Identification of rare variants in candidate genes associated with monogenic diabetes in polish mody-x patients.

Purpose: Monogenic diabetes (MD) is caused by a mutation in a single gene and accounts for approximately 2.5-6% of all diabetes cases. Maturity-onset diabetes of the young (MODY) is the most common form of MD. To date, 14 different genes have been identified and associated with the presence of MODY phenotype. However, the number of potential candidate genes with relevance to beta cell function and glucose metabolism is increasing as more research is published. The aim of the study was to identify potentially causative variants in selected candidate genes in patients with a clinical diagnosis of MD. Methods: Targeted Next-Generation Sequencing (tNGS) on Illumina NextSeq 550 platform involving Agilent SureSelectQXT Target Enrichment protocol for 994 patients with suspected MD was performed. In the next step, the sequencing data of 617 patients with no pathogenic variants in main MD-related genes were reanalysed for the presence of causative variants in six candidate genes (MTOR, TBC1D4, CACNA1E, MNX1, SLC19A2, KCNH6). The presence of the selected variants was confirmed by Sanger sequencing. Results: Seven heterozygous possibly damaging variants were identified in four candidate genes (MTOR, TBC1D4, CACNA1E, MNX1). Five changes were assessed as novel variants, not previously described in available databases. None of the described variants were present among patients previously diagnosed with MODY diabetes due to causative, pathogenic variants in known MODY-related genes. Conclusions: The results obtained seem to confirm the effectiveness of the NGS method in identifying potentially causative variants in novel candidate genes associated with MODY diabetes.

Novel potentially pathogenic variants detected in genes causing intellectual disability and epilepsy in Polish families.

BACKGROUND: Intellectual disability (ID) affects 1-3% of the world population. The number of genes whose dysfunctions cause intellectual disability is increasing. In addition, new gene associations are constantly being discovered, as well as specific phenotypic features for already identified genetic alterations are being described. The aim of our study was to search for pathogenic variants in genes responsible for moderate to severe intellectual disability and epilepsy, using a panel of targeted next-generation sequencing (tNGS) for diagnosis. METHODS: The group of 73 patients (ID, n=32; epilepsy, n=21; ID and epilepsy, n=18) was enrolled in the nucleus DNA (nuDNA) study using a tNGS panel (Agilent Technologies, USA). In addition, high coverage mitochondrial DNA (mtDNA) was extracted from the tNGS data for 54 patients. RESULTS: Fifty-two rare nuDNA variants, as well as 10 rare and 1 novel mtDNA variants, were found in patients in the study group. The 10 most damaging nuDNA variants were subjected to a detailed clinical analysis. Finally, 7 nuDNA and 1 mtDNA were found to be the cause of the disease. CONCLUSIONS: This shows that still a very large proportion of patients remain undiagnosed and may require further testing. The reason for the negative results of our analysis may be a non-genetic cause of the observed phenotypes or failure to detect the causative variant in the genome. In addition, the study clearly shows that analysis of the mtDNA genome is clinically relevant, as approximately 1% of patients with ID may have pathogenic variant in mitochondrial DNA.

Next- generation sequencing is an effective method for diagnosing patients with different forms of monogenic diabetes.

AIM: Monogenic diabetes (MD) represents 5-7% of antibody-negative diabetes cases and is a heterogeneous group of disorders. METHODS: We used targeted next-generation sequencing (NGS) on Illumina NextSeq 550 platform involving the SureSelect assay to perform genetic and clinical characteristics of a study group of 684 individuals, including 542 patients referred from 12 Polish Diabetes Centers with suspected MD diagnosed between December 2016 and December 2019 and their 142 family members (FM). RESULTS: In 198 probands (36.5%) and 66 FM (46.5%) heterozygous causative variants were confirmed in 11 different MD-related genes, including 31 novel mutations, with the highest number in the GCK gene (206/264), 22/264 in the HNF1A gene and 8/264 in the KCNJ11 gene. Of the 183 probands with MODY1-5 diabetes, 48.6% of them were diagnosed at the pre-diabetes stage and most of them (68.7%) were on diet only at the time of genetic diagnosis, while 31.3% were additionally treated with oral hypoglycaemic drugs and/or insulin. CONCLUSIONS: In summary, the results obtained confirm the efficacy of targeted NGS method in the molecular diagnosis of patients with suspected MD and broaden the spectrum of new causal variants, while updating our knowledge of the clinical features of patients defined as having MD.