Comparison of the role of dopamine, serotonin, and noradrenaline genes in ADHD, ODD and conduct disorder: multivariate regression analysis of 20 genes

Noradrenergic genes polymorphisms and response to methylphenidate in children with ADHD: A systematic review and meta-analysis

BACKGROUND

Attention-deficit hyperactivity disorder (ADHD) is the most common childhood-onset neurodevelopmental disorder, and methylphenidate (MPH) is considered one of the first-line medicine for ADHD. Unfortunately, this medication is only effective for some children with ADHD. This meta-analysis was conducted to evaluate whether noradrenergic gene polymorphisms impact the efficacy of MPH in children with ADHD.

METHODS

Candidate gene studies published in English until March 1, 2020, were identified through literature searches on PubMed, Web of Science, and Embase. Data were pooled from individual clinical trials considering MPH pharmacogenomics. According to the heterogeneity, the odds ratio and mean differences were calculated by applying fixed-effects or random-effects models.

RESULTS

This meta-analysis includes 15 studies and 1382 patients. Four polymorphisms of the NET gene (rs5569, rs28386840, rs2242446, rs3785143) and 2 polymorphisms of the α2A-adrenergic receptor gene (ADRA2A) gene (MspI and DraI) were selected for the analysis. In the pooled data from all studies, T allele carriers of the rs28386840 polymorphism were significantly more likely to respond to MPH (P < .001, ORTcarriers = 2.051, 95% confidence interval [CI]:1.316, 3.197) and showed a relationship with significantly greater hyperactive-impulsive symptoms improvement (P < .001, mean difference:1.70, 95% CI:0.24, 3.16). None of the ADRA2A polymorphisms correlated significantly with MPH response as a whole. However, G allele carriers of the MspI polymorphism showed a relationship with significantly inattention symptoms improvement (P < .001, mean difference:0.31, 95% CI: 0.15, 0.47).

CONCLUSION

Our meta-analysis results indicate that the noradrenergic gene polymorphisms may impact MPH response. The NET rs28386840 is linked to improved MPH response in ADHD children. And the ADRA2A MspI is associated with inattention symptom improvements. Further investigations with larger samples will be needed to confirm these results.Registration: PROSPERO (no. CRD42021265830).

Magnetic Resonance Spectroscopy in Adolescent Cannabis Users: Metabolites in the Anterior Cingulate Cortex Reflects Individual Differences in Personality Traits and can Affect Rehabilitation Compliance

Introduction

The anterior cingulate cortex (ACC) has shown to play a role in impulsivity, fear, and anxiety. Considering, its high glutamate receptor density, it was chosen as a region of interest to investigate the role of glutamate transmission in drug dependance. We investigated the correlations between personality trait scores and glutamate-to-glutamine (Glx) ratio concentrations in the ACC in order to evaluate if (1) personality traits may increase the probability of drug use and (2) drug use can modify cerebral metabolic pattern contributing to addictive behaviors.

Materials and Methods

Glx ratio concentrations in the ACC region were measured with high-resolution multivoxel proton magnetic resonance spectroscopy (1H-MRS). Personality traits were evaluated utilizing Cloninger's TCI-revised test. Bivariate correlations between personality scores of 28 teens cannabis users (males, mean age = 18.54 ± 2.80) were evaluated.

Results

In the ACC, we observed negative correlation between GG concentrations (r = -0.44, P = 0.05) and co-operativeness values (CO), choline (cho), and novelty seeking (NS) values (r = -0,45, P = 0.05). Low levels of glutamate and high levels of cho in the ACC were closely related to the CO and NS personality traits.

Conclusions

Metabolic and personality patterns seems to be related to the risk of substance predisposition in adolescents. Our data contribute a possible support to the "top-down" control of the ACC on brain metabolism, due to the particular cerebral metabolic pattern found in "drug-using" adolescents.

Vigilance, Inhibitory Control and Regional Cerebral Blood Oxygenation in the PFC - Differences in ADHD Types of Presentations

It is commonly believed that proven abnormalities in the structure and functioning of the prefrontal lobes affect cognitive deficits in children with ADHD. The purpose of the current study was to assess vigilance, inhibitory control, and regional cerebral blood oxygenation (rCBO2) in the prefrontal cortex (PFC) of children with ADHD. The study included 150 children with ADHD and 51 typically developing (TD) children aged 9-12 years. Children with ADHD showed a deficit in vigilance (assessed by the shortened version of the Mackworth clock task), inhibitory control (the Stroop task), different rCBO2 patterns in the PFC, as well as lower cortical activation during cognitive tasks. These differences are discussed in the context of the types of ADHD presentations.

Temperamental vulnerability to emotion dysregulation and risk for mental and physical health challenges

Emotion dysregulation characterizes many forms of psychopathology. Patterns of dysregulation occur as a function of a developmental process in which normative and adaptive emotion regulation skills fail to become part of the child's behavioral repertoire due to biological, psychological, and contextual processes and experiences. Here we highlight the processes involved in the dysregulation of temperamental anger and frustration that become core features of externalizing problems and place children at risk for more serious forms of psychopathology. We imbed these processes in a larger self-regulatory framework, and we discuss how they influence mental as well as physical health, using data from our 20-year longitudinal study following a large cohort of children into young adulthood. Recommendations are made for future research involving the integration of biological systems with mental and physical health outcomes.

Genetic alterations affecting the genes encoding the enzymes of the kynurenine pathway and their association with human diseases

Tryptophan is metabolized primarily via the kynurenine pathway (KP), which involves several enzymes, including indoleamine 2,3-dioxygenase, tryptophan 2,3 dioxygenase (TDO), kynurenine aminotransferases (KATs), kynurenine monooxygenase (KMO) etc. The majority of metabolites are neuroactive: some of them, such as kynurenic acid, show neuroprotective effects, while others contribute to free radical production, leading to neurodegeneration. Imbalance of the pathway is assumed to contribute to the development of several neurodegenerative diseases, psychiatric disorders, migraine and multiple sclerosis. Our aim was to summarize published data on genetic alterations of enzymes involved in the KP leading to disturbances of the pathway that can be related to different diseases. To achieve this, a PubMed literature search was performed for publications on genetic alterations of the KP enzymes upto April 2017. Several genetic alterations of the KP have been identified and have been proposed to be associated with diseases. Here we must emphasize that despite the large number of recognized genetic alterations, the number of firmly established causal relations with specific diseases is still small. The realization of this by those interested in the field is very important and finding such connections should be a major focus of related research. Polymorphisms of the genes encoding the enzymes of the KP have been associated with autism, multiple sclerosis and schizophrenia, and were shown to affect the immune response of patients with bacterial meningitis, just to mention a few. To our knowledge, this is the first comprehensive review of the genetic alterations of the KP enzymes. We believe that the identification of genetic alterations underlying diseases has great value regarding both treatment and diagnostics in precision medicine, as this work can promote the understanding of pathological mechanisms, and might facilitate medicinal chemistry approaches to substitute missing components or correct the disturbed metabolite balance of KP.

Medication therapy for attention deficit/hyperactivity disorder is associated with lower risk of fracture: a retrospective cohort study

The impact of pharmacotherapy for attention deficit/hyperactivity disorder on fracture risk has not been well studied. In this retrospective cohort study, medication therapy was associated with lower fracture incidence. Further studies are needed to better characterize the short-term and long-term effects of these medications on bone health and fracture risk.

INTRODUCTION

Attention deficit/hyperactivity disorder (ADHD) is associated with increased risk of bone fractures. The impact of pharmacotherapy with either stimulant or non-stimulant medications on fracture risk has not been well characterized. We performed a study to compare fracture incidence in ADHD patients treated with stimulant or non-stimulant medications vs. no pharmacotherapy.

METHODS

In this retrospective cohort study, data were extracted from a large electronic medical record. A total of 10,066 subjects with ADHD, 40 years or younger, were included. We extracted data regarding stimulant and non-stimulant ADHD medications, corticosteroids, fracture data, demographic data, and diabetes history.

RESULTS

A total of 1015 patients (10 %) sustained fractures. Multivariable Cox proportional hazard analysis indicated that compared to those with two or more prescriptions for an ADHD medication, individuals without documented medication therapy had a significantly increased hazard of fracture (hazard ratio [HR] 3.9, 95 % confidence interval [CI] 2.6-5.9). However, the hazard ratio for stimulant vs. non-stimulant medication (HR 0.92, 95 % CI 0.60-1.4) was not statistically significant.

CONCLUSIONS

Three times as many patients with no documented ADHD medication prescriptions suffer a fracture compared to patients with a history of two or more prescriptions for an ADHD medication. Treatment and adherence are thus important to prevent fracture in this population.

Neuropsychological performance measures as intermediate phenotypes for attention-deficit/hyperactivity disorder: A multiple mediation analysis

Genetic influences on dopaminergic neurotransmission have been implicated in attention-deficit hyperactivity disorder (ADHD) and are theorized to impact cognitive functioning via alterations in frontal-striatal circuitry. Neuropsychological functioning has been proposed to account for the potential associations between dopamine candidate genes and ADHD. However, to date, this mediation hypothesis has not been directly tested. Participants were 498 youth ages 6-17 years (mean M = 10.8 years, SD = 2.4 years, 55.0% male). All youth completed a multistage, multiple-informant assessment procedure to identify ADHD and non-ADHD cases, as well as a comprehensive neuropsychological battery. Youth provided a saliva sample for DNA analyses; the 480 base pair variable number of tandem repeat polymorphism of the dopamine active transporter 1 gene (DAT1) and the 120 base pair promoter polymorphism of the dopamine receptor D4 gene (DRD4) were genotyped. Multiple mediation analysis revealed significant indirect associations between DAT1 genotype and inattention, hyperactivity-impulsivity, and oppositionality, with specific indirect effects through response inhibition. The results highlight the role of neurocognitive task performance, particularly response inhibition, as a potential intermediate phenotype for ADHD, further elucidating the relationship between genetic polymorphisms and externalizing psychopathology.

Functional polymorphisms in BDNF and COMT genes are associated with objective differences in arithmetical functioning in a sample of young adults

BACKGROUND

Understanding the molecular genetics of complex human behaviors and functions remains a substantial challenge for the neurosciences. Previous studies have shown a genetic basis for individual differences in mathematical functioning; however, the specific genes remain to be completely identified. In the present study, we explored the possibility that 2 functional polymorphisms in candidate genes could be associated with differences in arithmetical performance.

METHODS

A computerized test to analyze performance in basic arithmetical calculations (additions and subtractions) was applied to 168 healthy young Colombian participants using the PEBL (Psychology Experiment Building Language) battery. DNA samples were genotyped for 2 functional SNPs in candidate genes: brain-derived neurotrophic factor (BDNF)-Val66Met and catechol-O-methyltransferase (COMT)-Val158Met.

RESULTS

We found significant differences for arithmetical processing scores between genotypes. For BDNF, Val/Val subjects had a worse performance (p value: 0.025) and for COMT, Val/Val carriers had a better performance (p value: 0.006). A multivariate model, including both BDNF and COMT genes, accounted for 7.1% of the variance in math processing scores.

DISCUSSION

To our knowledge, this is the first study finding associations of polymorphisms in BDNF and COMT genes with quantitative measures of numerical aptitude in healthy young participants. A future study of other genes involved in neural plasticity could be helpful to identify genetic correlates of arithmetical functioning, which will be important for the understanding of normal human behaviors and related neuropsychiatric disorders.

Co-modulation analysis of gene regulation in breast cancer reveals complex interplay between ESR1 and ERBB2 genes

BACKGROUND

Gene regulation is dynamic across cellular conditions and disease subtypes. From the aspect of regulation under modulation, regulation strength between a pair of genes can be modulated by (dependent on) expression abundance of another gene (modulator gene). Previous studies have demonstrated the involvement of genes modulated by single modulator genes in cancers, including breast cancer. However, analysis of multi-modulator co-modulation that can further delineate the landscape of complex gene regulation is, to our knowledge, unexplored previously. In the present study we aim to explore the joint effects of multiple modulator genes in modulating global gene regulation and dissect the biological functions in breast cancer.

RESULTS

To carry out the analysis, we proposed the Covariability-based Multiple Regression (CoMRe) method. The method is mainly built on a multiple regression model that takes expression levels of multiple modulators as inputs and regulation strength between genes as output. Pairs of genes were divided into groups based on their co-modulation patterns. Analyzing gene expression profiles from 286 breast cancer patients, CoMRe investigated ten candidate modulator genes that interacted and jointly determined global gene regulation. Among the candidate modulators, ESR1, ERBB2, and ADAM12 were found modulating the most numbers of gene pairs. The largest group of gene pairs was composed of ones that were modulated by merely ESR1. Functional annotation revealed that the group was significantly related to tumorigenesis and estrogen signaling in breast cancer. ESR1-ERBB2 co-modulation was the largest group modulated by more than one modulators. Similarly, the group was functionally associated with hormone stimulus, suggesting that functions of the two modulators are performed, at least partially, through modulation. The findings were validated in majorities of patients (> 99%) of two independent breast cancer datasets.

CONCLUSIONS

We have showed CoMRe is a robust method to discover critical modulators in gene regulatory networks, and it is capable of achieving reproducible and biologically meaningful results. Our data reveal that gene regulatory networks modulated by single modulator or co-modulated by multiple modulators play important roles in breast cancer. Findings of this report illuminate complex and dynamic gene regulation under modulation and its involvement in breast cancer.

The four causes of ADHD: a framework

In addition to the symptoms singled out by the diagnostic criteria for Attention-Deficit Hyperactivity Disorder (ADHD), a comprehensive definition should inform us of the events that trigger ADHD in both its acute and chronic manifestations; the neurobiology that underlies it; and the evolutionary forces that have kept it in the germ line of our species. These factors are organized in terms of Aristotle's four kinds of "causes," or explanations: formal, efficient, material, and final. This framework systematizes the nosology, biology, psychology, and evolutionary pressures that cause ADHD.

The possible involvement of genetic variants of NET1 in the etiology of attention-deficit/hyperactivity disorder comorbid with oppositional defiant disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) often coexist and shared some genetic influences. Evidence from the existing literature indicated that comorbid with ODD may increase the heterogeneity of ADHD genetics. Our present study sought to investigate the role of norepinephrine transporter gene (NET1) for ADHD comorbid with ODD.

METHODS

Six single nucleotide polymorphisms (SNPs) of NET1 were genotyped for a total of 1,815 ADHD cases, including 587 subjects (32.3%) with ODD. Chi-square tests were conducted for pseudo case-control study comparing allelic and genotypic distributions between ADHD with and without ODD. Among them, there were 1,249 probands together with their parents composing trios for family-based association studies using transmission disequilibrium tests (TDTs). In addition, 1,337 ADHD probands have detailed information of ODD symptoms and were included for quantitative analyses with genotypes using analyses of covariance (ANCOVA). To consider the overlap and correlation of other comorbidities with ODD and eliminate their potential confounding effect, we further repeated above analyses for 'pure ADHD+ODD' versus 'ADHD-only' after excluding other comorbidities except for ODD.

RESULTS

The pseudo case-control study showed different allelic and genotypic distributions of SNP rs3785143 between ADHD with ODD and those without ODD. Family-based association tests indicated overtransmission of the T allele of rs3785143 in ADHD with ODD trios, but no biased transmission in those without ODD. ANCOVA showed association between genotypes of rs3785143 with ODD symptoms in ADHD probands, especially with 'Argumentative/Defiant Behavior (ADB)' dimension after controlling gender, age, clinical subtypes and intelligence. Above association still existed after removing the samples with other comorbidities.

CONCLUSION

NET1 was associated with comorbidity of ODD and ODD symptoms in ADHD probands. Our findings emphasize the importance of considering the comorbidity of ODD in ADHD genetic studies, especially ADHD with ADB. However, further replication in independent sample or different populations is still needed.

Potential contribution of dopaminergic gene variants in ADHD core traits and co-morbidity: a study on eastern Indian probands

Association of dopaminergic genes, mainly receptors and transporters, with Attention Deficit Hyperactivity Disorder (ADHD) has been investigated throughout the world due to the importance of dopamine (DA) in various physiological functions including attention, cognition and motor activity, traits. However, till date, etiology of ADHD remains unknown. We explored association of functional variants in the DA receptor 2 (rs1799732 and rs6278), receptor 4 (exon 3 VNTR and rs914655), and transporter (rs28363170 and rs3836790) with hyperactivity, cognitive deficit, and co-morbid disorders in eastern Indian probands. Diagnostic and Statistical Manual for Mental Disorders-IV was followed for recruitment of nuclear families with ADHD probands (N = 160) and ethnically matched controls (N = 160). Cognitive deficit and hyperactive traits were measured using Conner's parents/teachers rating scale. Peripheral blood was collected after obtaining informed written consent and used for genomic DNA isolation. Genetic polymorphisms were analyzed by PCR-based methods followed by population- as well as family-based statistical analyses. Association between genotypes and cognitive/hyperactivity traits and co-morbidities was analyzed by the Multifactor dimensionality reduction (MDR) software. Case-control analysis showed statistically significant difference for rs6278 and rs28363170 (P = 0.004 and 1.332e-007 respectively) while family-based analysis exhibited preferential paternal transmission of rs28363170 '9R' allele (P = 0.04). MDR analyses revealed independent effects of rs1799732, rs6278, rs914655, and rs3836790 in ADHD. Significant independent effects of different sites on cognitive/hyperactivity traits and co-morbid disorders were also noticed. It can be summarized from the present investigation that these gene variants may influence cognitive/hyperactive traits, thereby affecting the disease etiology and associated co-morbid features.

Association of VAMP-2 and Syntaxin 1A Genes with Adult Attention Deficit Hyperactivity Disorder

OBJECTIVE

The etiology of attention deficit hyperactivity disorder (ADHD) has not been entirely clarified yet. Structural and metabolic differences at the prefrontal striatal cerebellary system and the interaction of gene and environment are the main factors that thought to play roles in the etiology. Genetic investigations are performed especially about the dopamine pathways and receptors. In this study; it was aimed to investigate the association of the synaptobrevin-2 (VAMP-2) gene Ins/Del polymorphism and syntaxin 1A gene intron 7 polymorphism, which take place in encoding presynaptic protein, with adult ADHD.

METHODS

One hundred thirty-nine patients, having ADHD aging between 18 and 60 years and 106 healthy people as controls were included into the study. DNA samples were extracted from whole blood and genetic analysis were performed.

RESULTS

A significant difference was determined between ADHD and VAMP-2 Ins/Del polymorphism and syntaxin 1A intron 7 polymorphism according to the control group. These polymorphisms were found not to be associated with subtypes of ADHD.

CONCLUSION

It is supposed that synaptic protein genes together with dopaminergic genes might have roles in the etiology of ADHD.

Exploring whether genetic differences between siblings explain sibling differences in criminal justice outcomes

Research has revealed that despite many similarities, siblings raised within the same household have also been found to be markedly different from one another. Behavioral differences between siblings have been primarily attributed to differential exposure to a wide variety of environmental influences. The potential role that between-sibling genetic differences play in the development of behavioral differences has been overlooked in the extant literature. The current study examines the association between differences in three dopaminergic polymorphisms (DAT1, DRD2, and DRD4) and differences in arrest, incarceration, and multiple arrests between siblings. Between-sibling difference scores were estimated for each examined polymorphism and each criminal justice outcome measure (along with all controls). Ordinary least squares (OLS) regression models were estimated to examine the potential association between genetic differences between siblings and differences in experiences within the criminal justice system. Models were estimated for the full sample and then for the same-sex male and female subsamples separately. The results provide preliminary evidence that between-sibling differences in some of the examined dopaminergic polymorphisms are associated with differences in contact with the criminal justice system. Findings are discussed in more detail and suggestions for future research are also provided.

A longitudinal analysis of the effects of a DRD4 polymorphism on marijuana use

The current study used a variable- and person-centered approach to examine whether a DRD4 polymorphism explained within-individual differences in frequency of marijuana use from adolescence into emerging adulthood. Data were analyzed from 1897 respondents from the genetic subsample of the National Longitudinal Study of Adolescent Health (Add Health) at waves I (ages 13-17), II (ages 14-18), and III (ages 21-25). Latent class growth model results revealed that marijuana use was characterized by four trajectories (non-users/experimenters, increasers, desisters, and chronic users), and that the DRD4 polymorphism differentiated increasers from non-users/experimenters. Overall, the results suggested that the DRD4 polymorphism may be relevant to differences in the developmental trajectories of marijuana use.

Association of genetic risk severity with ADHD clinical characteristics

This study sought to examine the association between the cumulative risk severity conferred by the total number of attention-deficit/hyperactivity disorder (ADHD) risk alleles of the DAT1 3'UTR variable number tandem repeat (VNTR), DRD4 Exon 3 VNTR, and 5-HTTLPR with ADHD characteristics, clinical correlates, and functional outcomes in a pediatric sample. Participants were derived from case-control family studies of boys and girls diagnosed with ADHD, a genetic linkage study of families with children with ADHD, and a family genetic study of pediatric bipolar disorder. Caucasian children 18 and younger with and without ADHD and with available genetic data were included in this analysis (N = 591). The association of genetic risk severity with sociodemographic, clinical characteristics, neuropsychological, emotional, and behavioral correlates was examined in the entire sample, in the sample with ADHD, and in the sample without ADHD, respectively. Greater genetic risk severity was significantly associated with the presence of disruptive behavior disorders in the entire sample and oppositional defiant disorder in participants with ADHD. Greater genetic risk severity was also associated with the absence of anxiety disorders, specifically with the absence of agoraphobia in the context of ADHD. Additionally, one ADHD symptom was significantly associated with greater genetic risk severity. Genetic risk severity is significantly associated with ADHD clinical characteristics and co-morbid disorders, and the nature of these associations may vary on the type (externalizing vs. internalizing) of the disorder.

Catecholaminergic gene variants: contribution in ADHD and associated comorbid attributes in the eastern Indian probands

Contribution of genes in attention deficit hyperactivity disorder (ADHD) has been explored in various populations, and several genes were speculated to contribute small but additive effects. We have assessed variants in four genes, DDC (rs3837091 and rs3735273), DRD2 (rs1800496, rs1801028, and rs1799732), DRD4 (rs4646984 and rs4646983), and COMT (rs165599 and rs740603) in Indian ADHD subjects with comorbid attributes. Cases were recruited following the Diagnostic and Statistical Manual for Mental Disorders-IV-TR after obtaining informed written consent. DNA isolated from peripheral blood leukocytes of ADHD probands (N = 170), their parents (N = 310), and ethnically matched controls (n = 180) was used for genotyping followed by population- and family-based analyses by the UNPHASED program. DRD4 sites showed significant difference in allelic frequencies by case-control analysis, while DDC and COMT exhibited bias in familial transmission (P < 0.05). rs3837091 “AGAG,” rs3735273 “A,” rs1799732 “C,” rs740603 “G,” rs165599 “G” and single repeat alleles of rs4646984/rs4646983 showed positive correlation with co-morbid characteristics (P < 0.05). Multi dimensionality reduction analysis of case-control data revealed significant interactive effects of all four genes (P < 0.001), while family-based data showed interaction between DDC and DRD2 (P = 0.04). This first study on these gene variants in Indo-Caucasoid ADHD probands and associated co-morbid conditions indicates altered dopaminergic neurotransmission in ADHD.

Interaction of the TaqIA polymorphism and poor parental socialization on changes in adolescent marijuana use

The current study uses data from the genetic subsample from the National Longitudinal Study of Adolescent Health (Add Health) in waves I and II (ages of 11-19 and 12-20 respectively) to investigate the interaction of the TaqIA polymorphism and poor parental socialization on changes in adolescent marijuana use. Results reveal that TaqIA interacts with poor parental rule setting, but not quality of mother-child communication, to influence changes in marijuana use. Adolescents who are homozygous for the A1 and whose parents allow the youth to set their own curfew experience significant increases in marijuana use during adolescence. In contrast, youths with the A1/A1 genotype whose parents do not allow the adolescent to set their own curfew experience significant decreases in the frequency of marijuana use. These results suggest that direct parental social control may effectively suppress the genetic risk of the A1/A1 genotype on marijuana use in adolescence. The study's limitations are noted.

Interaction of serotonin transporter linked polymorphic region and childhood neglect on criminal behavior and substance use for males and females

Childhood neglect has been cited as a risk factor for later substance abuse and criminal behavior. However, a large body of literature shows that a substantial percentage of neglected and abused individuals do not go on to abuse substances or engage in criminal behavior. The current study investigates whether a genetic variant (serotonin transporter linked polymorphic region [5-HTTLPR]) in the 5-hydroxytryptamine (5-HTT) gene moderates the effect of childhood neglect on alcohol use problems, marijuana use, and criminal behavior. Data from the National Longitudinal Study of Adolescent Health shows that 5-HTTLPR conditions the effect of neglect on marijuana use for females, but not for males. Findings also reveal a significant gene-environment correlation between 5-HTTLPR and neglect for females only. These results suggest that 5-HTTLPR is associated with an increased risk of neglect for females, and it also increases neglected females' risk of abusing marijuana.

Dopaminergic system genes in childhood aggression: possible role for DRD2

Excessive or deficient levels of extracellular dopamine have been hypothesized to contribute to a broad spectrum of mood, motor, and thought abnormalities, and dopaminergic system genes have been implicated in aggressive behaviour from animal and human studies. OBJECTIVE. We examined selected members of the dopaminergic system genes for association with child aggression.

METHOD

We analyzed polymorphisms in the dopamine transporter DAT1/SLC6A3, dopamine receptor DRD2, and DRD4 genes in our sample of pervasive childhood aggression consisting of 144 cases paired with 144 healthy controls, matched for sex and ethnicity.

RESULTS

Aggressive children were significantly more likely to have the at least one copy of the G allele for the DRD2 A-241G polymorphism (genotypic P=0.02; allelic P=0.01). The DRD2 rs1079598 CC genotype was overrepresented in aggressive children compared to controls (genotype P=0.04). The DRD2 TaqIA T allele (P=0.01) and the TT genotype (P=0.01) were also significantly overrepresented in aggressive children.

CONCLUSIONS

Our preliminary results suggest that three polymorphisms in DRD2 are associated with childhood aggression. Future studies are required to replicate the current results and to further explore the relationship between the dopamine system and aggressive behaviour in children.

Pathway based analysis of genotypes in relation to alcohol dependence

We introduce a method for detecting variants in several genes of related function with small effect on a phenotype of interest. Our method uses logistic regression to test whether multiple alleles within a functional set have significantly higher than expected predictive value, even though none individually may have strong individual effects. We illustrate this method by testing seven gene sets (including 48 genes), from a study with1350 single nucleotide polymorphisms in 130 addiction candidate genes studied in a sample of 575 alcohol dependence (AD) cases and 530 controls. We conclude that AD is related to variation in genes participating in Glutamate and GABA signaling, as has been reported elsewhere, and in stress response pathways, but not with genes in several other systems implicated in other drugs of abuse.

Aggressive behavior, related conduct problems, and variation in genes affecting dopamine turnover

A number of dopamine-related genes have been implicated in the etiology of violent behavior and conduct problems. Of these genes, the ones that code for the enzymes that influence the turnover of dopamine (DA) have received the most attention. In this study, we investigated 12 genetic polymorphisms in four genes involved with DA functioning (COMT, MAOA and MAOB, and DbetaH) in 179 incarcerated male Russian adolescents and two groups of matched controls: boys without criminal records referred to by their teachers as (a) "troubled-behavior-free" boys, n=182; and (b) "troubled-behavior" boys, n=60. The participants were classified as (1) being incarcerated or not, (2) having the DSM-IV diagnosis of conduct disorder (CD) or not, and (3) having committed violent or nonviolent crimes (for the incarcerated individuals only). The findings indicate that, although no single genetic variant in any of the four genes differentiated individuals in the investigated groups, various linear combinations (i.e., haplotypes) and nonlinear combinations (i.e., interactions between variants within and across genes) of genetic variants resulted in informative and robust classifications for two of the three groupings. These combinations of genetic variants differentiated individuals in incarceration vs. nonincarcerated and CD vs. no-CD groups; no informative combinations were established consistently for the grouping by crime within the incarcerated individuals. This study underscores the importance of considering multiple rather than single markers within candidate genes and their additive and interactive combinations, both with themselves and with nongenetic indicators, while attempting to understand the genetic background of such complex behaviors as serious conduct problems.

Meta-analysis of brain-derived neurotrophic factor p.Val66Met in adult ADHD in four European populations

Attention-deficit hyperactivity disorder (ADHD) is a multifactorial, neurodevelopmental disorder that often persists into adolescence and adulthood and is characterized by inattention, hyperactivity and impulsiveness. Before the advent of the first genome-wide association studies in ADHD, genetic research had mainly focused on candidate genes related to the dopaminergic and serotoninergic systems, although several other genes had also been assessed. Pharmacological data, analysis of animal models and association studies suggest that Brain-Derived Neurotrophic Factor (BDNF) is also a strong candidate gene for ADHD. Several polymorphisms in BDNF have been reported and studied in psychiatric disorders but the most frequent is the p.Val66Met (rs6265G > A) single nucleotide polymorphism (SNP), with functional effects on the intracellular trafficking and secretion of the protein. To deal with the inconsistency raised among different case-control and family-based association studies regarding the p.Val66Met contribution to ADHD, we performed a meta-analysis of published as well as unpublished data from four different centers that are part of the International Multicentre Persistent ADHD CollaboraTion (IMpACT). A total of 1,445 adulthood ADHD patients and 2,247 sex-matched controls were available for the study. No association between the p.Val66Met polymorphism and ADHD was found in any of the four populations or in the pooled sample. The meta-analysis also showed that the overall gene effect for ADHD was not statistically significant when gender or comorbidity with mood disorders were considered. Despite the potential role of BDNF in ADHD, our data do not support the involvement of p.Val66Met in the pathogenesis of this neuropsychiatric disorder.

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.

Molecular genetics of attention deficit hyperactivity disorder

Although twin studies demonstrate that ADHD is a highly heritable condition, molecular genetic studies suggest that the genetic architecture of ADHD is complex. The handful of genome-wide linkage and association scans that have been conducted thus far show divergent findings and are, therefore, not conclusive. Similarly, many of the candidate genes reviewed here (ie, DBH, MAOA, SLC6A2, TPH-2, SLC6A4, CHRNA4, GRIN2A) are theoretically compelling from neurobiological systems perspective but available data are sparse and inconsistent. However, candidate gene studies of ADHD have produced substantial evidence implicating several genes in the etiology of the disorder, with meta-analyses supportive of a role of the genes coding for DRD4, DRD5, SLC6A3, SNAP-25, and HTR1B in the etiology of ADHD.

The genetics of attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder that almost certainly represents the common outcome of multiple causal pathways and it is now generally accepted that genetic factors make a significant contribution to these pathways. Behavioral studies suggest a heritability of approximately 0.76. While molecular genetic approaches have identified a range of potential candidate genes, it is now clear that the genetics of ADHD are characterized by a number of genes each of which makes a small but significant contribution to the overall risk. Several genome-wide linkage studies have been conducted and, although there are considerable differences in findings between studies, several regions have been supported across several studies (bin 16.4, 5p13, 11q22-25, 17p11). The contribution of several candidate genes has been supported by meta-analyses (DRD4, DRD5, DAT1, HTR1B and SNAP25). Genome-wide association scans are starting to appear but have not yet had sufficient power to produce conclusive results. Gene-environment interactions, which are as yet relatively understudied, are likely to be of importance in fully understanding the role of genes in ADHD and will be discussed.

Associations of the DRD2 TaqIA polymorphism with impulsivity and substance use: preliminary results from a clinical sample of adolescents

BACKGROUND

The A1 allele of the TaqIA polymorphism (rs1800497) in the dopamine D2 receptor gene (DRD2) has been associated with substance use. It is unclear whether this allele is a marker for an underlying propensity for specifically developing a substance use disorder, or more generally to developing an externalizing psychiatric disorder highly correlated with substance use. It is also possible that DRD2 is related to a behavioral phenotype common to externalizing disorders and substance use.

METHOD

Data was obtained from 104 psychiatrically hospitalized adolescents in a larger assessment study. Adolescents were genotyped for the DRD2 TaqIA site, grouped as carriers of the A1 allele (A1+) or homozygous for the A2 allelle (A1-). Associations of the presence of the A1 allele with externalizing disorders, the intermediate phenotype of impulsivity, and measures of alcohol and drug use were examined.

RESULTS

A diagnosis of conduct disorder and impulsive behavior were both associated with severity of problem drinking and/or drug use. Further, interaction effects were found between the DRD2 TaqIA polymorphism and conduct disorder (trend level) as well as A1+ status and impulsivity, such that adolescents who were carriers of the A1 allele, and had conduct disorder or impulsive behavior, reported higher levels of problematic alcohol use than those who were non-carriers (A2/A2 or A1-). The same interaction effect between this polymorphism and impulsivity was found for severity of problem drug use. In contrast, no interaction effects were found between the DRD2 allele status and ADHD on severity of problem drinking or drug use.

DISCUSSION

These results suggest that the well documented relationship between conduct disorder, the behavioral phenotype of impulsivity, and problematic alcohol/drug use among adolescents may be moderated by A1 carrier status of the DRD2 gene.

Interaction of 5HTTLPR and marijuana use on property offending

This study uses data from the National Longitudinal Study of Adolescent Health to examine whether a polymorphism in the serotonin transporter gene (SHTTLPR) moderates the effects of marijuana use on property offending. The results reveal that 5HTTLPR interacts with marijuana use to predict significantly higher levels of property offending for African American females. The interaction coefficient is not statistically significant for Caucasian males, African American males, or Caucasian females. These findings suggest that marijuana use is associated only with higher levels of property offending among African American females who carry one or more copies of the 5HTTLPR short allele.

Exploration of 19 serotoninergic candidate genes in adults and children with attention-deficit/hyperactivity disorder identifies association for 5HT2A, DDC and MAOB

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder in which different genetic and environmental susceptibility factors are involved. Several lines of evidence support the view that at least 30% of ADHD patients diagnosed in childhood continue to suffer the disorder during adulthood and that genetic risk factors may play an essential role in the persistence of the disorder throughout lifespan. Genetic, biochemical and pharmacological studies support the idea that the serotonin system participates in the etiology of ADHD. Based on these data, we aimed to analyze single nucleotide polymorphisms across 19 genes involved in the serotoninergic neurotransmission in a clinical sample of 451 ADHD patients (188 adults and 263 children) and 400 controls using a population-based association study. Several significant associations were found after correcting for multiple testing: (1) the DDC gene was strongly associated with both adulthood (P=0.00053; odds ratio (OR)=2.17) and childhood ADHD (P=0.0017; OR=1.90); (2) the MAOB gene was found specifically associated in the adult ADHD sample (P=0.0029; OR=1.90) and (3) the 5HT2A gene showed evidence of association only with the combined ADHD subtype both in adults (P=0.0036; OR=1.63) and children (P=0.0084; OR=1.49). Our data support the contribution of the serotoninergic system in the genetic predisposition to ADHD, identifying common childhood and adulthood ADHD susceptibility factors, associations that are specific to ADHD subtypes and one variant potentially involved in the continuity of the disorder throughout lifespan.

Conduct disorder and ADHD: evaluation of conduct problems as a categorical and quantitative trait in the international multicentre ADHD genetics study

Attention-deficit/hyperactivity disorder (ADHD) is typically characterized by inattention, excessive motor activity, impulsivity, and distractibility. Individuals with ADHD have significant impairment in family and peer relations, academic functioning, and show high co-morbidity with a wide range of psychiatric disorders including oppositional defiant disorder (ODD), conduct disorder (CD), anxiety disorder, depression, substance abuse, and pervasive developmental disorder (PDD). Family studies suggest that ADHD + CD represents a specific subtype of the ADHD disorder with familial risk factors only partly overlapping with those of ADHD alone. We performed a hypothesis-free analysis of the GAIN-ADHD sample to identify markers and genes important in the development of conduct problems in a European cohort of individuals with ADHD. Using the Family-Based Association Test (FBAT) package we examined three measures of conduct problems in 1,043,963 autosomal markers. This study is part of a series of exploratory analyses to identify candidate genes that may be important in ADHD and ADHD-related traits, such as conduct problems. We did not find genome-wide statistical significance (P < 5 x 10(-7)) for any of the tested markers and the three conduct problem traits. Fifty-four markers reached strong GWA signals (P < 10(-5)). We discuss these findings in the context of putative candidate genes and the implications of these findings in the understanding of the etiology of ADHD + CD. We aimed to achieve insight into the genetic etiology of a trait using a hypothesis-free study design and were able to identify a number of biologically interesting markers and genes for follow-up studies.

Case-control and within-family tests for an association between conduct disorder and DAT1

BACKGROUND

Conduct disorder (CD) is characterized by a persistent pattern of violating age-appropriate norms and the rights of others, and is one of the most frequently diagnosed disorders among children. CD is moderately heritable, but we know of no reliable associations with specific genes. Evidence suggests that a variable number tandem repeat polymorphism of the dopamine transporter (DAT1) gene may be associated with externalizing behavior in children.

OBJECTIVE

To test for an association between the DAT1 gene and CD.

DESIGN

Case-control analyses and a transmission disequilibrium test (TDT) were conducted.

SETTING/PARTICIPANTS

Cases were (n=210) adolescents enrolled in a Colorado treatment program for conduct and substance use problems. Controls included adolescents matched to the probands in the treatment program and their siblings (n=162). The TDT was conducted using case families in which DNA from both parents was available (95 trios).

RESULTS

The case-control analysis of the full sample did not result in a significant association [chi2 (2,372)=0.13, P=0.94]. Cases with early-onset conduct problems had slightly more 10-repeat alleles than controls, although this difference was not significant [chi2 (2,264)=2.19, P=0.33, 9/10 odds ratio (OR)=1.58, 10/10 OR=2.14]. The TDT also did not result in a significant association [chi2(1)=0.12, P=0.94].

CONCLUSION

Results did not support an association between this polymorphism of the DAT1 gene and CD in adolescents.

Genetics of attention deficit hyperactivity disorder

Results of behavioral genetic and molecular genetic studies have converged to suggest that both genetic and nongenetic factors contribute to the development of attention deficit hyperactivity disorder (ADHD). Family, twin, and adoption studies provide compelling evidence that genes play a strong role in mediating susceptibility to ADHD. In contrast to a handful of genome-wide scans conducted thus far, many candidate gene studies of ADHD have produced substantial evidence implicating several genes in the etiology of the disorder. Yet, even these associations are small and consistent with the idea that the genetic vulnerability to ADHD is mediated by many genes of small effects. These small effects emphasize the need for future candidate gene studies to implement strategies that will provide enough statistical power to detect such small effects.

Genomic imprinting and human psychology: cognition, behavior and pathology

Imprinted genes expressed in the brain are numerous and it has become clear that they play an important role in nervous system development and function. The significant influence of genomic imprinting during development sets the stage for structural and physiological variations affecting psychological function and behaviour, as well as other physiological systems mediating health and well-being. However, our understanding of the role of imprinted genes in behaviour lags far behind our understanding of their roles in perinatal growth and development. Knowledge of genomic imprinting remains limited among behavioral scientists and clinicians and research regarding the influence of imprinted genes on normal cognitive processes and the most common forms of neuropathology has been limited to date. In this chapter, we will explore how knowledge of genomic imprinting can be used to inform our study of normal human cognitive and behavioral processes as well as their disruption. Behavioural analyses of rare imprinted disorders, such as Prader-Willi and Angelman syndromes, provide insight regarding the phenotypic impact of imprinted genes in the brain, and can be used to guide the study of normal behaviour as well as more common but etiologically complex disorders such as ADHD and autism. Furthermore, hypotheses regarding the evolutionary development of imprinted genes can be used to derive predictions about their role in normal behavioural variation, such as that observed in food-related and social interactions.

ADHD candidate gene study in a population-based birth cohort: association with DBH and DRD2

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) is a common childhood-onset disorder with a significant impact on public health. Although a genetic contribution to risk is evident, predisposing genetic determinants remain largely unknown despite extensive research. So far, the most promising candidate genes have been those involved in dopamine and serotonin pathways. This study tests a series of allelic variants within such candidate genes to determine their potential influence on ADHD susceptibility.

METHOD

We used a population sample ascertained from a birth cohort of a subpopulation of Finland, characterized by founder effect and isolation, thus minimizing genetic heterogeneity. The subjects were systematically ascertained using DSM-IV diagnostic criteria for ADHD from the Northern Finland Birth Cohort 1986 of more than 9,000 individuals, resulting in the study sample of 188 ADHD cases and 166 controls. We genotyped markers in 13 candidate genes, including critical components of dopamine and serotonin pathways.

RESULTS

We report evidence for association of ADHD with allelic variants of the dopamine beta-hydroxylase (DBH) and dopamine receptor D2 (DRD2) genes.

CONCLUSIONS

Our study supports the involvement of the dopamine pathway in the etiology of ADHD; specifically the genes DBH and DRD2 deserve more attention in further studies.

A gene x gene interaction between DRD2 and DRD4 is associated with conduct disorder and antisocial behavior in males

Background

Antisocial behaviors are complex polygenic phenotypes that are due to a multifactorial arrangement of genetic polymorphisms. Little empirical research, however, has been undertaken that examines gene × gene interactions in the etiology of conduct disorder and antisocial behavior. This study examined whether adolescent conduct disorder and adult antisocial behavior were related to the dopamine D2 receptor polymorphism (DRD2) and the dopamine D4 receptor polymorphism (DRD4).

Methods

A sample of 872 male participants from the National Longitudinal Study of Adolescent Health (Add Health) completed self-report questionnaires that tapped adolescent conduct disorder and adult antisocial behavior. DNA was genotyped for DRD2 and DRD4.

Results

Multivariate regression analysis revealed that neither DRD2 nor DRD4 had significant independent effects on conduct disorder or antisocial behavior. However, DRD2 interacted with DRD4 to predict variation in adolescent conduct disorder and in adult antisocial behavior.

Conclusion

The results suggest that a gene × gene interaction between DRD2 and DRD4 is associated with the development of conduct disorder and adult antisocial behavior in males.

Genetic variation and shared biological susceptibility underlying comorbidity in neuropsychiatry

Genetic factors underlying alcoholism, substance abuse, antisocial and violent behaviour, psychosis, schizophrenia and psychopathy are emerging to implicate dopaminergic and cannabinoid, but also monoaminergic and glutamatergic systems through the maze of promoter genes and polymorphisms. Candidate gene association studies suggest the involvement of a range of genes in different disorders of CNS structure and function. Indices of comorbidity both complicate the array of gene-involvement and provide a substrate of hazardous interactivity. The putative role of the serotonin transporter gene in affective-dissociative spectrum disorders presents both plausible genetic variation and complication of comorbidity The position of genetic variation is further complicated through ethnic, contextual and social factors that provide geometric progressions in the comordity already underlying diagnostic obstacles. The concept of shared biological susceptibility to two or more disorder conditions of comorbidity seems a recurring observation, e.g., bipolar disorder with alcoholism or schizophrenia with alcohol/substance abuse or diabetes with schizopsychotic disorder. Several lines of evidence seem to suggest that the factors influencing variation in one set of symptoms and those affecting one or more disorders are observed to a marked extent which ought to facilitate the search for susceptibility genes in comorbid brain disorders. Identification of regional genetic factors is awaited for a more compelling outline that ought eventually to lead to greater efficacy of symptom-disorder arrangements and an augmentation of current pharmacological treatment therapies.

Association between polymorphisms in serotonin transporter gene and attention deficit hyperactivity disorder in Chinese Han subjects

Prior work has shown reduced serotonin transmission to be associated with impulsivity and behavioral problems. The current study assessed the association between ADHD and two variants of the serotonin transporter gene: the 44-bp deletion/insertion polymorphism (5-HTTLPR) and the 17 bp-repeat polymorphism in intron 2 (STin2.VNTR). We hypothesized that ADHD phenotypes associated with impulsivity would show an association with these variants. Two-hundred and ninety-three ADHD trios were genotyped and analyzed using transmission disequilibrium test (TDT) analysis and haplotype analysis. We found no association between the STin2.VNTR and ADHD, but did find preferential transmission of the S allele of the 5-HTTLPR polymorphism (chi(2) = 5.751, P = 0.016) to probands with ADHD. Haplotype analysis found the L/10 haplotype was over-transmitted (chi(2) = 6.172, P = 0.013), while L/12 was under-transmitted to probands with ADHD (chi(2) = 4.866, P = 0.027).

A comprehensive in vitro screening of d-, l-, and dl-threo-methylphenidate: an exploratory study

dl-Methylphenidate (MPH) has been widely used to treat attention-deficit/hyperactivity disorder (ADHD) for the last half century. It had been exclusively available in the racemic form, i.e., a 50:50 mixture of d- and l-isomers. However, a single enantiomer formulation, d-MPH (dexmethylphenidate), became available for general clinical use in 2002. For this reason, the intrinsic pharmacological differences in the effects of d- and l-MPH have recently come under intense investigation. The primary therapeutic effects of MPH are generally recognized to reside in the d-isomer. The present investigation provides quantitative values for a broad range of receptor-level interactions of the individual MPH isomers to better characterize the distinction between dl-MPH versus d-MPH versus l-MPH as it relates to binding affinity at sites associated with relevant central nervous system (CNS) pharmacology, as well as peripheral physiology. Overall, there were few differences in binding affinities between d-MPH and the racemate whereas there were more apparent differences between d-MPH and l-MPH. d-MPH exhibited prominent affinity at the norepinephrine transporter (NET) site, even exceeding such affinity at the dopamine transporter (DAT). These results further demonstrate that affinity for catecholaminergic sites largely resides in the d-MPH isomer. Although binding affinity was not demonstrable at the serotonin (5-HT) transporter site (SERT), novel findings of the study included affinity for the 5-HT1A and 5-HT2B receptor sites for both d- and l-MPH, with d-MPH exerting by far the most predominant effects at these sites. Thus, the emerging data of favorable therapeutic effects of ADHD treatment with d-MPH (and dl-MPH) may be underpinned by affinity and potential pharmacologic effects at NET and DAT sites, as well as sites relevant to serotonergic neurotransmission that may modulate mood, cognition, and motor behavior. However, the present exploratory studies reflect receptor binding affinities only. The specific pharmacological activities (i.e., agonism vs. antagonism) of these compounds await further exploration.

The analysis of 51 genes in DSM-IV combined type attention deficit hyperactivity disorder: association signals in DRD4, DAT1 and 16 other genes

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder, starting in early childhood and persisting into adulthood in the majority of cases. Family and twin studies have demonstrated the importance of genetic factors and candidate gene association studies have identified several loci that exert small but significant effects on ADHD. To provide further clarification of reported associations and identify novel associated genes, we examined 1,038 single-nucleotide polymorphisms (SNPs) spanning 51 candidate genes involved in the regulation of neurotransmitter pathways, particularly dopamine, norepinephrine and serotonin pathways, in addition to circadian rhythm genes. Analysis used within family tests of association in a sample of 776 DSM-IV ADHD combined type cases ascertained for the International Multi-centre ADHD Gene project. We found nominal significance with one or more SNPs in 18 genes, including the two most replicated findings in the literature: DRD4 and DAT1. Gene-wide tests, adjusted for the number of SNPs analysed in each gene, identified associations with TPH2, ARRB2, SYP, DAT1, ADRB2, HES1, MAOA and PNMT. Further studies will be needed to confirm or refute the observed associations and their generalisability to other samples.