Cannabis use is a heritable trait that has been associated with adverse mental health outcomes. In the largest genome-wide association study (GWAS) for lifetime cannabis use to date (N = 184,765), we identified eight genome-wide significant independent single nucleotide polymorphisms in six regions. All measured genetic variants combined explained 11% of the variance. Gene-based tests revealed 35 significant genes in 16 regions, and S-PrediXcan analyses showed that 21 genes had different expression levels for cannabis users versus nonusers. The strongest finding across the different analyses was CADM2, which has been associated with substance use and risk-taking. Significant genetic correlations were found with 14 of 25 tested substance use and mental health-related traits, including smoking, alcohol use, schizophrenia and risk-taking. Mendelian randomization analysis showed evidence for a causal positive influence of schizophrenia risk on cannabis use. Overall, our study provides new insights into the etiology of cannabis use and its relation with mental health.

The authors explored the utility of the Difficulties in Emotion Regulation Scale (DERS) in assessing adolescents' emotion regulation. Adolescents (11-17 years; N = 870) completed the DERS and measures of externalizing and internalizing problems. Confirmatory factor analysis suggested a similar factor structure in the adolescent sample of the authors as demonstrated previously among adults. Furthermore, results indicated no gender bias in ratings of DERS factors on three scales (as evidenced by strong factorial gender invariance) and limited gender bias on the other three scales (as evidenced by metric invariance). Female adolescents scored higher on four of six DERS factors than male adolescents. DERS factors were meaningfully related to adolescents' externalizing and internalizing problems. Results suggest that scores on the DERS show promising internal consistency and validity in a community sample of adolescents.

A developmental cascade model linking symptoms of externalizing and internalizing psychopathology through three indices of peer relational difficulty (peer rejection, peer victimization, friendedness) was tested in a general population sample of 653 children followed annually from kindergarten to fourth grade. Rejection and victimization linked kindergarten externalizing problems with fourth-grade internalizing problems. Transactional links between rejection and victimization were found. In addition, peer rejection added to the development of externalizing problems. Friendedness did not add to the development of externalizing or internalizing problems. Cascade paths were similar for boys and girls. Over the period of kindergarten to fourth grade, psychopathology and peer relations become entangled, and the dynamic interplay between multiple manifestations of poor peer relations ultimately adds to the development of both externalizing and internalizing problems and their cross-time relation. Implications for research and prevention are discussed.

This study explored whether early elementary school aged children's externalizing problems impede academic functioning and foster negative social experiences such as peer victimization, thereby making these children vulnerable for developing internalizing problems and possibly increasing their externalizing problems. It also explored whether early internalizing problems contributed to an increase in externalizing problems. The study examined 1,558 Canadian children from ages 6 to 8years. Externalizing and internalizing problems, peer victimization, and school achievement were assessed annually. Externalizing problems lead to academic underachievement and experiences of peer victimization. Academic underachievement and peer victimization, in turn, predicted increases in internalizing problems and in externalizing problems. These pathways applied equally to boys and girls. No links from internalizing to externalizing problems were found.