It has been shown that there is a common genetic factor for addiction to illicit drugs, including cocaine and opiates (4,5). However alcohol and drug dependence also have substantial disorder-specific genetic loading (6). In the present study we detected both a general and specific effect for GABRA2: one of the uniquely African haplotypes appeared to be protective against any addiction, however it was specifically protective for heroin dependence. In contrast, the other uniquely African haplotype predicted heroin dependence only. Likewise, rs11503014 variation was predictive for any addiction and specifically for heroin addiction.
