A mutation of endothelial nitric oxide synthase (ecNOS)-a key enzyme of the endogenous nitrovasodilator system that is essential for the regulation of blood flow and blood pressure-may aggravate the progression to diabetic nephropathy and/or retinopathy. To investigate the association of ecNOS tandem repeat polymorphism with diabetic nephropathy, the ecNOS genotype was assessed in 82 Japanese type 2 diabetic patients without nephropathy, 94 patients with microalbuminuria, 39 patients with

more »

... pathy, and 1 5 5 healthy control subjects. The analysis revealed that type 2 diabetic patients with nephropathy (not with microalbuminuria) were significantly diff e r e n t from type 2 diabetic patients without nephropathy and healthy control subjects in genotype distribution (P = 0.0423) and frequency of the ecNOS4a allele (19.2% vs. 7.3 and 7.1%, respectively; P = 0.0078). The odds ratio of progression to diabetic nephropathy in diabetic patients who carry the mutated allele is about 2.87 compared with noncarriers. The stepwise multiple regression analysis in these patients showed that hypertension (F = 9.760) and ecNOS gene polymorphism (F = 5.298) are the relevant variables for n e p h r o p a t h y. However, no association was found between the ecNOS4a allele and hypertension or diabetic retinopathy. These results imply that the ecNOS gene polymorphism may be associated with progression to diabetic nephropathy in Japanese type 2 diabetic patients. D i a b e t e s 4 9 :5 0 0-503, 2000 N itroglycerin has been used for more than a century as a vasodilator for the treatment of coronary heart disease. Previous studies have confir m e d that an endogenous nitrovasodilator system in humans maintains a physiological vasodilator tone. In response to stimuli, such as hypoxia, shear stress, and pulsatile flo w, vascular endothelium cells synthesize picomoles of nitric oxide (NO) from the amino acid L-arginine by a constitutive, calcium/calmodulin dependent enzyme, endothelial cellular nitric oxide synthase (ecNOS) (1). The intraluminal release of NO mediates local vasodilatation (1,2) and antagonizes platelet aggregation (1-3) and inhibits vascular smooth muscle cell proliferation (2). The deletion of one of five nucleotide repeats (27 bp) in intron 4 (ecNOS4a allele) was suggested to be associated with coronary artery disease in Australian current and ex-smokers (4). The important role of NO release in the regulation of basal or stimulated vasodilatation suggests that an abnormal ecNOS activity due to a mutation could be implicated in different pathological conditions, such as hypertension and atherosclerosis, and may therefore aggravate retino-and/or renovascular injury in diabetic patients. Based on this rationale, we investigated the association of the ecNOS gene polymorphism with diabetic nephropathy and retinopathy in type 2 diabetic patients in a cross-sectional study. We demonstrated that this polymorphism is a risk factor for advanced diabetic nephropathy. The ecNOS genotype was assessed in 287 (n = 136 with retinopathy; n = 151 without retinopathy) randomly selected diabetic patients from Tokyo University and its affiliated clinics and in 155 healthy control subjects. Diabetic patients who were >30 years of age and had a known diabetes duration of at least 5 years were further grouped according to the stage of progression to diabetic nephropathy as follows: type 2 diabetic patients without nephropathy (n = 82), with microalbuminuria (n = 94) (who are at risk to progress to diabetic nephropathy [5,6]), and with diabetic nephropathy (n = 39). Microalbuminuria was defined as the average of three measurements of the ratio of urinary albumin to urinary creatinine between 20 and 200 mg/g creatinine in proteinuria-negative patients. Patients with diabetic nephropathy had retinopathy and persistent dipstick-positive proteinuria (no end-stage