Measures of childhood trauma were retrospectively derived from the CTQ. Longitudinal measures are preferable; for example a recent study (57)suggests that the GABRA2 × childhood trauma interaction might be moderated across development by other environmental factors. Nevertheless, the CTQ is widely used and has been shown to have high reliability and validity in both sexes, in different ethnic groups and in psychiatric patients (42,58–61). Although the overall dataset was large some of the analytical subsets were smaller hence the G×E interactions that we have detected may be an underestimate. Moreover, because of these power issues we had to combine the rs11503014 11/12 genotypes in all analyses. The controls were derived from two sources and although their mean age was appreciably lower than that of patients they had largely passed through the peak age of risk for onset of addictive disorders.
