DRD2 and substance dependence: Genes mapped to CpG sites with PC2 factor loading ≥ | 0.02| (n = 554 probes which mapped to 341 genes; Supplementary Table 1) include TTC12 [loading = −0.098 (top of the list); together with NCAM, ANNK1 and DRD2, forming a gene cluster which is associated with substance dependence (Mota et al., 2015)], GABBR1 (loading = −0.087; a GABAB receptor subunit), CSNK1D [loading = −0.068; related to circadian rhythm and lithium response in BD (Geoffroy et al., 2018)], and KCNC4 (loading = 0.044; a voltage-gated potassium channel).