Differential effects of DRD4 and DAT1 genotype on fronto-striatal gray matter volumes in a sample of subjects with attention deficit hyperactivity disorder, their unaffected siblings, and controls

Methylphenidate as a treatment option for substance use disorder: a transdiagnostic perspective

A transition in viewing mental disorders from conditions defined as a set of unique characteristics to one of the quantitative variations on a collection of dimensions allows overlap between disorders. The overlap can be utilized to extend to treatment approaches. Here, we consider the overlap between attention-deficit/hyperactivity disorder and substance use disorder to probe the suitability to use methylphenidate as a treatment for substance use disorder. Both disorders are characterized by maladaptive goal-directed behavior, impaired cognitive control, hyperactive phasic dopaminergic neurotransmission in the striatum, prefrontal hypoactivation, and reduced frontal cortex gray matter volume/density. In addition, methylphenidate has been shown to improve cognitive control and normalize associated brain activation in substance use disorder patients and clinical trials have found methylphenidate to improve clinical outcomes. Despite the theoretical basis and promising, but preliminary, outcomes, many questions remain unanswered. Most prominent is whether all patients who are addicted to different substances may equally profit from methylphenidate treatment.

Early musical training benefits to non-musical cognitive ability associated with the Gestalt principles

Musical training has been evidenced to facilitate music perception, which refers to the consistencies, boundaries, and segmentations in pieces of music that are associated with the Gestalt principles. The current study aims to test whether musical training is beneficial to non-musical cognitive ability with Gestalt principles. Three groups of Chinese participants (with early, late, and no musical training) were compared in terms of their performances on the Motor-Free Visual Perception Test (MVPT). The results show that the participants with early musical training had significantly better performance in the Gestalt-like Visual Closure subtest than those with late and no musical training, but no significances in other Gestalt-unlike subtests was identified (Visual Memory, Visual Discrimination, Spatial Relationship, Figure Ground in MVPT). This study suggests the benefit of early musical training on non-musical cognitive ability with Gestalt principles.

Heritability of cognitive abilities and regional brain structures in middle-aged to elderly East Asians

This study examined the single-nucleotide polymorphism heritability and genetic correlations of cognitive abilities and brain structural measures (regional subcortical volume and cortical thickness) in middle-aged and elderly East Asians (Korean) from the Gwangju Alzheimer's and Related Dementias cohort study. Significant heritability was found in memory function, caudate volume, thickness of the entorhinal cortices, pars opercularis, superior frontal gyri, and transverse temporal gyri. There were 3 significant genetic correlations between (i) the caudate volume and the thickness of the entorhinal cortices, (ii) the thickness of the superior frontal gyri and pars opercularis, and (iii) the thickness of the superior frontal and transverse temporal gyri. This is the first study to describe the heritability and genetic correlations of cognitive and neuroanatomical traits in middle-aged to elderly East Asians. Our results support the previous findings showing that genetic factors play a substantial role in the cognitive and neuroanatomical traits in middle to advanced age. Moreover, by demonstrating shared genetic effects on different brain regions, it gives us a genetic insight into understanding cognitive and brain changes with age, such as aging-related cognitive decline, cortical atrophy, and neural compensation.

Genetic variations influence brain changes in patients with attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a neurological and neurodevelopmental childhood-onset disorder characterized by a persistent pattern of inattentiveness, impulsiveness, restlessness, and hyperactivity. These symptoms may continue in 55-66% of cases from childhood into adulthood. Even though the precise etiology of ADHD is not fully understood, it is considered as a multifactorial and heterogeneous disorder with several contributing factors such as heritability, auxiliary to neurodevelopmental issues, severe brain injuries, neuroinflammation, consanguineous marriages, premature birth, and exposure to environmental toxins. Neuroimaging and neurodevelopmental assessments may help to explore the possible role of genetic variations on ADHD neuropsychobiology. Multiple genetic studies have observed a strong genetic association with various aspects of neuropsychobiological functions, including neural abnormalities and delayed neurodevelopment in ADHD. The advancement in neuroimaging and molecular genomics offers the opportunity to analyze the impact of genetic variations alongside its dysregulated pathways on structural and functional derived brain imaging phenotypes in various neurological and psychiatric disorders, including ADHD. Recently, neuroimaging genomic studies observed a significant association of brain imaging phenotypes with genetic susceptibility in ADHD. Integrating the neuroimaging-derived phenotypes with genomics deciphers various neurobiological pathways that can be leveraged for the development of novel clinical biomarkers, new treatment modalities as well as therapeutic interventions for ADHD patients. In this review, we discuss the neurobiology of ADHD with particular emphasis on structural and functional changes in the ADHD brain and their interactions with complex genomic variations utilizing imaging genetics methodologies. We also highlight the genetic variants supposedly allied with the development of ADHD and how these, in turn, may affect the brain circuit function and related behaviors. In addition to reviewing imaging genetic studies, we also examine the need for complementary approaches at various levels of biological complexity and emphasize the importance of combining and integrating results to explore biological pathways involved in ADHD disorder. These approaches include animal models, computational biology, bioinformatics analyses, and multimodal imaging genetics studies.

Novelty seeking is associated with increased body weight and orbitofrontal grey matter volume reduction

Novelty seeking (NS) has previously been identified as a personality trait that is associated with elevated body mass index (BMI) and obesity. Of note, both obesity and reduced impulse control - a core feature of NS - have previously been associated with grey matter volume (GMV) reductions in the orbitofrontal cortex (OFC). Yet, it remains unknown, if body weight-related grey matter decline in the OFC might be explained by higher levels of NS. To address this question, we studied associations between NS, BMI and brain structure in 355 healthy subjects. Brain images were pre-processed using voxel-based morphometry (VBM). BMI was calculated from self-reported height and weight. The Tridimensional Personality Questionnaire (TPQ) was used to assess NS. NS and BMI were associated positively (r = .137, p = .01) with NS being a significant predictor of BMI (B = 0.172; SE B = 0.05; ß = 0.184; p = 0.001). Significant associations between BMI and GMV specifically in the OFC (x = -44, y = 56, z = -2, t(350) = 4.34, k = 5, p_FWE = 0.011) did not uphold when correcting for NS in the model. In turn, a significant negative association between NS and OFC GMV was found independent of BMI (x = -2, y = 48, z = -10, t(349) = 4.42, k = 88, p_FWE = 0.008). Body mass-related grey matter decrease outside the OFC could not be attributed to NS. Our results suggest that body-weight-related orbitofrontal grey matter reduction can at least partly be linked to higher levels of NS. Given the pivotal role of the OFC in overweight as well as cognitive domains such as impulse inhibition, executive control and reward processing, its association with NS seems to provide a tenable neurobiological correlate for future research.

First Demonstration of Double Dissociation between COMT-Met158 and COMT-Val158 Cognitive Performance When Stressed and When Calmer

We present here the first evidence of the much-predicted double dissociation between the effect of stress on cognitive skills [executive functions (EFs)] dependent on prefrontal cortex (PFC) by catechol-O-methyltransferase (COMT) genotype. The COMT gene polymorphism with methionine (Met) at codon 158 results in more dopamine (DA) in PFC and generally better EFs, while with valine (Val) at codon 158 the result is less PFC DA and generally poorer EFs. Many have predicted that mild stress, by raising PFC DA levels should aid EFs of COMT-Vals (bringing their PFC DA levels up, closer to optimal) and impair EFs of COMT-Mets (raising their PFC DA levels past optimal). We tested 140 men and women in a within-subject crossover design using extremely mild social evaluative stress. On trials requiring EFs (incongruent trials) of the Flanker/Reverse Flanker task, COMT-Val158 homozygotes performed better when mildly stressed than when calmer, while COMT-Met158 carriers performed worse when mildly stressed. Two other teams previously tried to obtain this, but only found stress impairing EFs of COMT-Mets, not improving EFs of COMT-Vals. Perhaps we found both because we used a much milder stressor. Evidently, the bandwidth for stress having a facilitative effect on EFs is exceedingly narrow.

Neural Correlates of the Dual-Pathway Model for ADHD in Adolescents

OBJECTIVE

The dual-pathway model has been proposed to explain the heterogeneity in symptoms of attention deficit hyperactivity disorder (ADHD) by two independent psychological pathways based on distinct brain circuits. The authors sought to test whether the hypothesized cognitive and motivational pathways have separable neural correlates.

METHODS

In a longitudinal community-based cohort of 1,963 adolescents, the neuroanatomical correlates of ADHD were identified by a voxel-wise association analysis and then validated using an independent clinical sample (99 never-medicated patients with ADHD, 56 medicated patients with ADHD, and 267 healthy control subjects). The cognitive and motivational pathways were assessed by neuropsychological tests of working memory, intrasubject variability, stop-signal reaction time, and delay discounting. The associations were tested between the identified neuroanatomical correlates and both ADHD symptoms 2 years later and the polygenic risk score for ADHD.

RESULTS

Gray matter volumes of both a prefrontal cluster and a posterior occipital cluster were negatively associated with inattention. Compared with healthy control subjects, never-medicated patients, but not medicated patients, had significantly lower gray matter volumes in these two clusters. Working memory and intrasubject variability were associated with the posterior occipital cluster, and delay discounting was independently associated with both clusters. The baseline gray matter volume of the posterior occipital cluster predicted the inattention symptoms in a 2-year follow-up and was associated with the genetic risk for ADHD.

CONCLUSIONS

The dual-pathway model has both shared and separable neuroanatomical correlates, and the shared correlate in the occipital cortex has the potential to serve as an imaging trait marker of ADHD, especially the inattention symptom domain.

Rostral Anterior Cingulate Thickness Predicts the Emotional Psilocybin Experience

Psilocybin is the psychoactive compound of mushrooms in the psilocybe species. Psilocybin directly affects a number of serotonin receptors, with highest affinity for the serotonin 2A receptor (5HT-2Ar). Generally, the effects of psilocybin, and its active metabolite psilocin, are well established and include a range of cognitive, emotional, and perceptual perturbations. Despite the generality of these effects, there is a high degree of inter-individual variability in subjective psilocybin experiences that are not well understood. Others have shown brain morphology metrics derived from magnetic resonance imaging (MRI) can predict individual drug response. Due to high expression of serotonin 2A receptors (5HT-2Ar) in the cingulate cortex, and its prior associations with psilocybin, we investigate if cortical thickness of this structure predicts the psilocybin experience in healthy adults. We hypothesized that greater cingulate thickness would predict higher subjective ratings in sub-scales of the Five-Dimensional Altered State of Consciousness (5D-ASC) with high emotionality in healthy participants (n = 55) who received oral psilocybin (either low dose: 0.160 mg/kg or high dose: 0.215 mg/kg). After controlling for sex, age, and using false discovery rate (FDR) correction, we found the rostral anterior cingulate predicted all four emotional sub-scales, whereas the caudal and posterior cingulate did not. How classic psychedelic compounds induce such large inter-individual variability in subjective states has been a long-standing question in serotonergic research. These results extend the traditional set and setting hypothesis of the psychedelic experience to include brain structure metrics.

Parenting Practices and Adolescent Effortful Control: MAOA T941G Gene Polymorphism as a Moderator

Effortful control (EC) plays a crucial role in psychopathology disorders. Emerging studies have paid attention to the effects of G × E interaction on EC. The present study investigated interactions between monoamine oxidase A (MAOA) T941G polymorphism with parenting practices on EC in a sample of 1,531 Chinese adolescents. The adolescents completed the Early Adolescent Temperament Questionnaire-Revised (EATQ-R) EC scale and the Parenting Style Index provided during the study to assess EC and parenting practices, respectively. MAOA T941G polymorphism exerted no effect on adolescent EC; however, results revealed that the MAOA gene interacted with parental acceptance/involvement in their associations with EC among boys. Specifically, although increased levels of parental acceptance/involvement benefited all adolescents, boys with G alleles of the MAOA gene exhibited higher sensitivity to parental acceptance/involvement, compared with T carriers; this interaction was not significant among girls. This study is the first to identify MAOA × parenting interaction on adolescent EC, further contributing to the literature in MAOA gene-EC.

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.

Recent developments in the genetics of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a developmental psychiatric disorder that affects children and adults. ADHD is one of the psychiatric disorders with the strongest genetic basis according to familial, twin, and single nucleotide polymorphisms (SNP)-based epidemiological studies. In this review, we provide an update of recent insights into the genetic basis of ADHD. We discuss recent progress from genome-wide association studies (GWAS) looking at common variants as well as rare copy number variations. New analysis of gene groups, so-called functional ontologies, provide some insight into the gene networks afflicted, pointing to the role of neurodevelopmentally expressed gene networks. Bioinformatic methods, such as functional enrichment analysis and protein-protein network analysis, are used to highlight biological processes of likely relevance to the etiology of ADHD. Additionally, copy number variations seem to map on important pathways implicated in synaptic signaling and neurodevelopment. While some candidate gene associations of, for example, neurotransmitter receptors and signaling, have been replicated, they do not seem to explain significant variance in recent GWAS. We discuss insights from recent case-control SNP-GWAS that have presented the first whole-genome significant SNP in ADHD.

Effects of the 2-Repeat Allele of the DRD4 Gene on Neural Networks Associated With the Prefrontal Cortex in Children With ADHD

Objective: Genetic variation, especially polymorphism of the dopamine D4 receptor gene (DRD4), has been linked to deficits in self-regulation and executive functions and to attention deficit hyperactivity disorder (ADHD), and is related to the structural and functional integrity of the default mode network (DMN), the executive control network (ECN) and the sensorimotor network (SMN). The aim of this study was to explore the effects of the 2-repeat allele of the DRD4 gene on brain network connectivity and behaviors in children with ADHD.

Methods: Using independent component analysis (ICA) and dimension analyses, we examined resting-state functional magnetic resonance imaging (fMRI) data obtained from 52 Asian medicine-naive children with ADHD (33 2-repeat absent and 19 2-repeat present).

Results: We found that individuals with 2-repeat absent demonstrated increased within-network connectivity in the right precuneus of the DMN, the right middle frontal gyrus (MFG) of the SMN compared with individuals with 2-repeat present. Within the ECN, 2-repeat absent showed decreased within-network connectivity in the left inferior frontal gyrus (IFG) and the left anterior cingulate cortex. A deeper study found that connectivity strength of the left IFG was directly proportional to the Stroop reaction time in 2-repeat absent group, and as well as the right MFG in 2-repeat present group.

Conclusion: Polymorphisms of the DRD4 gene, specifically 2-repeat allele, had effects on the ECN, the SMN and the DMN, especially in the prefrontal cortex (PFC) circles. ADHD children with DRD4 2-repeat allele have aberrant resting-state within-network connectivity patterns in the left IFG and the right MFG related to dysfunction in inattention symptom. This study provided novel insights into the neural mechanisms underlying the effects of DRD4 2-repeat allele on ADHD.

Cingulate Cortical Thickness and Dopamine Transporter ( DAT1) Genotype in Children and Adolescents With ADHD

OBJECTIVE

This study aimed to examine the influence of dopamine transporter gene ( DAT1) 3'UTR genotype on cingulate cortical thickness in a large sample of children and adolescents with ADHD.

METHOD

Brain MRIs were acquired from 46 ADHD patients with homozygosity for the 10-repeat allele and 52 ADHD patients with a single copy or no copy of the allele. The cingulate cortex of each MRI scan was automatically parceled into sulci and gyri as well as into Brodmann areas (BA).

RESULTS

There were no group differences in age, gender, full-scale intelligence quotient, symptom severity, treatment status, comorbidity, or mean overall cortical thickness. Sulcus/gyrus- and BA-based analyses revealed that patients homozygous for the 10-repeat allele showed significantly greater thickness in right cingulate gyrus and right BA 24 compared with 9-repeat carriers.

CONCLUSION

These findings suggest that thickness of cingulate cortex is influenced by the presence of the 10-repeat allele in ADHD.

Dopamine D4 Receptor Gene Associated with the Frontal-Striatal-Cerebellar Loop in Children with ADHD: A Resting-State fMRI Study

Attention deficit hyperactivity disorder (ADHD) is a common childhood neuropsychiatric disorder that has been linked to the dopaminergic system. This study aimed to investigate the effects of regulation of the dopamine D4 receptor (DRD4) on functional brain activity during the resting state in ADHD children using the methods of regional homogeneity (ReHo) and functional connectivity (FC). Resting-state functional magnetic resonance imaging data were analyzed in 49 children with ADHD. All participants were classified as either carriers of the DRD4 4-repeat/4-repeat (4R/4R) allele (n = 30) or the DRD4 2-repeat (2R) allele (n = 19). The results showed that participants with the DRD4 2R allele had decreased ReHo bilaterally in the posterior lobes of the cerebellum, while ReHo was increased in the left angular gyrus. Compared with participants carrying the DRD4 4R/4R allele, those with the DRD4 2R allele showed decreased FC to the left angular gyrus in the left striatum, right inferior frontal gyrus, and bilateral lobes of the cerebellum. The increased FC regions included the left superior frontal gyrus, medial frontal gyrus, and rectus gyrus. These data suggest that the DRD4 polymorphisms are associated with localized brain activity and specific functional connections, including abnormality in the frontal-striatal-cerebellar loop. Our study not only enhances the understanding of the correlation between the cerebellar lobes and ADHD, but also provides an imaging basis for explaining the neural mechanisms underlying ADHD in children.

The dopamine transporter role in psychiatric phenotypes

The dopamine transporter (DAT) is one of the most relevant and investigated neurotransmitter transporters. DAT is a plasma membrane protein which plays a homeostatic role, controlling both extracellular and intracellular concentrations of dopamine (DA). Since unbalanced DA levels are known to be involved in numerous mental disorders, a wealth of investigations has provided valuable insights concerning DAT role into normal brain functioning and pathological processes. Briefly, this extensive but non-systematic review discusses what is recently known about the role of SLC6A3 gene which encodes the dopamine transporter in psychiatric phenotypes. DAT protein, SLC6A3 gene, animal models, neuropsychology, and neuroimaging investigations are also concisely discussed. To conclude, current challenges are reviewed in order to provide perspectives for future studies.

The Influence of DAT1, COMT, and BDNF Genetic Polymorphisms on Total and Subregional Hippocampal Volumes in Early Onset Heavy Cannabis Users

Introduction: Hippocampal neuroanatomy is affected by genetic variations in dopaminergic candidate genes and environmental insults, such as early onset of chronic cannabis exposure. Here, we examine how hippocampal total and subregional volumes are affected by cannabis use and functional polymorphisms of dopamine-relevant genes, including the catechol-O-methyltransferase (COMT), dopamine transporter (DAT1), and the brain-derived neurotrophic factor (BDNF) genes.

Material and Methods: We manually traced total hippocampal volumes and automatically segmented hippocampal subregions using high-resolution MRI images, and performed COMT, DAT1, and BDNF genotyping in 59 male Caucasian young adults aged 18–30 years. These included 30 chronic cannabis users with early-onset (regular use at <16 years) and 29 age-, education-, and intelligence-matched controls.

Results: Cannabis use and dopaminergic gene polymorphism had both distinct and interactive effects on the hippocampus. We found emerging alterations of hippocampal total and specific subregional volumes in cannabis users relative to controls (i.e., CA1, CA2/3, and CA4), and associations between cannabis use levels and total and specific subregional volumes. Furthermore, total hippocampal volume and the fissure subregion were affected by cannabis×DAT1 polymorphism (i.e., 9/9R and in 10/10R alleles), reflecting high and low levels of dopamine availability.

Conclusion: These findings suggest that cannabis exposure alters the normal relationship between DAT1 polymorphism and the anatomy of total and subregional hippocampal volumes, and that specific hippocampal subregions may be particularly affected.

XKR4 Gene Effects on Cerebellar Development Are Not Specific to ADHD

A single-nucleotide polymorphism (SNP) of the XKR4 gene has been linked to Attention-Deficit/Hyperactivity Disorder (ADHD). This gene is preferentially expressed in cerebellum, a brain structure implicated in this disorder. This study investigated the effects of this SNP on cerebellar development in children with and without ADHD. We collected 279 longitudinal T1-weighted structural images and DNA from 58 children with ADHD and 64 typically developing (TD) children matched for age, IQ, and gender. Groups were divided by the XKR4 rs2939678 SNP into A-allele carriers versus subjects homozygous for the G-allele. Cerebellar lobular volumes were segmented into 35 regions of interest using MAGeTBrain, an automated multi-atlas segmentation pipeline for anatomical MRI, and statistically analyzed using linear mixed models. We found decreased gray matter (GM) volumes in ADHD compared to TD children in bilateral lobules VIIIA, left VIIIB, right VIIB, and vermis VI. Furthermore, we found a linear age by gene interaction in left lobule VIIB where subjects homozygous for the G-allele showed a decrease in volume over time compared to A-allele carriers. We further found quadratic age × gene and age × diagnosis interactions in left lobule IV. Subjects homozygous for the G-allele (the genotype overtransmitted in ADHD) showed more suppressed, almost flat quadratic growth curves compared to A-allele carriers, similar to individuals with ADHD compared to controls. However, there was no interaction between genotype and diagnosis, suggesting that any effects of this SNP on cerebellar development are not specific to the disorder.

Brain imaging genetics in ADHD and beyond - Mapping pathways from gene to disorder at different levels of complexity

Attention-deficit/hyperactivity disorder (ADHD) is a common and often persistent neurodevelopmental disorder. Beyond gene-finding, neurobiological parameters, such as brain structure, connectivity, and function, have been used to link genetic variation to ADHD symptomatology. We performed a systematic review of brain imaging genetics studies involving 62 ADHD candidate genes in childhood and adult ADHD cohorts. Fifty-one eligible research articles described studies of 13 ADHD candidate genes. Almost exclusively, single genetic variants were studied, mostly focussing on dopamine-related genes. While promising results have been reported, imaging genetics studies are thus far hampered by methodological differences in study design and analysis methodology, as well as limited sample sizes. Beyond reviewing imaging genetics studies, we also discuss the need for complementary approaches at multiple levels of biological complexity and emphasize the importance of combining and integrating findings across levels for a better understanding of biological pathways from gene to disease. These may include multi-modal imaging genetics studies, bioinformatic analyses, and functional analyses of cell and animal models.

Differential Associations between Cortical Thickness and Striatal Dopamine in Treatment-Naïve Adults with ADHD vs. Healthy Controls

Alterations in catecholamine signaling and cortical morphology have both been implicated in the pathophysiology of attention deficit/hyperactivity disorder (ADHD). However, possible links between the two remain unstudied. Here, we report exploratory analyses of cortical thickness and its relation to striatal dopamine transmission in treatment-naïve adults with ADHD and matched healthy controls. All participants had one magnetic resonance imaging (MRI) and two [¹¹C]raclopride positron emission tomography scans. Associations between frontal cortical thickness and the magnitude of d-amphetamine-induced [¹¹C]raclopride binding changes were observed that were divergent in the two groups. In the healthy controls, a thicker cortex was associated with less dopamine release; in the ADHD participants the converse was seen. The same divergence was seen for baseline D2/3 receptor availability. In healthy volunteers, lower D2/3 receptor availability was associated with a thicker cortex, while in the ADHD group lower baseline D2/3 receptor availability was associated with a thinner cortex. Individual differences in cortical thickness in these regions correlated with ADHD symptom severity. Together, these findings add to the evidence of associations between dopamine transmission and cortical morphology, and suggest that these relationships are altered in treatment-naïve adults with ADHD.

Imaging genetics in neurodevelopmental psychopathology

Neurodevelopmental disorders are defined by highly heritable problems during development and brain growth. Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorders (ASDs), and intellectual disability (ID) are frequent neurodevelopmental disorders, with common comorbidity among them. Imaging genetics studies on the role of disease-linked genetic variants on brain structure and function have been performed to unravel the etiology of these disorders. Here, we reviewed imaging genetics literature on these disorders attempting to understand the mechanisms of individual disorders and their clinical overlap. For ADHD and ASD, we selected replicated candidate genes implicated through common genetic variants. For ID, which is mainly caused by rare variants, we included genes for relatively frequent forms of ID occurring comorbid with ADHD or ASD. We reviewed case-control studies and studies of risk variants in healthy individuals. Imaging genetics studies for ADHD were retrieved for SLC6A3/DAT1, DRD2, DRD4, NOS1, and SLC6A4/5HTT. For ASD, studies on CNTNAP2, MET, OXTR, and SLC6A4/5HTT were found. For ID, we reviewed the genes FMR1, TSC1 and TSC2, NF1, and MECP2. Alterations in brain volume, activity, and connectivity were observed. Several findings were consistent across studies, implicating, for example, SLC6A4/5HTT in brain activation and functional connectivity related to emotion regulation. However, many studies had small sample sizes, and hypothesis-based, brain region-specific studies were common. Results from available studies confirm that imaging genetics can provide insight into the link between genes, disease-related behavior, and the brain. However, the field is still in its early stages, and conclusions about shared mechanisms cannot yet be drawn.

Effects of dopaminergic genes, prenatal adversities, and their interaction on attention-deficit/hyperactivity disorder and neural correlates of response inhibition

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is often accompanied by impaired response inhibition; both have been associated with aberrant dopamine signalling. Given that prenatal exposure to alcohol or smoking is known to affect dopamine-rich brain regions, we hypothesized that individuals carrying the ADHD risk alleles of the dopamine receptor D4 (DRD4) and dopamine transporter (DAT1) genes may be especially sensitive to their effects.

METHODS

Functional MRI data, information on prenatal adversities and genetic data were available for 239 adolescents and young adults participating in the multicentre ADHD cohort study NeuroIMAGE (average age 17.3 yr). We analyzed the effects of DRD4 and DAT1, prenatal exposure to alcohol and smoking and their interactions on ADHD severity, response inhibition and neural activity.

RESULTS

We found no significant gene × environment interaction effects. We did find that the DRD4 7-repeat allele was associated with less superior frontal and parietal brain activity and with greater activity in the frontal pole and occipital cortex. Prenatal exposure to smoking was also associated with lower superior frontal activity, but with greater activity in the parietal lobe. Further, those exposed to alcohol had more activity in the lateral orbitofrontal cortex, and the DAT1 risk variant was associated with lower cerebellar activity.

LIMITATIONS

Retrospective reports of maternal substance use and the cross-sectional study design restrict causal inference.

CONCLUSION

While we found no evidence of gene × environment interactions, the risk factors under investigation influenced activity of brain regions associated with response inhibition, suggesting they may add to problems with inhibiting behaviour.

Age and DRD4 Genotype Moderate Associations Between Stimulant Treatment History and Cortex Structure in Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) has been associated with dopaminergic imbalance and subtle volume decreases in the brain. Stimulants acutely enhance dopaminergic neurotransmission. Long-term effects of prolonged manipulation of the dopaminergic system on brain structure remain poorly understood; they could be beneficial or unfavorable and could be moderated by common genetic variants and/or age.

METHOD

In a large observational ADHD cohort study (N = 316), the effects of cumulative stimulant treatment, genotype (for DAT1 haplotype and DRD4 variants), and treatment-by-genotype interactions on striatal, frontal, and hippocampal volumes and their interactions with age were evaluated.

RESULTS

No main effects of treatment were found. Associations between treatment and bilateral frontal and left hippocampal volume depended on DRD4 genotype and age. At a younger age and lower treatment levels, but not at a younger age and higher treatment levels, carriers of the DRD4 7R allele showed decreased frontal cortex volumes. At an older age, carriers and non-carriers showed smaller frontal volumes irrespective of treatment history. Left hippocampal volume was similar to that in controls at average treatment levels and increased with treatment only in carriers of the DRD4 risk allele and at a younger age. No interaction effects were found in the striatum.

CONCLUSION

Carriers of the DRD4 risk allele at a younger age might be sensitive to cortical remodeling after stimulant treatment. The cross-sectional nature of this study warrants cautious interpretation of age effects. The present findings, although of small effect size, might ultimately contribute to optimal care for individuals with ADHD.

Developmentally Sensitive Interaction Effects of Genes and the Social Environment on Total and Subcortical Brain Volumes

Smaller total brain and subcortical volumes have been linked to psychopathology including attention-deficit/hyperactivity disorder (ADHD). Identifying mechanisms underlying these alterations, therefore, is of great importance. We investigated the role of gene-environment interactions (GxE) in interindividual variability of total gray matter (GM), caudate, and putamen volumes. Brain volumes were derived from structural magnetic resonance imaging scans in participants with (N = 312) and without ADHD (N = 437) from N = 402 families (age M = 17.00, SD = 3.60). GxE effects between DAT1, 5-HTT, and DRD4 and social environments (maternal expressed warmth and criticism; positive and deviant peer affiliation) as well as the possible moderating effect of age were examined using linear mixed modeling. We also tested whether findings depended on ADHD severity. Deviant peer affiliation was associated with lower caudate volume. Participants with low deviant peer affiliations had larger total GM volumes with increasing age. Likewise, developmentally sensitive GxE effects were found on total GM and putamen volume. For total GM, differential age effects were found for DAT1 9-repeat and HTTLPR L/L genotypes, depending on the amount of positive peer affiliation. For putamen volume, DRD4 7-repeat carriers and DAT1 10/10 homozygotes showed opposite age relations depending on positive peer affiliation and maternal criticism, respectively. All results were independent of ADHD severity. The presence of differential age-dependent GxE effects might explain the diverse and sometimes opposing results of environmental and genetic effects on brain volumes observed so far.

Integrated analysis of gray and white matter alterations in attention-deficit/hyperactivity disorder

BACKGROUND

Magnetic resonance imaging (MRI) is able to provide detailed insights into the structural organization of the brain, e.g., by means of mapping brain anatomy and white matter microstructure. Understanding interrelations between MRI modalities, rather than mapping modalities in isolation, will contribute to unraveling the complex neural mechanisms associated with neuropsychiatric disorders as deficits detected across modalities suggest common underlying mechanisms. Here, we conduct a multimodal analysis of structural MRI modalities in the context of attention-deficit/hyperactivity disorder (ADHD).

METHODS

Gray matter volume, cortical thickness, surface areal expansion estimates, and white matter diffusion indices of 129 participants with ADHD and 204 participants without ADHD were entered into a linked independent component analysis. This data-driven analysis decomposes the data into multimodal independent components reflecting common inter-subject variation across imaging modalities.

RESULTS

ADHD severity was related to two multimodal components. The first component revealed smaller prefrontal volumes in participants with more symptoms, co-occurring with abnormal white matter indices in prefrontal cortex. The second component demonstrated decreased orbitofrontal volume as well as abnormalities in insula, occipital, and somato-sensory areas in participants with more ADHD symptoms.

CONCLUSIONS

Our results replicate and extend previous unimodal structural MRI findings by demonstrating that prefrontal, parietal, and occipital areas, as well as fronto-striatal and fronto-limbic systems are implicated in ADHD. By including multiple modalities, sensitivity for between-participant effects is increased, as shared variance across modalities is modeled. The convergence of modality-specific findings in our results suggests that different aspects of brain structure share underlying pathophysiology and brings us closer to a biological characterization of ADHD.

Enlarged striatal volume in adults with ADHD carrying the 9-6 haplotype of the dopamine transporter gene DAT1

The dopamine transporter gene, DAT1 (SLC6A3), has been studied extensively as a candidate gene for attention-deficit/hyperactivity disorder (ADHD). Different alleles of variable number of tandem repeats (VNTRs) in this gene have been associated with childhood ADHD (10/10 genotype and haplotype 10-6) and adult ADHD (haplotype 9-6). This suggests a differential association depending on age, and a role of DAT1 in modulating the ADHD phenotype over the lifespan. The DAT1 gene may mediate susceptibility to ADHD through effects on striatal volumes, where it is most highly expressed. In an attempt to clarify its mode of action, we examined the effect of three DAT1 alleles (10/10 genotype, and the haplotypes 10-6 and 9-6) on bilateral striatal volumes (nucleus accumbens, caudate nucleus, and putamen) derived from structural magnetic resonance imaging scans using automated tissue segmentation. Analyses were performed separately in three cohorts with cross-sectional MRI data, a childhood/adolescent sample (NeuroIMAGE, 301 patients with ADHD and 186 healthy participants) and two adult samples (IMpACT, 118 patients with ADHD and 111 healthy participants; BIG, 1718 healthy participants). Regression analyses revealed that in the IMpACT cohort, and not in the other cohorts, carriers of the DAT1 adult ADHD risk haplotype 9-6 had 5.9 % larger striatum volume relative to participants not carrying this haplotype. This effect varied by diagnostic status, with the risk haplotype affecting striatal volumes only in patients with ADHD. An explorative analysis in the cohorts combined (N = 2434) showed a significant gene-by-diagnosis-by-age interaction suggesting that carriership of the 9-6 haplotype predisposes to a slower age-related decay of striatal volume specific to the patient group. This study emphasizes the need of a lifespan approach in genetic studies of ADHD.

Influence of DAT1 and COMT variants on neural activation during response inhibition in adolescents with attention-deficit/hyperactivity disorder and healthy controls

BACKGROUND

Impairment of response inhibition has been implicated in attention-deficit/hyperactivity disorder (ADHD). Dopamine neurotransmission has been linked to the behavioural and neural correlates of response inhibition. The current study aimed to investigate the relationship of polymorphisms in two dopamine-related genes, the catechol-O-methyltransferase gene (COMT) and the dopamine transporter gene (SLC6A3 or DAT1), with the neural and behavioural correlates of response inhibition.

METHOD

Behavioural and neural measures of response inhibition were obtained in 185 adolescents with ADHD, 111 of their unaffected siblings and 124 healthy controls (mean age 16.9 years). We investigated the association of DAT1 and COMT variants on task performance and whole-brain neural activation during response inhibition in a hypothesis-free manner. Additionally, we attempted to explain variance in previously found ADHD effects on neural activation during response inhibition using these DAT1 and COMT polymorphisms.

RESULTS

The whole-brain analyses demonstrated large-scale neural activation changes in the medial and lateral prefrontal, subcortical and parietal regions of the response inhibition network in relation to DAT1 and COMT polymorphisms. Although these neural activation changes were associated with different task performance measures, no relationship was found between DAT1 or COMT variants and ADHD, nor did variants in these genes explain variance in the effects of ADHD on neural activation.

CONCLUSIONS

These results suggest that dopamine-related genes play a role in the neurobiology of response inhibition. The limited associations between gene polymorphisms and task performance further indicate the added value of neural measures in linking genetic factors and behavioural measures.

Neurobiology of ADHD From Childhood to Adulthood: Findings of Imaging Methods

OBJECTIVE

To review the pattern of morphological and functional brain changes in both children and adults with ADHD that emerges from the recent literature. In addition, the task of the present review is to explore how to understand the nature of the brain changes.

METHODS

Literature review.

RESULTS

Neuroimaging studies provide a multitude of information that currently allows us to expand the notions of ADHD neurobiology beyond its traditional understanding as a manifestation of frontostriatal dysfunction. They point to disorders of several other areas of the brain, particularly the anterior cingulum, the dorsolateral as well as ventrolateral prefrontal cortex, the orbitofrontal cortex, the superior parietal regions, the caudate nucleus, the thalamus, the amygdala and the cerebellum. Imaging studies point to the persistence of changes in both brain structure and function into adulthood, although there might be a tendency for improvement of caudate nucleus pathology. Changes in neuronal (dendritic) plasticity, which are under the modulatory influence of the dopaminergic system, may be in the background of disorders of brain morphology and anatomical connectivity with subsequent brain dysfunction. Growing evidence suggest that methylphenidate treatment can lead to improvement of brain changes seen in neuroimaging by its positive effect on neuroplasticity.

CONCLUSION

Changes in neuronal plasticity may be behind persisting brain changes in ADHD. Current treatment approaches seem to improve these neuroplastic processes, and, therefore, may have a positive effect on the neuropathology of ADHD.

Altered Corticostriatal Connectivity and Exploration/Exploitation Imbalance Emerge as Intermediate Phenotypes for a Neonatal Dopamine Dysfunction

Findings showing that neonatal lesions of the forebrain dopaminergic system in rodents lead to juvenile locomotor hyperactivity and learning deficits have been taken as evidence of face validity for the attention deficit hyperactivity disorder. However, the core cognitive and physiological intermediate phenotypes underlying this rodent syndrome remain unknown. Here we show that early postnatal dopaminergic lesions cause long-lasting deficits in exploitation of shelter, social and nutritional resources, and an imbalanced exploratory behavior, where nondirected local exploration is exacerbated, whereas sophisticated search behaviors involving sequences of goal directed actions are degraded. Importantly, some behavioral deficits do not diminish after adolescence but instead worsen or mutate, particularly those related to the exploration of wide and spatially complex environments. The in vivo electrophysiological recordings and morphological reconstructions of striatal medium spiny neurons reveal corticostriatal alterations associated to the behavioral phenotype. More specifically, an attenuation of corticostriatal functional connectivity, affecting medial prefrontal inputs more markedly than cingulate and motor inputs, is accompanied by a contraction of the dendritic arbor of striatal projection neurons in this animal model. Thus, dopaminergic neurons are essential during postnatal development for the functional and structural maturation of corticostriatal connections. From a bottom-up viewpoint, our findings suggest that neuropsychiatric conditions presumably linked to developmental alterations of the dopaminergic system should be evaluated for deficits in foraging decision making, alterations in the recruitment of corticostriatal circuits during foraging tasks, and structural disorganization of the frontostriatal connections.

The attentive brain: insights from developmental cognitive neuroscience

Visual attention functions as a filter to select environmental information for learning and memory, making it the first step in the eventual cascade of thought and action systems. Here, we review studies of typical and atypical visual attention development and explain how they offer insights into the mechanisms of adult visual attention. We detail interactions between visual processing and visual attention, as well as the contribution of visual attention to memory. Finally, we discuss genetic mechanisms underlying attention disorders and how attention may be modified by training.

Cortical thickness differences in the prefrontal cortex in children and adolescents with ADHD in relation to dopamine transporter (DAT1) genotype

Several lines of evidence suggest that the dopamine transporter gene (DAT1) plays a crucial role in attention deficit hyperactivity disorder (ADHD). Concretely, recent data indicate that the 10-repeat (10R) DAT1 allele may mediate neuropsychological functioning, response to methylphenidate, and even brain function and structure in children with ADHD. This study aimed to investigate the influence of 10R DAT1 on thickness of the prefrontal cortex in children and adolescents with ADHD. To this end, brain magnetic resonance images were acquired from 33 patients with homozygosity for the 10R allele and 30 patients with a single copy or no copy of the allele. The prefrontal cortex of each MRI scan was automatically parceled into regions of interest (ROIs) based on Brodmann areas (BA). The two groups were matched for age, gender, IQ, ADHD subtype, symptom severity, comorbidity and medication status. However, patients with two copies of the 10R allele exhibited significantly decreased cortical thickness in right BA 46 relative to patients with one or fewer copies of the allele. No other prefrontal ROI differed significantly between the two groups. Present findings suggest that cortical thickness of right lateral prefrontal cortex (BA 46) is influenced by the presence of the DAT1 10 repeat allele in children and adolescents with ADHD.

The role of age in association analyses of ADHD and related neurocognitive functioning: A proof of concept for dopaminergic and serotonergic genes

Elucidating genetic mechanisms involved in Attention-Deficit/Hyperactivity Disorder (ADHD) has been challenging. Relatively unexplored is the fact that genetic mechanisms can differ with age. The current study explored the association between dopaminergic and serotonergic genes, ADHD symptoms, and neurocognitive functioning in relation to age. Associations of three genetic ADHD risk factors, DAT1, DRD4, and 5-HTT with symptoms and six neurocognitive measures were explored in two samples of the NeuroIMAGE study: 756 children, adolescents, and young adults with ADHD, their siblings, and controls (M age 17 years, SD 3.2), and 393 parents with and without ADHD (M age 48 years, SD 4.8). Association analyses were performed in both samples, and effects were compared to address dichotomous age effects. Gene*age interactions were examined to address continuous age effects. Moderating effects of age were found for DRD4-7R carriership and ADHD symptoms in the adult group only; in the adolescents the 5-HTT LL genotype was differentially associated with inhibition and with motor timing at different ages, and to inhibition in adults; DAT1 10-6 haplotype carriership showed differential working memory performance depending on age. None of our effects survived correction for multiple comparisons. Our results are preliminary, but may point to differential genotype-phenotype associations at different ages. This can be seen as a proof of concept for the importance of age in dopaminergic and serotonergic genetic association analyses. Our findings are consistent with the idea that genetic and neurocognitive mechanisms underlying ADHD may change throughout life. © 2015 Wiley Periodicals, Inc.

Indirect association of DAT1 genotype with executive function through white matter volume in orbitofrontal cortex

The dopamine transporter (DAT1) gene has been associated with impulsivity and executive functioning. Further, DAT1 has been associated with brain structural characteristics and resting state connectivity. This study tested an indirect effect model in which DAT1 genotype (9-repeat (9R) carriers vs 10-repeat (10R) homozygotes) is linked to phenotypes representing impulsivity and executive function (planning behavior) through effects on white matter (WM) volumes in prefrontal cortex (PFC), particularly orbitofrontal cortex (OFC). Adolescents (ages 14-18, n=38) were recruited from substance use treatment (n=22) and the community (n=16) to increase phenotype variation. Results indicated that DAT1 10/10 genotype was associated with lower WM volume in the PFC, specifically the left OFC. Further, lower WM volume in the left OFC predicted more difficulties in self-reported planning behavior, but not impulsivity. Indirect effect analysis indicated that lower WM volume in the left OFC mediated the association between DAT1 10/10 genotype and difficulties in planning behavior. Results suggest a brain structural mechanism, involving lower WM volume in the left OFC, as a link in the association between DAT1 genotype and a specific aspect of executive function. Genetic effects on regional WM volume that are linked to behavioral outcomes could ultimately inform the development of tailored interventions that address an individual׳s unique risk factors.

Predicting childhood effortful control from interactions between early parenting quality and children's dopamine transporter gene haplotypes

Children's observed effortful control (EC) at 30, 42, and 54 months (n = 145) was predicted from the interaction between mothers' observed parenting with their 30-month-olds and three variants of the solute carrier family C6, member 3 (SLC6A3) dopamine transporter gene (single nucleotide polymorphisms in intron8 and intron13, and a 40 base pair variable number tandem repeat [VNTR] in the 3'-untranslated region [UTR]), as well as haplotypes of these variants. Significant moderating effects were found. Children without the intron8-A/intron13-G, intron8-A/3'-UTR VNTR-10, or intron13-G/3'-UTR VNTR-10 haplotypes (i.e., haplotypes associated with the reduced SLC6A3 gene expression and thus lower dopamine functioning) appeared to demonstrate altered levels of EC as a function of maternal parenting quality, whereas children with these haplotypes demonstrated a similar EC level regardless of the parenting quality. Children with these haplotypes demonstrated a trade-off, such that they showed higher EC, relative to their counterparts without these haplotypes, when exposed to less supportive maternal parenting. The findings revealed a diathesis-stress pattern and suggested that different SLC6A3 haplotypes, but not single variants, might represent different levels of young children's sensitivity/responsivity to early parenting.

Structural correlates of COMT Val158Met polymorphism in childhood ADHD: a voxel-based morphometry study

OBJECTIVES

The Val158-allele of the catechol-O-methyltransferase (COMT) Val158Met (rs4680) functional polymorphism has been identified as a risk factor for antisocial behaviour in attention-deficit/hyperactivity disorder (ADHD). Here, we used voxel-based morphometry to investigate the effects of Val158Met polymorphism on grey matter (GM) volumes in a sample of 7-13-year-old children.

METHODS

MRI and genotype data were obtained for 38 children with combined-type ADHD and 24 typically developing (TD) children. Four regions of interest were identified: striatum, cerebellum, temporal lobe and inferior frontal gyrus (IFG).

RESULTS

When compared to TD children, those with ADHD had a significant decrease of GM volume in the IFG. Volume in this region was negatively correlated with ratings of hyperactivity/impulsivity symptoms. Furthermore, the smaller GM volume in the IFG was attributed to the presence of the Met158-allele, as only children with ADHD carrying a Met158-allele exhibited such decrease in the IFG. Children with ADHD homozygotes for the Val158-allele presented increased GM volume in the caudate nucleus when compared with TD children.

CONCLUSIONS

This study provides the first evidence of a modulation of ADHD-related GM volume alterations by Val158Met in two key regions, possibly mediating the relationship between Val158Met polymorphism and antisocial behaviour in children with ADHD.

An association between a dopamine transporter gene (SLC6A3) haplotype and ADHD symptom measures in nonclinical adults

Previous genetic studies have postulated that attention deficit hyperactivity disorder (ADHD) should be regarded as the extreme end of a set of behavioural traits that can be continuously measured in the general population. The current study adopted a quantitative trait approach to examine the relationship between dopamine gene variants and self-reported ADHD symptoms in 517 nonclinical adults. Although genetic associations with variants of both the dopamine transporter (DAT1; SLC6A3) and D4 receptor (DRD4) genes have been reliably reported in children, results in adults are less consistent. We probed two potentially functional variable number of tandem repeat (VNTR) polymorphisms in the 3'UTR and intron 8 of DAT1, the 10-repeat and 6-repeat alleles of which respectively form a haplotype (10/6 DAT1 haplotype) that is associated with childhood ADHD. We also genotyped the exon 3 VNTR of DRD4, the 7-repeat allele of which is also an established risk factor for childhood ADHD. Permutation analysis showed an influence of the 10/6 DAT1 haplotype on both CAARS-G and CAARS-H (DSM-IV ADHD Symptoms Total and ADHD Index respectively), such that ADHD symptom scores increased with each additional copy of the 10/6 DAT1 haplotype. This result survived corrections for multiple comparisons both at the level of genotype and phenotype. A nominal association with CAARS-G was also found for the 7-repeat allele of the DRD4 VNTR however this did not survive multiple comparison correction. Our results provide further support for the influence of variation in the 10/6 DAT1 haplotype and individual differences in ADHD symptoms in adults.

Cognitive and neural correlates of the 5-repeat allele of the dopamine D4 receptor gene in a population lacking the 7-repeat allele

The 5-repeat allele of a common length polymorphism in the gene that encodes the dopamine D4 receptor (DRD4) is robustly associated with the risk of attention deficit hyperactivity disorder (ADHD) and substantially exists in Asian populations, which have a lower ADHD prevalence. In this study, we investigated the effect of this allele on microstructural properties of the brain and on its functional activity during externally directed attention-demanding tasks and creative performance in the 765 Asian subjects. For this purpose, we employed diffusion tensor imaging, N-back functional magnetic resonance imaging paradigms, and a test to measure creativity by divergent thinking. The 5-repeat allele was significantly associated with increased originality in the creative performance, increased mean diffusivity (the measure of how the tissue includes water molecules instead of neural and vessel components) in the widespread gray and white matter areas of extensive areas, particularly those where DRD4 is expressed, and reduced task-induced deactivation in the areas that are deactivated during the tasks in the course of both the attention-demanding working memory task and simple sensorimotor task. The observed neural characteristics of 5-repeat allele carriers may lead to an increased risk of ADHD and behavioral deficits. Furthermore, the increased originality of creative thinking observed in the 5-repeat allele carriers may support the notion of the side of adaptivity of the widespread risk allele of psychiatric diseases.

White matter microstructure and the variable adult outcome of childhood attention deficit hyperactivity disorder

Changes in cerebral cortical anatomy have been tied to the clinical course of attention deficit hyperactivity disorder (ADHD). We now ask if alterations in white matter tract microstructure are likewise linked with the adult outcome of childhood ADHD. Seventy-five young adults, 32 with ADHD persisting from childhood and 43 with symptom remission were contrasted against 74 never-affected comparison subjects. Using diffusion tensor imaging, we defined fractional anisotropy, a metric related to white matter microstructure, along with measures of diffusion perpendicular (radial) and parallel (axial) to the axon. Analyses were adjusted for head motion, age and sex, and controlled for multiple comparisons and medication history. Tract-based analyses showed that greater adult inattention, but not hyperactivity-impulsivity, was associated with significantly lower fractional anisotropy in the left uncinate (standardized β=-0.37, t=3.28, p=0.002) and inferior fronto-occipital fasciculi (standardized β=-0.37, t=3.29, p=0.002). The ADHD group with symptoms persisting into adulthood had significantly lower fractional anisotropy than the never-affected controls in these tracts, differences associated with medium to large effect sizes. By contrast, the ADHD group that remitted by adulthood did not differ significantly from controls. The anomalies were found in tracts that connect components of neural systems pertinent to ADHD, such as attention control (inferior fronto-occipital fasciculus) and emotion regulation and the processing of reward (the uncinate fasciculus). Change in radial rather than axial diffusivity was the primary driver of this effect, suggesting pathophysiological processes including altered myelination as future targets for pharmacological and behavioral interventions.

Changes in the development of striatum are involved in repetitive behavior in autism

BACKGROUND

Repetitive behavior is a core feature of autism and has been linked to differences in striatum. In addition, the brain changes associated with autism appear to vary with age. However, most studies investigating striatal differences in autism are cross-sectional, limiting inferences on development. In this study, we set out to 1) investigate striatal development in autism, using a longitudinal design; and 2) examine the relationship between striatal development and repetitive behavior.

METHODS

We acquired longitudinal structural magnetic resonance imaging scans from 86 individuals (49 children with autism, 37 matched control subjects). Each individual was scanned twice, with a mean scan interval time of 2.4 years. Mean age was 9.9 years at time 1 and 12.3 years at time 2. Striatal structures were traced manually with high reliability. Multivariate analyses of variance were used to investigate differences in brain development between diagnostic groups. To examine the relationship with behavior, correlations between changes in brain volumes and clinical measures were calculated.

RESULTS

Our results showed an increase in the growth rate of striatal structures for individuals with autism compared with control subjects. The effect was specific to caudate nucleus, where growth rate was doubled. Second, faster striatal growth was correlated with more severe repetitive behavior (insistence on sameness) at the preschool age.

CONCLUSIONS

This longitudinal study of brain development in autism confirms the involvement of striatum in repetitive behavior. Furthermore, it underscores the significance of brain development in autism, as the severity of repetitive behavior was related to striatal growth, rather than volume per se.

The role of prefrontal catecholamines in attention and working memory

While much progress has been made in identifying the brain regions and neurochemical systems involved in the cognitive processes disrupted in mental illnesses, to date, the level of detail at which neurobiologists can describe the chain of events giving rise to cognitive functions is very rudimentary. Much of the intense interest in understanding cognitive functions is motivated by the hope that it might be possible to understand these complex functions at the level of neurons and neural circuits. Here, we review the current state of the literature regarding how modulations in catecholamine levels within the prefrontal cortex (PFC) alter the neuronal and behavioral correlates of cognitive functions, particularly attention and working memory.

Association between the DAT1 gene and spatial working memory in attention deficit hyperactivity disorder

An association between attention deficit hyperactivity disorder (ADHD) and the dopamine transporter gene (DAT1) was reported in clinical samples. This study aimed to explore whether there was an association between DAT1 and spatial working memory (SWM), a promising endophenotype for ADHD. This family-based association sample consisted of 382 probands with DSM-IV ADHD and their family members (n = 1298) in Taiwan. The SWM task of the Cambridge Neuropsychological Test Automated Battery (CANTAB) was used to measure SWM of all participants. We screened 15 polymorphisms across the DAT1 gene, including 14 single nucleotide polymorphisms (SNPs) and the variable number of tandem repeat polymorphism in the 3'-untranslated region. We used the Family-Based Association Test (FBAT) to test the associations of genetic polymorphisms with the SWM measures. In single locus association analyses, two SNPs (rs2617605 and rs37020) were significantly associated with the double errors (adjusted p = 0.03 and 0.03, respectively) after adjustment for multiple testing. In haplotype analyses, a haplotype rs403636 (G)/rs463379 (C)/rs393795 (C)/rs37020 (G) was significantly associated with total within-search errors (minimal p = 0.001), within-search errors in eight boxes (minimal p = 0.002), total double errors (minimal p = 0.001) and double errors in eight boxes (minimal p = 0.004). Our finding of the haplotype rs403636 (G)/rs463379 (C)/rs393795 (C)/rs37020 (G) as a novel genetic marker for spatial working memory suggests that variation in DAT1 may provide insight into the pathways leading from genotype to phenotype of ADHD.

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.

Genome-wide association identifies genetic variants associated with lentiform nucleus volume in N = 1345 young and elderly subjects

Deficits in lentiform nucleus volume and morphometry are implicated in a number of genetically influenced disorders, including Parkinson's disease, schizophrenia, and ADHD. Here we performed genome-wide searches to discover common genetic variants associated with differences in lentiform nucleus volume in human populations. We assessed structural MRI scans of the brain in two large genotyped samples: the Alzheimer's Disease Neuroimaging Initiative (ADNI; N = 706) and the Queensland Twin Imaging Study (QTIM; N = 639). Statistics of association from each cohort were combined meta-analytically using a fixed-effects model to boost power and to reduce the prevalence of false positive findings. We identified a number of associations in and around the flavin-containing monooxygenase (FMO) gene cluster. The most highly associated SNP, rs1795240, was located in the FMO3 gene; after meta-analysis, it showed genome-wide significant evidence of association with lentiform nucleus volume (P MA  = 4.79 × 10(-8)). This commonly-carried genetic variant accounted for 2.68 % and 0.84 % of the trait variability in the ADNI and QTIM samples, respectively, even though the QTIM sample was on average 50 years younger. Pathway enrichment analysis revealed significant contributions of this gene to the cytochrome P450 pathway, which is involved in metabolizing numerous therapeutic drugs for pain, seizures, mania, depression, anxiety, and psychosis. The genetic variants we identified provide replicated, genome-wide significant evidence for the FMO gene cluster's involvement in lentiform nucleus volume differences in human populations.

Noradrenergic versus dopaminergic modulation of impulsivity, attention and monitoring behaviour in rats performing the stop-signal task: possible relevance to ADHD

RATIONALE

Deficient response inhibition is a prominent feature of many pathological conditions characterised by impulsive and compulsive behaviour. Clinically effective doses of catecholamine reuptake inhibitors are able to improve such inhibitory deficits as measured by the stop-signal task (SST) in humans and other animals. However, the precise therapeutic mode of action of these compounds in terms of their relative effects on dopamine (DA) and noradrenaline (NA) systems in prefrontal cortical and striatal regions mediating attention and cognitive control remains unclear.

OBJECTIVES

We sought to fractionate the effects of global catecholaminergic manipulations on SST performance by using receptor-specific compounds for NA or DA. The results are described in terms of the effects of modulating specific receptor subtypes on various behavioural measures such as response inhibition, perseveration, sustained attention, error monitoring and motivation.

RESULTS

Blockade of α2-adrenoceptors improved sustained attention and response inhibition, whereas α1 and β1/2 adrenergic receptor antagonists disrupted go performance and sustained attention, respectively. No relevant effects were obtained after targeting DA D1, D2 or D4 receptors, while both a D3 receptor agonist and antagonist improved post-error slowing and compulsive nose-poke behaviour, though generally impairing other task measures.

CONCLUSIONS

Our results suggest that the use of specific pharmacological agents targeting α2 and β noradrenergic receptors may improve existing treatments for attentional deficits and impulsivity, whereas DA D3 receptors may modulate error monitoring and perseverative behaviour.

Synaptogenesis in the fetal corpus striatum, globus pallidus, and substantia nigra: correlations with striosomes of Graybiel and dyskinesias in premature infants

Synaptogenesis can be detected in tissue sections by immunoreactivity for synaptophysin, a synaptic vesicle glycoprotein that serves as a marker of synaptic maturation. Reactivity was prospectively studied postmortem in sections of the striatum, globus pallidus, and substantia nigra in 172 normal human fetuses and neonates of 6 to 41 weeks' gestation. Caudate nucleus and putamen show patchy reactivity beginning at 13 weeks' gestation around some intracapsular neurons; the pattern is well developed in all regions before midgestation. Near-uniform reactivity throughout the striatum is achieved by 34 weeks, but subtle patchiness is still perceived at term. The globus pallidus shows uniform reactivity without stria from 13 weeks and the substantia nigra from 9 weeks. Synaptic patchiness in the fetal corpus striatum appears to correspond to the "striosomes of Graybiel" that define adjacent neurotransmitter-rich and neurotransmitter-poor zones. Clinical correlation is proposed with dystonic postures and athetoid movements observed in normal preterm neonates of 26 to 32 weeks.

Imaging gene and environmental effects on cerebellum in Attention-Deficit/Hyperactivity Disorder and typical development

This study investigates the effects of XKR4, a recently identified candidate gene for Attention-Deficit/Hyperactivity Disorder (ADHD), birth weight, and their interaction on brain volume in ADHD. XKR4 is expressed in cerebellum and low birth weight has been associated both with changes in cerebellum and with ADHD, probably due to its relation with prenatal adversity. Anatomical MRI scans were acquired in 58 children with ADHD and 64 typically developing controls and processed to obtain volumes of cerebrum, cerebellum and gray and white matter in each structure. DNA was collected from saliva. Analyses including data on birth weight were conducted in a subset of 37 children with ADHD and 51 controls where these data were retrospectively collected using questionnaires. There was an interaction between genotype and birth weight for cerebellum gray matter volume (p = .020). The combination of homozygosity for the G-allele (the allele previously found to be overtransmitted in ADHD) and higher birth weight was associated with smaller volume. Furthermore, birth weight was positively associated with cerebellar white matter volume in controls, but not ADHD (interaction: p = .021). The interaction of genotype with birth weight affecting cerebellum gray matter is consistent with models that emphasize increased influence of genetic risk-factors in an otherwise favorable prenatal environment. The absence of an association between birth weight and cerebellum white matter volume in ADHD suggests that other genetic or environmental effects may be at play, unrelated to XKR4. These results underscore the importance of considering environmental effects in imaging genetics studies.