Genetic contribution of the endothelial constitutive nitric oxide synthase gene to plasma nitric oxide levels

Abstract

Nitric oxide (NO) has an important physiological role in regulating vascular tone and is also relevant to many pathological processes including hypertension and atherosclerosis. Endothelial constitutive nitric oxide synthase (ecNOS) is the key enzyme in determining basal vascular wall NO production. We used a combination of maximum-likelihood-based statistical genetic methods to explore the contributions of the ecNOS gene and other unmeasured genes to basal NO production measured by its metabolites (NO(x): nitrite and nitrate) in 428 members of 108 nuclear families. Our initial quantitative genetic analysis estimated that approximately 30% of the variance in fasting NO(x) levels is due to genes (x2([1])=16.04, P=.000062). Complex segregation analysis detected the effects of both a single locus and residual polygenes on NO(x) levels, and measured genotype analysis showed that plasma NO(x) levels in those homozygous for the rare allele (64.9±7.8 μmol/L) were significantly higher (P=.000242) than those homozygous for the common allele (30.2±3.1 μmol/L). The results of the variance component linkage analysis were consistent with linkage of a quantitative trait locus in or near the ecNOS gene to variation in plasma NO(x) levels (P=.0066). While many environmental factors have been shown to alter transiently plasma NO(x) levels, our study is the first to identify a substantial effect of the ecNOS locus on the variance of plasma NO(x), ie basal NO production. This finding may be relevant to atherogenesis and NO-related disorders.