HNF1B-MODY: Clinical and Diagnostic Insights from a Case Report of Frequently Misdiagnosed Monogenic Diabetes

HNF1B-MODY (MODY 5) is a rare monogenic diabetes with multisystem manifestations, often misdiagnosed as polycystic kidney disease (PKD) or type 1 diabetes mellitus (T1DM). We report a 13-year-old male misdiagnosed with T1DM and autosomal recessive PKD, who presented with poorly controlled diabetes, renal cysts, pancreatic atrophy, and detectable C-peptide levels. Genetic testing confirmed a pathogenic HNF1B variant (c.544+1G>A). Based on clinical suspicion and family history, his mother’s sample was also tested and found positive for the same mutation. She had long-standing diabetes, CKD, and cardiovascular complications. Pedigree analysis revealed autosomal dominant inheritance with diabetes and renal manifestations in multiple relatives. These cases highlight the diagnostic challenges of HNF1B-MODY and underscore the importance of clinical suspicion in patients with diabetes, renal abnormalities, and a family history of clustering. Early genetic diagnosis enables tailored management and family screening to prevent complications.