Within the Netherlands Twin Register, several genotyping projects (additional to the first genome-wide genotyping study that was part of the GAIN-MDD study) have been undertaken whose data were combined in the current study to form the replication set. All individuals came from the NTR-Biobank study55. In total, 1 920 individuals with valid NEO-FFI and GWA data were available for replication. The mean age of participants was 46.9 years (SD=15) and 67% was female. This sample included 127 MZ twin pairs (254 twins) with phenotype data in both twins. Those twin pairs were treated as one case in the analysis by averaging their phenotypic scores, resulting in a sample with 1 793 subjects for analysis. For 1 475 subjects, GWA data were available on one SNP chip; for 318 subjects, GWA data were assessed on two chips. For the majority of 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
