GCK and type 2 diabetes mellitus: The glucokinase (GCK, the predominant hexokinase isoenzyme in the hepatic and pancreatic β cells) was one of the first candidate genes to be identified as a human “diabetogene,” since its heterozygote inactivating mutation was reported to be a sub-type of the maturity-onset diabetes of the young, causing reduced insulin secretion and hyperglycemia.