Thursday, October 16, 2008

Lipid profiles and African ancestry

Previous research has found that African ancestry is associated with healthier lipid profiles, compared to European ancestry, and that people of African descent in the UK have lower coronary heart disease compared to whites. Since sex also mediates the risk of cardiovascular disease, this study investigates four variants on the Y-chromosome, in "579 men of different ethnic groups (blacks, South Asians, and whites) from UK and in 301 whites in Italy." All Black and South Asian men were first generation immigrants, so that might be why they don't do any kind of adjustment for differing admixture proportions. Given their conclusion:
"In our study, the men of black African origin carrying the A alleles of both TBL1Y and USP9Y had a more favorable lipoprotein profile, characterized by lower levels of serum triglycerides and higher levels of HDL-cholesterol, thus indicating the existence of a “cardio-protective haplotype.” In contrast, in white men, both from the UK and Italy, and in people of South Asian origin, the lipoprotein profiles were not affected by these genotypes."
...they then have a pretty good discussion of the weaknesses and alternative explanations of their findings. They don't really discuss any kind of adaptive or evolutionary explanation for the population differences, other than to mention, regarding which alleles are ancestral, that:
"The data presented here suggest that G allele of TBL1Y and T allele of USP9Y, reported as the wild-type alleles in whites ( may be derived from the A alleles of both genes, which are the most frequent in black people of African origin."
Genetic Variants of Y Chromosome Are Associated With a Protective Lipid Profile in Black Men
Paola Russo; Alfonso Siani; Michelle A. Miller; Sharada Karanam; Teresa Esposito; Fernando Gianfrancesco; Gianvincenzo Barba; Fabio Lauria; Pasquale Strazzullo;Francesco P. Cappuccio
Arteriosclerosis, Thrombosis, and Vascular Biology. 2008;28:1569.

Abstract Objective— Gender and ethnicity modulate the phenotypic expression of cardiovascular risk factors. In particular, men are at higher risk of developing cardiovascular diseases compared to women, whereas black populations of African origin display reduced mortality from coronary heart disease (CHD) as compared to both whites and South Asians. Because the male-specific region (MSY) of the human Y chromosome is an obvious candidate for gender-related differences in the development of cardiovascular diseases, we aimed to identify genetic variants of MSY influencing cardiovascular risk profile in different ethnic groups. Methods and Results— We genotyped 4 polymorphisms of MSY (HindIII±, rs768983 of TBL1Y, rs3212292 of USP9Y, and rs9341273 of UTY genes) in 579 men of different ethnic groups (blacks, South Asians, and whites) from UK and in 301 whites in Italy. We found that the TBL1YA USP9YA haplotype, present only in blacks in whom it represents the most frequent allelic combinations (AA: n=125; all other combinations: n=45), was associated with lower levels of triglycerides (P=0.025) and higher levels of HDL-cholesterol (P=0.005) as compared to the other haplotypes. Conclusion— The TBL1YA USP9YA haplotype of the Y chromosome, present only in black people of African origin, attributes a favorable lipoprotein pattern, likely to contribute to their reduced susceptibility to coronary heart disease. The study evaluated the association of genetic variants of the male-specific region of the Y chromosome with cardiovascular risk factors in different ethnic groups. The most frequently observed haplotype in black people was associated with a favorable lipoprotein pattern, thus contributing to the lower rate of cardiovascular diseases in blacks.

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