Rare forms of monogenic diabetes in non-European individuals. First reports of CEL and RFX6 mutations from the Indian subcontinent

Monogenic diabetes is one of the few examples in metabolic diseases in which a real precision medicine approach can be implemented in daily clinical work. Unfortunately, most of what is known today comes from studies in Whites, thus leaving much uncertainty about the genetics and the clinical presentation of monogenic diabetes in non-Europeans. To fill this gap, we report here two pedigrees from Bangladesh with CEL- and RFX6- diabetes, two rare types of monogenic diabetes which have never been described so far in individuals of the Indian subcontinent. Next generation, Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA) were performed. Variants' interpretation was according to the American College of Medical Genetics and Genomics guidelines. In the pedigree with CEL-diabetes, a large and never described deletion of exon 2-11 of CEL (confirmed by MLPA) affecting the entire catalytic domain and being likely pathogenic (LP) was observed in both the proband (who had diabetes at 16) and his mother (diabetes at 31), but not in relatives with normoglycemia. In the pedigree with RFX6-diabetes, a LP protein truncation variant (PTV, p.Tyr192*) in RFX6 was found in both the proband (diabetes at 9) and his mother (diabetes at 30), thus suggesting high heterogeneity in disease onset. Normoglycemic relatives were not available for genetic testing. We report genetic features and clinical presentation of the first two cases of CEL- and RFX6-diabetes from the Indian subcontinent, thus contributing to fill the gap of knowledge on monogenic diabetes in non-Europeans.