Fibrodysplasia Ossificans Progressiva (FOP)

What Is FOP?

Fibrodysplasia ossificans progressiva (FOP) is a rare condition that affects about 1 in 1.6 million people. It causes extra bone (called heterotopic bone) to form in places where bone doesn’t normally grow, like tendons, ligaments, and other soft tissues.

What Causes FOP?

FOP is caused by a change (variant) in a gene called ACVR1.

What Are the Signs & Symptoms of FOP?

People with FOP have the gene change before birth, but most symptoms show up between ages 5 and 10. Signs can include:

• Big toe differences at birth: short, turned inward; an early clue to diagnosis
• Painful swelling or nodules under the skin on the scalp, neck, or back (often ages 1–10)
• Later, bone growth and swelling in the hips or knees (teens or adulthood)
• Pain where inflammation or swelling happens

How Is FOP Diagnosed? 

Doctors may suspect FOP if the big toes look different or if there are flare-ups of pain and extra bone growth.

• A genetic test can confirm an ACVR1 gene variant.
• Biopsies are not recommended, as they can trigger a flare-up. 

How Is FOP Treated? 

There is no cure yet, but treatment focuses on preventing and managing flare-ups: 

Preventing Flare-Ups

• Avoid falls and contact sports
• Follow vaccination guidelines from ifopa.org
• Avoid unnecessary biopsies, surgeries, or trauma
• Try to prevent viral illnesses when possible
• Physical and occupational therapy using gentle, active movements
• If surgery is required, a short course of steroids may help prevent flare-ups

Treating Flare-Ups When They Happen

• Short courses of steroids (about 4 days; may repeat if needed)
• Anti-inflammatory medicines like ibuprofen for pain and swelling
• Avoid surgery and biopsies if possible

New Treatment Option

• Palovarotene: a medication that helps slow or prevent new bone growth. 
  • For females age 8+ and males age 10+ with FOP
  • Taken daily; dose may increase during flare-ups

Studies of long-term outcomes using palovarotene and studies of new medications are ongoing.

What to Expect with Our Care Team

If FOP is suspected:

• We can help arrange genetic testing and confirm the diagnosis
• We will monitor blood work and imaging to check for effects on the body and arteries
• We’ll create a personalized care plan based on your child’s symptoms and needs

Additional Resources 

• International FOP Association