Population stratification in a case-control study of brain arteriovenous malformation in Latinos.
BACKGROUND
Genetic association studies conducted in admixed populations may be confounded by population stratification resulting in spurious associations. The purpose of this pilot study was to determine the presence and effect of population stratification in a case-control study of brain arteriovenous malformation (BAVM).


METHODS
We tested 83 ancestry informative markers in BAVM cases and healthy controls of self-reported Latino race/ethnicity (n = 294). Individual ancestry estimates (IAE) were obtained using the Structure program, assuming 3 underlying subpopulations. Summary chi(2) tests comparing genotype frequency of ancestry informative markers were used to detect stratification and IAE were included as covariates in logistic regression analysis to account for differences in genetic background.


RESULTS
Admixture estimates for Latinos (overall 47% native American, 45% European and 8% African ancestry) revealed heterogeneity between individuals within ancestral groups. The summary chi(2) test was significant (p = 0.005), suggesting ancestral differences between cases and controls. Furthermore, genetic ancestry was associated with frequency differences in a promoter variant in the IL-6 gene (IL-6 -174G>C). On average, subjects with the IL6 -174 GG genotype had 6% greater Native American ancestry (p = 0.023). Age- and sex-adjusted risk of BAVM associated with the IL-6 -174 GG genotype was 1.85 (95% CI 0.99-3.48, p = 0.055), and further adjustments for IAE yielded an OR of 1.96 (95% CI 1.03-3.72, p = 0.039).


CONCLUSIONS
The IL-6 -174G>C polymorphism was associated with increased risk of BAVM among Latinos after accounting for differences in ancestral background. These results suggest subtle, negative confounding and illustrate the importance of addressing population stratification in case-control studies conducted in admixed populations.
Center for Cerebrovascular Research, Department of Anesthesia and Perioperative Care, University of California, San Francisco, San Francisco, California 94110, USA. kimhel@anesthesia.ucsf.edu
Helen
H
Kim
Pirro G
PG
Hysi
Ludmila
L
Pawlikowska
Shweta
S
Choudhry
Esteban
E
González Burchard
Pui-Yan
PY
Kwok
Stephen
S
Sidney
Charles E
CE
McCulloch
William L
WL
Young
D000328:Adult; D001499:Bayes Theorem; D016022:Case-Control Studies; D005006:Ethnicity / Q000706:statistics & numerical data; D005260:Female; D014644:Genetic Variation; D005838:Genotype; D006630:Hispanic or Latino / Q000706:statistics & numerical data*; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics; D002538:Intracranial Arteriovenous Malformations / Q000453:epidemiology* / Q000235:genetics*; D008297:Male; D008390:Markov Chains; D009010:Monte Carlo Method; D016017:Odds Ratio; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D012307:Risk Factors; D011795:Surveys and Questionnaires; D055815:Young Adult
D015850:Interleukin-6