Early life is a sensitive period when microbiota-gut-brain interactions may have important impact on development. This study investigated the associations of the gut microbiota in the first three years of life (two, six, and 12 weeks, and one and three years) with problem behavior and executive functions in N = 64 three-year-old children. Higher relative abundance of Streptococcus at the age of two weeks, as well as its trajectory over time (including ages two, six and 12 weeks, and one and three years), was related to worse executive functions. Higher relative abundance of [Ruminococcus] torques group at the age of three years, as well as its trajectory from one to three years, was associated with less internalizing behavior. Besides, several robust age-specific associations were identified: higher Bifidobacterium relative abundance (age three years) was associated with more internalizing and externalizing issues; higher Blautia relative abundance (age three years) was linked to less internalizing behavior; and increased relative abundance of an unidentified Enterobacteriaceae genus (age two weeks) was related to more externalizing behavior. Our findings provide important longitudinal evidence that early-life gut microbiota may be linked to behavioral and cognitive development in low-risk children.

The objective is to highlight the clinical and social outcomes among adults who suffered from Attention-Deficit Hyperactivity Disorder (ADHD) in their childhood/adolescence. PubMed, PsycINFO, and Scopus databases were searched for prospective studies published during the last 5 years addressing patients with ADHD in childhood/adolescence followed-up to adulthood. We also included studies published before 2015 reported in other reviews with similar outcomes. Thousand four-hundred and eighty-five studies were identified, but only 39 were included for qualitative analysis and 27 for quantitative analysis. Overall, we found that ADHD persisted into adulthood with a mean rate of 43% and was mainly associated with both substance/alcohol use disorders and antisocial behavior and, less frequently, with anxiety and depressive disorders. The prevalence of persistent ADHD in adulthood reported by studies published after 2011 (55%) was higher than that reported by studies published previously from 1985 to 2011 (34%), suggesting a greater focus on ADHD in recent years. Our results highlight that ADHD can be considered not only a neurodevelopmental disorder, but also a persistent and complex condition, with detrimental consequences for quality of life in adulthood.

Problem behaviors are of increasing public health concern. Twin studies have revealed substantial genetic and environmental influences on children's behavior, and examining birth-weight difference could allow the identification of the specific contribution of multiple non-shared prenatal environmental factors. The Twins and Multiple Births Association Heritability Study, a UK, volunteer-based study, recruited mothers of twins aged 18 months to 5 years; 960 twins (480 pairs) were included in the analysis. Twins’ mothers answered questions relative to their pregnancy and their twins’ characteristics, and completed the Child Behavior Checklist (CBCL) 1½–5. The association between the absolute birth-weight difference and each CBCL scale's score difference was analyzed by means of multiple linear regressions. Expected mean CBCL score differences were calculated. In monozygotic (MZ) twins, statistically and clinically significant associations were found between intrapair birth-weight difference and difference in total problems, internalizing problems, and emotional reactiveness. No significant results were observed neither in dizygotic (DZ) twins when analyzed as a separate group nor in MZ and DZ twins combined. The results of the present study suggest that with increasing the absolute birth-weight difference, the intrapair difference in total problems, internalizing behaviors and emotionality increases, with smaller twins being at major risk for later behavior problems. Moreover, these results suggest a causal association between birth weight and behavior development.

Child Behavior Checklist questionnaires (Achenbach, 1992), filled in separately by mothers and fathers, were collected for an effective sample of 3501 Dutch 3-year-old twin pairs. To disentangle the child's phenotype from that of the rater, two contrasting models were fitted to the data. One model, called a Rater Bias model, is based on the assumption that both parents assess exactly the same behaviors in the child. A weaker alternative of this model, called a Psychometric model, assumes that apart from these common behavioral views, each parent also assesses a unique aspect of the child's behavior. A Psychometric model fitted the data of both Internalizing and Externalizing scales significantly better than a Rater Bias model. This implied that each parent provided unique information from his or her own perspective, apart from the common behavioral view. Using this best fitting model, the etiology of both the Internalizing and Externalizing scales was studied. Common factors (influencing behaviors similarly assessed by both parents) were more important than unique factors (influencing behaviors uniquely assessed by one parent). Common genetic factors explained about 50% of the variance of both scales, indicating a possible inborn vulnerability to childhood psychopathology. Common environmental factors not shared between twins (free of unreliability and error) explained around 14% of both scales, suggesting the importance of pure idiosyncratic experiences even for children as young as 3 years. Common environmental factors shared between twins (unconfounded by rater bias) were only found for the Externalizing scale, explaining 18% of the variance. Rater bias and unreliability, if present in the data, were included in the estimates of the unique factors. Unique genetic, shared, and nonshared environmental factors each explained around 8% of the variance for both scales. These small effects could be detected because of the large sample of twin pairs used.

This study compares standardized measures of childhood behavior problems in a community-based twin sample with those for normative samples from the general population. Maternal parent ratings on the Child Behavior Checklist (CBCL) for 1824 twins were compared with the CBCL normative sample. The results indicated that twins showed small but consistently higher levels of problem behaviors. These elevations were significant for older children on both internalizing and externalizing behaviors; for younger children the elevations were significant for externalizing but not internalizing behaviors.