Maturity‐Onset Diabetes of the Young (<scp>MODY</scp>) With <scp>HNF1B</scp> p.<scp>Glu105Lys</scp> Mutation Achieving Significant Insulin Reduction on Tirzepatide: A Case Report

This report describes the first case of maturity-onset diabetes in young (MODY) with HNF1B mutation started administration of the dual glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist, tirzepatide. A 26-year-old female with a 15-year history of diabetes mellitus was diagnosed with MODY, which is characterized by decreased insulin secretion. She was treated with tirzepatide, which significantly improved her glycemic management; insulin secretion increased the fasting serum C-peptide immunoreactivity from 0.36 to 1.09 ng/mL. The patient discontinued glimepiride, and her total daily insulin dose was reduced from 88 to 4 units. This report highlights the glucose-lowering effects of tirzepatide in a patient with MODY who has the HNF1B p.Glu105Lys mutation.