The population group of each participant was ascertained by one of two methods: First, for 6310 subjects, 41 ancestry informative markers (AIMs), including 36 short tandem repeats markers and 5 single nucleotide polymorphisms (SNPs) were genotyped (Yang et al., 2005). We used STRUCTURE software (Pritchard and Rosenberg, 1999) to analyze the AIMs, and to generate an ancestry proportion score for each individual. Subjects with African ancestry proportion scores < 0.5 were classified as EAs; otherwise, they were classified as AAs. Second, 96 AIMs, all SNPs, were genotyped for the remaining 1961 subjects. These AIMs were selected from SNPs included in the Illumina OminQuad genotyping microarray to maximize allele frequency differences between European, African, Asian, and other ancestry. STRUCTURE software was used to analyze the AIMs and group the subjects. In total, 4240 of the 8271 subjects were AAs, and 4031 subjects were EAs.
