Anne Lienhardt

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

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 characterised 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 per cent of methylation at seven 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, three sub-clusters of patients with sporadic PHP-Ib, that displayed different patterns of methylation, were identified: 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, parathyroid hormone concentration at the time of diagnosis correlated with the per cent 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 identifies subtypes of PHP-Ib. These epigenetic findings suggest mosaicism at least in some patients.

Analysis of AP2S1, a calcium-sensing receptor regulator, in familial and sporadic isolated hypoparathyroidism.

BACKGROUND Except after neck surgery, hypoparathyroidism is a rare disease caused by defects in genes involved in parathyroid gland development (TBX1/22q11.2 del, GCMB, GATA3, TBCE) or function [calcium sensing receptor (CASR), GNA11, PTH], or the autoimmune polyglandular syndrome type 1 (AIRE). Approximately 90% of sporadic cases and 30% of familial cases of isolated hypoparathyroidism remain unexplained. Recurrent missense mutations in AP2S1, a calcium-sensing receptor regulator, have been recently identified in familial hyperparathyroidism. AIM The aim of the study was to investigate AP2S1 as a putative hypoparathyroidism-causing gene. METHODS Sequencing analysis and quantitative genomic PCR of the AP2S1 gene in a large cohort of 10 index cases (from nine families) and 50 sporadic cases affected with isolated hypoparathyroidism were investigated. RESULTS AND CONCLUSIONS None of the 60 patients presented with nucleotidic changes or copy number variation in the AP2S1 gene, thereby excluding AP2S1 defects as a frequent cause of isolated hypoparathyroidism.

Treatment of heterotopic ossifications secondary to pseudohypoparathyroid.

Vincent Guigonis a,∗,b, Claire Bahans a,b, Korng Ea c, Emmanuelle Bourrat d, Anne Lienhardt a,b, Olivier Chabre e, Jeremy Jost f, Hadile Mutar a, Voa Ratsimbazafy f, Agnès Linglart g a Pédiatrie, CHU de Limoges, Limoges, France b CHREC, CHU de Limoges, Limoges, France c Rhumatologie, Lariboisière, AP–HP, Paris, France d Dermatologie, Robert-Debré, AP–HP, Paris, France e Endocrinologie, CHU de Grenoble, Grenoble, France f Pharmacie, CHU de Limoges, Limoges, France g Endocrinologie pédiatrique, Bicêtre, AP–HP, Le Kremlin-Bicêtre, France