Along these lines, previous studies have shown associations between GABRA2 variation and adolescent externalizing symptoms [8, 9], adolescent conduct disorder [10, 11], and adolescent rule-breaking behaviors [12]. However, one recent study did not replicate associations between GABRA2 and adolescent conduct disorder [13]. Although adult studies are lacking, one study found an association between GABRA2 and adult antisocial personality disorder [14]. Thus, the literature largely suggests that GABRA2 relates to conduct problems and externalizing symptoms in adolescent samples and in one adult sample. In contrast, there is little evidence that GABRA2 directly predicts adolescent alcohol phenotypes [8, 11–13]. However, there is more evidence in adult studies [15–24] and one recent meta-analysis [25] that found associations between GABRA2 variants and adult substance use phenotypes. It is possible that GABRA2 directly predicts adult, but not adolescent, alcohol phenotypes because environmental influences (e.g., peers and family) are more important than genetic influences in predicting adolescent substance use [26]. By adulthood, the impact of genetic influences increases substantially [26], possibly accounting for the more robust prediction of adult substance use by GABRA2.
