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Excessive and persistent aggressiveness is the most common behavioral problem that leads to psychiatric referrals among children. While half of the variance in childhood aggression is attributed to genetic factors, the biological mechanism and the interplay between genes and environment that results in aggression remains elusive. The purpose of this systematic review is to provide an overview of studies examining the genetics of childhood aggression irrespective of psychiatric diagnosis. PubMed, PsycINFO, and MEDLINE databases were searched using predefined search terms for aggression, genes and the specific age group. From the 652 initially yielded studies, eighty-seven studies were systematically extracted for full-text review and for further quality assessment analyses. Findings show that (i) investigation of candidate genes, especially of MAOA (17 studies), DRD4 (13 studies), and COMT (12 studies) continue to dominate the field, although studies using other research designs and methods including genome-wide association and epigenetic studies are increasing, (ii) the published articles tend to be moderate in sizes, with variable methods of assessing aggressive behavior and inconsistent categorizations of tandem repeat variants, resulting in inconclusive findings of genetic main effects, gene-gene, and gene-environment interactions, (iii) the majority of studies are conducted on European, male-only or male-female mixed, participants. To our knowledge, this is the first study to systematically review the effects of genes on youth aggression. To understand the genetic underpinnings of childhood aggression, more research is required with larger, more diverse sample sets, consistent and reliable assessments and standardized definition of the aggression phenotypes. The search for the biological mechanisms underlying child aggression will also benefit from more varied research methods, including epigenetic studies, transcriptomic studies, gene system and genome-wide studies, longitudinal studies that track changes in risk/ameliorating factors and aggression-related outcomes, and studies examining causal mechanisms.

Psychopathic traits in youth may lead to adult criminal behaviors/psychopathy. The Val158Met polymorphism of catechol-O-methyltransferase (COMT) may influence the risk for psychopathy-related behaviors, while acting as a biomarker for predicting treatment response to dopaminergic medications. The literature shows inconsistent findings, making the interpretation of COMT’s role difficult. The aims of this article are (i) to conduct a systematic review to analyze the effects of COMT Val158Met on psychopathic traits in children and adolescents, and (ii) to present new evidence on the developmental trajectory of the association of Val158Met and youth psychopathic traits. For the systematic review, a literature search was conducted using PubMed, EMBASE, OVID Medline and PsychINFO with the search terms for psychopathic traits, Val158Met and age of interest. In our genotype study, the COMT Val158Met genotype of 293 youth with European ancestry was analyzed in association with the psychopathy-related behavior scores from the Child Behavior Checklist and the Psychopathy Screening Device. To examine the potential influence of developmental changes, the sample was split into at or above and below age 13, and analyses were performed in males and females separately. The literature search yielded twenty-eight articles to be included in the systematic review, which demonstrated mixed results on the association depending on environmental factors, sex ratios, age groups and behavioral disorder diagnoses. The results from our genotype study revealed that Met homozygous youth in the below age 13 group and conversely Val carrier youth in the above age 13 group were more likely to display psychopathic traits. To our knowledge, this is the first study to systematically review the effects of COMT Val158Met on psychopathic traits in childhood and adolescence, and to provide new evidence on the changing effects of Val158Met on psychopathy-related behaviors with development. Elucidating the role of the COMT genotype in conjunction with the child versus adolescent stage of development for psychopathic traits may help predict treatment response, and may lead to early intervention and prevention strategies.

BackgroundViral respiratory tract infections (vRTIs) are a leading cause of paediatric hospitalisation and healthcare utilisation. Existing syndromic surveillance tools, including the WHO Severe Acute Respiratory Infection definition, demonstrate limited diagnostic accuracy in children whose symptom profiles vary widely. This study aimed to develop a machine learning (ML) model to predict microbiologically confirmed vRTIs in hospitalised children and to evaluate performance across age groups and viral pathogens.MethodsWe conducted a retrospective cross-sectional study of 2050 paediatric patients (<18 years) admitted with acute respiratory infections to two tertiary paediatric hospitals in Canada. Predictors included age, sex, hospital transfer status, chronic comorbidity status and 22 presenting symptoms. The primary outcome was microbiologically confirmed vRTI, determined by multiplex PCR or rapid antigen testing. Six ML algorithms were trained and the best-performing model, identified by area under the receiver operating characteristic curve (auROC), was tested on age subgroups, viral pathogens and sites.ResultsAmong 2050 patients (median (IQR) age 2.4 (0.8–5.2) years), 1831 (89.3%) tested positive, most commonly for respiratory syncytial virus (RSV) (38.7%) and enterovirus/rhinovirus (32.8%). Logistic regression with L2 regularisation demonstrated the best performance (auROC, 0.754; 95% CI 0.697 to 0.808; sensitivity, 69.2%; specificity, 69.9%), with greatest performance among children <1 year (auROC, 0.763) and RSV cases (auROC, 0.727).ConclusionsAn ML-based logistic regression model using admission data accurately predicted paediatric vRTIs, outperforming traditional syndromic surveillance definitions, especially among infants <1 year. By integrating ML models into hospital electronic medical records, healthcare systems can achieve enhanced respiratory virus surveillance, faster outbreak detection, greater diagnostic efficiency and improved pandemic preparedness.

Youth externalizing behaviours are serious public health concerns, with significant negative outcomes. These disruptive behaviours exhibit high heritability, with putative influences from the monoamine oxidase A (MAOA) and catecholamine-O-methyltransferase (COMT) genes. Literature points to a variable effect of genes on externalizing behaviours through development. This study aimed to examine the influence of development on the association between the genetic variants regulating the MAOA and COMT genes and externalizing behaviours in youth. Results from the cross-sectional (n=278-337) sample demonstrated that both MAOA-uVNTR and COMT Val158Met exhibit a significant change in the risk variant between childhood and adolescence for males, but not in females. Conversely, there was no significant interaction effect between Val158Met and assessment time on externalizing behaviours in the larger longitudinal ABCD (n=2363) sample. While replications with longer longitudinal studies are necessary, these results underscore the importance of considering the developmental stages when analyzing genetic risk of externalizing behaviours.

Psychopathic traits can lead to violence, making it a serious public health concern. Genetic factors contribute to the aetiology of psychopathy. We examined whether monoamine oxidase A (MAOA-uVNTR) was associated with psychopathic traits measured quantitatively from controls through clinically aggressive youth (n = 336). Subjects were sub-categorized into at or above, and below age 13 years. Results reveal that males below age 13 were more likely to display psychopathic traits with the MAOA long variant, whereas males above age 13 years were more likely to display with the short variant. This suggests that developmental factors may be crucial for understanding the role of the MAOA polymorphism in psychopathic traits in males.