2005

Fibrodysplasia Ossificans Progressiva (FOP), a disorder of Ectopic Osteogenesis, Misregulates Cell Surface Expression and Trafficking of BMPRIA*

Lourdes Serano de la Pena, Paul Billings, Jennifer L. Fiori, Jaimo Ahn, Frederick S. Kaplan, and Eileen Moore

Journal of Bone and Mineral Research
Volume 20, Number 7, 2005
Published online on March 7, 2005; doi: 10.1359/JBMR.050305
© American Society for Bone and Mineral Research

2002

ClinN Engl J Med 2002 Jan 10;346(2):99-106
Paternally inherited inactivating mutations of the GNAS1 gene in progressive osseous heteroplasia. Shore EM, Ahn J, Jan de Beur S, Li M, Xu M, Gardner RJ, Zasloff MA, Whyte MP, Levine MA, Kaplan FS.

Progressive osseous heteroplasia (POH), an autosomal dominant disorder, is characterized by extensive dermal ossification during childhood, followed by disabling and widespread heterotopic ossification of skeletal muscle and deep connective tissue. Occasional reports of mild heterotopic ossification in Albright's hereditary osteodystrophy (AHO) and a recent report of two patients with AHO who had atypically extensive heterotopic ossification suggested a common genetic basis for the two disorders. AHO is caused by heterozygous inactivating mutations in the GNAS1 gene that result in decreased expression or function of the alpha subunit of the stimulatory G protein (Gsalpha) of adenylyl cyclase. METHODS: We tested the hypothesis that GNAS1 mutations cause POH, using the polymerase chain reaction to amplify GNAS1 exons and exon-intron boundaries in 18 patients with sporadic or familial POH. RESULTS: Heterozygous inactivating GNAS1 mutations were identified in 13 of the 18 probands with POH. The defective allele in POH is inherited exclusively from fathers, a result consistent with a model of imprinting for GNAS1. Direct evidence that the same mutation can cause either POH or AHO was observed within a single family, in which the phenotype correlated with the parental origin of the mutant allele. CONCLUSIONS: Paternally inherited inactivating GNAS1 mutations cause POH. This finding extends the range of phenotypes derived from haploinsufficiency of GNAS1, provides evidence that imprinting is a regulatory mechanism for GNAS1 expression, and suggests that Gsalpha is a critical negative regulator of osteogenic commitment in nonosseous connective tissues.

2001

Clin Orthop 2001 Nov;(392):451-5
Answer: Marrow stem cell transplantation in fibrodysplasia ossificans progressiva. Emerson SG, Kaplan FS.

Clin Orthop 2001 Nov;(392):450-1
Question: Bone marrow transplant for fibrodysplasia ossificans progressiva: has the hour arrived? Altschuler EL.

Hum Pathol 2001 Aug;32(8):842-8
Mast cell involvement in fibrodysplasia ossificans progressiva. Gannon FH, Glaser D, Caron R, Thompson LD, Shore EM, Kaplan FS.

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.

Pediatr Radiol 2001 May;31(5):307-14
Fibrodysplasia ossificans progressiva. Mahboubi S, Glaser DL, Shore EM, Kaplan FS.

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare and disabling genetic disorder of connective tissue. The condition is characterized by congenital malformation of the great toes and by progressive heterotopic ossification of the tendons, ligaments, fasciae, and striated muscles. Fibrodysplasia ossificans progressiva occurs sporadically and is transmitted as a dominant trait with variable expression and complete penetrance. Reproductive fitness is low. There are fewer than 150 known patients with the disorder in the United States. A point prevalence of one affected patient in every 2 million of population has been observed. There is no sexual, racial, or ethnic predilection. The disease presents in early life; its course is unavoidably progressive. Most patients are confined to a wheelchair by the third decade of life and often succumb to pulmonary complications in the 5th/6th decade of life. At present there is no effective prevention or treatment. The recent discovery of overproduction of bone morphogenetic protein-4 in lesional cells and lymphocytic cells of affected patients provides a clue to both the underlying pathophysiology and potential therapy. The FOP gene has recently been mapped to human chromosome 4q 27-31.

2000

J Bone Miner Res 2000 Nov;15(11):2084-94
Progressive osseous heteroplasia. Kaplan FS, Shore EM.

Progressive osseous heteroplasia (POH) is a recently described genetic disorder of mesenchymal differentiation characterized by dermal ossification during infancy and progressive heterotopic ossification of cutaneous, subcutaneous, and deep connective tissues during childhood. The disorder can be distinguished from fibrodysplasia ossificans progressiva (FOP) by the presence of cutaneous ossification, the absence of congenital malformations of the skeleton, the absence of inflammatory tumorlike swellings, the asymmetric mosaic distribution of lesions, the absence of predictable regional patterns of heterotopic ossification, and the predominance of intramembranous rather than endochondral ossification. POH can be distinguished from Albright hereditary osteodystrophy (AHO) by the progression of heterotopic ossification from skin and subcutaneous tissue into skeletal muscle, the presence of normal endocrine function, and the absence of a distinctive habitus associated with AHO. Although the genetic basis of POH is unknown, inactivating mutations of the GNAS1 gene are associated with AHO. The report in this issue of the JBMR of 2 patients with combined features of POH and AHO--one with classic AHO, severe POH-like features, and reduced levels of Gsalpha protein and one with mild AHO, severe POH-like features, reduced levels of Gsalpha protein, and a mutation in GNAS1--suggests that classic POH also could be caused by GNAS1 mutations. This possibility is further supported by the identification of a patient with atypical but severe platelike osteoma cutis (POC) and a mutation in GNAS1, indicating that inactivating mutations in GNAS1 may lead to severe progressive heterotopic ossification of skeletal muscle and deep connective tissue independently of AHO characteristics. These observations suggest that POH may lie at one end of a clinical spectrum of ossification disorders mediated by abnormalities in GNAS1 expression and impaired activation of adenylyl cyclase. Analysis of patients with classic POH (with no AHO features) is necessary to determine whether the molecular basis of POH is caused by inactivating mutations in the GNAS1 gene.

J Bone Miner Res 2000 Nov;15(11):2074-83
Deficiency of the alpha-subunit of the stimulatory G protein and severe extraskeletal ossification. Eddy MC, De Beur SM, Yandow SM, McAlister WH, Shore EM, Kaplan FS, Whyte MP, Levine MA.

Progressive osseous heteroplasia (POH) is a rare disorder characterized by dermal ossification beginning in infancy followed by increasing and extensive bone formation in deep muscle and fascia. We describe two unrelated girls with typical clinical, radiographic, and histological features of POH who also have findings of another uncommon heritable disorder, Albright hereditary osteodystrophy (AHO). One patient has mild brachydactyly but no endocrinopathy, whereas the other manifests brachydactyly, obesity, and target tissue resistance to thyrotropin and parathyroid hormone (PTH). Levels of the alpha-subunit of the G protein (Gsalpha) were reduced in erythrocyte membranes from both girls and a nonsense mutation (Q12X) in exon 1 of the GNAS1 gene was identified in genomic DNA from the mildly affected patient. Features of POH and AHO in two individuals suggest that these conditions share a similar molecular basis and pathogenesis and that isolated severe extraskeletal ossification may be another manifestation of Gsalpha deficiency.

J Bone Miner Res 2000 Nov;15(11):2063-73
GNAS1 mutation and Cbfa1 misexpression in a child with severe congenital platelike osteoma cutis. Yeh GL, Mathur S, Wivel A, Li M, Gannon FH, Ulied A, Audi L, Olmstead EA, Kaplan FS, Shore EM.

We evaluated a 7-year-old girl with severe platelike osteoma cutis (POC), a variant of progressive osseous heteroplasia (POH). The child had congenital heterotopic ossification of dermis and subcutaneous fat that progressed to involve deep skeletal muscles of the face, scalp, and eyes. Although involvement of skeletal muscle is a prominent feature of POH, heterotopic ossification has not been observed in the head, face, or extraocular muscles. The cutaneous ossification in this patient was suggestive of Albright hereditary osteodystrophy (AHO); however, none of the other characteristic features of AHO were expressed. Inactivating mutations of the GNAS1 gene, which encodes the alpha-subunit of the stimulatory G protein of adenylyl cyclase, is the cause of AHO. Mutational analysis of GNAS1 using genomic DNA of peripheral blood and of lesional and nonlesional tissue from our patient revealed a heterozygous 4-base pair (bp) deletion in exon 7, identical to mutations that have been found in some AHO patients. This 4-bp deletion in GNAS1 predicts a protein reading frameshift leading to 13 incorrect amino acids followed by a premature stop codon. To investigate pathways of osteogenesis by which GNAS1 may mediate its effects, we examined the expression of the obligate osteogenic transcription factor Cbfa1/RUNX2 in lesional and uninvolved dermal fibroblasts from our patient and discovered expression of bone-specific Cbfa1 messenger RNA (mRNA) in both cell types. These findings document severe heterotopic ossification in the absence of AHO features caused by an inactivating GNAS1 mutation and establish the GNAS1 gene as the leading candidate gene for POH.

Clin Genet 2000 Oct;58(4):291-8
Linkage exclusion and mutational analysis of the noggin gene in patients with fibrodysplasia ossificans progressiva. Xu MQ, Feldman G, Le Merrer M, Shugart YY, Glaser DL, Urtizberea JA, Fardeau M, Connor JM, Triffitt J, Smith R, Shore EM, Kaplan FS

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare and disabling genetic disorder characterized by congenital malformation of the great toes and by progressive heterotopic endochondral ossification in predictable anatomical patterns. Although elevated levels of bone morphogenetic protein 4 (BMP4) occur in lymphoblastoid cells and in lesional cells of patients with FOP, mutations have not been identified in the BMP4 gene, suggesting that the mutation in FOP may reside in a BMP4-interacting factor or in another component of the BMP4 pathway. A powerful antagonist of BMP4 is the secreted polypeptide noggin. A recent case report described a heterozygous 42-bp deletion in the protein-coding region of the noggin gene in a patient with FOP. In order to determine if noggin mutations are a widespread finding in FOP, we examined 31 families with 1 or more FOP patients. Linkage analysis with an array of highly polymorphic microsatellite markers closely linked to the noggin gene was performed in four classically affected multigenerational FOP families and excluded linkage of the noggin locus to FOP (the multipoint lod score was -2 or less throughout the entire range of markers). We sequenced the noggin gene in affected members of all four families, as well as in 18 patients with sporadic FOP, and failed to detect any mutations. Single-strand conformation polymorphism (SSCP) analysis of 4 of these patients plus an additional 9 patients also failed to reveal any mutations. Among the samples analyzed by SSCP and DNA sequencing was an independently obtained DNA sample from the identical FOP patient previously described with the 42-bp noggin deletion; no mutation was detected. Examination of the DNA sequences of 20 cloned noggin PCR products, undertaken to evaluate the possibility of a somatic mutation in the noggin gene which could be carried by a small subset of white blood cells, also failed to detect the presence of the reported 42-bp deletion. We conclude that mutations in the coding region of noggin are not associated with FOP.

Clin Orthop 2000 May;(374):303-16
Osteogenic induction in hereditary disorders of heterotopic ossification. Shore EM, Glaser DL, Gannon FH

The formation of heterotopic bone within soft connective tissue is a common feature of at least three distinct genetic disorders of osteogenesis in humans: fibrodysplasia ossificans progressiva; progressive osseous heteroplasia; and Albright hereditary osteodystrophy. The pathobiologic characteristics of osteogenic induction, the histopathologic features of osteogenesis, the anatomic distribution of heterotopic lesions, and the developmental patterns of disease progression differ among all three conditions. The molecular and cellular basis of redirecting a mature connective tissue phenotype to form bone is a remarkable biological phenomenon with enormous implications for the control of bone regeneration, fracture healing, and disorders of osteogenesis.

Am J Hum Genet 2000 Jan;66(1):128-35
Fibrodysplasia ossificans progressiva, a heritable disorder of severe heterotopic ossification, maps to human chromosome 4q27-31. Feldman G, Li M, Martin S, Urbanek M, Urtizberea JA, Fardeau M, LeMerrer M, Connor JM, Triffitt J, Smith R, Muenke M, Kaplan FS, Shore EM

Fibrodysplasia ossificans progressiva (FOP) is a severely disabling, autosomal-dominant disorder of connective tissue and is characterized by postnatal progressive heterotopic ossification of muscle, tendon, ligament, and fascia and by congenital malformation of the great toes. To identify the chromosomal location of the FOP gene, we conducted a genomewide linkage analysis, using four affected families with a total of 14 informative meioses. Male-to-male transmission of the FOP phenotype excluded X-linked inheritance. Highly polymorphic microsatellite markers covering all human autosomes were amplified by use of PCR. The FOP phenotype is linked to markers located in the 4q27-31 region (LOD score 3.10 at recombination fraction 0). Crossover events localize the putative FOP gene within a 36-cM interval bordered proximally by D4S1625 and distally by D4S2417. This interval contains at least one gene involved in the bone morphogenetic protein-signaling pathway.

1999

Neuromuscul Disord 1999 Oct;9(6-7):434-5
61st ENMC-sponsored international workshop: Fibrodysplasia (myositis) ossificans progressiva (FOP), 10 12th July 1998, Naarden, The Netherlands. Smith R

No abstract available

Calcif Tissue Int 1999 Sep;65(3):250-5
Phenotypic and molecular heterogeneity in fibrodysplasia ossificans progressiva. Virdi AS, Shore EM, Oreffo RO, Li M, Connor JM, Smith R, Kaplan FS, Triffitt JT

Fibrodysplasia (myositis) ossificans progressiva (FOP) is an extremely rare inherited disorder in which progressive ossification of major striated muscles, often following injury, is associated with abnormal skeletal patterning. Altered expression of bone morphogenetic proteins may be a contributory cause. To examine this hypothesis, we compared the patterns of expression of bone morphogenetic proteins (BMPs) mRNAs from lymphoblastoid cell lines from two small multigenerational families with autosomal dominant transmission of FOP. Although affected members of both families showed the characteristic phenotype of FOP, one family was more severely affected than the other. Expression of mRNAs for BMP-1, 2, 3, 5, and 6 mRNAs were not detected within the more severely affected family, but BMP-4 mRNA was expressed in affected but not unaffected members of this family. The results of linkage exclusion analysis using a highly polymorphic microsatellite marker near the BMP-4 gene were consistent with linkage of FOP and BMP-4 in this family. Within the less severely affected family, affected and unaffected members showed similar levels of mRNA expression of BMPs 1, 2, 4, and 5, and linkage of FOP to the BMP-4 gene was excluded. It is concluded that clinical, radiographic, and biochemical data in these two families with FOP establish clinical and molecular heterogeneity and also suggest the possibility of genetic heterogeneity.

Am J Audiol 1999 Jun;8(1):29-33
Conductive hearing loss in individuals with fibrodysplasia ossificans progressiva. Levy CE, Lash AT, Janoff HB, Kaplan FS

Fibrodysplasia ossificans progressiva (FOP) is a very rare genetic disorder that is characterized by progressive heterotopic ossification of soft tissues and congenital malformation of the great toes. Although previous case studies have reported hearing loss in individuals with FOP, there have been no large-scale studies regarding the nature or cause of the hearing loss. Here, we report the findings of a two-part study. In Part I, we report the findings of a postal survey regarding hearing loss that was sent to 102 individuals with FOP. In Part II, we report the findings of on-site hearing evaluations of eight individuals with FOP. The findings of both studies indicate that individuals with FOP are at risk for hearing loss and that the type of loss is predominantly conductive in nature, similar to that seen in individuals who have otosclerosis.

Gravit Space Biol Bull 1999 May;12(2):27-38
Illustrative disorders of ectopic skeletal morphogenesis: a childhood parallax for studies in gravitational and space biology. Kaplan FS, Shore EM.

Heterotopic ossification is a key feature of at least three distinct genetic disorders of osteogenesis in humans: fibrodysplasia ossificans progressiva, progressive osseous heteroplasia, and Albright's hereditary osteodystrophy. All three conditions are genetic disorders of childhood, but the pathobiology of osteogenic induction, the histopathology of osteogenesis, the anatomic distribution of heterotopic lesions, and the developmental patterns of disease progression differ among the three conditions. The phenotypic distinction of these disorders is critically important in counselling patients and families as well as in advancing research to define the molecular pathophysiology of heterotopic osteogenesis in these disabling genetic disorders. Genetic disorders of tissue modeling and morphogenesis provide an important parallax to disturbances of tissue re-modeling that are of paramount importance to gravitational and space biologists as humans begin to explore and live in environments beyond the planet on which they evolved. Disorders of osteogenesis are of particular concern to space biologists due to the dramatic changes in skeletal biology in altered gravitational fields.

1998

Calcif Tissue Int 1998 Sep;63(3):221-9
The human bone morphogenetic protein 4 (BMP-4) gene: molecular structure and transcriptional regulation. Shore EM, Xu M, Shah PB, Janoff HB, Hahn GV, Deardorff MA, Sovinsky L, Spinner NB, Zasloff MA, Wozney JM, Kaplan FS

Bone morphogenetic protein 4 (BMP-4) is a vital regulatory molecule that functions throughout human development in mesoderm induction, tooth development, limb formation, bone induction, and fracture repair and is overexpressed in patients who have fibrodysplasia ossificans progressiva. The human gene encoding bone morphogenetic protein 4 (BMP-4) has been isolated and its structural organization characterized. The complete DNA sequence of an 11.2 kb region has been determined. BMP-4 mRNA is transcribed from four exons, although there is evidence that alternate first exons may be used. Transcript initiation occurs at variable positions within a GA-rich region of the DNA. The promoter region is GC-rich with no obvious TATA or CAAT consensus sequences, and contains both positive and negative transcriptional regulatory elements within the 3 kb 5' flanking region of the RNA start site. Comparison of the human and murine BMP-4 genes reveals highly conserved sequences not only in the exon-coding regions but also within the introns and 5' flanking regions. BMP-4 localizes to human chromosome 14q21 by fluorescence in situ hybridization, a location more centromeric than that recently reported. These studies provide a foundation for understanding the genetic regulation of this important gene in human development.