GCK and type 2 diabetes mellitus: In the Exeter subjects, there were no significant differences in cystatin C (adjusting for CKD-EPI eGFR, sex, age and BMI) between HNF1A-MODY and T1DM (p = 0.3), T2DM (p = 0.1), GCK-MODY (p = 0.4) and HNF4A-MODY (p = 0.9).