Enhancing diagnostic yield of monogenic diabetes through phenotypic and molecular reanalysis of 128 individuals with young onset hyperglycemia: highlighting the significance of accurate case characterization

Aim: Our objective is to enhance the molecular diagnostic precision in a cohort of unresolved monogenic diabetes cases, previously investigated by next-generation sequencing target panel (tNGS), through comprehensive bidirectional phenotypic and genotypic reanalysis. Methods: We analyzed molecular and clinical data from 128 unresolved cases referred between 2011 and 2019. These included 92 cases suspected of maturity-onset diabetes of the young (MODY), 12 of neonatal diabetes, 16 of familial partial lipodystrophy (FPLD), 7 of mitochondrial diabetes, and 1 of Wolfram syndrome. All cases were initially investigated using a tNGS panel comprising 51 nuclear genes and the complete mitochondrial genome. Results: Our extensive reanalysis process enhanced molecular diagnostic yields from 9 to 26%. Phenotypic reevaluation, entailing in-depth phenotyping, was instrumental in excluding 62 (48.4%) atypical cases. Genotypic reanalysis identified 5 previously overlooked molecular defects: two mutations in regulatory regions (one in the HNF1A promoter and another in the PTF1A enhancer); one in the MTTK mitochondrial gene; one in the MFN2 gene; and one in the GCK gene. Conclusions: Our findings indicate that a combined approach of genotypic and phenotypic reanalysis is an effective strategy for improving molecular diagnostic accuracy in individuals with suspected monogenic diabetes.