Europeans (case n = 303, control n = 555) [29]. Meta-analyses from 2015 (case n = 3423, control n = 3096) and 2018 (case n = 4529, control n = 4168) both found a small effect of rs1800497 on OUD risk, further supporting the relevance of this variant in at least Asian and European populations [30, 31]. Other variants and haplotypes (i.e. multiple variants on a single chromosome that are inherited together) across the DRD2/ANKK1 locus have also been implicated in OUD; however, most of these findings have yet to be replicated [26, 27, 30].
