Yuferov V, Butelman ER, Randesi M, et al. - Researchers evaluated if serotonin transporter gene (SLC6A4) variants are associated with cocaine exposure in individuals with an opioid dependence diagnosis, and also in non-dependent opioid users and if other single nucleotide polymorphisms (SNPs) of SLC6A4 may also be likewise associated. In a Caucasian cohort (n=591), they ascertained if variants of the SLC6A4 promoter repeats and two intronic SNPs, rs16965628 and rs2066713, are correlated with categorical diagnoses of opioid dependence (DSM-IV criteria) and with dimensional parts of cocaine use. The results of this study exhibited that in those with and without opioid dependence diagnosis, the functional SERT promoter tandem repeat genotype may be correlated to heavy cocaine exposure and more rapid increase in cocaine use.