Exposure to bullying victimization is associated with a wide-range of short and long-term adverse outcomes. However, the extent to which these associations reflect a causal influence of bullying victimization remains disputed. Here, we aimed to provide the most stringent evidence regarding the consequences of bullying victimization by meta-analyzing all relevant quasi-experimental (QE) studies. Multilevel random effects models and metaregression were employed to (a) estimate the pooled QE-adjusted effect size (Cohen d) for bullying victimization on outcomes and to (b) evaluate potential sources of heterogeneity. A total of 16 studies were included. We derived 101 QE-estimates from three different methods (twin design, fixed effects analysis, and propensity score matching) for three pools of outcomes (internalizing symptoms, externalizing symptoms, academic difficulties). QE-adjusted effects were small for internalizing symptoms (dadjusted = 0.27, 95% CI [0.05, 0.49]), and smaller for externalizing symptoms (dadjusted = 0.15, 95% CI [0.10, 0.21]) and academic difficulties (dadjusted = 0.10, 95% CI [0.06, 0.13]). Accounting for a shared rater effect between the exposure and the outcome further reduced the effect for internalizing (dnonshared rater = 0.14, 95% CI [0.05, 0.23]) and externalizing symptoms (dnonshared rater = 0.06, 95% CI [0.01, 0.11]). Finally, the adverse effects declined in the long-term, most markedly for internalizing symptoms (dlong-term = 0.06, 95% CI [-0.01, 0.13]). Based on the most stringent evidence available to date, findings indicate that bullying victimization may causally impact children's wellbeing in the short-term, especially anxiety and depression levels. The reduction of adverse effects over time highlights the potential for resilience in individuals who have experienced bullying. Secondary preventive interventions in bullied children should therefore focus on resilience and address children's preexisting vulnerabilities. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

It is unclear whether maltreatment types exert common or specific effects on mental health. In the current study, we aimed to systematically characterize the unique, shared and cumulative effects of maltreatment types on psychiatric symptoms, using data drawn from a community sample of high-risk youth (n=204, M=18.85). Analyses controlled for a range of potentially confounding variables, including socio-demographic variables, neighbourhood deprivation and levels of community violence exposure. Outcome measures included multi-informant reports of internalizing difficulties, as well as data on externalizing problems and trauma-related symptoms. We found that (i) consistent with previous studies, maltreatment types were highly interrelated and frequently co-occurred; (ii) symptom severity linearly increased with the number of maltreatment types experienced (more so for self-report vs informant ratings); and (iii) while most forms of maltreatment were significantly associated with mental health outcomes when examined individually, few unique effects were observed when modelling maltreatment types simultaneously, pointing to an important role of shared variance in driving maltreatment effects on mental health. Emotional abuse emerged as the main independent predictor of psychiatric symptomatology - over and above other maltreatment types - and this effect was comparable for males and females (i.e. no significant interaction with sex). Findings contribute to a better understanding of heterogeneity in individual responses to maltreatment.

Conduct problems are one of the most common reasons for a childhood referral to mental health and educational services, and they represent a substantial public health cost.¹ Children with conduct problems are at risk for developing life-course-persistent antisocial problems, as well as other mental and physical health problems.^2,3 Decades of developmental psychopathology research have shown that children with conduct problems are a heterogeneous group.⁴ The inclusion of callous-unemotional (CU) traits as a conduct disorder specifier to the next edition of the DSM-5 is currently being considered.⁵ Callous-unemotional traits (eg, lack of guilt and empathy) distinguish a particularly problematic and severe group of children with conduct disorder.⁴ Twin studies have suggested that conduct problems coupled with CU traits are highly heritable, while conduct problems in children without CU traits appear to be driven primarily by environmental influences.^6,7

One-third of children report having been bullied by their peers according to estimates from the World Health Organization.¹Childhood exposure to bullying refers to the experience of being a target of hostile behavior from other children (eg, being physically or verbally attacked)²; it is associated with a wide range of long-lasting adverse outcomes, particularly mental health outcomes such as anxiety.^3-5 A key challenge for current research is to probe the causal nature of these widespread associations.

Youth with high callous-unemotional traits (CU) are at risk for early-onset and persistent conduct problems. Research suggests that there may be different developmental pathways to CU (genetic/constitutional vs environmental), and that the absence or presence of co-occurring internalizing problems is a key marker. However, it is unclear whether such a distinction is valid. Intermediate phenotypes such as DNA methylation, an epigenetic modification regulating gene expression, may help to clarify etiological pathways. This is the first study to examine prospective inter-relationships between environmental risk (prenatal/postnatal) and DNA methylation (birth, age 7 and 9) in the prediction of CU (age 13), for youth low vs high in internalizing problems. We focused on DNA methylation in the vicinity of the oxytocin receptor (OXTR) gene as it has been previously implicated in CU. Participants were 84 youth with early-onset and persistent conduct problems drawn from the Avon Longitudinal Study of Parents and Children. For youth with low internalizing problems (46%), we found that (i) OXTR methylation at birth associated with higher CU (age 13) as well as decreased experience of victimization during childhood (evocative epigenetic-environment correlation; birth–age 7), (ii) higher prenatal parental risks (maternal psychopathology, criminal behaviors, substance use) associated with higher OXTR methylation at birth and (iii) OXTR methylation levels were more stable across time (birth–age 9). In contrast, for youth with high internalizing problems, CU were associated with prenatal risks of an interpersonal nature (that is, intimate partner violence, family conflict) but not OXTR methylation. Findings support the existence of distinct developmental pathways to CU.