OBJECTIVES: The objective of this study was to investigate whether differences in admixture in African American and Hispanic American adult women are associated with differences in gallbladder surgery. METHODS: Gallbladder surgery history on entry to the Women's Health Initiative's (WHI) study was used as a dichotomous outcome measure for this study. The proportion of European, sub-Saharan African, and Amerindian (AMI) admixture was estimated for 10,841 African American and 4,620 Hispanic American women in WHI using 92 ancestry informative markers. Logistic regression analyses assessed the relationship between admixture and gallbladder surgery in WHI women (enrollment at ages >50, mean age 61 years) with or without adjusting for multiple covariates, including measures of adiposity, parity, alcohol use, and education. RESULTS: There was a significant positive association between AMI admixture and the frequency of gallbladder surgery in Hispanic Americans. The odds ratio (OR) and 95% confidence intervals (CIs) for AMI admixture group was OR=2.97, CI=2.01-4.38, P<10 -4. Although there were strong positive associations with parity and adiposity, and negative associations with alcohol consumption and education, accounting for these covariates did not remove the admixture association (OR=2.46, CI=1.62-3.73). In contrast, the effect of African admixture was nearly indistinguishable from that of the European admixture, both of which were protective in the Hispanic American group, and African admixture had a marginal association with decreased gallbladder surgery in the African American group. Measures of adiposity were associated with increased risk for gallbladder surgery and remained significant after accounting for admixture and each of the other covariates. Education level and alcohol use were associated with decreased risk for gallbladder disease. However, after accounting for the other covariates these variably remained significant. CONCLUSIONS: AMI admixture is strongly associated with gallbladder surgery in women, even after adjustment for selected risk factors for cholelithiasis. Additional studies to ascertain the specific genetic risk factors underlying these associations are warranted.
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