The role of the endothelial nitric oxide synthase gene polymorphisms in sickle cell disease.

Abstract

Sickle cell disease (SCD) is a red blood cell disorder which results from a single mutation in the β- globin chain inducing the substitution of amino acid valine for glutamic acid at the sixth amino acid position. However, clinical heterogeneity is seen in SCD even when environmental conditions are similar. Single Nucleotide Polymorphisms (SNPs) in the endothelial nitric oxide synthase (eNOS) gene have been suggested to play part in the pathogenesis of SCD which may explain, at least in part, the difference in its clinical manifestation. Identification of a single nucleotide polymorphism that determines the severity of the clinical expression of the disease may prove beneficial in the management of sickle cell disease. This case-controlled study was intended to find out whether the SNPs G894T and T786C of eNOS gene are associated with the clinical manifestation of sickle cell disease and whether the level of oxidative stress resulting from the effect of reactive oxygen species has a positive correlation with the frequency of these SNPs. Blood samples of sixty five sickle cell disease patients (HbSS) and 105 normal controls, (HbAA), were obtained from the Sickle Cell Clinic at Mulago Hospital and Nakasero blood bank respectively. Genotypic analysis of the clinically significant eNOS variants T786C and G894T was carried out with a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and T-ARMS PCR assay respectively. The results of this study showed that the frequency of the SNP T786C was higher in sickle cell disease patients than in normal controls but, there was no difference in frequency between the cases and controls for the single nucleotide polymorphism G894T. In addition, there was no relationship between the level of oxidative stress and the percentage frequency between the cases and controls for the single nucleotide polymorphism G894T. In addition, there was no relationship between the level of oxidative stress and the percentage frequency of the SNP T786C among sickle cell disease patients (p = 0.089) as would be expected. Unlike G894T, endothelial nitric oxide synthase T786C variant may increase the risk of sickle cell disease severity in Ugandans.