title: Founder population-specific HapMap panel increases power in GWA studies through improved imputation accuracy and CNV tagging.
abstract: The combining of genome-wide association (GWA) data across populations represents a major challenge for massive global meta-analyses. Genotype imputation using densely genotyped reference samples facilitates the combination of data across different genotyping platforms. HapMap data is typically used as a reference for single nucleotide polymorphism (SNP) imputation and tagging copy number polymorphisms (CNPs). However, the advantage of having population-specific reference panels for founder populations has not been evaluated. We looked at the properties and impact of adding 81 individuals from a founder population to HapMap3 reference data on imputation quality, CNP tagging, and power to detect association in simulations and in an independent cohort of 2138 individuals. The gain in SNP imputation accuracy was highest among low-frequency markers (minor allele frequency [MAF] < 5%), for which adding the population-specific samples to the reference set increased the median R(2) between imputed and genotyped SNPs from 0.90 to 0.94. Accuracy also increased in regions with high recombination rates. Similarly, a reference set with population-specific extension facilitated the identification of better tag-SNPs for a subset of CNPs; for 4% of CNPs the R(2) between SNP genotypes and CNP intensity in the independent population cohort was at least twice as high as without the extension. We conclude that even a relatively small population-specific reference set yields considerable benefits in SNP imputation, CNP tagging accuracy, and the power to detect associations in founder populations and population isolates in particular.
authors.affiliation: Institute for Molecular Medicine Finland, FIMM, University of Helsinki, FI-00014 Helsinki, Finland.
authors.forename: Ida
authors.initials: I
authors.lastname: Surakka
authors.forename: Kati
authors.initials: K
authors.lastname: Kristiansson
authors.forename: Verneri
authors.initials: V
authors.lastname: Anttila
authors.forename: Michael
authors.initials: M
authors.lastname: Inouye
authors.forename: Chris
authors.initials: C
authors.lastname: Barnes
authors.forename: Loukas
authors.initials: L
authors.lastname: Moutsianas
authors.forename: Veikko
authors.initials: V
authors.lastname: Salomaa
authors.forename: Mark
authors.initials: M
authors.lastname: Daly
authors.forename: Aarno
authors.initials: A
authors.lastname: Palotie
authors.forename: Leena
authors.initials: L
authors.lastname: Peltonen
authors.forename: Samuli
authors.initials: S
authors.lastname: Ripatti
mesh_terms: D056915:DNA Copy Number Variations / Q000235:genetics*; D005387:Finland; D018703:Founder Effect; D005787:Gene Frequency; D005828:Genetics, Population; D055106:Genome-Wide Association Study / Q000379:methods*; D005838:Genotype; D006801:Humans; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D015203:Reproducibility of Results; D012984:Software; D044465:White People / Q000235:genetics*
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