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      The Clinical Spectrum of McCune-Albright Syndrome and Its Management

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          Abstract

          McCune-Albright syndrome (MAS) is a rare, mosaic disorder presenting along a broad clinical spectrum. Disease arises from somatic-activating GNAS mutations, leading to constitutive Gα<sub>s</sub> activation and ligand-independent signaling of the Gα<sub>s</sub>-coupled protein receptor. The phenotype is largely determined by location and extent of tissues in which the GNAS mutation is expressed, as well as the pathophysiologic effects of Gα<sub>s</sub> activation within these tissues. Patients pre­sent clinically with a variable combination of fibrous dysplasia of bone (FD), café-au-lait skin macules, and hyperfunctioning endocrinopathies. In bone, Gα<sub>s</sub> leads to impaired differentiation of skeletal stem cells and formation of discrete, expansile FD lesions, resulting in fractures, pain, and functional impairment. A systematic approach to diagnosis and management is critically important to optimize outcomes for patients with FD/MAS. There are no medical therapies capable of altering the disease course in FD; however, screening and treatment for endocrinopathies can mitigate some skeletal morbidities. This review summarizes current understanding of MAS pathophysiology, describes the spectrum of clinical features, and includes a detailed discussion of the recommended approach to diagnosis and management.

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          Activating mutations of the stimulatory G protein in the McCune-Albright syndrome.

          The McCune-Albright syndrome is a sporadic disease characterized by polyostotic fibrous dysplasia, café au lait spots, sexual precocity, and hyperfunction of multiple endocrine glands. These manifestations may be explained by a somatic mutation in affected tissues that results in activation of the signal-transduction pathway generating cyclic AMP (cAMP). We analyzed DNA from tissues of patients with the McCune-Albright syndrome for the presence of activating mutations of the gene for the alpha subunit of the G protein (Gs alpha) that stimulates cAMP formation. Genomic DNA fragments encompassing regions (exons 8 and 9) previously found to contain activating missense mutations of the Gs alpha gene (gsp mutations) in sporadically occurring pituitary tumors were amplified in tissues from four patients with the McCune-Albright syndrome by the polymerase chain reaction. The amplified DNA was analyzed for mutations by denaturing gradient gel electrophoresis and allele-specific oligonucleotide hybridization. We detected one of two activating mutations within exon 8 of the Gs alpha gene in tissues from all four patients, including affected endocrine organs (gonads, adrenal glands, thyroid, and pituitary) and tissues not classically involved in the McCune-Albright syndrome. In two of the patients, histidine was substituted for arginine at position 201 of Gs alpha, and in the other two patients cysteine was substituted for the same arginine residue. In each patient the proportion of cells affected varied from tissue to tissue. In two endocrine organs, the highest proportion of mutant alleles was found in regions of abnormal cell proliferation. Mutations within exon 8 of the Gs alpha gene that result in increased activity of the Gs protein and increased cAMP formation are present in various tissues of patients with the McCune-Albright syndrome. Somatic mutation of this gene early in embryogenesis could result in the mosaic population of normal and mutant-bearing tissues that may underlie the clinical manifestations of this disease.
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            The emerging mutational landscape of G proteins and G-protein-coupled receptors in cancer.

            Aberrant expression and activity of G proteins and G-protein-coupled receptors (GPCRs) are frequently associated with tumorigenesis. Deep sequencing studies show that 4.2% of tumours carry activating mutations in GNAS (encoding Gαs), and that oncogenic activating mutations in genes encoding Gαq family members (GNAQ or GNA11) are present in ~66% and ~6% of melanomas arising in the eye and skin, respectively. Furthermore, nearly 20% of human tumours harbour mutations in GPCRs. Many human cancer-associated viruses also express constitutively active viral GPCRs. These studies indicate that G proteins, GPCRs and their linked signalling circuitry represent novel therapeutic targets for cancer prevention and treatment.
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              Burosumab Therapy in Children with X-Linked Hypophosphatemia

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                Author and article information

                Journal
                HRP
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                1663-2818
                1663-2826
                2019
                June 2020
                19 December 2019
                : 92
                : 6
                : 347-356
                Affiliations
                Skeletal Disorders and Mineral Homeostasis Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, USA
                Author notes
                *Alison M. Boyce, National Institutes of Health, Building 30 Room 218 MSC 4320, Bethesda, MD 20892 (USA), E-Mail boyceam@mail.nih.gov
                Article
                504802 Horm Res Paediatr 2019;92:347–356
                10.1159/000504802
                7302983
                31865341
                a1b8fe30-8694-407f-b893-052350a7f712
                © 2019 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 10 July 2019
                : 14 November 2019
                Page count
                Figures: 2, Tables: 2, Pages: 10
                Categories
                Mini Review Article

                Endocrinology & Diabetes,Neurology,Nutrition & Dietetics,Sexual medicine,Internal medicine,Pharmacology & Pharmaceutical medicine
                Fibroblast growth factor 23,Metabolic bone disease,Mosaicism,Gαs ,Fibrous dysplasia

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