Samples were collected and genotyped at the consumer genetics company 23andMe, Inc., as described previously20 (link). Briefly, genotyping was performed on genomic DNA extracted from saliva samples. DNA was genotyped on one of two microarray platforms: the Illumina HumanHap550+ BeadChip platform, which includes more than 550,000 SNPs, or the Illumina HumanOmniExpress+ BeadChip which has a base set of 730,000 SNPs augmented with approximately 250,000 SNPs to obtain a superset of the HumanHap550+, as well as a custom set of about 30,000 SNPs.