Fibrodysplasia Ossificans Progressiva

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Fibrodysplasia Ossificans Progressiva is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • FOP
  • myositis ossificans progressiva

Disorder Subdivisions

  • None

General Discussion

Fibrodysplasia ossificans progressiva (FOP) is a very rare inherited connective tissue disorder characterized by the abnormal development of bone in areas of the body where bone is not normally present (heterotopic ossification), such as the ligaments, tendons, and skeletal muscles. Specifically, this disorder causes the body's skeletal muscles and soft connective tissues to undergo a metamorphosis, essentially a transformation into bone, progressively locking joints in place and making movement difficult or impossible. FOP is characterized by malformed big toes that are present at birth (congenital). Other skeletal malformations of the cervical spine and ribs and the abnormal development of bone at multiple soft tissue sites may lead episodically to stiffness in affected areas, limited movement, and eventual ankylosis of affected joints (neck, shoulders, elbows, hips knees, wrists, ankles, jaw, often in that order).

Episodic flare-ups (pre-osseous soft tissue swellings) of FOP usually begin during early childhood and progress throughout life. Most cases of FOP occur as the result of a sporadic new mutation. The genetic mutation that results in this disorder has been identified. FOP is caused by the mutation of a gene in the bone morphogenetic protein (BMP) pathway, which is important during the formation of the skeleton in the embryo and the repair of the skeleton following birth.


All individuals with classic FOP have malformations of the great toes and, in approximately 50% of cases, the thumbs. These changes in the skeleton are present at birth (congenital) and are the first clinical signs of this disorder. The most common malformation associated with FOP is a shortened great toe with a malformed distal first metatarsal and a missing or abnormal interphalangeal joint. Other malformations of the toes and fingers may include inward turning of the great toe toward the other toes (hallux valgus), abnormally short fingers and toes (microdactyly), and/or permanent fixation of the fifth finger in a bent position (clinodactyly). Other congenital signs of FOP include proximal medial tibial osteochondromas, malformation of the upper part of the spinal column (cervical vertebrae) and/or an abnormally short broad neck of the bone in the thigh that extends from the knee to the pelvis (femur).

Progressive bone formation in areas of the body where bone is not normally present (heterotopic ossification) usually occurs during early childhood, but can occur during adolescence, early adulthood, or throughout life. The abnormal development of bone may occur spontaneously, but most commonly follows an episode of soft tissue injury or a viral illness. The first sign of heterotopic ossification is the appearance of firm tender swellings on certain parts of the body, especially the back, neck, and/or shoulders. These soft tissue swellings mature through an endochondral pathway to form mature heterotopic bone. Bony growths usually involve tendons, ligaments, skeletal muscle tissue, and connective tissue such as fascia and aponeuroses. In some cases, pain and stiffness occurs in these areas. On some occasions, a low-grade fever may herald the development of these swellings. Although the swellings eventually regress, they also harden into mature bone as they decrease in size.

In the affected areas, bone slowly replaces connective tissue; in addition to skeletal muscle, bony growths also occur in various tendons, ligaments, and bands of fibrous tissue that support muscles (fascia). The neck, back, chest, arms, and legs are usually the first areas affected. The disease may eventually affect the hips, ankles, wrists, elbows, shoulders, and/or jaw as well as the abdominal wall. In some affected individuals, the progression of bone development may be rapid; in others, the process may be gradual. Even among identical twins, the disease progression may vary greatly, reflecting different traumatic episodes.

Chronic swelling in various parts of the body is a common physical characteristic of individuals with FOP. Swelling may occur along with the abnormal bone formation that characterizes FOP, or it may occur when newly-formed bone presses on lymphatic vessels, obstructing the flow of tissue fluid. In addition, swelling may also be caused by a lack of pumping action within the hardened (ossified) muscle and can cause blood and tissue fluids to pool in a limb (e.g., arms and/or legs).

Abnormal development of bone eventually leads to stiffness and limited movement of affected joints. If the jaw is involved, affected individuals may have trouble eating and/or speaking. In addition, abnormal development of bone may lead to progressive deformity of the spine including side-to-side (scoliosis) and, in some cases, front-to-back curvature of the spine (kyphosis). In some cases, the bone that develops in abnormal areas may fracture. As the disease progresses, individuals with FOP experience limited mobility that causes problems with balance, difficulty walking and/or sitting, and/or severely restricted movement.

FOP may eventually result in complete immobilization. Affected individuals may experience progressive pain and stiffness in affected areas, complete fusion of the spine, and/or pain in certain areas of the body caused by abnormal bony growths that compress the nerves in these areas (entrapment neuropathies). As mobility begins to deteriorate, affected individuals may exhibit an increased susceptibility to respiratory infection or right sided congestive heart failure. In some cases of FOP variants, individuals may exhibit hair loss or mild cognitive delay. Hearing impairment is seen in approximately 50% of affected individuals.


Most cases of FOP occur sporadically. Where a familial pattern has been identified, FOP is inherited as an autosomal dominant trait with complete penetrance.

In April 2006, an international team of researchers led by Eileen M. Shore, PhD, and Frederick S. Kaplan, MD, of the University of Pennsylvania, published results of research identifying the genetic mutation that causes FOP. The team found that FOP is caused by a mutation of a gene on chromosome 2 (2q23-24) for a receptor in the BMP signaling pathway called ACVR1.

Bone morphogenetic proteins are regulatory proteins involved in the embryonic formation and after-birth (post-natal) repair of the skeleton. The gene identified as the FOP gene encodes a BMP receptor called Activin Receptor Type IA, or ACVR1, one of four known BMP Type I receptors. BMP receptors help determine the fate of the stem cells in which they are expressed. Classic FOP occurs when a particular amino acid in the ACVR1 protein is substituted for another amino acid at a specific location. In 2012, an ACVR1 knock-in mouse was reported with the same phenotype as human FOP. Extremely rare and illustrative phenotypic and genotypic variants of FOP have been reported, but in all patients, heterozygous activating mutations are present in the ACVR1 gene.

Chromosomes, present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22, and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome, and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further subdivided into many numbered bands, which specify the location of the thousands of genes that are present on each chromosome. For example, chromosome 2q23-24 refers to a location between bands 23 and 24 on the long arm of chromosome 2.

Genes are on the chromosomes that are inherited from the father and the mother. Phenotypic variation (including genetic diseases) is determined by the genes that specify a particular trait.

Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy, regardless of the sex of the resulting child.

Affected Populations

FOP is a very rare inherited connective tissue disorder that was first identified in the 17th century. Of an estimated 3000 affected individuals worldwide, there are approximately 800 known patients. This disorder affects both genders and all ethnicities.

Malformations of the toes and fingers may be present at birth (congenital); abnormal development of extra-skeletal bone usually occurs during early childhood. In some rare cases, onset of abnormal bone growth may not occur until late adolescence or early adulthood. Affected individuals may have periods of time where they are free of new episodes of bone growths. However, new bone growth may begin at any time for no apparent reason (spontaneously).

Standard Therapies


Misdiagnosis of FOP is common but can be avoided simply by examining the individual's toes for the characteristic feature, short great toes. The diagnosis may be confirmed by a thorough clinical evaluation, characteristic physical findings, and sequencing of the ACVR1 gene.


Biopsies should be avoided because the tests may result in rapid bone formation in those areas where tissue is removed. Intramuscular injections (e.g., immunizations) must be avoided, and dental therapy should preclude injections of local anesthetics and stretching of the jaw. In addition, individuals should avoid any situations, such as falls, that may cause blunt trauma, since trauma may cause abnormal bone development in most cases. Various viral illnesses including influenza and influenza-like illnesses may provoke flare-ups of the condition.

In affected individuals with an increased susceptibility to respiratory infections due to progressive mobility impairment, certain steps may be taken to prevent such infection, such as preventative (prophylactic) antibiotic therapy.

There are no known effective treatments for FOP. Certain types of drugs have been used to relieve pain and swelling associated with FOP during acute flare-ups (most notably corticosteroids) and non-steroidal anti-inflammatory medication between flare-ups.

Affected individuals may benefit from occupational therapy. Special shoes, braces, and other devices that assist in walking and weight-bearing have been used to help people with FOP. Affected individuals may have their physicians contact an occupational therapist who can help obtain special devices or tools to assist them in daily activities.

Genetic counseling may be of benefit for families with the hereditary form of FOP. A team approach for infants with this disorder will also be of benefit and may include special social, educational, and medical services. Other treatment is symptomatic and supportive.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:

For information about clinical trials conducted in Europe, contact:

It is hoped that the discovery of the FOP gene and the mutation that causes FOP will lead to future research on possible ways to treat the disease itself, and not just its symptoms.

Investigational therapies for FOP might include antiangiogenic agents, retinoic acid receptor gamma-selective agonists and BMP antagonists. Corticosteroids, cox-2 inhibitors, leukotriene inhibitors, and thalidomide have also been explored.

Contacts for additional information about fibrodysplasia ossificans progressiva:

Frederick S. Kaplan, M.D.

Isaac & Rose Nassau Professor of Orthopaedic Molecular Medicine

Chief, Division of Orthopaedic Molecular Medicine

Perelman School of Medicine

University of Pennsylvania

c/o Department of Orthopaedic Surgery

Hospital of The University of Pennsylvania


3400 Spruce Street

Philadelphia, PA 19104-4283

tel: 215-349-8726

fax: 215-349-5928


Eileen M. Shore, PhD

Professor, Departments of Orthopaedic Surgery and Genetics

Perelman School of Medicine

University of Pennsylvania

424 Stemmler Hall

3450 Hamilton Walk

Philadelphia, PA 19104-6081

phone: 215-898-2330

fax: 215-573-2133




Kasper, DL, Fauci AS, Longo DL, et al., eds. Harrison's Principles of Internal Medicine.

16th ed. McGraw-Hill Companies. New York, NY; 2005:2286.

Kaplan FS, Shore EM. Fibrodysplasia Ossificans Progressiva. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:713-14.


Zimmer C. The mystery of the second skeleton. Atlantic Monthly. 2013; 311(5): 72-82.

Shore EM, Kaplan FS. Role of altered signal transduction in heterotopic ossification and fibrodysplasia ossificans progressiva. Curr Osteoporosis Rep. 2011;9: 83-88.

Shore EM, Kaplan FS. Inherited human diseases of heterotopic bone formation. Nat Rev Rheumatol. 2010;6: 518-527.

Kaplan FS, Groppe J, Shore EM. When one skeleton is enough: approaches and strategies for the treatment of fibrodysplasia ossificans progressiva (FOP). Drug Discovery Today: Therapeutic Strategies. 2009;5:255-262.

Kaplan FS, Pignolo RJ, Shore EM. The FOP metamorphogene encodes a novel type I receptor that dysregulates BMP signaling. Cytokine Growth Factor Reviews. 2009;20:399-407.

Shore EM, Kaplan FS. Insights from a rare genetic disorder of extra-skeletal bone formation, fibrodysplasia ossificans progressiva (FOP). Bone. 2008;43: 427-433.

Kaplan FS, LeMerrer M, Glaser D, Pignolo RJ, Goldsby RE, Kitterman JA, Groppe J, Shore EM. Fibrodysplasia ossificans progressiva. Best Pract Res Clin Rheumatol. 2008; 22:191-205.

Kaplan FS, Groppe J, Pignolo RJ, Shore EM. Morphogen receptor genes and metamorphogenes: skeleton keys to the metamorphosis. Ann NY Acad Sci. 2007; 1116:113-133.


Kaplan FS, Pignolo RJ, Shore EM. The Twenty-Second Annual Report of the Fibrodysplasia Ossificans Progressiva (FOP) Collaborative Research Project. June, 2013:1-42.

Chakkalakal SA, Zhang D, Culbert AL, Convente MR, Caron RJ, Wright AC, Maidment AD, Kaplan FS, Shore EM. An Acvr1 Knock-in mouse has fibrodysplasia ossificans progressiva. J Bone Miner Res. 2012; 27: 1746-1756.

Kaplan FS, Shore EM, Pignolo RJ. (eds), and The International Clinical Consortium on FOP. The medical management of fibrodysplasia ossificans progressiva: current treatment considerations. Clin Proc Intl Clin Consort FOP. 2011;4:1-100.

Kaplan FS, Shore EM. Derailing heterotopic ossification and RARing to go. Nat Med. 2011;17: 420-421.

Kaplan FS, Zasloff MA, Kitterman JA, Shore EM, Hong CC, Rocke DM. Early mortality and cardiorespiratory failure in patients with fibrodysplasia ossificans progressiva. J Bone Joint Surg Am. 2010;92: 686-691.

Medici D, Shore EM, Lounev VY, Kaplan FS, Kalluri R, Olsen BJ. Conversion of vascular endothelial cells into multipotent stem-like cells. Nat Med 16: 1400-1406, 2010

Kaplan FS, Xu M, Seemann P, Connor JM, Glaser DL, Carroll L, Delai, P, Xu M, Seemann P, Fastnacht-Urban E, Forman SJ, Gillessen-Kaesbach G, Hoover-Fong J, Köster B, Pauli RM, Reardon W, Zaidi S-A, Zasloff M, Morhart R, Mundlos S, Groppe J, and Shore EM.Classic and atypical fibrodysplasia ossificans progressiva (FOP) phenotypes are caused by mutations in the bone morphogenetic protein (BMP) type I receptor ACVR1. Hum Mutat. 2009;30(3):379-390.

Lounev V, Ramachandran R, Wosczyna MN, Yamamoto M, Maidment ADA, Shore EM, Glaser DL, Goldhamer DJ, Kaplan FS. Identification of progenitor cells that contribute to heterotopic skeletogenesis. J Bone Joint Surg Am. 2009;91:652-663.

Shen Q, Little SC, Xu M, Haupt J, Ast C, Katagiri T, Mundlos S, Seemann P. Kaplan FS, Mullins MC, Shore EM. The fibrodysplasia ossificans progressiva R206H ACVR1 mutation activates BMP-independent chondrogenesis and zebrafish embryo ventralization. J Clin Invest. 2009;119(11):3462-3472.

Moore RE, Dormans JP, Drummond DS, Shore EM, Kaplan FS, Auerbach JD. Chin-on-chest deformity in patients with fibrodysplasia ossificans progressiva: a case series. J Bone Joint Surg Am 91: 1497-1502, 2009.

Deirmengian GK, Hebela NM, O'Connell M, Glaser DL, Shore EM, Kaplan FS. Proximal tibial osteochondromas in patients with fibrodysplasia ossificans progressiva. J Bone Joint Surg Am. 2008;90:366-374.

Adegbite NS, Xu M, Kaplan FS, Shore EM, Pignolo RJ. Diagnostic and mutational spectrum of progressive osseous heteroplasia (POH) and other forms of GNAS-based heterotopic ossification. Am J Med Genet A. 2008;146A:1788-1796.

Kaplan FS, Xu M, Glaser DL Collins F, Connor M, Kitterman J, Sillence D, Zackai E, Ravitsky V, Zasloff M, Ganguly A, Shore EM. Early diagnosis of fibrodysplasia ossificans progressiva. Pediatrics. 2008;121:e1295-e1300.

Kaplan FS, Glaser DL, Shore EM, Pignolo RJ, Xu M, Zhang Y, Senitzer D, Forman SJ, Emwerson SG. Hematopoietic stem cell contribution to ectopic skeletogenesis. J Bone Joint Surg Am. 2007; 89:347-357.

Kaplan FS, Shore EM. Supplement to the Fifteenth Annual report: The Patient and Family Guidebook Guidebook to the FOP Gene. 2006:23-47.

Shore EM, Xu M, Feldman GJ, Fenstermacher DA, Cho T-J, Choi IH, Connor JM, Delai P, Glaser DL, Le Merrer M, Morhart R, Rogers JG, Smith R, Triffitt JT, Urtizberea JA, Zasloff M, Brown MA, Kaplan FS. A recurrent mutation in the BMP type I receptor ACVR1 causes inherited and sporadic fibrodysplasia ossificans progressiva. Nature Genetics. 2006;38:525-527.

Kitterman JA, Kantanie S, Rocke DM, Kaplan FS. Iatrogenic harm caused by diagnostic errors in fibrodysplasia ossificans progressiva. Pediatrics. 2005;116:e654-61.

Schaffer AA, Kaplan FS, Tracy MR, et al. Developmental anomalies of the cervical spine in patients with fibrodysplasia ossificans progressiva are distinctly different from those in patients with Klippel-Feil syndrome: clues from the BMP signaling pathway. Spine. 2005:30:1379-85.


Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Fibrodysplasia Ossificans Progressiva; FOP. Entry No:135100. Last Updated10/01/2013. Available at: Accessed Jan 28, 2014.


International FOP Association

P.O. Box 196217

Winter Springs, FL 32719-6217

Tel: (407)365-4194

Fax: (407)365-3213



March of Dimes Birth Defects Foundation

1275 Mamaroneck Avenue

White Plains, NY 10605

Tel: (914)997-4488

Fax: (914)997-4763


NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases

Information Clearinghouse

One AMS Circle

Bethesda, MD 20892-3675


Tel: (301)495-4484

Fax: (301)718-6366

Tel: (877)226-4267

TDD: (301)565-2966



Progressive Osseous Heteroplasia Association

5327 Westpointe Plaza Drive #113

Columbus, OH 43228

Tel: (614)887-7642



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223


For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see