Understanding FOP

Patient Voice spoke with Dr. Angela Cheung about fibrodysplasia ossificans progressiva (FOP), an ultra-rare musculoskeletal condition that transforms muscle and tendon into bone. She explores how understanding of the disease has evolved in recent years and why it’s especially challenging to develop therapies for ultra-rare patient populations.

Photography by Patient Voice.

Dr. Cheung is a Senior Clinician Scientist at the Toronto General Hospital Research Institute and the Schroeder Arthritis Institute. She also established the University of Toronto Centre for Excellence in Skeletal Health Assessment and the Osteoporosis Program at the University Health Network.

1. What is FOP and how does it affect one's body?

Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare disease occurring in around one in two million people. It’s a musculoskeletal condition that causes the formation of abnormal bone due to a mutation in a gene that codes a protein that affects bone development. Patients with FOP have a propensity to form bone in places where there shouldn’t be any bone — basically, over time, muscles and tendons are transformed into bone in a process called heterotopic ossification. This can severely restrict movement and negatively impact patients’ functioning in their daily activities. 

Some people think of FOP as having a second skeleton. The extra skeleton immobilizes the joints of the body, leading to stiffness and permanent immobility. Patients become fixed in a certain position and they’re trapped in this skeleton. That’s where the term “tin soldier” comes from — there’s a film called Tin Soldiers all about this disease. 

2. When, and how, is FOP typically diagnosed?

The average age of diagnosis for patients with FOP is 7.5 years, but FOP is often missed until the teenage years or even into young adulthood. For some, it takes even longer to get diagnosed. Because it’s so extremely rare, FOP is often unrecognized by clinicians and misdiagnosed as something else, like bone cancer for example. That being said, there’s a simple way to recognize FOP in early childhood: the abnormal formation of the big toe. Kids with FOP often look like they have a bunion on their big toe.

For older patients, FOP is typically diagnosed after a flare-up. It usually starts with minor trauma, such as a fall, which results in patients experiencing inflammation in the tissue, especially muscles and tendons. They’ll notice swelling, redness, warmth, and pain in the injured area, and then it will harden over time as the abnormal bone formation occurs. Patients often seek care due to the pain, which can then lead to a diagnosis.

"FOP is often missed until the teenage years or even into young adulthood. For some, it takes even longer to get diagnosed."

3. Has your understanding of FOP evolved throughout your career?

I entered this field about eight years ago, when I was looking after a patient with FOP. My understanding evolved as I got to know the patients and their families and caregivers, as well as the scientists, clinicians, and pharmaceutical companies who are all working together to find a cure for this horrible condition. Because FOP is so ultra-rare, all of these stakeholders work together incredibly closely. 

The FOP community is very collaborative and resilient, and I’ve learned a lot from them. I’ve also been powerfully inspired by the patients, whom I’ve gotten to know quite well. I now have a better understanding of their day-to-day struggles and have been moved by their resilience and adaptability.

4. What kinds of challenges are associated with caring for, and developing novel therapeutics for, ultra-rare patient populations?

One of the challenges of looking after ultra-rare diseases is that there are so few patients. In Canada, for example, there are about 20 or 25 FOP patients nationwide. They’re spread across a vast area and so accessing specialists who have a lot of experience is difficult. Developing medicines for this population is also a challenge. 

The usual route for developing medications is to test them in a lot of patients in large clinical trials, but because FOP is an ultra-rare disease, we just don’t have enough patients for these kinds of trials. We have to be much more innovative in how we design studies, how we approach approving possible treatments, and how we get these treatments into the hands of patients in all provinces. 

5. Why is it a hopeful time for Canada’s FOP community?

Because we know the exact genetic cause of FOP, progress in FOP research has actually moved way faster than with some other more common conditions. And FOP researchers are very dedicated to trying to find solutions, interventions, and cures for these patients. 

There’s currently one FOP treatment approved by Health Canada, which is a major milestone. We’re now working on getting patients access to this treatment — so that’s hopeful. And there are multiple other treatment clinical trials going on right now around the world. I’m hoping that these trials will show beneficial effects so that they can be put on the market too, giving patients a range of medication options.

Another reason it’s a hopeful time is that we’re trying to develop a gene therapy that would help to treat FOP way earlier, and potentially to even stop it in utero. We hope to get to a point where we’ll one day be able to identify FOP in unborn babies and to provide gene therapy in utero to prevent kids from having to grow up with this painful and life-altering disease.

The Canadian FOP Network (CFOPN) is volunteer-run organization dedicated to raising awareness of, and research funds for, Canadians who live with fibrodysplasia ossificans progressiva (FOP). Visit to learn more.

This content was supported by Ipsen Biopharmaceuticals Canada Inc. This page was developed by Patient Voice, and the supporter did not influence the final article or editorial themes of this content.