When type 1 diabetes isn’t the answer: A case series of siblings with misdiagnosed diabetes mellitus later confirmed as maturity-onset diabetes of the young

A BSTRACT Maturity-onset diabetes of the young (MODY) is an uncommon, monogenic form of diabetes that is often misdiagnosed as type 1 or type 2 diabetes, leading to unnecessary insulin therapy and missed opportunities for targeted management. We describe two siblings initially diagnosed with type 1 diabetes during adolescence and treated with insulin for several years. Two siblings, ages 16 and 19, have a family history of diabetes and were diagnosed with type 1 diabetes when they were young. Both twins maintained substantial endogenous insulin secretion and exhibited negative or low-titer diabetic autoantibodies in spite of long-term insulin therapy. Both patients were successfully switched from insulin to contemporary treatments, particularly GLP-1 receptor agonists, after a clinical reevaluation revealed suspicion of MODY. This led to better glycemic control without hypoglycemia. When young patients with atypical diabetes presentations have retained β-cell function, negative antibodies, and a strong family history, clinicians should keep a high index of suspicion for MODY.