Previous studies have shown that STZ-mediated β-cell ablation does not induce diabetes in the Gcgr-/- mouse model (Conarello et al., 2006; Lee et al., 2011; 2012), giving rise to the hypothesis that mice cannot develop hyperglycemia in absence of glucagon action (Unger and Cherrington, 2012). This evidence concerns the gene GCG and diabetes mellitus.