There are several subtypes of MODY caused by mutations in at least 14 known genes (HNF4A, GCK, HNF1A, PDX1, HNF1B, NEUROD1, KLF11, CEL, PAX4, INS, BLK, ABCC8, KCNJ11, APPL1), which have in common a primary defect in insulin secretion associated with pancreatic beta cell dysfunction [5]. The gene discussed is GCK; the disease is MODY.