Nitric oxide synthase gene polymorphisms and diabetic nephropathy

Susceptibility to diabetic nephropathy in subjects with Type 1 diabetes is mainly genetically determined. Excess cardiovascular risk associated with diabetes is overwhelmingly concentrated in patients with nephropathy. Endothelial dysfunction is a feature of cardiovascular disease, hypertension, dyslipidaemia and smoking, all of which are associated with diabetic nephropathy. Nitric oxide regulates endothelial function and so genes encoding nitric oxide synthases could confer susceptibility to nephropathy. Recently positive associations have been reported. We examined polymorphisms within NOS3 and NOS2A, the genes encoding endothelial- and inducible nitric oxide synthase, for association with nephropathy.

Large case-control studies of patients with Type 1 diabetes and overt nephropathy who had hypertension and diabetic retinopathy. The control group comprised Type 1 diabetic subjects who have been on insulin for 50 or more years and have an extremely low risk of nephropathy. Genotyping was by PCR and agarose- or automated polyacrylamide gel electrophoresis using fluorescence-labelled primers.

NOS3 intron 4 genotype frequencies (n=860: 464 cases, 396 control subjects) were 2.6%, 23.3%, 74.1% and 2.3%, 22.7%, 75.0% for aa, ab and bb genotypes; p=0.935. NOS2A promoter genotype frequencies (n=715: 358 cases, 357 control subjects) were 0.3%, 16.8%, 83.0% and 0.3% 17.6% and 82.1% for +/+, +/- and -/- genotypes (p=0.952).

In our cohort of Caucasian subjects with Type 1 diabetes there is no association between either of the polymorphisms studied and diabetic nephropathy. The previous suggestion from smaller studies that the intron 4 polymorphism in NOS3 could play a role in susceptibility to the disease is not confirmed.