Background: Variation at the cholesteryl ester transfer protein (CETP) gene locus has been implicated in determining the levels and activity of CETP, apoAI and high-density lipoprotein (HDL) plasma concentration and the risk of developing coronary artery disease.
Study design: The effects of two common polymorphisms of CETP, TaqIB in intron 1 and isoleucine 405 to valine (I405-->V) in exon 14, were examined in a sample of 822 men age 18-28 years from 11 countries in Europe who had participated in a study (the European Atherosclerosis Research Study II) of the offspring of myocardial infarction sufferers before the age of 55 years and age-matched control subjects.
Results: The frequency of the rare TaqIB allele (B2) and the rare V405 allele was 0.44 and 0.28 respectively and was the same in different regions of Europe. There was a moderate linkage disequilibrium between the two polymorphisms in all the regions (D' = +0.31, P < 0.001), explained by the preferential association between the two common alleles, B1 and I405. There was a statistically significant association of the rare alleles for both the polymorphisms with lower activity of CETP (P < 0.001), 11.2% lower for the TaqIB and 7.0% lower for the I405-->V polymorphism. The TaqIB polymorphism explained 9.1% (P < 0.001) and I405-->V explained 3.7% (P < 0.001) of the variance in CETP activity, and in combination these genotypes explained 12.0% of the variance (P < 0.001). Overall, subjects whose fathers had had an early coronary heart disease had 2.4% higher plasma CETP activity than those without such family history, which became statistically significant when adjusted for the effect of the genotypes (P = 0.015), but the significance disappeared after adjustment for the effect of lipids. There was a statistically significant effect of the TaqIB polymorphism on both plasma HDL cholesterol and apoAI level (P < 0.001), with those homozygous for the rare B2 allele having the highest level. Those individuals homozygous for the rare V405 allele had the highest HDL and apoAI levels, although these effects only reached statistical significance for HDL (P < 0.03).
Conclusion: These results suggest that the TaqIB and I405-->V polymorphisms represent two independent functional variations in the CETP gene that may affect the activity of CETP and thus plasma levels of HDL.