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Hormone and bone diseases

Fibrodysplasia ossificans progressiva (FOP)

A very rare disease in which muscle and connective tissue turn into bone over time. The joints gradually lock and movement becomes limited.

Not part of the panel of Türkiye's National Newborn Screening Programme (heel-prick test). Source

Orphanet has a guideline for emergency doctors for this disease (language: French). See on Orphanet

Prepare an emergency card

This page is translated from the Turkish original.

This disease is followed through the “Hormone and bone diseases” group.

Understanding the disease

This section has not yet been reviewed by a physician. It summarises patient information from sources such as MedlinePlus, Orphanet and the NHS in plain language. The disease can differ from person to person; talk to your doctor about diagnosis and treatment.

What happens in this disease?

A change in the ACVR1 gene keeps a switch that turns on bone-making permanently on. This is why new bone forms outside the skeleton, in the muscles and ligaments. The process usually begins in early childhood in the neck and shoulders. A knock, a fall or illnesses such as flu can trigger flare-ups.

Which symptoms can occur?

Symptoms progress over time.

  • Differently shaped big toes from birth (in almost all)
  • Painful swelling flare-ups in the muscles
  • Increasing limitation of movement in the joints
  • Not being able to open the mouth fully; difficulty speaking and eating
  • Shortness of breath as the rib cage stiffens
  • Short thumbs (sometimes)

How is it diagnosed?

Looking at the big toes is an important clue for the diagnosis. The diagnosis is confirmed by examination and a genetic test of the ACVR1 gene. Taking a tissue sample can trigger new bone formation; this is why it is avoided.

Treatment and care

There are approved medicine treatments specifically for the disease that reduce new bone formation. In the US, the first was approved in 2023. Avoiding injections into muscle, falls and knocks is important. During flare-ups, treatment for pain and swelling is given. Occupational therapy and aids make daily life easier. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

It is passed on through dominant inheritance. Most cases start with a new gene change, with no family history. In a small number of people the change comes from an affected parent. For each child of an affected person, the chance of passing it on is 1 in 2. Genetic counselling is recommended.

Source: MedlinePlus Genetics: Fibrodysplasia ossificans progressiva · NORD: Fibrodysplasia Ossificans Progressiva · FDA: FDA Approves Second Treatment for Fibrodysplasia Ossificans Progressiva

Key facts

How common is it?
Prevalence: <1 per 1 000 000 (Worldwide)
When does it usually start?
Childhood
Gene(s) involved
ACVR1

These facts are taken from Orphanet and MedlinePlus records (last checked: October 7, 2026). Frequency values are approximate ranges.

You are not alone: patient associations in Türkiye

Non-profit patient and family organizations in Türkiye working on this disease or disease group. Links are for information; Doktorclub is not affiliated with these organizations and does not endorse them.

We could not find a patient association specific to this disease.

For all rare diseases: Nadir Hastalıklar Federasyonu

Support and help

Doktorclub does not diagnose, recommend treatments or refer you to hospitals or doctors. These pages are meant to help you talk with your doctor.

News about FOP

Clinical trials (ClinicalTrials.gov)

A clinical trial is a regulated study that tests whether a new treatment is safe and whether it works, in patients who volunteer. Most trials look for a certain age, genetic change and health condition. Taking part is voluntary.

This list is not a treatment recommendation. Treatments tested in phase 1–3 trials are investigational (experimental): their efficacy and safety have not yet been proven and they are not approved treatments. Taking part depends on each trial’s criteria and a physician’s assessment; the first step is to talk to the doctor who manages your care.

Questions you can ask your doctor

  • Could this trial be suitable for us?
  • If we take part, how would current treatment and check-ups be affected?
  • Where does the trial take place, and how are travel and accommodation handled?
  • What happens if we want to leave the trial?

ClinicalTrials.gov lists 5 active interventional studies for this disease. 1 is recruiting now; none has a site in Türkiye. Last checked: October 7, 2026.

Selected records (studies with a site in Türkiye first):

See all studies on ClinicalTrials.gov · Joining clinical trials

Hormone and bone diseases: other news

Medical codes (for talking with your doctor and finding sources)

These codes identify the disease in international classifications and databases. They can help when you talk with your doctor or look for reliable sources.

Orphanet code: ORPHA:337 · ICD-11 FB31.1

Codes checked against WHO ICD-11 and Orphanet on October 7, 2026.

This page provides general information and does not replace diagnosis or treatment. Talk to your doctor about symptoms, diagnosis and treatment.

The information on these pages is for general information only and does not replace medical advice. Talk to your doctor about diagnosis and treatment decisions. In an emergency in Türkiye, call 112.

Every update is based on an open source and labeled with its level of evidence. No advertising and no drug brand names. Our scientific principles

This page was translated from Turkish by the Doktorclub editorial team.