Up to 3.5% of cases are diagnosed before 30 years of age [9], but most of these patients are misdiagnosed as having either type 1 or type 2 diabetes, the most prevalent being deficiencies of glucokinase (GCK) hepatocyte nuclear factor-1 alpha (HNF1A)), and hepatocyte nuclear factor-4 alpha (HNF4A), formerly known as MODY2, MODY3, MODY1. This evidence concerns the gene HNF1A and type 2 diabetes mellitus.