The aim of this study was to perform familial co-segregation analysis and functional trial in vivo during mixed meal tolerance test (MMTT) of novel variants in diabetes candidate genes.
Methods: This study is a continuation of collaborative research project “Genetic diabetes in Lithuania” with the cohort of 1209 young diabetes patients. Prior screening for GADA, IA-2, IAA, ZnT8A confirmed type 1 diabetes (T1D) diagnosis in 88.1% (n=1065) of patients, and targeted next-generation sequencing (NGS) identified 3.5% (n=42) pathogenic variants in MODY genes. After screening for autoimmune markers, and genetic analysis, 102 patients were classified as having diabetes of unknown etiology. 12/102 were found to have novel variants in potential diabetes genes (RFX2, RREB1, SLC5A1 (three patients with variants in this gene: 2 were brothers with c.1415T>C variant, and one unrelated - c.932A>T), GCKR, MC4R, CASP10, TMPRSS6, HGFAC, DACH1, ZBED3). Co-segregation analysis and MMTT were carried out in order to study pancreatic beta-cell function in subjects with specific variants.
Results: MMTT analysis showed that probands with novel variants in MC4R, CASP10, TMPRSS6, HGFAC, SLC5A1 (c.1415T>C) had sufficient residual beta-cell function with stimulated C-peptide (CP) >200 pmol/L. Seven individuals with variants in RFX2, RREB1, GCKR, DACH1, ZBED3 and SLC5A1 (one of brothers c.1415T>C, and proband with c.932A>T) presented with complete beta-cell failure during MMTT. No statistical differences were found between patients with sufficient CP production and those with complete beta-cell failure when comparing age at the onset and duration of diabetes. Nineteen family members were included in co-segregation analysis, no diabetes cases were reported among them. Only in patient with the variant c.1894G>A in RFX2 gene, none of the family members were affected by proband’s variant.
Conclusion: Functional beta-cell study in vivo allowed to select five most probable genes for monogenic diabetes. Familial co-segregation analysis showed that novel variant in RFX2 gene could be a possible cause of diabetes in the proband. Future functional analysis of these genes in vitro could support or rule out the genetic background as a cause of diabetes.
15 Sep 2022 - 17 Sep 2022