Tung et al. suggested cut-off values for fasting and post-glucagon C-peptide levels in distinguishing T1DM from T2DM to be 2.1 ng/mL and 3.3 ng/mL, respectively, with post-glucagon C-peptide levels having better discriminating power than fasting C-peptide levels [5]. This evidence concerns the gene GCG and type 1 diabetes mellitus.