N-acetyltransferase-2 polymorphism, smoking and type 1 diabetic nephropathy.

The N-acetyltransferase (NAT2) polymorphism has been suggested to be related to diabetic microvascular complications. To study the distribution of NAT2 genotypes in Caucasian type 1 diabetic patients with and without diabetic nephropathy, 214 adult type 1 diabetic patients and 53 healthy individuals were genotyped by polymerase chain reaction-restriction fragment length polymorphism. In addition, 75 young type 1 diabetic patients were genotyped, and 70 of them also phenotyped by caffeine. Of the adult patients, 83 had normal albumin excretion, 58 had microalbuminuria, and 73 had overt diabetic nephropathy. NAT2 allele frequencies were similarly distributed between the diabetic patients and healthy individuals: 0.29/0.2 5 (NAT2*4), 0.03/0.04 (NAT2*7B), 0.25/0.27 (NAT2*6A), and 0.43/0.44 (NAT2*5B), and within the diabetic subgroups. Because smoking is a known risk factor for diabetic nephropathy, nonsmoking and smoking patients were analysed separately. NAT2 allele frequencies differed significantly between the nonsmoking normoalbuminuric, microalbuminuric and nephropathic patients: 0.18/0.41/0.30 (NAT2*4), 0.04/0.00/0.02 (NAT2*7B), 0.35/0.18/0.17 (NAT2*6A), 0.43/0.41/0.50 (NAT2*5B), P = 0.013. In nonsmoking fast acetylators odds ratio for microalbuminuria and nephropathy was 3.1 (95% confidence interval 1.36-7.05), P = 0.007 by logistic regression. In smokers, a nonsignificant odds ratio was found [0.31 (95% confidence interval 0.08-1.2), P = 0.09]. Smoking is a strong confounding factor in relation to NAT2 analyses and diabetic nephropathy. According to our data, in nonsmoking type 1 diabetic patients fast NAT2 genotype implies an increased risk for diabetic nephropathy.