Cocaine addiction is a complex behaviour that arises from the interactions between genetic and environmental risk factors. Twin studies indicate that the heritability of cocaine addiction is approximately 60% and fits a complex polygenic model [1]. Cocaine binds strongly to the dopamine transporter, and this blockade of dopamine reuptake is perhaps the key mechanism leading to cocaine addiction [2]. In fact, some studies have already reported genetic markers in dopaminergic brain systems associated with cocaine dependence [3]–[5]. However, many of those markers are also associated with other psychiatric disorders or substance-related disorders other than cocaine-related disorders and therefore might not be specific markers for the cocaine dependency risk [6]–[8]. The results of twin studies indicate that the heritability of substance dependence can be general or drug-specific, suggesting that specific genetic markers increase susceptibility to dependence on distinct drugs [9], [10]. In one of the largest studies of cocaine dependence to date [3] various polymorphisms were found to be associated with the cocaine-dependent phenotype, as has also been demonstrated in animal studies involving markers related to the dopaminergic reward system and to other biochemical pathways [11], [12].
