Maturity-onset diabetes of the young (MODY), while rare, is the most common form of monogenic diabetes, estimated to affect 1%-2% of people with diabetes. There have been at least 13 gene mutations identified that make up the subtypes of MODY. Mutations to the GCK, HNF1A, and HNF4A genes account for more than 90% of cases. The 3 most common subtypes, in order, are MODY3 (HNF1A mutation), MODY2 (GCK mutation), and MODY1 (HNF4A mutation). Treatment depends on the exact subtype.

MODY typically presents before age 25. The mutations that cause MODY are most often inherited in an autosomal dominant fashion and all result in some level of impaired effectiveness of the beta cells in the pancreas. These patients do not fit the classic characteristics of either type 1 diabetes mellitus (T1DM; ie, autoantibodies present) or type 2 diabetes mellitus (T2DM; ie, obese, older age). When correctly treated, MODY has a slower progression with less severe outcomes than either T1DM or T2DM.