Fibrodysplasia ossificans progressiva (FOP), a disorder of ectopic osteogenesis, misregulates cell surface expression and trafficking of BMPRIA

Evolutionary mutant models for human disease

Although induced mutations in traditional laboratory animals have been valuable as models for human diseases, they have some important limitations. Here, we propose a complementary approach to discover genes and mechanisms that might contribute to human disorders: the analysis of evolutionary mutant models in which adaptive phenotypes mimic maladaptive human diseases. If the type and mode of action of mutations favored by natural selection in wild populations are similar to those that contribute to human diseases, then studies in evolutionary mutant models have the potential to identify novel genetic factors and gene-by-environment interactions that affect human health and underlie human disease.

Insights from a rare genetic disorder of extra-skeletal bone formation, fibrodysplasia ossificans progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is a rare human genetic disorder of extensive and debilitating extra-skeletal bone formation. While the challenges of investigating a rare condition are many, the potential benefits are also great - not only for the specific disease under investigation, but also for the unique perspective on how cells normally function and the mechanisms that underlie more common disorders. This review will illustrate some of the many insights that we have gained by studying FOP.

Fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP), a rare and disabling genetic condition of congenital skeletal malformations and progressive heterotopic ossification (HO), is the most catastrophic disorder of HO in humans. Episodic disease flare-ups are precipitated by soft tissue injury, and immobility is cumulative. Recently, a recurrent mutation in activin receptor IA/activin-like kinase 2 (ACVR1/ALK2), a bone morphogenetic protein (BMP) type I receptor, was reported in all sporadic and familial cases of classic FOP, making this one of the most highly specific disease-causing mutations in the human genome. The discovery of the FOP gene establishes a critical milestone in understanding FOP, reveals a highly conserved target for drug development in the transforming growth factor (TGF)-beta/BMP signalling pathway, and compels therapeutic approaches for the development of small molecule signal transduction inhibitors for ACVR1/ALK2. Present management involves early diagnosis, assiduous avoidance of iatrogenic harm, and symptomatic amelioration of painful flare-ups. Effective therapies for FOP, and possibly for other common conditions of HO, may potentially be based on future interventions that block ACVR1/ALK2 signalling.

Dysregulated BMP signaling and enhanced osteogenic differentiation of connective tissue progenitor cells from patients with fibrodysplasia ossificans progressiva (FOP)

The study of FOP, a disabling genetic disorder of progressive heterotopic ossification, is hampered by the lack of readily available connective tissue progenitor cells. We isolated such cells from discarded primary teeth of patients with FOP and controls and discovered dysregulation of BMP signaling and rapid osteoblast differentiation in FOP cells compared with control cells.

INTRODUCTION

Fibrodysplasia ossificans progressiva (FOP), the most disabling condition of progressive heterotopic ossification in humans, is caused by a recurrent heterozygous missense mutation in activin receptor IA (ACVR1), a bone morphogenetic protein (BMP) type I receptor, in all classically affected individuals. A comprehensive understanding of FOP has been limited, in part, by a lack of readily available connective tissue progenitor cells in which to study the molecular pathology of this disorder.

MATERIALS AND METHODS

We derived connective tissue progenitor cells from discarded primary teeth (SHED cells) of patients with FOP and controls and examined BMP signaling and osteogenic differentiation in these cells.

RESULTS

SHED cells transmitted BMP signals through both the SMAD and p38 mitogen-activated protein kinase (MAPK) pathways and responded to BMP4 treatment by inducing BMP responsive genes. FOP cells showed ligand-independent BMP signaling and ligand-dependent hyper-responsiveness to BMP stimulation. Furthermore, FOP cells showed more rapid differentiation to an osteogenic phenotype than control cells.

CONCLUSIONS

This is the first study of BMP signaling and osteogenic differentiation in connective tissue progenitor cells from patients with FOP. Our data strongly support both basal and ligand-stimulated dysregulation of BMP signaling consistent with in silico studies of the mutant ACVR1 receptor in this condition. This study substantially extends our understanding of dysregulated BMP signaling in a progenitor cell population relevant to the pathogenesis of this catastrophic disorder of progressive ectopic ossification.

Proximal tibial osteochondromas in patients with fibrodysplasia ossificans progressiva

BACKGROUND

Fibrodysplasia ossificans progressiva is a rare autosomal dominant disorder characterized by congenital malformation of the great toes and by progressive heterotopic ossification of skeletal muscle and soft connective tissues. The disorder is caused by a recurrent missense mutation in the glycine-serine activation domain of activin A receptor type I, a bone morphogenetic protein (BMP) type-I receptor, in all classically affected individuals. Osteochondromas of the proximal part of the tibia are benign osteochondral neoplasms or orthotopic lesions of skeletal remodeling associated with dysregulated BMP signaling and have been considered an atypical feature of fibrodysplasia ossificans progressiva, but they may be underdiagnosed because of their often asymptomatic nature. The purpose of the present study was to determine the prevalence and characteristics of proximal tibial osteochondromas in individuals who have fibrodysplasia ossificans progressiva.

METHODS

Over a period of thirty months, we evaluated all patients with new and established fibrodysplasia ossificans progressiva for the presence of proximal tibial osteochondromas on the basis of medical history, physical examination, and radiographic studies. We quantified the prevalence of osteochondromas and characterized the types of osteochondromas to identify relevant trends.

RESULTS

Ninety-six patients (including fifty-two female patients and forty-four male patients) with fibrodysplasia ossificans progressiva were evaluated on the basis of a history and physical examination. Plain radiographs were available for sixty-seven patients. Ninety percent of all patients had osteochondroma of the proximal part of the tibia. These lesions usually were asymptomatic, most commonly were bilateral, and typically were located at the pes anserinus. Seventy-five percent of the lesions were pedunculated, and 25% were sessile.

CONCLUSIONS

Proximal tibial osteochondromas are a common phenotypic feature of fibrodysplasia ossificans progressiva, a finding that expands the recognized consequences of recurrent activating mutations in activin A receptor type I to include not only congenital skeletal malformations and heterotopic skeletogenesis but also benign osteochondral neoplasms or orthotopic lesions of skeletal modeling. The present study provides insight into the genetic basis of osteochondroma formation in patients with fibrodysplasia ossificans progressiva and possibly into that of more common conditions in which these lesions occur.

Regulation of chondrogenesis and chondrocyte differentiation by stress

Chondrogenesis and endochondral ossification are the cartilage differentiation processes that lead to skeletal formation and growth in the developing vertebrate as well as skeletal repair in the adult. The exquisite regulation of these processes, both in normal development and in pathologic situations, is impacted by a number of different types of stress. These include normal stressors such as mechanical loading and hypoxia as well pathologic stressors such as injury and/or inflammation and environmental toxins. This article provides an overview of the processes of chondrogenesis and endochondral ossification and their control at the molecular level. A summary of the influence of the most well-understood normal and pathologic stressors on the differentiation program is also presented.

When one skeleton is enough: approaches and strategies for the treatment of fibrodysplasia ossificans progressiva (FOP)

A heterozygous missense mutation in activin receptor IA/activin-like kinase-2 (ACVR1/ALK2), a bone morphogenetic protein (BMP) type I receptor, is responsible for fibrodysplasia ossificans progressiva (FOP), the most catastrophic disorder of skeletal metamorphosis in humans. The discovery of the FOP gene establishes a crucial milestone in understanding FOP, reveals a highly conserved target in the BMP signaling pathway for drug development and specifically stimulates therapeutic approaches for the development of inhibitors for ACVR1/ALK2 signaling. Effective therapies for FOP, and possibly for more common conditions of heterotopic ossification, will be based on interventions that selectively block promiscuous ACVR1/ALK2 signaling, and/or themolecular triggers, responding cells and tissue microenvironments that facilitate aberrant skeletal metamorphosis in a permissive genetic background of increased BMP pathway activity.

Skeletal metamorphosis in fibrodysplasia ossificans progressiva (FOP)

Metamorphosis, the transformation of one normal tissue or organ system into another, is a biological process rarely studied in higher vertebrates or mammals, but exemplified pathologically by the extremely disabling autosomal dominant disorder fibrodysplasia ossificans progressiva (FOP). The recurrent single nucleotide missense mutation in the gene encoding activin receptor IA/activin-like kinase-2 (ACVR1/ALK2), a bone morphogenetic protein type I receptor that causes skeletal metamorphosis in all classically affected individuals worldwide, is the first identified human metamorphogene. Physiological studies of this metamorphogene are beginning to provide deep insight into a highly conserved signaling pathway that regulates tissue stability following morphogenesis, and that when damaged at a highly specific locus (c.617G > A; R206H), and triggered by an inflammatory stimulus permits the renegade metamorphosis of normal functioning connective tissue into a highly ramified skeleton of heterotopic bone. A comprehensive understanding of the process of skeletal metamorphosis, as revealed by the rare condition FOP, will lead to the development of more effective treatments for FOP and, possibly, for more common disorders of skeletal metamorphosis.

Over-expression of BMP4 and BMP5 in a child with axial skeletal malformations and heterotopic ossification: a new syndrome

Bone morphogenetic proteins (BMPs) are a highly conserved class of signaling molecules that induce ectopic cartilage and bone formation in vivo. Dysregulated expression of bone morphogenetic protein 4 (BMP4) is found in the cells of patients who have fibrodysplasia ossificans progressiva (FOP), a genetic disorder of axial and appendicular skeletal malformation and progressive heterotopic ossification. Loss of function mutations in the bone morphogenetic protein 5 (bmp5) gene leading to under-expression of BMP5 cause the murine short ear syndrome, characterized by small malformed ears and a broad range of axial skeletal malformations. We found features reminiscent of both the short ear mouse and FOP in a child with malformed external ears, multiple malformations of the axial skeleton, and progressive heterotopic ossification in the neck and back. We examined BMP mRNA expression in transformed lymphocytes by semi-quantitative RT-PCR and protein expression by ELISA assays and immunohistochemistry. Elevated levels of BMP4 and BMP5 mRNA and protein were detected in the patient's cells while levels of BMP2 mRNA were unchanged. Our data suggest that dysregulated expression of BMP4 and BMP5 genes is associated with an array of human axial skeletal abnormalities similar to the short ear mouse and FOP.

Functional modeling of the ACVR1 (R206H) mutation in FOP

Individuals with fibrodysplasia ossificans progressiva are born with malformations of the great toes and develop a heterotopic skeleton during childhood because of an identical heterozygous mutation in the glycine-serine activation domain of ACVR1, a bone morphogenetic protein type I receptor. Substitution of adenine for guanine at nucleotide 617 replaces an evolutionarily conserved arginine with histidine at residue 206 of ACVR1 in all classically affected individuals, making this one of the most highly conserved disease-causing mutations in the human genome. To better understand the molecular constraints and physiological implications of this mutation, we performed in silico modeling of wild-type and mutant ACVR1. In both the wild-type ACVR1 model and template crystal structures (TbetaRI), the conserved arginine appears to form a salt bridge with an invariant aspartate residue. Although lysine, a conservative substitution in BMPRIA and BMPRIB, can be readily accommodated, histidine at residue 206 (like in fibrodysplasia ossificans progressiva) would participate in a salt bridge with the aspartate only at decreased intracellular pH and with extensive structural rearrangement. Protein modeling predicts that substitution with histidine, and only histidine, creates a pH-sensitive switch within the activation domain of the receptor that leads to ligand-independent activation of ACVR1 in fibrodysplasia ossificans progressiva.

A new era for fibrodysplasia ossificans progressiva: a druggable target for the second skeleton

Fibrodysplasia ossificans progressiva (FOP) is a disabling genetic condition that leads to the formation of a second (heterotopic) skeleton, and is the most catastrophic disorder of heterotopic ossification in humans. Throughout childhood and early adult life, FOP progressively immobilizes all of the joints of the normotopic skeleton, rendering movement impossible. At present, there is no effective prevention or treatment. Recently, a recurrent mutation in the glycine-serine activation domain of the activin receptor IA/activin-like kinase-2, a bone morphogenetic protein type I receptor, was reported in all sporadic and familial cases of classic FOP, making this one of the most highly specific disease-causing mutations in the human genome. The discovery of the FOP gene establishes a critical milestone in understanding FOP, reveals a highly conserved druggable target in the TGF-beta/bone morphogenetic protein signaling pathway and compels therapeutic approaches for the development of small molecule signal transduction inhibitors for activin-like kinase-2. Effective therapies for FOP, and possibly for a vast array of more common conditions of heterotopic ossification, will be based on blocking activin-like kinase-2, a critical node in the BMP signaling pathway.

Hematopoietic stem-cell contribution to ectopic skeletogenesis

BACKGROUND

Fibrodysplasia ossificans progressiva is a rare genetic disorder of ectopic skeletogenesis associated with dysregulation of bone morphogenetic protein (BMP) signaling. Hematopoietic cells have been implicated in the ectopic skeletogenesis of fibrodysplasia ossificans progressiva, and their replacement has been postulated as a possible cure. However, the definitive contribution of hematopoietic cells to the pathogenesis of ectopic skeletogenesis remains obscure.

METHODS

We employed both careful clinical observation and in vivo murine transplantation studies to more precisely determine the contribution of hematopoietic cells to ectopic skeletogenesis. We identified a patient with fibrodysplasia ossificans progressiva who had undergone bone marrow transplantation for the treatment of intercurrent aplastic anemia twenty-five years earlier and investigated whether the clinical course of the fibrodysplasia ossificans progressiva had been influenced by bone marrow replacement or immunosuppression, or both. In complementary studies, we transplanted hematopoietic stem cells from constitutively expressing LacZ transgenic mice to identify the contribution of hematopoietic cells to BMP4-induced heterotopic ossification, a histopathologic model of fibrodysplasia ossificans progressiva.

RESULTS

We found that replacement of hematopoietic cells was not sufficient to prevent ectopic skeletogenesis in the patient with fibrodysplasia ossificans progressiva but pharmacologic suppression of the apparently normal donor immune system following transplantation in the new host modulated the activity of the fibrodysplasia ossificans progressiva and diminished the expression of skeletal ectopia. In complementary murine transplantation studies, we found that cells of hematopoietic origin contributed to the early inflammatory and late marrow-repopulating stages of BMP4-induced heterotopic ossification but were not represented in the fibroproliferative, chondrogenic, or osteogenic stages of heterotopic ossification. Interestingly, both recombinant human BMP4 induction in an animal model and the dysregulated BMP signaling pathway in a patient with fibrodysplasia ossificans progressiva were sufficient to recruit at least two populations of cells, one of hematopoietic origin and at least one of non-hematopoietic origin, that contribute to the formation of an ectopic skeleton.

CONCLUSIONS

Taken together, these findings demonstrate that bone marrow transplantation did not cure fibrodysplasia ossificans progressiva in the patient in this study, most likely because the hematopoietic cell population is not the site, or at least not the dominant site, of the intrinsic dysregulation of the BMP signaling pathway in fibrodysplasia ossificans progressiva. However, following transplantation of bone marrow from a presumably normal donor, immunosuppression of the immune system appeared to ameliorate activation of ectopic skeletogenesis in a genetically susceptible host. Thus, cells of hematopoietic origin may contribute to the formation of an ectopic skeleton, although they are not sufficient to initiate the process alone.

HSPG modulation of BMP signaling in fibrodysplasia ossificans progressiva cells

Cell surface heparan sulfate proteoglycans (HSPGs) play important roles in morphogen gradient formation and cell signaling. Bone morphogenetic protein (BMP) signaling is dysregulated in fibrodysplasia ossificans progressiva (FOP), a disabling disorder of progressive heterotopic bone formation. Here, we investigated the role of HSPG glycosaminoglycan (GAG) side chains on BMP signaling and found increased total and HSPG-specific GAG chain levels and dysregulation in HSPG modulation of BMP signaling in FOP lymphoblastoid cells (LCLs). Specifically, HSPG profiling demonstrated abundant mRNA and protein levels of glypican 1 and syndecan 4 on control and FOP LCLs, with elevated core protein levels on FOP cells. Targeted downregulation of glypican 1 core protein synthesis by siRNA enhanced BMP signaling in control and FOP cells, while reduction of syndecan 4-core protein synthesis decreased BMP signaling in control, but not FOP cells. These results suggest that FOP cells are resistant to the stimulatory effects of cell surface HSPG GAG chains, but are susceptible to the inhibitory effects, as shown by downregulation of glypican 1. These data support that HSPG modulation of BMP signaling is altered in cells from patients with FOP and that altered HSPG-related BMP signaling may play a role in the pathogenesis of the disease.

The role of noggin in human mesenchymal stem cell differentiation

Noggin is a secreted protein that inhibits the binding of bone morphogenetic proteins (BMPs) to their cognate receptor. Its role in human mesenchymal stem cell differentiation has not been well studied. Here, we studied the effect of noggin on human mesenchymal stem cell differentiation induced by inflammatory cytokines (activated T-cell conditioned medium (ACTTCM) or the combination of four T-cell cytokines, TNF-alpha, TGF-beta, IFN-gamma, and IL-17 (TTII)), BMPs, or dexamthasone (DEX). HMSC treated with TTII alone rapidly induced alkaline phosphatase (AlkP) activity. Inclusion of noggin resulted in an additive effect. Noggin acted additively with DEX to induce a significantly higher level of AlkP induction than either noggin or DEX alone. Noggin was examined for its ability to inhibit mineralization in long-term cultures of HMSC stimulated with BMP-2, BMP-6, BMP-7, DEX, or TTII. Surprisingly, noggin alone induced mineralization while it did not inhibit mineralization induced by TTII or BMP-2, BMP-6, or BMP-7. Interestingly, when HMSC were treated with both noggin and DEX they acted synergistically to induce mineralization nearly 3-fold over DEX alone and 30-fold over noggin alone. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that T-cell cytokines induced noggin, Runx2, BMP-2, and osteocalcin gene expression, while noggin alone induced BMP-2 and osteocalcin gene expression, but not Runx2, although it increased the expression of ActRII, a receptor for BMP-2. These results suggest that in HMSC, the anabolic action of inflammation on bone formation occurs through the induction of noggin, which then induces BMP-2 receptor and BMP-2 leading to the activation of the differentiation process.

Heterotopic ossification in the residual limbs of traumatic and combat-related amputees

Reports on the occurrence and treatment of heterotopic ossification in amputees are rare. Heterotopic ossification in the residual limbs of amputees may cause pain and skin breakdown and complicate or prevent optimal prosthetic fitting and utilization. Basic science research has shed light on the cellular and molecular basis for this disease process, but many questions remain unanswered. The recent experience of the military amputee centers with traumatic and combat-related amputations has demonstrated a surprisingly high prevalence of heterotopic ossification in residual limbs. Primary prophylactic regimens, such as nonsteroidal anti-inflammatory drugs and local irradiation, which have proved to be effective in preventing and limiting heterotopic ossification in other patient populations, have not been studied in amputees and generally are not feasible in the setting of acute traumatic amputation. When nonsurgical measures such as activity and repeated prosthetic modifications fail to provide relief, surgical excision has provided good early clinical results, with low rates of recurrence and acceptable complication rates in military amputees.

Dysregulation of the BMP-4 signaling pathway in fibrodysplasia ossificans progressiva

Identification of gene mutations in Mendelian disorders is often determined by linkage analysis and positional cloning, an approach that is difficult for fibrodysplasia ossificans progressiva (FOP) due to a low reproductive fitness that results in a small number of multigenerational families showing inheritance of the disease. Altered signaling pathways can be investigated as a complementary method to identify the consequences of the mutated gene responsible for FOP and to identify potential therapeutic targets. Candidate signaling pathways for FOP are those that malfunctioning could account for the malformation of the great toes during embryonic development and could explain the postnatal progressive heterotopic endochondral ossification. Signaling pathways that fit these criteria are the BMP signaling pathway and its interacting pathways. A large body of data suggest that the BMP-4 signaling pathway is dysregulated in FOP.

Bone morphogenetic proteins and their antagonists

Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic proteins (BMPs) are unique because they induce the commitment of mesenchymal cells toward cells of the osteoblastic lineage and also enhance the differentiated function of the osteoblast. BMP activities in bone are mediated through binding to specific cell surface receptors and through interactions with other growth factors. BMPs are required for skeletal development and maintenance of adult bone homeostasis, and play a role in fracture healing. BMPs signal by activating the mothers against decapentaplegic (Smad) and mitogen activated protein kinase (MAPK) pathways, and their actions are tempered by intracellular and extracellular proteins. The BMP antagonists block BMP signal transduction at multiple levels including pseudoreceptor, inhibitory intracellular binding proteins, and factors that induce BMP ubiquitination. A large number of extracellular proteins that bind BMPs and prevent their binding to signaling receptors have emerged. The extracellular antagonists are differentially expressed in cartilage and bone tissue and exhibit BMP antagonistic as well as additional activities. Both intracellular and extracellular antagonists are regulated by BMPs, indicating the existence of local feedback mechanisms to modulate BMP cellular activities.

Dysregulation of the BMP-p38 MAPK signaling pathway in cells from patients with fibrodysplasia ossificans progressiva (FOP)

FOP is a disabling disorder in which skeletal muscle is progressively replaced with bone. Lymphocytes, our model system for examining BMP signaling, cannot signal through the canonical Smad pathway unless exogenous Smad1 is supplied, providing a unique cell type in which the BMP-p38 MAPK pathway can be examined. FOP lymphocytes exhibit defects in the BMP-p38 MAPK pathway, suggesting that altered BMP signaling underlies ectopic bone formation in this disease.

INTRODUCTION

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by progressive heterotopic ossification of connective tissues. Whereas the primary genetic defect in this condition is unknown, BMP4 mRNA and protein and BMP receptor type IA (BMPRIA) protein are overexpressed in cultured lymphocytes from FOP patients, supporting that altered BMP signaling is involved in this disease. In this study, we examined downstream signaling targets to study the BMP-Smad and BMP-p38 mitogen-activated protein kinase (MAPK) pathways in FOP.

MATERIALS AND METHODS

Protein phosphorylation was assayed by immunoblots, and p38 MAPK activity was measured by kinase assays. To examine BMP target genes, the mRNA expression of ID1, ID3, and MSX2 was determined by quantitative real-time PCR. Statistical analysis was performed using Student's t-test or ANOVA.

RESULTS

FOP lymphocytes exhibited increased levels of p38 phosphorylation and p38 MAPK activity in response to BMP4 stimulation. Furthermore, in response to BMP4, FOP cells overexpressed the downstream signaling targets ID1 by 5-fold and ID3 by 3-fold compared with controls. ID1 and ID3 mRNA induction was specifically blocked with a p38 MAPK inhibitor, but not extracellular signal-related kinase (ERK) or c-Jun N-terminal kinase (JNK) inhibitors. MSX2, a known Smad pathway target gene, is not upregulated in control or FOP cells in response to BMP, suggesting that lymphocytes do not use this limb of the BMP pathway. However, introduction of Smad1 into lymphocytes made the cells competent to regulate MSX2 mRNA after BMP4 treatment.

CONCLUSIONS

Lymphocytes are a cell system that signals primarily through the BMP-p38 MAPK pathway rather than the BMP-Smad pathway in response to BMP4. The p38 MAPK pathway is dysregulated in FOP lymphocytes, which may play a role in the pathogenesis of FOP.

A recurrent mutation in the BMP type I receptor ACVR1 causes inherited and sporadic fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disorder of skeletal malformations and progressive extraskeletal ossification. We mapped FOP to chromosome 2q23-24 by linkage analysis and identified an identical heterozygous mutation (617G --> A; R206H) in the glycine-serine (GS) activation domain of ACVR1, a BMP type I receptor, in all affected individuals examined. Protein modeling predicts destabilization of the GS domain, consistent with constitutive activation of ACVR1 as the underlying cause of the ectopic chondrogenesis, osteogenesis and joint fusions seen in FOP.

Iatrogenic harm caused by diagnostic errors in fibrodysplasia ossificans progressiva

BACKGROUND

Little is known about diagnostic errors for a disease worldwide. Such errors could alter the disease's natural history, especially if unwarranted interventions cause irreversible harm. Fibrodysplasia ossificans progressiva (FOP), a rare, autosomal dominant genetic disease characterized by episodes of permanent heterotopic ossification of soft tissues, occurs worldwide without racial, ethnic, or geographic predilection. There is no effective treatment, and soft-tissue trauma (eg, biopsies, surgical procedures, intramuscular injections, or mandibular blocks for dental procedures) and viral illnesses are likely to induce episodes of rapidly progressive heterotopic ossification, with resultant permanent loss of motion in the affected area. Accurate diagnoses can be made on the basis of the clinical findings of tumor-like swellings on the head, neck, back, or shoulders and characteristic short great toes with hallux valgus-like malformations and missing interphalangeal joints. On the basis of conversations with numerous individuals with FOP, we suspected that diagnostic errors with FOP are common and often associated with inappropriate and harmful diagnostic and therapeutic procedures.

OBJECTIVE

To document the frequency of diagnostic errors with FOP and complications resulting from misdiagnoses.

DESIGN

A questionnaire requesting detailed demographic, diagnostic, and treatment information was sent to all 269 patient-members of the International FOP Association; the sampling frame included > 90% of all known FOP patients worldwide. We received 138 replies (51% response) from 25 countries. The age range was 2 to 71 years; there were 78 female subjects and 60 male subjects. In addition, to assess the availability and adequacy of information about FOP, we reviewed 184 English-language textbooks in relevant specialties published in the past 20 years.

RESULTS

Incorrect diagnoses were given initially to 87% of individuals with FOP. This astonishing rate of diagnostic errors occurred worldwide, regardless of ethnicity, geographic background, or misdiagnosing physician's specialty. The most common incorrect diagnosis was cancer (32%). The mean period from the onset of symptoms to correct diagnosis was 4.1 years, and the median number of physicians consulted before the correct diagnosis of FOP was 6. For 67% of patients, unnecessary invasive procedures (biopsies) were performed; 68% received inappropriate therapies. Forty-nine percent of all patients reported permanent loss of mobility resulting from invasive medical interventions that caused posttraumatic ossification. Notably, only 8% of the 184 textbooks that were reviewed contained adequate descriptions of FOP, including the caution that trauma can accelerate the process of heterotopic ossification.

CONCLUSIONS

Diagnostic errors and inappropriate medical procedures, which may lead to permanent harm, can alter the natural history of a disease. In FOP, the astonishing rates of diagnostic errors and inappropriate invasive medical procedures likely result from lack of physician awareness because of failure of information transfer.