The genetics of attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder in Medical Learners and Physicians and a Potentially Helpful Educational Tool

Purpose

Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by functionally impairing levels of inattention and/or hyperactive-impulsive behavior. It affects 3% to 5% of adults. This perspective piece aims to highlight the occurrence of ADHD in medical learners and physicians, including its reported prevalence in these groups, why reported rates may reflect underestimates, consequences of untreated symptoms, and a potentially helpful innovative educational tool to assist these individuals with a critical aspect of medical training and practice.

Results

Despite recent attention being paid to concerning levels of depression, anxiety, and burnout in medical learners and physicians, comparatively little attention has been devoted to the occurrence of ADHD in these groups. Reported rates of ADHD in medical learners and physicians, though low compared to rates of other mental health conditions and compared to rates of ADHD in the general population, may represent underestimates for a variety of reasons. The consequences of untreated ADHD symptoms are likely numerous and significant for these groups. Research has shown that about half of adults with ADHD discontinue prescribed treatment (stimulant medication) over time due to lack of perceived effectiveness, highlighting the need for durable, effective interventions to help medical learners and physicians with ADHD during and after their training. An innovative educational tool to assist medical learners and physicians with ADHD with a critical facet of their training and practice - the reading of scientific articles - is proposed, including a description of the tool, rationale for its design, practical considerations around implementation, and proposed directions for future research.

Conclusion

Untreated ADHD in medical learners and physicians may have numerous and significant consequences that can adversely impact training, practice, and ultimately patient care. These challenges warrant proper support for medical learners and physicians with ADHD via evidence-based treatments, program-based accommodations, and innovative educational tools.

Driving risks of young drivers with symptoms of attention deficit hyperactivity disorder: association with the dopamine transporter gene VNTR polymorphism

BACKGROUND

Road traffic injuries are a leading cause of death for young adults, and young drivers with higher expression of symptoms of attention deficit-hyperactivity disorder (ADHD) could pose an even greater risk in traffic. Dopaminergic dysfunction has been found to occur in ADHD, with the dopamine transporter (DAT) gene VNTR polymorphism (DAT1 VNTR; rs28363170) being one of the most consistent genetic markers. Thus, we aimed at clarifying how the ADHD symptoms and the DAT1 VNTR relate to risk-taking behaviour in traffic, impulsivity and driving anger in young drivers.

METHOD

We used data of two traffic behaviour study samples (n = 741, mean age = 23.3 ± 7.2 years; n = 995, mean age = 22.9 ± 8.1 years) and the Estonian Children Personality Behaviour and Health Study (ECPBHS; traffic behaviour data n = 1,016, mean age = 25.2 ± 2.1 years). ADHD symptoms were assessed by self-report with the Adult ADHD Self-Report Scale (ASRS v1.1) and impulsivity with the Adaptive and Maladaptive Impulsivity Scale. Traffic behavioural measures were either self-reported (Driver Behaviour Questionnaire, Driving Anger Scale) or obtained from databases (registered accidents and violations).

RESULTS

Drivers with more self-reported ADHD symptoms also reported more risk-taking in traffic and had more of recorded traffic accidents and violations. DAT1 9 R carriers had a higher probability of high traffic risk behaviour only if they also had ADHD symptoms.

CONCLUSION

Higher level of ADHD symptoms is a significant risk factor in traffic, and carrying of the DAT1 9 R allele appears to aggravate these risks.

ADGRL3, FGF1 and DRD4: Linkage and Association with Working Memory and Perceptual Organization Candidate Endophenotypes in ADHD

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurobehavioral disorder that affects children worldwide, with detrimental long-term consequences in affected individuals. ADHD-affected patients display visual-motor and visuospatial abilities and skills that depart from those exhibited by non-affected individuals and struggle with perceptual organization, which might partially explain impulsive responses. Endophenotypes (quantifiable or dimensional constructs that are closely related to the root cause of the disease) might provide a more powerful and objective framework for dissecting the underlying neurobiology of ADHD than that of categories offered by the syndromic classification. In here, we explore the potential presence of the linkage and association of single-nucleotide polymorphisms (SNPs), harbored in genes implicated in the etiology of ADHD (ADGRL3, DRD4, and FGF1), with cognitive endophenotypes related to working memory and perceptual organization in 113 nuclear families. These families were ascertained from a geographical area of the Caribbean coast, in the north of Colombia, where the community is characterized by its ethnic diversity and differential gene pool. We found a significant association and linkage of markers ADGRL3-rs1565902, DRD4-rs916457 and FGF1-rs2282794 to neuropsychological tasks outlining working memory and perceptual organization such as performance in the digits forward and backward, arithmetic, similarities, the completion of figures and the assembly of objects. Our results provide strong support to understand ADHD as a combination of working memory and perceptual organization deficits and highlight the importance of the genetic background shaping the neurobiology, clinical complexity, and physiopathology of ADHD. Further, this study supplements new information regarding an ethnically diverse community with a vast African American contribution, where ADHD studies are scarce.

Evolutionary conservations, changes of circadian rhythms and their effect on circadian disturbances and therapeutic approaches

The circadian rhythm is essential for the interaction of all living organisms with their environments. Several processes, such as thermoregulation, metabolism, cognition and memory, are regulated by the internal clock. Disturbances in the circadian rhythm have been shown to lead to the development of neuropsychiatric disorders, including attention-deficit hyperactivity disorder (ADHD). Interestingly, the mechanism of the circadian rhythms has been conserved in many different species, and misalignment between circadian rhythms and the environment results in evolutionary regression and lifespan reduction. This review summarises the conserved mechanism of the internal clock and its major interspecies differences. In addition, it focuses on effects the circadian rhythm disturbances, especially in cases of ADHD, and describes the possibility of recombinant proteins generated by eukaryotic expression systems as therapeutic agents as well as CRISPR/Cas9 technology as a potential tool for research and therapy. The aim is to give an overview about the evolutionary conserved mechanism as well as the changes of the circadian clock. Furthermore, current knowledge about circadian rhythm disturbances and therapeutic approaches is discussed.

Polymorphisms of Dopamine Receptor Genes and Parkinson's Disease: Clinical Relevance and Future Perspectives

Parkinson’s disease (PD) is a neurodegenerative disease caused by loss of dopaminergic neurons in the midbrain. PD is clinically characterized by a variety of motor and nonmotor symptoms, and treatment relies on dopaminergic replacement. Beyond a common pathological hallmark, PD patients may present differences in both clinical progression and response to drug therapy that are partly affected by genetic factors. Despite extensive knowledge on genetic variability of dopaminergic receptors (DR), few studies have addressed their relevance as possible influencers of clinical heterogeneity in PD patients. In this review, we summarized available evidence regarding the role of genetic polymorphisms in DR as possible determinants of PD development, progression and treatment response. Moreover, we examined the role of DR in the modulation of peripheral immunity, in light of the emerging role of the peripheral immune system in PD pathophysiology. A better understanding of all these aspects represents an important step towards the development of precise and personalized disease-modifying therapies for PD.

Shared alterations in resting-state brain connectivity in adults with attention-deficit/hyperactivity disorder and their unaffected first-degree relatives

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a developmental condition that often persists into adulthood with extensive negative consequences on quality of life. Despite emerging evidence indicating the genetic basis of ADHD, investigations into the familial expression of latent neurocognitive traits remain limited.

METHODS

In a group of adult ADHD probands (n = 20), their unaffected first-degree relatives (n = 20) and typically developing control participants (n = 20), we assessed endophenotypic alterations in the default mode network (DMN) connectivity during resting-state functional magnetic resonance imaging in relation to cognitive performance and clinical symptoms. In an external validation step, we also examined the dimensional nature of this neurocognitive trait in a sample of unrelated healthy young adults (n = 100) from the Human Connectome Project (HCP).

RESULTS

The results illustrated reduced anti-correlations between the posterior cingulate cortex/precuneus and right middle frontal gyrus that was shared between adult ADHD probands and their first-degree relatives, but not with healthy controls. The observed connectivity alterations were linked to higher ADHD symptoms that was mediated by performance in a sustained attention task. Moreover, this brain-based neurocognitive trait dimensionally explained ADHD symptom variability in the HCP sample.

CONCLUSIONS

Alterations in the default mode connectivity may represent a dimensional endophenotype of ADHD, hence a significant aspect of the neuropathophysiology of this disorder. As such, brain network organisation can potentially be employed as an important neurocognitive trait to enhance statistical power of genetic studies in ADHD and as a surrogate efficacy endpoint in the development of novel pharmaceuticals.

Siblings and Birth Order-Are They Important for the Occurrence of ADHD?

Objective: The associations of birth order, number of siblings, and ADHD was examined. Method: The analysis based on representative, epidemiological data from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) study (N = 13,488). Results: An increased risk for ADHD in firstborn versus youngest born children (odds ratio [OR] = 1.31, 95% confidence interval [CI] [1.09, 1.58]) and also versus children with no sibling (OR = 1.31, 95% CI [1.03, 1.68]) was revealed, while number of siblings was not associated with ADHD. Results remained stable after controlling for confounders. Conclusion: Firstborn children may receive simultaneously less parental resources and more responsibilities if younger siblings are born. This happens during the vulnerable developmental period of ADHD. In addition, due to higher levels of insecurity, parents are assumed to focus more on potential physical or psychological abnormities in their firstborn children. This may result in a diagnostic bias in firstborn children.

Trajectories of academic achievement for students with attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is associated with negative social and occupational outcomes across the life course. However, there has been limited population-based research that quantifies the impact of ADHD on academic achievement and academic trajectories.

AIMS

To compare academic performance and academic trajectories of students with ADHD with students without a mental disorder.

SAMPLE

Data were drawn from Young Minds Matter, a national population-based sample of 6,310 Australian children and adolescents aged 4-17 years. Using linked achievement test data, the academic performance and trajectories of 327 students with ADHD were compared with those of 3,916 students without a mental disorder.

METHODS

Survey data were combined with scores on national standardized tests for literacy and numeracy over an 8-year period.

RESULTS

In Year 3, students with ADHD were on average 1 year behind students with no mental disorder in reading and numeracy, and 9 months behind in writing. In Year 9, the gaps were much larger with students with ADHD on average 2.5 years behind in reading, 3 years behind in numeracy, and 4.5 years behind in writing.

CONCLUSIONS

Students with ADHD have substantially lower achievement in reading, writing, and numeracy. Writing was the most adversely affected domain. For example, in Year 9 students with ADHD were on average writing at a Year 5 level. Children and adolescents with ADHD need substantial support to manage inattention, impulsivity, and hyperactivity. Skilled remediation in literacy and numeracy is required throughout all school years.

Plasmalogens, platelet-activating factor and beyond - Ether lipids in signaling and neurodegeneration

Glycerol-based ether lipids including ether phospholipids form a specialized branch of lipids that in mammals require peroxisomes for their biosynthesis. They are major components of biological membranes and one particular subgroup, the plasmalogens, is widely regarded as a cellular antioxidant. Their vast potential to influence signal transduction pathways is less well known. Here, we summarize the literature showing associations with essential signaling cascades for a wide variety of ether lipids, including platelet-activating factor, alkylglycerols, ether-linked lysophosphatidic acid and plasmalogen-derived polyunsaturated fatty acids. The available experimental evidence demonstrates links to several common players like protein kinase C, peroxisome proliferator-activated receptors or mitogen-activated protein kinases. Furthermore, ether lipid levels have repeatedly been connected to some of the most abundant neurological diseases, particularly Alzheimer's disease and more recently also neurodevelopmental disorders like autism. Thus, we critically discuss the potential role of these compounds in the etiology and pathophysiology of these diseases with an emphasis on signaling processes. Finally, we review the emerging interest in plasmalogens as treatment target in neurological diseases, assessing available data and highlighting future perspectives. Although many aspects of ether lipid involvement in cellular signaling identified in vitro still have to be confirmed in vivo, the compiled data show many intriguing properties and contributions of these lipids to health and disease that will trigger further research.

Catechol-O-methyltransferase Val158Met Genotype and Early-Life Family Adversity Interactively Affect Attention-Deficit Hyperactivity Symptoms Across Childhood

Attention-deficit hyperactivity disorder (ADHD) is among the most commonly diagnosed psychiatric disorders of childhood. The dopaminergic system has been shown to have substantial effects on its etiology, with both functional Catechol-O-methyltransferase (COMT) Val158Met genotype and early-life environmental adversity involved in the risk of inattention and hyperactivity/impulsivity symptoms. In this prospective longitudinal study, we examined for the first time the impact of proximal and distal early-life family adversity and COMT Val158Met polymorphism gene - both the direct and the interactive effects, on children's ADHD symptoms across childhood. Data came from the Family Life Project, a prospective longitudinal study of 1,292 children and families in high poverty from birth to 11 years. In infancy, data regarding socioeconomic (SES)-risk-factors, observed-caregiving behaviors, and DNA genotyping were collected. In early and middle childhood teachers rated the occurrence and severity of the child's ADHD symptoms. Multilevel growth curve models revealed independent effects of COMT, early-life SES-risk and negative caregiving on ADHD symptoms in early and middle childhood. Significant gene-environment interactions were found, indicating that overall, carriers of at least one COMT158Met allele were more sensitive to early-life adversity, showing higher inattention and hyperactivity/impulsivity symptoms severity in childhood when exposed to high SES-risk factors in infancy, compared to Val-Val carriers. Findings provide new insights into the complex etiology of ADHD and underline the need for further investigation of the neuronal mechanisms underlying gene-environment interactions. Findings might have implications for prevention and intervention strategies with a focus on early-life family relationships in genetically at-risk children.

Disturbed neurotransmitter homeostasis in ether lipid deficiency

Plasmalogens, the most prominent ether (phospho)lipids in mammals, are structural components of most cellular membranes. Due to their physicochemical properties and abundance in the central nervous system, a role of plasmalogens in neurotransmission has been proposed, but conclusive data are lacking. Here, we targeted this issue in the glyceronephosphate O-acyltransferase (Gnpat) KO mouse, a model of complete deficiency in ether lipid biosynthesis. Throughout the study, focusing on adult male animals, we found reduced brain levels of various neurotransmitters. In the dopaminergic nigrostriatal tract, synaptic endings but not neuronal cell bodies were affected. Neurotransmitter turnover was altered in ether lipid-deficient murine as well as human post-mortem brain tissue. A generalized loss of synapses did not account for the neurotransmitter deficits, since the levels of several presynaptic proteins appeared unchanged. However, reduced amounts of vesicular monoamine transporter indicate a compromised vesicular uptake of neurotransmitters. As exemplified by norepinephrine, the release of neurotransmitters from Gnpat KO brain slices was diminished in response to strong electrical and chemical stimuli. Finally, addressing potential phenotypic correlates of the disturbed neurotransmitter homeostasis, we show that ether lipid deficiency manifests as hyperactivity and impaired social interaction. We propose that the lack of ether lipids alters the properties of synaptic vesicles leading to reduced amounts and release of neurotransmitters. These features likely contribute to the behavioral phenotype of Gnpat KO mice, potentially modeling some human neurodevelopmental disorders like autism or attention deficit hyperactivity disorder.

Efficacy of intervention at traffic schools reducing impulsive action, and association with candidate gene variants

OBJECTIVE

Road traffic injuries are the leading cause of death among young people. Recognition of the contribution of impulsive behaviour may help novice drivers to behave more safely. Previously a brief intervention focusing on impulsive traffic behaviour conducted by psychologists in driving schools had been effective. The aim of this study was an independent re-evaluation of the effect of the intervention, as conducted by driving school teachers, and assessment of the potential associations with candidate genotypes.

METHODS

Driving school students (mean age 22.5, SD=7.9) were divided into intervention (n=704) and control (n=737) groups. Driving school teachers were trained to administer the intervention which consisted of a lecture and group work (1.5 h in total) on impulsivity. Traffic offences and crashes were monitored during 3 years, using police and traffic insurance fund databases. Functional polymorphisms of the dopamine transporter (DAT) and serotonin transporter genes (DAT1 VNTR and 5-HTTLPR) were assessed.

RESULTS

The intervention significantly lowered general traffic risk and prevalence of traffic accidents. DAT1 VNTR 9R carriers, particularly males, had higher general traffic risk in the whole sample. Female 5-HTTLPR s' allele carriers of the intervention group had the lowest general traffic risk. Intervention was most effective in female DAT1 VNTR 10R/10R homozygotes.

CONCLUSIONS

Brief impulsivity-centred intervention appears as a promising strategy for preventing risk-taking behaviour in novice drivers and can be fully integrated to driving school curriculum.

Evidence of concurrent and prospective associations between early maltreatment and ADHD through childhood and adolescence

PURPOSE

An emerging body of work suggests a link between childhood maltreatment and attention-deficit hyperactivity disorder (ADHD). However, research examining the role of maltreatment in the early course of the disorder lacks robust evidence from longitudinal studies. Our aim was to examine concurrent and prospective associations between maltreatment experiences and ADHD diagnosis and sex differences, and to estimate the association between repetitive maltreatment exposure and ADHD through childhood and adolescence.

METHODS

Data were obtained from the Boricua Youth Study, a longitudinal study of 2480 children and adolescents of Puerto Rican background. Neglect, physical, emotional and sexual abuse, and foster placement were regressed on ADHD diagnosis measured at each of three waves using the Diagnostic Interview Schedule for Children-IV. Multilevel regressions estimated the effects of exposure on ADHD, adjusted by age, sex, income, household education, parental psychopathology, comorbidity and ADHD medication status.

RESULTS

Emotional abuse and foster placement had robust associations with ADHD diagnosis. For girls, physical abuse had a threefold increase in the odds of having ADHD diagnosis; for boys, associations were observed only for emotional abuse. Prospective models examining the risk of ADHD following maltreatment provided initial evidence for the effects of physical abuse on ADHD, and a linear trend for repetitive exposure suggested increased probability for disorder persistence.

CONCLUSIONS

Associations between early maltreatment and ADHD were robust. Different categories of maltreatment increase the likelihood of ADHD for girls and boys. Increased exposure to maltreatment may predict symptom persistence. Interventions addressing ADHD must consider the effects of both sex and family environment.

Relapse of drunk driving and association with traffic accidents, alcohol-related problems and biomarkers of impulsivity

OBJECTIVE

Individual biological predispositions should play a role in risky driving behaviour. Platelet monoamine oxidase (MAO) activity, dopamine transporter gene (DAT1) and neuropeptide S receptor 1 (NPSR1) gene polymorphisms have been identified as markers of impulsivity, alcohol use and excessive risk-taking. We aimed to find out how this knowledge on neurobiology of impulsivity applies to drunk driving and traffic behaviour in general.

METHODS

We have longitudinally examined the behaviour of drunk drivers (n = 203) and controls (n = 211) in traffic, in association with their alcohol-related problems, personality measures and the three biomarkers. We analysed differences between the subjects based on whether they had committed driving while impaired by alcohol (DWI) violation in a 10-year time period after recruitment or not and investigated further, what kind of predictive value do the different biomarkers have in committing DWI and other traffic violations and accidents.

RESULTS

The original drunk drivers group had lower platelet MAO activity but further DWI was not significantly associated with this measure. Being a NPSR1 T-allele carrier contributed to the risk of repeatedly committing DWI. DAT1 9R carriers in contrast were involved in more traffic accidents by their own fault (active accidents), compared to 10R homozygotes in the whole sample. All groups with DWI also had significantly more alcohol-related problems and higher scores in maladaptive impulsivity compared to controls without DWI.

CONCLUSIONS

Established biological markers of alcohol use and impulsivity can be reliably associated with everyday traffic behaviour and help in contributing to the understanding of the need for more personalized prevention activities.

Stress response genes associated with attention deficit hyperactivity disorder: A case-control study in Chinese children

To explore the associations between stress response genes and attention deficit hyperactivity disorder (ADHD) in children, we conducted a case-control study consisting of 406 newly diagnosed ADHD cases and 432 controls in Wuhan, China. We genotyped the candidate genes, nuclear receptor subfamily 3 group C member 1(NR3C1) and solute carrier family 6 member 4(SLC6A4), using the Sequenom MassARRAY technology. After correction by Bonferroni (α' = 0.05/6 = 0.008), the rs6191 SNP was found to be associated with a reduced risk of ADHD in the dominant model (OR = 0.564, 95% CI = 0.389-0.819, P = 0.003) while the rs25531 SNP was associated with an increased risk of ADHD in the multiplicative model (OR = 1.380, 95% CI = 1.111-1.714, P = 0.004). Additionally, both the rs6191 and rs25531 SNPs were significantly associated with the attention deficit factor (P = 0.006, P = 0.003, respectively) but not with the hyperactivity/impulsivity factor in the Swanson, Nolan and Pelham-IV Questionnaire (SNAP-IV) scale. Furthermore, we found that these two SNPs were significantly associated with pure ADHD, and not affected by the comorbidities (P =  0.001, P =  0.007, respectively). Besides, there was an interaction between these two SNPs. This study demonstrated the role of NR3C1 and SLC6A4 polymorphisms in ADHD, yet independent replication of the findings of this study in multi-center and multi-stage studies with large samples is warranted in the future.

Reduced Prefrontal Gyrification in Carriers of the Dopamine D4 Receptor 7-Repeat Allele With Attention Deficit/Hyperactivity Disorder: A Preliminary Report

Objective: Structural and functional abnormalities have been noted in the prefrontal cortex of individuals with neurodevelopmental disorders such as attention deficit/hyperactivity disorder (ADHD). Cortical thickness and gyrification, both of which have been reported as abnormal in the prefrontal cortex in ADHD, are thought to be modulated by genetic influences during neural development. This study aimed to investigate the effects of a polymorphism of the dopamine DRD4 gene (the 7-repeat (7R) "risk" allele) on thickness and gyrification as distinct parameters of prefrontal cortical structure in children with ADHD. Method: Structural images and genetic samples were obtained from 49 children aged 9-15 years (25 with ADHD and 24 matched controls), and measures of cortical thickness and gyrification for inferior, middle, and superior frontal cortex were calculated. Results: A significant interaction between diagnosis and genotype on prefrontal gyrification was observed, largely driven by reduced inferior frontal gyrification in patients who carried the DRD4 7R allele. Furthermore, inferior frontal gyrification-but not thickness-related to everyday executive functioning in 7R allele carriers across groups. Conclusions: Prefrontal gyrification is reduced in children with ADHD who also carry the DRD4 7R allele, and it relates to critical functional skills in the executive domain in carriers of the risk allele. More broadly, these effects highlight the importance of considering precise neurodevelopmental mechanisms through which risk alleles influence cortical neurogenesis and migration.

Genetic association study of dyslexia and ADHD candidate genes in a Spanish cohort: Implications of comorbid samples

Dyslexia and attention deficit hyperactivity disorder (ADHD) are two complex neuro-behaviorally disorders that co-occur more often than expected, so that reading disability has been linked to inattention symptoms. We examined 4 SNPs located on genes previously associated to dyslexia (KIAA0319, DCDC2, DYX1C1 and FOXP2) and 3 SNPs within genes related to ADHD (COMT, MAOA and DBH) in a cohort of Spanish children (N = 2078) that met the criteria of having one, both or none of these disorders (dyslexia and ADHD). We used a case-control approach comparing different groups of samples based on each individual diagnosis. In addition, we also performed a quantitative trait analysis with psychometric measures on the general population (N = 3357). The results indicated that the significance values for some markers change depending on the phenotypic groups compared and/or when considering pair-wise marker interactions. Furthermore, our quantitative trait study showed significant genetic associations with specific cognitive processes. These outcomes advocate the importance of establishing rigorous and homogeneous criteria for the diagnosis of cognitive disorders, as well as the relevance of considering cognitive endophenotypes.

COMT Val158Met Polymorphism and Social Impairment Interactively Affect Attention-Deficit Hyperactivity Symptoms in Healthy Adolescents

The dopaminergic system has been shown to have substantial effects on the etiology of attention-deficit hyperactivity disorder (ADHD). However, while some studies found a significant direct effect, others did not. In this context, social behavior might play an important role as a factor that is related both to the dopaminergic system and ADHD. In a large epidemiological sample of adolescents (N = 462; 16-17 years), we assessed the level of ADHD symptoms using the Strengths and Difficulties Questionnaire, social behavior using the Social Responsiveness Scale, and the allelic distribution of the dopaminergic catechol-O-methyltransferase (COMT) Val158Met polymorphism. We found a significant association between COMT and social impairment, insofar as Met-allele carriers showed increased levels of social impairment. Moreover, social impairment significantly determined an association between COMT and ADHD (explained variance: 19.09%). This effect did not significantly differ between males and females. COMT and social impairment might interactively affect ADHD symptomatology, and could thus represent significant gene-phenotypic risk factors for ADHD symptomatology. This might have interesting implications for prevention and intervention strategies with a focus on social behavior in genetically at-risk individuals.

Neurodevelopmental disorders in prison inmates: comorbidity and combined associations with psychiatric symptoms and behavioural disturbance

The identification and management of inmates with neurodevelopmental disorders (ND) has been insufficiently addressed in the literature. We estimated the proportion of cases with Attention deficit/hyperactivity disorder (ADHD), Autism spectrum disorder (ASD) and Intellectual disability (ID) in prison, their comorbidity, and associations with disruptive behaviours and with psychiatric symptoms. Further, we examined the role of coexisting ND on psychiatric symptoms and attitudes toward violence. All 390 male inmates underwent an assessment that included the Diagnostic Interview for ADHD in Adults 2.0, the Autism Quotient, the Learning Disability Screening Questionnaire, the Brief Symptom Inventory (BSI), and measures of disruptive behaviours and attitudes towards violence. The percentage of cases with ADHD, ASD and ID were 25%, 9% and 9%. Inmates with ADHD and those with ID had significantly higher levels of disruptive behaviours. The combined ADHD/ASD group had significantly higher scores on global severity symptoms than either ADHD or ASD only. Meanwhile, the combined ADHD/ID group had significantly higher scores of behavioural disturbance than the ADHD-only group. Our findings show the extent of ND in prison, their inter-relations and associations with further mental health problems. Vulnerabilities conferred by ND within the criminal justice system should be addressed via interventions and preventative strategies.

A Prospective 30-Year Follow-Up of ADHD Associated With Perinatal Risks

OBJECTIVE

Longitudinal follow-up of ADHD suggests a poorer outcome in those affected. Studies extending to 30 years however are rare. We investigated the adult outcome of ADHD associated with perinatal risks (PRs), treated non-pharmacologically.

METHOD

A study group of 122 participants (86 men, 36 women) with PR-associated ADHD was followed-up from birth and compared with a control group also prospectively studied.

RESULTS

The study group showed more cognitive, motor perception, and learning impairments as well as psychiatric problems at ages 5, 9, and 16. At age 30, the study group reported less education, more involuntary job dismissals and more alcohol abuse. Self-reported ADHD symptoms were still prevalent in adulthood.

CONCLUSION

ADHD symptoms persist and impair the long-term educational, occupational, and psychiatric outcome. ADHD in participants with PR appears to follow a course seen in studies of unselected ADHD.

Exposure to sevoflurane anesthesia during development does not impair aspects of attention during adulthood in rats

Exposure to general anesthetic agents during development has been associated with neurotoxicity and long-term behavioral impairments in rodents and non-human primates. The phenotype of anesthetic-induced cognitive impairment has a robust learning and memory component, however less is known about other psychological domains. Data from retrospective human patient studies suggest that children undergoing multiple procedures requiring general anesthesia are at increased risk of attention deficit hyperactivity disorder. We therefore assessed whether single or repeated exposures of neonatal rats to general anesthesia caused long-term attentional impairments. Female or male Long-Evans pups were exposed to 2.5% sevoflurane for 2h on postnatal day (P) 7, or for 2h each on P7, P10 and P13. Rats were behaviorally tested in late adolescence on the sustained attention task and on the attentional set shifting task. There was no compelling evidence for anesthetic-induced impairment in attentional processing in adult rats exposed to general anesthesia as neonates. These results suggest that, at least at the developmental stage tested here, the phenotype of anesthetic-induced cognitive impairment does not involve disruptions to attentional processing.

Lack of kinase-independent activity of PI3Kγ in locus coeruleus induces ADHD symptoms through increased CREB signaling

Although PI3Kγ has been extensively investigated in inflammatory and cardiovascular diseases, the exploration of its functions in the brain is just at dawning. It is known that PI3Kγ is present in neurons and that the lack of PI3Kγ in mice leads to impaired synaptic plasticity, suggestive of a role in behavioral flexibility. Several neuropsychiatric disorders, such as attention-deficit/hyperactivity disorder (ADHD), involve an impairment of behavioral flexibility. Here, we found a previously unreported expression of PI3Kγ throughout the noradrenergic neurons of the locus coeruleus (LC) in the brainstem, serving as a mechanism that regulates its activity of control on attention, locomotion and sociality. In particular, we show an unprecedented phenotype of PI3Kγ KO mice resembling ADHD symptoms. PI3Kγ KO mice exhibit deficits in the attentive and mnemonic domains, typical hyperactivity, as well as social dysfunctions. Moreover, we demonstrate that the ADHD phenotype depends on a dysregulation of CREB signaling exerted by a kinase-independent PI3Kγ-PDE4D interaction in the noradrenergic neurons of the locus coeruleus, thus uncovering new tools for mechanistic and therapeutic research in ADHD.

The Association of SNAP25 Gene Polymorphisms in Attention Deficit/Hyperactivity Disorder: a Systematic Review and Meta-Analysis

Attention deficit/hyperactivity disorder (ADHD) is one of the most highly heritable psychiatric disorders in childhood. The risk gene mutation accounts for about 60 to 90 % cases. Synaptosomal-associated protein of 25 kDa (SNAP-25) is a presynaptic plasma membrane protein which is expressed highly and specifically in the neuronal cells. A number of evidences have suggested the role of SNAP-25 in the etiology of ADHD. Notably, the animal model of coloboma mouse mutant bears a ∼2-cM deletion encompassing genes including SNAP25 and displays spontaneous hyperkinetic behavior. Previous investigators have reported association between SNPs in SNAP25 and ADHD, and controversial results were observed. In this study, we analyzed the possible association between six polymorphisms (rs3746544, rs363006, rs1051312, rs8636, rs362549, and rs362998) of SNAP25 and ADHD in a pooled sample of ten family-based studies and four case-control studies by using meta-analysis. The combined analysis results were significant only for rs3746544 (P = 0.010) with mild association (odds ratio (OR) = 1.14). And, the meta-analysis data for rs8636, rs362549, and rs362998 are the first time to be reported; however, no positive association was detected. In conclusion, we report some evidence supporting the association of SNAP25 to ADHD. Future research should emphasize genome-wide association studies in more specific subgroups and larger independent samples.

Hyperactivity and impaired attention in Gamma aminobutyric acid transporter subtype 1 gene knockout mice

OBJECTIVES

Attention-deficit hyperactivity disorder (ADHD) is a common neurobehavioural disorder. It is conceivable that Gamma aminobutyric acid (GABA) neurotransmission is implicated in the pathophysiology of ADHD. This study investigated the effect of GABA transporter 1 (GAT-1) on the anxiety-like behaviours and cognitive function in knockout mice.

METHODS

In all, 20 adult male mice were divided into two groups: wild-type (WT) group and GAT-1-/- group. The open field test, elevated O-maze (EZM) and Morris water maze were used to evaluate behavioural traits relevant to ADHD.

RESULTS

Compared with WT mice, the GAT-1-/- mice travelled longer and displayed an enhanced kinematic velocity with the significant reduction of rest time in the open field test (p<0.05). The EZM showed that GAT-1-/- mice displayed a significant increase in total entries into the open sectors and the closed sectors compared with the WT mice. The WT mice showed shorter latencies after the training session (p<0.01), whereas the GAT-1-/- mice made no difference during probe test, the GAT-1-/- mice spent less time in the target quadrant (p<0.01).

CONCLUSION

Our results demonstrated that GAT-1-/- mice have phenotypes of hyperactivity, impaired sustained attention and learning deficiency, and the performance of GAT-1-/- mice is similar to ADHD symptoms. So, the study of the GAT-1-/- mice may provide new insights into the mechanisms and the discovery of novel therapeutics for the treatment of ADHD.

Lack of association of polymorphisms in six candidate genes in colombian adhd patients

BACKGROUND

Attention Deficit and Hyperactivity Disorder (ADHD) is a common childhood neuropsychiatric condition. The disorder has a multifactorial background, with heritability estimates of around 76%, suggesting an important role of genetic factors. Candidate genes include those related to dopaminergic (e.g. DRD4, DRD5, SLC6A3 and DBH)and serotoninergic (e.g.HTR1B and SLC6A4) pathways.

PURPOSE

To explore the association of common polymorphisms in six genes (DRD4, DRD5, SLC6A3, DBH, HTR1B and SLC6A4) and the susceptibility to ADHD in a Colombian sample population.

METHODS

trios and 152 healthy controls were recruited. Genotyping of the six polymorphisms was performed using described PCR-based protocols. A TDT analysis was used to test if there was preferential allelic transmission for any of the six polymorphisms. Additionally, a case-control analysis was performed to test for association of the serotoninergic (HTR1B and SLC6A4) polymorphisms with ADHD.

RESULTS

Through the TDT analysis there was no preferential allelic transmission for any of the studied variants. Case-control analysis did not show association.

CONCLUSION

This is the first study in Latin America to describe six polymorphisms in a group of patients with ADHD. There was no evidence of association for any of the studied polymorphic variants in this Colombian ADHD sample. Further research, with larger sample sizes and study of endophenotypes, is needed in this population to confirm and extend the results.

Psychological Consequences of Early Global Deprivation

The English & Romanian Adoptees (ERA) study follows children who spent their first years of life in extremely depriving Romanian institutions before they were adopted by families in the UK. The ERA study constitutes a “natural experiment” that allows the examination of the effects of radical environmental change from a profoundly depriving institutional environment to an adoptive family home. The cohort has been assessed at ages 4, 6, 11, and 15 years, and has provided seminal insights into the effects of early global deprivation. The current paper focuses on the long-term psychological sequelae associated with deprivation experiences. These deprivation-specific problems (DSPs) constitute a striking pattern of behavioral impairments, in its core characterized by deficits in social cognition and behavior, as well as quasi-autistic features, often accompanied by cognitive impairment and symptoms of attention-deficit/hyperactivity disorder (ADHD). Possible moderating influences, including variations in family environment, pre-adoption characteristics, and genetic variation, will be discussed to answer the question why some individuals have prospered while others have struggled. Apart from findings on the moderating effect of variation in genes associated with serotonergic and dopaminergic signaling involving specific phenotypes, heterogeneity in outcome is largely unexplained. The review concludes with an outlook on currently ongoing and future research of the ERA study cohort, which involves the investigation of neurobiological and epigenetic mechanisms as possible mediators of the long-term effects of institutional deprivation.

Genetic Influence on Slope Variability in a Childhood Reflexive Attention Task

Individuals are not perfectly consistent, and interindividual variability is a common feature in all varieties of human behavior. Some individuals respond more variably than others, however, and this difference may be important to understanding how the brain works. In this paper, we explore genetic contributions to response time (RT) slope variability on a reflexive attention task. We are interested in such variability because we believe it is an important part of the overall picture of attention that, if understood, has the potential to improve intervention for those with attentional deficits. Genetic association studies are valuable in discovering biological pathways of variability and several studies have found such associations with a sustained attention task. Here, we expand our knowledge to include a reflexive attention task. We ask whether specific candidate genes are associated with interindividual variability on a childhood reflexive attention task in 9–16 year olds. The genetic makers considered are on 11 genes: APOE, BDNF, CHRNA4, COMT, DRD4, HTR4, IGF2, MAOA, SLC5A7, SLC6A3, and SNAP25. We find significant associations with variability with markers on nine and we discuss the results in terms of neurotransmitters associated with each gene and the characteristics of the associated measures from the reflexive attention task.

Maternal alcohol consumption

Background Despite decades of research, the aetiology of attention deficit disorder with hyperactivity (ADHD) remains largely unknown. Next to a strong genetic component, increasing evidence suggests additional adverse impact of environmental factors, two of which have, although controversially, withstood meta-analysis: gestational exposure to smoking (OR 2.39) and low birth weight (OR 2.64). Several studies have investigated a possible association between prenatal exposure to alcohol and ADHD, although the matter is complicated due to foetal alcohol syndrome disorders (FASD) with ADHD-like symptoms. Questions Can an estimate of the effect of gestational exposure to alcohol for ADHD be determined? What is the relevance of primary care services in screening and intervention in mild to moderate drinking in pregnant women? Method MEDLINE, Cinahl, PsychInfo, EMBASE (1995-2008) were searched for articles in English, supplemented by a manual search. Out of 23 reviewed studies, three were included in the metaanalysis; one further study was added to undertake a sub-analysis comparing severe versus mild alcohol consumption. Summary odds ratios (OR) were extracted and fixed/random-effects meta-analysis were used for combining the OR's. Heterogeneity across the studies was formally assessed using Cochran's Q. Results An OR of 2.33 (95% CI, 1.18-4.61), (z = 2.43, p = 0.02) suggests that exposed children are 2.33 times more likely to have ADHD than non exposed children. Discussion Our meta-analysis suggests that children exposed to alcohol during pregnancy are at risk for ADHD. However, evidence is sparse and it remains uncertain whether a causal association exists. Further research is needed into dose-response relationship, timing of exposure, influence of genetic factors involved in maternal alcohol abuse and the role of FASD in ADHD-like symptoms. If a detrimental effect of mild to moderate drinking on the offspring is supported by stronger evidence, primary care services could have a major role in prevention and early intervention. This would be in addition to their already established role in helping heavy drinking mothers.

Genetic and pharmacological modulation of the steroid sulfatase axis improves response control; comparison with drugs used in ADHD

Maladaptive response control is a feature of many neuropsychiatric conditions, including attention deficit hyperactivity disorder (ADHD). As ADHD is more commonly diagnosed in males than females, a pathogenic role for sex-linked genes has been suggested. Deletion or point mutation of the X-linked STS gene, encoding the enzyme steroid sulfatase (STS) influences risk for ADHD. We examined whether deletion of the Sts gene in the 39,X(Y*)O mouse model, or pharmacological manipulation of the STS axis, via administration of the enzyme substrate dehydroepiandrosterone sulfate or the enzyme inhibitor COUMATE, influenced behavior in a novel murine analog of the stop-signal reaction time task used to detect inhibitory deficits in individuals with ADHD. Unexpectedly, both the genetic and pharmacological treatments resulted in enhanced response control, manifest as highly specific effects in the ability to cancel a prepotent action. For all three manipulations, the effect size was comparable to that seen with the commonly used ADHD therapeutics methylphenidate and atomoxetine. Hence, converging genetic and pharmacological evidence indicates that the STS axis is involved in inhibitory processes and can be manipulated to give rise to improvements in response control. While the precise neurobiological mechanism(s) underlying the effects remain to be established, there is the potential for exploiting this pathway in the treatment of disorders where failures in behavioral inhibition are prominent.

Association of SNAP-25 Gene Ddel and Mnll Polymorphisms with Adult Attention Deficit Hyperactivity Disorder

OBJECTIVE

The synaptosomal-associated protein of 25 kDa (SNAP-25) gene is a presynaptic plasma membrane protein and an integral component of the vesicle docking and fusion machinery mediating secretion of neurotransmitters. Previously, several studies reported association between SNAP-25 and attention deficit hyperactivity disorder (ADHD). We investigated whether these SNAP-25 polymorphisms (MnlI T/G and DdelI T/C) were also associated with ADHD in the Turkish population.

METHODS

Our study comprised unrelated 139 subjects who met DSM-IV criteria for ADHD and 73 controls and all were of Turkish origin. Genetic analyses were performed and patients were evaluated with Wender-Utah Rating Scale and Adult ADD/ADHD DSM IV-Based Diagnostic Screening and Rating Scale.

RESULTS

SNAP-25 DdelI polymorphism was not associated with ADHD but there was a statistically significant difference between ADHD patients and controls for SNAP-25 MnlI polymorphism. For SNAP-25 MnlI polymorphism patients with G/G genotype of the SNAP-25 gene MnlI polymorphism had higher Wender-Utah scores and higher scores in the 1st and 3rd parts of adult ADD/ADHD Scale.

CONCLUSION

We detected a significant association of the MnlI polymorphism in our ADHD sample which was similar to previous findings. Our study also revealed that SNAP-25 MnlI polymorphism was also associated with symptom severity of ADHD. This study is also, the first report on the association of SNAP-25 with ADHD in the Turkish population.

Sex differences in attention Deficit Hyperactivity Disorder: candidate genetic and endocrine mechanisms

Attention Deficit Hyperactivity Disorder (ADHD) is a developmental condition characterised by severe inattention, pathological impulsivity and hyperactivity; it is relatively common affecting up to 6% of children, and is associated with a risk of long-term adverse educational and social consequences. Males are considerably more likely to be diagnosed with ADHD than females; the course of the disorder and its associated co-morbidities also appear to be sensitive to sex. Here, I discuss fundamental biological (genetic and endocrine) mechanisms that have been shown to, or could theoretically, contribute towards these sexually dimorphic phenomena. Greater understanding of how and why the sexes differ with respect to ADHD vulnerability should allow us to identify and characterise novel protective and risk factors for the disorder, and should ultimately facilitate improved diagnosis, prognosis and treatment.

Addressing the inverse care law: the role of community paediatric services

BACKGROUND

Children's health suffers disproportionately from the effects of poverty. The inverse care law states that those who need care the most are the least likely to receive it. Community paediatricians are well placed to address health inequalities in children.

AIMS

To explore, using routinely collected data, whether we address health inequalities and the inverse care law, particularly for certain conditions targeted by our specialty.

METHODS

Five years of data were analysed, during which health equity audits have led to service changes in order to tackle inequities. The data include postcodes, allowing each child to be assigned to a deprivation quintile, and a range of diagnoses, including five sentinel conditions: attention deficit hyperactivity disorder (ADHD) on medication, autistic spectrum disorder (ASD), epilepsy, cerebral palsy and Down's syndrome. This allowed analysis of the caseload by deprivation index for these conditions, comparison with the background population and exploration of time trends.

RESULTS

The number of children on the caseload and their distribution across the quintiles remained stable. The proportion of deprived children (i.e. in the lowest two quintiles) on the caseload over the last five years taken together is 56%, compared to 44% in the background population. The numbers of children with ADHD on medication has almost quadrupled in deprived quintiles and doubled in the least deprived quintile, while the numbers of children with this diagnosis in the most deprived is four times that in the least deprived. Numbers of children with ASD have also increased in each quintile. In contrast, the number of children with epilepsy and cerebral palsy did not show much variation, but those from deprived quintiles made up a greater proportion of the caseload.

CONCLUSIONS

Routine data collection demonstrates that inequalities are addressed using all four quality domains of service provision and sentinel conditions more likely to affect deprived children are targeted. We believe it is possible for all services to collect and analyse data thus with minimal effort, thereby providing a foundation from which to address the inverse care law.

Gamma aminobutyric acid transporter subtype 1 gene knockout mice: a new model for attention deficit/hyperactivity disorder

Attention deficit/hyperactivity disorder (ADHD) is characterized by hyperactivity, impaired sustained attention, impulsivity, and is usually accompanied by varying degrees of learning difficulties and lack of motor coordination. However, the pathophysiology and etiology of ADHD remain inconclusive so far. Our previous studies have demonstrated that the gamma aminobutyric acid transporter subtype 1 (GAT1) gene knockout (ko) mouse (gat1-/-) is hyperactive and exhibited impaired memory performance in the Morris water maze. In the current study, we found that the gat1-/- mice showed low levels of attentional focusing and increased impulsivity. In addition, the gat1-/- mice displayed ataxia characterized by defects in motor coordination and balance skills. The hyperactivity in the ko mice was reduced by both methylphenidate and amphetamine. Collectively, these results suggest that GAT1 ko mouse is a new animal model for ADHD studying and GAT1 may be a new target to treat ADHD.

Genetic mediators of neurocognitive outcomes in survivors of childhood acute lymphoblastic leukemia

PURPOSE

Survivors of childhood acute lymphoblastic leukemia (ALL) are at increased risk for neurocognitive problems, with significant interindividual variability in outcome. This study examined genetic polymorphisms associated with variability in neurocognitive outcome.

PATIENTS AND METHODS

Neurocognitive outcomes were evaluated at the end of therapy in 243 survivors treated on an institutional protocol featuring risk-adapted chemotherapy without prophylactic cranial irradiation. Polymorphisms in genes related to pharmacokinetics or pharmacodynamics of antileukemic agents, drug metabolism, oxidative stress, and attention problems in noncancer populations were examined as predictors of outcome, using multiple general linear models and controlling for age at diagnosis, sex, race, and treatment intensity.

RESULTS

Compared with national norms, the cohort demonstrated significantly higher rates of problems on direct assessment of sustained attention (P = .01) and on parent ratings of attention problems (P = .02). Children with the A2756G polymorphism in methionine synthase (MS) were more likely to demonstrate deficits in attentiveness (P = .03) and response speed (P = .02), whereas those with various polymorphisms in glutathione S-transferase demonstrated increased performance variability (P = .01) and reduced attentiveness (P = .003). Polymorphisms in monoamine oxidase (T1460CA) were associated with increased attention variability (P = .03). Parent-reported attention problems were more common in children with the Cys112Arg polymorphism in apoliopoprotein E4 (P = .01).

CONCLUSION

These results are consistent with our previous report of association between attention problems and MS in an independent cohort of long-term survivors of childhood ALL treated with chemotherapy only. The results also raise the possibility of an impact from genetic predispositions related to oxidative stress and CNS integrity.

Twin and sibling studies using health insurance data: the example of attention deficit/hyperactivity disorder (ADHD)

Background and Aims

Twin studies are used to assess the contribution of genetic factors to the aetiology of diseases. To show the feasibility of such research on the basis of health insurance data, we analysed twin and sibling data on the attention deficit/hyperactivity disorder (ADHD) in the German Pharmacoepidemiological Research Database (GePaRD).

Methods

The GePaRD consists of data from four statutory health insurances, including around 17% of the total population of Germany. Among those insured in 2005, we identified 286,653 non-twin sibling pairs and 12,486 twin pairs. Each pair consisted of an index child (6 to 12 years old) and a co-sibling of equal age or up to five years older. ADHD cases were identified by hospital or ambulatory ICD-10 diagnoses (F90.0 or F90.1) and prescriptions. We estimated tetrachoric correlations, percentage of concordant pairs, concordance rates, and heritability. Weighted estimates for the indirect assessment of mono- and dizygotic pairs were derived.

Results

Tetrachoric correlations were highest for twin pairs of the same sex (males: 0.85, 95% CI 0.81–0.89; females: 0.81, 95% CI 0.73–0.88) and lowest for opposite-sex non-twin sibling pairs (0.43, 95% CI 0.41–0.45). Heritability estimates were 0.88 (95% CI: 0.79–0.97) for males and 0.77 (95% CI: 0.60–0.95) for females.

Conclusions

The study clearly reproduced the well-known strong genetic component in the aetiology of ADHD. This approach could be used for further assessments of genetic components in other diseases.

Amphetamine-induced locomotion in a hyperdopaminergic ADHD mouse model depends on genetic background

We previously generated a knock-in mouse line with a cocaine-insensitive dopamine transporter (DAT-CI mice). These mice lost several behavioral responses to cocaine, but retained their response to amphetamine. DAT-CI mice are hyperdopaminergic due to reduced DAT function, and may thus be a good model for studying attention deficit hyperactivity disorder (ADHD). These mice had been behaviorally characterized while they were on a mixed genetic background. However as the colony was propagated over time, the mixed genetics were shifted toward a pure C57Bl/6J background--via a common breeding scheme known as "backcrossing." Several phenotypes appeared to have changed during this time frame. In this study, we investigated whether backcrossing altered the hyperlocomotive phenotype and behavioral responses to amphetamine, a drug used to treat ADHD. C57-congenic DAT-CI mice had high spontaneous locomotor activity that could be suppressed by low doses of amphetamine. Furthermore, their locomotion was not stimulated by very high doses of amphetamine (20mg/kg). After the reversion to a mixed genetic background by breeding with the 129 strain, the C57:129 hybrid DAT-CI mice displayed reduced basal locomotor activity compared to the C57-congenic mutant mice, and regained locomotor stimulation by high-dose amphetamine. The calming effect of amphetamine at low doses was retained in both strains. In summary, reduced DAT function in DAT-CI mice leads to a hyperdopaminergic state, and an ADHD-like phenotype in both strains. The data show that the genetic background of DAT-CI mice affects their locomotor phenotypes and their responses to amphetamine. Since the differences in genetic background between the strains of mice have a significant impact on the ADHD-like phenotype and the response to amphetamine, further study with these strains could identify the genetic underpinnings affecting the severity of ADHD-related symptoms and the treatment response.

Additive effects of the dopamine D2 receptor and dopamine transporter genes on the error-related negativity in young children

The error-related negativity (ERN) is a negative deflection in the event-related potential that occurs approximately 50 ms following the commission of an error at fronto-central electrode sites. Previous models suggest dopamine plays a role in the generation of the ERN. We recorded event-related potentials (ERPs) while 279 children aged 5-7 years completed a simple Go/No-Go task; the ERN was examined in relation to the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes. Results suggest an additive effect of the DRD2 and DAT1 genotype on ERN magnitude such that children with at least one DRD2 A1 allele and children with at least one DAT1 9 allele have an increased (i.e. more negative) ERN. These results provide further support for the involvement of dopamine in the generation of the ERN.

Effects of the DRD4 genotype on neural networks associated with executive functions in children and adolescents

Genetic variants within the dopamine D4 receptor gene (DRD4) are among the strongest and most consistently replicated molecular genetic findings in attentional functioning as well as attention deficit hyperactivity disorder (ADHD). Functionally, the 7-repeat allele of the DRD4-48 base pair repeat gene leads to a sub-sensitive postsynaptic D4 receptor, which is expressed at a particularly high density in the frontal lobes. We used fMRI to investigate the influence of the 7-repeat allele on BOLD (Blood Oxygen Level Dependency) responses in 26 healthy children and adolescents while they performed a combined stimulus-response Incompatibility Task (IC) and a Time Discrimination Task (TT).

7-repeat non-carriers exhibited increased neural activation of the left middle and inferior frontal gyrus (IFG) in the IC and greater cerebellar activation in the TT. Furthermore, the 7-repeat non-carriers exhibited a stronger coupling in haemodynamic responses between left IFG and the anterior cingulate cortex (ACC) during the IC and between cerebellar activation and brain regions that have high DRD4 density, including the IFG and the ACC during the TT. Our results indicate that the 7-repeat allele influences both regional brain activation patterns as well as connectivity patterns between neural networks of incompatibility and temporal processing.

Externalizing behaviors are associated with SNPs in the CHRNA5/CHRNA3/CHRNB4 gene cluster

There is strong evidence for shared genetic factors contributing to childhood externalizing disorders and substance abuse. Externalizing disorders often precede early substance experimentation, leading to the idea that individuals inherit a genetic vulnerability to generalized disinhibitory psychopathology. Genetic variation in the CHRNA5/CHRNA3/CHRNB4 gene cluster has been associated with early substance experimentation, nicotine dependence, and other drug behaviors. This study examines whether the CHRNA5/CHRNA3/CHRNB4 locus is correlated also with externalizing behaviors in three independent longitudinally assessed adolescent samples. We developed a common externalizing behavior phenotype from the available measures in the three samples, and tested for association with 10 SNPs in the gene cluster. Significant results were detected in two of the samples, including rs8040868, which remained significant after controlling for smoking quantity. These results expand on previous work focused mainly on drug behaviors, and support the hypothesis that variation in the CHRNA5/CHRNA3/CHRNB4 locus is associated with early externalizing behaviors.

Annual research review: impact of advances in genetics in understanding developmental psychopathology

It was hoped that diagnostic guidelines for, and treatment of, child psychiatric disorders in DSM-5 would be informed by the wealth of clinical genetic research related to neurodevelopmental disorders. In spite of remarkable advances in genetic technology, this has not been the case. Candidate gene, genome-wide association, and rare copy number variant (CNV) studies have been carried out for attention-deficit/hyperactivity disorder (ADHD), Autism, Tourette's Syndrome, and schizophrenia, with intriguing results, but environmental factors, incomplete penetrance, pleiotropy, and genetic heterogeneity, underlying any given phenotype have limited clinical translation. One promising approach may be the use of developmental brain imaging measures as more relevant phenotypes. This is particularly important, as subtle abnormalities in timing and expression of gene pathways underlying brain development may well link these disorders and be the ultimate target of treatments.

Astrocyte-specific disruption of SynCAM1 signaling results in ADHD-like behavioral manifestations

SynCAM1 is an adhesion molecule involved in synaptic differentiation and organization. SynCAM1 is also expressed in astroglial cells where it mediates astrocyte-to astrocyte and glial-neuronal adhesive communication. In astrocytes, SynCAM1 is functionally linked to erbB4 receptors, which are involved in the control of both neuronal/glial development and mature neuronal and glial function. Here we report that mice carrying a dominant-negative form of SynCAM1 specifically targeted to astrocytes (termed GFAP-DNSynCAM1 mice) exhibit disrupted diurnal locomotor activity with enhanced and more frequent episodes of activity than control littermates during the day (when the animals are normally sleeping) accompanied by shorter periods of rest. GFAP-DNSynCAM1 mice also display high levels of basal activity in the dark period (the rodent's awake/active time) that are attenuated by the psychostimulant D,L-amphetamine, and reduced anxiety levels in response to both avoidable and unavoidable provoking stimuli. These results indicate that disruption of SynCAM1-dependent astroglial function results in behavioral abnormalities similar to those described in animals model of attention-deficit hyperactive disorder (ADHD), and suggest a hitherto unappreciated contribution of glial cells to the pathophysiology of this disorder.

Genetic risks and ADHD symptomatology: exploring the effects of parental antisocial behaviors in an adoption-based study

A great deal of research has examined the etiology of attention-deficit/hyperactivity disorder (ADHD) and ADHD symptomatologies. Genetic factors are consistently shown to explain a significant proportion of variance in measures of ADHD. The current study adds to this body of research by examining whether genetic liabilities for criminality and alcoholism have effects on the development of ADHD symptomatologies. Analyses based on a sample of adoptees drawn from the National Longitudinal Study of Adolescent Health (Add Health) revealed that ADHD symptomatologies were elevated among adoptees who had biological mothers and fathers who had been arrested or who were alcoholics. These results suggest that part of the covariation between ADHD and antisocial behaviors may be the result of genetic factors that have general effects across a range of maladaptive outcomes.

Candidate system analysis in ADHD: evaluation of nine genes involved in dopaminergic neurotransmission identifies association with DRD1

OBJECTIVES

Several pharmacological and genetic studies support the involvement of the dopamine neurotransmitter system in the aetiology of attention-deficit hyperactivity disorder (ADHD). Based on this information we evaluated the contribution to ADHD of nine genes involved in dopaminergic neurotransmission (DRD1, DRD2, DRD3, DRD4, DRD5, DAT1, TH, DBH and COMT).

METHODS

We genotyped a total of 61 tagging single nucleotide polymorphisms (SNPs) in a sample of 533 ADHD patients (322 children and 211 adults), 533 sex-matched unrelated controls and additional 196 nuclear ADHD families from Spain.

RESULTS

The single- and multiple-marker analysis in both population and family-based approaches provided preliminary evidence for the contribution of DRD1 to combined-type ADHD in children (P=8.8e-04; OR=1.50 (1.18-1.90) and P=0.0061; OR=1.73 (1.23-2.45)) but not in adults. Subsequently, we tested positive results for replication in an independent sample of 353 German families with combined-type ADHD children and replicated the initial association between DRD1 and childhood ADHD (P=8.4e-05; OR=3.67 (2.04-6.63)).

CONCLUSIONS

The replication of the association between DRD1 and ADHD in two European cohorts highlights the validity of our finding and supports the involvement of DRD1 in childhood ADHD.

Loss of striatal cannabinoid CB1 receptor function in attention-deficit / hyperactivity disorder mice with point-mutation of the dopamine transporter

Abnormal dopamine (DA) transmission in the striatum plays a pivotal role in attention-deficit/hyperactivity disorder (ADHD). As striatal DA signalling modulates the endocannabinoid system (ECS), the present study was aimed at investigating cannabinoid CB1 receptor (CB1R) function in a model of ADHD obtained by triple point-mutation in the dopamine transporter (DAT) gene in mice, making them insensitive to cocaine [DAT cocaine-insensitive (DAT-CI) mice]. DAT-CI mice had a marked hyperactive phenotype, and neurophysiological recordings revealed that the sensitivity of CB1Rs controlling GABA-mediated synaptic currents [CB1Rs((GABA)) ] in the striatum was completely lost. In contrast, CB1Rs modulating glutamate transmission [CB1Rs((Glu)) ], and GABA(B) receptors were not affected in this model of ADHD. In DAT-CI mice, the blockade of CB1R((GABA)) function was complete even after cocaine or environmental manipulations activating the endogenous DA-dependent reward system, which are known to sensitize these receptors in control animals. Conversely, the hedonic property of sucrose was intact in DAT-CI mice, indicating normal sweet perception in these animals. Our results point to CB1Rs as novel molecular players in ADHD, and suggest that therapeutic strategies aimed at interfering with the ECS might prove effective in this disorder.

Steroid sulfatase-deficient mice exhibit endophenotypes relevant to attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder (ADHD) is a common neurodevelopmental condition characterised by inattention, impulsivity and hyperactivity; it is frequently co-morbid with anxiety and conduct disorders, sleep perturbation and abnormal consummatory behaviours. Recent studies have implicated the neurosteroid-modulating enzyme steroid sulfatase (STS) as a modulator of ADHD-related endophenotypes. The effects of steroid sulfatase deficiency on homecage activity, feeding/drinking behaviours, anxiety-related behaviours (assayed in light-dark box and open field paradigms), social dominance and serum steroid hormone levels were determined by comparing 40,XY and 39,X(Y*)O mice. Subsequently, mice administered the steroid sulfatase inhibitor COUMATE acutely were compared to vehicle-treated mice on behavioural tasks sensitive to enzyme deficiency to dissociate between its developmental and ongoing effects. 39,X(Y*)O mice exhibited heightened reactivity to a novel environment, hyperactivity in the active phase, and increased water (but not food) consumption relative to 40,XY mice during a 24h period; the former group also demonstrated evidence for heightened emotional reactivity. There was no difference in social dominance between the 40,XY and 39,X(Y*)O mice. COUMATE administration had no effect on homecage activity, water consumption or anxiety measures in the open field. 39,X(Y*)O mice exhibited significantly lower dehydroepiandrosterone (DHEA) serum levels than 40,XY mice, but equivalent corticosterone levels. Together with previous data, the present results suggest that steroid sulfatase may influence core and associated ADHD behavioural endophenotypes via both developmental and ongoing mechanisms, and that the 39,X(Y*)O model may represent a useful tool for elucidating the neurobiological basis of these endophenotypes.

Animal models of attention-deficit/hyperactivity disorder

Attention-deficit hyperactivity disorder (AD/HD) is a clinically heterogenous disorder including hyperactivity, impulsivity, and inattention. Both psychostimulant and non-psychostimulant drugs such as methylphenidate and atomoxetine, respectively, to modulate catecholeamine neurotransmission are used as current pharmacotherapies for AD/HD. Multiple lines of evidence suggest that genetic factors play major roles in the etiology of AD/HD. meta-Analyses and pooled data analyses have suggested associations between AD/HD and polymorphisms in genes encoding monoamine neurotransmission molecules. There has been considerable research on this disorder using genetic, pharmacological, and neuroimaging approaches, and several animal models of AD/HD such as spontaneously hypertensive rat (SHR), dopamine transporter (DAT) knockout mice, coloboma mutant mouse, and Grin1 mutant mouse have been reported. These animal models are valuable tools for investigating molecular, cellular, and behavioral mechanisms as well as the neural development and circuit mechanisms of AD/HD. Here, we review the recent literature on animal models of AD/HD and discuss their advantages and limitations.

Dopamine transporter (DAT1) and dopamine receptor D4 (DRD4) genotypes differentially impact on electrophysiological correlates of error processing

Recent studies as well as theoretical models of error processing assign fundamental importance to the brain's dopaminergic system. Research about how the electrophysiological correlates of error processing—the error-related negativity (ERN) and the error positivity (Pe)—are influenced by variations of common dopaminergic genes, however, is still relatively scarce. In the present study, we therefore investigated whether polymorphisms in the DAT1 gene and in the DRD4 gene, respectively, lead to interindividual differences in these error processing correlates. One hundred sixty participants completed a version of the Eriksen Flanker Task while a 26-channel EEG was recorded. The task was slightly modified in order to increase error rates. During data analysis, participants were split into two groups depending on their DAT1 and their DRD4 genotypes, respectively. ERN and Pe amplitudes after correct responses and after errors as well as difference amplitudes between errors and correct responses were analyzed. We found a differential effect of DAT1 genotype on the Pe difference amplitude but not on the ERN difference amplitude, while the reverse was true for DRD4 genotype. These findings are in line with predictions from theoretical models of dopaminergic transmission in the brain. They furthermore tie results from clinical investigations of disorders impacting on the dopamine system to genetic variations known to be at-risk genotypes.

Maternal separation affects dopamine transporter function in the spontaneously hypertensive rat: an in vivo electrochemical study

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a developmental disorder characterised by symptoms of inattention, impulsivity and hyperactivity. The spontaneously hypertensive rat (SHR) is a well-characterised model of this disorder and has been shown to exhibit dopamine dysregulation, one of the hypothesised causes of ADHD. Since stress experienced in the early stages of life can have long-lasting effects on behaviour, it was considered that early life stress may alter development of the dopaminergic system and thereby contribute to the behavioural characteristics of SHR. It was hypothesized that maternal separation would alter dopamine regulation by the transporter (DAT) in ways that distinguish SHR from control rat strains.

METHODS

SHR and control Wistar-Kyoto (WKY) rats were subjected to maternal separation for 3 hours per day from postnatal day 2 to 14. Rats were tested for separation-induced anxiety-like behaviour followed by in vivo chronoamperometry to determine whether changes had occurred in striatal clearance of dopamine by DAT. The rate of disappearance of ejected dopamine was used as a measure of DAT function.

RESULTS

Consistent with a model for ADHD, SHR were more active than WKY in the open field. SHR entered the inner zone more frequently and covered a significantly greater distance than WKY. Maternal separation increased the time that WKY spent in the closed arms and latency to enter the open arms of the elevated plus maze, consistent with other rat strains. Of note is that, maternal separation failed to produce anxiety-like behaviour in SHR. Analysis of the chronoamperometric data revealed that there was no difference in DAT function in the striatum of non-separated SHR and WKY. Maternal separation decreased the rate of dopamine clearance (k-1) in SHR striatum. Consistent with this observation, the dopamine clearance time (T100) was increased in SHR. These results suggest that the chronic mild stress of maternal separation impaired the function of striatal DAT in SHR.

CONCLUSIONS

The present findings suggest that maternal separation failed to alter the behaviour of SHR in the open field and elevated plus maze. However, maternal separation altered the dopaminergic system by decreasing surface expression of DAT and/or the affinity of DAT for dopamine, increasing the time to clear dopamine from the extracellular fluid in the striatum of SHR.