The relationship between the Glu298Asp and intron 4 polymorphisms of endothelial nitric oxide synthase in an Hispanic population with preeclampsia

Abstract

Endothelial nitric oxide synthase (eNOS) enzymatically converts L-arginine to L-citrulline within endothelial cells. This reaction results in the release of nitric oxide (NO). NO mediates vascular smooth muscle relaxation and has been proposed to be an important regulator of blood pressure homoeostasis during pregnancy. Our laboratory previously demonstrated an association between preeclampsia and a polymorphism (27 bp repeat) within intron 4 (I-4) of the eNOS gene (NOS3). We sought to establish whether a missense mutation (Glu298Asp) within exon 7 (E-7) of NOS3 co-segregates with the I-4 polymorphism. We also studied the combined effect of the NOS3 I-4 polymorphism and NOS3 E-7 mutation on clinical phenotype.

Methods: Genomic DNA was extracted from blood of 54 women with preeclampsia (PET) and 37 controls. Genotyping was performed by PCR (I-4) and PCR-RFLP analysis (E-7). Women with at least one NOS3 I-4 copy allele were designated A and those with the more common 5 copy were scored B. Women with at least one E-7 mutation were designated M and those with no mutation were designated N. All products were scored using a 1.5% agarose gel.

Results: One of 5 women homozygous for the I-4 A-allele also had an E-7 mutation. None of the four women homozygous for the E-7 mutation had the I-4 A-allele. All women homozygous for the E-7 mutation were identified within the control group. Among women with PET, those scored as B/M had significantly higher blood urea nitrogen (18.6 mg/dl) when compared to those scored as B/N (9.8 mg/dl), A/N (10.6 mg/dl), and A/M (10.5 mg/dl). Women with a B/M score also had a significantly greater urine dip-stick protein value (median 3 vs. 2.5) and higher weight on admission (201 vs. 164 Ibs) than women scored as B/N.

Conclusion: The I-4 polymorphism and the E-7 mutation in NOS3 do not appear to co-segregate. The E-7 mutation of NOS3 may have specific influences on the phenotypic features observed among women with preeclampsia.