Introduction/AimsMaturity-Onset Diabetes of the Young (MODY) is a monogenic non-autoimmune diabetes with 14 different genetic forms. MODY-related mutations are rarely found in the Tunisian population. Here, we explored MODY related genes sequences among seventeen unrelated Tunisian probands qualifying the MODY clinical criteria.Materials and MethodsThe GCK and HNF1A genes were systematically analyzed by direct sequencing in all probands. Then, clinical exome sequencing of 4,813 genes was performed on three unrelated patients. Among them, 130 genes have been reported to be involved in the regulation of glucose metabolism, β-cell development, differentiation and function. All identified variants were analyzed according to their frequencies in the GnomAD database and validated by direct sequencing.ResultsWe identified the previously reported GCK mutation (rs1085307455) in one patient. The clinical features of the MODY2 proband were similar to previous reports. In this study, we revealed rare and novel alterations in GCK (rs780806456) and ABCC8 (rs201499958) genes with uncertain significance. We also found two likely benign alterations in HNF1A (rs1800574) and KLF11 (rs35927125) genes with minor allele frequencies similar to those depicted in public databases. No pathogenic variants have been identified through clinical exome analysis.ConclusionsThe most appropriate patients were selected, following a strict clinical screening approach, for genetic testing. However, the known MODY1-13 genes could not explain most of the Tunisian MODY cases, suggesting the involvement of unidentified genes in the majority of Tunisian affected families.

Background: Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications and has a rising prevalence worldwide. Environmental and genetic factors contribute to GDM risk. Describing familial cases of GDM can help identify the disease's genetic components.Methods: Here, we report the case of an Emirati female patient affected with early GDM and familial history of diabetes with a significant level of insulin resistance. As a first step, we investigated the GCK and HNF1A gene sequences by direct sequencing and then performed a clinical exome sequencing (CES) of the patient's genomic DNA covering 6,670 genes.Results: Our findings showed the absence of any pathogenic variants in the GCK and HNF1A gene sequences. In addition, the CES excluded all maturity-onset diabetes of the young (MODY)-related genes. However, two rare homozygous variants in the insulin receptor substrate 1 (IRS1) gene were identified: p.Pro948Leu (gnomAD minor allele frequency (MAF) = 7.5 × 10 -5 ) and p.Arg1221Cys (gnomAD MAF = 5.6 × 10 -5 ). These variants were absent in a set of healthy Emirati individuals. Both variants are highly conserved among mammalians but have never previously been reported among the same haplotype or individual. p.Pro948Leu and p.Arg1221Cys are localized close to two important functional phosphorylation sites recognized by PI3K (hTyr941) and SHP2 (hTyr1229), respectively. Moreover, the independent and combined effect of the two variants on protein stability was predicted to be destabilizing. Conclusion:Our investigation emphasized the role of downstream regulators of insulin signaling in GDM pathophysiology and identified IRS1 as a candidate gene to explain chronic insulin resistance. In addition, the patient showed significant health improvement after lifestyle modifications and oral antidiabetic administration, even after withdrawing insulin injections.