Gliclazide Challenge Testing as an Alternative Diagnostic Tool for Hepatocyte Nuclear Factor-1-Alpha Maturity Onset Diabetes of the Young.

Background: Hepatocyte nuclear factor-1-alpha monogenic diabetes (HNF1-alpha DM), formerly known as maturity-onset diabetes of the young type 3 (MODY 3), is often misdiagnosed as type 1 or type 2 diabetes. In regions where genetic testing is unavailable, alternative diagnostic approaches are needed. Case report: A 20-year-old woman was initially diagnosed with type 1 diabetes after an incidental finding of hyperglycaemia. Despite adherence to treatment, she experienced recurrent hypoglycaemia on basal-bolus insulin, receiving over 2600 injections in 8 years. Autoantibodies were negative, C-peptide levels were preserved, and her estimated probability of MODY exceeded 10%. While awaiting genetic testing, she underwent a "glicazide challenge test", which showed a marked stimulatory response in blood glucose and C-peptide levels. Subsequent testing confirmed HNF1-alpha MODY. Insulin was stopped, and she was started on low dose gliclazide, achieving excellent control with minimal hypoglycaemia. Conclusion: This case demonstrates the gliclazide challenge test's potential as an alternative diagnostic and therapeutic tool in suspected maturity-onset diabetes of the young when genetic testing is limited. LEARNING POINTS: Young patients with atypical diabetes (negative autoantibodies, preserved C-peptide, recurrent hypoglycaemia on insulin) should prompt consideration of monogenic diabetes, and the Exeter maturity-onset diabetes of the young calculator is a valuable screening tool for clinicians.A gliclazide challenge test with serial C-peptide measurement can provide a simple, functional assessment of sulfonylurea sensitivity, supporting the diagnosis of maturity-onset diabetes of the young, in centres where genetic testing is limited or delayed.Early recognition of maturity-onset diabetes of the young allows safe transition from insulin to sulfonylureas, preventing years of unnecessary injections, reducing hypoglycaemic episodes, and improving long-term quality of life.