A Young Patient with HNF1A-MODY and an Elevated HbA1c

Abstract Maturity-onset diabetes of the young (MODY) is the predominant form of monogenic diabetes, affecting 1 to 5% of diabetes patients. It has autosomal dominant inheritance but occasional de novo mutations. Its clinical features encompass early-onset hyperglycemia, residual pancreatic function, and absence of insulin resistance or beta cell autoimmunity, which are managed primarily with glucose-lowering medications. Increasing awareness of MODY's clinical importance among health care professionals, researchers, and policymakers may enhance screening and diagnostic approaches. We describe the case of a 16-year-old adolescent boy presenting with polyuria and polydipsia. He had no significant past medical history but a notable family history of diabetes, including prediabetes and type 2 diabetes, across three generations. On evaluation, his vitals were stable. Initial investigations revealed hyperglycemia with a point-of-care glucose of 222 mg/dL, HbA1c of 10.4%, and no ketonuria. C-peptide levels were 0.9 ng/mL, and diabetes autoantibodies were negative. The patient was started on insulin therapy and transitioned to basal-bolus insulin. Genetic testing was performed due to strong familial history and absence of autoantibodies, revealing a heterozygous HNF1A gene mutation consistent with HNF1A-MODY. He was switched to gliclazide 60 mg daily, achieving excellent glycemic control with an HbA1c of 5.3% at 3 months of follow-up. First-degree relatives were referred for MODY genetic testing. In HNF1A–MODY, the glycemic profile typically presents with slight fasting hyperglycemia and notably elevated glucose levels post-glucose intake, accompanied by a gradual decline in insulin secretion and deteriorating glucose regulation, necessitating treatment. It is generally uncommon to have significant hyperglycemia and elevation of HbA1c in MODY patients, as seen in the case discussed. Clinicians need a comprehensive grasp of MODY's epidemiology and pathogenesis to precisely diagnose patients, tailor individualized treatment plans and monitoring, and screen relatives of those affected by diabetes mellitus.