Cognitive ability and risk for substance misuse in men : genetic and environmental correlations in a longitudinal nation-wide family study.

Abstract

Aims. To investigate the association between cognitive ability in late adolescence and subsequent substance misuse-related events in men, and to study the underlying genetic and environmental correlations. Design. A population-based longitudinal study with three different family-based designs. Cox proportional hazards models were conducted to investigate the association at the individual level. Bivariate quantitative genetic modeling in (1) full brothers and maternal half-brothers, (2) full brothers reared together and apart, and (3) monozygotic and dizygotic twin brothers was used to estimate genetic and environmental correlations. Setting. Register-based study in Sweden. Participants. The full sample included 1,402,333 Swedish men born 1958-1991 and conscripted at mean age 18.2 (SD=0.5) years. 1,361,066 men who had no substance misuse events before cognitive assessment at mandatory military conscription were included in the Cox regression models with a follow-up time of up to 35.6 years. Measures. Cognitive ability was assessed at conscription with the Swedish Enlistment Battery. Substance misuse events included alcohol and drug related court convictions, medical treatments, and deaths, available from governmental registries Findings. Lower cognitive ability in late adolescence predicted an increased risk for substance misuse events (hazard ratio [HR] for a 1-stanine unit decrease in cognitive ability: 1.29, 95% CI: 1.29-1.30). The association was somewhat attenuated within clusters of full brothers (HR=1.21, 95% CI: 1.20-1.23). Quantitative genetic analyses indicated that the association was primarily due to genetic influences; the genetic correlations ranged between -.39 (95% CI: -.45, -.34) and -.52 (-.55, -.48) in the three different designs. Conclusions. Our findings from different family designs indicate that shared genetic influences underlie the association between low cognitive ability and subsequent risk for substance misuse events.The Academy of FinlandThe Swedish Research Council for Health, Working Life and Welfare.The Swedish Research CouncilThe Swedish Research Council through the Swedish Initiative for Research on Microdata in the Social And Medical Sciences (SIMSAM)Manuscrip