Pregnancy, delivery and infancy complications and attention deficit hyperactivity disorder: issues of gene-environment interaction

A Systematic Review and Meta-analysis of Prenatal, Birth, and Postnatal Factors Associated with Attention-Deficit/Hyperactivity Disorder in Children

Previous studies have shown mixed results on the relationship between prenatal, birth, and postnatal ("pregnancy-related") risk factors and attention-deficit/hyperactivity disorder (ADHD). We conducted meta-analyses to identify potentially modifiable pregnancy-related factors associated with ADHD. A comprehensive search of PubMed, Web of Science, and EMBASE in 2014, followed by an updated search in January 2021, identified 69 articles published in English on pregnancy-related risk factors and ADHD for inclusion. Risk factors were included in the meta-analysis if at least three effect sizes with clear pregnancy-related risk factor exposure were identified. Pooled effect sizes were calculated for ADHD overall, ADHD diagnosis, inattention, and hyperactivity/impulsivity. Odds ratios (OR) were calculated for dichotomous measures and correlation coefficients (CC) for continuous measures. Prenatal factors (pre-pregnancy weight, preeclampsia, pregnancy complications, elevated testosterone exposure), and postnatal factors (Apgar score, neonatal illness, no breastfeeding) were positively associated with ADHD overall; the findings for ADHD diagnosis were similar with the exception that there were too few effect sizes available to examine pre-pregnancy weight and lack of breastfeeding. Prenatal testosterone was significantly associated with inattention and hyperactivity/impulsivity. Effect sizes were generally small (range 1.1-1.6 ORs, -0.16-0.11 CCs). Risk factors occurring at the time of birth (perinatal asphyxia, labor complications, mode of delivery) were not significantly associated with ADHD. A better understanding of factors that are consistently associated with ADHD may inform future prevention strategies. The findings reported here suggest that prenatal and postnatal factors may serve as potential targets for preventing or mitigating the symptoms of ADHD.

Predicting childhood ADHD-linked symptoms from prenatal and perinatal data in the ABCD cohort

This study investigates the capacity of pre/perinatal factors to predict attention-deficit/hyperactivity disorder (ADHD) symptoms in childhood. It also explores whether predictive accuracy of a pre/perinatal model varies for different groups in the population. We used the ABCD (Adolescent Brain Cognitive Development) cohort from the United States (N = 9975). Pre/perinatal information and the Child Behavior Checklist were reported by the parent when the child was aged 9-10. Forty variables which are generally known by birth were input as potential predictors including maternal substance-use, obstetric complications and child demographics. Elastic net regression with 5-fold validation was performed, and subsequently stratified by sex, race/ethnicity, household income and parental psychopathology. Seventeen pre/perinatal variables were identified as robust predictors of ADHD symptoms in this cohort. The model explained just 8.13% of the variance in ADHD symptoms on average (95% CI = 5.6%-11.5%). Predictive accuracy of the model varied significantly by subgroup, particularly across income groups, and several pre/perinatal factors appeared to be sex-specific. Results suggest we may be able to predict childhood ADHD symptoms with modest accuracy from birth. This study needs to be replicated using prospectively measured pre/perinatal data.

Pregnancy complications and childhood mental health: is the association modified by sex or adverse social circumstances? Findings from the 'growing up in Ireland' national infant cohort study

Specific pregnancy complications, socioeconomic position and sex have all been independently associated with child mental health outcomes, but their combined effects remain unclear. We examined whether total number of complications experienced in the pregnancy associated with mental health at 5 and 9-years, and whether this varied by sex or adverse social circumstances. Pregnancy complications were self-reported at 9-months post-natally from a list of 16 complications. Parents completed the Strengths and Difficulties Questionnaire (SDQ) when their child was 5 and 9-years. The primary outcome was the SDQ-total and scoring in the clinical range (> 16) was a secondary outcome. We applied generalized linear mixed models to a large nationally representative Irish cohort (GUI; n = 11,134). Analyses were adjusted for sex, adverse social circumstances (at 9-months), and gestational smoking. We included an interaction term between pregnancy complications and each variable respectively in separate models to examine if associations varied by sex or adverse circumstances.After controlling for covariates, total complications associated with mental health at 5 and 9-years. Each additional pregnancy complication conferred a 10% higher total-SDQ score (exponentiated co-efficient 1.10 [95%CI 1.06-1.14], 1.20 [1.15-1.26], 1.20 [1.12-1.29] and 1.34 [1.21-1.48] for 1, 2, 3 and 4 + complications respectively). For the dichotomised outcome, generally increasing odds for clinical levels of mental health difficulties were observed (OR 1complication = 1.89, 95%CI [1.37-2.59]; OR 2complications = 2.31, 95%CI [1.53-3.50]; OR 3complications = 1.77, 95%CI [0.89-3.52]; OR 4 + complications = 6.88, 95%CI [3.29-14.40]). Females had significantly lower odds of exhibiting clinically significant mental health difficulties than males (OR = 0.43, 95%CI[0.32-0.57]).There was no evidence that the association between pregnancy complications and child's mental health varied by sex or social circumstances at 5 or 9-years. Males exposed to numerous pregnancy complications in the context of adverse social circumstances had the highest predicted probability of having mental health difficulties in middle childhood.

Pre- and Perinatal Risk Factors for Youth with Autism Spectrum Disorder Versus Youth with Other Mental Health Disorders

Research has linked pre- and perinatal complications (PPCs) with increased risk for autism spectrum disorder (ASD). However, PPCs are also known risk factors for other mental health disorders. This study explored which PPCs are specific risk factors for ASD, as opposed to other forms of psychopathology, among a large sample of clinically-referred youth. Archival data were used from 1177 youth who were evaluated at a hospital-based autism clinic. Results from logistic regressions indicated that use of tobacco, alcohol, or drugs, or experiencing amniocentesis predicted inclusion in the non-ASD group, while physical difficulties with delivery predicted inclusion in the ASD group. Possible explanations and implications for these findings are discussed.

Association of labor epidural analgesia exposure with long-term risk of autism spectrum disorder in offspring: A meta-analysis of observational studies

LAY ABSTRACT

A previous meta-analysis has demonstrated a superior analgesic efficacy of epidural analgesia (e.g. labor epidural analgesia) in comparison with non-epidural approaches. The widely accepted safety of labor epidural analgesia also endorses its current popularity in obstetric practice. However, the results of a recent large-scale longitudinal study that demonstrated a significant increase in risk of autism spectrum disorder in offspring from mothers with labor epidural analgesia exposure have raised some concerns over the safety of its use. The current meta-analysis aimed at examining the strength of evidence regarding this issue based on updated clinical data. Through systematically reviewing seven eligible observational studies involving 4,021,406 children from electronic databases, our results showed a slight but statistically significant increase in risk of autism spectrum disorder in children with exposure to labor epidural analgesia compared with those without. The finding was consistent in subgroup analysis focusing on siblings and children delivered vaginally. Nevertheless, despite the tendency of an increased risk of autism spectrum disorder in children exposed to labor epidural analgesia <4 h, this effect was not observed in those exposed to labor epidural analgesia >8 h (data from two studies). In conclusion, the level of evidence linking labor epidural analgesia to autism spectrum disorder development in offspring was very low based on the latest data because of the small effect size and the finding of a lack of cumulative dose-response effect in the current analysis. Further studies are warranted to provide an insight into this issue.

Prenatal exposure to a natural disaster and early development of psychiatric disorders during the preschool years: stress in pregnancy study

BACKGROUND

Growing evidence shows an association between in utero exposure to natural disasters and child behavioral problems, but we still know little about the development of specific psychopathology in preschool-aged children.

METHODS

Preschool children (n = 163, mean age = 3.19, 85.5% racial and ethnic minorities) and their parents (n = 151) were evaluated annually at ages 2-5 to assess the emergence of psychopathology using the Preschool Age Psychopathological Assessment (PAPA), a parent-report structured diagnostic interview developed for preschool-age children. Sixty-six (40.5%) children were exposed to Sandy Storm (SS) in utero and 97 (59.5%) were not. Survival analysis evaluated patterns of onset and estimated cumulative risks of psychopathology among exposed and unexposed children, in total and by sex. Analyses were controlled for the severity of objective and subjective SS-related stress, concurrent family stress, and demographic and psychosocial confounders, such as maternal age, race, SES, maternal substance use, and normative prenatal stress.

RESULTS

Exposure to SS in utero was associated with a substantial increase in depressive disorders (Hazard Ratio (HR) = 16.9, p = .030), anxiety disorders (HR = 5.1, p < .0001), and attention-deficit/disruptive behavioral disorders (HR = 3.4, p = .02). Diagnostic rates were elevated for generalized anxiety disorder (GAD; HR = 8.5, p = .004), attention-deficit/hyperactivity disorder (ADHD; HR = 5.5, p = .01), oppositional-defiant disorder (ODD; HR = 3.8, p = .05), and separation-anxiety disorder (SAD; HR = 3.5, p = .001). Males had distinctively elevated risks for attention-deficit/disruptive behavioral disorders (HR = 7.8, p = .02), including ADHD, CD, and ODD, whereas females had elevated risks for anxiety disorders (HR = 10.0, p < .0001), phobia (HR = 2.8, p = .02) and depressive disorders (HR = 30.0, p = .03), including SAD, GAD, and dysthymia.

CONCLUSIONS

The findings demonstrate that in utero exposure to a major weather-related disaster (SS) was associated with increased risk for psychopathology in children and provided evidence of distinct psychopathological outcomes as a function of sex. More attention is needed to understand specific parent, child, and environmental factors which account for this increased risk, and to develop mitigation strategies.

Explaining the Association Between Fetal Growth and Childhood ADHD Symptoms: Cross-cohort Replication

The association between restricted fetal growth and symptoms of attention deficit/hyperactivity disorder (ADHD) in childhood is well-replicated and robust. However, fetal growth is determined by many prenatal factors and associations with mental health may be confounded by familial and social context. In this study, we sought to quantify the relative contributions of prenatal factors and familial confounds to the association between fetal growth and ADHD symptoms. Two independent cohorts were analyzed, the Adolescent Brain Cognitive Development study (ABCD; United States) and the Growing Up in Ireland (GUI) study. ADHD symptoms were measured by the Child Behavior Checklist (ABCD) and the Strengths & Difficulties questionnaire (GUI) at age 9-10. Using sequential regression models, we assessed the change-in-association between fetal growth and ADHD symptoms after controlling for sex, familial factors (socioeconomic/demographic factors & family psychiatric history) and prenatal factors (pregnancy complications & maternal substance-use during pregnancy). Converging findings from cohorts suggested that over a quarter of the association between fetal growth and ADHD symptoms is attributable to familial confounds. The degree to which the association was explained by prenatal factors differed by cohort-pregnancy complications explained a larger proportion of the effect in ABCD (7.9%) than GUI (2.7%), and maternal substance-use explained a larger proportion of the effect in GUI (22.7%) compared to ABCD (4.8%). Different explanations of the fetal growth-ADHD association across cohorts suggests cohort-specific, and potentially nationally-specific, risk factors for fetal growth and related neurodevelopmental outcomes. The evidence suggests early prevention of ADHD in Ireland should focus on minimizing maternal smoking during pregnancy. In the US, prevention and treatment of pregnancy complications are highlighted as viable targets for intervention.

Prefrontal Cortex Dopamine Transporter Gene Network Moderates the Effect of Perinatal Hypoxic-Ischemic Conditions on Cognitive Flexibility and Brain Gray Matter Density in Children

BACKGROUND

Genetic polymorphisms of the dopamine transporter gene (DAT1) and perinatal complications associated with poor oxygenation are risk factors for attentional problems in childhood and may show interactive effects.

METHODS

We created a novel expression-based polygenic risk score (ePRS) reflecting variations in the function of the DAT1 gene network (ePRS-DAT1) in the prefrontal cortex and explored the effects of its interaction with perinatal hypoxic-ischemic-associated conditions on cognitive flexibility and brain gray matter density in healthy children from two birth cohorts-MAVAN from Canada (n = 139 boys and girls) and GUSTO from Singapore (n = 312 boys and girls).

RESULTS

A history of exposure to several perinatal hypoxic-ischemic-associated conditions was associated with impaired cognitive flexibility only in the high-ePRS group, suggesting that variation in the prefrontal cortex expression of genes involved in dopamine reuptake is associated with differences in this behavior. Interestingly, this result was observed in both ethnically distinct birth cohorts. Additionally, parallel independent component analysis (MAVAN cohort, n = 40 children) demonstrated relationships between single nucleotide polymorphism-based ePRS and gray matter density in areas involved in executive (cortical regions) and integrative (bilateral thalamus and putamen) functions, and these relationships differ in children from high and low exposure to hypoxic-ischemic-associated conditions.

CONCLUSIONS

These findings reveal that the impact of conditions associated with hypoxia-ischemia on brain development and executive functions is moderated by genotypes associated with dopamine signaling in the prefrontal cortex. We discuss the potential impact of innovative genomic and environmental measures for the identification of children at high risk for impaired executive functions.

Neurodevelopmental Prognostic Factors in 73 Neonates with the Birth Head Injury

Objective

The objective of this study was to reinterpret the neurodevelopmental prognostic factors that are associated with birth head injury by performing a long-term follow-up.

Methods

Seventy-three neonates with head injuries were retrospectively analyzed after a duration of 10.0±7.3 years to determine the correlations between perinatal factors, including gender, head circumference, gestational age, body weight, and mode of delivery, and head injury factors from radiologic imaging with social, fine motor, language, and motor developmental quotients.

Results

There was a statistically significant difference between perinatal factors and head injury factors with respect to head circumference, body weight, gestational age, mode of delivery, Apgar scores at 1 min, cephalohematoma, subdural hemorrhage, subarachnoid hemorrhage, and hypoxic injury, but no direct correlation by regression analysis was observed between perinatal factors and developmental quotients. Of the head injury factors, falx hemorrhage showed a significant indirect relationship with the language and motor developmental quotients. Mode of delivery, subgaleal hematoma, cephalohematoma, greenstick skull fracture, epidural hemorrhage (EDH), tentorial hemorrhage, brain swelling, and hypoxic injury showed an indirect relationship with social development.

Conclusion

In terms of perinatal factors and head injury factors, mode of delivery, subgaleal hematoma, cephalohematoma, greenstick skull fracture, EDH, tentorial hemorrhage, falx hemorrhage, brain swelling, and hypoxic injury displayed an indirect relationship with long-term development, and therefore these factors require particular attention for perinatal care.

Predicting attention deficit hyperactivity disorder using pregnancy and birth characteristics

PURPOSE

The aim of this study was to evaluate maternal, prenatal, perinatal, and postpartum parameters as risk factors for the later development of an attention deficit hyperactivity disorder (ADHD) in the child.

METHODS

Women who had given birth at Erlangen University Hospital between 1996 and 1999 were sent a questionnaire in 2009. The results of the questionnaire were correlated with the prospectively collected data for the births in 1996-1999.

RESULTS

A total of 573 mother and child pairs were analyzed. Forty-four of the mothers reported that their child had ADHD (7.7%). No significant associations were found for the following parameters: mother's age; mother's educational level; number of the pregnancy; maternal weight before and at the end of pregnancy; mother's height; alcohol consumption during pregnancy; mode of delivery; gestational week; birthweight; umbilical artery blood values; Apgar score at 5 and 10 min; or breastfeeding. The parameters of smoking in pregnancy and an Apgar score lower than 7 after 1 min were significantly associated with a risk for later development of ADHD.

CONCLUSIONS

This analysis of maternal, prenatal, perinatal, and postnatal parameters found that smoking in pregnancy and a low Apgar score 1 min after birth are associated with a significantly greater risk for the development of ADHD. Beyond the question of the causal mechanism involved, this is a relevant finding, since smoking during pregnancy is a preventable risk factor.

Perinatal Risk Factors and ADHD in Children and Adolescents: A Hierarchical Structure of Disorder Predictors

OBJECTIVE

The aim of the study was to hierarchically assess the predictive power of low and high birth weight, pre-term and post-term birth, and low Apgar score as the risk factors for ADHD.

METHOD

The data of 132 boys diagnosed with ADHD and 146 boys from control group, aged 6 to 18 years, have been analyzed. The boys were categorized according to term of birth, birth weight, and Apgar score. CART method (Classification and Regression Trees) was used for assessment of the relationship between perinatal factors and the risk of ADHD.

RESULTS

Low Apgar score (21.97% vs. 13.01%) and post-term birth (12.12% vs. 0.68%) were more frequent in the sample than in the control group. CART method additionally indicated low birth weight as associated with the risk of ADHD. Among analyzed risk factors, Apgar score had the highest predictive value.

CONCLUSION

The decreased Apgar score is the most important perinatal risk factor of ADHD. Research results also indicated a high significance of post-term birth in predicting the disorder.

Resting-State Hyperperfusion of the Supplementary Motor Area in Catatonia

Catatonia is a psychomotor syndrome that not only frequently occurs in the context of schizophrenia but also in other conditions. The neural correlates of catatonia remain unclear due to small-sized studies. We therefore compared resting-state cerebral blood flow (rCBF) and gray matter (GM) density between schizophrenia patients with current catatonia and without catatonia and healthy controls. We included 42 schizophrenia patients and 41 controls. Catatonia was currently present in 15 patients (scoring >2 items on the Bush Francis Catatonia Rating Scale screening). Patients did not differ in antipsychotic medication or positive symptoms. We acquired whole-brain rCBF using arterial spin labeling and GM density. We compared whole-brain perfusion and GM density over all and between the groups using 1-way ANCOVAs (F and T tests). We found a group effect (F test) of rCBF within bilateral supplementary motor area (SMA), anterior cingulate cortex, dorsolateral prefrontal cortex, left interior parietal lobe, and cerebellum. T tests indicated 1 cluster (SMA) to be specific to catatonia. Moreover, catatonia of excited and retarded types differed in SMA perfusion. Furthermore, increased catatonia severity was associated with higher perfusion in SMA. Finally, catatonia patients had a distinct pattern of GM density reduction compared to controls with prominent GM loss in frontal and insular cortices. SMA resting-state hyperperfusion is a marker of current catatonia in schizophrenia. This is highly compatible with a dysregulated motor system in catatonia, particularly affecting premotor areas. Moreover, SMA perfusion was differentially altered in retarded and excited catatonia subtypes, arguing for distinct pathobiology.

A Set-Based Mixed Effect Model for Gene-Environment Interaction and Its Application to Neuroimaging Phenotypes

Imaging genetics is an emerging field for the investigation of neuro-mechanisms linked to genetic variation. Although imaging genetics has recently shown great promise in understanding biological mechanisms for brain development and psychiatric disorders, studying the link between genetic variants and neuroimaging phenotypes remains statistically challenging due to the high-dimensionality of both genetic and neuroimaging data. This becomes even more challenging when studying gene-environment interaction (G×E) on neuroimaging phenotypes. In this study, we proposed a set-based mixed effect model for gene-environment interaction (MixGE) on neuroimaging phenotypes, such as structural volumes and tensor-based morphometry (TBM). MixGE incorporates both fixed and random effects of G×E to investigate homogeneous and heterogeneous contributions of multiple genetic variants and their interaction with environmental risks to phenotypes. We discuss the construction of score statistics for the terms associated with fixed and random effects of G×E to avoid direct parameter estimation in the MixGE model, which would greatly increase computational cost. We also describe how the score statistics can be combined into a single significance value to increase statistical power. We evaluated MixGE using simulated and real Alzheimer's Disease Neuroimaging Initiative (ADNI) data, and showed statistical power superior to other burden and variance component methods. We then demonstrated the use of MixGE for exploring the voxelwise effect of G×E on TBM, made feasible by the computational efficiency of MixGE. Through this, we discovered a potential interaction effect of gene ABCA7 and cardiovascular risk on local volume change of the right superior parietal cortex, which warrants further investigation.

[Pre- and perinatal risk factors in autism spectrum disorder and attention deficit/hyperactivity disorder]

Objective

Epidemiological studies indicate the relevance of pre- and perinatal risk factors for the genesis of attention deficit/hyperactivity disorder and autism spectrum disorder. This study compares potential risk factors in a clinical sample of children with ADHD, ASD, the combination of both diseases, ADHD and oppositional defiant or conduct disorder (ADHD & ODD/CD) and examined whether the existence of additional risk factors promotes the occurrence of combined diseases.

Method

We compared the pre- and perinatal risk factors of 341 patients (299 boys, 42 girls) from a clinical population, differentiating between children with ADHD (n=80), ASD (n=122), ADHD & ASD (n=55), or ADHD & ODD/CD (n=84).

Results

We observed a higher rate of maternal smoking, a higher rate of migration, and lower parental education among the children with ADHD & ODD/CD compared to those with ASD or ADHD. The rate of migration background was higher among the children with ASD compared to children with ADHD. Miscarriage was a specific risk factor for ADHD & ASD.

Conclusion

Numerous risk factors described in epidemiological studies occurred only rarely in our clinical sample. The distribution of most risk factors was comparable between the examined diseases.

Recalled Initiation and Duration of Maternal Breastfeeding Among Children with and Without ADHD in a Well Characterized Case-Control Sample

Early environmental influences are increasingly of interest in understanding ADHD as a neurodevelopmental condition, particularly in light of recognition that gene by environment interplay are likely involved in this condition. Breastfeeding duration predicts cognitive development, as well as development of brain white matter connectivity, in areas similar to those seen in ADHD. Prior studies show an association between breastfeeding and ADHD but without adequate evaluation of ADHD. A case control cohort of 474 children aged 7-13 years was examined, 291 with well characterized ADHD (71.5 % male) and the rest typically developing controls (51.9 % male). Mothers retrospectively reported on breast feeding initiation and duration. Initiation of breastfeeding was not associated with child ADHD, but shorter duration of breastfeeding was associated with child ADHD with a medium effect size (d = 0.40, p < 0.05); this effect held after covarying a broad set of potential confounders, including child oppositional defiant and conduct problems and including maternal and paternal ADHD symptoms. Effects were replicated across both parent and teacher ratings of child ADHD symptoms. Shorter duration of breastfeeding is among several risk factors in early life associated with future ADHD, or else longer duration is protective. The direction of this effect is unknown, however. It may be that some children are more difficult to breastfeed or that breastfeeding provides nutrients or other benefits that reduce future chance of ADHD.

[Minimal cerebral dysfunctions and ADHD in adulthood]

Attention deficit hyperactivity disorder (ADHD) is of great importance not only in children but also in adults; however, despite extensive research there are still many unsolved questions with respect to the diagnosis. Patients not only suffer from attention deficits and hyperactivity but also a variety of other problems, such as dyspraxia, problems with stimulus discrimination, dysgrammatism, legasthenia, or motor coordination problems. Furthermore, there are also psychopathological disorders, such as problems with memory, formal thinking, emotional modulation, drive and vegetative stability, in the sense of a psycho-organic syndrome. Such syndromes have long been known in psychiatry under terms, such as complex capacity disorders, minimal cerebral dysfunction (MCD), minimal brain dysfunction (MBD), mild psycho-organic syndrome, psycho-organic axis syndrome, mild cognitive impairment, developmental disorder and developmental biological syndrome. Etiological data with respect to genetics and early childhood brain trauma support the notion of a psychobiological disorder for complex cerebral dysfunction in the sense of a psycho-organic syndrome. Depending on the individual life and work situation, these additional symptoms of ADHD are in many cases of greater relevance for life adjustment than the core symptoms, depending on the individual life and work situations. The concept of minimal cerebral dysfunction describes the ADHD problem better and has a direct bearing on the diagnosis, therapy and sociomedical care of the patients.

The Effect of Perinatal Hypoxic/Ischemic Injury on Tyrosine Hydroxylase Expression in the Locus Coeruleus of the Human Neonate

We have previously shown that perinatal hypoxic/ischemic injury (HII) may cause selective vulnerability of the mesencephalic dopaminergic neurons of human neonate. In the present study, we investigated the effect of perinatal HII on the noradrenergic neurons of the locus coeruleus (LC) of the same sample. We studied immunohistochemically the expression of tyrosine hydroxylase (TH, first limiting enzyme for catecholamine synthesis) in LC neurons of 15 autopsied infants (brains collected from the Greek Brain Bank) in relation to the neuropathological changes of acute or chronic HII of the neonatal brain. Our results showed that perinatal HII appears to affect the expression of TH and the size of LC neurons of the human neonate. In subjects with neuropathological lesions consistent with abrupt/severe HII, intense TH immunoreactivity was found in almost all neurons of the LC. In most of the neonates with neuropathological changes of prolonged or older injury, however, reduction in cell size and a decrease or absence of TH staining were observed in the LC. Intense TH immunoreactivity was found in the LC of 3 infants of the latter group, who interestingly had a longer survival time and had been treated with anticonvulsant drugs. Based on our observations and in view of experimental evidence indicating that the reduction of TH-immunoreactive neurons occurring in the LC after perinatal hypoxic insults persists into adulthood, we suggest that a dysregulation of monoaminergic neurotransmission in critical periods of brain development in humans is likely to predispose the survivors of perinatal HII, in combination with genetic susceptibility, to psychiatric and/or neurological disorders later in life.

Cumulative biomedical risk and social cognition in the second year of life: prediction and moderation by responsive parenting

At 18 months, children show marked variability in their social-cognitive skill development, and the preponderance of past research has focused on constitutional and contextual factors in explaining this variability. Extending this literature, the current study examined whether cumulative biomedical risk represents another source of variability in social cognition at 18 months. Further, we aimed to determine whether responsive parenting moderated the association between biomedical risk and social cognition. A prospective community birth cohort of 501 families was recruited at the time of the child's birth. Cumulative biomedical risk was measured as a count of 10 prenatal/birth complications. Families were followed up at 18 months, at which point social-cognitive data was collected on children's joint attention, empathy, cooperation, and self-recognition using previously validated tasks. Concurrently, responsive maternal behavior was assessed through observational coding of mother-child interactions. After controlling for covariates (e.g., age, gender, child language, socioeconomic variables), both cumulative biomedical risk and maternal responsivity significantly predicted social cognition at 18 months. Above and beyond these main effects, there was also a significant interaction between biomedical risk and maternal responsivity, such that higher biomedical risk was significantly associated with compromised social cognition at 18 months, but only in children who experienced low levels of responsive parenting. For those receiving comparatively high levels of responsive parenting, there was no apparent effect of biomedical risk on social cognition. This study shows that cumulative biomedical risk may be one source of inter-individual variability in social cognition at 18 months. However, positive postnatal experiences, particularly high levels of responsive parenting, may protect children against the deleterious effects of these risks on social cognition.

Traditional Chinese medicine in the treatment of ADHD: a review

This review covers an introduction of traditional Chinese medicine (TCM) in treating attention-deficit/hyperactivity disorder (ADHD), focusing on the traditional theoretic basis from the perspective of TCM regarding ADHD's cause, pathogenesis, methods of syndrome differentiation, and rationale for treatment. The authors present commonly accepted and successfully practiced clinical procedures used in China for diagnosis and treatment of ADHD by TCM clinicians along with the supportive clinical evidence. The authors hope to inspire more research to better understand the mechanisms underlying the therapies and to promote appropriate incorporation of TCM therapies with Western pharmacologic treatment to better help patients with ADHD.

Environmental risk factors by gender associated with attention-deficit/hyperactivity disorder

BACKGROUND

Early environmental risk factors associated with attention-deficit/hyperactivity disorder (ADHD) have been increasingly suggested. Our study investigates the maternal, pregnancy, and newborn risk factors by gender for children prescribed stimulant medication for treatment of ADHD in Western Australia.

METHODS

This is a population-based, record linkage case-control study. The records of all non-Aboriginal children and adolescents born in Western Australia and aged <25 years who were diagnosed with ADHD and prescribed stimulant medication (cases = 12,991) were linked to the Midwives Notification System (MNS) to obtain maternal, pregnancy, and birth information. The control population of 30,071 children was randomly selected from the MNS.

RESULTS

Mothers of children with ADHD were significantly more likely to be younger, be single, have smoked in pregnancy, have labor induced, and experience threatened preterm labor, preeclampsia, urinary tract infection in pregnancy, or early term delivery irrespective of the gender of the child, compared with the control group. In the fully adjusted model, a novel finding was of a possible protective effect of oxytocin augmentation in girls. Low birth weight, postterm pregnancy, small for gestational age infant, fetal distress, and low Apgar scores were not identified as risk factors.

CONCLUSIONS

Smoking in pregnancy, maternal urinary tract infection, being induced, and experiencing threatened preterm labor increase the risk of ADHD, with little gender difference, although oxytocin augmentation of labor appears protective for girls. Early term deliveries marginally increased the risk of ADHD. Studies designed to disentangle possible mechanisms, confounders, or moderators of these risk factors are warranted.

Association of genetic risk severity with ADHD clinical characteristics

This study sought to examine the association between the cumulative risk severity conferred by the total number of attention-deficit/hyperactivity disorder (ADHD) risk alleles of the DAT1 3'UTR variable number tandem repeat (VNTR), DRD4 Exon 3 VNTR, and 5-HTTLPR with ADHD characteristics, clinical correlates, and functional outcomes in a pediatric sample. Participants were derived from case-control family studies of boys and girls diagnosed with ADHD, a genetic linkage study of families with children with ADHD, and a family genetic study of pediatric bipolar disorder. Caucasian children 18 and younger with and without ADHD and with available genetic data were included in this analysis (N = 591). The association of genetic risk severity with sociodemographic, clinical characteristics, neuropsychological, emotional, and behavioral correlates was examined in the entire sample, in the sample with ADHD, and in the sample without ADHD, respectively. Greater genetic risk severity was significantly associated with the presence of disruptive behavior disorders in the entire sample and oppositional defiant disorder in participants with ADHD. Greater genetic risk severity was also associated with the absence of anxiety disorders, specifically with the absence of agoraphobia in the context of ADHD. Additionally, one ADHD symptom was significantly associated with greater genetic risk severity. Genetic risk severity is significantly associated with ADHD clinical characteristics and co-morbid disorders, and the nature of these associations may vary on the type (externalizing vs. internalizing) of the disorder.

Background, clinical features and treatment of attention deficit hyperactivity disorder in children

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is an early onset, clinically heterogeneous, complex neurobiological disorder, defined by symptoms of inattention and hyperactivity/impulsivity and has been associated with a broad range of impairments for those affected. Additionally, ADHD in children and adolescents is frequently associated with psychiatric comorbidities. This review provides an overview of the epidemiology, neurobiology, genetics, diagnosis and most recent pharmacological approaches for treatment with a focus on safety and efficacy and describes the use of medications used to treat ADHD in special populations.

AREAS COVERED

PubMed, Cochrane database, Essential Evidence and Uptodate were searched for relevant articles about stimulant and non-stimulant pharmacological approaches in ADHD.

EXPERT OPINION

Data supporting the safety and efficacy of both stimulant and non-stimulant formulations have significantly grown over the past decade and more efforts are being made to tailor medications to the needs of the patients and their families. Pharmacogenomics research is evolving, but predictors of treatment response and side effects remain largely unknown. Other unmet clinical needs include long-term follow-up studies of the safety and efficacy of medications for those with ADHD alone, or with comorbidities and in special populations including preschoolers.

Is there an association between perinatal complications and attention-deficit/hyperactivity disorder-inattentive type in children and adolescents?

OBJECTIVE

The objective of the present study is to investigate the association between attention deficit/hyperactivity disorder (ADHD), predominantly inattentive type (ADHD-I) and prenatal, delivery and early postnatal complications (PDPC).

METHOD

In a case-control design, we assessed a sample of 124 children and adolescents with ADHD-I and 124 non-ADHD controls (6-17 years old) from both a non-referred (n = 200) and a clinical sample (n = 48). Cases and controls, matched by gender and age, were systematically evaluated through structured diagnostic interviews. Prenatal, delivery and early postnatal complications (PDPC), as well as potential confounders were evaluated by direct interview with biological mothers.

RESULTS

Conditional logistic regression analysis showed that children and adolescents whose mothers presented more PDPC had a significantly higher risk for ADHD-I (p = 0.005; OR = 1.25; CI 95%: 1.1-1.5).

CONCLUSIONS

In a case-control study, we expanded to ADHD-I previous findings suggesting the association between perinatal factors and broadly defined ADHD. Due to the preventable nature of some of these PDPC, our results have clear impact in public mental health policies.

Vulnerability of the mesencephalic dopaminergic neurons of the human neonate to prolonged perinatal hypoxia: an immunohistochemical study of tyrosine hydroxylase expression in autopsy material

Experimental studies indicate that hypoxia to the fetus, a common occurrence in many birth complications in humans, results in long-term disturbances of the central dopaminergic (DA) systems that persist in adulthood. Because dysregulation of DA systems is involved in the pathophysiology of many neurological and psychiatric disorders, we investigated the effects of perinatal hypoxia on the mesencephalic DA neurons of the human neonate using immunohistochemistry. We studied the expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme in catecholamine synthesis, in substantia nigra, and ventral tegmental area of 18 neonates in relation to the age and severity/duration of hypoxic injury estimated by neuropathological criteria. In severe/abrupt perinatal hypoxia, intense TH staining was observed in substantia nigra, ventral tegmental area, and, surprisingly, in the nonpreganglionic Edinger-Westphal nucleus. In severe/prolonged hypoxia, there was a striking reduction or even absence of TH immunoreactivity in all the mesencephalic nuclei. These observations suggest that at early states of perinatal hypoxia, there is a massive increase in dopamine synthesis and release that is followed by feedback blockage of dopamine synthesis through inhibition of TH by the end product dopamine. Early dysregulation of DA neurotransmission could predispose infant survivors of severe perinatal hypoxia to dopamine-related neurological and/or cognitive deficits later in life.

Interaction of dopamine transporter gene and observed parenting behaviors on attention-deficit/hyperactivity disorder: a structural equation modeling approach

Emerging evidence suggests that some individuals may be simultaneously more responsive to the effects from environmental adversity and enrichment (i.e., differential susceptibility). Given that parenting behavior and a variable number tandem repeat polymorphism in the 3'untranslated region of the dopamine transporter (DAT1) gene are each independently associated with attention-deficit/hyperactivity disorder (ADHD), our goal was to evaluate the potential interactive effects of child DAT1 genotype with positive and negative parenting behaviors on childhood ADHD. We recruited an ethnically diverse sample of 150 six- to nine-year-old boys and girls with and without ADHD. Children were genotyped for a common polymorphism of the DAT1 gene, and objective counts of observed parenting behavior (i.e., negativity and praise) were obtained from a valid parent-child interaction task. Structural equation modeling was used to examine the interactive effects of DAT1 and observed parenting with a latent ADHD factor. We detected a significant interaction between observed praise and child DAT1 (coded additively), which suggested that praise was associated with increased ADHD, but only among youth with the 9/10 genotype. In addition, a marginally significant interaction between DAT1 (coded additively and recessively) and observed negativity emerged for ADHD, such that negativity was positively associated with ADHD but only for youth with the 9/9 genotype. Although differential susceptibility theory was not fully supported, these preliminary results suggest that interactive exchanges between parenting behavior and child genotype potentially contribute to the development of ADHD. Clinical implications for interactions between parenting behavior and child genotype are discussed.

Disruptive behaviour disorders: a systematic review of environmental antenatal and early years risk factors

Disruptive behaviour disorders (DBDs), including attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD) and conduct disorder (CD) are chronic disorders with significant overlap in aetiology and presentation. An integrative examination of environmental risk factors is lacking. Six literature searches of web-based bibliographic databases were completed to identify literature on DBDs in general and five disorders in particular: CD, ODD, ADHD, deficits of attention, motor control and perception, and reactive attachment disorder. Searches were filtered to focus on studies including diagnostic assessment, focussing on environmental risk and protective factors in the first 4 years of life. The database searches generated 9806 papers of which 47 were reviewed after filters had been applied. The evidence suggests links between a number of early life risk factors and DBDs, including prenatal cigarette smoking and alcohol use, prenatal viral illness, maternal stress and anxiety, low birthweight, peri-partum and early neonatal complications, parental stress and parenting styles in infancy, early deprivation, adoption and separation. Despite the understanding that there is sharing of risk factors between the DBDs, there has been a disproportionate focus on the role of certain risk factors at the expense of others and the field is weakened by difficulties in controlling for all potential confounding variables.

Pre- and perinatal risk factors in adults with attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent and disabling lifespan disorder, but little is yet known about risk factors for ADHD persisting beyond adolescence. The present study investigates the association between pregnancy and birth complications and ADHD in adulthood.

METHODS

We used data from the Medical Birth Registry of Norway to compare pre-and perinatal risk factors among 2323 adults approved for medical treatment for ADHD, with the remaining population born during the same years, 1967-1987, and surviving into adulthood (n = 1,170,073). Relative risks (RR) adjusted for potential confounders were calculated.

RESULTS

Preterm (< 37 weeks of gestation) and extremely preterm birth (< 28 weeks of gestation) were associated with 1.3- and 5-fold increased risks of ADHD, respectively. Birth weights <2500 g and <1500 g also increased the risk of ADHD (RR: 1.5, 95% confidence interval [CI]: 1.2-1.8, and RR: 2.1, 95% CI: 1.3-3.6, respectively). Five-minute Apgar scores <4 and <7 were associated with 2.8- and 1.5-fold increased risks of persisting ADHD, respectively. Maternal epilepsy (RR: 1.7, 95% CI: 1.1-2.7) and offspring oral cleft (RR: 2.8, 95% CI: 1.6-4.9) occurred more frequently among adult ADHD patients.

CONCLUSIONS

This is the first population-based study of pre-and perinatal risk factors in adults with ADHD. We show that low birth weight, preterm birth, and low Apgar scores increase the risk of ADHD, persisting up to 40 years after birth. The increased risk of ADHD related to oral cleft and to maternal epilepsy warrants further investigation to explore possible causal mechanisms.

Perinatal Pitocin as an early ADHD biomarker: neurodevelopmental risk?

OBJECTIVE

To investigate a potential relationship between coincidental increases in perinatal Pitocin usage and subsequent childhood ADHD onset in an attempt to isolate a specific risk factor as an early biomarker of this neurodevelopmental disorder.

METHOD

Maternal labor/delivery and corresponding childbirth records of 172 regionally diverse, heterogeneous children, ages 3 to 25, were examined with respect to 21 potential predictors of later ADHD onset, including 17 selected obstetric complications, familial ADHD incidence, and gender. ADHD diagnosis and history of perinatal Pitocin exposure distinguished groups for comparison.

RESULTS

Results revealed a strong predictive relationship between perinatal Pitocin exposure and subsequent childhood ADHD onset (occurring in 67.1% of perinatal Pitocin cases vs. 35.6% in nonexposure cases, χ(2)=16.99, p<.001). Fetal exposure time, gestation length, and labor length also demonstrated predictive power, albeit significantly lower.

CONCLUSION

The findings warrant further investigation into the potential link between perinatal Pitocin exposure and subsequent ADHD diagnosis.

Perinatal, maternal, and fetal characteristics of children diagnosed with attention-deficit-hyperactivity disorder: results from a population-based study utilizing the Swedish Medical Birth Register

AIM

The aim of this study was to evaluate the impact of pre- and perinatal factors on the risk of developing attention-deficit-hyperactivity disorder (ADHD).

METHOD

We investigated the medical history of 237 children (206 male; 31 female) from Malmö, Sweden born between 1986 and 1996 and in whom a diagnosis of ADHD (Diagnostic and Statistical Manual of Mental Disorders-IIIR or IV) was subsequently made at the Department of Child and Adolescent Psychiatry, Lund University, and a reference group of 31,775 typically developing children from Malmö using data from the Swedish Medical Birth Register.

RESULTS

The results of multiple logistic regression analysis revealed that ADHD was significantly associated with a young maternal age (odds ratio [OR] for 5 y increase 0.87; 95% confidence interval [CI] 0.76-0.99), maternal smoking (OR 1.35; 95% CI 1.14-1.60), maternal birthplace in Sweden (OR 2.04; 95% CI 1.45-2.94), and preterm birth <32 weeks (OR 3.05; 95% CI 1.39-6.71), and a male predominance (OR 6.38; 95% CI 4.37-9.32). Apgar scores at 5 minutes below 7 were significantly associated with ADHD in the univariable analysis (OR 2.60; 95% CI 1.15-5.90). The population-attributable fraction of ADHD caused by the perinatal factors studied was estimated to be 2.8%.

INTERPRETATION

The results indicate that the studied factors constitute weak risk factors for developing ADHD.

The meaning of childhood attention-deficit hyperactivity symptoms in patients with a first-episode of schizophrenia-spectrum psychosis

OBJECTIVE

To examine childhood ADHD symptoms in regard to their association with a number of illness-related variables including risk factors, early neurodevelopment, premorbid functioning and clinical characteristics in patients with schizophrenia-spectrum psychoses.

METHODS

One-hundred and twenty-two first-episode patients with DSM-IV schizophrenia-spectrum disorders were retrospectively assessed by means of their biological mothers for childhood ADHD symptoms. Using correlational analyses and hierarchical regression models, the severity of ADHD symptoms was examined in relation to familial liability to schizophrenia, obstetric complications, milestones attainment delay, premorbid functioning during childhood and adolescence, age at illness onset, episode psychopathology and response to treatment after one-month trial with antipsychotic medication.

RESULTS

Twenty-one patients (17%) met DSM-IV criteria for childhood ADHD. Univariate analyses showed that severity of childhood ADHD symptoms was related to male gender, obstetric complications, delayed milestones attainment, poor school functioning and an earlier age of onset of psychotic symptoms. Hierarchical regression analyses showed that severity of childhood ADHD symptoms was independently predicted by obstetric complications and neurodevelopmental delay, with no further variables entering in the regression models. Path analyses showed that obstetric complications had both direct and indirect effects, through neurodevelopmental delay, on ADHD symptoms.

CONCLUSIONS

These findings are consistent with a neurodevelopmental model of schizophrenia and with the hypothesis of shared environmental risk factors between ADHD and schizophrenia-spectrum disorders. Childhood ADHD symptoms in schizophrenia-spectrum disorders appear to be an epiphenomenon of obstetric complications and early neurodevelopment delay with no further influence on the clinical expression of the illness.

Late-preterm birth and its association with cognitive and socioemotional outcomes at 6 years of age

INTRODUCTION

Late-preterm birth (34-36 weeks' gestation) has been associated with a risk for long-term cognitive and socioemotional problems. However, many studies have not incorporated measures of important contributors to these outcomes, and it is unclear whether effects attributed to gestational age are separate from fetal growth or its proxy, birth weight for gestational age.

METHOD

Data came from a study of low- and normal-weight births sampled from urban and suburban settings between 1983 and 1985 (low birth weight, n = 473; normal birth weight; n = 350). Random sampling was used to pair singletons born late-preterm with a term counterpart whose birth weight z score was within 0.1 SD of his or her match (n = 168 pairs). With random-effects models, we evaluated whether pairs differed in their IQ scores and teacher-reported behavioral problems at the age of 6 years.

RESULTS

In adjusted models, late-preterm birth was associated with an increased risk of full-scale (adjusted odds ratio [aOR]: 2.35 [95% confidence interval (CI): 1.20-4.61]) and performance (aOR: 2.04 [95% CI: 1.09-3.82]) IQ scores below 85. Late-preterm birth was associated with higher levels of internalizing and attention problems, findings that were replicated in models that used thresholds marking borderline or clinically significant problems (aOR: 2.35 [95% CI: 1.28-4.32] and 1.76 [95% CI: 1.04-3.0], respectively).

CONCLUSIONS

Late-preterm birth is associated with behavioral problems and lower IQ at the age of 6, independent of maternal IQ, residential setting, and sociodemographics. Future research is needed to investigate whether these findings result from a reduction in gestational length, in utero (eg, obstetric complications) or ex-utero (eg, neonatal complications) factors marked by late-preterm birth, or some combination of these factors.

European consensus statement on diagnosis and treatment of adult ADHD: The European Network Adult ADHD

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is among the most common psychiatric disorders of childhood that persists into adulthood in the majority of cases. The evidence on persistence poses several difficulties for adult psychiatry considering the lack of expertise for diagnostic assessment, limited treatment options and patient facilities across Europe.

METHODS

The European Network Adult ADHD, founded in 2003, aims to increase awareness of this disorder and improve knowledge and patient care for adults with ADHD across Europe. This Consensus Statement is one of the actions taken by the European Network Adult ADHD in order to support the clinician with research evidence and clinical experience from 18 European countries in which ADHD in adults is recognised and treated.

RESULTS

Besides information on the genetics and neurobiology of ADHD, three major questions are addressed in this statement: (1) What is the clinical picture of ADHD in adults? (2) How can ADHD in adults be properly diagnosed? (3) How should ADHD in adults be effectively treated?

CONCLUSIONS

ADHD often presents as an impairing lifelong condition in adults, yet it is currently underdiagnosed and treated in many European countries, leading to ineffective treatment and higher costs of illness. Expertise in diagnostic assessment and treatment of ADHD in adults must increase in psychiatry. Instruments for screening and diagnosis of ADHD in adults are available and appropriate treatments exist, although more research is needed in this age group.

Measured gene-by-environment interaction in relation to attention-deficit/hyperactivity disorder

OBJECTIVE

To summarize and evaluate the state of knowledge regarding the role of measured gene-by-environment interactions in relation to attention-deficit/hyperactivity disorder.

METHOD

A selective review of methodologic issues was followed by a systematic search for relevant articles on measured gene-by-environment interactions; the search yielded 16 studies, which are discussed in qualitative fashion.

RESULTS

Relatively consistent evidence points to the interaction of genotype with psychosocial factors in the development of attention-deficit/hyperactivity disorder. The next step is to identify the mechanisms on the environment side and the gene combinations on the genetic side accounting for this effect. In contrast, evidence for gene-by-environment interactions involving pre- and perinatal risk factors is generally negative or unreplicated. The aggregate effect size for psychosocial interaction with genotype is more than double that for the interaction of pre- and perinatal risks with genotype. Only a small fraction of candidate environments and gene markers has been studied, and multivariate methods to integrate multiple gene or environment markers have yet to be implemented.

CONCLUSIONS

Gene-by-environment interaction appears likely to prove fruitful in understanding the etiology of attention-deficit/hyperactivity disorder. Findings to date already suggest new avenues of investigation particularly involving psychosocial mechanisms and their interplay with genotype. Further pursuit of theoretically promising leads is recommended.

Parenting of 7-month-old infants at familial risk for attention deficit/hyperactivity disorder

Patterns of interaction between parents and 7-month-old boys at familial risk for attention deficit/hyperactivity disorder (ADHD) and a comparison group were studied during a warm-up and two play episodes. The sample included 78 (47 at-risk, 31 comparison) mother-child and 45 (27 at-risk, 18 comparison) father-child dyads. A coding system developed by G. Kochanska (1997, 1998) was used. Infants in the risk group did not differ from the comparison group in the rate of emission of infant-related events. However, they received less adequate responsivity from both their fathers and their mothers to these events, and specifically to negative emotions or distress, than did the comparison group. Maternal psychopathology did not account for these findings. Mothers were more adequately responsive than were fathers, especially for physiological needs. The association between nonoptimal interaction in infancy and the development of ADHD is discussed.

Gene-environment interactions in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous disorder characterized by inattention, impulsivity, and/or hyperactivity in children and adults. Putative environmental risk factors for ADHD include toxin and prenatal smoke exposure, low socioeconomic status, and parental marital instability and discord. Genetic associations with ADHD have been found in the dopaminergic, serotonergic, and noradrenergic neurotransmitter systems, but findings are inconsistent across studies. Herein, we review studies of gene-environment interactions for ADHD to better understand how genetic and environmental risk factors may contribute to the disorder in a nonindependent fashion, which may account in part for the inconsistent findings on genetic associations. Although evidence of interactions between prenatal substance exposure and the dopamine genes DAT1 and DRD4 was found, findings across studies have been mixed. We discuss these findings and the future directions and limitations of current gene-environment research.

Does HPA-axis activity mediate the relationship between obstetric complications and externalizing behavior problems? The TRAILS study

To examine whether HPA-axis activity mediates the relationship between obstetric complications (OCs) and externalizing behavior problems, and to investigate whether this model is different for boys and girls. In a population-based cohort of 1,768 10- to 12-year-old early adolescents, we assessed the cortisol awakening response and evening cortisol levels. Externalizing behavior problems were assessed using the Child Behavior Checklist and the Youth Self-Report. OCs were retrospectively assessed in a parent interview. OCs significantly predicted externalizing behavior problems, but OCs did not predict HPA-axis activity. Thus, the mediation model was not supported. In addition to the relationship between HPA-axis activity and externalizing behavior problems, which is specific for girls, there is also a relationship between OCs and externalizing behavior problems. However, these two mechanisms are not related to each other indicating that HPA-axis activity is not a mediator in the relationship between OCs and externalizing behavior problems. Future research should focus on understanding the mechanism through which OCs cause externalizing behavior problems.

Understanding genes, environment and their interaction in attention-deficit hyperactivity disorder: is there a role for neuroimaging?

Attention-deficit hyperactivity disorder (ADHD) has an established heritable component, but identifying the genes involved has proven difficult. To date, the two most investigated risk genes in ADHD are the DRD4 and DAT1-genes. However, individual risk genes have only explained up to 1% of the variance in the phenotype, suggesting that they represent only relatively small risk factors for ADHD. As such, the role of environmental factors, gene-gene and gene-environment interactions are being investigated. However, studies have not always been able to address the neurobiological mechanisms by which environmental factors and interactions with genes exert their effect on the ADHD-phenotype. Neuroimaging is being used as a tool to investigate the neurobiological effects of individual risk genes. We suggest it could also be applied to investigate the mechanisms involved in environmental effects and interactions between genetic and environmental factors.

Risk factors for learning-related behavior problems at 24 months of age: population-based estimates

We used a large sample of singleton children to estimate the effects of socioeconomic status (SES), race/ethnicity, gender, additional socio-demographics, gestational and birth factors, and parenting on children's risk for learning-related behavior problems at 24 months of age. We investigated to what extent these factors increased a child's risk of displaying inattention, a lack of task persistence, disinterest, non-cooperation, or frustration as he or she completed a series of cognitive and physical tasks with a non-caregiver. Results indicated that boys are about twice as likely as girls to display learning-related behavior problems. Children from lower SES households are about twice as likely as those from high SES households to display such behavior problems, which is largely attributable to the effects of having a mother with a low educational level. Statistically controlling for these factors, we found consistently significant patterns of elevated learning-related behavior problems for some Asian and Native American children. Results for African-American children were mixed. Hispanic children did not have consistently elevated risks of problem behaviors. Only small portions of these effects are explained by variation in the children's gestational or birth characteristics. A significant portion, but still less than half of the socio-demographic effects are attributable to measured features of the children's parenting. This study helps provide population-based estimates of children's risk for learning-related behavior problems while at an age when early interventions are most effective.

Externalizing behaviors in preadolescents: familial risk to externalizing behaviors, prenatal and perinatal risks, and their interactions

BACKGROUND

Accumulating evidence indicates that there is a rich and varied interplay between persons and their environments, which strongly suggests that this involves gene-environment correlations and interactions. We investigated whether familial risk (FR) to externalizing behaviors and prenatal and perinatal risk factors, separately or in interaction with each other, predicted externalizing behaviors.

METHODS

The subjects were 10- to 12-year-old preadolescents who were taking part in TRAILS, a large prospective population-based cohort study (N = 2,230). Regression analyses were used to determine the relative contribution of FR and prenatal and perinatal risks to parent and teacher ratings of inattention, hyperactivity/impulsivity aggression, and delinquency.

RESULTS

Regression models explained between 6 and 11% of the variance of externalizing behaviors. We found main effects of FR (vs. no FR), macrosomia (birth weight > 4,500 g), maternal prenatal smoking (MPS), pregnancy and delivery complications (PDCs), and gender that were rather consistent across rater and outcome measures. For some outcome measures, the effect of MPS and PDCs depended on the presence of FR. These included both positive and negative interaction effects. Correlations between FR and prenatal and perinatal risks were significant but rather low.

CONCLUSIONS

Both main effects and interaction effects of FR and prenatal and perinatal risks contributed to externalizing behaviors in preadolescents, but all effects were of small size. Further research including use of candidate gene polymorphisms is necessary to identify the underlying neurobiological mechanisms of these main and interaction effects.