Perinatal risk factors interacting with catechol O-methyltransferase and the serotonin transporter gene predict ASD symptoms in children with ADHD

Prevalence of co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder among children in the United States

LAY ABSTRACT

Autism spectrum disorder and attention deficit/hyperactivity disorder are neurodevelopmental disorders that often co-occur in children. However, there are few large, nationally representative studies examining the prevalence of co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder in children. The aim of this study was to estimate the prevalence of parent-reported co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder in the United States and examine associations between having co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder and sociodemographic and household factors. Data were analyzed from the 2016-2018 National Survey of Children's Health. A total of 88,051 children aged 3-17 years old were included in the analysis. Statistical analyses were conducted to assess the associations between sociodemographic and household characteristics and current co-occurrence of autism spectrum disorder and attention deficit/hyperactivity disorder. Approximately 1.2% of children (740,816) aged 3-17 years had co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder. Children who were male, older, reported poor health, or had public or combined public and private health insurance were more likely to have co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder. Conversely, children who were Black, non-Hispanic or multi-racial/other, non-Hispanic were less likely to report co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder than White non-Hispanics. Findings suggest implementing early developmental screening and surveillance for co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder, and coordinating strategies that optimize early identification and intervention for all children suspected of having co-occurring autism spectrum disorder and attention deficit/hyperactivity disorder, particularly those from underrepresented groups.

Maternal serotonin transporter genotype and offsprings' clinical and cognitive measures of ADHD and ASD

Serotonin (5-HT) is an important factor for prenatal neurodevelopment whereby its neurotrophic actions can be regulated through maternal-fetal interactions. We explored if maternal 5-HTTLPR genotype is associated with clinical and cognitive measures of attention-deficit/hyperactivity disorder (ADHD) and comorbid autism spectrum disorder (ASD) in typically-developing and ADHD-diagnosed offspring, beyond classical inheritance and environmental- and comorbidity-mediators/confounders. Family-based variance decomposition analyses were performed incorporating 6-31 year-old offsprings' as well as parental genotypes of 462 ADHD and control families from the NeuroIMAGE cohort. Dependent measures were offsprings' ADHD symptom- and ASD trait-scores and cognitive measures including executive functioning (including response inhibition and cognitive flexibility), sustained attention, reward processing, motor control, and emotion recognition. Offsprings' stereotyped behavior was predicted by an interaction between maternal 5-HTTLPR genotype and offsprings' sex. Furthermore, offspring of mothers with low-expressing genotypes demonstrated larger reward-related reductions in reaction time. While specifically adult male offspring of these mothers reported a faster reversal learning with less errors, specifically young female offspring of these mothers were more accurate in identifying happy faces. Adult offspring from the mothers with low-expressing 5-HTTLPR genotypes were also slower in identifying happy faces. However, this association seemed to be mediated by offsprings' high anxiety levels. In sum, we found some support for a role of the maternal 5-HT system in modulating fetal brain development and behavior. Offsprings' cognitive measures might be more sensitive to small alterations within the maternal 5-HT system than their ADHD and ASD clinical phenotypes. Further studies are needed to specify the association between maternal genotype and risk for neurodevelopmental disorders.

The Interplay Between Prenatal Adversity, Offspring Dopaminergic Genes, and Early Parenting on Toddler Attentional Function

Background: Few studies have explored the complex gene-by-prenatal environment-by-early postnatal environment interactions that underlie the development of attentional competence. Here, we examined if variation in dopamine-related genes interacts with prenatal adversity to influence toddler attentional competence and whether this influence is buffered by early positive maternal behavior. Methods: From the Maternal Adversity, Vulnerability and Neurodevelopment cohort, 134 participants (197 when imputing missing data) had information on prenatal adversity (prenatal stressful life events, prenatal maternal depressive symptoms, and birth weight), five dopamine-related genes (DAT1, DRD4, DRD2, COMT, BDNF), observed maternal parenting behavior at 6 months and parent-rated toddler attentional competence at 18 and 24 months. The Latent Environmental and Genetic Interaction (LEGIT) approach was used to examine genes-by-prenatal environment-by-postnatal environment interactions while controlling for sociodemographic factors and postnatal depression. Results: Our hypothesis of a three-way interaction between prenatal adversity, dopamine-related genes, and early maternal parenting behavior was not confirmed. However, consistent two-way interactions emerged between prenatal adversity and dopamine-related genes; prenatal adversity and maternal parenting behavior, and dopamine-related genes and maternal parenting behavior in relation to toddler attentional competence. Significant interaction effects were driven by the DAT1, COMT, and BDNF genotypes; prenatal stressful life events; maternal sensitivity, tactile stimulation, vocalization, and infant-related activities. Conclusions: Multiple dopamine-related genes affected toddler attentional competence and they did so in interaction with prenatal adversity and the early rearing environment, separately. Effects were already visible in young children. Several aspects of early maternal parenting have been identified as potential targets for intervention.

Examining the autistic traits in children and adolescents diagnosed with attention-deficit hyperactivity disorder and their parents

BACKGROUND

Attention-Deficit Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) are two of the most frequently-observed neurodevelopmental disorders. Autistic traits are detected frequently in children who have ADHD. This study aimed to examine autism symptoms in children diagnosed with ADHD and their parents; and also, to investigate parental risk factors that increase autistic traits in children. Besides the risk factors related to pregnancy, birth and developmental history were examined.

METHODS

Two groups were created consisting of 66 children diagnosed with ADHD and 33 children not diagnosed with ADHD and their parents. Autism symptoms were screened with the Autism Behavior Checklist (ABC) in children, and Autism Spectrum Quotient (AQ) in parents. Also, Adult ADD/ADHD DSM-IV Based Diagnostic Screening and Rating Scale and Wender Utah Rating Scale (WURS) were used to determine ADHD symptoms in parents.

RESULTS

It was determined that there were more autism symptoms in children who were diagnosed with ADHD than in the control group without ADHD. There were more autistic symptoms in boys and the presence of Oppositional Defiant Disorder (ODD). Although there were more ADHD symptoms in the parents of children diagnosed with ADHD, it was determined that they did not differ from parents in the control group in terms of autism symptoms. It was also determined that maternal and paternal ADHD symptoms were predictive for autism symptoms in children. It was also shown that maternal smoking during pregnancy is associated with more autistic traits.

CONCLUSION

ASD and ADHD show high levels of comorbidity. The etiology remains unclear. Both ADHD and ASD show strong hereditary transition. We found that maternal and paternal ADHD symptoms predict autism symptoms in children with ADHD. However, more studies are needed to reveal the etiology.

Spontaneous theory of mind in adults with attention-deficit/hyperactivity disorder

Spontaneous theory of mind (ToM) is an unconscious and automatic understanding of others' mental states. Recently, individuals with attention-deficit hyperactivity disorder (ADHD) have been shown to have social and communication difficulties, and ToM in ADHD has come under scrutiny. Although some studies have employed explicit ToM tasks to this end with contradictory results, none, to our knowledge, has investigated spontaneous ToM in individuals with ADHD. Therefore, we performed this study to examine implicit mentalizing in adults with ADHD using the anticipatory-looking paradigm designed by Senju et al. (2009) with a sample of 24 adults with ADHD and 18 neurotypical adults. The total fixation times to three areas of interest, i.e., the actor and the false-belief congruent and incongruent sides of the scene were measured. We found that neither group showed looking bias toward either the false-belief congruent or incongruent side. We interpret that this similar gaze pattern and the absence of looking bias to the false-belief incongruent side in both groups is indicative of intact implicit ToM in adults with ADHD. Adults with ADHD looked significantly less at the actor than did neurotypical individuals, possibly due to inattention and further experimental modifications should be considered.

The Co-Occurrence of Autism Spectrum Disorder in Children With ADHD

Objective: Children with ADHD frequently present with autism spectrum disorder (ASD) symptomatology, yet there is a notable gap in the treatment needs of this subpopulation, including whether the presence of ASD may be associated with more severe ADHD symptoms. Method: Data from the 2014 National Survey of the Diagnosis and Treatment of ADHD and Tourette Syndrome (n = 2,464) were used to compare children diagnosed with ADHD and ASD with children with ADHD, but not ASD. Children were classified as needing treatment if it was received or their parents reported it was needed, but not received. Results: Approximately one in eight children currently diagnosed with ADHD was also diagnosed with ASD. Children diagnosed with both disorders had greater treatment needs, more co-occurring conditions, and were more likely to have a combined hyperactive/impulsive and inattentive ADHD subtype. Conclusion: These findings highlight the complexity of children diagnosed with both ADHD and ASD.

Impact of autism-associated genetic variants in interaction with environmental factors on ADHD comorbidities: an exploratory pilot study

Attention-deficit/hyperactivity disorder (ADHD) is determined by genetic and environmental factors, and shares genetic risk with ASD. Functional single-nucleotide polymorphisms of the metabotropic glutamatergic signaling pathway are reported to increase the risk for ASD. The aim of this pilot study was to explore the main effects of respective ASD variants as well as their interaction effects with well-replicated ADHD environmental risk factors on the risk for ADHD, ADHD symptom severities, and comorbidities. We included 318 children with ADHD, aged 5-13 years, and their parents (N = 164 trios, N = 113 duos, N = 41 singletons). Interaction of ASD risk variants CYFIP1-rs7170637, CYFIP1-rs3693, CAMK4-rs25925, and GRM1-rs6923492 with prenatal biological and lifetime psychosocial risk factors was explored in a subsample with complete environmental risk factors (N = 139 trios, N = 83 duos, two singletons) by transmission disequilibrium test and stepwise regression analyses. We identified nominally significant (alpha < 0.05) GxE interactions of acute life events with CYFIP1-rs3693 on ADHD diagnosis (p = 0.004; fdr = 0.096) but no significant association of any single marker. Further results suggest that the risk for comorbid disruptive disorders was significantly modulated by GxE interactions between familial risk factors and CAMK4-rs25925 (p = 0.001; fdr = 0.018) and prenatal alcohol exposure with CYFIP1-rs3693 (p = 0.003; fdr = 0.027); both findings survived correction for multiple testing (fdr value < 0.05). Nominal significant GxE interactions moderating the risk for anxiety disorders have also been identified, but did not pass multiple testing corrections. This pilot study suggests that common ASD variants of the glutamatergic system interact with prenatal and lifetime psychosocial risk factors influencing the risk for ADHD common comorbidities and thus warrants replication in larger samples.

Differences in Sensitivity to Environment Depending on Catechol-O-Methyltransferase (COMT) Gene? A Meta-analysis of Child and Adolescent Gene-by-Environment Studies

To date, several gene-by-environment (G×E) meta-analyses have been conducted to provide cumulative G×E evidence from previous inconsistent empirical studies; however, these meta-analyses have mainly focused on the serotonin transporter gene (5-HTTLPR). The present study aimed to conduct the first meta-analysis that tested whether and how an important dopaminergic gene-the catechol-O-methyltransferase (COMT) gene contributed to differences in child and adolescent environmental sensitivity. A total of 22 studies with 20,528 participants involving in various developmental outcomes (e.g., externalizing problems, emotional problems, cognitive development and social behaviors) met the inclusion criteria. The pooled effect size of environment-outcome associations in the Met-allele carriers (r = 0.11, 95% CI = [0.07, 0.15], p < .001) did not significantly differ from that in the Val/Val homozygotes (r = 0.14, 95% CI = [0.08, 0.20], p < 0.001) (Q_contrast (1) = 0.37, p = 0.54). The aggregated Liptak-Stouffer Z-score that combined the p-values of the COMT-environment interaction yield a nonsignificant result (p = 0.52). Moreover, outcome domain, sample age, ethnicity and assessment methods for the environment and the outcome did not moderate the effect sizes. Thus far, the COMT Val158Met polymorphism fails to explain the differences in sensitivity to environment. Future studies might incorporate more factors, such as polygenic effects of genetic pathways, epigenetics (EpiG) processing and sexual dimorphism, into the COMT-environment interaction equation.

Research Review: The role of obstetric and neonatal complications in childhood attention deficit and hyperactivity disorder - a systematic review

BACKGROUND

Attention deficit and hyperactivity disorder (ADHD) is a developmental disorder characterized by an inability to sustain attention, activity levels and impulse control, and, according to the latest studies, the prevalence is about 8% and in some countries less than 1%. Currently, it is well-known that complications during the perinatal period have significant implications on child's physical and mental health. Purpose of the present paper is to review the literature about the association between perinatal complications and future risk of an ADHD diagnosis.

METHODS

A research in the main database sources has been conducted to obtain a systematic review on the perinatal risk factors of ADHD.

RESULTS

Among perinatal complications, available data indicate low birth weight (LBW) (Cohen's d effect size range: 0.31-1.64-small effect size) and preterm birth (PB) (range d: 0.41-0.68) as the most important factors associated with a future diagnosis of ADHD.

CONCLUSIONS

PB and LBW children should be carefully monitored for an early diagnosis of ADHD limiting the impact of the disease in life span. A systematic review focusing on these risk factors have not been published until now, in the next future preventive strategies should be developed in order to minimize ADHD onset.

Associations of endocrine stress-related gene polymorphisms with risk of autism spectrum disorders: Evidence from an integrated meta-analysis

Autism spectrum disorders (ASD) are related to serotonin transporter (5-HTT) and catechol-O-methyl transferase (COMT) as two most monoaminergic polymorphic variations. However, multiple studies assessing rs4680 and 5-HTTLPR variants in ASD have reported inconsistent results. Therefore, we conducted an integrated meta-analysis to combine case-control and transmission/disequilibrium test (TDT) studies to determine whether COMT and 5-HTT are associated with ASD. We searched multiple electronic databases (PubMed, EmBase and Web of Science) to identify studies assessing the rs4680 and 5-HTTLPR variants in ASD from Jan 1997 to Dec 2016. Then allelic data from case-control and TDT studies were analyzed by the Catmap package in the R software. A total of 5 studies were eligible for the meta-analysis of rs4680, including 3 case-control, 1 TDT and 1 TDT & case-control studies. Meanwhile, 22 studies of 5-HTTLPR were available, including 16 TDT, 4 case-control and 2 TDT & case-control studies. The current meta-analysis included 814 ASD cases, 741 controls and 311 families related to rs4680; 749 ASD cases, 1,118 controls and 1,861 families relevant to 5-HTTLPR were also evaluated. For rs4680, the pooled OR was 1.18 (95% CI = 0.87-1.59, P = 0.29, P_{heterogeneity}  < 0.00001). There was no significant association of rs4680 with risk of ASD between the two subgroups. For 5-HTTLPR, the pooled OR was 1.05 (95% CI = 0.92-1.20, P = 0.4652, P_{heterogeneity}  < 0.00001). Meanwhile, we found no significant risk in individual case-control or TDT studies. The above findings indicated that neither COMT rs4680 nor 5-HTT 5-HTTLPR polymorphism significantly affects ASD risk. Autism Res 2017, 10: 1722-1736. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Our results showed no evidence of significant association of either COMT rs4680 or 5-HTT 5-HTTLPR variants with ASD, showing that these two genes may not be major susceptible genetic factors in ASD occurrence, and may have a reciprocal action with each other in combination with environmental factors. These findings further provide evidence that a single gene variant may not dictate autism occurrence, but possibly contributes to a specific phenotype or subtype of ASD.

Does Prenatal Valproate Interact with a Genetic Reduction in the Serotonin Transporter? A Rat Study on Anxiety and Cognition

There is ample evidence that prenatal exposure to valproate (or valproic acid, VPA) enhances the risk of developing Autism Spectrum Disorders (ASD). In line with this, a single injection of VPA induces a multitude of ASD-like symptoms in animals, such as rats and mice. However, there is equally strong evidence that genetic factors contribute significantly to the risk of ASD and indeed, like most other psychiatric disorders, ASD is now generally thought to results from an interaction between genetic and environmental factors. Given that VPA significantly impacts on the serotonergic system, and serotonin has strong biochemical and genetic links to ASD, we aimed to investigate the interaction between genetic reduction in the serotonin transporter and prenatal valproate administration. More specifically, we exposed both wildtype (SERT^+/+) rats and rats heterozygous for the serotonin transporter deletion (SERT^+/-) to a single injection of 400 mg/kg VPA at gestational day (GD) 12. The offspring, in adulthood, was assessed in four different tests: Elevated Plus Maze and Novelty Suppressed Feeding as measures for anxiety and prepulse inhibition (PPI) and latent inhibition as measures for cognition and information processing. The results show that prenatal VPA significantly increased anxiety in both paradigm, reduced PPI and reduced conditioning in the latent inhibition paradigm. However, we failed to find a significant gene-environment interaction. We propose that this may be related to the timing of the VPA injection and suggest that whereas GD12 might be optimal for affecting normal rat, rats with a genetically compromised serotonergic system may be more sensitive to VPA at earlier time points during gestation. Overall our data are the first to investigate gene ^* environmental interactions in a genetic rat model for ASD and suggest that timing may be of crucial importance to the long-term outcome.

Peer influence as a potential magnifier of ADHD diagnosis

The prevalence of Attention Deficit and Hyperactivity Disorder (ADHD) is growing in America, but its cause is unclear. Scholars have identified many environmental factors that can cause or confound ADHD diagnosis, but epidemiological studies that try to control for confounding factors still find evidence that rates of ADHD diagnosis are increasing. As a preliminary explanation to ADHD's increasing prevalence, this article examines whether core ADHD diagnostic traits are subject to peer influence. If ADHD diagnosis can be confounded by peer influence, there are several mechanisms that could have caused increased rates of diagnosis. With data drawn from two schools across three waves in the National Longitudinal Survey of Adolescent Health (n = 2193), the author uses a stochastic actor oriented model to estimate the effect of peer influence on inattention, controlling for alternative network and behavioral causes. Results indicate that respondents have a strong likelihood to modify their self-reports of inattention, a core ADHD trait, to resemble that of their friends.

Integrating autism-related symptoms into the dimensional internalizing and externalizing model of psychopathology. The TRAILS Study

Problems associated with Autism Spectrum Disorder (ASD) occur frequently in the general population and often co-occur with problems in other domains of psychopathology. In the research presented here these co-occurrence patterns were investigated by integrating a dimensional approach to ASDs into the more general dimensional framework of internalizing and externalizing psychopathology. Factor Analysis was used to develop hierarchical and bi-factor models covering multiple domains of psychopathology in three measurement waves of a longitudinal general population sample (N = 2,230, ages 10-17, 50.8% female). In all adequately fitting models, autism related problems were part of a specific domain of psychopathology that could be distinguished from the internalizing and externalizing domains. Optimal model fit was found for a bi-factor model with one non-specific factor and four specific factors related to internalizing, externalizing, autism spectrum problems and problems related to attention and orientation. Autism-related problems constitute a specific domain of psychopathology that can be distinguished from the internalizing and externalizing domains. In addition, the co-occurrence patterns in the data indicate the presence of a strong general factor.

Environmental chemical exposures and autism spectrum disorders: a review of the epidemiological evidence

In the past decade, the number of epidemiological publications addressing environmental chemical exposures and autism has grown tremendously. These studies are important because it is now understood that environmental factors play a larger role in causing autism than previously thought and because they address modifiable risk factors that may open up avenues for the primary prevention of the disability associated with autism. In this review, we covered studies of autism and estimates of exposure to tobacco, air pollutants, volatile organic compounds and solvents, metals (from air, occupation, diet, dental amalgams, and thimerosal-containing vaccines), pesticides, and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. We included studies that had individual-level data on autism, exposure measures pertaining to pregnancy or the 1st year of life, valid comparison groups, control for confounders, and adequate sample sizes. Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations, some environmental exposures showed associations with autism, especially traffic-related air pollutants, some metals, and several pesticides, with suggestive trends for some volatile organic compounds (e.g., methylene chloride, trichloroethylene, and styrene) and phthalates. Whether any of these play a causal role requires further study. Given the limited scope of these publications, other environmental chemicals cannot be ruled out, but have not yet been adequately studied. Future research that addresses these and additional environmental chemicals, including their most common routes of exposures, with accurate exposure measurement pertaining to several developmental windows, is essential to guide efforts for the prevention of the neurodevelopmental damage that manifests in autism symptoms.

Differential susceptibility to effects of maternal sensitivity? A study of candidate plasticity genes

Here we tested whether there was genetic moderation of effects of early maternal sensitivity on social–emotional and cognitive–linguistic development from early childhood onward and whether any detected Gene × Environment interaction effects proved consistent with differential-susceptibility or diathesis–stress models of Person × Environment interaction (N= 695). Two new approaches for evaluating models were employed with 12 candidate genes. Whereas maternal sensitivity proved to be a consistent predictor of child functioning across the primary-school years, candidate genes did not show many main effects, nor did they tend to interact with maternal sensitivity/insensitivity. These findings suggest that the developmental benefits of early sensitive mothering and the costs of insensitive mothering look more similar than different across genetically different children in the current sample. Although acknowledgement of this result is important, it is equally important that the generally null Gene × Environment results reported here not be overgeneralized to other samples, other predictors, other outcomes, and other candidate genes.

Catechol-O-methyltransferase gene methylation and substance use in adolescents: the TRAILS study

Substance use often starts in adolescence and poses a major problem for society and individual health. The dopamine system plays a role in substance use, and catechol-O-methyltransferase (COMT) is an important enzyme that degrades dopamine. The Val(108/158) Met polymorphism modulates COMT activity and thus dopamine levels, and has been linked to substance use. COMT gene methylation, on the other hand, may affect expression and thus indirectly COMT activity. We investigated whether methylation of the COMT gene was associated with adolescents' substance use. Furthermore, we explored whether the COMT Val(108/158) Met polymorphism interacts with COMT gene methylation in association with substance use. In 463 adolescents (mean age=16, 50.8% girls), substance use (cigarette smoking, alcohol and cannabis use) was assessed with self-report questionnaires. From blood samples, COMT Val(108/158) Met genotype and methylation rates of membrane bound (MB) and soluble (S) COMT promoters were assessed. MB-COMT promoter methylation was associated with non-daily smoking [odds ratio (OR)=1.82, P=0.03], but not with daily smoking (OR=1.20, P=0.34), MB-COMT promoter methylation was not associated with alcohol use. Adolescents with the Met/Met genotype and high rates of MB-COMT promoter methylation were less likely to be high-frequent cannabis users than adolescents with the Val/Val or Val/Met genotype. S-COMT promoter methylation was not associated with substance use. These results indicate that there is an association between substance use and COMT gene methylation. Although this association is complex, combining genetic and epigenetic variation of the COMT gene may be helpful in further elucidating the influence of the dopamine system on substance use in adolescence.

Empirically based phenotypic profiles of children with pervasive developmental disorders: interpretation in the light of the DSM-5

This study aimed to contribute to the Diagnostic and Statistical Manual (DSM) debates on the conceptualization of autism by investigating (1) whether empirically based distinct phenotypic profiles could be distinguished within a sample of mainly cognitively able children with pervasive developmental disorder (PDD), and (2) how profiles related to diagnoses and co-occurring behavioral and emotional problems. Six classes with distinct profiles were discerned. Three classes showed profiles not completely in line with the proposed DSM-5 conceptualization of autism. These classes included relatively many cognitively able individuals with PDD-not otherwise specified. However, profiles seemed to suit other diagnostic categories, such as social communication disorder. These alternative diagnoses could retain eligibility for services, and might adequately fit more specifically targeted interventions.

Attention deficit hyperactivity disorder

Over the last two decades, there have been numerous technical and methodological advances available to clinicians and researchers to better understand attention deficit hyperactivity disorder (ADHD) and its etiology. Despite the growing body of literature investigating the disorder's pathophysiology, ADHD remains a complex psychiatric disorder to characterize. This chapter will briefly review the literature on ADHD, with a focus on its history, the current genetic insights, neurophysiologic theories, and the use of neuroimaging to further understand the etiology. We address some of the major concerns that remain unclear about ADHD, including subtype instability, heterogeneity, and the underlying neural correlates that define the disorder. We highlight that the field of ADHD is rapidly evolving; the descriptions provided here will hopefully provide a sturdy foundation for which to build and improve our understanding of the disorder.

Beyond risk, resilience, and dysregulation: Phenotypic plasticity and human development

We provide a theoretical and empirical basis for the claim that individual differences exist in developmental plasticity and that phenotypic plasticity should be a subject of study in its own right. To advance this argument, we begin by highlighting challenges that evolutionary thinking poses for a science of development and psychopathology, including for the diathesis–stress framework that has (fruitfully) guided so much empirical inquiry on developmental risk, resilience, and dysregulation. With this foundation laid, we raise a series of issues that the differential-susceptibility hypothesis calls attention to, while highlighting findings that have emerged over just the past several years and are pertinent to some of the questions posed. Even though it is clear that this new perspective on Person × Environment interaction is stimulating research and influencing how hypotheses are framed and data interpreted, a great many topics remain that need empirical attention. Our intention is to encourage students of development and psychopathology to treat phenotypic plasticity as an individual-difference construct while exploring unknowns in the differential-susceptibility equation.

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.

Decreased serum levels of brain-derived neurotrophic factor in adults with attention-deficit hyperactivity disorder

It has been hypothesized that brain-derived neurotrophic factor (BDNF) is involved in the pathogenesis of attention-deficit hyperactivity disorder (ADHD), although experimental data regarding the contribution of BDNF gene polymorphisms to this psychiatric disorder are controversial. Recently, changes in BDNF serum levels have been reported in children with ADHD, but there are no studies about the possible role of this neurotrophin in adults. A total of 54 Caucasoid ADHD adults, including the predominantly inattentive and combined types (aged 33.43 ± 8.99 yr) and 59 Caucasoid unrelated healthy controls (aged 35.52 ± 9.37 yr) were included in a study to evaluate BDNF levels in serum. Medical, neurological and psychiatric co-morbidities were excluded. Clinical data concerning ADHD diagnosis and blood samples for patients and controls were collected. BDNF serum levels were significantly lower in adults with ADHD compared to healthy controls (p < 0.0001). Although the combined type of ADHD subgroup displayed lower BDNF serum levels than the inattentive type, the differences did not reach statistical significance. No significant correlations were found between serum BDNF levels and scores on the Conners' Adult ADHD Rating Subscales. These results suggest a role for BDNF in ADHD, at least in those patients whose disorder persists throughout life. Low BDNF levels may contribute to the neurodevelopmental deficits of ADHD and to the persistence of the disorder into adulthood. BDNF differences between ADHD subtypes should be further studied.

Autism risk factors: genes, environment, and gene-environment interactions

The aim of this review is to summarize the key findings from genetic and epidemiological research, which show that autism is a complex disorder resulting from the combination of genetic and environmental factors. Remarkable advances in the knowledge of genetic causes of autism have resulted from the great efforts made in the field of genetics. The identification of specific alleles contributing to the autism spectrum has supplied important pieces for the autism puzzle. However, many questions remain unanswered, and new questions are raised by recent results. Moreover, given the amount of evidence supporting a significant contribution of environmental factors to autism risk, it is now clear that the search for environmental factors should be reinforced. One aspect of this search that has been neglected so far is the study of interactions between genes and environmental factors.

Smoking during pregnancy and risk of autism spectrum disorder in a Finnish National Birth Cohort

BACKGROUND

Results of previous population-based studies examining associations between smoking during pregnancy and autism spectrum disorders (ASD) are contradictory. Furthermore, there is a lack of population-based studies examining the relationship between smoking during pregnancy and the main diagnostic subtypes of ASD.

METHODS

We conducted a population-based nested case-control study based on the Finnish Prenatal Study of Autism (FIPS-A) among liveborn infants delivered in Finland between 1987 and 2005. Data on maternal smoking during pregnancy were available from the Finnish Medical Birth Register (FMBR) since October 1990. Data on ASD in the offspring were obtained from the Finnish Hospital Discharge Register (FHDR).

RESULTS

Among the three subtypes of ASD, maternal smoking during the whole pregnancy was associated with an increased risk of pervasive developmental disorder (PDD) (odds ratio 1.2, 95% confidence interval 1.0, 1.5). The increase in odds persisted after controlling for maternal age, mother's socio-economic and psychiatric status, and infant's weight for gestational age. However, smoking exposure limited to the first trimester was not associated with PDD or any of the other ASD subtypes.

CONCLUSIONS

Maternal smoking is related to a modest increase in risk of PDD, while no associations were observed for childhood autism and Asperger's syndrome.

Effects of divorce on Dutch boys' and girls' externalizing behavior in Gene × Environment perspective: Diathesis stress or differential susceptibility in the Dutch Tracking Adolescents' Individual Lives Survey study?

The effects of divorce on children's behavioral development have proven to be quite varied across studies, and most developmental and family scholars today appreciate the great heterogeneity in divorce effects. Thus, this inquiry sought to determine whether select dopaminergic genes previously associated with externalizing behavior and/or found to moderate diverse environmental effects (dopamine receptors D2 and D4, catechol-O-methyltransferase) might moderate divorce effects on adolescent self-reported externalizing problems; and, if so, whether evidence of gene–environment (G × E) interaction would prove consistent with diathesis–stress or differential-susceptibility models of environmental action. Data from the first and third wave of the Dutch Tracking Adolescents' Individual Lives Survey (n = 1,134) revealed some evidence of G × E interaction reflecting diathesis–stress but not differential susceptibility. It is intriguing that some evidence pointed to “vantage sensitivity,” which are benefits accruing to those with a specific genotype when their parents remained together, the exact opposite of diathesis–stress. The limits of this work are considered, especially with regard to the conditions for testing differential susceptibility, and future directions are outlined.

The impact of serotonin transporter (5-HTTLPR) genotype on the development of resting-state functional connectivity in children and adolescents: a preliminary report

A fundamental component of brain development is the formation of large-scale networks across the cortex. One such network, the default network, undergoes a protracted development, displaying weak connectivity in childhood that strengthens in adolescence and becomes most robust in adulthood. Little is known about the genetic contributions to default network connectivity in adulthood or during development. Alterations in connectivity between posterior and frontal portions of the default network have been associated with several psychological disorders, including anxiety, autism spectrum disorders, schizophrenia, depression, and attention-deficit/hyperactivity disorder. These disorders have also been linked to variants of the serotonin transporter linked polymorphic region (5-HTTLPR). The LA allele of 5-HTTLPR results in higher serotonin transporter expression than the S allele or the rarer LG allele. 5-HTTLPR may influence default network connectivity, as the superior medial frontal region has been shown to be sensitive to changes in serotonin. Also, serotonin as a growth factor early in development may alter large-scale networks such as the default network. The present study examined the influence of 5-HTTLPR variants on connectivity between the posterior and frontal structures and its development in a cross-sectional study of 39 healthy children and adolescents. We found that children and adolescents homozygous for the S allele (S/S, n=10) showed weaker connectivity in the superior medial frontal cortex compared to those homozygous for the LA allele (LA/LA, n=13) or heterozygotes (S/LA, S/LG, n=16). Moreover, there was an age-by-genotype interaction, such that those with LA/LA genotype had the steepest age-related increase in connectivity between the posterior hub and superior medial frontal cortex, followed by heterozygotes. In contrast, individuals with the S/S genotype had the least age-related increase in connectivity strength. This preliminary report expands our understanding of the genetic influences on the development of large-scale brain connectivity and lays down the foundation for future research and replication of the results with a larger sample.

Epigenetics in Developmental Disorder: ADHD and Endophenotypes

Heterogeneity in attention-deficit/hyperactivity disorder (ADHD), with complex interactive operations of genetic and environmental factors, is expressed in a variety of disorder manifestations: severity, co-morbidities of symptoms, and the effects of genes on phenotypes. Neurodevelopmental influences of genomic imprinting have set the stage for the structural-physiological variations that modulate the cognitive, affective, and pathophysiological domains of ADHD. The relative contributions of genetic and environmental factors provide rapidly proliferating insights into the developmental trajectory of the condition, both structurally and functionally. Parent-of-origin effects seem to support the notion that genetic risks for disease process debut often interact with the social environment, i.e., the parental environment in infants and young children. The notion of endophenotypes, markers of an underlying liability to the disorder, may facilitate detection of genetic risks relative to a complex clinical disorder. Simple genetic association has proven insufficient to explain the spectrum of ADHD. At a primary level of analysis, the consideration of epigenetic regulation of brain signalling mechanisms, dopamine, serotonin, and noradrenaline is examined. Neurotrophic factors that participate in the neurogenesis, survival, and functional maintenance of brain systems, are involved in neuroplasticity alterations underlying brain disorders, and are implicated in the genetic predisposition to ADHD, but not obviously, nor in a simple or straightforward fashion. In the context of intervention, genetic linkage studies of ADHD pharmacological intervention have demonstrated that associations have fitted the "drug response phenotype," rather than the disorder diagnosis. Despite conflicting evidence for the existence, or not, of genetic associations between disorder diagnosis and genes regulating the structure and function of neurotransmitters and brain-derived neurotrophic factor (BDNF), associations between symptoms-profiles endophenotypes and single nucleotide polymorphisms appear reassuring.

Prenatal Maternal Stress Associated with ADHD and Autistic Traits in early Childhood

Research suggests that offspring of mothers who experience high levels of stress during pregnancy are more likely to have problems in neurobehavioral development. There is preliminary evidence that prenatal maternal stress (PNMS) is a risk factor for both autism and attention deficit hyperactivity disorder (ADHD), however most studies do not control for confounding factors and no study has investigated PNMS as a risk factor for behaviors characteristic of these disorders in early childhood. A population cohort of 2900 pregnant women were recruited before their 18th week of pregnancy and investigated prospectively. Maternal experience of stressful life events was assessed during pregnancy. When offspring were age 2 years, mothers completed the child behavior checklist. Multiple regression showed that maternal stressful events during pregnancy significantly predicted ADHD behaviors in offspring, after controlling for autistic traits and other confounding variables, in both males (p = 0.03) and females (p = 0.01). Similarly, stressful events during pregnancy significantly predicted autistic traits in the offspring after controlling for ADHD behaviors and confounding variables, in males only (p = 0.04). In conclusion, this study suggests that PNMS, in the form of typical stressful life events such as divorce or a residential move, show a small but significant association with both autistic traits and ADHD behaviors independently, in offspring at age 2 years, after controlling for multiple antenatal, obstetric, postnatal, and sociodemographic covariates. This finding supports future research using epigenetic, cross-fostering, and gene–environment interaction designs to identify the causal processes underlying this association.