The significant change in mean serum 1,5-AG was noticed only in T2DM, for which it was −6.57 ± 7.34 mg/ml (p = 0.04), but not in HNF1A-MODY (−0.10 ± 4.21 mg/ml, p = 0.94) or GCK-MODY (−0.86 ± 4.16 mg/ml, p = 0.38). Here, GCK is linked to type 2 diabetes mellitus.