Non-type 1 and non-type 2 diabetes in a young man due to novel mutation in HNF1A

Maturity-onset diabetes of the young (MODY) is an autosomal dominant monogenic form of diabetes. This report describes a case with hepatocyte nuclear factor 1-alpha (<i>HNF1A</i>)-MODY due to a novel heterozygous <i>HNF1A</i> mutation. The patient presented with hyperglycaemia and glycosuria in the absence of diabetic ketoacidosis. Family history was notable for early-onset diabetes. Genetic testing confirmed a previously unreported pathogenic <i>HNF1A</i> variant. Treatment with a GLP-1 receptor agonist and metformin reduced glycated haemoglobin from 10.2% to 6.0% within 3 months. This case highlights the importance of genetic screening in early-onset diabetes, which is frequently misdiagnosed as type 1 or type 2 diabetes, and expands the spectrum of <i>HNF1A</i> mutations relevant to precision medicine.