title: Novel microdeletions affecting the GNAS locus in pseudohypoparathyroidism: characterization of the underlying mechanisms.
abstract: BACKGROUND
  Pseudohypoparathyroidism type Ia (PHP1A) is a rare endocrine disorder characterized by hypocalcemia, hyperphosphatemia, multiple hormonal resistance, and features of Albright hereditary osteodystrophy. When the phenotype is present but not associated with hormonal resistance, it is called psedopseudohypoparathyroidism (PPHP). Both entities have been associated to GNAS haploinsufficiency, and are mostly caused by inherited inactivating mutations at GNAS gene that codes for the stimulatory alpha subunit of G protein, although the cause remains unidentified in approximately 30% of patients.
  
  
  OBJECTIVE
  The aims of our work were 1) to identify GNAS locus defects in 112 patients with clinical diagnosis of PHP1A/PPHP and no point mutations at GNAS, to improve molecular diagnostic and genetic counseling; 2) to outline the underlying molecular mechanism(s).
  
  
  METHODS
  Methylation-specific-multiplex ligation-dependent probe amplification, qPCR, array comparative genomic hybridization, and long-PCR were used to search for genomic rearrangements at chromosome 20q and to identify their boundaries. We used different bioinformatic approaches to assess the involvement of the genomic architecture in the origin of the deletions.
  
  
  RESULTS
  We discovered seven novel genomic deletions, ranging from 106-bp to 2.6-Mb. The characterization of five of seven deletion breakpoints and the definition of the putative molecular mechanisms responsible for these rearrangements revealed that Alu sequences play a major role in determining the genetic instability of the region.
  
  
  CONCLUSIONS
  We observed that deletions at GNAS locus represent a significant cause of PPHP/PHP1A and that such defects are mostly associated with Alu-mediated recombination events. Their investigation revealed to be fundamental as, in some cases, they could be misdiagnosed as imprinting defects.
authors.affiliation: Molecular (Epi)Genetics Laboratory (I.G., A.P., G.P.dN.), BioAraba National Health Institute, Hospital Universitario Araba-Txagorritxu, Vitoria-Gasteiz, 01009, Spain; Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Endocrinology and Diabetology Unit, Department of Clinical Sciences and Community Health (F.M.E., P.B., G.M.), University of Milan, Milan, 20122, Italy; INSERM U986 (A.L., C.S.), Hôpital Bicêtre, Le Kremlin Bicêtre, 94270, France; Service d'Endocrinologie Pédiatrique (A.L.), Hôpital Bicêtre-Assistance Publique Hôpitaux de Paris, 75475, France; Centre de Référence des Maladies Rares du Métabolisme du calcium et du phosphore Hôpital Bicêtre (A.L., C.S.), Le Kremlin Bicêtre, 94270, France; Laboratoire de Biochimie Hormonale et Génétique (C.S., C.K.), Hôpital Bichat Claude Bernard-Assistance Publique Hôpitaux de Paris, Paris, 75018, France; Department of Public Health and Pediatrics (L.dS.), University of Turin, Regina Margherita Children's Hospital, Turin, 10126, Italy; Service de génétique (J.T.R.C.), Centre hospitalier universitaire, Sherbrooke, J1G 2E8, Canada; Department of Pediatric Endocrinology (R.C.), University Hospital, Angers, 49007, France; Pediatric Endocrine Unit (Y.T.-R., O.A.), Ha'Emek Medical Center, Afula, 18101, Israel.
authors.forename: Intza
authors.initials: I
authors.lastname: Garin
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Elli
authors.forename: Agnes
authors.initials: A
authors.lastname: Linglart
authors.forename: Caroline
authors.initials: C
authors.lastname: Silve
authors.forename: Luisa
authors.initials: L
authors.lastname: de Sanctis
authors.forename: Paolo
authors.initials: P
authors.lastname: Bordogna
authors.forename: Arrate
authors.initials: A
authors.lastname: Pereda
authors.forename: Joe T R
authors.initials: JT
authors.lastname: Clarke
authors.forename: Caroline
authors.initials: C
authors.lastname: Kannengiesser
authors.forename: Regis
authors.initials: R
authors.lastname: Coutant
authors.forename: Yardena
authors.initials: Y
authors.lastname: Tenebaum-Rakover
authors.forename: Osnat
authors.initials: O
authors.lastname: Admoni
authors.forename: Guiomar Perez
authors.initials: GP
authors.lastname: de Nanclares
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mantovani
mesh_terms: D000293:Adolescent; D000328:Adult; D020087:Alu Elements / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D002864:Chromogranins; D015331:Cohort Studies; D055028:Comparative Genomic Hybridization; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics*; D017353:Gene Deletion; D056426:Genetic Loci; D006801:Humans; D007223:Infant; D008297:Male; D025202:Molecular Diagnostic Techniques; D011547:Pseudohypoparathyroidism / Q000235:genetics*; D055815:Young Adult
chemical_list: D002864:Chromogranins; C406732:GNAS protein, human; D019205:GTP-Binding Protein alpha Subunits, Gs