Review: Apolipoprotein E (Apo E) gene polymorphism and coronary heart disease in Asian populations.

Apolipoprotein E (Apo E) is a basic component of very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL). It plays an important role in the clearance of cholesterol from circulation, and thereby slows down the process of atherosclerosis. Its 3 isoforms, E2, E3 and E4 are encoded by 3 alleles, e2, e3 and e4, respectively. E3 is the most common isoform in most populations in the world, while E2 is the least frequent isoform. A meta-analysis of several studies conducted on Asian populations revealed that carriers of e4 allele had 42% higher risk of coronary heart disease (CHD), while e2 allele had no significant association with this disease. Epidemiological studies performed in this region showed that E3 was the most prevalent isoform and most likely to be involved in CHD in Asia. Studies conducted in India indicated that individuals with e3/4 and e4/4 genotypes had considerably higher prevalence of dyslipidemia as compared to other genotypes, and hypertensive patients had high frequency of e4 allele. However, several other studies failed to show a relationship between ApoE gene polymorphism and CHD. Inadequate statistical power, low allele frequency, CHD phenotypes could be some of the possible reasons for conflicting results of some of these studies. This area of research is wide open and epidemiological studies with large sample size would be required to ascertain the relationships between ApoE gene polymorphism and CHD.