Tuesday, June 10, 2008

DRD4 and BMI in nomadic vs. settled Kenyans

This paper (abstract below) looks at the association between BMI and the 7R variant of DRD4 often associated with ADHD and novelty seeking behavior (in humans and birds) and inter-racial mating - by same two first authors as this paper. It's also been invoked as a variant that could be selected for in a multilevel (i.e. group selection) density dependent way. I've been very interested in this gene ever since Harpending and Cochran's paper a few years back in PNAS called "In our genes" about what groups in the world have the 7R allele at a high frequency and the link to potential selection benefits - migratory behavior, cad vs. dad male behavior, warfare etc... it's been a while since I've read it.

In this paper they find an association between the 7R variant and BMI among the nomadic, but not among the settled group in Kenya. I have yet to read the paper, and would like to see how they attempt to explain this. They don't find a difference in 7R allele frequency between the two groups.

Razib also blogged on this paper and put up a map of the worldwide distribution of the 7R DRD4 allele, a table from this paper, and a link to "In our genes".

Dopamine receptor genetic polymorphisms and body composition in undernourished pastoralists: An exploration of nutrition indices among nomadic and recently settled Ariaal men of northern Kenya
Dan T.A. Eisenberg , Benjamin Campbell , Peter B. Gray and Michael D. Sorenson
BMC Evolutionary Biology 2008, 8:173
Abstract (provisional) Background Minor alleles of the human dopamine receptor polymorphisms, DRD2/TaqI A and DRD4/48bp, are related to decreased functioning and/or numbers of their respective receptors and have been shown to be correlated with body mass, height and food craving. In addition, the 7R minor allele of the DRD4 gene is at a higher frequency in nomadic compared to sedentary populations. Here we examine polymorphisms in the DRD2 and DRD4 genes with respect to body mass index (BMI) and height among men in two populations of Ariaal pastoralists, one recently settled (n = 87) and the other still nomadic (n = 65). The Ariaal live in northern Kenya, are chronically undernourished and are divided socially among age-sets. Results Frequencies of the DRD4/7R and DRD2/A1 alleles were 19.4% and 28.2%, respectively and did not differ between the nomadic and settled populations. BMI was higher in those with one or two DRD4/7R alleles in the nomadic population, but lower among the settled. Post-hoc analysis suggests that the DRD4 differences in BMI were due primarily to differences in fat free body mass. Height was unrelated to either DRD2/TaqI A or DRD4/48bp genotypes. Conclusions Our results indicate that the DRD4/7R allele may be more advantageous among nomadic than settled Ariaal men. This result suggests that a selective advantage mediated through behaviour may be responsible for the higher frequency of the 7R alleles in nomadic relative to sedentary populations around the world. In contrast to previous work, we did not find an association between DRD2 genotypes and height. Our results support the idea that human phenotypic expression of genotypes should be rigorously evaluated in diverse environments and genetic backgrounds.

No comments:

Locations of visitors to this page