Although often misdiagnosed initially as the more common type 1 or type 2 diabetes, maturity-onset diabetes of the young (MODY) is a group of diseases characterized by inherited early-onset diabetes (usually in adolescence or early adulthood) from a single gene mutation. 

Severity of the diabetes symptoms associated with MODY vary depending on the type of MODY diagnosed. MODY 2 appears to be the mildest form of the disease, often only causing mild hyperglycemia and impaired glucose tolerance. MODY 1 and 3 may require treatment with insulin, much like type 1 diabetes. MODY accounts for about 1 to 5 percent of all cases of diabetes in adults in the U.S. Family members of people with MODY are at greatly increased risk for the condition. MODY should be considered when three successive generations in a family have been diagnosed with mild diabetes (not requiring insulin) before age 25 and appear neither obese nor significantly insulin-resistant.