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

ABSTRACT: 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 ?-subunit of the stimulatory G protein (Gs?), as well as a large variant (XL?s) derived from the paternal allele. The mutations causing MAS affect both GNAS products, but whether XL?s, like Gs?, 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 Gs?) were present in all the previously reported and five of the new cases. The mutation was detected within the paternally expressed XL?s transcript in five and the maternally expressed NESP55 transcript in four cases. Tissues carrying paternal mutations appeared to have higher XL?s mRNA levels than maternal mutations. The human XL?s mutant analogous to Gs?-R201H (XL?s-R543H) showed markedly higher basal cAMP accumulation than wild-type XL?s in transfected cells. Wild-type XL?s demonstrated higher basal and isoproterenol-induced cAMP signaling than Gs? and co-purified with G?1?2 in transduced cells. XL?s 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. XL?s mRNA was also expressed in murine bone marrow stromal cells and preosteoblastic MC3T3-E1 cells. Our findings are consistent with the possibility that constitutive XL?s activity adds to the molecular pathogenesis of MAS and fibrous dysplasia of bone.

SUBMITTER: Mariot V

PROVIDER: S-EPMC3021591 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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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.

Mariot Virginie V Wu Joy Y JY Aydin Cumhur C Mantovani Giovanna G Mahon Matthew J MJ Linglart Agnès A Bastepe Murat M

Bone 20100929 2

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 unknow ...[more]

PMID: 20887824

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Project description:McCune-Albright syndrome (MAS) is classically defined by the clinical triad of fibrous dysplasia of bone (FD), café-au-lait skin spots, and precocious puberty (PP). It is a rare disease with estimated prevalence between 1/100,000 and 1/1,000,000. FD can involve a single or multiple skeletal sites and presents with a limp and/or pain, and, occasionally, a pathologic fracture. Scoliosis is common and may be progressive. In addition to PP (vaginal bleeding or spotting and development of breast tissue in girls, testicular and penile enlargement and precocious sexual behavior in boys), other hyperfunctioning endocrinopathies may be involved including hyperthyroidism, growth hormone excess, Cushing syndrome, and renal phosphate wasting. Café-au-lait spots usually appear in the neonatal period, but it is most often PP or FD that brings the child to medical attention. Renal involvement is seen in approximately 50% of the patients with MAS. The disease results from somatic mutations of the GNAS gene, specifically mutations in the cAMP regulating protein, Gs alpha. The extent of the disease is determined by the proliferation, migration and survival of the cell in which the mutation spontaneously occurs during embryonic development. Diagnosis of MAS is usually established on clinical grounds. Plain radiographs are often sufficient to make the diagnosis of FD and biopsy of FD lesions can confirm the diagnosis. The evaluation of patients with MAS should be guided by knowledge of the spectrum of tissues that may be involved, with specific testing for each. Genetic testing is possible, but is not routinely available. Genetic counseling, however, should be offered. Differential diagnoses include neurofibromatosis, osteofibrous dysplasia, non-ossifying fibromas, idiopathic central precocious puberty, and ovarian neoplasm. Treatment is dictated by the tissues affected, and the extent to which they are affected. Generally, some form of surgical intervention is recommended. Bisphosphonates are frequently used in the treatment of FD. Strengthening exercises are recommended to help maintaining the musculature around the FD bone and minimize the risk for fracture. Treatment of all endocrinopathies is required. Malignancies associated with MAS are distinctly rare occurrences. Malignant transformation of FD lesions occurs in probably less than 1% of the cases of MAS.

Project description:ContextMcCune-Albright syndrome (MAS) is caused by sporadic mutations of the GNAS. Patients exhibit features of acromegaly. In most patients, GH-secreting pituitary adenomas have been held responsible for this presentation. However, surgical adenomectomy rarely eliminates excess GH production.ObjectiveThe aim of this study was to elucidate pituitary pathology in patients with MAS and to explain the basis of failure of adenomectomy to eliminate GH hypersecretion.Design and settingWe conducted a case series at the National Institutes of Health.Intervention(s)Interventions included medical therapy and transsphenoidal surgery.Patients and main outcome measuresWe studied clinical and imaging features and the histology and molecular features of the pituitary of four acromegalic MAS patients.ResultsWe identified widespread and diffuse pituitary gland disease. The primary pathological changes were characterized by hyperplastic and neoplastic change, associated with overrepresentation of somatotroph cells in structurally intact tissue areas. Genetic analysis of multiple microdissected samples of any type of histological area consistently revealed identical GNAS mutations in individual patients. The only patient with remission after surgery received complete hypophysectomy in addition to removal of multiple GH-secreting tumors.ConclusionsThese findings indicate developmental effects of GNAS mutation on the entire anterior pituitary gland. The pituitary of individual cases contains a spectrum of changes with regions of normal appearing gland, hyperplasia, and areas of fully developed adenoma formation, as well as transitional stages between these entities. The primary change underlying acromegaly in MAS patients is somatotroph hyperplasia involving the entire pituitary gland, with or without development of somatotroph adenoma. Thus, successful clinical management, whether it is medical, surgical, or via irradiation, must target the entire pituitary, not just the adenomas evident on imaging.

Project description:Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare bone and endocrine disorder arising along a broad spectrum. Long-bone fractures are a common, painful, and potentially disabling complication. However, fracture prevalence and risk factors have not been well-established, making it difficult to predict which patients are at risk for a severe course. Clinical and imaging data were reviewed from two large, well-phenotyped cohorts (National Institutes of Health [NIH] in the United States and the Leiden University Medical Center [LUMC] in the Netherlands) to identify long-bone fractures at FD sites. Skeletal burden score was quantified using bone scintigraphy. Multiple linear regressions were performed to identify clinical associations with fractures. A total of 419 patients were included (186 NIH, 233 LUMC); 194 (46%) had MAS endocrinopathies. Median age at last follow-up was 30.2 years (range 3.2-84.6, interquartile range [IQR] 25.5), and median skeletal burden score was 16.6 (range 0-75, IQR 33). A total of 48 (59%) patients suffered one or more lifetime fracture (median 1, range 0-70, IQR 4). Median age at first fracture was 8 years (range 1-76, IQR 10). Fracture rates peaked between 6 and 10 years of age and decreased thereafter. Lifetime fracture rate was associated with skeletal burden score (β = 0.40, p < 0.01) and MAS hyperthyroidism (β = 0.22, p = 0.01). Younger age at first fracture was associated with skeletal burden score (β = -0.26, p = 0.01) and male sex (β = -0.23, p = 0.01). Both skeletal burden score >25 and age at first fracture ≤7 years were associated with a higher total number of lifetime fractures (median 4, range 1-70, IQR 5 versus median 1, range 1-13, IQR 1) (p < 0.01). In conclusion, higher skeletal burden score and MAS hyperthyroidism are associated with long-bone fractures in FD/MAS. Both skeletal burden score ≥25 and age at first fracture ≤7 years are associated with a higher lifetime long-bone fracture risk and may predict a more severe clinical course. These results may allow clinicians to identify FD/MAS patients at risk for severe disease who may be candidates for early therapeutic interventions. © 2021 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Dataset Information

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

Publications

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.

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