Endocrine Abstracts

Introduction and Objectives: Although Next Generation Sequencing (NGS) technologies have significantly improved the molecular diagnosis of MODy, there is still a high percentage of cases in which the clinical suspicion remains without confirmatory molecular diagnosis. The main objective was to identify new candidate genes for MODy, by means of targeted NGS of a cohort of adult patients with clinically suspected MODy, in whom variants in the 14 known MODy genes implicated in its etiology were previously excluded.

Subjects and methods: Descriptive study that included 51 adult patients with diabetic debut before the age of 35 years, negative pancreatic autoimmunity, no clinical or analytical data of insulin resistance, negative ultrasensitive C-reactive protein, BMI < 25, and first-degree family history of DM. Genomic DNA samples were sequenced using a proprietary targeted NGS panel to analyze 482 genes associated with dysglycemia (MonDiabV4 panel). Filtering, classification and prioritization of variants was performed with help of VarSeqV2.5 and Alamut Visual Plus V1.9 programs, using confidence and quality criteria, (depth >100x; % bp 20x >95%), allele frequency <1% (gnomAD V2.1.1 controls), impact (‘missense’, ‘nonsense’, ‘frameshift‘) and in silico prediction of pathogenicity (CADD V1.4, score >20).

Results: 100% presented heterozygous predicted deleterious variants in more than one gene, with a mean of 3.8±1.4 variants/case (range 2-6), 11 not previously described. 95.5% were missense, 2.2% frameshift or nonsense, and all were classified as variants of uncertain significance (VUS), using ACMG criteria. They were identified mostly in genes involved in the regulation of insulin secretion, in order of frequency: CACNA1D, CACNA1B, CACNA1G, CACNA1H, CACNA2D2 and CACNA2D4 (23.8%), all encoding subunits of voltage-dependent calcium channels expressed in pancreatic β-cells; in SLC2A2, SLC22A3, SLC27A2, SLC6A1 and SLC6A13 (14. 3%), encoding transporters of type 2 glucose, organic cations, long-chain fatty acids, and GABA, respectively; or in VPS13C (10.7%), WFS1(5.9%), ADCy5 (4.7%), ADCyAP1 (3.6%) and ANK1 (1.2%). Deleterious variants were also identified in genes associated with the following pathophysiological mechanisms: reduced β-cell survival (SIRT1, SERPINB4, THADA), impaired insulin biosynthesis (PLCXD3), insulin exocytosis (ETV5), insulin signaling (ADAMTS9, KLF14, TBC1D4, BMP3), and pancreatic islet development and differentiation (RFX6, NOTCH2, GATA6, FOXA2).

Conclusion: NGS reveals a wide array of new candidate genes for MODy and suggests in most cases, a multifactorial genetic component that differs from DM2 by its earlier clinical presentation and absence of metabolic syndrome and inflammation.