The specificity of the genetic risk score was examined by correlating it with other substance dependence symptom counts (i.e., alcohol, nicotine, or marijuana, again controlling for demographic covariates). Within the training sample, this cocaine-based score explained 0.53% to 1.04% of the variance in alcohol, nicotine, or marijuana dependence symptoms (p = 0.004 – 0.04). However, in the testing sample the cocaine-derived genetic risk score explained only 0.004%, 0.010%, and 0.003% of the sample variance in alcohol, nicotine, and marijuana symptoms, respectively (all with p-values greater than 0.78, Figure 1). This demonstrates that this cocaine-identified dopaminergic genetic risk score accounted for variance in cocaine dependence symptoms within the testing sample that was largely independent of variance associated with other substance problems.
