The co-twin’s adolescent cannabis use status is indicative of genetic loading and the pattern of prevalence of rVUS in twins as a function of their concordance status for adolescent cannabis use was quite striking (Table 3). Twins concordant for adolescent cannabis exposure, presumably representing the highest degree of familial vulnerability, were most likely to report rVUS while twins concordantly unexposed (i.e. both twins either never used cannabis or used at a later age) were least likely to report rVUS. Within discordant pairs, whether for a dichotomous definition (Table 3) or continuously reported age (Table S3), the exposed (i.e. adolescent onset) twin was at consistently greater likelihood of reporting rVUS than her unexposed (never/late-onset) co-twin. Notably, the adolescent-onset twins from discordant pairs were marginally less likely to report rVUS than their counterparts from concordant exposed pairs indicating an attenuation of vulnerability to rVUS as a function of co-twin’s adolescent-onset cannabis use status. Similarly, even though they did not start using cannabis during adolescence, unexposed members of discordant pairs were somewhat more likely to report rVUS than concordantly never/late-onset users. These results
