Chronic Stressors and Adolescents' Externalizing Problems: Genetic Moderation by Dopamine Receptor D4. The TRAILS Study

Gene-by-Environment Interaction Effects of Social Adversity on Externalizing Behavior in ABCD Youth

This study tested whether multiple domains of social adversity, including neighborhood opportunity/deprivation and life stress, moderate genetic (A), common environmental (C), and unique environmental (E) influences on externalizing behaviors in 760 same-sex twin pairs (332 monozygotic; 428 dizygotic) ages 10-11 from the ABCD Study. Proportion of C influences on externalizing behavior increased at higher neighborhood adversity (lower overall opportunity). A decreased and C and E increased at lower levels of educational opportunity. A increased at lower health-environment and social-economic opportunity levels. For life stress, A decreased and E increased with number of experienced events. Results for educational opportunity and stressful life experiences suggest a bioecological gene-environment interaction pattern such that environmental influences predominate at higher levels of adversity, whereas limited access to healthcare, housing, and employment stability may potentiate genetic liability for externalizing behavior via a diathesis-stress mechanism. More detailed operationalization of social adversity in gene-environment interaction studies is needed.

The Cumulative Impact of Chronic Stressors on Risks of Myocardial Infarction in US Older Adults

OBJECTIVE

This study aimed to investigate the association between cumulative exposure to chronic stressors and the incidence of myocardial infarction (MI) in US older adults.

METHODS

Nationally representative prospective cohort data of adults 45 years and older (n = 15,109) were used to investigate the association between the cumulative number of chronic stressors and the incidence of MI in US older adults. Proportional hazards models adjusted for confounding risk factors and differences by sex, race/ethnicity, and history of MI were assessed.

RESULTS

The median age of participants was 65 years, 714 (4.7%) had a prior MI, and 557 (3.7%) had an MI during follow-up. Approximately 84% of participants reported at least one chronic stressor at baseline, and more than half reported two or more stressors. Multivariable models showed that risks of MI increased incrementally from one chronic stressor (hazard ratio [HR] = 1.28, 95% confidence interval [CI] = 1.20-1.37) to four or more chronic stressors (HR = 2.71, 95% CI = 2.08-3.53) compared with those who reported no stressors. These risks were only partly reduced after adjustments for multiple demographic, socioeconomic, psychosocial, behavioral, and clinical risk factors. In adults who had a prior MI (p value for interaction = .038), we found that risks of a recurrent event increased substantially from one chronic stressor (HR = 1.30, 95% CI = 1.09-1.54) to four or more chronic stressors (HR = 2.85, 95% CI = 1.43-5.69).

CONCLUSIONS

Chronic life stressors are significant independent risk factors for cardiovascular events in US older adults. The risks associated with multiple chronic stressors were especially high in adults with a previous MI.

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.

Maternal care of heterozygous dopamine receptor D4 knockout mice: Differential susceptibility to early-life rearing conditions

The differential susceptibility hypothesis proposes that individuals who are more susceptible to the negative effects of adverse rearing conditions may also benefit more from enriched environments. Evidence derived from human experiments suggests the lower efficacy dopamine receptor D4 (DRD4) 7‐repeat as a main factor in exhibiting these for better and for worse characteristics. However, human studies lack the genetic and environmental control offered by animal experiments, complicating assessment of causal relations. To study differential susceptibility in an animal model, we exposed Drd4^+/− mice and control litter mates to a limited nesting/bedding (LN), standard nesting (SN) or communal nesting (CN) rearing environment from postnatal day (P) 2‐14. Puberty onset was examined from P24 to P36 and adult females were assessed on maternal care towards their own offspring. In both males and females, LN reared mice showed a delay in puberty onset that was partly mediated by a reduction in body weight at weaning, irrespective of Drd4 genotype. During adulthood, LN reared females exhibited characteristics of poor maternal care, whereas dams reared in CN environments showed lower rates of unpredictability towards their own offspring. Differential susceptibility was observed only for licking/grooming levels of female offspring towards their litter; LN reared Drd4^+/− mice exhibited the lowest and CN reared Drd4^+/− mice the highest levels of licking/grooming. These results indicate that both genetic and early‐environmental factors play an important role in shaping maternal care of the offspring for better and for worse.