@article {122, title = {Human Demographic History Impacts Genetic Risk Prediction across Diverse Populations.}, journal = {Am J Hum Genet}, volume = {107}, year = {2020}, month = {2020 10 01}, pages = {788-789}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2020.08.020}, author = {Martin, Alicia R and Gignoux, Christopher R and Walters, Raymond K and Wojcik, Genevieve L and Neale, Benjamin M and Gravel, Simon and Daly, Mark J and Bustamante, Carlos D and Kenny, Eimear E} } @article {95, title = {Impact of admixture and ancestry on eQTL analysis and GWAS colocalization in GTEx.}, journal = {Genome Biol}, volume = {21}, year = {2020}, month = {2020 09 11}, pages = {233}, abstract = {

BACKGROUND: Population structure among study subjects may confound genetic association studies, and lack of proper correction can lead to spurious findings. The Genotype-Tissue Expression (GTEx) project largely contains individuals of European ancestry, but the v8 release also includes up to 15\% of individuals of non-European ancestry. Assessing ancestry-based adjustments in GTEx improves portability of this research across populations and further characterizes the impact of population structure on GWAS colocalization.

RESULTS: Here, we identify a subset of 117 individuals in GTEx (v8) with a high degree of population admixture and estimate genome-wide local ancestry. We perform genome-wide cis-eQTL mapping using admixed samples in seven tissues, adjusted by either global or local ancestry. Consistent with previous work, we observe improved power with local ancestry adjustment. At loci where the two adjustments produce different lead variants, we observe 31 loci (0.02\%) where a significant colocalization is called only with one eQTL ancestry adjustment method. Notably, both adjustments produce similar numbers of significant colocalizations within each of two different colocalization methods, COLOC and FINEMAP. Finally, we identify a small subset of eQTL-associated variants highly correlated with local ancestry, providing a resource to enhance functional follow-up.

CONCLUSIONS: We provide a local ancestry map for admixed individuals in the GTEx v8 release and describe the impact of ancestry and admixture on gene expression, eQTLs, and GWAS colocalization. While the majority of the results are concordant between local and global ancestry-based adjustments, we identify distinct advantages and disadvantages to each approach.

}, issn = {1474-760X}, doi = {10.1186/s13059-020-02113-0}, author = {Gay, Nicole R and Gloudemans, Michael and Antonio, Margaret L and Abell, Nathan S and Balliu, Brunilda and Park, YoSon and Martin, Alicia R and Musharoff, Shaila and Rao, Abhiram S and Aguet, Francois and Barbeira, Alvaro N and Bonazzola, Rodrigo and Hormozdiari, Farhad and Ardlie, Kristin G and Brown, Christopher D and Im, Hae Kyung and Lappalainen, Tuuli and Wen, Xiaoquan and Montgomery, Stephen B} } @article {53, title = {Polygenic adaptation on height is overestimated due to uncorrected stratification in genome-wide association studies.}, journal = {Elife}, volume = {8}, year = {2019}, month = {2019 Mar 21}, abstract = {

Genetic predictions of height differ among human populations and these differences have been interpreted as evidence of polygenic adaptation. These differences were first detected using SNPs genome-wide significantly associated with height, and shown to grow stronger when large numbers of sub-significant SNPs were included, leading to excitement about the prospect of analyzing large fractions of the genome to detect polygenic adaptation for multiple traits. Previous studies of height have been based on SNP effect size measurements in the GIANT Consortium meta-analysis. Here we repeat the analyses in the UK Biobank, a much more homogeneously designed study. We show that polygenic adaptation signals based on large numbers of SNPs below genome-wide significance are extremely sensitive to biases due to uncorrected population stratification. More generally, our results imply that typical constructions of polygenic scores are sensitive to population stratification and that population-level differences should be interpreted with caution.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor{\textquoteright}s assessment is that all the issues have been addressed (see decision letter).

}, issn = {2050-084X}, doi = {10.7554/eLife.39702}, author = {Sohail, Mashaal and Maier, Robert M and Ganna, Andrea and Bloemendal, Alex and Martin, Alicia R and Turchin, Michael C and Chiang, Charleston Wk and Hirschhorn, Joel and Daly, Mark J and Patterson, Nick and Neale, Benjamin and Mathieson, Iain and Reich, David and Sunyaev, Shamil R} } @article {39, title = {Imputation-Aware Tag SNP Selection To Improve Power for Large-Scale, Multi-ethnic Association Studies.}, journal = {G3 (Bethesda)}, volume = {8}, year = {2018}, month = {2018 10 03}, pages = {3255-3267}, abstract = {

The emergence of very large cohorts in genomic research has facilitated a focus on genotype-imputation strategies to power rare variant association. These strategies have benefited from improvements in imputation methods and association tests, however little attention has been paid to ways in which array design can increase rare variant association power. Therefore, we developed a novel framework to select tag SNPs using the reference panel of 26 populations from Phase 3 of the 1000 Genomes Project. We evaluate tag SNP performance mean imputed r at untyped sites using leave-one-out internal validation and standard imputation methods, rather than pairwise linkage disequilibrium. Moving beyond pairwise metrics allows us to account for haplotype diversity across the genome for improve imputation accuracy and demonstrates population-specific biases from pairwise estimates. We also examine array design strategies that contrast multi-ethnic cohorts single populations, and show a boost in performance for the former can be obtained by prioritizing tag SNPs that contribute information across multiple populations simultaneously. Using our framework, we demonstrate increased imputation accuracy for rare variants (frequency < 1\%) by 0.5-3.1\% for an array of one million sites and 0.7-7.1\% for an array of 500,000 sites, depending on the population. Finally, we show how recent explosive growth in non-African populations means tag SNPs capture on average 30\% fewer other variants than in African populations. The unified framework presented here will enable investigators to make informed decisions for the design of new arrays, and help empower the next phase of rare variant association for global health.

}, keywords = {Computational Biology, Databases, Nucleic Acid, Ethnic Groups, Genetic Association Studies, Genetics, Population, Genome-Wide Association Study, Humans, Linkage Disequilibrium, Models, Genetic, Polymorphism, Single Nucleotide, Reproducibility of Results, Selection, Genetic}, issn = {2160-1836}, doi = {10.1534/g3.118.200502}, author = {Wojcik, Genevieve L and Fuchsberger, Christian and Taliun, Daniel and Welch, Ryan and Martin, Alicia R and Shringarpure, Suyash and Carlson, Christopher S and Abecasis, Goncalo and Kang, Hyun Min and Boehnke, Michael and Bustamante, Carlos D and Gignoux, Christopher R and Kenny, Eimear E} } @article {14, title = {Human Demographic History Impacts Genetic Risk Prediction across Diverse Populations.}, journal = {Am J Hum Genet}, volume = {100}, year = {2017}, month = {2017 Apr 06}, pages = {635-649}, abstract = {

The vast majority of genome-wide association studies (GWASs) are performed in Europeans, and their transferability to other populations is dependent on many factors (e.g., linkage disequilibrium, allele frequencies, genetic architecture). As medical genomics studies become increasingly large and diverse, gaining insights into population history and consequently the transferability of disease risk measurement is critical. Here, we disentangle recent population history in the widely used 1000 Genomes Project reference panel, with an emphasis on populations underrepresented in medical studies. To examine the transferability of single-ancestry GWASs, we used published summary statistics to calculate polygenic risk scores for eight well-studied phenotypes. We identify directional inconsistencies in all scores; for example, height is predicted to decrease with genetic distance from Europeans, despite robust anthropological evidence that West Africans are as tall as Europeans on average. To gain deeper quantitative insights into GWAS transferability, we developed a complex trait coalescent-based simulation framework considering effects of polygenicity, causal allele frequency divergence, and heritability. As expected, correlations between true and inferred risk are typically highest in the population from which summary statistics were derived. We demonstrate that scores inferred from European GWASs are biased by genetic drift in other populations even when choosing the same causal variants and that biases in any direction are possible and unpredictable. This work cautions that summarizing findings from large-scale GWASs may have limited portability to other populations using standard approaches and highlights the need for generalized risk prediction methods and the inclusion of more diverse individuals in medical genomics.

}, keywords = {Americas, Genetic Predisposition to Disease, Genetics, Medical, Genetics, Population, Haplotypes, Human Genome Project, Humans, Multifactorial Inheritance, Racial Groups}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2017.03.004}, author = {Martin, Alicia R and Gignoux, Christopher R and Walters, Raymond K and Wojcik, Genevieve L and Neale, Benjamin M and Gravel, Simon and Daly, Mark J and Bustamante, Carlos D and Kenny, Eimear E} }