A Family-Based Genome Wide Association Study of Externalizing Behaviors

Developmental genetic effects on externalizing behavior and alcohol use: Examination across two longitudinal samples

Externalizing behavior in early adolescence is associated with alcohol use in adolescence and early adulthood and these behaviors often emerge as part of a developmental sequence. This pattern can be the result of heterotypic continuity, in which different behaviors emerge over time based on an underlying shared etiology. In particular, there is largely a shared genetic etiology underlying externalizing and substance use behaviors. We examined whether polygenic risk for alcohol use disorder predicted (1) externalizing behavior in early adolescence and alcohol use in adolescence in the Early Steps Multisite sample and (2) externalizing behavior in adolescence and alcohol use in early adulthood in the Project Alliance 1 (PAL1) sample. We examined associations separately for African Americans and European Americans. When examining European Americans in the Early Steps sample, greater polygenic risk was associated with externalizing behavior in early adolescence. In European Americans in PAL1, we found greater polygenic risk was associated with alcohol use in early adulthood. Effects were largely absent in African Americans in both samples. Results imply that genetic predisposition for alcohol use disorder may increase risk for externalizing and alcohol use as these behaviors emerge developmentally.

Polygenic Risk for Aggression Predicts Adult Substance Use Disorder Diagnoses via Substance Use Offending in Emerging Adulthood and is Moderated by a Family-Centered Intervention

A substance use offense reflects an encounter with law enforcement and the court system in response to breaking the law which may increase risk for substance use problems later in life. Individuals may also be at risk for substance use offending and substance use problems based on genetic predisposition. We examined a mediation model in which polygenic risk for aggression predicted adult substance use disorder diagnoses (SUD) via substance use offending in emerging adulthood. In addition, we explored for potential attenuation of genetic influences on these outcomes by a family-based intervention, the Family Check-Up (FCU). Secondary data analyses based upon the Project Alliance 1 sample was conducted among those with genetic data (n = 631; 322 from control and 309 from FCU intervention). The sample was ethnically diverse (30% African American, 44% European American, 6% Latinx, 4% Asian American, 3% Native American, and 13% Other). Greater polygenic risk for aggression was found to increase risk for substance use violations (age 19-23), which in turn was associated with greater likelihood of being diagnosed with SUD at age 27. A gene-by-intervention effect was found in which individuals in the control group had greater risk for SUD with increasing polygenic risk for aggression. Some convergence in results was found when replicating analyses in African American and European American subgroups. Results imply that genetic predisposition may increase risk for problematic substance use later in life via antisocial behavior, such as substance use offending, and that this can be attenuated by a family-centered intervention.

Birth Complications and Negative Emotionality Predict Externalizing Behaviors in Young Twins: Moderations with Genetic and Family Risk Factors

We examined interactions among genetic, biological, and ecological variables predicting externalizing behaviors in preschool and middle childhood. Specifically, we examined prediction of externalizing behaviors from birth complications and negative emotionality, each moderated by genetic risk for aggression and ecological risk factors of insensitive parenting and low family income. At ages 4 and 5 years, 170 twin pairs and 5 triplet sets (N = 355 children) were tested; 166 of those children were tested again at middle childhood (M = 7.9 years). Multilevel linear modeling results showed generally that children at high genetic risk for aggression or from low-income families were likely to have high scores on externalizing, but for children not at high risk, those with increased birth complications or more negative emotionality had high scores on externalizing. This study underscores the importance of considering biological variables as moderated by both genetic and ecological variables as they predict externalizing behaviors across early childhood.

Estimation of Parental Effects Using Polygenic Scores

Offspring resemble their parents for both genetic and environmental reasons. Understanding the relative magnitude of these alternatives has long been a core interest in behavioral genetics research, but traditional designs, which compare phenotypic covariances to make inferences about unmeasured genetic and environmental factors, have struggled to disentangle them. Recently, Kong et al. (2018) showed that by correlating offspring phenotypic values with the measured polygenic score of parents' nontransmitted alleles, one can estimate the effect of "genetic nurture"-a type of passive gene-environment covariation that arises when heritable parental traits directly influence offspring traits. Here, we instantiate this basic idea in a set of causal models that provide novel insights into the estimation of parental influences on offspring. Most importantly, we show how jointly modeling the parental polygenic scores and the offspring phenotypes can provide an unbiased estimate of the variation attributable to the environmental influence of parents on offspring, even when the polygenic score accounts for a small fraction of trait heritability. This model can be further extended to (a) account for the influence of different types of assortative mating, (b) estimate the total variation due to additive genetic effects and their covariance with the familial environment (i.e., the full genetic nurture effect), and (c) model situations where a parental trait influences a different offspring trait. By utilizing structural equation modeling techniques developed for extended twin family designs, our approach provides a general framework for modeling polygenic scores in family studies and allows for various model extensions that can be used to answer old questions about familial influences in new ways.