ossificans progressiva (FOP) say that they have “desperately waited” years for a medicine to “stop the disease in its tracks”.

FOP is a genetic disorder which causes the human body to generate extra bones where they ought not to grow.

That can include within muscles, tendons, ligaments and other connective tissue.

The bone growth typically occurs after flare-ups, which may be provoked by minor injuries or sickness.

The condition is life-limiting as it results in progressive immobility, along with difficulties speaking, swallowing and breathing.

However, the new “disease-modifying” treatment has now been shown to cut new bone growth by over 90 per cent, decrease flare-ups and potentially provide renewed hope for surgical options in the future.

FOP ranks among the world's rarest medical conditions, impacting just one in every million people.

Data provided by the charity FOP Friends indicates that there are 70 patients across the UK, with only 900 recorded cases found worldwide.

The charity said that “treatments can only change lives if patients can access them” as it called on health officials to approve the drug garetosmab for NHS use.

The new treatment, also known as Pasatru and made by Regeneron, is an antibody that blocks a protein called activin A, which has been found to be critical in the development of new abnormal growth development in people with FOP.

Because the disease is so rare, the clinical trial took place in 16 countries and regions, including the UK.

It involved 63 adults with FOP with an average age of 27 who were split into three groups: one group received a dummy drug, or placebo, another was given a low dose of garetosmab and the other received a higher dose.

After just over a year of treatment, the total number of new abnormal bone growths was significantly lower among the groups who received the treatment.

People who had the placebo had an average of 19 new ‘lesions’ while people who received the treatment had just one or two.

Those taking the higher dose also saw a reduction in flare-ups, researchers found.

Writing in The Lancet, the authors said: “The current treatment landscape for FOP is marked by unmet need.

“However, the findings from this study provide strong evidence supporting the efficacy and safety of garetosmab in adults with FOP.”

They went on: “Given its efficacy in preventing the formation of new heterotopic bone lesions, reducing flare-ups, and reducing the total volume of new heterotopic bone lesions, garetosmab has the potential to become an efficacious disease-modifying treatment for FOP, with a generally well-tolerated safety profile.

“By dramatically reducing the process of heterotopic ossification, long term preservation of mobility and function is anticipated, as further ankyloses of joints will potentially not occur with garetosmab treatment.

“Moreover, the ability of garetosmab to prevent new bone formation in FOP might allow its use as a basis to reconsider surgical remobilisation efforts, which could allow for the significant return of function for many people with FOP suffering from immobilised joints, and which has so far been avoided due to the induction of exuberant aberrant bone formation by surgical intervention.”

Chris Bedford-Gay, FOP Friends founder and trustee, said that the community “has desperately waited for a way to stop FOP in its tracks”.

He said: “For many years, our community has hoped for the day there would be a treatment for FOP, a way to stop the devastating, irreversible condition impacting our lives.

“Now, over 15 years since we joined the battle when our eldest son, Oliver, was diagnosed just after his first birthday, we finally have not one, but two potential treatments heading to the UK.”

The US medicines regulator has approved garetosmab and another treatment called zilurgisertib.

Mr Bedford-Gay said this “is the moment a life-changing treatment comes that bit closer”, adding: “For patients, parents and carers who have watched helplessly as FOP steals mobility and independence piece by piece, this news proves that our fight, the years of fundraising, advocating and participating in clinical trials, has not been in vain.

“However, for our community here in the UK, celebration is mixed with anxiety – treatments can only change lives if patients can access them.

“As part of FOP Friends, and as a dad to a child with FOP, my focus now shifts to the UK regulatory pathway.

“We must argue the case for all FOP patients in the UK to have access to these treatments, ensuring we do not have to wait a single day longer than necessary for this life-altering medicine.

“Our job now, as a community, is to persuade the UK regulatory authorities that these new treatments are safe, effective and life-changing for FOP patients, their families and beyond.

“Soon we will have a weapon against FOP. But for now, our fight must continue.”