Genetics of attention-deficit hyperactivity disorder (ADHD)

Cryo-EM structure of the dopamine transporter with a novel atypical non-competitive inhibitor bound to the orthosteric site

The regulation of dopamine (DA) removal from the synaptic cleft is a crucial process in neurotransmission and is facilitated by the sodium- and chloride-coupled dopamine transporter DAT. Psychostimulant drugs, cocaine, and amphetamine, both block the uptake of DA, while amphetamine also triggers the release of DA. As a result, they prolong or even amplify neurotransmitter signaling. Atypical inhibitors of DAT lack cocaine-like rewarding effects and offer a promising strategy for the treatment of drug use disorders. Here, we present the 3.2 Å resolution cryo-electron microscopy structure of the Drosophila melanogaster dopamine transporter (dDAT) in complex with the atypical non-competitive inhibitor AC-4-248. The inhibitor partially binds at the central binding site, extending into the extracellular vestibule, and locks the transporter in an outward open conformation. Our findings propose mechanisms for the non-competitive inhibition of DAT and attenuation of cocaine potency by AC-4-248 and provide a basis for the rational design of more efficacious atypical inhibitors.

Novel pharmacological targets for GABAergic dysfunction in ADHD

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopment disorder that affects approximately 5% of the population. The disorder is characterized by impulsivity, hyperactivity, and deficits in attention and cognition, although symptoms vary across patients due to the heterogenous and polygenic nature of the disorder. Stimulant medications are the standard of care treatment for ADHD patients, and their effectiveness has led to the dopaminergic hypothesis of ADHD in which deficits in dopaminergic signaling, especially in cortical brain regions, mechanistically underly ADHD pathophysiology. Despite their effectiveness in many individuals, almost one-third of patients do not respond to stimulant treatments and the long-term negative side effects of these medications remain unclear. Emerging clinical evidence is beginning to highlight an important role of dysregulated excitatory/inhibitory (E/I) balance in ADHD. These deficits in E/I balance are related to functional abnormalities in glutamate and Gamma-Aminobutyric Acid (GABA) signaling in the brain, with increasing emphasis placed on GABAergic interneurons driving specific aspects of ADHD pathophysiology. Recent genome-wide association studies (GWAS) have also highlighted how genes associated with GABA function are mutated in human populations with ADHD, resulting in the generation of several new genetic mouse models of ADHD. This review will discuss how GABAergic dysfunction underlies ADHD pathophysiology, and how specific receptors/proteins related to GABAergic interneuron dysfunction may be pharmacologically targeted to treat ADHD in subpopulations with specific comorbidities and symptom domains. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Pre- and post-treatment evaluation of routine blood analysis in patients with attention deficit hyperactivity disorder and comparison with the healthy control group

This study aimed to examine potential disparities in hematologic inflammation parameters between children diagnosed with attention deficit hyperactivity disorder (ADHD) and their healthy counterparts and to determine whether atomoxetine treatment induced any alterations in inflammation indicators. This case-control study involved 43 children aged 6-13 years, 22 diagnosed with ADHD for the first time, and 21 healthy children. In all children, complete blood count and albumin, C-reactive protein (CRP), thyroid stimulating hormone (TSH), free thyroxine (free T4), folate, vitamin B12, aspartate aminotransferase (AST), alanine transaminase (ALT), creatinine and urea values were performed. Children with ADHD were started on atomoxetine treatment, and one month later, the blood test was repeated for those who commenced treatment. Neutrophil (p = 0.005), platelet (PLT) (p = 0.002), neutrophil/lymphocyte ratio (NLR) (p = 0.001), platelet/lymphocyte ratio (PLR) (p < 0.001), systemic immune /inflammation index (SII) (p < 0.001) and pan-immune-inflammation value (PIV) (p = 0.025) parameters were found to be significantly higher than the control group, while the lymphocyte value (p = 0.001) was found to be significantly lower. In those in the ADHD group, lymphocyte (p = 0.041) and albumin (p = 0.027) values increased significantly after treatment. The results of this study show the increase in inflammation in drug-naive ADHD patients and the partial improvement after treatment. However, there is a need to evaluate inflammation in larger samples after longer-term treatments and follow-ups.

The Effect of Drug Use, Body Mass Index and Blood Pressure on Oxidative Stress Levels in Children and Adolescents with Attention Deficit and Hyperactivity Disorder

Objective

The aim of this study was to determine the correlation between clinical variables such as body mass index, blood pressure, drug use and oxidative stress level in children and adolescents with attention deficit and hyperactivity disorder (ADHD).

Methods

Total oxidant status (TOS), total antioxidant status (TAS), oxidative stress index (OSI), malondialdehyde (MDA) and superoxide dismutase (SOD) activity were measured in the serum of 51 patients (38 male, 13 female) diagnosed with ADHD according to DSM-5 diagnostic criteria and 32 control subjects (12 male, 20 female). The Kiddie Schedule for Affective Disorders and Schizophrenia Present and Lifetime Version was applied to all participants.

Results

The mean TOS, OSI, MDA values were determined to be significantly higher (p < 0.001) and the mean SOD value was lower in the ADHD group (p < 0.001). Multivariate regression analysis indicated significantly lower SOD and diastolic blood pressure values and significantly higher MDA in the ADHD group compared to the control group (p < 0.01). Low SOD (sensitivity 90.2%, specificity 78.0%) and high MDA (sensitivity 86.3%, specificity 81.2%) were determined to be predictive parameters for diagnosing ADHD. In univariate analysis, the mean TOS, OSI and SOD values were higher in ADHD patients under medication, while the mean TAS was higher in patients not using medication (p < 0.01). Only TOS was significant in multivariate logistic regression analysis (p < 0.01).

Conclusion

The results of this study demonstrate that impaired oxidative balance may play a role in the etiology of ADHD.

PM2.5 exposure and incident attention-deficit/hyperactivity disorder during the prenatal and postnatal periods: A birth cohort study

Only a few studies have assessed the effects of fine particulate matter (PM_2.5) exposure during the prenatal and postnatal periods on the development of attention-deficit/hyperactivity disorder (ADHD). We investigated the association of exposure to PM_2.5 during pregnancy and early life with ADHD. This birth cohort consisted of 425,736 singleton live-term births between 2004 and 2015 in Taiwan. Daily PM_2.5 concentrations were derived from a 1-km satellite-based estimation model. A time-dependent Cox model was used to assess the effects of PM_2.5 on ADHD during the first, second, and third trimesters and from age 1-5 years after birth. The distributed lag nonlinear model was utilized to explore the dose-response relationship. Total 9,294 children were diagnosed with ADHD during the study period. The hazard ratio (HR) of ADHD was significantly associated with a 10 μg/m³ increase in PM_2.5 during the first trimester (HR = 1.26; 95% confidence interval [CI]: 1.13-1.40) and increased at PM_2.5 over 16 μg/m³. For postnatal periods, the HR of ADHD was significantly associated with increased PM_2.5 at the first to third year of life (HR ranged between 1.40 and 1.87). According to the dose-response relationship of exposure to PM_2.5 at the third year of life, the HR of ADHD was significantly associated with PM_2.5 above 16 μg/m³ and sharply increased as PM_2.5 >50 μg/m³. We did not observe a significant modification of sex on the relation between PM_2.5 and ADHD. Exposure of pregnant women to PM_2.5 above 16 μg/m³ from conception to the early life of their children may increase the risk of ADHD. The government should improve the criteria for air quality control and meet the WHO air quality guidelines to protect pregnant women and children from developing ADHD in the future.

Modulation of Spatial Memory Deficit and Hyperactivity in Dopamine Transporter Knockout Rats via α2A-Adrenoceptors

Attention deficit hyperactivity disorder (ADHD) is manifested by a specific set of behavioral deficits such as hyperactivity, impulsivity, and inattention. The dopamine neurotransmitter system is postulated to be involved in the pathogenesis of ADHD. Guanfacine, a selective α2A-adrenoceptor agonist, is prescribed for ADHD treatment. ADHD also is known to be associated with impairment of multiple aspects of cognition, including spatial memory, however, it remains unclear how modulation of the norepinephrine system can affect these deficits. Hyperdopaminergic dopamine transporter knockout (DAT-KO) rats are a valuable model for investigating ADHD. The DAT-KO rats are hyperactive and deficient in spatial working memory. This work aimed to evaluate the effects of noradrenergic drugs on the fulfillment of spatial cognitive tasks by DAT-KO rats. The rats were tested in the Hebb - Williams maze during training and following noradrenergic drugs administration. The efficiency of spatial orientation was assessed as to how fast the animal finds an optimal way to the goal box. Testing in a new maze configuration allowed us to evaluate the effects of drug administration after the acquisition of the task rules. The behavioral variables such as the distance traveled, the time to reach the goal box, and the time spent in the error zones were analyzed. It has been observed that α2A-adrenoceptor agonist Guanfacine (0.25 mg/kg) had only a minimal inhibitory effect on hyperactivity of DAT-KO rats in the maze but significantly ameliorated their perseverative pattern of activity and reduced the time spent in the error zones. In contrast, α2A-adrenoceptor antagonist Yohimbine, at the dose of 1 mg/kg, increased the distance traveled by DAT-KO rats and elevated the number of perseverative reactions and the time spent in the error zones. Guanfacine caused minimal effects in wild-type rats, while Yohimbine altered several parameters reflecting a detrimental effect on the performance in the maze. These data indicate that modulation of α2A-adrenoceptor activity potently affects both dopamine-dependent hyperactivity and cognitive dysfunctions. Similar mechanisms may be involved in the beneficial effects of Guanfacine on cognitive deficits in ADHD patients. This study further supports the translational potential of DAT-KO rats for testing new pharmacological drugs.

The Interplay Between Prenatal Adversity, Offspring Dopaminergic Genes, and Early Parenting on Toddler Attentional Function

Background: Few studies have explored the complex gene-by-prenatal environment-by-early postnatal environment interactions that underlie the development of attentional competence. Here, we examined if variation in dopamine-related genes interacts with prenatal adversity to influence toddler attentional competence and whether this influence is buffered by early positive maternal behavior. Methods: From the Maternal Adversity, Vulnerability and Neurodevelopment cohort, 134 participants (197 when imputing missing data) had information on prenatal adversity (prenatal stressful life events, prenatal maternal depressive symptoms, and birth weight), five dopamine-related genes (DAT1, DRD4, DRD2, COMT, BDNF), observed maternal parenting behavior at 6 months and parent-rated toddler attentional competence at 18 and 24 months. The Latent Environmental and Genetic Interaction (LEGIT) approach was used to examine genes-by-prenatal environment-by-postnatal environment interactions while controlling for sociodemographic factors and postnatal depression. Results: Our hypothesis of a three-way interaction between prenatal adversity, dopamine-related genes, and early maternal parenting behavior was not confirmed. However, consistent two-way interactions emerged between prenatal adversity and dopamine-related genes; prenatal adversity and maternal parenting behavior, and dopamine-related genes and maternal parenting behavior in relation to toddler attentional competence. Significant interaction effects were driven by the DAT1, COMT, and BDNF genotypes; prenatal stressful life events; maternal sensitivity, tactile stimulation, vocalization, and infant-related activities. Conclusions: Multiple dopamine-related genes affected toddler attentional competence and they did so in interaction with prenatal adversity and the early rearing environment, separately. Effects were already visible in young children. Several aspects of early maternal parenting have been identified as potential targets for intervention.

Duration of breast feeding and attention-deficit/hyperactivity disorder in United States preschool-aged children

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by difficulties sustaining attention and controlling hyperactivity and impulsive behavior. Population-based studies concerning the association between breast-feeding duration and ADHD among preschool-aged children in the United States (U.S.) have been sparse.

AIMS

To determine whether there is an association between the duration of breast feeding and ADHD in U.S. children aged 2-5 years.

METHODS AND PROCEDURES

We used nationally representative data from the 2016, 2017, and 2018 National Survey of Children's Health (NSCH) to examine the association between breast-feeding duration and ADHD in U.S. preschool-aged children. Sample characteristics were compared using Rao-Scott chi-square test, and adjusted prevalence odds ratios and 95 % confidence intervals were estimated using unconditional logistic regression.

OUTCOMES AND RESULTS

Of the 20,453 children eligible for our study, 1.5 % had received a diagnosis of ADHD and 77.5 % were reported to have been fed human milk as infants. Prevalence odds of ADHD were 57 % lower among children fed human milk for 6-12 months compared to children never fed human milk after controlling for potential confounders. Among children with durations of breast feeding lasting less than 6 months or lasting 12 months or longer, prevalence odds of ADHD were not significantly lower than the comparison group, children who were never fed human milk, after controlling for potential confounders.

CONCLUSIONS AND IMPLICATIONS

We noted an inverse association between breast feeding durations of 6-12 months and parent-reported diagnosis of ADHD in preschool-aged children in the U.S. Future studies should use longitudinal designs to examine ADHD and duration of breast-feeding measures.

Opposite Control of Excitatory and Inhibitory Synapse Formation by Slitrk2 and Slitrk5 on Dopamine Neurons Modulates Hyperactivity Behavior

The neurodevelopmental origin of hyperactivity disorder has been suggested to involve the dopaminergic system, but the underlying mechanisms are still unknown. Here, transcription factors Lmx1a and Lmx1b are shown to be essential for midbrain dopaminergic (mDA) neuron excitatory synaptic inputs and dendritic development. Strikingly, conditional knockout (cKO) of Lmx1a/b in postmitotic mDA neurons results in marked hyperactivity. In seeking Lmx1a/b target genes, we identify positively regulated Slitrk2 and negatively regulated Slitrk5. These two synaptic adhesion proteins promote excitatory and inhibitory synapses on mDA neurons, respectively. Knocking down Slitrk2 reproduces some of the Lmx1a/b cKO cellular and behavioral phenotypes, whereas Slitrk5 knockdown has opposite effects. The hyperactivity caused by this imbalance in excitatory/inhibitory synaptic inputs on dopamine neurons is reproduced by chronically inhibiting the ventral tegmental area during development using pharmacogenetics. Our study shows that alterations in developing dopaminergic circuits strongly impact locomotor activity, shedding light on mechanisms causing hyperactivity behaviors.

Effect of palmitoylation on the dimer formation of the human dopamine transporter

The human dopamine transporter (hDAT) is one in three members of the monoamine transporter family (MAT). hDAT is essential for regulating the dopamine concentration in the synaptic cleft through dopamine reuptake into the presynaptic neuron; thereby controlling hDAT dopamine signaling. Dysfunction of the transporter is linked to several psychiatric disorders. hDAT and the other MATs have been shown to form oligomers in the plasma membrane, but only limited data exists on which dimeric and higher order oligomeric states are accessible and energetically favorable. In this work, we present several probable dimer conformations using computational coarse-grained self-assembly simulations and assess the relative stability of the different dimer conformations using umbrella sampling replica exchange molecular dynamics. Overall, the dimer conformations primarily involve TM9 and/or TM11 and/or TM12 at the interface. Furthermore, we show that a palmitoyl group (palm) attached to hDAT on TM12 modifies the free energy of separation for interfaces involving TM12, suggesting that S-palmitoylation may change the relative abundance of dimers involving TM12 in a biological context. Finally, a comparison of the identified interfaces of hDAT and palmitoylated hDAT to the human serotonin transporter interfaces and the leucine transporter interface, suggests similar dimer conformations across these protein family.

The Role of ADHD in Predicting the Development of Violent Behavior Among Juvenile Offenders: Participation Versus Frequency

Past research has identified attention-deficit/hyperactivity disorder (ADHD) as a risk factor for engagement in violent offending. Despite the link between the disorder and violent offending, this risk factor has yet to be examined as a predictor of heterogeneity in the development of violent offending among juvenile offenders. It is likely that the impulsivity, genetic link, and generally chronic disorder course which are characteristics of the disorder play roles in predicting violent offending, which is consistent with both self-control theory and general developmental theory related to early life deficits and life-course persistent offending. Past research has also elucidated a developmental trajectory model of violent offending, which is utilized by the present research. The present research examines ADHD as a risk factor predicting trajectory group assignment. The Pathways to Desistance data followed 1,354 juvenile offenders for 84 months following conviction for a serious offense. Using multinomial logistic regression, this study extends past research on the development of violent offending among juvenile offenders by examining ADHD as a risk factor predicting assignment to violent offending trajectory groups. Results indicate that meeting criteria for ADHD at baseline predicted membership to all trajectory groups relative to the Abstaining group when all covariates were included. This increase in risk is highest for the trajectory group characterized by the highest frequency of violent offending. This indicates the relevance of identifying and treating ADHD among juvenile offenders to best mitigate risk of violent recidivism throughout adolescence and early adulthood.

Brain Network Connectivity and Association with Catechol-O-Methyltransferase Gene Polymorphism in Korean Attention-Deficit Hyperactivity Disorder Children

OBJECTIVE

We sought to determine if the links between and within the default mode network (DMN) and dorsal attention network (DAT) exhibited different conditions according to catechol-O-methyltransferase (COMT) gene polymorphism in relationship to attention-deficit hyperactivity disorder (ADHD) symptoms.

METHODS

Fifty-seven children with ADHD and 48 healthy controls (HCs) were administered an intelligence test, the Children's Depression Inventory, the Korean ADHD rating scale, and continuous performance test. Resting-state brain functional MRI scans were obtained, and COMT genotyping was performed to distinguish valine carriers and methionine homozygotes.

RESULTS

Compared to controls, children with ADHD showed increased ADHD scale scores, increased visual commission errors, and increased functional connectivity (FC) within the DMN and DAT. Compared to all children with ADHD, children with the methionine homozygote and those who were valine carriers showed increased FC within the DMN and DAT and decreased FC between the DMN and DAT. FC within the DMN was also increased in HC valine carriers compared to HC children with the methionine homozygote, and in children with ADHD who were valine carriers compared to HC valine carriers.

CONCLUSION

We observed increased brain connectivity within the DMN and DAT and altered brain connectivity within and between the DMN and DAT associated with COMT polymorphism in children with ADHD.

Interaction between lead and noradrenergic genotypes affects neurocognitive functions in attention-deficit/hyperactivity disorder: a case control study

BACKGROUND

Lead is known to be associated with attention-deficit/hyperactivity disorder (ADHD) even at low concentrations. We aimed to evaluate neurocognitive functions associated with lead in the blood and the interactions between lead and dopaminergic or noradrenergic pathway-related genotypes in youths with ADHD.

METHODS

A total of 259 youths with ADHD and 96 healthy controls (aged 5-18 years) enrolled in this study. The Korean Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime version was conducted for psychiatric diagnostic evaluation. Blood lead levels were measured, and their interaction with dopaminergic or noradrenergic genotypes for ADHD; namely, the dopamine transporter (DAT1), dopamine receptor D4 (DRD4), and alpha-2A-adrenergic receptor (ADRA2A) genotypes were investigated. All participants were assessed using the ADHD Rating Scale-IV (ADHD-RS). Participants also completed the continuous performance test (CPT) and Stroop Color-Word Test (SCWT). Analysis of covariance was used for comparison of blood lead levels between ADHD and control groups. A multivariable linear regression model was used to evaluate the associations of blood lead levels with the results of ADHD-RS, CPT, and SCWT; adjusted for intelligence quotient (IQ), age, and sex. A path analysis model was used to identify the mediating effects of neurocognitive functions on the effects of blood lead on ADHD symptoms. To evaluate the effect of the interaction between blood lead and genes on neuropsychological functions, hierarchical regression analyses were performed.

RESULTS

There was a significant difference in blood lead levels between the ADHD and control groups (1.4 ± 0.5 vs. 1.3 ± 0.5 μg/dL, p = .005). Blood lead levels showed a positive correlation with scores on omission errors(r = .158, p = .003) and response time variability (r = .136, p = .010) of CPT. In the multivariable linear regression model, blood lead levels were associated with omission errors (B = 3.748, p = .045). Regarding the effects of lead on ADHD symptoms, hyperactivity-impulsivity was mediated by omission errors. An interaction effect was detected between ADRA2A DraI genotype and lead levels on omission errors (B = 5.066, p = .041).

CONCLUSIONS

Our results indicate that neurocognitive functions at least partly mediate the association between blood lead levels and ADHD symptoms, and that neurocognitive functions are affected by the interaction between blood lead levels and noradrenergic genotype.

Determining the association between polymorphisms of the DAT1 and DRD4 genes with attention deficit hyperactivity disorder in children from Java Island

Attention deficit hyperactivity disorder (ADHD) is one of the most common neurobehavioural in the children. Genetic factor is known one of the factors which contributed in ADHD development. VNTR polymorphism in 3'UTR exon 15 of DAT1 gene and exon 3 of DRD4 gene are reported to be associated in ADHD. In this study we examine the association of ADHD with VNTR polymorphism of DAT1 and DRD4 gene in Indonesian children. Sixty-five ADHD children and 70 normal children (6-13 years of age), were included in the study, we matched by age and gender. ADHD was diagnosed by DSM-IV. We performed a casecontrol study to found the association between ADHD and VNTR polymorphism of DAT1 and DRD4 genes. The 10-repeat allele of DAT1 and 2-repeat allele of DRD4 were higher in Indonesian children. Although the frequency of these allele was higher, but it was similar both in ADHD and control groups. Neither DAT1 nor DRD4 gene showed showed significant difference in genotype distribution and frequency allele between both groups (p > 0.05). No association between ADHD and VNTR polymorphism of DAT1 and DRD4 genes found in Indonesian children. This data suggest that DAT1 and DRD4 do not contribute to etiology of ADHD in Indonesian children. Further studies are needed to clarify association between VNTR polymorphism of DAT1 and DRD4 genetic with ADHD of Indonesian children in larger sample size and family based study.

The effect of phosphatidylserine containing Omega3 fatty-acids on attention-deficit hyperactivity disorder symptoms in children: A double-blind placebo-controlled trial, followed by an open-label extension

Objective

To study the efficacy and safety of phosphatidylserine (PS) containing Omega3 long-chain polyunsaturated fatty acids attached to its backbone (PS-Omega3) in reducing attention-deficit/ hyperactivity disorder (ADHD) symptoms in children.

Method

A 15-week, double-blind, placebo-controlled phase followed by an open-label extension of additional 15 weeks. Two hundred ADHD children were randomized to receive either PS-Omega3 or placebo, out of them, 150 children continued into the extension. Efficacy was assessed using Conners’ parent and teacher rating scales (CRS-P,T), Strengths and Difficulties Questionnaire (SDQ), and Child Health Questionnaire (CHQ). Safety evaluation included adverse events monitoring.

Results

The key finding of the double-blind phase was the significant reduction in the Global:Restless/impulsive subscale of CRS-P and the significant improvement in Parent impact-emotional (PE) subscale of the CHQ, both in the PS-Omega3 group. Exploratory subgroup analysis of children with a more pronounced hyperactive/impulsive behavior, as well as mood and behavior-dysregulation, revealed a significant reduction in the ADHD-Index and hyperactive components. Data from the open-label extension indicated sustained efficacy for children who continued to receive PS-Omega3. Children that switched to PS-Omega3 treatment from placebo showed a significant reduction in subscales scores of both CRS-P and the CRS-T, as compare to baseline scores. The treatment was well tolerated.

Conclusions

The results of this 30-week study suggest that PS-Omega3 may reduce ADHD symptoms in children. Preliminary analysis suggests that this treatment may be especially effective in a subgroup of hyperactive-impulsive, emotionally and behaviorally-dysregulated ADHD children.

The role of environmental influences in the complex relationship between borderline personality disorder and attention-deficit/hyperactivity disorder: review of recent findings

BACKGROUND

In recent years, the existence of possible developmental pathways from childhood Attention-Deficit/Hyperactivity Disorder (ADHD) to adult Borderline Personality Disorder (BPD) has been suggested. The existence of common genetic factors has been described but there is little evidence on the role of environmental factors in the possible transition from one disorder to another throughout life. The main goal of this work is to review the literature about the existing evidence on childhood traumas as factors that mediate the risk of developing BPD in children with ADHD.

METHODS

A literature search was conducted using PubMed, Science Direct and PsychInfo databases. Criteria included studies of BPD and ADHD relationships and childhood traumas as environmental influences from epidemiological or clinical samples.

RESULTS

The review only identified 4 studies that matched the search criteria. All studies retrospectively analyzed childhood traumas, and adult patients with BPD, with or without comorbid ADHD, were the most frequently mentioned. The analyzed evidence reinforces the relationship between the number of childhood traumas and higher clinical severity. Three of these analyzed studies describe an increased the risk of children with ADHD who report emotional and sexual traumatic experiences to develop BPD in adulthood.

CONCLUSIONS

The experience of traumatic childhood events, especially those of an emotional type, may have a mediating effect of an increased risk of developing adult BPD in childhood ADHD patients. However, to consider them as risk factors, more studies, and especially longitudinal studies, are necessary to clarify the probable transactional process between the two disorders. Evidence from these studies may be helpful to develop early intervention programs to reduce the functional impairment associated with the two disorders.

Altered methyltetrahydrofolate reductase gene polymorphism in mothers of children with attention deficit and hyperactivity disorder

Attention Deficit and Hyperactivity Disorder (ADHD) is one of the most common psychiatric disorders in childhood and causes significant functional impairments in children. Behavioral genetic and molecular genetic studies have provided significant evidence in terms of highlighting the etiology of ADHD. Folate deficiency during pregnancy is an established risk factor for ADHD. Polymorphisms in the Methyltetrahydrofolate Reductase (MTHFR) encoding gene, such as A1298C and C667T, are associated with the decreased bioavailability of folate, and this condition can act like folate deficiency. In the literature, no study has investigated MTHFR polymorphisms in mothers of children with ADHD. Sixty-four children diagnosed with ADHD and their mothers as well as 40 healthy children and their mothers participated in this study. MTHFR polymorphisms were investigated in all participants. Comparison of the C677C and A1298C MTHFR polymorphisms in children with and without ADHD revealed no significant differences. We found that the maternal C677C_CT genotype counts, both observed and expected values, were significantly different from those based on Hardy-Weinberg Principle Analysis in the ADHD group. The most important result of this study was that maternal C677C MTHFR gene polymorphisms are significant risk factors in for ADHD, and we argue that children with ADHD are exposed to folate deficiency, even if their mothers received a sufficient amount of folate during pregnancy. This result also highlights one of the genetic factors of ADHD. Further studies should be performed to confirm this finding.

Using Cell Cultures for the Investigation of Treatments for Attention Deficit Hyperactivity Disorder: A Systematic Review

BACKGROUND

Advances in basic and molecular biology have promoted the use of cell cultures in a wide range of areas, including the evaluation of drug efficacy, safety and toxicity.

OBJECTIVE

This article aims to provide a general overview of the methodological parameters of cell cultures used to investigate therapeutic options for Attention Deficit Hyperactivity Disorder.

METHOD

A systematic search was performed in the electronic databases PubMed, Scopus, and DOAJ. In vitro experimental studies using cell cultures were included.

RESULTS

A total of 328 studies were initially identified, with 16 included for qualitative synthesis. Seven studies used neuronal cells (SH-SY5Y neuroblastoma and PC12 cell line) and nine used nonneuronal cells. All the studies described the culture conditions, but most studies were inconsistent with regard to reporting results and raw data. Only one-third of the studies performed cell viability assays, while a further 30% conducted gene expression analysis. Other additional tests included electrophysiological evaluation and transporter activity. More than 50% of the studies evaluated the effects of drugs such as methylphenidate and atomoxetine, while plant extracts were assessed in four studies and polyunsaturated fatty acids in one.

CONCLUSION

We suggested a flowchart to guide the planning and execution of studies, and a checklist to be completed by authors to allow the standardized reporting of results. This may guide the elaboration of laboratory protocols and further in vitro studies.

Cluster analysis profiling of behaviors in zebrafish larvae treated with antidepressants and pesticides

Antidepressants are used by a substantial number of women in their childbearing years. Treatment may continue during pregnancy, since untreated depression poses a risk to the mother and child. However, many antidepressants readily pass through the placental barrier to reach the fetus or may be ingested by the newborn via breastmilk. Little is known about the effects of antidepressants on brain development and subsequent behavior in young children. In the current study, we used zebrafish as a model system to examine the neurodevelopmental effects of three commonly prescribed antidepressants, sertraline, duloxetine and bupropion. Zebrafish were exposed to these antidepressants during development and were examined for changes in larval avoidance behavior, activity, social behaviors, and anxiety-related behaviors. The results show that antidepressants commonly affect larval swim speeds and resting, and differentially affect other behaviors depending upon the exposure period. Using cluster analysis profiling, we compared the obtained results to previous reports on behavioral defects induced by organophosphate pesticides. We found that the behavioral profiles induced by antidepressants and pesticides overlap, indicating a common mechanism of action. We conclude that developmental antidepressant exposures lead to specific behavioral changes in zebrafish larvae. At present, it is not known if antidepressants have similar effects in human development.

A Gut Feeling: A Hypothesis of the Role of the Microbiome in Attention-Deficit/Hyperactivity Disorders

Attention-deficit/hyperactivity disorder (ADHD) is a neurologic disorder characterized by hyperactivity/impulsivity and/or inattentiveness, with genetic and environmental factors contributing to the disorder. With the growing recognition of the microbiome’s role in many neurological disorders, the authors propose that it may also be implicated in ADHD. Here, we describe several evolving areas of research to support this hypothesis. First, a unique composition of gut bacteria has been identified and linked to behaviors in ADHD. Second, our research found an increased incidence of 2 gastrointestinal symptoms (constipation and flatulence) in children with ADHD, as compared to controls. Finally, emerging data may be interpreted to suggest that immune dysregulation in ADHD be associated with an altered microbiome, low-grade inflammation, and gastrointestinal dysfunction. Although more studies are needed to elucidate exact mechanisms and causality, we propose that an altered microbiome, gastrointestinal symptoms, and immune dysregulation may be associated with the ADHD phenotypes.

Meta-Analysis of Case-Control and Family-Based Associations Between the 5-HTTLPR L/S Polymorphism and Susceptibility to ADHD

OBJECTIVE

The aim of this study was to determine whether the serotonin transporter-linked polymorphic region (5-HTTLPR) L (long)/S (short) polymorphism is associated with susceptibility to ADHD.

METHOD

We conducted a meta-analysis of case-control associations and the transmission disequilibrium test (TDT) between the 5-HTTLPR L/S polymorphism and ADHD.

RESULTS

A total of 19 comparison studies were included in this meta-analysis. Our meta-analysis of the case-control studies showed no association between ADHD and the 5-HTTLPR S allele, for all study participants (odds ratio [OR] = 1.075, 95% confidence interval [CI] = [0.990, 1.167], p = .085), or for the European or Asian population. The TDT indicated no association between ADHD and the 5-HTTLPR S allele, for all study participants (OR = 1.078, 95% CI = [0.962, 1.207], p = .196).

CONCLUSION

This meta-analysis of case-control studies and TDT showed a lack of association between the 5-HTTLPR L/S polymorphism and ADHD.

Glutamatergic synapses in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) are a group of diseases whose symptoms arise during childhood or adolescence and that impact several higher cognitive functions such as learning, sociability and mood. Accruing evidence suggests that a shared pathogenic mechanism underlying these diseases is the dysfunction of glutamatergic synapses. We summarize present knowledge on autism spectrum disorders (ASD), intellectual disability (ID), Down syndrome (DS), Rett syndrome (RS) and attention-deficit hyperactivity disorder (ADHD), highlighting the involvement of glutamatergic synapses and receptors in these disorders. The most commonly shared defects involve α-amino-3-hydroxy-5-methyl- 4-isoxazole propionic acid receptors (AMPARs), N-methyl-d-aspartate receptors (NMDARs) and metabotropic glutamate receptors (mGluRs), whose functions are strongly linked to synaptic plasticity, affecting both cell-autonomous features as well as circuit formation. Moreover, the major scaffolding proteins and, thus, the general structure of the synapse are often deregulated in neurodevelopmental disorders, which is not surprising considering their crucial role in the regulation of glutamate receptor positioning and functioning. This convergence of defects supports the definition of neurodevelopmental disorders as a continuum of pathological manifestations, suggesting that glutamatergic synapses could be a therapeutic target to ameliorate patient symptomatology.

Dimer Interface of the Human Serotonin Transporter and Effect of the Membrane Composition

The oligomeric state of membrane proteins has recently emerged in many cases as having an effect on their function. However, the intrinsic dynamics of their spatial organization in cells and model systems makes it challenging to characterize. Here we use molecular dynamics (MD) simulations at multiple resolutions to determine the dimer conformation of the human serotonin transporter (hSERT). From self-assembly simulations we predict dimer candidates and subsequently quantify their relative strength. We use umbrella sampling (US) replica exchange MD simulations for which we present extensive analysis of their efficiency and improved sampling compared to regular US MD simulations. The data shows that the most stable hSERT dimer interface is symmetrical and involves transmembrane helix 12 (TM12), similar to the crystal structure of the bacterial homologue LeuT, but with a slightly different orientation. We also describe the supramolecular organization of hSERT from a 250 μs self-assembly simulation. Finally, the effects of the presence of phosphatidylinositol bisphosphate or cholesterol in the membrane model has been quantified for the TM12-TM12 predicted interface. Collectively, the presented data bring new insight to the area of protein and lipid interplay in biological membranes.

A direct interaction of cholesterol with the dopamine transporter prevents its out-to-inward transition

Monoamine transporters (MATs) carry out neurotransmitter reuptake from the synaptic cleft, a key step in neurotransmission, which is targeted in the treatment of neurological disorders. Cholesterol (CHOL), a major component of the synaptic plasma membrane, has been shown to exhibit a modulatory effect on MATs. Recent crystal structures of the dopamine transporter (DAT) revealed the presence of two conserved CHOL-like molecules, suggesting a functional protein-CHOL direct interaction. Here, we present extensive atomistic molecular dynamics (MD) simulations of DAT in an outward-facing conformation. In the absence of bound CHOL, DAT undergoes structural changes reflecting early events of dopamine transport: transition to an inward-facing conformation. In contrast, in the presence of bound CHOL, these conformational changes are inhibited, seemingly by an immobilization of the intracellular interface of transmembrane helix 1a and 5 by CHOL. We also provide evidence, from coarse grain MD simulations that the CHOL sites observed in the DAT crystal structures are preserved in all human monoamine transporters (dopamine, serotonin and norepinephrine), suggesting that our findings might extend to the entire family.

Altered GABAergic Signaling in Brain Disease at Various Stages of Life

In the healthy brain, gamma-aminobutyric acid (GABA) is regulated by neurons and glia. This begs the question: what happens in the malfunctioning brain? There are many reasons why diseases occur, including genetic mutations, systemic problems, and environmental influences. There are also many ways in which GABA can become dysregulated, such as through alterations in its synthesis or release, and changes in systems that respond to it. Notably, dysregulation of GABA can have a large impact on the brain. To date, few reviews have examined brain diseases in which dysregulation of GABA is implicated as an underlying factor. Accordingly, the time is ripe for investigating alterations in GABAergic signaling that may play a role in changes in neuronal activity observed in the major brain disorders that occur during various stages of life. This review is meant to provide a better understanding of the role of GABA in brain health and contributor to social problems from a scientific perspective.

Dynamic thiol/disulfide homeostasis in children with attention deficit hyperactivity disorder and its relation with disease subtypes

BACKGROUND

The aim of this study was to evaluate a novel oxidative stress marker (thiol/disulfide homeostasis) in attention deficit hyperactivity disorder (ADHD) children for the first time in literature.

METHODS

Ninety children with ADHD diagnosed according to DSM-V and as control group, 65 healthy children were included to the study. Native thiol, total thiol, disulfide, disulfide/native thiol, disulfide/total thiol were compared between the groups.

RESULTS

Total and native thiol levels were significantly higher whereas the disulfide/native thiol ratios were significantly lower in children with ADHD. ADHD combined type appeared to have higher disulfide, disulfide/native thiol and disulfide/total thiol ratios compared to other subtypes. Disulfide levels of the males with ADHD were significantly higher than those of the females with ADHD.

CONCLUSION

This study suggests that thiol/disulfide homeostasis is abnormal in children with ADHD. It may be used as a novel OS marker in ADHD children because it is easy, practical, fully automated and relatively inexpensive.

Integrating care for neurodevelopmental disorders by unpacking control: A grounded theory study

BACKGROUND

To establish integrated healthcare pathways for patients with neurodevelopmental disorders (ND) such as autism spectrum disorder and attention-deficit hyperactivity disorder is challenging. This study sets out to investigate the main concerns for healthcare professionals when integrating ND care pathways and how they resolve these concerns.

METHODS

Using classic grounded theory (Glaser), we analysed efforts to improve and integrate an ND care pathway for children and youth in a Swedish region over a period of 6 years. Data from 42 individual interviews with a range of ND professionals, nine group interviews with healthcare teams, participant observation, a 2-day dialogue conference, focus group meetings, regional media coverage, and reports from other Swedish regional ND projects were analysed.

RESULTS

The main concern for participants was to deal with overwhelming ND complexity by unpacking control, which is control over strategies to define patients' status and needs. Unpacking control is key to the professionals' strivings to expand constructive life space for patients, to squeeze health care to reach available care goals, to promote professional ideologies, and to uphold workplace integrity. Control-seeking behaviour in relation to ND unpacking is ubiquitous and complicates integration of ND care pathways.

CONCLUSIONS

The Unpacking control theory expands central aspects of professions theory and may help to improve ND care development.

A Genetic Polymorphism of the Human Dopamine Transporter Determines the Impact of Sleep Deprivation on Brain Responses to Rewards and Punishments

Despite an emerging link between alterations in motivated behavior and a lack of sleep, the impact of sleep deprivation on human brain mechanisms of reward and punishment remain largely unknown, as does the role of trait dopamine activity in modulating such effects in the mesolimbic system. Combining fMRI with an established incentive paradigm and individual genotyping, here, we test the hypothesis that trait differences in the human dopamine transporter (DAT) gene-associated with altered synaptic dopamine signalling-govern the impact of sleep deprivation on neural sensitivity to impending monetary gains and losses. Consistent with this framework, markedly different striatal reward responses were observed following sleep loss depending on the DAT functional polymorphisms. Only participants carrying a copy of the nine-repeat DAT allele-linked to higher phasic dopamine activity-expressed amplified striatal response during anticipation of monetary gain following sleep deprivation. Moreover, participants homozygous for the ten-repeat DAT allele-linked to lower phasic dopamine activity-selectively demonstrated an increase in sensitivity to monetary loss within anterior insula following sleep loss. Together, these data reveal a mechanistic dependency on human of trait dopaminergic function in determining the interaction between sleep deprivation and neural processing of rewards and punishments. Such findings have clinical implications in disorders where the DAT genetic polymorphism presents a known risk factor with comorbid sleep disruption, including attention hyperactive deficit disorder and substance abuse.

Increased oxidative stress in children with attention deficit hyperactivity disorder

OBJECTIVES

The purpose of this study was to investigate oxidative stress in children with attention deficit hyperactivity disorder (ADHD).

METHODS

Total oxidant status (TOS), total antioxidant status (TAS), paraxonase-1 (PON-1) and arylesterase (ARE) activity were measured in 76 children (44 boys, 32 girls) diagnosed with ADHD according to the DSM-IV and 78 healthy children (46 boys, 32 girls).

RESULTS

Age and sex were similar between the groups (P > 0.05). TOS and the oxidative stress index (OSI) were higher in the patient group than the control group (P < 0.001). PON-1 (P = 0.002), ARE (P = 0.010) activity and TAS (P < 0.001) were lower in the patient group than the control group.

DISCUSSION

We found decreased PON-1, ARE activity and TAS, and increased TOS and OSI in children with ADHD. Our study showed that there is significantly increased oxidative stress in children with ADHD.

Measured Prenatal and Estimated Postnatal Levels of Polychlorinated Biphenyls (PCBs) and ADHD-Related Behaviors in 8-Year-Old Children

BACKGROUND

Epidemiologic studies of postnatal PCB exposure and behavior have not reported consistent evidence of adverse associations, possibly because of challenges in exposure estimation. We previously developed a pharmacokinetic model to improve estimation of children's PCB exposure.

OBJECTIVES

We aimed to assess whether estimated serum PCB levels in infancy are associated with attention deficit/hyperactivity disorder (ADHD)-related behaviors at 8 years of age among children whose cord serum PCB levels were previously shown to be associated with ADHD-related behaviors.

METHODS

We used a pharmacokinetic model to estimate monthly serum polychlorinated biphenyl (PCB)-153 levels in 441 infants (ages 1-12 months) based on parameters such as breastfeeding and cord serum PCB-153 levels. Behavior was evaluated at age 8 using the Conners' Rating Scale for Teachers (CRS-T). Associations between PCB-153 levels and ADHD-related CRS-T indices were assessed using multivariable quantile regression at the 50th and 75th percentiles of CRS-T scores, where higher percentiles reflect more adverse behaviors.

RESULTS

Cord serum PCB-153 levels (median, 38 ng/g lipids) were associated with ADHD-related behaviors, although statistical significance was observed with quantile regression models only at the 75th percentile. Associations with postnatal exposure estimates were attenuated. For example, hyperactive-impulsive behavior scores at age 8 years were 0.9 points (95% CI: 0.2, 2.5), 0.5 points (95% CI: 0.3, 2.3), and 0.3 points (95% CI: -0.2, 1.5) higher in association with interquartile range increases in serum PCB-153 at birth, 2 months, and 12 months of age, respectively.

CONCLUSIONS

Associations between estimated postnatal PCB-153 exposures and ADHD-related behaviors at 8 years of age were weaker than associations with PCB-153 concentrations measured in cord serum at birth.

CITATION

Verner MA, Hart JE, Sagiv SK, Bellinger DC, Altshul LM, Korrick SA. 2015. Measured prenatal and estimated postnatal levels of polychlorinated biphenyls (PCBs) and ADHD-related behaviors in 8-year-old children. Environ Health Perspect 123:888-894; http://dx.doi.org/10.1289/ehp.1408084.

The behavioural response of mice lacking NK₁ receptors to guanfacine resembles its clinical profile in treatment of ADHD

Background and Purpose

Mice with functional ablation of substance P-preferring neurokinin-1 receptors (NK1R−/− mice) display behavioural abnormalities resembling those in attention deficit hyperactivity disorder (ADHD). Here, we investigated whether the ADHD treatment, guanfacine, alleviated the hyperactivity and impulsivity/inattention displayed by NK1R−/− mice in the light/dark exploration box (LDEB) and 5-choice serial reaction–time task (5-CSRTT), respectively. Following reports of co-morbid anxiety in ADHD, we also investigated effects of guanfacine on anxiety-like behaviour displayed by NK1R−/− and wild-type (WT) mice in the elevated plus maze (EPM).

Experimental Approach

Mice were treated with guanfacine (0.1, 0.3 or 1.0 mg·kg⁻¹, i.p.), vehicle or no injection and tested in the 5-CSRTT or the LDEB. Only the lowest dose of guanfacine was used in the EPM assays.

Key Results

In the 5-CSRTT, a low dose of guanfacine (0.1 mg·kg⁻¹) increased attention in NK1R−/− mice, but not in WT mice. This dose did not affect the total number of trials completed, latencies to respond or locomotor activity in the LDEB. Impulsivity was decreased by the high dose (1.0 mg·kg⁻¹) of guanfacine, but this was evident in both genotypes and is likely to be secondary to a generalized blunting of behaviour. Although the NK1R−/− mice displayed marked anxiety-like behaviour, guanfacine did not affect the behaviour of either genotype in the EPM.

Conclusions and Implications

This evidence that guanfacine improves attention at a dose that did not affect arousal or emotionality supports our proposal that NK1R−/− mice express an attention deficit resembling that of ADHD patients.

Linked Articles

This article is part of a themed section on Animal Models in Psychiatry Research. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-20

Association of SNAP-25, SLC6A2, and LPHN3 with OROS methylphenidate treatment response in attention-deficit/hyperactivity disorder

OBJECTIVES

Our study aimed to identify the association of norepinephrine transporter gene (SLC6A2), synaptosomal-associated protein of the 25-kDa gene (SNAP-25), and latrophilin 3 gene (LPHN3) with osmotic-controlled release oral delivery system methylphenidate (OROS MPH) treatment response.

METHODS

One hundred thirty-nine children and adolescents with attention-deficit/hyperactivity disorder (ADHD) were recruited. We selected rs192303, rs3785143 in SLC6A2; rs3746544 (1065 T>G) in SNAP-25; and rs6551665, rs1947274, and rs2345039 in LPHN3 to examine the association of OROS MPH treatment response with each single nucleotide polymorphism. We first defined good response group when the Korean version of the ADHD rating scale score at 8 weeks was decreased for more than 50% of baseline scores and compared genotype frequencies in good response group with poor group. Second, we defined it when the Clinical Global Impression-Improvement score at 8 weeks was 1 or 2, and we also analyzed the genotype frequencies.

RESULTS

There was a significant association between the 1065 T>G of SNAP-25 gene and OROS MPH response, with the good response group defined by the Korean version of ADHD rating scale scores; 33.3% of the subjects with GG genotype showed a good response, whereas 74.7% of those with TT genotype and 72.5% of those with TG genotype showed good responses (P=0.034). SLC6A2 rs192303 was related with OROS MPH treatment response when we defined good treatment response by Clinical Global Impression-Improvement (P=0.009).

CONCLUSIONS

Our study suggested that SNAP-25 gene and SLC6A2 were involved with OROS MPH response.

Distinct lncRNA expression profiles in the prefrontal cortex of SD rats after exposure to methylphenidate

Methylphenidate (MPH) is a central nervous system stimulant that is widely used to treat attention deficit hyperactivity disorder (ADHD) and has been shown to improve attention, cognitive function and behaviors in both patients and animal models of ADHD. Even among normal healthy people, MPH can facilitate the consolidation of memories and improve declarative memory. Using microarray techniques, we aimed to find new pharmacology profile of MPH. A Làt maze experiment showed that locomotor activity and non-selective attention were affected by 2 weeks of exposure to MPH. Then, we identified long non-coding RNA (lncRNA) signatures in the prefrontal cortex of rats; 461 up-regulated lncRNAs and 97 down-regulated lncRNAs were found in the MPH-exposed group compared with the control group using fold-change >1.5. GO and KEGG pathway analyses indicated biological functions related to the metabolism of neural chemical compounds and nerve cell development. Furthermore, we reported changes in uc.173+ related to the UBE2B gene, which may affect neurite outgrowth and axonal regeneration. At the same time, MRAK081997 associated with the DHFR gene may be involved in axon regeneration in the rodent central nervous system through DNA methylation. Our study showed distinct expression profiles of lncRNAs in the normal rat prefrontal cortex after exposure to MPH, offering information for further research of MPH and may suggesting a new therapeutic target for ADHD.

Intra-Individual Response Variability Assessed by Ex-Gaussian Analysis may be a New Endophenotype for Attention-Deficit/Hyperactivity Disorder

Intra-individual variability of response times (RTisv) is considered as potential endophenotype for attentional deficit/hyperactivity disorder (ADHD). Traditional methods for estimating RTisv lose information regarding response times (RTs) distribution along the task, with eventual effects on statistical power. Ex-Gaussian analysis captures the dynamic nature of RTisv, estimating normal and exponential components for RT distribution, with specific phenomenological correlates. Here, we applied ex-Gaussian analysis to explore whether intra-individual variability of RTs agrees with criteria proposed by Gottesman and Gould for endophenotypes. Specifically, we evaluated if normal and/or exponential components of RTs may (a) present the stair-like distribution expected for endophenotypes (ADHD > siblings > typically developing children (TD) without familiar history of ADHD) and (b) represent a phenotypic correlate for previously described genetic risk variants. This is a pilot study including 55 subjects (20 ADHD-discordant sibling-pairs and 15 TD children), all aged between 8 and 13 years. Participants resolved a visual Go/Nogo with 10% Nogo probability. Ex-Gaussian distributions were fitted to individual RT data and compared among the three samples. In order to test whether intra-individual variability may represent a correlate for previously described genetic risk variants, VNTRs at DRD4 and SLC6A3 were identified in all sibling-pairs following standard protocols. Groups were compared adjusting independent general linear models for the exponential and normal components from the ex-Gaussian analysis. Identified trends were confirmed by the non-parametric Jonckheere-Terpstra test. Stair-like distributions were observed for μ (p = 0.036) and σ (p = 0.009). An additional "DRD4-genotype" × "clinical status" interaction was present for τ (p = 0.014) reflecting a possible severity factor. Thus, normal and exponential RTisv components are suitable as ADHD endophenotypes.

Attention Deficit Hyperactivity Disorder in the Light of the Epigenetic Paradigm

Attention deficit hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder characterized by a definite behavioral pattern that might lead to performance problems in the social, educational, or work environments. In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, the symptoms of ADHD were restricted to those associated with cognitive (attention deficit) and behavioral (hyperactivity/impulsivity) deficits, while deficient emotional self-regulation, a relevant source of morbidity, was left out. The etiology of it is complex, as its exact causes have not yet been fully elucidated. ADHD seems to arise from a combination of various genetic and environmental factors that alter the developing brain, resulting in structural and functional abnormalities. The aim of this paper was to review epigenetics and ADHD focused on how multidimensional mechanisms influence the behavioral phenotype.

Bipolar disorder and parental psychopathology

PURPOSE

Few population-based studies have examined the association between parental psychopathology and bipolar disorder (BPD) in offspring. One limitation is lack of control for potential confounding by indicators of parental socio-economic status or maternal smoking during pregnancy. Furthermore, none of them included analyses restricted to parental diagnoses received prior to the birth of the offspring. Associations could not be affected by child-related factors affecting the parent in such analyses. This study explores associations between those parental psychiatric disorders diagnosed at any point of time as well as those diagnosed before offspring birth, and BPD in offspring.

METHODS

In this nested case-control study, we identified 1,861 cases, age up to 25 years, 3,643 matched controls, and their parents from Finnish national registers. The associations were examined using conditional logistic regression, calculating odds ratios (OR) and adjusting for region of birth, parental age and education and mother's smoking during pregnancy.

RESULTS

Anytime diagnosed parental disorders associating with BPD in offspring (95% confidence interval) were BPD [OR (maternal) 5.2 (2.52-10.62); OR (paternal) 8.1 (3.77-17.26)], schizophrenia and related psychoses [OR (maternal) 3.1 (1.69-5.84); OR (paternal) 4.5 (1.97-10.27)], other affective disorders [OR (maternal) 3.0 (2.08-4.21); OR (paternal) 3.0 (1.97-4.47)] and maternal anxiety disorders OR 2.6 (1.08-6.42). Statistically significant associations were also found for parental schizophrenia and related psychoses, and other affective disorders, diagnosed before offspring birth.

CONCLUSIONS

BPD is associated with many parental psychiatric disorders, particularly BPD and schizophrenia and related psychoses. The associations must be partially due to child-independent factors. Covariate adjustments had only a minor impact on the associations.

Differential perinatal risk factors in children with attention-deficit/hyperactivity disorder by subtype

We compared the attention-deficit/hyperactivity disorder(ADHD) combined subtype (ADHD-C) to the ADHD inattentive subtype (ADHD-I) in terms of genetic, perinatal, and developmental risk factors as well as clinical and neuropsychological characteristics. A total of 147 children diagnosed with ADHD between the ages of 6 and 15 years participated in this study. The parents of the children completed the structured diagnostic interview, the ADHD Rating Scale-IV, the Children's Behavior Checklist, and structured questionnaires on perinatal risk factors, and the children underwent a neuropsychological test and were genotyped. A total of 502 children without ADHD were recruited from the community as a healthy control group. The ADHD-C children showed more severe externalizing symptoms, showed more deficits in a continuous performance test, and were more likely to have comorbid disorders. Maternal stress during pregnancy, postpartum depression, and changes in the primary caretaker during first 3 years were significantly associated with both ADHD-I and ADHD-C. The ADHD-I group was less likely to have received regular prenatal check-ups and more likely to have had postnatal medical illness than the ADHD-C group. There were no significant differences in the genotype frequencies of the dopamine transporter (DAT1) and the serotonin transporter -linked polymorphic region (5-HTTLPR) polymorphisms between ADHD-I and ADHD-C groups. This study shows that the inattentive subtype of ADHD is different from the combined subtype in many parameters including severity of symptoms, comorbidity, neuropsychological characteristics, and environmental risk factors.

Detection of auto-antibodies to DAT in the serum: interactions with DAT genotype and psycho-stimulant therapy for ADHD

Interest is rising for auto-immune contribution in neuro-psychiatry. We evaluated the auto-antibodies against dopamine transporter (DAT aAbs) in 61 children (46 ADHD who met DSM-IV-TR criteria, 15 healthy controls).

METHODS

ADHD patients were assigned, according to severity, either to a non-pharmacological therapy (NPT, N=32) or to a pharmacological treatment (PT, N=14) with methylphenidate (MPH). In ADHD children, blood samples were withdrawn twice, at recruitment (T0 basal) and after 6 weeks (T1); following 16 excluded subjects, DAT genotype was characterized (9-repeat or 10-repeat alleles; N=15 each). After 18 months of NPT or PT, some patients (carrying at least one 9-repeat allele) were blood sampled again (T2), for comparison with healthy controls (final n=8) RESULTS: Compared to NPT, basal DAT aAbs titers were higher within most severe patients (then assigned to PT), specifically if carrying a DAT 10/10 genotype. DAT aAbs levels of NPT group resulted highly correlated with distinct subscales of Conners' Parent/Teacher Scales (Rs>0.34), especially within DAT 10/10 genotype (Rs>0.53). While T1 titers were elevated over T0 baseline for NPT children, such an increase was not observed in PT patients carrying at least one 9-repeat allele, who also showed behavioral response to subchronic MPH. After 12-24 months of MPH exposure, DAT aAbs titers in PT subjects were comparable to those of healthy controls, while titers remained significantly elevated in NPT patients. Data warrant further research on serum DAT aAbs, which could be used to confirm ADHD diagnosis and/or to monitor therapeutic efficacy of MPH.

Atomoxetine reduces hyperactive/impulsive behaviours in neurokinin-1 receptor 'knockout' mice

Background

Mice with functional ablation of the neurokinin-1 receptor gene (NK1R^−/−) display behavioural abnormalities which resemble the hyperactivity, inattention and impulsivity seen in Attention Deficit Hyperactivity Disorder (ADHD). Here, we investigated whether the established ADHD treatment, atomoxetine, alleviates these abnormalities when tested in the light/dark exploration box (LDEB) and 5-Choice Serial Reaction-Time Task (5-CSRTT).

Methods

Separate cohorts of mice were tested in the 5-CSRTT and LDEB after treatment with no injection, vehicle or atomoxetine (5-CSRTT: 0.3, 3 or 10 mg/kg; LDEB: 1, 3 or 10 mg/kg).

Results

Atomoxetine reduced the hyperactivity displayed by NK1R^−/− mice in the LDEB at a dose (3 mg/kg) which did not affect the locomotor activity of wildtypes. Atomoxetine (10 mg/kg) also reduced impulsivity in NK1R^−/− mice, but not wildtypes, in the 5-CSRTT. No dose of drug affected attention in either genotype.

Conclusions

This evidence that atomoxetine reduces hyperactive/impulsive behaviours in NK1R^−/− mice consolidates the validity of using NK1R^−/− mice in research of the aetiology and treatment of ADHD.

•

We compared the behavioural response to atomoxetine in NK1R^−/− and wildtype mice.

•

Atomoxetine reduced hyperactivity and impulsivity in NK1R^−/− mice but not wildtypes.

•

This was not explained by changes in animals' emotional status or motor motivation.

•

NK1R^−/− mice are more sensitive to atomoxetine (an ADHD treatment) than wildtypes.

•

These findings consolidate the NK1R^−/− mouse model of ADHD.

Molecular genetic studies of ADHD and its candidate genes: a review

Attention-deficit/hyperactivity disorder (ADHD) is a common childhood-onset psychiatric disorder with high heritability. In recent years, numerous molecular genetic studies have been published to investigate susceptibility loci for ADHD. These results brought valuable candidates for further research, but they also presented great challenge for profound understanding of genetic data and general patterns of current molecular genetic studies of ADHD since they are scattered and heterogeneous. In this review, we presented a retrospective review of more than 300 molecular genetic studies for ADHD from two aspects: (1) the main achievements of various studies were summarized, including linkage studies, candidate-gene association studies, genome-wide association studies and genome-wide copy number variation studies, with a special focus on general patterns of study design and common sample features; (2) candidate genes for ADHD have been systematically evaluated in three ways for better utilization. The thorough summary of the achievements from various studies will provide an overview of the research status of molecular genetics studies for ADHD. Meanwhile, the analysis of general patterns and sample characteristics on the basis of these studies, as well as the integrative review of candidate ADHD genes, will propose new clues and directions for future experiment design.

Behavioral and pharmacological evaluation of a selectively bred mouse model of home cage hyperactivity

Daily levels of physical activity vary greatly across individuals and are strongly influenced by genetic background. While moderate levels of physical activity are associated with improved physical and mental health, extremely high levels of physical activity are associated with behavioral disorders such as attention deficit hyperactivity disorder (ADHD). However, the genetic and neurobiological mechanisms relating hyperactivity to ADHD or other behavioral disorders remain unclear. Therefore, we conducted a selective breeding experiment for increased home cage activity starting with a highly genetically variable population of house mice and evaluated the line for correlated responses in other relevant phenotypes. Here we report results through Generation 10. Relative to the Control line, the High-Active line traveled approximately 4 times as far in the home cage (on days 5 and 6 of a 6-day test), displayed reduced body mass at maturity, reduced reproductive success, increased wheel running and open field behavior, decreased performance on the rotarod, decreased performance on the Morris water maze that was not rescued by acute administration of d-amphetamine, reduced hyperactivity from chronically administered low clinical doses of d-amphetamine, and increased numbers of new cells and neuronal activation of the dentate gyrus. Standardized phenotypic differences between the lines were compared to estimates expected from genetic drift to evaluate whether the line differences could have resulted from random effects as opposed to correlated responses to selection. Results indicated line differences in body mass and locomotor responses to low doses of amphetamine were more likely due to selection than drift. The efficacy of low doses of d-amphetamine in ameliorating hyperactivity support the High-Active line as a useful model for exploring the etiology of hyperactivity-associated comorbid behavioral disorders.

Human endogenous retroviruses and ADHD

OBJECTIVES

Several lines of evidences suggest that human endogenous retroviruses (HERVs) are implicated in the development of many complex diseases with a multifactorial aetiology and a strong heritability, such as neurological and psychiatric diseases. Attention deficit hyperactivity Disorder (ADHD) is a neurodevelopmental disorder that results from a complex interaction of environmental, biological and genetic factors. Our aim was to analyse the expression levels of three HERV families (HERV-H, K and W) in patients with ADHD.

METHODS

The expression of retroviral mRNAs from the three HERV families was evaluated in peripheral blood mononuclear cells (PBMCs) from 30 patients with ADHD and 30 healthy controls by quantitative RT-PCR.

RESULTS

The expression levels of HERV-H are significantly higher in patients with ADHD compared to healthy controls, while there are no differences in the expression levels of HERV-K and W.

CONCLUSIONS

Since the ADHD aetiology is due to a complex interaction of environmental, biological and genetic factors, HERVs may represent one link among these factors and clinical phenotype of ADHD. A future confirmation of HERV-H overexpression in a larger number of ADHD patients will make possible to identify it as a new parameter for this clinical condition, also contributing to deepen the study on the role of HERVs in the neurodevelopment diseases.

Underdiagnosis of attention-deficit/hyperactivity disorder in adult patients: a review of the literature

OBJECTIVE

To raise awareness of attention-deficit/hyperactivity disorder (ADHD) as an underdiagnosed, undertreated, often comorbid, and debilitating condition in adults.

DATA SOURCES

PubMed was searched using combinations of keywords, including ADHD, adult, diagnosis, identify, prevalence, and comorbid, to find articles published between 1976 and 2013.

STUDY SELECTION

In total, 99 articles were selected for inclusion on the basis of their relevance to the objective and importance to and representation of ADHD research, including international guidelines for adults with ADHD.

RESULTS

In a large proportion of children with ADHD, symptoms persist into adulthood. However, although adults with ADHD often experience chaotic lifestyles, with impaired educational and vocational achievement and higher risks of substance abuse and imprisonment, many remain undiagnosed and/or untreated. ADHD is usually accompanied by other psychiatric comorbidities (such as major depressive disorder, anxiety disorder, and alcohol abuse). Indeed, adults with ADHD are more likely to present to a psychiatric clinic for treatment of their comorbid disorders than for ADHD, and their ADHD symptoms are often mistaken for those of their comorbidities. Untreated ADHD in adults with psychiatric comorbidities leads to poor clinical and functional outcomes for the patient even if comorbidities are treated. Effective treatment of adults' ADHD improves symptoms, emotional lability, and patient functioning, often leading to favorable outcomes (eg, safer driving, reduced criminality). A few medications have now been approved for use in adults with ADHD, while a multimodal approach involving psychotherapy has also shown promising results. Conclusions General psychiatrists should familiarize themselves with the symptoms of ADHD in adults in order to diagnose and manage ADHD and comorbidities appropriately in these patients.

Neuroimaging and ADHD: fMRI, PET, DTI findings, and methodological limitations

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by pervasive and developmentally inappropriate levels of inattention, impulsivity, and hyperactivity. There is no conclusive cause of ADHD although a number of etiologic theories have been advanced. Research across neuroanatomical, neurochemical, and genetic disciplines collectively support a physiological basis for ADHD and, within the past decade, the number of neuroimaging studies concerning ADHD has increased exponentially. The current selective review summarizes research findings concerning ADHD using functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and diffusion tensor imaging (DTI). Although these technologies and studies offer promise in helping to better understand the physiologic underpinnings of ADHD, they are not without methodological problems, including inadequate sensitivity and specificity for psychiatric disorders. Consequently, neuroimaging technology, in its current state of development, should not be used to inform clinical practice.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

Diagnostic shortfalls in early childhood chronic stress: a review of the issues

Clinical effects of early childhood chronic stress should be regarded as causing a developmental brain injury. However, current diagnostic constructs fail to capture the associated disabilities in emotional-behavioural regulation of stress and attachment functions adequately. We first focus on neglect as a prototypical early childhood chronic stressor; next we explore clinical associations of neglect; and finally we cite research pertaining to possible underlying pathophysiology of the effects of early childhood chronic stress. In addition, we discuss diagnostic labels that children with histories of early childhood neglect commonly acquire, and implications for treatment.