Transcriptomic Signature and Pro-Osteoclastic Secreted Factors of Abnormal Bone-Marrow Stromal Cells in Fibrous Dysplasia

Fibrous dysplasia (FD) is a mosaic skeletal disorder caused by somatic activating variants of GNAS encoding for Gαs and leading to excessive cyclic adenosine monophosphate signaling in bone-marrow stromal cells (BMSCs). The effect of Gαs activation in the BMSC transcriptome and how it influences FD lesion microenvironment are unclear. We analyzed changes induced by Gαs activation in the BMSC transcriptome and secretome. RNAseq analysis of differential gene expression of cultured BMSCs from patients with FD and healthy volunteers, and from an inducible mouse model of FD, was performed, and the transcriptomic profiles of both models were combined to build a robust FD BMSC genetic signature. Pathways related to Gαs activation, cytokine signaling, and extracellular matrix deposition were identified. To assess the modulation of several key secreted factors in FD pathogenesis, cytokines and other factors were measured in culture media. Cytokines were also screened in a collection of plasma samples from patients with FD, and positive correlations of several cytokines to their disease burden score, as well as to one another and bone turnover markers, were found. These data support the pro-inflammatory, pro-osteoclastic behavior of FD BMSCs and point to several cytokines and other secreted factors as possible therapeutic targets and/or circulating biomarkers for FD.

Patient-Derived Organoids Recapitulate Pathological Intrinsic and Phenotypic Features of Fibrous Dysplasia

Fibrous dysplasia (FD) is a rare bone disorder characterized by the replacement of normal bone with benign fibro-osseous tissue. Developments in our understanding of the pathophysiology and treatment options are impeded by the lack of suitable research models. In this study, we developed an in vitro organotypic model capable of recapitulating key intrinsic and phenotypic properties of FD. Initially, transcriptomic profiling of individual cells isolated from patient lesional tissues unveiled intralesional molecular and cellular heterogeneity. Leveraging these insights, we established patient-derived organoids (PDOs) using primary cells obtained from patient FD lesions. Evaluation of PDOs demonstrated preservation of fibrosis-associated constituent cell types and transcriptional signatures observed in FD lesions. Additionally, PDOs retained distinct constellations of genomic and metabolic alterations characteristic of FD. Histological evaluation further corroborated the fidelity of PDOs in recapitulating important phenotypic features of FD that underscore their pathophysiological relevance. Our findings represent meaningful progress in the field, as they open up the possibility for in vitro modeling of rare bone lesions in a three-dimensional context and may signify the first step towards creating a personalized platform for research and therapeutic studies.

A pathogenic role for brain-derived neurotrophic factor (BDNF) in fibrous dysplasia of bone

Brain derived neurotrophic factor (BDNF) is a neurotrophin, expressed in the central nervous system and in peripheral tissues, that is regulated by the Gsα/cAMP pathway. In bone, it regulates osteogenesis and stimulates RANKL secretion and osteoclast formation in osteolytic tumors such as Multiple Myeloma. Fibrous dysplasia (FD) of bone is a rare genetic disease of the skeleton caused by gain-of-function mutations of the Gsα gene in which RANKL-dependent enhanced bone resorption is a major cause of bone fragility and clinical morbidity. We observed that BDNF transcripts are expressed in human FD lesions. Specifically, immunolocalization studies performed on biopsies obtained from FD patients revealed the expression of BDNF in osteoblasts and, to a lower extent, in the spindle-shaped cells within the fibrous tissue. Therefore, we hypothesized that BDNF can play a role in the pathogenesis of FD by stimulating RANKL secretion and bone resorption. To test this hypothesis, we used the EF1α-GsαR201C mouse model of the human disease (FD mice). Western blot analysis revealed a higher expression of BDNF in bone segments of FD mice compared to WT mice and the immunolabeling pattern within mouse FD lesions was similar to that observed in human FD. Treatment of FD mice with a monoclonal antibody against BDNF reduced the fibrous tissue along with the number of osteoclasts and osteoblasts within femoral lesions. These results reveal BDNF as a new player in the pathogenesis of FD and a potential molecular mechanism by which osteoclastogenesis may be nourished within FD bone lesions. They also suggest that BDNF inhibition may be a new approach to reduce abnormal bone remodeling in FD.

Fibrous dysplasia in children and its management

PURPOSE OF REVIEW

The purpose of this review is to provide a comprehensive overview into the diagnosis and management of fibrous dysplasia (FD) in children.

RECENT FINDINGS

FD is a mosaic disorder arising from somatic Gα s variants, leading to impaired osteogenic cell differentiation. Fibro-osseous lesions expand during childhood and reach final disease burden in early adulthood. The mainstay of treatment focuses on surgical correction of skeletal deformities, physiatric care, and medical management of associated hyperfunctioning endocrinopathies. Bisphosphonates may be helpful to treat bone pain, but do not alter lesion quality or progression. Emerging evidence suggests that the RANKL inhibitor denosumab may be effective in improving lesion activity and mineralization, however further studies are needed to determine the potential utility of this and other novel therapies, particularly in children with FD.

SUMMARY

Management of children with FD has unique challenges related to skeletal growth and age-related lesion progression. Inclusion of children in clinical research is critical to develop effective treatment strategies to treat FD lesions and prevent their development.

Fibrous dysplasia animal models: A systematic review

BACKGROUND

Fibrous dysplasia (FD) is a rare genetic bone disorder resulting in an overproduction of cAMP leading to a structurally unsound tissue, caused by a genetic mutation in the guanine nucleotide-binding protein gene (GNAS). In order to better understand this disease, several animal models have been developed with different strategies and features.

OBJECTIVE

Conduct a systematic review to analyze and compare animal models with the causative mutation and features of FD.

METHODS

A PRISMA search was conducted in Scopus, PubMed, and Web of Science. Studies reporting an in vivo model of FD that expressed the causative mutation were included for analysis. Models without the causative mutation, but developed an FD phenotype and models of FD cell implantation were included for subanalysis.

RESULTS

Seven unique models were identified. The models were assessed and compared for their face validity, construct validity, mosaicism, and induction methods. This was based on the features of clinical FD that were reported within the categories of: macroscopic features, imaging, histology and histomorphometry, histochemical and cellular markers, and blood/urine markers.

LIMITATIONS

None of the models reported all features of FD and some features were only reported in one model. This made comparing models a challenge, but indicates areas where further research is necessary.

CONCLUSION

The benefits and disadvantages of every model were assessed from a practical and scientific standpoint. While all published reports lacked complete data, the models have nonetheless informed our understanding of FD and provided meaningful information to guide researchers in bench and clinical research.

Genotype-Phenotype Correlation in Fibrous Dysplasia/McCune-Albright Syndrome

CONTEXT

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare bone and endocrine disorder resulting in fractures, pain, and disability. There are no targeted or effective therapies to alter the disease course. Disease arises from somatic gain-of-function variants at the R201 codon in GNAS, replacing arginine by either cysteine or histidine. The relative pathogenicity of these variants is not fully understood.

OBJECTIVE

This work aimed 1) to determine whether the most common GNAS variants (R201C and R201H) are associated with a specific clinical phenotype, and 2) to determine the prevalence of the most common GNAS variants in a large patient cohort.

METHODS

This retrospective cross-sectional analysis measured the correlation between genotype and phenotype characterized by clinical, biochemical, and radiographic data.

RESULTS

Sixty-one individuals were genotyped using DNA extracted from tissue or circulating cell-free DNA. Twenty-two patients (36.1%) had the R201C variant, and 39 (63.9%) had the R201H variant. FD skeletal disease burden, hypophosphatemia prevalence, fracture incidence, and ambulation status were similar between the 2 groups. There was no difference in the prevalence of endocrinopathies, ultrasonographic gonadal or thyroid abnormalities, or pancreatic involvement. There was a nonsignificant association of cancer with the R201H variant.

CONCLUSION

There is no clear genotype-phenotype correlation in patients with the most common FD/MAS pathogenic variants. The predominance of the R201H variant observed in our cohort and reported in the literature indicates it is likely responsible for a larger burden of disease in the overall population of patients with FD/MAS, which may have important implications for the future development of targeted therapies.

Osteosarcoma of the Mandible in a Patient with Florid Cemento-Osseous Dysplasia and Li-Fraumeni Syndrome: A Rare Coincidence

Cemento-osseous dysplasia (COD) is the most common benign fibro-osseous lesion of the jaws and generally considered non-neoplastic and self-limited. Here, we present a 30-year old female who noticed a bilateral swelling of her posterior mandible with irregular periapical mineralization and incomplete root resorption on panoramic radiographs. A biopsy revealed florid COD and no further treatment was initiated. 9 years later, she presented with a progressive expansion of her left posterior mandible after being treated for bilateral breast cancer 4 and 8 years before. CT scans showed expansile and densely mineralized lesions in all four quadrants with the left posterior mandible showing a focal penetration of the buccal cortical bone. Biopsies revealed an osteoblastic high-grade osteosarcoma in the left and a COD in the right mandible, notably with cellular atypia in the spindle cell component. The patient underwent segmental resection of the left mandible with clear margins and adjuvant chemotherapy. Subsequent genetic testing identified a heterozygous germline TP53 mutation (p.V173G) which confirmed the clinically suspected Li-Fraumeni syndrome (LFS). 3 years after the resection, the patient is free of disease and the other foci of COD remained stable in size on follow-up imaging analyses. Our case illustrates LFS-related osteosarcoma developing within florid COD. Given the rarity of this coincidence, a causative relation between the two lesions seems unlikely but in patients with tumor predisposition syndromes it might be advisable to closely monitor even benign lesions like COD.

Changes in gene expression in human skeletal stem cells transduced with constitutively active Gsα correlates with hallmark histopathological changes seen in fibrous dysplastic bone

Fibrous dysplasia (FD) of bone is a complex disease of the skeleton caused by dominant activating mutations of the GNAS locus encoding for the α subunit of the G protein-coupled receptor complex (Gsα). The mutation involves a substitution of arginine at position 201 by histidine or cysteine (Gsα^{R201H or R201C}), which leads to overproduction of cAMP. Several signaling pathways are implicated downstream of excess cAMP in the manifestation of disease. However, the pathogenesis of FD remains largely unknown. The overall FD phenotype can be attributed to alterations of skeletal stem/progenitor cells which normally develop into osteogenic or adipogenic cells (in cis), and are also known to provide support to angiogenesis, hematopoiesis, and osteoclastogenesis (in trans). In order to dissect the molecular pathways rooted in skeletal stem/progenitor cells by FD mutations, we engineered human skeletal stem/progenitor cells with the Gsα^R201C mutation and performed transcriptomic analysis. Our data suggest that this FD mutation profoundly alters the properties of skeletal stem/progenitor cells by pushing them towards formation of disorganized bone with a concomitant alteration of adipogenic differentiation. In addition, the mutation creates an altered in trans environment that induces neovascularization, cytokine/chemokine changes and osteoclastogenesis. In silico comparison of our data with the signature of FD craniofacial samples highlighted common traits, such as the upregulation of ADAM (A Disintegrin and Metalloprotease) proteins and other matrix-related factors, and of PDE7B (Phosphodiesterase 7B), which can be considered as a buffering process, activated to compensate for excess cAMP. We also observed high levels of CEBPs (CCAAT-Enhancer Binding Proteins) in both data sets, factors related to browning of white fat. This is the first analysis of the reaction of human skeletal stem/progenitor cells to the introduction of the FD mutation and we believe it provides a useful background for further studies on the molecular basis of the disease and for the identification of novel potential therapeutic targets.

Unusual Presentation of Fibrous Dysplasia in an Elderly Patient

Fibrous Dysplasia is a benign fibro-osseous lesion occurring throughout the skeletal system with a predilection for craniofacial bones, long bones, and ribs. Fibrous dysplasia develops during bone formation and growth with a variable natural evolution. It is considered a genetic nonheritable disease resulting from missense mutations that occur postzygotically in the GNAS1 gene. This mutation leads to a focal congenital failure of proper bone formation and arrest at the woven bone stage. In turn, this leads to a decreased mechanical strength, causing bone pain, pathological fractures, and skeletal deformities. Besides clinical examination, fibrous dysplasia is diagnosed based on the results of radiographic imaging and the microscopic histopathological findings. On CT scan, fibrous dysplasia shows the characteristic "Ground-glass" appearance with well-defined borders. On MRI, fibrous dysplasia has a low signal intensity on T1-weighted MRI and variable signal intensity on T2-weighted MRI. We hereby report a case of an unusual presentation of fibrous dysplasia in a 67-year-old female presenting to the emergency department with generalized malaise and lower limb pain. Fibrous dysplasia may present in the elderly population and can be difficult to differentiate from other malignant and benign lesions affecting the skeletal system.

Fibrous Dysplasia/McCune-Albright Syndrome: Clinical and Translational Perspectives

Fibrous dysplasia (FD) is an uncommon and debilitating skeletal disorder resulting in fractures, deformity, functional impairment, and pain. It arises from post-zygotic somatic activating mutations in GNAS, in the cAMP-regulating transcript α-subunit, Gsα. Constitutive Gs signaling results in activation of adenylyl cyclase and dysregulated cAMP production. In the skeleton, this leads to the development of FD lesions with abnormal bone matrix, trabeculae, and collagen, produced by undifferentiated mesenchymal cells. FD may occur in isolation or in combination with extraskeletal manifestations, including hyperfunctioning endocrinopathies and café-au-lait macules, termed McCune-Albright syndrome (MAS). This review summarizes current clinical and translational perspectives in FD/MAS, with an emphasis on FD pathogenesis, natural history, pre-clinical and clinical investigation, and future directions.

Receptor-Activator of Nuclear KappaB Ligand Expression as a New Therapeutic Target in Primary Bone Tumors

The receptor-activator of nuclear kappaB ligand (RANKL) signaling pathway plays an important role in the regulation of bone growth and mediates the formation and activation of osteoclasts. Osteoclasts are involved in significant bone resorption and destruction. Denosumab is a fully human monoclonal antibody against RANKL that specifically inhibits osteoclast differentiation and bone resorption. It has been approved for use for multiple myeloma and bone metastases, as well as for giant cell tumor of bone. However, there is no previous report quantitatively, comparing RANKL expression in histologically varied bone tumors. Therefore, we analyzed the mRNA level of various bone tumors and investigated the possibility of these tumors as a new therapeutic target for denosumab. We examined RANKL mRNA expression in 135 clinical specimens of primary and metastatic bone tumors using real-time PCR. The relative quantification of mRNA expression levels was performed via normalization with RPMI8226, a human multiple myeloma cell line that is recognized to express RANKL. Of 135 cases, 64 were also evaluated for RANKL expression by using immunohistochemistry. Among all of the tumors investigated, RANKL expression and the RANKL/osteoprotegerin ratio were highest in giant cell tumor of bone. High RANKL mRNA expression was observed in cases of aneurysmal bone cyst, fibrous dysplasia, osteosarcoma, chondrosarcoma, and enchondroma, as compared to cases of multiple myeloma and bone lesions from metastatic carcinoma. RANKL-positive stromal cells were detected in six cases: five cases of GCTB and one case of fibrous dysplasia. The current study findings indicate that some primary bone tumors present new therapeutic targets for denosumab, particularly those tumors expressing RANKL and those involving bone resorption by osteoclasts.

Proceedings of the American Association of Oral and Maxillofacial Surgeons 2015 Research Summit

The Fifth Biennial Research Summit of the American Association of Oral and Maxillofacial Surgeons and its Committee on Research Planning and Technology Assessment was held in Rosemont, Illinois on May 6 and 7, 2015. The goal of the symposium is to provide a forum for the most recent clinical and scientific advances to be brought to the specialty. The proceedings of the events of that summit are presented in this report.

GNAS Spectrum of Disorders

The GNAS complex locus encodes the alpha-subunit of the stimulatory G protein (Gsα), a ubiquitous signaling protein mediating the actions of many hormones, neurotransmitters, and paracrine/autocrine factors via generation of the second messenger cAMP. GNAS gives rise to other gene products, most of which exhibit exclusively monoallelic expression. In contrast, Gsα is expressed biallelically in most tissues; however, paternal Gsα expression is silenced in a small number of tissues through as-yet-poorly understood mechanisms that involve differential methylation within GNAS. Gsα-coding GNAS mutations that lead to diminished Gsα expression and/or function result in Albright's hereditary osteodystrophy (AHO) with or without hormone resistance, i.e., pseudohypoparathyroidism type-Ia/Ic and pseudo-pseudohypoparathyroidism, respectively. Microdeletions that alter GNAS methylation and, thereby, diminish Gsα expression in tissues in which the paternal Gsα allele is normally silenced also cause hormone resistance, which occurs typically in the absence of AHO, a disorder termed pseudohypoparathyroidism type-Ib. Mutations of GNAS that cause constitutive Gsα signaling are found in patients with McCune-Albright syndrome, fibrous dysplasia of bone, and different endocrine and non-endocrine tumors. Clinical features of these diseases depend significantly on the parental allelic origin of the GNAS mutation, reflecting the tissue-specific paternal Gsα silencing. In this article, we review the pathogenesis and the phenotypes of these human diseases.

La dysplasie fibreuse: état des lieux

La dysplasie fibreuse des os est une affection osseuse bénigne congénitale mais non héréditaire, où l'os normal est remplacé par un tissu fibreux renfermant une ostéogenèse immature. Elle est due à une mutation du gène GNAS 1sur le chromosome 20q13, une mutation activatrice de la sous-unité α de la protéine G. C'est une pathologie qui est le plus souvent silencieuse, de découverte fortuite sur une radiographie standard ou révélée par une douleur osseuse ou une fracture pathologique. L'imagerie et l'histologie, quand elle est nécessaire, permettent d’établir le diagnostic. Bien qu'il ne s'agisse pas d'une tumeur, elle est souvent classée dans la catégorie des tumeurs osseuses bénignes pour des raisons de diagnostic différentiel radiographique et anatomopathologique. Elle peut être monostotique ou polyostotique. L'approche thérapeutique est essentiellement symptomatique. Quelques publications récentes ont suggéré l'intérêt majeur d'un bisphosphonate, en particulier le pamidronate, qui diminuerait les douleurs et stimulerait une reminéralisation progressive des zones ostéolytiques chez les patients traités. D'autres traitements tels que la thérapie ciblée sont en cours d’évaluation.

Fibrous dysplasia and fibroblast growth factor-23 regulation

Fibrous dysplasia (FD) is a skeletal disorder caused by activating mutations in Gsα that result in elevations in cAMP. A feature of FD is elevated blood levels of the bone cell-derived phosphaturic hormone, fibroblast growth factor-23 (FGF23). FGF23 regulates serum phosphorus and active vitamin D levels by action on proximal renal tubule cells. An essential step in the production of biologically active FGF23 is glycosylation by the UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyl transferase (ppGalNAc-T3). In the absence of glycosylation, FGF23 is processed into inactive N- and C-terminal proteins by a subtilisin proprotein convertase, probably furin. Normally, most if not all circulating FGF23 is intact. In FD, C-terminal levels are elevated, suggesting altered FGF23 processing. Altered processing in FD is the result of a cAMP-dependent, coordinated decrease in ppGalNAc-T3 and an increase in furin enzyme activity. These findings, and emerging data from other diseases, suggest regulation of FGF23 processing may be a physiologically important process.

Potent constitutive cyclic AMP-generating activity of XLαs implicates this imprinted GNAS product in the pathogenesis of McCune-Albright syndrome and fibrous dysplasia of bone

Patients with McCune-Albright syndrome (MAS), characterized primarily by hyperpigmented skin lesions, precocious puberty, and fibrous dyslasia of bone, carry postzygotic heterozygous mutations of GNAS causing constitutive cAMP signaling. GNAS encodes the α-subunit of the stimulatory G protein (Gsα), as well as a large variant (XLαs) derived from the paternal allele. The mutations causing MAS affect both GNAS products, but whether XLαs, like Gsα, can be involved in the pathogenesis remains unknown. Here, we investigated biopsy samples from four previously reported and eight new patients with MAS. Activating mutations of GNAS (Arg201 with respect to the amino acid sequence of Gsα) were present in all the previously reported and five of the new cases. The mutation was detected within the paternally expressed XLαs transcript in five and the maternally expressed NESP55 transcript in four cases. Tissues carrying paternal mutations appeared to have higher XLαs mRNA levels than maternal mutations. The human XLαs mutant analogous to Gsα-R201H (XLαs-R543H) showed markedly higher basal cAMP accumulation than wild-type XLαs in transfected cells. Wild-type XLαs demonstrated higher basal and isoproterenol-induced cAMP signaling than Gsα and co-purified with Gβ1γ2 in transduced cells. XLαs mRNA was measurable in mouse calvarial cells, with its level being significantly higher in undifferentiated cells than those expressing preosteoblastic markers osterix and alkaline phosphatase. XLαs mRNA was also expressed in murine bone marrow stromal cells and preosteoblastic MC3T3-E1 cells. Our findings are consistent with the possibility that constitutive XLαs activity adds to the molecular pathogenesis of MAS and fibrous dysplasia of bone.

Skeletal progenitors and the GNAS gene: fibrous dysplasia of bone read through stem cells

Activating mutations of the GNAS gene, which causes fibrous dysplasia of bone (FD), lead to remarkable changes in the properties of skeletal progenitors, and it is these changes that mediate the pathological effect of this gene on bone. Mutated skeletal stem cells lose the ability to differentiate into adipocytes, and to maintain in situ, and transfer heterotopically, the hematopoietic microenvironment, leading to abnormal bone marrow histology in FD. They overexpress molecular effectors of osteoclastogenesis, thus promoting inappropriate bone resorption leading to fragility of FD bone. They express the phosphate-regulating hormone FGF-23 at normal levels, whose excess in the serum of FD patients correlates with the mass of osteogenic cells within FD lesions, leading to osteomalacia and deformity of the FD bone, and revealing that bone is an endocrine organ regulating renal handling of phosphate. Mechanisms of allelic selection and stem cell selection occur in mutated skeletal stem cells and contribute to the inherent diversity and evolution over time in FD. The definition of the etiological role of GNAS mutations marks the watershed between many decades of descriptive observation and the definition of cellular and molecular mechanisms that would explain and hopefully allow for a cure for the disease. Placing stem cells at center stage has permitted substantial advances in one decade, and promises more for the one to come.

[Abnormal expression of c-myc, p53, p16 protein and GNAS1 gene mutation in fibrous dysplasia]

OBJECTIVE

To study the significance of c-myc, p53 and p16 protein expression in fibrous dysplasia, to detect the GNAS1 gene mutation in fibrous dysplasia, and to explore the property of fibrous dysplasia.

METHODS

The expression of c-myc, p53 and p16 protein was evaluated by immunohistochemistry SP method in 35 cases of fibrous dysplasia including 1 FD with malignancy, 1 Mazabraud syndrome and 20 control cases (10 cases of bony callus, 10 cases of osteosarcoma). Genomic DNA extraction, PCR amplification and gene sequencing were used to detect GNAS1 gene mutation in 35 cases of fibrous dysplasia.

RESULTS

C-myc protein immunoreactivity was detected in 91 percentage of FD (P = 0.001). Compared with the negative control group, the difference was significant. P16 positive was detected in 34 FD cases (P = 0.001). The difference was significant as compared with the positive control group. Positive p53 protein expression was detected in the only 1 case of fibrous dysplasia with malignant transformation. PCR amplification was successful in 12 of 35 FD cases. Two of the 12 FD cases were detected to have GNAS1 gene mutation, in which 1 case was FD of Mazabraud syndrome, 1 case was a monostotic lesion.

CONCLUSIONS

C-myc could be another protooncogene in addition to c-fos in the fibrous dysplasia disease. P53 protein overexpression could be useful in the diagnosis of FD malignancy and in the prediction of the prognosis of FD. The abnormal expression of the gene p16 might play an important role in the formation of FD. The GNAS1 mutation exist in FD. All of the results indicate that FD could be a neoplasia disease, caused by multiple factors leading to a dysfunction of bone development.

[Fibrous dysplasia of bone in a young male]

Fibrous dysplasia of bone is a skeletal disease due to a specific mutation in the GNAS1 gene with a broad spectrum of clinical presentations ranging from isolated monostotic and polyostotic forms to associations with other extra-skeletal manifestations (McCune-Albright syndrome). The main complications are bone pain, deformities and fractures and sometimes cranial nerve compression and the development of bone sarcomas. Traumatologic surgery represents the principal approach in complicated lesions. Currently, the efficacy of pharmacological therapies is fairly limited. Cyclic administration of intravenous biphosphonates is the most effective approach to achieve symptomatic improvement and to lower the risk of fractures, although more evidence from well-designed randomized clinical trials evaluating the safety and efficacy of these treatments is still required. We present a case of polyostotic fibrous dysplasia of bone in a 19-year-old male.

Benign fibro-osseous lesions of the craniofacial complex. A review

Benign fibro-osseous lesions of the craniofacial complex are represented by a variety of disease processes that are characterized by pathologic ossifications and calcifications in association with a hypercellular fibroblastic marrow element. The current classification includes neoplasms, developmental dysplastic lesions and inflammatory/reactive processes. The definitive diagnosis can rarely be rendered on the basis of histopathologic features alone; rather, procurement of a final diagnosis is usually dependent upon assessment of microscopic, clinical and imaging features together. Fibrous dysplasia and osteitis deformans constitute two dysplastic lesions in which mutations have been uncovered. Other dysplastic bone diseases of the craniofacial complex include florid osseous dysplasia, focal cemento-osseous dysplasia and periapical cemental dysplasia, all showing a predilection for African descent individuals; although no specific genetic alterations in DNA coding have yet to be uncovered and most studies have been derived from predominant high African descent populations. Ossifying fibromas are neoplastic lesions with four subtypes varying with regard to behavior and propensity for recurrence after surgical excision. The clinicopathologic and molecular features of this unique yet heterogeneous group of diseases are reviewed.

[Fibrous dysplasia of bone]

Fibrous dysplasia of bone is a congenital non hereditary benign bone disease, where normal bone is replaced by a fibrous-like tissue with immature osteogenesis. Prevalence is difficult to estimate, due to frequent asymptomatic lesions. Bone lesions are mono- or polyostotic and may be associated with bone pain and fragility, leading to fractures. In some patients or bone sites, they are hypertrophic, responsible for neurological complications. Imaging and, when necessary, histology are the cornerstones of the diagnosis. A common molecular defect, i.e. activating mutations of the GNAS gene, encoding the a subunit of the Gs protein in target cells, is responsible for bone cell alterations as well as for the involvement of other cells/tissues bearing the same molecular defect (melanocytes, endocrine cells). These mutations affect only somatic cells and are therefore not hereditary: antenatal diagnosis is not appropriate for this disease and genetic counselling is not very useful, except for reassuring the patients. The conventional therapeutic approach is essentially symptomatic (pain killers) and orthopaedic (prevention and treatment of bone complications). Recent publications have focused attention on pamidronate, which rapidly relieves bone pain in most patients, and progressively increases bone mineralization in osteolytic areas in about half of the patients. Tubular phosphate wasting is common and should be treated with phosphate supplement and calcitriol. The prognosis should improve with therapeutic advances, but this remains to be properly evaluated.

[Fibrous dysplasia: molecular clonality analysis of 21 cases]

OBJECTIVE

To investigate the neoplastic nature of fibrous dysplasia by molecular clonality approaches.

METHODS

Twenty-one cases of fibrous dysplasia were examined by clonality assays based on X-chromosomal inactivation mosiacism. Lesional and non-lesional tissues were microdissected from paraffin sections followed by DNA extraction. The DNA was predigested by HpaII or HhaI, and then amplified by nested PCR targeting phosphoglycerate kinase (PGK) and androgen receptor (AR) genes. Single nucleotide polymorphism (SNP) at the PGK locus was identified by incubation of the PCR products with Bst XI and agarose gel electrophoresis, and CAG repeat length polymorphism at AR locus was determined by denaturing polyacrylamide gel electrophoresis and visualized by silver staining.

RESULTS

Microscopically, all 21 cases showed characteristic features of fibrous dysplasia, including spindle fibrous cell proliferation and immature bone trabeculae at various proportions. DNA polymorphisms at AR locus and SNP of PGK gene were found in 15 of 21, and 4 of 21 cases, respectively. All 19 cases were monoclonal in nature. Two cases showed no polymorphism at either AR or PGK gene locus.

CONCLUSIONS

Fibrous dysplasia is likely a clonal, neoplastic process. Additional studies of larger number of cases are needed for a definitive conclusion.

GNAS mutation detection is related to disease severity in girls with McCune-Albright syndrome and precocious puberty

BACKGROUND

McCune-Albright syndrome (MAS) is characterized by a triad of gonadotropin-independent precocious puberty, café au lait skin pigmentation and fibrous dysplasia of bone. MAS is due to activating mutations of GNAS, the gene encoding Gsalpha. Interest exists in the use of GNAS mutation analysis to make a definitive diagnosis when the phenotype is not diagnostic, i.e. in partial forms of MAS. The utility of using peripheral blood for mutation analysis in this setting has not been thoroughly evaluated.

OBJECTIVE

We performed a systematic analysis of genomic DNA for the detection of GNAS activating mutations in girls with MAS who presented with precocious puberty to evaluate whether identification of an activating mutation in peripheral blood is related to the presence of other features of MAS.

STUDY DESIGN

Genomic DNA was isolated from blood from 13 girls with gonadotropin-independent precocious puberty. A polymerase chain reaction (PCR)-based technique was performed for GNAS mutation identification.

RESULTS

GNAS activating mutations were identified in 4 patients, all of whom had classic MAS based on clinical evidence.

CONCLUSIONS

Detection of activating mutations in leukocyte genomic DNA extracted from peripheral blood samples from girls with gonadotropin-independent precocious puberty was associated with the presence of other phenotypic manifestations of MAS. Until improvements in the diagnostic utility of GNAS activating mutation analysis from leukocyte genomic DNA occur, such testing in patients with atypical forms of MAS should continue to be reserved for research settings.

A sensitive mutation-specific screening technique for GNAS1 mutations in cases of fibrous dysplasia: the first report of a codon 227 mutation in bone

AIMS

To report on the mutation-specific restriction enzyme digest (MSRED) method using paraffin-embedded tissue as a means of detecting GNAS1 mutations in fibrous dysplasia (FD), and to determine if any of the reported GNAS1 mutations in endocrine neoplasms, not previously documented in FD, can be found in FD.

METHODS AND RESULTS

Sixty-seven cases of extragnathic FD were analysed as two groups, 1997-2002 and 2003-06, chosen because tissue fixation and decalcification methods were more accurately recorded in the latter. MSRED revealed that between 2003 and 2006, 93% of 28 'in house' extragnathic cases harboured a GNAS1 mutation, compared with 75% of 32 cases before 2003. Fixation times of no more than 48 h and decalcification in ethylenediamine tetraacetic acid gave the best results. Of the 56 mutations detected (five gnathic, 51 extragnathic), 32 (57%) were R201H, 21 (38%) were R201C and three (5%) were Q227L. Two Q227L extragnathic cases had unusual clinical/radiological findings. No mutations were detected in osteofibrous dysplasia.

CONCLUSION

Detection of GNAS1 mutations by MSRED is a valuable adjunct to the histopathological diagnosis of FD. This is the first report of a Q227L mutation in FD, although it has been previously documented in pituitary adenoma.

GNAS transcripts in skeletal progenitors: evidence for random asymmetric allelic expression of Gs alpha

Activating mutations of the Gsalpha gene, encoded by the guanine nucleotide-binding protein, alpha stimulating (GNAS) locus located on chromosome 20q13, underlie different clinical phenotypes characterized by skeletal lesions [fibrous dysplasia (FD) of bone], extraskeletal diseases (mainly endocrine hyperfunction and skin hyperpigmentation) and variable combinations thereof [the McCune-Albright syndrome (MAS)]. This clinical heterogeneity is commonly assumed to reflect the post-zygotic origin of the mutation. However, the pattern of imprinting of the Gsalpha gene in some human post-natal tissues suggests that parental-dependent epigenetic mechanisms may also play a role in the phenotypic effect of the mutated GNAS genotype. FD lesions are generated by mutated clonogenic osteoprogenitors that reside, along with their normal counterparts, in FD bone marrow stroma. We analyzed the allelic expression pattern of Gsalpha and other GNAS alternative transcripts in the progeny of normal and mutated clonogenic stromal cells isolated in vitro from a series of informative FD/MAS patients. We report here for the first time that the two Gsalpha alleles are unequally expressed in both normal and FD-mutated stromal clones. However, in contrast to imprinting, the ratio of Gsalpha allelic expression is randomly established in different clones from the same patient. This result suggests that a parental-independent modulation of Gsalpha expression occurs in clonogenic osteoprogenitor cells and, at the single cell level, may impact on the severity of an FD lesion. Furthermore, we show that normal and mutated clonogenic stromal cells express GNAS alternative transcripts other than the common Gsalpha, some of which may be relevant to the development of FD.

Kraniofaziale Fibröse Dysplasie: Observieren oder Operieren?

BACKGROUND

The aetiologic correlations of fibrous dysplasia (FD) are more and more decoded by molecular biology, improved imaging procedures, and the use of computer assisted surgery--thus a review of present diagnostics and therapy methods is evaluated.

METHOD

The valid methods of diagnostic and therapy procedures of craniofacial FD were retrospectively analysed in a collective of 9 patients in consideration of literature. The criteria of the decision for diagnosis and surgical procedures were evaluated.

RESULTS

According to the literature, diagnosis was ascertained with modern CT and MRI scans. Bone scintigraphy was only used additionally in particular questions. In case of unclear radiological findings histomorphological procedures were used complementarily to distinguish FD from other bone tumors. The aim of surgical intervention was to reduce pain, to restore the function in compression symptoms, to recover original ostia, or to restore the natural geometry of the face.

CONCLUSIONS

Current imaging procedures allow differential diagnosis from other benign bone tumors but also from malignancies. The therapy of FD is conservative (wait and scan) or operative in dependence on the localisation, the extension and the clinical manifestations of the disease. In the future molecular biological methods could function as supporting instrument for diagnosis if histomorphological results are not meaningful.

Ossifying fibroma vs fibrous dysplasia of the jaw: molecular and immunological characterization

Ossifying fibroma and fibrous dysplasia of the jaw are maxillofacial fibro-osseous lesions that should be distinguished each other by a pathologist because they show distinct patterns of disease progression. However, both lesions often show similar histological and radiological features, making distinction between the two a diagnostic dilemma. In this study, we performed immunological and molecular analyses of five ossifying fibromas, four cases of extragnathic fibrous dysplasia, and five cases of gnathic fibrous dysplasia with typical histological and radiographic features. First, we examined the difference between fibrous dysplasia and ossifying fibroma in the expression of Runx2 (which determined osteogenic differentiation from mesenchymal stem cells) and other osteogenic markers. Fibroblastic cells in fibrous dysplasia and ossifying fibroma showed strong Runx2 expression in the nucleus. The bone matrices of both lesions showed similar expression patterns for all markers tested except for osteocalcin. Immunoreactivity for osteocalcin was strong throughout calcified regions in fibrous dysplasia, but weak in ossifying fibroma lesions. Second, we performed PCR analysis with peptide nucleic acid (PNA) for mutations at the Arg(201) codon of the alpha subunit of the stimulatory G protein gene (GNAS), which has reported to be a marker for extragnathic fibrous dysplasia. All nine cases of extragnathic or gnathic fibrous dysplasia were positive for this mutation. On the other hand, none of the five cases of ossifying fibroma showed the mutation. These findings indicate that although fibrous dysplasia and ossifying fibroma are similar disease entities, especially in the demonstration of the osteogenic lineage in stromal fibroblast-like cells, they show distinct differences that can be revealed by immunohistochemical detection of osteocalcin expression. Furthermore, PCR analysis with PNA for GNAS mutations at the Arg(201) codon is a useful method to differentiate between fibrous dysplasia and ossifying fibroma.

McCune-Albright syndrome with acromegaly and fibrous dysplasia associated with the GNAS gene mutation identified by sensitive PNA-clamping method

A 16-year-old girl presented with McCune-Albright syndrome associated with acromegaly and fibrous dysplasia. Brain MRI demonstrated a pituitary tumor. X-ray films showed bone deformities, and 99TmO4 bone scintigraphy revealed increased uptake of radioactivity in the affected bones. Although the serum FGF23 level was increased, the serum calcium, phosphate, and active vitamin D levels were all within normal limits. GNAS gene mutation was detected at neither codon 201 nor 227 by conventional PCR-based direct sequencing analysis. We performed a selective PCR with peptide nucleic acid (PNA) clamping to increase the sensitivity for gene mutation detection and identified the R201C GNAS mutation.

G(s)alpha mutations in fibrous dysplasia and McCune-Albright syndrome

Fibrous dysplasia (FD) is a focal bone lesion composed of immature mesenchymal osteoblastic precursor cells. Some FD patients also have hyperpigmented skin lesions (café-au-lait spots), gonadotropin-independent sexual precocity, and/or other endocrine and nonendocrine manifestations (McCune-Albright syndrome [MAS]). MAS results from somatic mutations occurring during early development, resulting in a widespread mosaic of normal and mutant-bearing cells, which predicts that the clinical presentation of each patient is determined by the extent and distribution of abnormal cells. These mutations encode constitutively active forms of G(s)alpha, the ubiquitously expressed G protein alpha-subunit that couples hormone receptors to intracellular cAMP generation. These mutations lead to substitution of amino acid residues that are critical for the intrinsic GTPase activity that is normally required to deactivate the G protein. This leads to prolonged activation of G(s)alpha and its downstream effectors even with minimal receptor activation. This explains why MAS patients have stimulation of multiple peripheral endocrine glands in the absence of circulating stimulatory pituitary hormones and increased skin pigment, which is normally induced by melanocyte-stimulating hormone through G(s)alpha/cAMP. Similar mutations are also present in 40% of pituitary tumors in acromegaly patients and less commonly in other endocrine tumors. FD results from increased cAMP in bone marrow stromal cells, leading to increased proliferation and abnormal differentiation. Parental origin of the mutated allele may also affect the clinical presentation, because G(s)alpha is imprinted and expressed only from the maternal allele in some tissues (e.g., pituitary somatotrophs).

Pegvisomant for the treatment of gsp-mediated growth hormone excess in patients with McCune-Albright syndrome

CONTEXT

GH excess affects approximately 20% of the patients with McCune-Albright syndrome (MAS). MAS is caused by sporadic, postzygotic, activating mutations in the GNAS gene, which codes for the cAMP-regulating protein, G(s)alpha (gsp oncogene). These same mutations are found in approximately one third of the sporadic cases of acromegaly.

OBJECTIVE

We examined efficacy of the GH receptor antagonist, pegvisomant, in controlling gsp oncogene-mediated GH excess and skeletal disease (fibrous dysplasia of bone) associated with MAS.

SETTING AND PATIENTS

Five MAS patients with GH excess were treated with 20 mg/d sc injection of pegvisomant for 12 wk in a randomized, double-blind, placebo-controlled crossover study at the National Institutes of Health.

MAIN OUTCOME MEASURES

The primary measure of efficacy was normalization of IGF-I. Secondary outcome measures were reduction in serum IGF binding protein-3 (IGFBP-3), improvement of fatigue and sweating, and reduction in markers of bone metabolism and bone pain.

RESULTS

Combined mean changes in serum IGF-I at 6 and 12 wk were -236.4 ng/ml (53%, P < 0.005) and -329.8 ng/ml (62%, P < 0.001), respectively. IGFBP-3 decreased by 0.8 mg/liter (24%, P < 0.01) and 2.9 mg/liter (37%, P < 0.005), respectively. There were no significant changes in signs and symptoms of acromegaly or markers of bone metabolism and bone pain, nor was there a significant change in pituitary size. Retrospective comparison of the degree of control achieved with pegvisomant vs. other medications (long-acting octreotide +/- dopamine agonist) in the same group showed that the two regimens were similarly effective.

CONCLUSIONS

Pegvisomant effectively reduced IGF-I and IGFBP-3 levels in gsp-mediated GH excess but had no effect on fibrous dysplasia.

Expression of FGF23 is correlated with serum phosphate level in isolated fibrous dysplasia

Fibrous dysplasia (FD) patients sometimes suffer from concomitant hypophosphatemic rickets/osteomalacia, resulting from renal phosphate wasting. It was recently reported that FD tissue in the patients with McCune-Albright syndrome (MAS) expressed fibroblast growth factor-23 (FGF-23), which is now known to be as a pathogenic phosphaturic factor in patients with oncogenic osteomalacia and X-linked hypophosphatemic rickets. Since it remains controversial whether serum phosphate levels are influenced by FGF23 expressions in FD tissue, isolated FD patients without MAS syndrome were examined for the relationship between FGF23 expressions, circulating levels of FGF-23 and phosphate to negate the effects of MAS-associated endocrine abnormalities on serum phosphate. Eighteen paraffin embedded FD tissues and 2 frozen tissues were obtained for the study. Sixteen of 18 isolated FD tissues were successfully analyzed GNAS gene, which exhibited activated mutations observed in MAS. Eight of 16 FD tissues, which exhibited GNAS mutations, revealed positive staining for FGF-23. These evidence indicate that postzygotic activated mutations of GNAS is necessary for the FD tissue formation by mosaic distribution of mutated osteogenic cell lineage, but is not sufficient to elevate FGF23 expression causing generalized osteomalacia with severe renal phosphate wasting. The expression level of FGF23 in isolated FD tissue with hypophosphatemic osteomalacia determined by real-time PCR was abundant close to the levels in OOM tumors. Osteoblasts/osteocytes in woven bone were predominant source of circulating FGF-23 in FD tissues by immunohistochemistry. A negative correlation of the intensity of FGF-23 staining with serum inorganic phosphate levels indicated that the expression of FGF23 in focal FD tissues could be a prominent determinant of serum phosphate levels in isolated FD patient. These data provide novel insights into the regulatory mechanism of serum inorganic phosphate levels in isolated FD patients and extend the notion that FGF-23 originating from FD tissue may cause hypophosphatemia not only in isolated FD patients but also in the patients with MAS syndrome.

Activating Gs a mutation rarely occurs in musculoskeletal tumors other than fibrous dysplasia

BACKGROUND

Activating Gs a mutations have been identified in most instances of fibrous dysplasia (FD). This mutation leads to consistently elevated intracellular cyclic adenosine monophosphate (cAMP) levels, with various biological consequences. The development of secondary sarcoma in FD is a rare but well-established phenomenon. This finding raised the possibility that a common gene mutation exists in these tumors.

MATERIALS AND METHODS

The expression of the Gs a mutation was examined in 16 cell lines and 173 musculoskeletal tumor tissues, including 13 cases of FD, via RT-PCR and sequence analysis.

RESULTS

No expression of a Gs a mutation was detected in any cell line or clinical tissue sample, excluding FD tissues. Direct sequence analysis demonstrated results identical to those of RT-PCR.

CONCLUSION

Activating Gs a mutation rarely occurs in musculoskeletal tumors other than FD. The occurrence of most sarcomas displays no correlation with Gs a mutations.

Fibroblast growth factor 23 and its receptors

Fibroblast growth factor 23 (FGF23) is a circulating factor that plays critical roles in phosphate and vitamin D metabolism, as evidenced by the fact that FGF23 missense mutations cause autosomal dominant hypophosphatemic rickets (ADHR). Autosomal dominant hypophosphatemic rickets is characterized by hypophosphatemia with inappropriately normal 1,25-dihydroxyvitamin D concentrations, as well as bone pain, fracture and rickets. This phenotype parallels that of patients with tumor induced osteomalacia (TIO), X-linked hypophosphatemic rickets (XLH), and fibrous dysplasia (FD), in whom elevated serum FGF23 levels are often observed. The fibroblast growth factor receptors (FGFR1-4) play key roles in skeletal development, as well as in normal metabolic processes. Several FGFR isoforms that potentially mediate the activity of FGF23 have been implicated. In the short term, these findings will lead to further understanding of FGF23 function, and potentially in the long term, to targeted therapies in disorders of hypo- and hyperphosphatemia that involve FGF23.

Juvenile psammomatoid ossifying fibroma of the neurocranium. Report of four cases

Juvenile psammomatoid ossifying fibroma (JPOF) is a benign fibroosseous lesion predominantly arising within the paranasal sinuses in children and young adults. Neurocranial occurrence is exceedingly rare and a location within the neurocranial portion of the temporal bone has not been described. The authors report on one case of sinonasal JPOF secondarily extending into the cranial cavity and three cases primarily affecting the neurocranial bones to increase clinical awareness of this uncommon tumor, which may be easily mistaken for meningioma. Moreover, the absence of activating missense mutations of the GNAS1 gene in two cases strongly argues against a relationship between JPOF and fibrous dysplasia.

FGF23 and disorders of phosphate homeostasis

It is well known that fibroblast growth factor (FGF) family members are associated with embryonic development and are critical for basic metabolic functions. This review will focus upon fibroblast growth factor-23 (FGF23) and its roles in disorders associated with phosphate handling. The discovery that mutations in FGF23 were responsible for the isolated renal phosphate wasting disorder autosomal dominant hypophosphatemic rickets (ADHR) has ascribed novel functions to the FGF family. FGF23 circulates in the bloodstream, and animal models demonstrate that FGF23 controls phosphate and Vitamin D homeostasis through the regulation of specific renal proteins. The ADHR mutations in FGF23 produce a protein species less susceptible to proteolytic processing. X-linked hypophosphatemic rickets (XLH), tumor-induced osteomalacia (TIO), and fibrous dysplasia of bone (FD) are disorders involving phosphate homeostasis that share phenotypes with ADHR, indicating that FGF23 may be a common denominator for the pathophysiology of these syndromes. Our understanding of FGF23 will help to develop novel therapies for phosphate wasting disorders, as well as for disorders of increased serum phosphate, such as tumoral calcinosis, a rare disorder, and renal failure, a common disorder.

A novel technique based on a PNA hybridization probe and FRET principle for quantification of mutant genotype in fibrous dysplasia/McCune-Albright syndrome

Somatic mutations are present in various proportions in numerous developmental pathologies. Somatic activating missense mutations of the GNAS gene encoding the Gs(alpha) protein have previously been shown to be the cause of fibrous dysplasia of bone (FD)/McCune-Albright syndrome (MAS). Because in MAS patients, tissues as diverse as melanocytes, gonads and bone are affected, it is generally accepted that the GNAS mutation in this disease must have occurred early in development. Interestingly, it has been shown that the development of an active FD lesion may require both normal and mutant cells. Studies of the somatic mosaic states of FD/MAS and many other somatic diseases need an accurate method to determine the ratio of mutant to normal cells in a given tissue. A new method for quantification of the mutant:normal ratio of cells using a PNA hybridization probe-based FRET technique was developed. This novel technique, with a linear sensitivity of 2.5% mutant alleles, was used to detect the percentage mutant cells in a number of tissue and cell culture samples derived from FD/MAS lesions and could easily be adapted for the quantification of mutations in a large spectrum of diseases including cancer.

Cytogenetic distinction among benign fibro-osseous lesions of bone in children and adolescents: value of karyotypic findings in differential diagnosis

Benign fibro-osseous lesions of bone (BFOL) comprise a group of clinically distinct entities with significant histologic overlap and often occur in children and adolescents. Because of prior studies indicating that these lesions possess distinct karyotypic abnormalities, we conducted a retrospective review of cytogenetic analyses performed in a series of 16 BFOL in children and adolescents diagnosed at two institutions. These comprised five cases with the diagnosis of ossifying fibroma, four with osteofibrous dysplasia, and seven with fibrous dysplasia arising in the skeleton of 16 children and adolescents. All cases were analyzed using standard G-banding techniques on fresh tumors explanted in tissue culture media. Spectral karyotyping (SKY) and fluorescence in situ hybridization (FISH) were used to analyze selected metaphases of a talar lesion with the histologic features of ossifying fibroma. All four confirmed ossifying fibromas, including the talar lesion, contained clonal aberrations fusing breakpoints on Xq26 and 2q33, and one case with dissimilar histology did not. Three of four osteofibrous dysplasias contained multiple copies of chromosomes 8, 12, and/or 21. All but two fibrous dysplasia cases exhibited either a completely normal karyotype or single cell aberrations. One fibrous dysplasia had subtle chromosomal abnormalities not seen in other cases in the series, and another had complex abnormalities involving multiple chromosomes. Our current and published results indicate that cytogenetics might be of ancillary use in the diagnosis of BFOL and that a characteristic chromosomal arrangement is associated with ossifying fibroma.

The identification of monoclonality in fibrous dysplasia by methylation-specific polymerase chain reaction for the human androgen receptor gene

The nature of fibrous dysplasia, a well-known and relatively common bone lesion, is controversial. We report here the first polymerase chain reaction (PCR)-based clonality analysis of fibrous dysplasia in which 11 cases obtained from females with a polymorphism at the human androgen receptor gene locus ( HUMARA) were examined using a methylation-specific PCR procedure. This assay allowed accurate evaluation of the clonality status of this disease by eliminating restriction enzyme digestion that had been used previously in conventional HUMARA analysis. Eight samples proved to be informative for the assay, and they all showed non-random X-chromosome inactivation, indicative of a monoclonal pattern. These findings demonstrate a clonal origin for fibrous dysplasia, suggesting that the disease is a neoplastic lesion rather than a "dysplastic" process, as has been generally believed.

Benign fibro-osseous diseases of the maxillofacial bones. A review and differential diagnosis

Benign fibro-osseous lesions (BFOLs) of the maxillofacial bones represent a diverse group of pathologic conditions that includes developmental lesions, reactive or dysplastic diseases, and neoplasms. Owing to substantial overlap of the histopathologic findings, subclassification of BFOLs may be problematic. Moreover, this is not merely an academic exercise because the therapeutic management of BFOLs varies depending on the actual disease process. To further complicate matters, a number of other disease processes demonstrate clinical, radiographic, and microscopic features that bear resemblance to those encountered in recognized fibro-osseous conditions. The objective of this article is to review the most current clinicopathologic, radiographic, and molecular studies of BFOLs to aid the surgical pathologist in the recognition and diagnosis of this diverse group of maxillofacial lesions. A discussion of the various disease processes that occasionally may be confused with BFOLs also is included.

Activating Gs α mutation at the arg201 codon in liposclerosing myxofibrous tumor

Liposclerosing myxofibrous tumor (LSMFT) is a benign fibro-osseous lesion that is characterized by mixture of histologic elements including lipoma, fibroxanthoma, myxoma, ischemic ossification, and fibrous dysplasia (FD)-like features. These tissue components are seen in the original reports of FD; however, the relationship between LSMFT and FD is not clear. Point mutation of the alpha subunit of G protein (Gs alpha), which increases cyclic adenosine monophosphate formation, has been recognized as the cause of McCune-Albright syndrome as well as polyostotic and monostotic FD of bone. Gs alpha mutation at the Arg201 codon in 2 patients of LSMFT was demonstrated in the present study. Although direct sequencing analysis using the fresh-frozen materials could not detect the mutation, the polymerase chain reaction fragmentation length polymorphism (PCR-RFLP) disclosed the missense point mutation Gs alpha at the Arg201 codon in 2 cases involving LSMFT. This result strongly suggests that a subset of LSMFT is a variant form of FD.

Osteomalacic and hyperparathyroid changes in fibrous dysplasia of bone: core biopsy studies and clinical correlations

Deposition, mineralization, and resorption of FD bone compared with unaffected bone from FD patients was investigated in iliac crest biopsy specimens from 13 patients. Compared with unaffected bone, lesional FD bone seemed to be very sensitive to the effects of PTH and renal phosphate wasting, which respectively bring about hyperparathyroid or osteomalacic changes in the lesional bone.

INTRODUCTION

Fibrous dysplasia is a genetic noninherited disease caused by activating mutations of the GNAS1 gene, resulting in the deposition of qualitatively abnormal bone and marrow. This study was designed to learn more about the local processes of bone deposition, mineralization, and resorption within lesional fibrous dysplasia (FD) bone compared with unaffected bone of FD patients.

METHODS

Histology, histomorphometry, and quantitative back-scattered electron imaging (qBSE) analysis was conducted on affected and unaffected biopsy specimens from 13 patients and correlated to markers of bone metabolism.

RESULTS AND CONCLUSIONS

There was a marked excess of unmineralized osteoid with a nonlamellar structure and a reduced mineral content in mineralized bone within FD lesions (p < 0.001). A negative correlation (p = 0.05) between osteoid thickness (O.Th) and renal tubular phosphate reabsorption (measured as TmP/GFR) was observed for lesional bone, but not for unaffected bone, in which no histological or histomorphometric evidence of osteomalacia was observed in patients with renal phosphate wasting. Histological and histomorphometric evidence of increased bone resorption was variable in lesional bone and correlated with serum levels of parathyroid hormone (PTH). Hyperparathyroidism-related histological changes were observed in fibrous dysplastic bone, but not in the unaffected bone, of patients with elevated serum PTH secondary to vitamin D deficiency. Our data indicate that, compared with unaffected bone, lesional FD bone is very sensitive to the effects of PTH and renal phosphate wasting, which, respectively, bring about hyperparathyroid or osteomalacic changes in the lesional bone. Osteomalacic and hyperparathyroid changes, which emanate from distinct metabolic derangements (which superimpose on the local effects of GNAS1 mutations in bone), influence, in turn, the severity and type of skeletal morbidity in FD.

Is McCune-Albright syndrome overlooked in subjects with fibrous dysplasia of bone?

OBJECTIVE

McCune-Albright syndrome (MAS) is characterized by a clinical triad of endocrinopathies, café au lait pigmentation, and polyostotic fibrous dysplasia of bone. We hypothesized that children diagnosed with fibrous dysplasia are not routinely being evaluated for coexisting endocrine dysfunction or MAS. Our objective was to prospectively screen subjects with fibrous dysplasia for endocrine disease and G(s)alpha gene (GNAS1 )-activating mutations.

STUDY DESIGN

Nine subjects who presented with fibrous dysplasia and were followed in orthopedic clinics were evaluated for other manifestations of MAS. Genomic DNA was isolated from blood, and mutation analysis of GNAS1 was performed.

RESULTS

On physical examination, 5 of 9 subjects were found to have café au lait pigmentation. Three of 9 subjects had TSH levels below the normal range. One of these subjects was found to have hyperthyroidism and was treated by total thyroidectomy. GNAS1 mutations were identified in 5 of 9 subjects with either monostotic or polyostotic fibrous dysplasia of bone.

CONCLUSIONS

We conclude that a substantial proportion of children being followed for fibrous dysplasia of bone have unrecognized clinical and laboratory features of MAS. These children are at risk for endocrinopathy and should be screened accordingly.

Natural history and treatment of fibrous dysplasia of bone: a multicenter clinicopathologic study promoted by the European Pediatric Orthopaedic Society

A multicenter study on fibrous dysplasia of bone (FD) was promoted by the European Pediatric Orthopaedic Society in 1999 in order to gain insight into the natural history of the disease and to evaluate current diagnostic and therapeutic approaches. We collected and reviewed clinical, radiographic, pathological, and molecular genetic data when possible, from a total of 64 cases diagnosed as either monostotic FD (MFD), polyostotic FD (PFD), or McCune-Albright syndrome (MAS), evaluated or treated in 11 participating centers. Results from the initial analysis of the series indicate five main points: (1) Significant diagnostic pitfalls affect the diagnosis of MFD and, to a lesser extent, PFD in orthopedic centers and allied radiology and pathology facilities, which may be circumvented by the adoption of stringent diagnostic criteria, and in some cases by the analysis of FD-associated GNAS1 mutations. (2) MFD carries a significant risk for fracture in the face of limited disease in the proximal femur, whereas its tendency to progress is restricted to a minority of cases, and long-term outcome is usually satisfactory, regardless of treatment, in non-progressive cases. (3) The profile of tibial disease, both in MFD and in PFD, is markedly different from that of femoral disease. (4) As expected, MAS patients have the most extensive disease and the most complicated course, regularly experience multiple fractures, and require adequate surgical treatment. It appears that conservative treatment of femoral fracture, or curettage and cancellous bone grafting, or fixation with screws and plates are not indicated for the treatment of femoral fractures in these patients and should all be discouraged. Internal fixation with intramedullary nails provides stabilization of extensively affected bones, and prevents further fractures and major deformities, and thus providing a better option both for acute and elective surgery in patients with extensive involvement of the femur or of other limb long bones. (5) Evaluation of patients with FD at orthopedic centers should include, but rarely does, a thorough evaluation of endocrine profile and phosphate metabolism, and proper pathological and radiographic assessment.

Melatonin deficiency and fibrous dysplasia: might a relation exist?

Fibrous dysplasia of bone might be monostotic, polystotic, or occurs as a part of McCune-Albright syndrome and Jaffe-Lichtenstein syndrome. Activating mutations of GNAS1 gene was identified in patients with fibrous dysplasia. However, fibrous dysplasia might occur in the absence of these mutations and fibrous dysplastic tissue was produced in vitro by the effects of excess exogenous cAMP on human osteogenic cells. It was proved that the fibrous dysplastic tissue is deficient in bone sialoprotein. Melatonin deficiency might be hypothesized in syndromes associated with fibrous dysplasia or formation of fibrous dysplasia-like tissue. The receptor RZR/ROR is the nuclear receptor of melatonin and the human bone sialoprotein gene contains a RZR/ROR response element. It was supposed that binding of melatonin to its membrane receptors results in changes in the levels of activity of nuclear cAMP that lead to alteration of expression of bone sialoprotein. Also, melatonin deficiency might increase cAMP in bone through its effect on prostaglandins of the E group. Further, melatonin deficiency might explain precocious puberty in cases of McCune-Albright syndrome. We might hypothesize that melatonin deficiency might play a role in development of fibrous dysplasia in some cases.

[Cellular and molecular biology of fibrous dysplasia]

Several recent studies reflect major progress on the molecular biology and on the mechanisms of the lesions of fibrous dysplasia (monostotic and polyostotic forms) as well as the McCune-Albright syndrome. This review includes a detailed histological description of fibrous dysplasia: disorganized collagen fibers, woven bone formation, immature cytology of the osteoblasts and preosteoblastic cells. Histological lesions are also associated with an alteration of bone proteins: such as an increase in the expression of osteonectin, decrease of osteopontin and bone sialoprotein. Cell cultures of dysplasic osteoblastic cells have shown that the bone lesions are the result of abnormalities of the proliferation and differentiation of bone forming cells with a rise in CAMP levels. Poorly differentiated cells are associated with the formation of disorganized collagen fibers and with a trouble of synthesis of bone proteins. All these findings are linked to mutations of the Gs alpha (sub-unit alpha) protein. Various activating mutations are described as well as the molecular mechanisms of different forms of fibrous dysplasia, involving specially the c-fos proto-oncogene. Therapeutic implications are quoted, specially calcitonin and bisphosphonates.