Maturity-onset diabetes of the young 3 (MODY₃) is an autosomal dominant monogenic diabetes mellitus characterized by defective β-cell function and non-insulin-dependent early-onset diabetes mellitus. The facts that patients with MODY₃ are often misdiagnosed as type 1 and type 2 diabetes mellitus and genetic diagnosis is expensive, make its diagnosis very challenging. In this study, we reported a case of MODY₃, which was verified to be caused by a mutation in hepatocyte nuclear factor 1α gene (c.598C>T, p.Arg200Trp). In addition, the patient had a neuroendocrine tumor simultaneously, and a KMT2D gene mutation (c.5587C>G, p.Pro1863Ala) might be associated with this leson.

Key words: maturity-onset diabetes of the young 3, intestinal neuroendocrine tumor, hepatocyte nuclear factor 1α, mutation