Maturity-onset diabetes of the young (MODY) is a heterogeneous group of monogenic, non-insulin-dependent diabetes mellitus, characterized by autosomal dominant transmission and the development of severe hyperglycemia generally before the age of 25 years.1 Of these, hepatocyte nuclear factor 1α (HNF1α) -MODY is the most common and most severe. The gene discussed is HNF1A; the disease is MODY.