Limb swelling in patients who have fibrodysplasia ossificans progressiva

Fibrodysplasia Ossificans Progressiva: A Report of Four Cases

Fibrodysplasia ossificans progressiva (FOP) is a rare disease with less than a thousand confirmed cases. It is a severely disabling genetic condition that affects soft tissues and is characterized by progressive extraskeletal heterotopic ossification and great toe deformities.

The mode of FOP inheritance is autosomal dominant with no association to race, gender, or geographic distribution. While laboratory results and imaging studies support the identification of FOP, the diagnosis of this rare condition is mainly clinical. Recently, FOP has been linked to a mutation of the ACVR1/ALK2 gene that induces osteoblast activation. 

We are reporting four cases of fibrodysplasia ossificans progressiva over a period of two years (2014-2016). Three out of four cases were treated conservatively. The first case was treated by excision of a bony bar, and the patient developed progressive bony formation and restriction of movement afterwards.

Almost always, FOP needs to be treated conservatively with non-steroidal anti-inflammatory drugs (NSAIDs) and gentle physiotherapy. Aside from anesthetic complications, surgical interventions provoke more bone formation, hence the recurrent joint restriction. Therefore, surgery should only be reserved for severely disabling deformities.

Treatment of heterotopic ossification through remote ATP hydrolysis

Heterotopic ossification (HO) is the pathologic development of ectopic bone in soft tissues because of a local or systemic inflammatory insult, such as burn injury or trauma. In HO, mesenchymal stem cells (MSCs) are inappropriately activated to undergo osteogenic differentiation. Through the correlation of in vitro assays and in vivo studies (dorsal scald burn with Achilles tenotomy), we have shown that burn injury enhances the osteogenic potential of MSCs and causes ectopic endochondral heterotopic bone formation and functional contractures through bone morphogenetic protein-mediated canonical SMAD signaling. We further demonstrated a prevention strategy for HO through adenosine triphosphate (ATP) hydrolysis at the burn site using apyrase. Burn site apyrase treatment decreased ATP, increased adenosine 3',5'-monophosphate, and decreased phosphorylation of SMAD1/5/8 in MSCs in vitro. This ATP hydrolysis also decreased HO formation and mitigated functional impairment in vivo. Similarly, selective inhibition of SMAD1/5/8 phosphorylation with LDN-193189 decreased HO formation and increased range of motion at the injury site in our burn model in vivo. Our results suggest that burn injury-exacerbated HO formation can be treated through therapeutics that target burn site ATP hydrolysis and modulation of SMAD1/5/8 phosphorylation.

The Diversity of the Clinical Phenotypes in Patients With Fibrodysplasia Ossificans Progressiva

Background

The clinical presentation, phenotypic characterization and natural history of fibrodysplasia ossificans progressiva (FOP) are diverse and the natural history of the disease is, to a certain extent, different from one patient to another.

Methods

In a series of 11 patients (eight girls and three boys, aged 0 - 16 years), variable clinical presentations were the landmarks of these patients. At birth, all of our patients manifested short great toes in a valgus position. Marfan syndrome was the suggested diagnosis in three children aged 3 - 8 years and in two pre-adult patients. Clinical symptoms were torticollis, painful spine, and painful and marked limitation of the pelvic movements. Monophalangia associated with Marfanoid habitus was also a prevailing clinical presentation.

Results

Our results were based upon the appearance of the earliest pathologic feature of FOP in correlation with the clinical presentation. In infants (0 - 1 year), three infants showed congenital hallux valgus and stiff spine. In the pediatric group (3 - 8 years), all children showed no mutation in the fibrillin-1 (FBN1) gene. Their prime presentation was a progressive torticollis with simultaneous development of erythematous subfascial nodules, most commonly located on the posterior neck and back. In pre-adult group (10 - 16 years), four patients presented with monophalangia associated with painful movements because of the progressive heterotopic ossification of the spine and the weight bearing zones and marked elevation of alkaline phosphatase. Genetic confirmation has been performed in six patients who manifested the classical mutation of the ACVR1 gene. The rest of the patients were assessed via clinical and radiographic phenotypes.

Conclusion

The early recognition of FOP can be performed by noticing the short halluces and thumbs at early infancy and later on the high alkaline phosphatase activity in areas of heterotopic ossification. Misconception of FOP is of common practice and eventually unnecessary diagnostic biopsies might deteriorate the progression of the condition. The detection of ACVR1 gene mutation was a confirmatory procedure. Interestingly, the timing of the onset and the location of progressive heterotopic ossifications were extremely variable and confusing among our group of patients.

Granting immunity to FOP and catching heterotopic ossification in the Act

The progressive transformation of one organ system into another is a fundamental signature of fibrodysplasia ossificans progressiva (FOP), the most catastrophic form of extraskeletal bone formation in humans. In all affected individuals, FOP is caused by heterozygous missense gain-of-function mutations in Activin receptor A type I (ACVR1), a bone morphogenetic protein (BMP) type I receptor. Loss of autoinhibition of the mutant receptor (mACVR1) results in dysregulated BMP pathway signaling, and is necessary for the myriad developmental features of FOP, but does not appear sufficient to induce the episodic flare-ups that lead to disabling post-natal heterotopic endochondral ossification (HEO) and that are a hallmark of the disease. Post-natal FOP flare-ups strongly implicate an underlying immunological trigger involving inflammation and the innate immune system. Recent studies implicate canonical and non-canonical TGFβ/BMP family ligands in the amplification of mACVR1 signaling leading to the formation of FOP lesions and resultant HEO. BMP and Activin ligands that stimulate mACVR1 signaling also have critical regulatory functions in the immune system. Cross-talk between the morphogenetic and immunological pathways that regulate tissue maintenance and wound healing identifies potential robust therapeutic targets for FOP. Here we review current evidence for an immunological trigger for flare-ups and HEO in FOP, propose a working schema for the pathophysiology of observed phenomena, and highlight outstanding questions under investigation.

Fibrodysplasia ossificans progressiva without characteristic skeletal anomalies

Fibrodysplasia ossificans progressiva (FOP) is a rare but extremely disabling genetic disease of the skeletal system. This disease is characterized by progression of heterotopic ossification within skeletal muscles, ligaments and tendons. Most patients with FOP are misdiagnosed early in life before the appearance of heterotopic ossification and undergo diagnostic procedures such as biopsy that can cause lifelong disability. Almost all of the patients have some peculiar congenital anomalies, including short great toes, hallux valgus, short thumbs and hypoplasia of digital phalanges. These congenital defects support the diagnosis of FOP, but are not constantly observed in the totality of patients. If necessary, genetic studies can be performed to confirm the diagnosis. Once diagnosed, patients should be advised in order to avoid unnecessary traumas, surgical procedures, biopsies, intramuscular injections and vaccinations. Here, we describe a patient with FOP without characteristic congenital skeletal anomalies.

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.

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.

Mast cell involvement in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a catastrophic genetic disorder of progressive heterotopic ossification associated with dysregulated production of bone morphogenetic protein 4 (BMP4), a potent osteogenic morphogen. Postnatal heterotopic ossification in FOP is often heralded by hectic episodes of severe post-traumatic connective tissue swelling and intramuscular edema, followed by an intense and highly angiogenic fibroproliferative mass. The abrupt appearance, intense size, and rapid intrafascial spread of the edematous preosseous fibroproliferative lesions implicate a dysregulated wound response mechanism and suggest that cells and mediators involved in inflammation and tissue repair may be conscripted in the growth and progression of FOP lesions. The central and coordinate role of inflammatory mast cells and their mediators in tissue edema, wound repair, fibrogenesis, angiogenesis, and tumor invasion prompted us to investigate the potential involvement of mast cells in the pathology of FOP lesions. We show that inflammatory mast cells are present at every stage of the development of FOP lesions and are most pronounced at the highly vascular fibroproliferative stage. Mast cell density at the periphery of FOP lesional tissue is 40- to 150-fold greater than in normal control skeletal muscle or in uninvolved skeletal muscle from FOP patients and 10- to 40-fold greater than in any other inflammatory myopathy examined. These findings document mobilization and activation of inflammatory mast cells in the pathology of FOP lesions and provide a novel and previously unrecognized target for pharmacologic intervention in this extremely disabling disease.

Fibrodysplasia ossificans progressiva: case report

Fibrodysplasia ossificans progressiva is a rare genetic disease characterized by widespread soft tissue ossification and congenital stigmata of the extremities. We report on a male child followed for ten years since the age of 3 years and 9 months, when the diagnosis was made. He was born with bilateral hypoplasic hallux valgus and ventricular septal defect, corrected by trans-sternal approach when 32 months old. Restriction of neck mobility followed and foci of ectopic ossification appeared. Four crises of disease exacerbation were treated with oral prednisone and/or other antiinflammatory drugs. Sodium etidronate 5 to 10 mg/kg/day was prescribed intermittently during about six years but was discontinued due to osteopenia. The disease course has been relentless, with severe movement restriction including the chest wall. A review showed few similar case reports in the Brazilian literature. We revisit the criteria for diagnosis and the essentials of management and treatment.