Evaluation in Monogenic Diabetes of the Impact of GCK, HNF1A, and HNF4A Variants on Splicing through the Combined Use of In Silico Tools and Minigene Assays

Improving detection of monogenic diabetes through reanalysis of GCK variants of uncertain significance

AIMS

To assess the utility of reanalysing GCK variants of uncertain significance (VUS) as an intervention to improve the detection of monogenic diabetes.

METHODS

We examined GCK VUS in a local cohort of individuals with suspected monogenic diabetes and re-curated each variant against the recent ClinGen GCK-specific variant classification guidelines.

RESULTS

Variant reanalysis achieved a new 'likely pathogenic' classification (i.e., positive results) in 4/8 identified VUS. The single most common newly applied criterion indicating variant pathogenicity was a confirmed phenotype of GCK-hyperglycaemia. RNA sequencing and segregation studies were performed in two cases but not additive to reclassification.

CONCLUSIONS

This is the first VUS reclassification study in monogenic diabetes using gene-specific guidelines. Within the limits of this small study, we observed a high rate (50%) of VUS upgrades to a positive result, thereby confirming the utility of VUS reanalysis- particularly with biochemical phenotyping- in increasing the detection of monogenic diabetes. We recommend HbA1c, fasting blood glucose and either pancreatic autoantibody negativity or a small oral glucose tolerance test increment as a feasible minimum dataset to inform variant classification at the individual patient level, noting the ongoing work of the ClinGen Monogenic Diabetes Expert Panel in systematically reviewing GCK variants at the international level.

HNF1B Transcription Factor: Key Regulator in Renal Physiology and Pathogenesis

The HNF1B gene, located on chromosome 17q12, encodes a transcription factor essential for the development of several organs. It regulates the expression of multiple genes in renal, pancreatic, hepatic, neurological, and genitourinary tissues during prenatal and postnatal development, influencing processes such as nephrogenesis, cellular polarity, tight junction formation, cilia development, ion transport in the renal tubule, and renal metabolism. Mutations that alter the function of Hnf1b deregulate those processes, leading to various pathologies characterized by both renal and extrarenal manifestations. The main renal diseases that develop are polycystic kidney disease, hypoplastic or dysplastic kidneys, structural abnormalities, Congenital Anomalies of the Kidney and Urinary Tract (CAKUT), and electrolyte imbalances such as hyperuricemia and hypomagnesemia. Extrarenal manifestations include Maturity-Onset Diabetes of the Young (MODY), hypertransaminasemia, genital and urinary tract malformations, Autism Spectrum Disorder (ASD), and other neurodevelopmental disorders. Patients with HNF1B alterations typically carry either punctual mutations or a monoallelic microdeletion in the 17q12 region. Future research on the molecular mechanisms and genotype-phenotype correlations in HNF1B-related conditions will enhance our understanding, leading to improved clinical management, genetic counseling, monitoring, and patient care.