Admixture --- BMI, and blood pressure

In this paper, authors look at a population of 3207 African Americans and 1506 Hispanics (Mexican Americans from Starr County, Texas). They used Structure and 284 autosomal microsatellites in their IA analyses. They find median NA ancestry in Hispanics to be 35%. Their results are somewhat surprising in that they find a postive correlation between Caucasian admixture and BMI.

Racial admixture and its impact on BMI and blood pressure in African and Mexican Americans

Hua Tang, Eric Jorgenson, Maya Gadde, Sharon L. R. Kardia, D. C. Rao, Xiaofeng Zhu, Nicholas J. Schork, Craig L. Hanis, Neil Risch

Human Genetics: Published Online, 05 May 2006

Abstract: Admixed populations such as African Americans and Hispanic Americans present both challenges and opportunities in genetic epidemiologic research. Because of variation in admixture levels among individuals, case-control association studies may be subject to stratification bias. On the other hand, admixed populations also present special opportunities both for examining the role of genetic and environmental factors for observed racial/ethnic differences, and for possibly mapping alleles that contribute to such differences. Here we examined the distribution and relationship of individual admixture (IA) estimates with BMI and three measures of blood pressure in two admixed populations in the NHLBI Family Blood Pressure Program (FBPP): African Americans and Mexican Americans. For the African Americans, we observed modest but significant differences in average African IA among four recruitment sites. We observed a slight excess of African IA among hypertensives compared to normotensives, and a positive (non-significant) regression of African IA on blood pressure in untreated participants. Within Mexican Americans, we found no difference in average IA between hypertensives and normotensives, but a positive (marginally significant) regression of African IA on diastolic blood pressure. We also observed a significant positive regression of Caucasian IA (and negative regression of Native American IA) on BMI. Our results are suggestive of genetic differences between Africans and non-Africans that influence blood pressure, but such effects are likely to be modest compared to environmental ones. Excess obesity among Native Americans compared to whites is not consistent with a simple genetic explanation.