The results from our case-control samples supported the results from our family samples, but were generally stronger, possibly because the case-control sample had higher power than the family sample to detect SNP effects. Family-based analyses revealed an association of rs6719226 with OD in AA families, and rs6713532 with CD in EA families (Table 3). Similarly, case-control analyses demonstrated a trend for an association between rs6719226 and OD in AAs, and a significant association of rs6713532 with AD or CD in EAs (Table 4). Moreover, rs1866146 was strongly associated with substance dependence traits in both AAs and EAs, even after the conservative Bonferroni correction. Rs6713532 was in a moderate LD with rs1866146 in EA samples. It is unknown whether rs6713532 is a separate disease variant or the positive association generated from this marker is due to its LD with the downstream variant rs1866146. Further studies are warranted to clarify whether the effects of these two variants are related or independent.
