While converging evidence suggests that both environmental and genetic factors underlie variations in diurnal cortisol, the extent to which these sources of influence vary according to socioeconomic status (SES) has seldom been investigated, particularly in adolescence. To investigate whether a distinct genetic and environmental contribution to youth’s diurnal cortisol secretion emerges according to family SES and whether the timing of these experiences matters. Participants were 592 twin pairs, who mostly came from middle-income and intact families and for whom SES was measured in childhood and adolescence. Diurnal cortisol was assessed at age 14 at awakening, 30 min later, in the afternoon and evening over four nonconsecutive days. SES–cortisol phenotypic associations were specific to the adolescence period. Specifically, higher awakening cortisol levels were detected in wealthier backgrounds, whereas higher cortisol awakening response (CAR) and diurnal changes were present at both ends of the SES continuum. Moreover, smaller genetic contributions emerged for awakening cortisol in youth from poorer compared to wealthier backgrounds. The results suggest that the relative contribution of inherited factors to awakening cortisol secretion may be enhanced or suppressed depending on the socio-family context, which may help to decipher the mechanisms underlying later adjustment.

Stress associated with caring for a mentally ill spouse can adversely affect the health status of caregivers and their children. Adding to the stress of caregiving is the stigma often placed against spouses and children of people with mental illness. Contrary to mental illness, many physical disorders such as cancer may be less stigmatized (expect pulmonary cancer). In this study, we measured externalized and internalized stigma, as well as psychological (depressive symptoms and stressful life events) and physiological (basal salivary cortisol levels) markers of stress in 115 spouses and 154 children of parents suffering from major depressive disorder, cancer, or no illness (control group). The results show that spouses and children from families with parental depression present significantly more externalized stigma than spouses and children from families with parental cancer or no illness, although we find no group differences on internalized stigma. The analysis did not show a significant group difference either for spouses or their children on depressive symptomatology, although spouses from the parental depression group reported greater work/family stress. Finally, we found that although for both spouses children the awakening cortisol response was greater on weekdays than on weekend days, salivary cortisol levels did not differ between groups. Bayes factor calculated on the null result for cortisol levels was greater than 100, providing strong evidence for the null hypothesis H0. Altogether, these results suggest an impact of stigma toward mental health disorder on psychological markers of stress but no impact of stigma on physiological markers of stress. We suggest that these results may be due to the characteristics of the families who participated in the present study.

This paper is a revised and updated edition of a previous description of the Quebec Newborn Twin Study (QNTS), an ongoing prospective longitudinal follow-up of a birth cohort of twins born between 1995 and 1998 in the greater Montreal area, Québec, Canada. The goal of QNTS is to document individual differences in the cognitive, behavioral, and social-emotional aspects of developmental health across childhood, their early genetic and environmental determinants, as well as their putative role in later social-emotional adjustment, school, health, and occupational outcomes. A total of 662 families of twins were initially assessed when the twins were aged 6 months. These twins and their family were then followed regularly. QNTS now has 16 waves of data collected or planned, including 5 in preschool. Over the last 24 years, a broad range of physiological, cognitive, behavioral, school, and health phenotypes were documented longitudinally through multi-informant and multimethod measurements. QNTS also entails extended and detailed multilevel assessments of proximal (e.g., parenting behaviors, peer relationships) and distal (e.g., family income) features of the child’s environment. QNTS children and a subset of their parents have been genotyped, allowing for the computation of a variety of polygenic scores. This detailed longitudinal information makes QNTS uniquely suited for the study of the role of the early years and gene–environment transactions in development.

There is a relative consensus about the detrimental impact of childhood maltreatment on later mental health problems and behavioral difficulties. Prior research suggests that neurophysiological stress mechanisms may partly mediate this association. However, inconsistent findings regarding hypothalamic-pituitary-adrenal axis and sympathetic responses to stress complicate this investigation. Furthermore, the concordance in these two stress systems is not well understood. We tested whether the severity of maltreatment affected the association between maltreatment and cortisol and heart rate (HR) stress responses and the symmetry of these responses. Participants were 155 males (56 maltreated and 99 controls) aged 18 to 35 years. Cortisol and HR were measured in response to the Trier Social Stress Test. Childhood maltreatment, sociodemographic factors, and health-related factors were measured using self-reported questionnaires. Maltreated participants had higher cortisol responses to stress in comparison to controls. However, a shift from moderate to lower to higher cortisol responses was noted as the severity of the experiences increased. Participants exposed to more experiences of maltreatment also showed a greater symmetry between cortisol and HR stress responses. Our findings provide further support for persistent dysregulation of the HPA axis following childhood maltreatment, of which the expression and symmetry with the sympathetic system may change according to the severity of experiences.

Early-onset conduct problems (CP) are a key predictor of adult criminality and poor mental health. While previous studies suggest that both genetic and environmental risks play an important role in the development of early-onset CP, little is known about potential biological processes underlying these associations. In this study, we examined prospective associations between DNA methylation (cord blood at birth) and trajectories of CP (4–13 years), using data drawn from the Avon Longitudinal Study of Parents and Children. Methylomic variation at seven loci across the genome (false discovery rate < 0.05) differentiated children who go on to develop early-onset (n = 174) versus low (n = 86) CP, including sites in the vicinity of the monoglyceride lipase (MGLL) gene (involved in endocannabinoid signaling and pain perception). Subthreshold associations in the vicinity of three candidate genes for CP (monoamine oxidase A [MAOA], brain-derived neurotrophic factor [BDNF], and FK506 binding protein 5 [FKBP5]) were also identified. Within the early-onset CP group, methylation levels of the identified sites did not distinguish children who will go on to persist versus desist in CP behavior over time. Overall, we found that several of the identified sites correlated with prenatal exposures, and none were linked to known genetic methylation quantitative trait loci. Findings contribute to a better understanding of epigenetic patterns associated with early-onset CP.

We investigated the antecedents and consequences of chronic victimization by bullies across a school transition using a genetically sensitive longitudinal design. Data were from the Environmental Risk Longitudinal Twin Study (E-Risk), an epidemiological cohort of 2,232 children. We used mothers' and children's reports of bullying victimization during primary school and early secondary school. Children who experienced frequent victimization at both time points were classed as “chronic victims” and were found to have an increased risk for mental health problems and academic difficulties compared to children who were bullied only in primary school, children bullied for the first time in secondary school, and never-bullied children. Biometric analyses revealed that stability in victimization over this period was influenced primarily by genetic and shared environmental factors. Regression analyses showed that children's early characteristics such as preexistent adjustment difficulties and IQ predicted chronic versus transitory victimization. Family risk factors for chronic victimization included socioeconomic disadvantage, low maternal warmth, and maltreatment. Our results suggest that bullying intervention programs should consider the role of the victims' behaviors and family background in increasing vulnerability to chronic victimization. Our study highlights the importance of widening antibullying interventions to include families to reduce the likelihood of children entering a pathway toward chronic victimization.