Quantification of the methylation at the GNAS locus identifies subtypes of sporadic pseudohypoparathyroidism type Ib

Stéphanie Maupetit-Méhouas (1) , Virginie Mariot (1) , Christelle Reynes (2) , Gyulène Bertrand (3) , François Feuillet (4) , Jean-Claude Carel (5) , Dominique Simon (5) , Hélène Bihan (6) , Vincent Gajdos (7) , Eve Devouge (8) , Savitha Shenoy (9) , Placide Agbo-Kpati (10) , Anne Ronan (11) , Catherine Naud (12) , Anne Lienhardt-Roussie (13) , Caroline Silve (1, 3) , Agnès Linglart (1, 14)

1 U986 - Immunologie et génétique du diabète de type 1, génétique multifactorielle en endocrinologie pédiatrique
2 MTI - Molécules Thérapeutiques in silico
3 Service de biochimie hormonale, métabolique et génétique
4 NGERE - Nutrition-Génétique et Exposition aux Risques Environnementaux
5 Service d'endocrinologie
6 Service d'endocrinologie, diabétologie, maladies métaboliques [Avicenne]
7 Service de pédiatrie [Béclère]
8 Service de pédiatrie
9 Leicester Royal Infirmary
10 Service de pédiatrie
11 Hunter Genetics Unit
12 Service de Pédiatrie
13 Service de Pédiatrie médicale [CHU Limoges]
14 CHU Saint-Antoine [AP-HP]

BACKGROUND: Pseudohypoparathyroidism type Ib (PHP-Ib) is due to epigenetic changes at the imprinted GNAS locus including loss of methylation at the A/B differentially methylated region (DMR) and sometimes at the XL and AS DMRs and gain of methylation at the NESP DMR. Objective: To investigate if quantitative measurement of the methylation at the GNAS DMRs identifies subtypes of PHP-Ib. DESIGN AND METHODS: In 19 patients with PHP-Ib and 7 controls, methylation was characterized at the four GNAS DMRs through combined bisulfite restriction analysis and quantified through cytosine-specific real-time PCR in blood lymphocyte DNA. Results: A principal component analysis using the percent of methylation at 7 cytosines of the GNAS locus provided three clusters of subjects (controls n=7, autosomal dominant PHP-Ib with loss of methylation restricted to the A/B DMR n=3 and sporadic PHP-Ib with broad GNAS methylation changes n=16) that matched perfectly the combined bisulfite restriction analysis classification. Furthermore, we identified three sub-clusters of patients with sporadic PHP-Ib that displayed different patterns of methylation: incomplete changes at all DMRs compatible with somatic mosaicism (n=5), profound epigenetic changes at all DMRs (n=8), and unmodified methylation at XL in contrast with the other DMRs (n=3). Interestingly, PTH level at the time of diagnosis correlated with the percent of methylation at the A/B DMR. Conclusion: Quantitative assessment of the methylation in blood lymphocyte DNA is of clinical relevance, allows the diagnosis of PHP-Ib and suggests that, at least in some patients, the epigenetic defect is mosaic.

Mots clés: Endocrinology; Molecular genetics

Stéphanie Maupetit-Méhouas, Virginie Mariot, Christelle Reynes, Gyulène Bertrand, François Feuillet, et al.. Quantification of the methylation at the GNAS locus identifies subtypes of sporadic pseudohypoparathyroidism type Ib. Journal of Medical Genetics, 2010, 48 (1), pp.55. ⟨10.1136/jmg.2010.081356⟩. ⟨hal-00579025⟩