Addiction is a polygenetic and multifactorial phenotype [65], and several gene-environment association studies have been carried out in the last decades; however, mixed results have been found [66]. The present study, by using a relatively large sample, focused on a functional genetic correlate of stress sensitivity and emotion processing [9, 27]. Yet, the effect of a single genetic polymorphism typically accounts for a minor percentage of the variance in a phenotype [67], and contributes in concert with other factors to explain a certain phenotype, thus the study of stress-related polygenic risk indexes is prompted. Of relevance to the dopaminergic hypothesis of addiction, the interaction between attachment and dopaminergic genotype has been investigated in relation to alcohol use problems in young adults, but no association has been found [68]. Moreover, females should also be studied, since sex differences in stress reactivity and addiction are rather the rule than the exception [69, 70]; FKBP5 genotype was for instance found to mediate the cortisol stress response in male but not female young adults [71]. The findings on humans have to be understood with respect to these boundaries (see also Strengths and Limitations) and call for independent replications.
