Using the results of our genome-wide scan, we examined associations between each endophenotype and two target sets of specific candidate SNPs implicated in previous studies of P3 or P3-related activity (N = 183; P3-specific candidate SNPs) or in recent meta-analyses of disorders associated with the endophenotypes examined in this special issue (N = 1,180; endophenotype-general candidate SNPs). The latter included alcohol and drug dependence, cocaine abuse, smoking and nicotine dependence, ADHD, schizophrenia, bipolar disorder, and major depression, or related phenotypes, such as heavy drinking or excessive consumption, and the personality characteristic of excitement seeking (Iacono et al., 2014). SNPs in the candidate sets but not on the Illumina array were imputed (Iacono et al., 2014). Analyses of imputed SNPs used allele dosage as the independent variable, which is a count of the minor allele weighted by the posterior probability of each genotype. We used Bonferroni-corrected significance thresholds for both sets, with significance criteria of 2.73 × 10−4 and 4.24 × 10−5 for P3-specific and endophenotype-general SNPs, respectively.
