Peer substance involvement modifies genetic influences on regular substance involvement in young women

Abstract

Aims: Peer substance involvement (PSI) is a robust correlate of adolescent substance use. A small number of genetically informative studies suggest that shared genetic and environmental factors contribute to this association. We examine mechanisms by which PSI influences the etiology of regular substance involvement (RSI), particularly in women.

Design: Population-based cohort study of twin women from the US Midwest.

Participants: 2176 twin women.

Measurements: To examine the relationship between self-reported PSI during adolescence and a composite RSI representing regular tobacco, alcohol and cannabis use during young adulthood, using genetically informative correlation, moderation and joint correlation-moderation models.

Findings: There was evidence for a significant additive genetic X environment interaction. PSI was moderately heritable (h(2) = 0.25). Genetic, shared and non-shared influences on RSI overlapped with influences on PSI (genetic correlation of 0.43). Even after controlling for these shared genetic influences, RSI was more heritable in those reporting greater PSI.

Conclusions: While young women may select peers based on certain dispositional traits (e.g. permissiveness towards substance use), the social milieu constructed by PSI does modify the architecture of increased RSI in those individuals with increasing levels of PSI being associated with stronger expression of heritable influences.

Figure 1

The correlated influences (Panel A), moderating influences (Panel B) and joint correlation-moderating influence (Panel C) twin models used to test the relationship between peer substance involvement (PSI) and regular substance involvement (RSI). For Panel C, while moderation of only additive genetic (A) influences is shown, C (shared environment) and E (non-shared environment) were similarly overlapping and moderated by PSI. For instance, total shared environmental influences on RSI were represented by (C₂₁+Y₁*PSI)² + (C₂₂+Y₂*PSI)².

Figure 2

Panel A represents results from the moderating influences model. The total variance as well as the contributions of additive genetic (A) and non-shared environmental factors (E) are shown – as noted in Table 3, shared environmental influences (C) were not statistically significant here and hence, are not shown – estimates are un-standardized, such that at each level of PSI, total variance = A+E. Panel B and C represent results from the joint correlation-moderating influences models. Panel B presents unstandardized results while panel C presents standardized variance components.