Fibrodysplasia ossificans progressiva, a heritable disorder of severe heterotopic ossification, maps to human chromosome 4q27-31

Fibrodysplasia ossificans progressiva: A rare disease with spinal deformity and severe hip dysfunction

INTRODUCTION

Progressive fibrous dysplasia ossification (FOP) is a rare genetic disease characterized by congenital bone malformations and soft tissue masses that progress to heterotopic ossification. Congenital great toe deformity and progressive heterotopic ossifications with an anatomical and temporal pattern are the two classical clinical characteristics of FOP. We present a unique case of FOP characterized by mandibular angle fascial contracture and back and iliopsoas muscle ossification managed via surgery in a 13 year old girl.

CASE PRESENTATION

A 13 year old girl with a history of right cervical fascial release surgery and back heterotopic osteotomy presented to our clinic due to recurrence of heterotopic ossification, scoliosis, and progressive joint stiffness. Computed tomography (CT) or magnetic resonance imaging (MRI) examination confirmed heterotopic ossification of the left back and left iliopsoas muscle and spinal scoliosis. Two years after the surgery, the patient presented with recurrence of back heterotopic ossification and rapidly advancing ossification of the left iliopsoas muscle. Six months after surgery, the patient had no disability, pain and clinical recurrence, and the joint function recovered.

CONCLUSIONS

In patients with multiple-site heterotopic ossification caused by FOP, oral function and hip stiffness improve with detailed facial release surgery and rehabilitation treatment. However, dorsal fascia ossification and spinal scoliosis can recur shortly after resection.

A Three-Generation Pedigree of Multifocal Heterotopic Ossification With Bilateral Involvement

Heterotopic ossification (HO) can be classified as nonhereditary HO (NHHO) or hereditary HO (HHO). Hereditary HO includes 2 different forms: fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH). Each of these disorders is caused by mutations in a single (different) gene. Clinical diagnosis of FOP can be confirmed by sequence analysis of the ACVR1 gene. Fewer than 10 families with autosomal dominant inheritance of FOP have been reported. The authors report clinical manifestations, pedigree analysis, and mutational analysis of the ACVR1 in a 3-generation Chinese family with 4 individuals presenting multifocal and bilateral involvement of HO. Clinical features of affected individuals of the family were not consistent with the classic FOP or atypical FOP. Exon sequencing was performed on every family member and 3 sporadic NHHO patients who did not belong to this family. All family members and 3 sporadic NHHO patients carried 2 hereditary homozygous silent mutations- c.270C>T and c.690G>A-the new and unique mutations in ACVR1. These results may suggest that the affected individuals in this family present a novel FOP-variant syndrome or a new form of HHO. To the authors' knowledge, this is the first well-documented instance of a 3-generation Chinese family with multifocal and bilateral involvement of HO. [Orthopedics. 2021;44(1):e139-e145.].

Fibrodysplasia ossificans progressiva (stone man syndrome): a case report

Background

Fibrodysplasia ossificans progressiva is an ultrarare autosomal dominant disorder and disabling syndrome characterized by postnatal progressive heterotopic ossification of the connective tissue and congenital malformation of the big toes. Fibrodysplasia ossificans progressiva has worldwide prevalence of about 1 in 2 million births. Nearly 90% of patients with fibrodysplasia ossificans progressiva are misdiagnosed and mismanaged and thus undergo unnecessarily interventions. So far, the number of reported existing cases worldwide is about 700. Clinical examination, radiological evaluation, and genetic analysis for mutation of the ACVR1 gene are considered confirmatory tools for early diagnosis of the disease. Association of fibrodysplasia ossificans progressiva with heterotopic ossification is well documented; however, postsurgical exaggerated response has never been reported previously, to the best of our knowledge.

Case presentation

We report a case of a 10-year-old Pakistani boy brought by his parents to our institution. He had clinical and radiological features of fibrodysplasia ossificans progressive and presented with multiple painful lumps on his back due to hard masses and stiffness of his shoulders, neck, and left hip. He underwent surgical excision of left hip ossification followed by an exaggerated response in ossification with early disability. Radiological examination revealed widespread heterotopic ossification. All of his laboratory blood test results were normal.

Conclusion

Fibrodysplasia ossificans progressiva is a very rare and disabling disorder that, if misdiagnosed, can lead to unnecessary surgical intervention and disastrous results of early disability. We need to spread knowledge to physicians and patients’ family members about the disease, as well as its features for early diagnosis and how to prevent flare-up of the disease to promote better quality of life in these patients.

Targeting heterotopic ossification by inhibiting activin receptor‑like kinase 2 function (Review)

Heterotopic ossification (HO) refers to the appearance of osteoblasts in soft tissues under pathological conditions, such as trauma or infection. HO arises in an unpredictable way without any recognizable initiation. Activin receptor-like kinase-2 (ALK2) is a type I cell surface receptor for bone morphogenetic proteins (BMPs). The dysregulation of ALK2 signaling is associated with a variety of diseases, including cancer and HO. At present, the prevention and treatment of HO in the clinic predominantly includes nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates and other drug treatments, low-dose local radiation therapy and surgical resection, rehabilitation treatment and physical therapy. However, most of these therapies have adverse effects. These methods do not prevent the occurrence of HO. The pathogenesis of HO is not being specifically targeted; the current treatment strategies target the symptoms, not the disease. These treatments also cannot solve the fundamental problem of the occurrence of HO. Therefore, scholars have been working to develop targeted therapies based on the pathogenesis of HO. The present review focuses on advances in the understanding of the underlying mechanisms of HO, and possible options for the prevention and treatment of HO. In addition, the role of ALK2 in the process of HO is introduced and the progress made towards the targeted inhibition of ALK2 is discussed. The present study aims to offer a platform for further research on possible targets for the prevention and treatment of HO.

Recent Topics in Fibrodysplasia Ossificans Progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease that is characterized by the formation of heterotopic bone tissues in soft tissues, such as skeletal muscle, ligament, and tendon. It is difficult to remove such heterotopic bones via internal medicine or invasive procedures. The identification of activin A receptor, type I (ACVR1)/ALK2 gene mutations associated with FOP has allowed the genetic diagnosis of FOP. The ACVR1/ALK2 gene encodes the ALK2 protein, which is a transmembrane kinase receptor in the transforming growth factor-β family. The relevant mutations activate intracellular signaling in vitro and induce heterotopic bone formation in vivo. Activin A is a potential ligand that activates mutant ALK2 but not wild-type ALK2. Various types of small chemical and biological inhibitors of ALK2 signaling have been developed to establish treatments for FOP. Some of these are in clinical trials in patients with FOP.

Conserved signaling pathways underlying heterotopic ossification

Heterotopic ossification (HO), a serious disorder of extra-skeletal bone formation, occurs as a common complication of trauma or in rare genetic disorders. Many conserved signaling pathways have been implicated in HO; however, the exact underlying molecular mechanisms for many forms of HO are still unclear. The emerging picture is that dysregulation of bone morphogenetic protein (BMP) signaling plays a central role in the process, but that other conserved signaling pathways, such as Hedgehog (HH), Wnt/β-catenin and Fibroblast growth factors (FGF), are also involved, either through cross-talk with BMP signaling or through other independent mechanisms. Deep understanding of the conserved signaling pathways is necessary for the effective prevention and treatment of HO. In this review, we update and integrate recent progress in this area. Hopefully, our discussion will point to novel promising, druggable loci for further translational research and successful clinical applications.

Myositis ossificans after navigated knee surgery: A report of two cases and literature review

Computer-assisted surgery is now a common procedure in the field of orthopedics. We present two patients who developed myositis ossificans, a rare complication after navigated knee surgery. Due to careful follow-up and conservative treatment, surgical excision was avoided in both patients with good clinical results. Development of myositis ossificans after navigated knee surgery should be considered in cases of thigh pain and restricted range of motion of the knee.

The revolution in human monogenic disease mapping

The successful completion of the Human Genome Project (HGP) was an unprecedented scientific advance that has become an invaluable resource in the search for genes that cause monogenic and common (polygenic) diseases. Prior to the HGP, linkage analysis had successfully mapped many disease genes for monogenic disorders; however, the limitations of this approach were particularly evident for identifying causative genes in rare genetic disorders affecting lifespan and/or reproductive fitness, such as skeletal dysplasias. In this review, we illustrate the challenges of mapping disease genes in such conditions through the ultra-rare disorder fibrodysplasia ossificans progressiva (FOP) and we discuss the advances that are being made through current massively parallel (“next generation”) sequencing (MPS) technologies.

Mutation Detection in Activin A Receptor, Type I (ACVR1) Gene in Fibrodysplasia Ossificans Progressiva in An Iranian Family

Fibrodysplasia Ossificans Progressiva (FOP, MIM 135100) is a rare genetic disease that is often inherited sporadically in an autosomal dominant pattern. The disease manifests in early life with malformed great toes and, its episodic and progressive bone formation in skeletal muscle after trauma is led to extra-articular ankylosis. In this study, a 17 year-old affected girl born to a father with chemical injury due to exposure to Mustard gas during the Iran-Iraq war, and her first degree relatives were examined to find the genetic cause of the disease. The mutation c.617G>A in the Activin A receptor, type I (ACVR1) gene was found in all previously reported patients with FOP. Therefore, peripheral blood samples were taken from the patient and her first-degree relatives. DNA was extracted and PCR amplification for ACVR1 was performed. The sequencing of ACVR1 showed the existence of the heterozygous c.617G>A mutation in the patient and the lack of it in her relatives. Normal result of genetic evaluation in relatives of the patient, ruled out the possibility of the mutation being inherited from parents. Therefore, the mutation causing disease in the child, whether is a new mutation with no relation to the father's exposure to chemical gas, or in case of somatic mutation due to exposure to chemical gas, the mutant cells were created in father's germ cells and were not detectable in his blood sample.

Imaging diagnosis: fibrodysplasia ossificans progressiva in a cat

A 1‐year‐old female cat was presented for progressive alopecia, gait abnormalities, and stiffness. Radiography demonstrated multiple calcified lesions within the soft tissues of the cervical and thoracic spine, shoulder, and limbs. Postmortem computed tomography provided more detailed information on the distribution, pattern, and extension of lesions. In addition, computed tomography helped guide sample selection for histopathology. The final diagnosis was fibrodysplasia ossificans progressiva. This is a rare disorder of unknown etiology, characterized by fibrosis and heterotopic bone formation in connective tissues. To the authors’ knowledge, this is the first report describing this disease in a European cat.

Unusually severe limitation of the jaw attributable to fibrodysplasia ossificans progressiva: a case report with cone-beam computed tomography findings

Fibrodysplasia ossificans progressiva (FOP) is a rare hereditary connective tissue disease characterized by the progressive ectopic ossification of ligaments, tendons, and facial and skeletal muscles throughout life. Symptoms begin in childhood as localized soft tissue swellings. Immobility and articular dysfunction appear with involvement of the spine and proximal extremities. The temporomandibular joint (TMJ) is a critical component involved in the maxillofacial region, resulting in severe limitation of masticatory function, although TMJ involvement is rare. We report a case of FOP presenting as severely limited TMJ movements owing to ectopic calcification of the left coronoid process. In addition to the clinical examination, panoramic radiography and cone-beam computed tomography images were obtained. The case is presented and the clinical and imaging findings, differential diagnosis, and treatment modalities are discussed.

Animal models of typical heterotopic ossification

Heterotopic ossification (HO) is the formation of marrow-containing bone outside of the normal skeleton. Acquired HO following traumatic events is a common and costly clinical complication. In contrast, hereditary HO is rarer, progressive, and life-threatening. Substantial effort has been directed towards understanding the mechanisms underlying HO and finding efficient treatments. However, one crucial limiting factor has been the lack of relevant animal models. This article reviews the major currently available animal models, summarizes some of the insights gained from these studies, and discusses the potential future challenges and directions in HO research.

Acceptable outcome following resection of bilateral large popliteal space heterotopic ossification masses in a spinal cord injured patient: a case report

Spinal cord injury is a well-known predisposing factor for development of heterotopic ossification around the joints especially hip and elbow. Heterotopic ossification about the knee is usually located medially, laterally or anteriorly; besides, the knee is generally fixed in flexion. There are only a few reports of heterotopic bone formation at the posterior aspect of the knee (popliteal space) and fixation of both knees in extension; so, there is little experience in operative management of such a problem.Here, we present a 39-years old paraplegic man who was referred to us five years after trauma with a request of above knee amputation due to sever impairment of his life style and adaptive capacity for daily living because of difficulties in using wheelchair. The principle reason for the impairment was fixed full extension of both knees as the result of bilateral large heterotopic ossification masses in popliteal fossae. The bony masses were surgically resected with acceptable outcome. The anatomic position of the ossified masses as well as ankylosis of both knees in full extension, and the acceptable functional outcome of surgery which was done after a long period of five years following injury makes this case unique.

Heterotopic ossification following traumatic brain injury and spinal cord injury

Heterotopic ossification associated with neurologic injury, or neurogenic heterotopic ossification, tends to form at major synovial joints surrounded by spastic muscles. It is commonly associated with traumatic brain or spinal cord injury and with other causes of upper motor neuron lesions. Heterotopic ossification can result in a variety of complications, including nerve impingement, joint ankylosis, complex regional pain syndrome, osteoporosis, and soft-tissue infection. The associated decline in range of motion may greatly limit activities of daily living, such as positioning and transferring and maintenance of hygiene, thereby adversely affecting quality of life. Management of heterotopic ossification is aimed at limiting its progression and maximizing function of the affected joint. Nonsurgical treatment is appropriate for early heterotopic ossification; however, surgical excision should be considered in cases of joint ankylosis or significantly decreased range of motion before complications arise. Patient selection, timing of excision, and postoperative prophylaxis are important components of proper management.

Inhibition of extracellular matrix assembly induces the expression of osteogenic markers in skeletal muscle cells by a BMP-2 independent mechanism

Background

The conversion of one cell type into another has been suggested to be, at the molecular level, the consequence of change(s) in the expression level of key developmental genes. Myoblasts have the ability to differentiate either to skeletal muscle or osteogenic lineage depending of external stimuli. Extracellular matrix (ECM) has been shown to be essential for skeletal muscle differentiation, through its direct interaction with myoblasts' cell receptors. We attempt to address if ECM also plays a role in the osteogenic differentiation of skeletal muscle cells.

Results

Inhibition of proteoglycan sulfation by sodium chlorate in myoblast cultures strongly affects ECM synthesis and deposition and induces the expression of the osteogenic lineage markers alkaline phosphatase (ALP) and osteocalcin in mononuclear cells. Induction of ALP by sodium chlorate does not affect the expression of specific muscle determination transcription factors, such as MyoD and Myf-5, in the same cells. The osteogenic transcription factor Cbfa-1 expression is also unaffected. Induction of ALP is not inhibited by a soluble form of BMP receptor IA. This suggests that the deviation of the myogenic pathway of C2C12 myoblasts into the osteogenic lineage by inhibitors of proteoglycan sulfation is BMP-2 independent. The increase of osteogenic markers expression can be totally prevented by an exogenous ECM. Interestingly, a similar BMP-2-independent ALP activity induction can be observed in myoblasts cultured on an ECM previously synthesized by BMP-2 treated myoblasts. Under in vivo conditions of increased ECM turn-over and deposition, as in the mdx dystrophic muscle and during skeletal muscle regeneration, an induction and relocalization of ALP is observed in a subpopulation of skeletal muscle fibers, whereas in normal skeletal muscle, ALP expression is restricted to blood vessels and some endomysial mononuclear cells.

Conclusion

These results suggest that signals arising from the ECM induce the expression of osteogenic markers in muscle cells by a mechanism independent of BMP-2 and without affecting the expression of key muscle or osteogenic determination genes. An induction and relocalization of ALP is also observed in mdx and regenerating skeletal muscles, in vivo conditions of increased muscle ECM deposition or turnover.

The Spectrum of Pediatric Fibroblastic and Myofibroblastic Tumors

Fibroblastic and myofibroblastic tumors in neonates, infants, and children provide a diagnostic dilemma in surgical pathology due to their relative rarity and similarity in appearances. These tumors may be congenital or occur early during the first years of life or later during the first and second decades of life. The morphologic, immunocytochemical, ultrastructural, cytogenetic, and molecular features of the more "common" pediatric fibroblastic and myofibroblastic tumors are reviewed. In addition, the importance of a multimodal approach to tumor diagnosis is emphasized, with correlation with treatment and outcome differences among these unique fibroblastic and myofibroblastic tumors. The importance of providing an accurate diagnosis with pediatric fibroblastic and myofibroblastic tumors cannot be overstated, because treatment, prognosis, follow-up, and outcome are based on the initial assessment of these fascinating, but oftentimes, perplexing tumors.

The role of the plain radiograph in the characterisation of soft tissue tumours

A radiograph is often the first investigation to be requested when a patient presents with limb pain or a mass. Whilst we do not advocate that this is the only investigation to be employed in the evaluation of such patients, a working knowledge of the variety of abnormal findings that can present in the soft tissues on radiographs remains useful. We reviewed the radiographic findings of soft tissue masses from a prospectively compiled database of all such lesions presenting to a specialist orthopaedic oncology service over the past 8 years. Of the cohort of 1,058 individuals with a proven soft tissue tumour, 454 had had a radiograph taken of the affected area. Of these, 281 (62%) patients had a positive radiographic finding. The most common findings were a visible soft tissue mass (n = 141), the presence of calcification (n = 76), fat (n = 32) and evidence of bone involvement (n = 62). More than one finding was sometimes present in the same patient. These findings were present in both benign and malignant tumours. This review article describes the incidence and diagnostic relevance of these plain film findings for suspected soft tissue tumours.

Enchondral ossification of muscles of the calf: a case report on a new form of heterotopic ossification

Enchondral ossification of two muscles of the calf is reported in a child. The ossified muscles were removed with good resultant function. This represents a new form of heterotopic ossification.

Biological activity of a genetically modified BMP-2 variant with inhibitory activity

Background

Alterations of the binding epitopes of bone morphogenetic protein-2 (BMP-2) lead to a modified interaction with the ectodomains of BMP receptors. In the present study the biological effect of a BMP-2 double mutant with antagonistic activity was evaluated in vivo.

Methods

Equine-derived collagenous carriers were loaded with recombinant human BMP-2 (rhBMP-2) in a well-known dose to provide an osteoinductive stimulus. The study was performed in a split animal design: carriers only coupled with rhBMP-2 (control) were implanted into prepared cavities of lower limb muscle of rats, specimens coupled with rhBMP-2 as well as BMP-2 double mutant were placed into the opposite limb in the same way. After 28 days the carriers were explanted, measured radiographically and characterized histologically.

Results

As expected, the BMP-2 loaded implants showed a typical heterotopic bone formation. The specimens coupled with both proteins showed a significant decreased bone formation in a dose dependent manner.

Conclusion

The antagonistic effect of a specific BMP-2 double mutant could be demonstrated in vivo. The dose dependent influence on heterotopic bone formation by preventing rhBMP-2 induced osteoinduction suggests a competitive receptor antagonism.

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.

An unusual case of rapidly progressive contractures: Case report and brief review

An 8-year-old boy, diagnosed as cervical dystonia, was referred to our tertiary center. After a trivial trauma he had developed painful lumps in the axial region, which was followed by restricted movements of neck, shoulder, and abdominal muscles over 4 months. He had kyphoscoliosis, torticollis, rigid abdomen, and multiple muscle contractures. He also had short great toes. A detailed skeletal survey showed calcification in the soft tissues surrounding the shoulder anterior chest wall, thorax, and paraspinal muscles; there was also beaking of vertebrae, which was confirmed by CT thorax. This report showcases the diagnostic challenge posed by myositis ossificans progressiva, which can rarely cause rapidly progressing muscle contractures. A brief review of literature is also presented.

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.

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.

Amino-bisphosphonates in heterotopic ossification: first experience in five consecutive cases

STUDY DESIGN

Retrospective, observational study in five consecutive cases.

OBJECTIVES

The management of heterotopic ossification (HO), a frequent complication after spinal cord injury (SCI) and after orthopaedic surgery, is a therapeutic challenge with high recurrence rates of over 50%. Conflicting data were reported for Etidronate. The use of the more potent new generation of amino-bisphosphonates has been put forward in different inflammatory, dysmorphogenic bone disease. In order to try and halt the underlying dysfunctional bone metabolism we have studied the action of pamidronate in five consecutive high-risk patients with established HO of different etiology undergoing surgical removal.

SETTING

University Hospital of Basel, Switzerland, Division of Endocrinology, Diabetology and Clinical Nutrition and the Department of Orthopedic Surgery.

METHODS

In all five patients, ranging from 47 to 68 years of age, we used continuous pamidronate infusions perioperatively at a dosage of 120 mg in the first 12 h and subsequent reduction to 75-60-30-15 mg/12 h over a period of 10-14 days.

RESULTS

None of these patients showed clinical, radiographical and laboratory signs of HO recurrence or new forming HO in the follow-up 5-54 month after surgery. Potential side effects of high-dose bisphosphonate therapy such as osteoporosis and osteomalacia were not reported in any case.

CONCLUSION

We postulate that pamidronate might have pronounced beneficial effects in high-risk patients with established HO undergoing excision surgery. Since the therapeutic window of amino-bisphosphonates has not yet been defined and the minimal necessary doses for preventing new HO are unknown, further studies are encouraged to confirm our findings and to identify the necessary dosage and duration of treatment and to pinpoint, which patients will benefit most from this treatment.

Fibrodysplasia ossificans progressiva: case report

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disorder characterized by postnatal progressive heterotopic ossification of the connective tissue and congenital malformation of the big toes. We report on a nine-year-old girl with clinical and radiological features of FOP. She was born with bilateral hallux valgus and at the age of nine presented an indurate mass in the left cervical region that was painful. A significant decreased range of motion in all levels of the spine and shoulder girdle was found. The radiographs showed heterotopic ossification in the thoracic region. The patient had two outbreaks of the disease ("flare-ups") that were treated with prednisone 2 mg/kg/day for four days. After the "flare-ups", she had a continuous therapy with a Cox-2 inhibitor (25 mg/day) and a leukotriene inhibitor, montelukast (10 mg/day).

Heterotopic ossification: a review

Heterotopic ossification is the formation of bone in the soft tissues. Soft tissue bone deposition may range from the minimal and inconsequential to massive and clinically significant. In some clinical settings it is a predictable finding with an unpredictable course and in other settings it may be diagnostically confounding. Heterotopic ossification may be encountered in clinically disparate disease processes and circumstances. We review the genetic, neurogenic, post-traumatic, post-surgical and "reactive" causes of heterotopic ossification and discuss some current concepts of its pathogenesis.

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

FOP is a disorder in which skeletal muscle is progressively replaced with bone. FOP lymphocytes, a model system for exploring the BMP pathway in these patients, exhibit a defect in BMPRIA internalization and increased activation of downstream signaling, suggesting that altered BMP receptor trafficking underlies ectopic bone formation in this disease.

INTRODUCTION

Fibrodysplasia ossificans progressiva (FOP) is a severely disabling disorder characterized by progressive heterotopic ossification of connective tissues. Whereas the genetic defect and pathophysiology of this condition remain enigmatic, BMP4 mRNA and protein are overexpressed, and mRNAs for a subset of secreted BMP antagonists are not synthesized at appropriate levels in cultured lymphocytes from FOP patients. These data suggest involvement of altered BMP signaling in the disease. In this study, we investigate whether the abnormality is associated with defective BMP receptor function in lymphocytes.

MATERIALS AND METHODS

Cell surface proteins were quantified by fluorescence-activated cell sorting (FACS). Protein phosphorylation was assayed by immunoprecipitation and immunoblotting. Protein synthesis and degradation were examined by [35S]methionine labeling and pulse-chase assays. mRNA was detected by RT-PCR.

RESULTS

FOP lymphocytes expressed 6-fold higher levels of BMP receptor type IA (BMPRIA) on the cell surface compared with control cells and displayed a marked reduction in ligand-stimulated internalization and degradation of BMPRIA. Moreover, in control cells, BMP4 treatment increased BMPRIA phosphorylation, whereas BMPRIA showed ligand-insensitive constitutive phosphorylation in FOP cells. Our data additionally support that the p38 mitogen-activated protein kinase (MAPK) signaling pathway is a major BMP signaling pathway in these cell lines and that expression of inhibitor of DNA binding and differentiation 1 (ID-1), a transcriptional target of BMP signaling, is enhanced in FOP cells.

CONCLUSIONS

These data extend our previous observations of misregulated BMP4 signaling in FOP lymphocytes and show that cell surface overabundance and constitutive phosphorylation of BMPRIA are associated with a defect in receptor internalization. Altered BMP receptor trafficking may play a significant role in FOP pathogenesis.

[Progressive myositis ossificans. Utility of bone scintigraphy]

47 year old woman affected by myositis ossificans, with muscular calcifications in her evolution. Bone scintigraphy showed increased polyfocal activity as well as uptake of different intensity in soft tissues. The bone scintigraphy allows for early identification of ossification areas in soft tissues, as it can even detect injuries earlier than that observed with other image techniques. It is considered to be very useful in the diagnosis and establishment of the extension of the process, as well as follow-up.

Inherited ossifying diseases

Inherited ossifying diseases are relatively uncommon diseases leading ta a great disability and life-threatening complications. Fibrodysplasia Ossificans Progressiva is characterized by the association of skeletal abnormalities mainly in great toes, and enchondral ossifications in tendons and muscles. BMP dysregulation seems to be the main underlying mechanism of the heterotopic ossifications. The genetic basis remain controversial between a mutation on chromosome 4 or 17. Progressive Osseous Heteroplasia (HOP), more recently described, shares some similarities with Albrights hereditary osteodystrophy. In HOP, the intramembranous ossifications progressively developped from the dermis to the deeper layer. The genetic abnormality involved the GNAS 1 gene leading to an inactivation of the alpha subunit of the G protein-complex. Some therapeutic approaches have been tried: angiogenesis inhibition, mast cell inhibition; others remained in project: BMP 4 inhibition; actually there is no proved efficacy of any of them.

Influenza-like viral illnesses and flare-ups of fibrodysplasia ossificans progressiva

Flare-ups of fibrodysplasia ossificans progressiva are most commonly triggered by soft tissue trauma. After observing severe flare-ups of fibrodysplasia ossificans progressiva in two half-sisters with culture-confirmed influenza B infections, we hypothesized that influenza-like viral illnesses also can trigger fibrodysplasia ossificans progressiva flare-ups. To address this hypothesis, we designed a questionnaire to assess whether patients with fibrodysplasia ossificans progressiva experienced influenza symptoms during the 2000 to 2001 influenza season, and whether these symptoms were correlated with flare-ups of the condition. The questionnaire was sent to patients with fibrodysplasia ossificans progressiva worldwide. Of the 264 patients surveyed, 123 (47%) responded. The survey revealed that the risk of a disease flare-up of fibrodysplasia ossificans progressiva during an influenza-like viral illness was increased at least threefold and possibly much more. The survey data strongly supported the hypothesis that influenza-like viral illnesses are associated with disease flare-ups in patients who have fibrodysplasia ossificans progressiva. Influenza-like viral illnesses may be a source of previously unrecognized muscle injury leading to heterotopic ossification and permanent loss of mobility in these patients. These findings have important implications for understanding and preventing environmental triggers of disease activity in this population of patients genetically susceptible to progressive heterotopic ossification.

Fibrodysplasia ossificans progressiva

A 2-year-old boy presented with low-grade fever and multiple progressive painful swellings over upper dorsal trunk and supraclavicular region with progressive stiffening of skin for the last 2 months. Examination revealed dysmorphic face, proximally placed thumb and bilateral hallux valgus. Hence, a diagnosis of Fibrodysplasia Ossificans Progressiva was entertained.

Heterotopic ossification

Heterotopic ossification, the formation of bone in soft tissue, requires inductive signaling pathways, inducible osteoprogenitor cells, and a heterotopic environment conducive to osteogenesis. Little is known about the molecular pathogenesis of this condition. Research into two rare heritable and developmental forms, fibrodysplasia ossificans progressiva and progressive osseous heteroplasia, has provided clinical, pathologic, and genetic insights. In fibrodysplasia ossificans progressiva, overexpression of bone morphogenetic protein 4 and underexpression of multiple antagonists of this protein highlight the potential role of a potent morphogenetic gradient. Research on fibrodysplasia ossificans progressiva also has led to the identification of the genetic cause of progressive osseous heteroplasia: inactivating mutations in the alpha subunit of the gene coding for the stimulatory G protein of adenylyl cyclase. Better understanding of the complex developmental and molecular pathology of these disorders may lead to more effective strategies to prevent and treat other, more common forms of heterotopic ossification.

The spine in fibrodysplasia ossificans progressiva: a case report

STUDY DESIGN

A case report of fibrodysplasia ossificans progressiva (FOP).

OBJECTIVES

To report a very rare cause of back pain.

SUMMARY OF BACKGROUND DATA

FOP is an autosomal dominant disorder with overexpression of bone morphogenetic protein 4 and negative HLA B27. Pathognomonic are congenital malformations of the big toes.

METHODS

The authors report on a patient with FOP who presented with back pain at their outpatient clinic.

RESULTS

On physical examination, several indurated masses were visible and palpable close to the left and right scapula and the thoracic spine. These were not tender or painful, nor warmed or inflamed. A significantly decreased range of motion of all levels of the spine and the shoulder were found. On the radiographs, segmentation defects of the cervical and lumbar spine as well as synostoses of the spinal processes were seen. The cervical vertebral bodies were small and unusually high. Heterotopic ossifications could be discerned in the lumbar postural muscles and the facet joints of the spine were ankylosed. Additionally to these findings, on the thoracic radiographs ossifications of the muscles of the shoulder girdle could be seen. The pathognomonic shortening of the first metatarsal bone and the proximal phalanx was bilaterally present. The surface shaded 3D-reconstruction of the computed tomography of the trunk showed multiple bulky and confluating ossifications of the shoulder girdle. The spinal processes of the thoracic spine were anklyosed by massive ossifications of the postural muscles.

CONCLUSIONS

In FOP, diagnosis can be made by the typical clinical and radiological features.

Ankylosis of the jaw in a patient with fibrodysplasia ossificans progressiva

A case of fibrodysplasia ossificans progressiva (FOP) is presented. This uncommon connective tissue disease tends to produce progressing ectopic osteogenesis. Because there are no reported curative procedures for TMJ ankylosis occurring in this condition, a palliative surgical approach is described. Etiology, diagnosis, and prognosis of the disease is reviewed. Recent research in BMP cytokine-induced bone repair may allow new approaches to treating this debilitating disease in the future.

Stromal cells of fibrodysplasia ossificans progressiva lesions express smooth muscle lineage markers and the osteogenic transcription factor Runx2/Cbfa-1: clues to a vascular origin of heterotopic ossification?

Fibrodysplasia ossificans progressiva (FOP) is a rare heritable genetic disorder, which is characterized pathologically by sporadic episodes of explosive growth of mesenchymal cells in skeletal muscle followed by cellular differentiation to heterotopic bone through an endochondral process. This study examined the histological origin and differentiation state of stromal cells in early FOP lesions and investigated the association between the phenotype of these FOP cells and bone formation. Interestingly, FOP lesional stromal cells were found to display characteristics of the smooth muscle (SM) cell lineage and are therefore potentially of vascular origin. These cells co-express multiple SM lineage markers along with multiple proteins associated with bone formation including the obligate osteogenic transcription factor Runx2/Cbfa-1. It is hypothesized that the stromal cells of early FOP lesions may be locally recruited vascular cells or cells of the bone marrow stroma and that these cells maintain the potential (given the correct environmental stimuli) to differentiate along an endochondral ossification pathway.

Anesthetic management in fibrodysplasia ossificans progressiva (FOP): a case report

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disorder of connective tissue, which has significant implications on anesthetic management of affected patients, e.g., application of difficult airway algorithm, avoiding any trauma during venous cannulation. FOP has received very limited reviews in the published anesthesia literature. We describe perioperative care of a 21-year-old female with established diagnosis of FOP presenting for hysteroscopy followed by dilatation and curettage. Multiorgan abnormalities of FOP are reviewed and available anesthetic options are analyzed and compared.

Paresis of a bone morphogenetic protein-antagonist response in a genetic disorder of heterotopic skeletogenesis

BACKGROUND

Fibrodysplasia ossificans progressiva is a rare genetic disorder characterized by congenital malformations of the great toes and by progressive heterotopic bone formation. Bone morphogenetic protein-4 (BMP-4) messenger ribonucleic acid (mRNA) and protein are uniquely overexpressed in lymphocytes and lesional cells from patients who have fibrodysplasia ossificans progressiva. However, the BMP-4 gene is not mutated in fibrodysplasia ossificans progressiva. The activities of BMPs are specified in part by the formation of morphogen gradients that are further regulated by an array of secreted antagonists. Recent studies have indicated that BMP-4 upregulates the expression of the BMP antagonists noggin, gremlin, and follistatin, thereby establishing an autoregulatory feedback loop. Therefore, a defect in the feedback pathway between BMP-4 and one or more of its extracellular antagonists could contribute to the elevated BMP-4 activity characteristic of fibrodysplasia ossificans progressiva.

METHODS

Basal and BMP-4-induced expression of noggin, gremlin, follistatin, and chordin mRNA were investigated in control and fibrodysplasia ossificans progressiva lymphoblastoid cell lines with use of reverse transcriptase-polymerase chain reaction and Northern analysis.

RESULTS

In the absence of exogenous BMP-4 stimulation (basal state), steady-state levels of all of the BMP antagonists that were investigated were similar in fibrodysplasia ossificans progressiva and control cell lines. Upon stimulation with recombinant human BMP-4, control lymphoblastoid cell lines exhibited a marked increase in expression of noggin and gremlin mRNA. Fibrodysplasia ossificans progressiva cells, however, showed a dramatically attenuated response to BMP-4 stimulation compared with that of controls.

CONCLUSIONS

These data indicate a paresis of a BMP-antagonist response, suggesting the loss of a negative feedback mechanism by which cells normally regulate the magnitude and boundaries of ambient morphogenetic signals. This paresis may account in part for the increased BMP-4 activity in fibrodysplasia ossificans progressiva.

Bone morphogenetic protein-4 regulation in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva is a rare genetic disorder in which connective tissues are replaced with heterotopic bone through an endochondral process. Bone morphogenetic protein-4 messenger ribonucleic acid and protein levels are elevated in the cells of patients with fibrodysplasia ossificans progressiva, but the molecular mechanism of this steady-state elevation is unknown. Nuclear run-on assays and messenger ribonucleic acid stability assays were done to examine the molecular mechanisms of increased bone morphogenetic protein-4 messenger ribonucleic acid. The bone morphogenetic protein-4 transcription rate in patient cells was found to be enhanced fivefold to sevenfold over normal control cells, suggesting that elevated steady-state levels of this transcript were attributable at least in part to an enhancement in transcription initiation. The stability of bone morphogenetic protein-4 messenger ribonucleic acid was found to be similar for patient and control cells and to have an extremely brief half-life, with bone morphogenetic protein-4 messenger ribonucleic acid almost completely decayed (75%) by 40 minutes. This unusually brief half-life suggests that a high fidelity control over temporal expression of the bone morphogenetic protein 4-message can be maintained. The data document that enhanced transcription rather than increased messenger ribonucleic acid stability is responsible for the elevation in steady-state levels of bone morphogenetic protein-4 messenger ribonucleic acid, and suggest that an inappropriate enhancement of the rate of bone morphogenetic protein-4 transcription plays a critical role in the molecular pathophysiology of fibrodysplasia ossificans progressiva.

International nosology and classification of constitutional disorders of bone (2001)

The last International Classification of Constitutional Disorders of Bone was published in 1998. Since then rapid advances have been made in identifying the molecular changes responsible for defined conditions and new disorders are constantly being delineated. For these reasons a further update on the classification is appropriate. It has been expended to not only the osteochondrodysplasias (33 groups) but also genetically determined dysostoses (3 groups).

[Biphosphonates in children: present and future]

Biphosphonates are synthetic analogs of the natural pyrophosphate molecule, introduced primarily for the treatment of Paget disease of bone. Their main mechanism of action consisting in an inhibition of osteoclastic activity is critical for treatment of disorders including an increased bone resorption. In childhood osteoporosis (especially osteogenesis imperfecta), hypercalcemia and heterotopic calcifications are the three main situations in which they have been successfully used, with however few follow-up and no controlled studies. The evolution of these compounds generating more potent products, given orally, with limited effect on bone mineralization should allow an extension of their use in pediatric patients. Multicentric studies are now necessary to specify their efficacy and guidelines for use in children.