Functional validation of a non-canonical HNF1B splice-site variant in MODY5

Mutations in the HNF1B gene can cause developmental and functional abnormalities in multiple organs such as the pancreas, kidneys, and liver. The patient is a 19-year-old male with normal growth and development, presenting with a 9-year history of diabetes that remains poorly controlled despite intensive subcutaneous insulin therapy. His clinical features include surgically managed bilateral cataracts, hyperuricemia, and bilateral renal cysts. Family history is significant for diabetes in paternal and maternal uncles.

This combination of early onset, multiorgan involvement, and familial pattern strongly suggests monogenic diabetes, indicating the need for genetic analysis to confirm the diagnosis and guide management. This study performed genetic sequencing on a patient suspected of maturity-onset diabetes of the young (MODY), followed by a Minigene assay on the identified variant of uncertain significance.

Trio-whole-genome sequencing (Trio-WGS) identified the de novo HNF1B splice-site variant (NM_000458.4: c.544+3_544+6delAAGT). The Minigene experiments indicate that this point mutation affects the splicing function of HNF1B gene with producing a truncated protein of 170 amino acids.

In this study, we identified a de novo splicing mutation in the HNF1B gene through combined genomic analysis and functional verification, confirming that it leads to aberrant mRNA splicing. For patients with early-onset diabetes and extra-renal manifestations, if genetic screening for HNF1B exons and canonical splice sites yields negative results, the pathogenic potential of variants in introns and non-canonical splice sites should be carefully considered.