ESPE Abstracts

Introduction: Primary Generalized Glucocorticoid Resistance or Chrousos syndrome (CS) is a rare sporadic or familial disorder characterized by generalized, partial tissue insensitivity to glucocorticoids. Mutations of the NR3C1 gene, which encodes the human glucocorticoid receptor, have been identified in many but not all patients with CS.

Objective: To identify novel genes related to CS in patients without NR3C1 gene mutations.

Patients and methods: Ten patients (six males, four females) with CS but without NR3C1 gene mutations, and two patients with CS associated with NR3C1 gene mutations (positive controls) underwent Whole Exome Sequencing (WES) on Ion Proton platform (ThermoFisher Scientific USA). Bioinformatic analysis was carried out employing the variant annotation and filtration of the Ion Reporter and VarAFT applications; the variant annotation was carried out in comparison with the Ch37(hg19).

Results: Using bioinformatics tools and a threshold of 50 reads/variant, 500 exonic non synonymous or frameshift variants were identified. Ingenuity Pathway Analysis (IPA, Qiagen) revealed that these changes were present in 390 genes involved in 5 different pathways, one of which was that of steroid hormone biosynthesis and/or actions; however, none of the identified variants were pathogenic. An in silico panel, including all the glucocorticoid-related genes, was designed to search for mutations. No pathologic variation was identified in any of the samples. The presence of common homozygous and heterozygous pathologic variants was searched and compared among the two NR3C1 mutation carriers and the 10 patients not carrying NR3C1 gene mutation. In all 12 patients, three genes with homozygous and six with heterozygous variants were detected. The variants were evaluated for their pathogenicity employing various in silico analysis tools, and the possible interaction of the genes to the NR3C1 was explored. Two of these variants were further evaluated: the TRIM28 gene (KAP1;TF1B;RNF96;TIF1B; PPP1R157) variant c.688C>T:p.R230X and the SLC4A2 gene variant, c.1511A>C:p.N504T. The TRIM28 gene is ubiquitously expressed and encodes a protein that mediates transcriptional control by interaction with the Kruppel-associated box repression domain found in many transcription factors, including the glucocorticoid receptor. This mutation is not present in the 1000 Genomes or the ExAC browser. The SLC4A2 gene encodes a member of the anion exchanger family of membrane transport proteins.

Conclusions: We identified a novel TRIM28 gene novel stop codon mutation, R230X, in all patients with CS, irrespectively of the presence of NR3C1 mutation. This mutant might be involved in the pathophysiology of CS.