The critical role of glucagon in the maintenance of glucose homeostasis had been further illustrated in the Gcgr−/− mice when adenoviral restoration of hepatic GCGR expression consented to the occurrence of diabetes in these mice after streptozotocin destroyed their β-cells (Lee et al., 2012), suggesting that hepatic glucagon suppression is a key therapeutic target in diabetes. Here, GCG is linked to diabetes mellitus.