Association of extracellular-superoxide dismutase phenotype with the endothelial constitutive nitric oxide synthase polymorphism.

The distribution of extracellular-superoxide dismutase (EC-SOD) levels in healthy Australian subjects was consistent with two distinct phenotypes in which the smaller group of subjects (3.3%) had 15-fold higher levels. The EC-SOD levels in individuals homozygous for endothelial constitutive nitric oxide synthase 4a (ecNOS4a), a rare allele for ecNOS repeat polymorphism at intron 4, were significantly lower than those in ecNOS4A/a and ecNOS4AIA subjects. Furthermore, NO levels were negatively correlated with the EC-SOD levels in common EC-SOD phenotype subjects. Whilst the mechanism remains speculative, it is possible that there is a significant interaction between EC-SOD and ecNOS, or that common factor(s), either genetic or environmental, influence both of them.