DNA was extracted from blood samples and SNP genotyping was performed with the Illumina 610k Quad Bead chip either by deCODE Genetics (Brisbane cohort) or WTCRF (LBC1921 and LBC1921 cohorts) or with a modified Illumina 610k chip by the Wellcome Trust Sanger Institute, Cambridge, UK (HBCS). In the Brisbane adolescent twin cohort, genotype data (1817 samples) were checked for pedigree, sex, and Mendelian errors, and for ancestry (using HapMap3 and GenomeEUTwin individuals as a reference panel). Five individuals were removed because of gender inconsistencies, and 28 individuals (14 twin pairs) because of non-European ancestry. Quality control filters, as previously described (Medland et al., 2009), ensured no samples had a call rate ≤.95, and that all SNPs included in analyses had the following characteristics: call rate ≥.95, minor allele frequency ≥.01, and HWE test with P ≥ 1 × 10−6. In the LBC cohorts (LBC1936 = 1042 and LBC1921 = 526 samples), individuals were checked for disagreement between genetic and reported gender (n = 12 in LBC1936 and n = 1 in LBC1921). Relatedness between subjects was investigated and, for any
