Familiality and molecular genetics of attention networks in ADHD

Gene-gene and gene-environmental interaction of dopaminergic system genes in Pakistani children with attention deficit hyperactivity disorder

Background

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder influenced by genetic and environmental factors. This study examined the specific gene variants, dopamine transporter 1 (DAT1) rs6350, dopamine receptor D3 (DRD3) rs6280, dopamine receptor D2 (DRD2) rs6277, and catechol-O-methyltransferase (COMT) rs4633, in relation to ADHD among Pakistani children by exploring the potential gene-gene and gene-environment interactions.

Methods

A total of 100 cases of ADHD and 100 healthy children were recruited. The tetra-primer amplification refractory mutation system (ARMS) assays were designed for genotyping the selected variants in both groups, and their association with ADHD was determined in different genetic models. Gene-gene and gene-environmental interactions were determined by the multifactor dimensionality reduction (MDR) method.

Results

The DAT1 rs6350 SNV AA genotype showed a significantly increased risk for ADHD in the codominant and recessive models. Conversely, the AG genotype demonstrated a protective factor for ADHD in the codominant and overdominant models. The DRD3 rs6280 T allele exhibited a decreased risk for ADHD, and the TT genotype showed a reduced risk in the recessive and log-additive models. No association between the DRD2 rs6277 and COMT rs4633 SNVs with ADHD was found in our population. The MDR analysis of the best three-fold interaction model showed redundancy between DAT1 rs6350 and DRD3 rs6280; however, the risk was increased with the gender variable, which showed a weak synergistic interaction with these SNVs.

Conclusion

Genes associated with dopaminergic neurotransmission may contribute to the occurrence of ADHD. Furthermore, gene-gene and gene-environmental interactions may increase ADHD susceptibility.

Attention deficit in primary-school-age children with attention deficit hyperactivity disorder measured with the attention network test: a systematic review and meta-analysis

Objective

To review and meta-analyze patterns of attention deficit in primary-school-age children with ADHD measured with the neuropsychological attention network test (ANT).

Methods

Six electronic databases were searched to 5.05.2022. Selection criteria included prospective cohort and intervention studies; ANT used; primary-school-age; diagnosis of ADHD/at high risk.

Results

Seven studies met inclusion criteria (N = 3,826). Compared with controls, children with ADHD had higher scores for Reaction Time (Hedges' g = 0.433; 95% CI: 0.135-0.731), Reaction Time Variability (Hedges' g = 0.334; 95% CI: 0.012-0.657), and Alerting Network (Hedges' g = 0.235; 95% CI: 0.021-0.449) while children at high risk had higher Alerting Network scores (Hedges' g = 0.176; 95% CI: 0.003-0.349) and Correctness scores (Hedges' g = 1.956; 95% CI: 0.020-3.892).

Conclusions

Children with ADHD and at risk of ADHD had different ANT results from children without ADHD only for the alerting network. There were no significant differences for executive and orienting outcomes. Children at risk of ADHD also made more errors (commission and omission) measured with the ANT compared with children without ADHD. Reaction time was longer and reaction time variability higher in children with ADHD than in children without ADHD, and in children at risk of ADHD compared with children without ADHD.

Preregistration

A protocol has been registered with the International Prospective Register of Systematic Reviews (PROSPERO) database (registration number: CRD42021249768).

The Attention Network Test Database: ADHD and Cross-Cultural Applications

Attention is a central component of cognitive and behavioral processes and plays a key role in basic and higher-level functioning. Posner's model of attention describes three components or networks of attention: the alerting, which involves high intensity states of arousal; the orienting, which involves the selective direction of attention; and the executive control, which involves cognitive functions such as conflict resolution and working memory. The Attention Network Test (ANT) is a computerized testing measure that was developed to measure these three networks of attention. This project describes the ANT, its widely used variants, and the recently developed ANT Database, a repository of data extracted from all studies that have used the ANT as of 2019. To illustrate the potential uses of the database, two meta-analyses conducted using the ANT Database are described. One explores task performance in children with and without attention deficit/hyperactivity disorder (ADHD). The other one explores regional differences between studies conducted in China, Europe, and the United States. We are currently in the process of integrating the database into a publicly available web interface. When that work is complete, researchers, clinicians, and the general public will be able to use the database to explore topics of interest related to attention.

Attention as neurocognitive endophenotype of ADHD across the life span: a family study

Endophenotypes mediate pathways between genetic variations and the psychiatric phenotype, or share genetic risk with the psychiatric phenotype. Identifying endophenotypes is an important step to unravel disease pathways underlying complex psychiatric phenotypes such as ADHD. Potential viable endophenotypes for ADHD across the lifespan are neurocognitive measures of basic attention functions, such as sustained attention, and executive attention functions (EF), such as inhibition. The present study evaluated the endophenotype criteria of familiality and state-independency for measures of basic attention and EF in affected- and unaffected parents of children with ADHD (N = 139), and typically developing children (N = 60). In addition, the added value of neurocognitive measures relative to questionnaire data in genetically informed designs was explored by comparing the intergenerational transmission of neurocognitive measures to those of ADHD symptom scores. Results revealed small-to-medium-sized familial effects of ADHD for reaction time measures of EF components and state-independency given familial effects. Parent-child correlations as estimates of intergenerational transmission of those neurocognitive measures were not higher than those of behavioral ADHD symptom ratings. Taken together, our results argue against neurocognitive measures as pivotal endophenotypes for ADHD across the lifespan. If studied as neurocognitive endophenotypes of ADHD in adults, reaction time measures of executive-rather than basic attention function-seem to be more sensitive.

EEG Source Imaging Indices of Cognitive Control Show Associations with Dopamine System Genes

Cognitive or executive control is a critical mental ability, an important marker of mental illness, and among the most heritable of neurocognitive traits. Two candidate genes, catechol-O-methyltransferase (COMT) and DRD4, which both have a roles in the regulation of cortical dopamine, have been consistently associated with cognitive control. Here, we predicted that individuals with the COMT Met/Met allele would show improved response execution and inhibition as indexed by event-related potentials in a Go/NoGo task, while individuals with the DRD4 7-repeat allele would show impaired brain activity. We used independent component analysis (ICA) to separate brain source processes contributing to high-density EEG scalp signals recorded during the task. As expected, individuals with the DRD4 7-repeat polymorphism had reduced parietal P3 source and scalp responses to response (Go) compared to those without the 7-repeat. Contrary to our expectation, the COMT homozygous Met allele was associated with a smaller frontal P3 source and scalp response to response-inhibition (NoGo) stimuli, suggesting that while more dopamine in frontal cortical areas has advantages in some tasks, it may also compromise response inhibition function. An interaction effect emerged for P3 source responses to Go stimuli. These were reduced in those with both the 7-repeat DRD4 allele and either the COMT Val/Val or the Met/Met homozygous polymorphisms but not in those with the heterozygous Val/Met polymorphism. This epistatic interaction between DRD4 and COMT replicates findings that too little or too much dopamine impairs cognitive control. The anatomic and functional separated maximally independent cortical EEG sources proved more informative than scalp channel measures for genetic studies of brain function and thus better elucidate the complex mechanisms in psychiatric illness.

The genetics of anxiety-related negative valence system traits

NIMH's Research Domain Criteria (RDoC) domain of negative valence systems (NVS) captures constructs of negative affect such as fear and distress traditionally subsumed under the various internalizing disorders. Through its aims to capture dimensional measures that cut across diagnostic categories and are linked to underlying neurobiological systems, a large number of phenotypic constructs have been proposed as potential research targets. Since "genes" represent a central "unit of analysis" in the RDoC matrix, it is important for studies going forward to apply what is known about the genetics of these phenotypes as well as fill in the gaps of existing knowledge. This article reviews the extant genetic epidemiological data (twin studies, heritability) and molecular genetic association findings for a broad range of putative NVS phenotypic measures. We find that scant genetic epidemiological data is available for experimentally derived measures such as attentional bias, peripheral physiology, or brain-based measures of threat response. The molecular genetic basis of NVS phenotypes is in its infancy, since most studies have focused on a small number of candidate genes selected for putative association to anxiety disorders (ADs). Thus, more research is required to provide a firm understanding of the genetic aspects of anxiety-related NVS constructs. © 2016 Wiley Periodicals, Inc.

Genetic associations with reflexive visual attention in infancy and childhood

This study elucidates genetic influences on reflexive (as opposed to sustained) attention in children (aged 9-16 years; N = 332) who previously participated as infants in visual attention studies using orienting to a moving bar (Dannemiller, 2004). We investigated genetic associations with reflexive attention measures in infancy and childhood in the same group of children. The genetic markers (single nucleotide polymorphisms and variable number tandem repeats on the genes APOE, BDNF, CHRNA4, COMT, DRD4, HTR4, IGF2, MAOA, SLC5A7, SLC6A3, and SNAP25) are related to brain development and/or to the availability of neurotransmitters such as acetylcholine, dopamine, or serotonin. This study shows that typically developing children have differences in reflexive attention associated with their genes, as we found in adults (Lundwall, Guo & Dannemiller, 2012). This effort to extend our previous findings to outcomes in infancy and childhood was necessary because genetic influence may differ over the course of development. Although two of the genes that were tested in our adult study (Lundwall et al., 2012) were significant in either our infant study (SLC6A3) or child study (DRD4), the specific markers tested differed. Performance on the infant task was associated with SLC6A3. In addition, several genetic associations with an analogous child task occurred with markers on CHRNA4, COMT, and DRD4. Interestingly, the child version of the task involved an interaction such that which genotype group performed poorer on the child task depended on whether we were examining the higher or lower infant scoring group. These findings are discussed in terms of genetic influences on reflexive attention in infancy and childhood.

Genetic Influence on Slope Variability in a Childhood Reflexive Attention Task

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

Neuropsychological and dimensional behavioral trait profiles in Costa Rican ADHD sib pairs: Potential intermediate phenotypes for genetic studies

Attention deficit hyperactivity disorder (ADHD) is associated with substantial functional impairment in children and in adults. Many individuals with ADHD have clear neurocognitive deficits, including problems with visual attention, processing speed, and set shifting. ADHD is etiologically complex, and although genetic factors play a role in its development, much of the genetic contribution to ADHD remains unidentified. We conducted clinical and neuropsychological assessments of 294 individuals (269 with ADHD) from 163 families (48 multigenerational families created using genealogical reconstruction, 78 affected sib pair families, and 37 trios) from the Central Valley of Costa Rica (CVCR). We used principal components analysis (PCA) to group neurocognitive and behavioral variables using the subscales of the Child Behavior Checklist (CBCL) and 15 neuropsychological measures, and created quantitative traits for heritability analyses. We identified seven cognitive and two behavioral domains. Individuals with ADHD were significantly more impaired than their unaffected siblings on most behavioral and cognitive domains. The verbal IQ domain had the highest heritability (92%), followed by auditory attention (87%), visual processing speed and problem solving (85%), and externalizing symptoms (81%). The quantitative traits identified here have high heritabilities, similar to the reported heritability of ADHD (70-90%), and may represent appropriate alternative phenotypes for genetic studies. The use of multigenerational families from a genetically isolated population may facilitate the identification of ADHD risk genes in the face of phenotypic and genetic heterogeneity.

Increased brain activity to unpleasant stimuli in individuals with the 7R allele of the DRD4 gene

The aim of the study was to examine functional brain activity in response to unpleasant images in individuals with the 7-repeat (7R) allele compared to individuals with the 4-repeat (4R) allele of the dopamine receptor D4 (DRD4) gene (VNTR in exon 3). Based on the response ready hypothesis, individuals with the DRD4-4R/7R genotype were expected to show greater functional brain activity in response to unpleasant compared to neutral stimuli in specific regions of the frontal, temporal, parietal and limbic lobes, which form the networks involved in attentional, emotional, and preparatory responses. Functional Magnetic Resonance Imaging activity was studied in 26 young adults (13 with the DRD4-4R/7R genotype and 13 with the DRD4-4R/4R genotype). Participants were asked to look at and subjectively rate unpleasant and neutral images. Results showed increased brain activity in response to unpleasant images compared to neutral images in the right temporal lobe in participants with the DRD4-4R/7R genotype versus participants with the DRD4-4R/4R genotype. The increase in right temporal lobe activity in individuals with DRD4-4R/7R suggests greater involvement in processing negative emotional stimuli. Intriguingly, no differences were found between the two genotypes in the subjective ratings of the images. The findings corroborate the response ready hypothesis, which suggests that individuals with the 7R allele are more responsive to negative emotional stimuli compared to individuals with the 4R allele of the DRD4 gene.

Biomarkers in the diagnosis of ADHD--promising directions

The etiology and pathogenesis of attention-deficit/hyperactivity disorder (ADHD) are unclear and a more valid diagnosis would certainly be welcomed. Starting from the literature, we built an hypothetical pyramid representing a putative set of biomarkers where, at the top, variants in DAT1 and DRD4 genes are the best candidates for their associations to neuropsychological tasks, activation in specific brain areas, methylphenidate response and gene expression levels. Interesting data come from the noradrenergic system (norepinephrine transporter, norepinephrine, 3-methoxy-4-hydroxyphenylglycol, monoamine oxidase, neuropeptide Y) for their altered peripheral levels, their association with neuropsychological tasks, symptomatology, drugs effect and brain function. Other minor putative genetic biomarkers could be dopamine beta hydroxylase and catechol-O-methyltransferase. In the bottom, we placed endophenotype biomarkers. A more deep integration of "omics" sciences along with more accurate clinical profiles and new high-throughput computational methods will allow us to identify a better list of biomarkers useful for diagnosis and therapies.

Neural correlates of inhibitory control and functional genetic variation in the dopamine D4 receptor gene

BACKGROUND

The dopamine D4 receptor gene (DRD4) has been implicated in psychiatric disorders in which deficits of self-regulation are a prominent feature (e.g., attention-deficit hyperactivity disorder and substance use disorders) and in dopamine D4 receptor insensitivity within prefrontal regions of the brain. Our hypothesis was that carriers of 7-repeats in the Variable Number of Tandem Repeats (VNTR) of DRD4 (7R+) would recruit prefrontal brain regions involved in successful inhibitory control to a lesser degree than non-carriers (7R-) and demonstrate less inhibitory control as confirmed by observation of locally reduced blood oxygenation level dependent (BOLD) % signal change and lower accuracy while performing "No-Go" trials of a Go/No-Go task.

METHODS

Participants (age=18, n=62, 33 females) were recruited from the general population of the St. Louis, Missouri region. Participants provided a blood or saliva sample for genotyping, completed drug and alcohol-related questionnaires and IQ testing, and performed a Go/No-Go task inside of a 3T fMRI scanner.

RESULTS

Go/No-Go task performance did not significantly differ between 7R+ and 7R- groups. Contrast of brain activity during correct "No-Go" trials with a non-target letter baseline revealed significant BOLD activation in a network of brain regions previously implicated in inhibitory control including bilateral dorsolateral prefrontal, inferior frontal, middle frontal, medial prefrontal, subcortical, parietal/temporal, and occipital/cerebellar brain regions. Mean BOLD % signal change during "No-Go" trials was significantly modulated by DRD4 genotype, with 7R+ showing a lower hemodynamic response than 7R- in right anterior prefrontal cortex/inferior frontal gyrus, left premotor cortex, and right occipital/cerebellar areas. Follow-up analyses suggested that 7-repeat status accounted for approximately 5-6% of the variance in the BOLD response during "No-Go" trials.

DISCUSSION

The DRD4 7-repeat allele may alter dopaminergic function in brain regions involved in inhibitory control. When individuals must inhibit a prepotent motor response, presence of this allele may account for 5-6% of the variance in BOLD signal in brain regions critically associated with inhibitory control, but its influence may be associated with a greater effect on brain than on behavior in 18-year-olds from the general population.

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

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

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

Molecular genetics of attention-deficit/hyperactivity disorder: an overview

As heritability is high in attention-deficit/hyperactivity disorder (ADHD), genetic factors must play a significant role in the development and course of this disorder. In recent years a large number of studies on different candidate genes for ADHD have been published, most have focused on genes involved in the dopaminergic neurotransmission system, such as DRD4, DRD5, DAT1/SLC6A3, DBH, DDC. Genes associated with the noradrenergic (such as NET1/SLC6A2, ADRA2A, ADRA2C) and serotonergic systems (such as 5-HTT/SLC6A4, HTR1B, HTR2A, TPH2) have also received considerable interest. Additional candidate genes related to neurotransmission and neuronal plasticity that have been studied less intensively include SNAP25, CHRNA4, NMDA, BDNF, NGF, NTF3, NTF4/5, GDNF. This review article provides an overview of these candidate gene studies, and summarizes findings from recently published genome-wide association studies (GWAS). GWAS is a relatively new tool that enables the identification of new ADHD genes in a hypothesis-free manner. Although these latter studies could be improved and need to be replicated they are starting to implicate processes like neuronal migration and cell adhesion and cell division as potentially important in the aetiology of ADHD and have suggested several new directions for future ADHD genetics studies.