the 1 475 subjects genotyped on one chip (N=1 286; 87%), genotyping was part of the NTR2 genotyping study using the Illumina Human660W-Quad chip. These subjects were unrelated and unselected for any phenotype. The remaining subjects were genotyped as part of the GenomEUtwin study (N=137 subjects; Illumina 370k chip), an Attention Deficit Hyperactivity Disorder study (N=34 subjects; Affymetrix 6.0) and the MDD2000 study (N=18 MDD cases; Illumina 907K chip). Quality control of genotype data and subsequent imputation using IMPUTE software was conducted on separate sets, and on the full set of all genotyped individuals within the NTR. For the purposes of this replication study, after imputation we selected the SNPs from the discovery set that showed genome-wide significance, checked their quality and subsequently analyzed the SNPs.
