The variables which comprise the externalizing factors differed between adolescence and young adulthood. The variables used in young adulthood reflect problems and impairment related to substance use and externalizing behaviors (i.e. DSM symptom counts of AUD, CUD, CD, and ASPD). The variables from adolescence, however, reflect greater problems and impairment related to impulsive and rule breaking behaviors (i.e. ODD and CD symptoms) than endorsement of any cannabis use and frequency of alcohol use. As expected, the externalizing factors differ somewhat between adolescence and young adulthood, corresponding to expected developmental changes. Despite these differences in how the externalizing factor was defined, associations between the EXT PGS and externalizing behavior were relatively consistent. This suggests that the EXT PGS may confer risk for externalizing behaviors in part, due to a shared mechanistic process (i.e. liability for impaired behavioral control) that is expressed differentially across development. Future studies examining these associations longitudinally are needed to provide a more comprehensive understanding of how phenotypic expression of genetic liability unfolds.
