Objective. The transmission of anxiety within families is well-recognised, but the underlying processes are poorly understood. Twin studies of adolescent anxiety demonstrate both genetic and environmental influence, and multiple aspects of parenting are associated with offspring anxiety. To date, the Children-ofTwins design has not been used to evaluate the relative contributions of genetic versus direct transmission of anxiety from parents to their offspring. Method. Anxiety and neuroticism measures were completed by 385 monozygotic and 486 dizygotic same-sex twin families (37% male twin pair families) from the Twin and Offspring Study in Sweden (TOSS). Structural equation models tested for the presence of both genetic and environmental transmission from one generation to the next. Results. For both anxiety and neuroticism the models provide support for significant direct environmental transmission from parents to their adolescent offspring. In contrast there was no evidence of significant genetic transmission. Conclusions. The association between parental and offspring anxiety largely arises due to a direct association between parents and their children independent of genetic confounds. The lack of genetic transmission may reflect there being different genetic effects on these traits in adolescence and adulthood. Direct environmental transmission is in line with developmental theories of anxiety suggesting that children and adolescents learn anxious behaviours from their parents via a number of pathways such as modelling. Future analyses should combine children-of-twins data with child twin data in order to examine whether this direct effect solely represents parental influences on the offspring or whether it also includes child/adolescent anxiety evoking parental anxiety.

Environmental factors shared by co-twins affect BMI in childhood, but little evidence for their contribution was found in late adolescence. Our results suggest that genetic factors play a major role in the variation of BMI in adolescence among populations of different ethnicities exposed to different environmental factors related to obesity.

Parental psychopathology, parenting style, and the quality of intra-familial relationships are all associated with child mental health outcomes. However, most research can say little about the causal pathways underlying these associations. This is because most studies are not genetically informative and are therefore not able to account for the possibility that associations are confounded by gene-environment correlation. That is, biological parents provide not only a rearing environment for their child but also contribute 50% of their genes. Any associations between parental phenotype and child phenotype are therefore potentially confounded. One technique for disentangling genetic from environmental effects is the Children-of-Twins (CoT) method. This involves using datasets comprising twin parents and their children to distinguish genetic from environmental associations between parent and child phenotypes. The CoT technique has grown in popularity in the last decade and we predict that this surge in popularity will continue. In the present article we explain the CoT method for those unfamiliar with its use. We present the logic underlying this approach, discuss strengths and weaknesses and highlight important methodological considerations for researchers interested in the CoT method. We also cover variations on basic CoT approaches, including the extended-CoT method, capable of distinguishing forms of geneenvironment correlation. We then present a systematic review of all of the behavioral CoT studies published to date. These studies cover such diverse phenotypes as psychosis, substance abuse, internalizing, externalizing, parenting and marital difficulties. In reviewing this literature we highlight past applications, identify emergent patterns, and suggest avenues for future research.Keywords: children-of-twins; gene-environment correlation; intergenerational transmission; parenting; psychiatric epidemiology.Theories of parenting propose that parents impact the development of their children in a variety of ways: At one level parental characteristics are predictive of child characteristics -many traits tend to run in families and this is often interpreted as evidence for the impact of parent behavior on child development. For example, anxious parents often rear anxious children (Murray et al., 2008) and it has been suggested that this is because children learn such behavior from their parents (Murray et al., 2008;Rachman, 1977;. Proponents of social learning theory (Bandura, 1977) might suggest that this learning occurs via processes of imitation and modelling, and evidence also indicates that the learning process can be more direct and involve the verbal transmission of information from parent to child (Field & Purkis, 2011).Although children may learn behaviors through imitating and listening to their parents, parents often seek to influence their children's behavior in more direct ways, through the parenting behaviors that they direct towards their child. For example, the punishment and praise of chil...

BackgroundPrevious studies have found significant associations between maternal prenatal and postpartum depression and child behavior problems (CBP). The present study investigates whether associations remain in a prospective, longitudinal design adjusted for familial confounding.MethodsThe sample comprised 11,599 families including 17,830 siblings from the Norwegian Mother and Child Cohort study. Mothers reported depressive symptoms at gestational weeks 17 and 30, as well as 6 months, 1.5, 3, and 5 years postpartum. Fathers’ depression was measured at gestational week 17. At the last three time‐points, child internalizing and externalizing problems were concurrently assessed. We performed multilevel analyses for internalizing and externalizing problems separately, using parental depression as predictors. Analyses were repeated using a sibling comparison design to adjust for familial confounding.ResultsAll parental depressive time‐points were significantly and positively associated with child internalizing and externalizing problems. After sibling comparison, however, only concurrent maternal depression was significantly associated with internalizing [estimate = 2.82 (1.91–3.73, 95% CI)] and externalizing problems [estimate = 2.40 (1.56–3.23, 95% CI)]. The effect of concurrent maternal depression on internalizing problems increased with child age.ConclusionsOur findings do not support the notion that perinatal maternal depression is particularly detrimental to children's psychological development, as the most robust effects were found for maternal depression occurring during preschool years.

Height variation is known to be determined by both genetic and environmental factors, but a systematic description of how their influences differ by sex, age and global regions is lacking. We conducted an individual-based pooled analysis of 45 twin cohorts from 20 countries, including 180,520 paired measurements at ages 1–19 years. The proportion of height variation explained by shared environmental factors was greatest in early childhood, but these effects remained present until early adulthood. Accordingly, the relative genetic contribution increased with age and was greatest in adolescence (up to 0.83 in boys and 0.76 in girls). Comparing geographic-cultural regions (Europe, North-America and Australia, and East-Asia), genetic variance was greatest in North-America and Australia and lowest in East-Asia, but the relative proportion of genetic variation was roughly similar across these regions. Our findings provide further insights into height variation during childhood and adolescence in populations representing different ethnicities and exposed to different environments.