title: Quantitative analysis of methylation defects and correlation with clinical characteristics in patients with pseudohypoparathyroidism type I and GNAS epigenetic alterations.
abstract: BACKGROUND
  Pseudohypoparathyroidism type I (PHP-I) includes two main subtypes, PHP-Ia and -Ib. About 70% of PHP-Ia patients, who show Albright hereditary osteodystrophy (AHO) associated with resistance toward multiple hormones (PTH/TSH/GHRH/gonadotropins), carry heterozygous mutations in the α-subunit of the stimulatory G protein (Gsα) exons 1-13, encoded by the guanine nucleotide binding-protein α-stimulating activity polypeptide 1 (GNAS), whereas the majority of PHP-Ib patients, who classically display hormone resistance limited to PTH and TSH with no AHO sign, have methylation defects in the imprinted GNAS cluster. Recently methylation defects have been detected also in patients with PHP and different degrees of AHO, indicating a molecular overlap between the two forms.
  
  
  OBJECTIVE
  The objectives of the study were to collect patients with the following characteristics: clinical PHP-I (with or without AHO), no mutation in Gsα coding sequence, but the presence of GNAS methylation alterations and to investigate the existence of correlations between the degree of the epigenetic defect and the severity of the disease.
  
  
  METHODS
  We quantified GNAS methylation alterations by both PCR-pyrosequencing and methylation specific-multiplex ligation-dependent probe amplification assay in genomic DNA from 63 patients with PHP-I and correlated these findings with clinical parameters (age at diagnosis; calcium, phosphorus, PTH, TSH levels; presence or absence of each AHO sign).
  
  
  RESULTS
  By both approaches, the degree of the imprinting defect did not correlate with the onset of the disease, the severity of endocrine resistances, or with the presence/absence of specific AHO signs.
  
  
  CONCLUSIONS
  Similar molecular alterations may lead to a broad spectrum of diseases, from isolated PTH resistance to complete PHP-Ia, and the degree of methylation alterations does not reflect or anticipate the severity and the type of different PHP/AHO manifestations.
authors.affiliation: Department of Clinical Sciences and Community Health (F.M.E., M.F., A.M.B., E.P., P.B.-P., A.S., G.M.), Endocrinology and Diabetology Unit, University of Milan, Fondazione Istituto di Ricovero e Cura a Carattere Scientifico, Ca' Granda Ospedale Maggiore Policlinico, and Center of Molecular and Genetic Epidemiology (V.B., L.T.), Department of Clinical Sciences and Community Health, Università di Milano and Fondazione Cà Granda Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale Maggiore Policlinico, 20122 Milan, Italy; and Department of Public Health and Pediatrics (L.d.S.), University of Turin, and Regina Margherita Children's Hospital, 10126 Turin, Italy.
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Elli
authors.forename: Luisa
authors.initials: L
authors.lastname: de Sanctis
authors.forename: Valentina
authors.initials: V
authors.lastname: Bollati
authors.forename: Letizia
authors.initials: L
authors.lastname: Tarantini
authors.forename: Marcello
authors.initials: M
authors.lastname: Filopanti
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Barbieri
authors.forename: Erika
authors.initials: E
authors.lastname: Peverelli
authors.forename: Paolo
authors.initials: P
authors.lastname: Beck-Peccoz
authors.forename: Anna
authors.initials: A
authors.lastname: Spada
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mantovani
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002864:Chromogranins; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D011547:Pseudohypoparathyroidism / Q000175:diagnosis / Q000235:genetics*; D012720:Severity of Illness Index; D055815:Young Adult
chemical_list: D002864:Chromogranins; C406732:GNAS protein, human; D019205:GTP-Binding Protein alpha Subunits, Gs