The Effects of Apo E Polymorphism on the Distribution of Lipids and Risk of Myocardial Infarction

Apolipoprotein E (apo E) is an important structural constituent of serum chylomicrons, very low density lipoproteins (VLDL) and high density lipoproteins (HDL). Apo E can be recognized by B, E-receptors, thus allowing a specific uptake of its carrying lipoprotein particles, especially chylomicron and VLDL remmants, by the liver. The gene for this apo E is located on chromosome 19q13.2 and is highly polymorphic.The three common alleles are epsilon 2, epsilon 3, and epsilon 4. These three apo E alleles encode for three protein isoforms, such that three homozygous (E2/2, E3/3, E4/4) and three heterozygous (E3/2, E4/3, E4/2) phenotypes are expressed. Although the relative frequencies of epsilon 2, epsilon3, and epsilon4 alleles in Caucasians are approximately 0.08, 0.77 and 0.15, respectively. A different frequency exists in Chinese. The relative frequency of the epsilon 3 allele was higher while the frequency of epsilon 4 was lower in the Chinese population. Individuals with apo E4/4 phenotype had the highest serum total cholesterol and LDL cholesterol concentrations, whereas the lowest levels were associated with apo E2/2 phenotype. There was also a trend for individuals carrying the epsilon 2 allele to have a higher HDL cholesterol level. No relationship between apo E phenotype and triglyceride level was observed in Chinese. The observations that apo E genes are associated with serum lipid concentrations suggest that they might contribute to the genetic risk for the development of coronary artery disease. The frequencies of apo E phenotypes in patients with myocardial infarction and controls were different in Chinese. A significant decrease in the frequency of E3/2 in patients was noted. Although the prevalence of the E4/3 phenotype was higher in patients, this was without significant difference from the controls. Finally, the present evidence, together with other reports, suggests that apo E polymorphism is associated with coronary heart disease. Apo E3/2 phenotype might be protective and apo E4/3 phenotype might increase the risk of myocardial infarction.