Maturity-onset diabetes of the young (MODY) is caused by a genetic change (mutation) that reduces insulin production and raises the blood sugar level. Most people with MODY become diabetic before age 25 years. Several types of MODY are caused by different gene mutations. The severity of the diabetes depends on the type of MODY. One type, known as MODY5, results from a mutation in the hepatocyte nuclear factor-1 (HNF-1) gene. People with MODY5 may have kidney disease, although not the type that is typical for diabetes. Some also may have malformed genital organs. However, MODY5 is uncommon, and few studies describe the clinical and genetic findings associated with the disease.