Objective: Genetic determinants are important in diabetic nephropathy (DN). Oxidative stress has also emerged as an important pathogenic factor in DN and vascular NADH oxidase is a major source of reactive oxygen species (ROS). Previous small studies reported a strong but contradictory association between functional genetic variation of p22(phox), an important subcomponent of NADH oxidase, and DN. We investigated the association between two common functional single nucleotide polymorphisms (SNPs) (-930 A > G and +242 C > T) and DN in a much larger group of Chinese patients with Type 2 diabetes mellitus (T2DM).
Research design and methods: Case-control study of Chinese subjects with long-standing T2DM (> 10 years). Cases (n = 306) were subjects with a spot urinary albumin : creatinine ratio (ACR) of > 113 mg/mmol or elevated serum creatinine. Control subjects (n = 306) had ACR < 3.3 mg/mmol and normal serum creatinine. Genotyping was carried out by standard PCR and restriction fragment length polymorphism analysis.
Results: Gender distribution, age, duration of diabetes and HbA(1c) were similar in cases and control subjects. Distribution of genotypes in the control subjects for both SNPs was consistent with the Hardy-Weinberg equilibrium. Distribution of genotypes did not differ significantly between cases and control subjects for both polymorphisms-+2424C > T: cases CC 84.6%, CT 15.0%, TT 0.4% and control subjects CC 87.6%, CT 11.8%, TT 0.6% (P = 0.45); -930 A > G: cases AA 40.5%, AG 41.8%, GG 17.7% and control subjects AA 38.2%, AG 49.0%, GG 12.8% (P = 0.12). Distribution of alleles was also similar-+2424 C > T: cases C 92.2%, T 7.8% and control subjects C 93.5%, T 6.5% (P = 0.66); -930 A > G cases A 61.4%, G 38.6% and control subjects A 62.7%, G 37.3% (P = 0.38). We estimated that our study has approximately 80% power to detect a relative risk of 1.65 (for +242 C > T) and 1.35 (for -930 A > G) conferred by the minor allele, respectively.
Conclusions: In contrast with previous small studies, our data suggest that these SNPs do not confer significantly increased susceptibility to DN secondary to T2DM in Chinese subjects.