Only one study compared 2‐hour C‐peptide (2‐h CP) between GCK‐MODY and HNF1A‐MODY (SMD 0.44 [95% CI 0.05, 0.83] nmol/l, p = .03, n = 1)/type 2 diabetes (SMD −0.71 [95% CI −1.01, −0.41] nmol/l, p < .001, n = 1) patients. This evidence concerns the gene GCK and type 2 diabetes mellitus.