To date, five proteins have been identified whose genetic absence or impairment causes MODY, the enzyme glucokinase (GCK/MODY2) and four transcription factors: hepatocyte nuclear factor (HNF) 4α/MODY1, HNF-1α/MODY3, insulin promoter factor 1/MODY4 and HNF-1β/MODY5. This evidence concerns the gene GCK and MODY.