Several of the four SNPs included in our genetic risk score have been previously investigated for association with substance use or other psychiatric phenotypes. While a recent report found no association between rs9817063 (in DRD3) and case-control cocaine dependence status in an African American sample (Bloch et al. 2009), rs5326 (in DRD1) has been associated with heroin addiction (Levran et al. 2009), as well as with tardive dyskinesia among patients with schizophrenia on long-term antipsychotic treatment (Lai et al. 2011).
