CST4 and type 1 diabetes mellitus: Among male T1DM patients with DN, the GG genotype carriers also showed tendency decreased but not significant mean values of creatinine (1.68 ± 0.57 mg/mL vs. 2.29 ± 2.07 and 2.46 ± 2.05 mg/mL) and cystatin (1.85 ± 0.87 mg/L vs. 2.35 ± 1.77 and 2.52 ± 1.76 mg/L) levels compared to the TT and TG genotype carriers.