The role of the nervous system, genetics, hormones involved in metabolic homeostasis (such as insulin, glucagon, GLP-1 and GIP), glucolipotoxicity diets and feeding behaviours, sedentary lifestyles, altered islet architecture, the immune system, altered islet-cell behaviour, UCP2, altered extrapancreatic behaviour and risk factors (such as psychological stress) have in T2D aetiology and pathogenesis remains to be mechanistically understood. This evidence concerns the gene GCG and type 2 diabetes mellitus.