The CODATwins Project: The Current Status and Recent Findings of COllaborative Project of Development of Anthropometrical Measures in Twins.

The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural-geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.

Environmental influence of problematic social relationships on adolescents' daily cortisol secretion: a monozygotic twin-difference study.

BACKGROUND: This study investigated the potential environmental effects of peer victimization and the quality of relationships with parents and friends on diurnal cortisol secretion in mid-adolescence. METHOD: This study used the monozygotic (MZ) twin-difference design to control for genetic effects and thus estimate the unique environmental influences on diurnal cortisol. Participants were 136 MZ twin pairs (74 female pairs) for whom cortisol was assessed four times per day over four collection days grouped in a 2-week period in grade 8 (mean age = 14.07 years). Participants also provided self-reports of peer victimization from grade 4 to grade 8 and of the relationship quality with the mother, father and best friend in grade 8. RESULTS: The expected pattern of diurnal cortisol secretion was observed, with high levels at awakening followed by an increase 30 min later and a progressive decrease subsequently. Controlling for a host of confounders, only within-twin pair differences in peer victimization and a problematic relationship with the mother were significantly linked to twin differences in diurnal cortisol secretion. Specifically, whereas a more problematic mother-child relationship was associated with morning cortisol secretion, peer victimization was linked to cortisol secretion later in the day (diurnal slope). CONCLUSIONS: Controlling for genetic influences and other confounders, stressful relationships with peers and the mother exert unique and time-specific environmental influences on the pattern of diurnal cortisol secretion in mid-adolescence.

A longitudinal twin study of physical aggression during early childhood: evidence for a developmentally dynamic genome.

BACKGROUND: Physical aggression (PA) tends to have its onset in infancy and to increase rapidly in frequency. Very little is known about the genetic and environmental etiology of PA development during early childhood. We investigated the temporal pattern of genetic and environmental etiology of PA during this crucial developmental period. METHOD: Participants were 667 twin pairs, including 254 monozygotic and 413 dizygotic pairs, from the ongoing longitudinal Quebec Newborn Twin Study. Maternal reports of PA were obtained from three waves of data at 20, 32 and 50 months. These reports were analysed using a biometric Cholesky decomposition and linear latent growth curve model. RESULTS: The best-fitting Cholesky model revealed developmentally dynamic effects, mostly genetic attenuation and innovation. The contribution of genetic factors at 20 months substantially decreased over time, while new genetic effects appeared later on. The linear latent growth curve model revealed a significant moderate increase in PA from 20 to 50 months. Two separate sets of uncorrelated genetic factors accounted for the variation in initial level and growth rate. Non-shared and shared environments had no effect on the stability, initial status and growth rate in PA. CONCLUSIONS: Genetic factors underlie PA frequency and stability during early childhood; they are also responsible for initial status and growth rate in PA. The contribution of shared environment is modest, and perhaps limited, as it appears only at 50 months. Future research should investigate the complex nature of these dynamic genetic factors through genetic-environment correlation (r GE) and interaction (G×E) analyses.

The quality of adolescents' friendships: associations with mothers' interpersonal relationships, attachments to parents and friends, and prosocial behaviors.

Adolescents' friendship quality and observed emotional expression with their best friends were predicted from reports of their mother's interpersonal relationships-specifically the quality of her marriage and social network. Two models explaining these relationships received support. Consistent with an Attachment Theory model, adolescents' perceptions of marital quality predicted attachment security with mother, father and friends. Security of attachment to friends in turn predicted best friendship quality, but not affective behavior with the friend. A Social Learning Theory model was also supported, in which perceptions of both marital quality and mother's social network quality predicted adolescents' prosocial behavior. Prosocial behavior in turn predicted both best friendship quality and affective behavior with the friend.

Reactive and proactive aggression: predictions to physical violence in different contexts and moderating effects of parental monitoring and caregiving behavior.

This study aimed at (a) comparing the links of proactive and reactive aggression at 13 years of age to delinquency-related violence and dating violence at ages 16 and 17, and (b) examining the moderating effects of parental supervision, and mother's and father's warmth and caregiving behaviors on these links. Based on a sample of 525 Caucasian boys, the results showed that proactive aggression uniquely predicted delinquency-related violence, whereas reactive aggression uniquely predicted later dating violence. The relation between proactive aggression and delinquency-related violence, however, was moderated by parental supervision. The relation between reactive aggression and dating violence was moderated by mother's warmth and caregiving behavior. The implications of the findings for the theoretical and practical distinction between proactive and reactive aggression are discussed.

Developmental profiles of peer social preference over the course of elementary school: associations with trajectories of externalizing and internalizing behavior.

Using a new longitudinal clustering technique, this study aimed to (a) empirically identify groups of children with distinct longitudinal profiles of peer social preference during elementary school; (b) compare these groups regarding their longitudinal pattern of classification into J. D. Coie, K. A. Dodge, and H. Coppotelli's (CDC; 1982) sociometric categories; and (c) compare these groups regarding their longitudinal trajectories of antisocial, hyperactive, and anxious behavior. Based on 299 children, 3 groups were identified: a stable popular group, a stable average group, and an unpopular group whose social preference decreased over time. Each of the groups showed considerable overlap over time with their closest corresponding CDC category (popular, average, rejected). Growth curve analyses showed that externalizing and internalizing behavior generally decreased over time, but overall means and the rates of decrease differed in the 3 groups.

Gambling, delinquency, and drug use during adolescence: mutual influences and common risk factors.

The purpose of this study was threefold: (1) to assess the possible mutual influence between gambling, substance use, and delinquency over a two-year period during mid adolescence, (2) to test whether variables that are usually predictive of delinquency and substance use also predict gambling, and (3) to test whether the links between the three problem behaviors could be, at least partially, accounted for by common antecedent factors (impulsivity, parental supervision, and deviant friends) assessed during early adolescence. Seven hundred and seventeen boys participated in the study. Impulsivity, parental supervision, and friends' deviancy were collected when participants were 13 and 14 years of age. Gambling, substance use, and delinquency were collected through self-reports at ages 16 and 17 years. Results showed no influence or modest influence of problem behaviors on each other from age 16 to age 17 years, once current links and auto-correlations were accounted for. Conversely, the cross-sectional links between the three problem behaviors at each age were moderately high. Impulsivity, low parental supervision, and deviant friends were predictively related to each problem. Finally, a significant, although modest, portion of the covariance between the three problem behaviors was accounted for by these three predictors. The present findings contradict previous findings about the influence of gambling on other problem behaviors and support the notion of a "general problem behavior syndrome" fed by generic risk factors.

Influence of deviant friends on delinquency: searching for moderator variables.

Three categories of potential moderators of the link between best friend's deviancy and boys' delinquency during early adolescence were investigated: personal (i.e., disruptiveneness profile during childhood, attitude toward delinquency), familial (i.e., parental monitoring, attachment to parents), and social (i.e., characteristics of other friends). Best friend's and other friends' deviancy were assessed during preadolescence through the use of peer ratings. Potential moderators were assessed at the same age period with teacher ratings or self-reports. Finally, delinquent behaviors were assessed at ages 13 and 14, as well as age 10 for control purposes, with self-reports. Results showed that boys' disruptiveness profiles during childhood, attachment to parents, and attitude toward delinquency moderated the link between best friend's deviancy and later delinquent behaviors. Other friends' deviancy and parental monitoring had main effects but no moderating effects. These results help clarify the conditions under which exposure to a deviant best friend can influence boys' delinquent behaviors. They also help to reconcile different theoretical explanations of the role of deviant friends in the development of delinquency.

Disruptive behavior, peer association, and conduct disorder: testing the developmental links through early intervention.

We tested three competing models regarding the role of deviant friends in the trajectory linking early disruptiveness with later conduct problems through the use of a preventive intervention program. The program was implemented during the second and third grade. One model predicted that the program would positively affect later conduct problems by facilitating nondeviant peer association during early adolescence. The second model predicted a direct impact of the program on later conduct problems through the reduction of early disruptiveness. The third model predicted an interaction between postintervention disruptiveness and association with less deviant friends. The results showed that the program's effects on later conduct problems were mediated by the reduction in disruptiveness and by the association with less deviant friends. However, the positive effect of associating with less deviant friends depended on whether children's disruptiveness had been reduced or not by their participation in the program, thus supporting the third model. We recommend using intervention studies to test developmental models.