Converging methods in studying attention-deficit/hyperactivity disorder: what can we learn from neuroimaging and genetics?

Caffeine and adenosine A2A receptors rescue neuronal development in vitro of frontal cortical neurons in a rat model of attention deficit and hyperactivity disorder

Although some studies have supported the effects of caffeine for treatment of Attention deficit and hyperactivity disorder (ADHD), there were no evidences about its effects at the neuronal level. In this study, we sought to find morphological alterations during in vitro development of frontal cortical neurons from Spontaneoulsy hypertensive rats (SHR, an ADHD rat model) and Wistar-Kyoto rats (WKY, control strain). Further, we investigated the effects of caffeine and adenosine A₁ and A_2A receptors (A₁R and A_2AR) signaling. Cultured cortical neurons from WKY and SHR were analyzed by immunostaining of microtubule-associated protein 2 (MAP-2) and tau protein after treatment with either caffeine, or A₁R and A_2AR agonists or antagonists. Besides, the involvement of PI3K and not PKA signaling was also assessed. Neurons from ADHD model displayed less neurite branching, shorter maximal neurite length and decreased axonal outgrowth. While caffeine recovered neurite branching and elongation from ADHD neurons via both PKA and PI3K signaling, A_2AR agonist (CGS 21680) promoted more neurite branching via PKA signaling. The selective A_2AR antagonist (SCH 58261) was efficient in recovering axonal outgrowth from ADHD neurons through PI3K and not PKA signaling. For the first time, frontal cortical neurons were isolated from ADHD model and they presented disturbances in the differentiation and outgrowth. By showing that caffeine and A_2AR may act at neuronal level rescuing ADHD neurons outgrowth, our findings strengthen the potential of caffeine and A_2AR receptors as an adjuvant for ADHD treatment.

Effects of childhood exposure to PM2.5 in a Memphis pediatric asthma cohort

The effects of childhood exposure to ambient air pollution and their influences on healthcare utilization and respiratory outcomes in Memphis pediatric asthma cohort are still unknown. This study seeks to (1) investigate individual-level associations between asthma and exposure measures in high asthma rate and low asthma rate areas and (2) determine factors that influence asthma at first year of a child's life, first 2 years, first 5 years, and during their childhood. Datasets include physician-diagnosed asthma patients, on-road and individual PM_2.5 emissions, and high-resolution spatiotemporal PM_2.5 estimates. Spatial analytical and logistic regression models were used to analyze the effects of childhood exposure on outcomes. Increased risk was associated with African American (AA) (odds ratio (OR) = 3.09, 95% confidence interval (CI) 2.80-3.41), aged < 5 years old (OR = 1.31, 95% 1.17-1.47), public insurance (OR = 2.80, 95% CI 2.60-3.01), a 2.5-km radius from on-road emission sources (OR = 3.06, 95% CI 2.84-3.30), and a 400-m radius from individual PM_2.5 sources (OR = 1.33, 95% CI 1.25-1.41) among the cohort with residence in high asthma rate areas compared to low asthma rates areas. A significant interaction was observed between race and insurance with the odds of AA being approximately five times (OR = 4.68, 95% CI 2.23-9.85), public insurance being about three times (OR = 2.65, 95% CI 1.68-4.17), and children in their first 5 years of life have more hospital visits than other age groups. Findings from this study can guide efforts to minimize emissions, manage risk, and design interventions to reduce disease burden.

ADHD and maturation of brain white matter: A DTI study in medication naive children and adults

Several diffusion tensor imaging (DTI) studies in attention deficit hyperactivity disorder (ADHD) have shown a delay in brain white matter (WM) development. Because these studies were mainly conducted in children and adolescents, these WM abnormalities have been assumed, but not proven to progress into adulthood. To provide further insight in the natural history of WM maturation delay in ADHD, we here investigated the modulating effect of age on WM in children and adults. 120 stimulant-treatment naive male ADHD children (10-12 years of age) and adults (23-40 years of age) with ADHD (according to DSM-IV; all subtypes) were included, along with 23 age and gender matched controls. Fractional anisotropy (FA) values were compared throughout the WM by means of tract-based spatial statistics (TBSS) and in specific regions of interest (ROIs). On both TBSS and ROI analyses, we found that stimulant-treatment naive ADHD children did not differ in FA values from control children, whereas adult ADHD subjects had reduced FA values when compared to adult controls in several regions. Significant age × group interactions for whole brain FA (p = 0.015), as well as the anterior thalamic radiation (p = 0.015) suggest that ADHD affects the brain WM age-dependently. In contrast to prior studies conducted in medicated ADHD children, we did not find WM alterations in stimulant treatment naïve children, only treatment-naïve adults. Thus, our findings suggest that the reported developmental delay in WM might appear after childhood, and that previously reported differences between ADHD children and normal developing peers could have been attributed to prior ADHD medications, and/or other factors that affect WM development, such as age and gender.

Cortical Thickness in Young Treatment-Naive Children With ADHD

OBJECTIVE

This study aimed to investigate the cortical thickness in areas of the brain that are hypothesized to be involved in response inhibition and error-monitoring behaviors. The authors hypothesized that children with ADHD would have a thinner prefrontal cortex (PFC) and anterior cingulate cortex (ACC) than healthy children.

METHOD

In all, 25 ADHD and 25 healthy control male children (5-12 years) underwent magnetic resonance imaging.

RESULTS

The authors found thinner right superior frontal gyrus in ADHD patients compared with controls (t = 2.01, df = 45, p = .049). The older children with ADHD drove this effect when participants were further subdivided into a younger and older age group (older participants: p = .004; younger participants: p = ns).

CONCLUSION

These findings have implications for the developmental trajectory of the frontal lobe in ADHD.

The Roots of Autism and ADHD Twin Study in Sweden (RATSS)

Neurodevelopmental disorders affect a substantial minority of the general population. Their origins are still largely unknown, but a complex interplay of genetic and environmental factors causing disturbances of the central nervous system's maturation and a variety of higher cognitive skills is presumed. Only limited research of rather small sample size and narrow scope has been conducted in neurodevelopmental disorders using a twin-differences design. The Roots of Autism and ADHD Twin Study in Sweden (RATSS) is an ongoing project targeting monozygotic twins discordant for categorical or dimensional autistic and inattentive/hyperactive-impulsive phenotypes as well as other neurodevelopmental disorders, and typically developing twin controls. Included pairs are 9 years of age or older, and comprehensively assessed for psychopathology, medical history, neuropsychology, and dysmorphology, as well as structural, functional, and molecular brain imaging. Specimens are collected for induced pluripotent (iPS) and neuroepithelial stem cells, genetic, gut bacteria, protein-/monoamine, and electron microscopy analyses. RATSS's objective is to generate a launch pad for novel surveys to understand the complexity of genotype-environment-phenotype interactions in autism spectrum disorder and attention-deficit hyperactivity disorder (ADHD). By October 2013, RATSS had collected data from 55 twin pairs, among them 10 monozygotic pairs discordant for autism spectrum disorder, seven for ADHD, and four for other neurodevelopmental disorders. This article describes the design, recruitment, data collection, measures, collected pairs' characteristics, as well as ongoing and planned analyses in RATSS. Potential gains of the study comprise the identification of environmentally mediated biomarkers, the emergence of candidates for drug development, translational modeling, and new leads for prevention of incapacitating outcomes.

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.

Neuroimaging in children, adolescents and young adults with psychological trauma

Childhood psychological trauma is a strong predictor of psychopathology. Preclinical research points to the influence of this type of trauma on brain development. However, the effects of psychological trauma on the developing human brain are less known and a challenging question is whether the effects can be reversed or even prevented. The aim of this review is to give an overview of neuroimaging studies in traumatized juveniles and young adults up till 2012. Neuroimaging studies in children and adolescents with traumatic experiences were found to be scarce. Most studies were performed by a small number of research groups in the United States and examined structural abnormalities. The reduction in hippocampal volume reported in adults with PTSD could not be confirmed in juveniles. The most consistent finding in children and adolescents, who experienced psychological trauma are structural abnormalities of the corpus callosum. We could not identify any studies investigating treatment effects. Neuroimaging studies in traumatized children and adolescents clearly lag behind studies in traumatized adults as well as studies on ADHD and autism.

A Review of the Pathophysiology, Etiology, and Treatment of Attention-Deficit Hyperactivity Disorder (ADHD)

Objective: To review the pathophysiology, etiology, and treatment of attention-deficit hyperactivity disorder (ADHD). Data Sources and Data Extraction: A literature search was conducted in PubMed and EMBASE using the terms attention deficit hyperactive disorder, ADHD, pathophysiology, etiology, and neurobiology. Limits applied were the following: published in the past 10 years (January 2003 to August 2013), humans, review, meta-analysis, and English language. These yielded 63 articles in PubMed and 74 in EMBASE. After removing duplicate/irrelevant articles, 86 articles and their relevant reference citations were reviewed. Data Synthesis: ADHD is a neurological disorder that affects children, but symptoms may persist into adulthood. Individuals suffering from this disorder exhibit hyperactivity, inattention, impulsivity, and problems in social interaction and academic performance. Medications used to treat ADHD such as methylphenidate, amphetamine, and atomoxetine indicate a dopamine/norepinephrine deficit as the neurochemical basis of ADHD, but the etiology is more complex. Moreover, these agents have poor adverse effect profiles and a multitude of drug interactions. Because these drugs are also dispensed to adults who may have concomitant conditions or medications, a pharmacist needs to be aware of these adverse events and drug interactions. This review, therefore, focuses on the pathophysiology, etiology, and treatment of ADHD and details the adverse effects and drug interaction profiles of the drugs used to treat it. Conclusions: Published research shows the benefit of drug therapy for ADHD in children, but given the poor adverse effect and drug interaction profiles, these must be dispensed with caution.

A comparison of phenylketonuria with attention deficit hyperactivity disorder: do markedly different aetiologies deliver common phenotypes?

Phenylketonuria (PKU) is a well-defined metabolic disorder arising from a mutation that disrupts phenylalanine metabolism and so produces a variety of neural changes indirectly. Severe cognitive impairment can be prevented by dietary treatment; however, residual symptoms may be reported. These residual symptoms appear to overlap a more prevalent childhood disorder: Attention Deficit/Hyperactivity Disorder (ADHD). However, the aetiology of ADHD is a vast contrast to PKU: it seems to arise from a complex combination of genes; and it has a substantial environmental component. We ask whether these two disorders result from two vastly different genotypes that converge on a specific core phenotype that includes similar dysfunctions of Gray's (Gray, 1982) Behavioural Inhibition System (BIS), coupled with other disorder-specific dysfunctions. If so, we believe comparison of the commonalities will allow greater understanding of the neuropsychology of both disorders. We review in detail the aetiology, treatment, neural pathology, cognitive deficits and electrophysiological abnormalities of PKU; and compare this with selected directly matching aspects of ADHD. The biochemical and neural pathologies of PKU and ADHD are quite distinct in their causes and detail; but they result in the disorder in the brain of large amino acid levels, dopamine and white matter that are very similar and could explain the overlap of symptoms within and between the PKU and ADHD spectra. The common deficits affect visual function, motor function, attention, working memory, planning, and inhibition. For each of PKU and ADHD separately, a subset of deficits has been attributed to a primary dysfunction of behavioural inhibition. In the case of ADHD (excluding the inattentive subtype) this has been proposed to involve a specific failure of the BIS; and we suggest that this is also true of PKU. This accounts for a substantial proportion of the parallels in the superficial symptoms of both disorders and we see this as linked to prefrontal, rather than more general, dysfunction of the BIS.

Principles underlying the use of multiple informants' reports

Researchers use multiple informants' reports to assess and examine behavior. However, informants' reports commonly disagree. Informants' reports often disagree in their perceived levels of a behavior ("low" versus "elevated" mood), and examining multiple reports in a single study often results in inconsistent findings. Although researchers often espouse taking a multi-informant assessment approach, they frequently address informant discrepancies using techniques that treat discrepancies as measurement error. Yet, recent work indicates that researchers in a variety of fields often may be unable to justify treating informant discrepancies as measurement error. In this review, the authors advance a framework (Operations Triad Model) outlining general principles for using and interpreting informants' reports. Using the framework, researchers can test whether or not they can extract meaningful information about behavior from discrepancies among multiple informants' reports. The authors provide supportive evidence for this framework and discuss its implications for hypothesis testing, study design, and quantitative review.

ADHD: an integration with pediatric traumatic brain injury

This review examines the long-standing finding that ADHD is a common sequela of pediatric traumatic brain injury (PTBI) in light of the current conceptualization of ADHD as a dimensional, neuropsychologically heterogeneous disorder. The review contends that this conceptualization established the basis for concluding that frequently occurring symptoms caused by PTBI, such as slow processing speed, emotional dysregulation and disinhibition, are indicative of ADHD. Consequently, it concludes that ADHD following PTBI is even more common than the 30% rate the current literature suggests. It provides recommendations for the assessment and treatment of ADHD associated with PTBI.

Altered serotonergic function may partially account for behavioral endophenotypes in steroid sulfatase-deficient mice

The X-linked gene STS encodes the steroid hormone-modulating enzyme steroid sulfatase. Loss-of-function of STS, and variation within the gene, have been associated with vulnerability to developing attention deficit hyperactivity disorder (ADHD), a neurodevelopmental condition characterized by inattention, severe impulsivity, hyperactivity, and motivational deficits. ADHD is commonly comorbid with a variety of disorders, including obsessive-compulsive disorder. The neurobiological role of steroid sulfatase, and therefore its potential role in ADHD and associated comorbidities, is currently poorly understood. The 39,X(Y)*O mouse, which lacks the Sts gene, exhibits several behavioral abnormalities relevant to ADHD including inattention and hyperactivity. Here, we show that, unexpectedly, 39,X(Y)*O mice achieve higher ratios than wild-type mice on a progressive ratio (PR) task thought to index motivation, but that there is no difference between the two groups on a behavioral task thought to index compulsivity (marble burying). High performance liquid chromatography analysis of monoamine levels in wild type and 39,X(Y)*O brain tissue regions (the frontal cortex, striatum, thalamus, hippocampus, and cerebellum) revealed significantly higher levels of 5-hydroxytryptamine (5-HT) in the striatum and hippocampus of 39,X(Y)*O mice. Significant correlations between hippocampal 5-HT levels and PR performance, and between striatal 5-HT levels and locomotor activity strongly implicate regionally-specific perturbations of the 5-HT system as a neurobiological candidate for behavioral differences between 40,XY and 39,X(Y)*O mice. These data suggest that inactivating mutations and functional variants within STS might exert their influence on ADHD vulnerability, and disorder endophenotypes through modulation of the serotonergic system.

Neural and behavioral endophenotypes in ADHD

In recent years, descriptive symptom-based approaches of attention deficit hyperactivity disorder (ADHD) have been increasingly replaced by more sophisticated endophenotype-based strategies, better suited to investigate its pathophysiological basis, which is inherently heterogeneous. Measurements derived from neuroimaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) constitute endophenotypes of growing interest, capable of providing unprecedented windows on neurochemical and neuroanatomical components of psychiatric conditions. This chapter reviews the current state of knowledge regarding putative neural and behavioral endophenotypes of ADHD, across the lifespan. To this end, recent evidence drawn from molecular and structural neuroimaging studies are discussed in the light of widely accepted neuropsychological and pharmacological models of ADHD.

Cingulate, frontal, and parietal cortical dysfunction in attention-deficit/hyperactivity disorder

Functional and structural neuroimaging have identified abnormalities of the brain that are likely to contribute to the neuropathophysiology of attention-deficit/hyperactivity disorder (ADHD). In particular, hypofunction of the brain regions comprising the cingulo-frontal-parietal cognitive-attention network have been consistently observed across studies. These are major components of neural systems that are relevant to ADHD, including cognitive/attention networks, motor systems, and reward/feedback-based processing systems. Moreover, these areas interact with other brain circuits that have been implicated in ADHD, such as the "default mode" resting state network. The ADHD imaging data related to cingulo-frontal-parietal network dysfunction will be selectively highlighted here to help facilitate its integration with the other information presented in this special issue. Together, these reviews will help shed light on the neurobiology of ADHD.

Basic impairments in regulating the speed-accuracy tradeoff predict symptoms of attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is characterized by poor optimization of behavior in the face of changing demands. Theoretical accounts of ADHD have often focused on higher-order cognitive processes and typically assume that basic processes are unaffected. It is an open question whether this is indeed the case.

METHOD

We explored basic cognitive processing in 25 subjects with ADHD and 30 typically developing children and adolescents with a perceptual decision-making paradigm. We investigated whether individuals with ADHD were able to balance the speed and accuracy of decisions.

RESULTS

We found impairments in the optimization of the speed-accuracy tradeoff. Furthermore, these impairments were directly related to the hyperactive and impulsive symptoms that characterize the ADHD-phenotype.

CONCLUSIONS

These data suggest that impairments in basic cognitive processing are central to the disorder. This calls into question conceptualizations of ADHD as a "higher-order" deficit, as such simple decision processes are at the core of almost every paradigm used in ADHD research.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Regional differences in cerebral perfusion associated with the alpha-2A-adrenergic receptor genotypes in attention deficit hyperactivity disorder

BACKGROUND

Neurobiologic studies have suggested that dysregulation of central noradrenergic systems may be involved in the pathophysiology of attention deficit hyperactivity disorder (ADHD), and it has been hypothesized that genetic changes in the norepinephrine pathways might contribute to dysfunction of the prefrontal cortex circuits in ADHD. We previously reported decreased cerebral blood flow in the right lateral prefrontal cortex and both orbitofrontal cortices in children with ADHD. Genetic investigations have shown that the alpha-2A-adrenergic receptor gene (ADRA2A) is associated with ADHD. Our aim was to examine whether the presence of a risk allele of the ADRA2A MspI polymorphism is associated with differences in regional cerebral blood flow in boys with ADHD.

METHODS

We recruited 21 Korean boys with ADHD (mean age 9.9, standard deviation [SD] 2.7 yr) and 11 age- and sex-matched controls (mean age 10.6 [SD 2.1] yr). Each participant underwent technetium-99m-hexamethylpropylene amine oxime ((99m)Tc-HMPAO) single-photon emission computed tomography. We performed image analyses with voxe-wise t statistics using SPM2.

RESULTS

We found regional hypoperfusion in the prefrontal regions, including the right orbitofrontal and right medial gyri, and the bilateral putamen and cerebellum in boys with ADHD relative to controls (p < 0.0005, uncorrected for multiple comparisons). Boys with ADHD who carried the C allele (n = 13) at the ADRA2A MspI polymorphism had reduced perfusion in the bilateral orbitofrontal regions compared with those without the C allele (n = 8) (p < 0.0005, uncorrected for multiple comparisons).

LIMITATIONS

This study was limited by the small sample size, and we did not obtain genetic data from the controls.

CONCLUSION

Our findings suggest that regional differences in cerebral perfusion in the orbitofrontal cortex represent an intermediate neuroimaging phenotype associated with the ADRA2A MspI polymorphism; these data support the validity of the noradrenergic hypothesis regarding the pathophysiology of ADHD.

Attention-deficit/hyperactivity disorder and attention networks

Research attempting to elucidate the neuropathophysiology of attention-deficit/hyperactivity disorder (ADHD) has not only shed light on the disorder itself, it has simultaneously provided new insights into the mechanisms of normal cognition and attention. This review will highlight and integrate this bidirectional flow of information. Following a brief overview of ADHD clinical phenomenology, ADHD studies will be placed into a wider historical perspective by providing illustrative examples of how major models of attention have influenced the development of neurocircuitry models of ADHD. The review will then identify major components of neural systems potentially relevant to ADHD, including attention networks, reward/feedback-based processing systems, as well as a 'default mode' resting state network. Further, it will suggest ways in which these systems may interact and be influenced by neuromodulatory factors. Recent ADHD imaging data will be selectively provided to both illustrate the field's current level of knowledge and to show how such data can inform our understanding of normal brain functions. The review will conclude by suggesting possible avenues for future research.

The heterogeneity of causes and courses of attention-deficit/hyperactivity disorder

OBJECTIVE

Attention-deficit / Hyperactivity Disorder (ADHD) is a frequent mental disorder with onset in childhood and persistence into adulthood in a sizeable number of people. Despite a rather simple clinical definition, ADHD has many facets because of frequent co-morbid disorders and varying impact on psychosocial functioning. Thus, there is considerable heterogeneity in various domains.

METHOD

A review of recent research findings in: i) selected domains of aetiology reflecting the role of genes, brain structures and functioning and the interplay of causal factors and ii) clinical heterogeneity in terms of co-morbidities, gender effects, courses and outcomes.

RESULTS

Molecular genetic studies have identified a number of candidate genes which have a small effect on behavioural variation in ADHD. In the most recent Genome Scan Meta Analysis of seven ADHD linkage studies, genome-wide significant linkage was identified on chromosome 16. The volume of both the total brain and various regions including the prefrontal cortex, the caudate nucleus and the vermis of the cerebellum is smaller in ADHD. Functional MRI has documented a specific deficit of frontostriatal networks in ADHD. Integrative aetiological models have to take the interaction of gene and environment on various dysfunctions into account. Clinical heterogeneity results from frequent associations with various co-morbidities, the impact of the disorder on psychosocial functioning, and gender effects. Partly, these effects are evident also in the course and outcome of ADHD.

CONCLUSION

ADHD is a chronic mental disorder with a complex aetiology. So far, various neurobiological factors have been identified that need to be studied further to better understand their interaction with environmental factors. The clinical presentation and the long-term course of ADHD are manifold.