ESPE Abstracts

Background: Maturity Onset Diabetes of the Young (MODY) constitutes a genetically and clinically heterogeneous type of Monogenic Diabetes (MD). It is characterized by early onset, autosomal dominant inheritance and a defect in β cell insulin secretion. To date 14 different MODY subtypes have been reported each one with a distinct genetic aetiology. However four are the most common subtypes, namely MODY 1 (HNF4A), MODY2 (GCK), MODY3 (HNF1A), MODY 5 (HNF1B).

Objective: To identify the molecular defect of 48 MODY patients employing the methodology of Next Generation Sequencing (NGS) Targeted Gene Panel (TGP).

Patients and methods: We studied 48 patients who met MODY criteria; young age of onset, autosomal dominant inheritance and b cell defect. Forty of them had been previously tested by Sanger sequencing of the genes GCK, HNF1A, HNF4A and HNF1B according to their phenotype, but a mutation had not been identified. A panel of 7 MODY genes (GCK, HNF1A, HNF4A, HNF1B, INS, ABCC8, KCNJ11) was designed by the Thermo Fisher Scientific Ion AmpliSeq Designer platform (version 5.6). NGS was performed on the Ion Torrent Personal Genome Machine (PGM) platform (Thermo Fisher Scientific, Waltham, MA, USA). Bioinformatic tools were used to test the pathogenicity of the new variants detected.

Results: Pathogenic variants were identified in 11 of the 48 MODY patients tested (23%). All variants were point mutations; two nonsense, eight missense and 1 splice site. Three novel pathogenic variants were detected in: GCK (p.Cys371X), HNF1A (p.Asn402Tyr) and ABCC8 (p.Met1513Thr). Three patients were found to be heterozygotes for GCK, two patients for HNF1A, one for HNF1B and four for ABCC8 variants. One patient was found to carry two different gene variants, one of the GCK gene (p.Tyr61X) and one of the ABCC8 gene (p.Leu135Val). All mutations were confirmed by Sanger sequencing in the patients and the parents with the MODY phenotype (when available).

Conclusions: The application of NGS TGP offered genetic diagnosis in 11/48 MODY patients, and allowed the identification of three novel gene mutations. Although the diagnosis rate is approximately 25% and a large number of MODY patients remain without the exact MODY type identification, the application of NGS methodology in MD diagnosis provide rapid results, is cost effective compared to Sanger sequencing and increases diagnostic accuracy. Accurate genetic diagnosis and determination of the MODY subtype is very important for the choice of the right treatment, disease prognosis and family counselling.