There is considerable evidence for both shared and nonshared genetic factors between different forms of substance dependence. Our initial study tested case-control-based association between CNR1 and DD, which categorized CD cases and OD cases together, and alcohol dependence was also included in that initial study, but the specific association between CNR1 and CD (nEA=175, nAA =136) was not analyzed previously (Zuo et al 2007). The present study greatly increased the sample size of CD cases (nEA=299, nAA=406) and analyzed the specific association between CNR1 and CD. In the present study, we also tested for family-based associations between CNR1 and CD in two independent large samples, i.e., an EA family sample (n=734) and an AA family sample (n=834). The present study extended the initial study and had different study targets of interest.
