Fibrodysplasia Ossificans Progressiva or FOP is an ultra-rare genetic disorder that causes bone to form where it should not – outside of the skeleton and in the soft and connective tissues such as in the muscles, tendons and ligaments.1,2
The process of bone forming outside of the skeleton is called Heterotopic Ossification or HO.3 Over time HO leads to ribbons, sheets and plates of extra bone forming in places throughout the body where bone should not be.1
*This is an artistic portrayal.
Once formed, this extra bone does not go away and can lead to joint stiffness. Where it forms across the joints it can progressively restrict normal movement, potentially causing locked joints (such as locked arms or a locked back).1,4
Extra bone formation in people living with FOP can be triggered by knocks and falls and certain medical procedures, such as taking a biopsy or having an intramuscular injection.5
FOP is caused by having a faulty copy of a gene. Scientists discovered that the gene responsible is Activin-Like Kinase 2 or ACtiVin Receptor type-1 (ALK2/ACVR1).
In people without FOP, this gene produces a normal protein. This protein interacts with specific bone-forming proteins called Bone Morphogenetic Proteins (BMPs). And through this interaction, normal bone is formed.
However, in people with FOP, this faulty gene leads to a malformed, overactive protein. This overactive protein leads to the formation of extra bone.
A person who is living with FOP would need to have either inherited a faulty copy of the ALK2/ACVR1 or ‘FOP gene’ from a parent with the condition or had a spontaneous mutation occur in the gene while developing in the womb. Most cases of FOP occur in people with no family history of the disease.7
FOP is a congenital genetic condition which means that it is present at birth. However, the diagnosis will often not be made until much later in childhood when a flare-up arouses suspicion.8 There is one clear warning sign of FOP, however, and that is being born with turned-in great toes that may look like bunions (hallux valgus) but they are not.
There is currently no cure for FOP and management is primarily focused on:9
Only around one or two people per million have the condition.1 The number of people living with FOP at any one time varies from country to country.10
Bone that forms following a FOP flare-up is the same bone that the body makes normally. This bone is just formed in the wrong place, such as soft connective tissue like ligaments and tendons or certain muscles. Over time this bone may start to build up and restrict movement across the joints and cause problems with mobility.1,4
FOP is an ultra-rare genetic disorder that is present from birth.7 It is caused by a defect in the ALK2/ACVR1 gene which is involved in the normal formation of bone.7
Nearly nine out of 10 people living with FOP are misdiagnosed with another condition before they are diagnosed with FOP.8 Common misdiagnoses include bunions and other disorders affecting the bones and soft tissues. Swellings occurring during FOP flare-ups can also be mistaken for tumors.8
A diagnosis of FOP can be made based on clinical signs and symptoms such as having turned-in great toes and recurring flare-ups. There is also a genetic test for the FOP gene that can confirm a diagnosis of FOP.9,11,12
FOP can affect girls as well as boys regardless of their race, ethnicity or country of origin.5 And while FOP can be inherited, the majority of patients with FOP experienced a spontaneous genetic mutation.
The extra bone that is formed does not go away.1,3 This means it can build up over time and make it difficult for some people living with FOP to move and perform their normal everyday tasks. Recognizing and avoiding certain activities to help prevent FOP flare-ups is important to try to limit the formation of additional bone.1,4
Since the FOP gene was discovered, doctors and researchers have been working hard to better understand this condition and how it affects patients. 7,11,12
From providing medical care to social support, many different healthcare professionals work together to provide the best care for people living with FOP.11,12
In 2019, a third of the world’s FOP population was part of the International Fibrodysplasia Ossificans Progressiva Association (IFOPA). IFOPA is an international non-profit organization that provides support to people living with FOP and their families through education and support programs.13