Pathways to Youth Behavior: The Role of Genetic, Neural, and Behavioral Markers

Chronic pain and delinquency partially explain the effect of the DRD4 gene polymorphism on adult substance use

Background: The dopamine receptor D4 [DRD4] has been reported to be associated with substance use. Yet, the roles that health conditions and behaviors may play in such association are understudied.Objective: This longitudinal study investigated the potential mediation effects of chronic pain and delinquency in adolescence on the association between the DRD4 2-repeat allele and substance use in adulthood. Sex, witnessing violence, and experiencing violence were also examined as potential moderators for the mediation pathways.Methods: We used the restricted and candidate gene data from the National Longitudinal Study of Adolescent to Adult Health (Waves I-IV) to conduct secondary analysis (N = 8,671; 47% male). A two-step approach was adopted to examine the mediation effects regarding four substance use outcomes in adulthood: number of lifetime alcohol use disorder symptoms, lifetime regular smoker status, past-month smoking, and lifetime "pain killer" misuse. The moderation effects were investigated using stratification and permutation.Results: The DRD4 2-repeat allele was associated with all adulthood substance use outcomes through adolescent chronic pain and delinquency (AORs/IRR range 1.08-3.78; all ps<0.01). The association between delinquency and smoking was higher among females. The association between delinquency and substance use was lower among the participants who witnessed violence in adolescence.Conclusions: This study identified modifiable mediators underlying the association between the DRD4 2-repeat allele and substance use behaviors, concluding that chronic pain and delinquency partially explain the effect of the DRD4 gene polymorphism on adult substance use.

Cold-Blooded and on Purpose: A Review of the Biology of Proactive Aggression

Proactive aggression (PA) is a planned and unprovoked form of aggression that is most often enacted for personal gain or in anticipation of a reward. Frequently described as "cold-blooded" or goal oriented, PA is thought to be associated with low autonomic arousal. With this view in mind, we performed a scoping review of the biological correlates of PA and identified 74 relevant articles. Physiological findings indicated a robust association between PA and reduced resting heart rate, and to a lesser extent a relationship between PA and decreased heart rate and skin conductance reactivity, perhaps indicating dampened sympathetic function. The twin literature identified PA as a heritable trait, but little evidence implicates specific genes in the pathogenesis of PA. Neuroimaging studies of PA pinpoint impaired amygdala function in the assessment and conditioning of aversive stimuli, which may influence the establishment of behavioral patterns. Nodes of the default mode network were identified as possible neural correlates of PA, suggesting that altered function of this network may be involved in the genesis of PA. Given the overlap of PA with reactive aggression and the overall behavioral complexity of PA, it is clear that multiple endophenotypes of PA exist. This comprehensive review surveys the most salient neurobiologically informed research on PA.

Trajectories of brain development reveal times of risk and factors promoting resilience to alcohol use during adolescence

Alcohol use disorder (AUD) is recognized as harmful for the developing brain. Numerous studies have sought environmental and genetic risk factors that predict the development of AUD, but recently identified resilience factors have emerged as protective. This chapter reviews normal processes of brain development in adolescence and emerging adulthood, delineates disturbed growth neurotrajectories related to heavy drinking, and identifies potential endogenous, experiential, and time-linked brain markers of resilience. For example, concurrent high dorsolateral prefrontal activation serving inhibitory control and low nucleus accumbens activation serving reward functions engender positive adaptation and low alcohol use. Also discussed is the role that moderating factors have in promoting risk for or resilience to AUD. Longitudinal research on the effects of all levels of alcohol drinking on the developing brain remains crucial and should be pursued in the context of resilience, which is a promising direction for identifying protective biomarkers against developing AUDs.

Longitudinal Links between Adolescent and Peer Conduct Problems and Moderation by a Sensitivity Genetic Index

The most extensively studied influence on adolescent conduct problem behaviors is peers, and the literature points to genetics as one source of individual differences in peer influence. The purpose of this study was to test the hypothesis that an environmental sensitivity genetic index comprised of DRD4, 5-HTTLPR, and GABRA2 variation would moderate the association between peer and adolescent conduct problems. Latent growth modeling was applied to PROSPER project longitudinal data from adolescents and their peers. Results showed the hypothesis was supported; adolescents with more copies of putative sensitivity alleles were more strongly influenced by their peers. The interaction form was consistent with differential susceptibility in follow-up analyses. Strengths and weaknesses of genetic aggregates for sensitivity research are discussed.

Time-varying Effects of GABRG1 and Maladaptive Peer Behavior on Externalizing Behavior from Childhood to Adulthood: Testing Gene × Environment × Development Effects

Engagement in externalizing behavior is problematic. Deviant peer affiliation increases risk for externalizing behavior. Yet, peer effects vary across individuals and may differ across genes. This study determines gene × environment × development interactions as they apply to externalizing behavior from childhood to adulthood. A sample (n = 687; 68% male, 90% White) of youth from the Michigan Longitudinal Study was assessed from ages 10 to 25. Interactions between γ-amino butyric acid type A receptor γ1 subunit (GABRG1; rs7683876, rs13120165) and maladaptive peer behavior on externalizing behavior were examined using time-varying effect modeling. The findings indicate a sequential risk gradient in the influence of maladaptive peer behavior on externalizing behavior depending on the number of G alleles during childhood through adulthood. Individuals with the GG genotype are most vulnerable to maladaptive peer influences, which results in greater externalizing behavior during late childhood through early adulthood.

The Impact of Genes on Adolescent Substance Use: A Developmental Perspective

Purpose

This review discusses the importance of understanding the impact of genetic factors on adolescent substance use within a developmental framework. Methods for identifying genetic factors, relevant endophenotypes and intermediate phenotypes, and gene-environment interplay effects will be reviewed.

Findings

Prior work supports the role of polygenic variation on adolescent substance use. Mechanisms through which genes impact adolescent phenotypes consist of differences in neural structure and function, early temperamental differences, and problem behavior. Gene-environment interactions are characterized by increased vulnerability to both maladaptive and adaptive contexts.

Summary

Developmental considerations in genetic investigations highlight the critical role that polygenic variation has on adolescent substance use. Yet, determining what to do with this information, especially in terms of personalized medicine, poses ethical and logistic challenges.

Developmental Change in Adolescent Delinquency: Modeling Time-Varying Effects of a Preventative Intervention and GABRA2 Halpotype Linked to Alcohol Use

Better integrating human developmental factors in genomic research is part of a set of next steps for testing gene-by-environment interaction hypotheses. This study adds to this work by extending prior research using time-varying effect modeling (TVEM) to evaluate the longitudinal associations between the PROSPER preventive intervention delivery system, a GABRA2 haplotype linked to alcohol use, and their interaction on adolescent delinquency. Logistic and Poisson analyses on eight waves of data spanning ages 11 to 19 (60% female, 90% Caucasian) showed the intervention reduced delinquency from ages 13 to 16. Moreover, interaction analysis revealed that the effect of the multicomponent intervention was significantly greater for T-allele carriers of the GABRA2 SNP rs279845, but only during the 13 to 16 age period. The results are discussed in terms of adolescent delinquency normativeness, implications for preventive intervention research, and the utility of incorporating development in GxE research.

Adolescent Brain Development: Implications for Understanding Risk and Resilience Processes Through Neuroimaging Research

This special section focuses on research that utilizes neuroimaging methods to examine the impact of social relationships and socioemotional development on adolescent brain function. Studies include novel neuroimaging methods that further our understanding of adolescent brain development. This special section has a particular focus on how study findings add to our understanding of risk and resilience. In this introduction to the special section, we discuss the role of neuroimaging in developmental science and provide a brief review of neuroimaging methods. We present key themes that are covered in the special section articles including: (1) emerging methods in developmental neuroscience, (2) emotion-cognition interaction, and (3) the role of social relationships in brain function. We conclude our introduction with future directions for integrating developmental neuroscience into the study of adolescence, and highlight key points from the special section's commentaries which include information on the landmark Adolescent Brain Cognitive Development (ABCD) study.

Broadening the Impact of Developmental Neuroscience on the Study of Adolescence

Having been a significance source of the renewed interested in the adolescent period, developmental neuroscience now needs to build upon its achievements to date and expand in several areas in order to broaden its impact upon the field. Addressing both typical and atypical development, examining the interaction between brain development and the social environment, studying change over time, and including attention to population diversity can help to produce a truly integrative science of adolescent development. The papers in the special section provide nice examples of how developmental neuroscience can make such expansions and continue to contribute to the field in the years to come.