The independent correlation of the impact of lipoprotein(a) levels and apolipoprotein E polymorphism on carotid artery intima thickness

Background. Apolipoprotein E (apoE) plays a key role in lipoprotein metabolism. It occurs in three isoforms E2, E3 and E4. These isoforms have different impacts on plasma lipoprotein levels. The allele, or gene, coding apoE4 is considered a candidate for premature atherosclerosis development while the apoE2 gene is assumed to be protective. Lipoprotein(a) is also atherogenic and its increased plasma concentration is presumed to be an independent risk factor for premature atherosclerosis. Lipoprotein(a) is a protein depositing directly into the atheromatous plaques, enhancing cholesterol oxidation, competitively inhibiting plasminogen formation and thus having a prothrombogenic effect. The aim of our study was to establish a relationship between common carotid artery intima thickness and two independent risk factors, apoE polymorphism and elevation of plasma lipoprotein(a) levels. Methods. A cross-sectional study was performed on 114 patients who were referred to the lipid clinic for primary hyperlipoproteinaemia The patients received no treatment prior to examination. Plasma levels of total cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol, apoA, apoB, lipoprotein(a) and the apoE genotype were determined and the carotid artery intima thickness was measured using ultrasonography. Results. The relative frequencies of apoE2, E3 and E4 were 0.049, 0.830 and 0.121. The equality of carotid intima thickness was tested using the Kruskal-Wallis test. Medians of intima thickness in a subgroup with the allele E2 were 0.72 mm, in a subgroup with the E3/E3 genotype 0.70 mm and in a subgroup with the E4 allele 0.80 mm. The relationship between carotid intima thickness and lipoprotein(a) levels was tested using Spearman's correlation coefficient. Conclusions. No statistically significant differences of carotid intima thickness among subgroups divided according to their apoE genotype were found. No relationship between carotid intima thickness and lipoprotein(a) levels was found. On the contrary a close relationship between carotid intima thickness and age and also some of the plasma lipid Variables was recorded using the method of multivariate linear regression.