DAT1 methylation is associated with methylphenidate response on oppositional and hyperactive-impulsive symptoms in children and adolescents with ADHD

G-quadruplex formation at human DAT1 gene promoter: Effect of cytosine methylation

The dopamine transporter gene (DAT1), a recognized genetic risk factor for attention deficit hyperactivity disorder (ADHD) is principally responsible for the regulation of dopamine synaptic levels and serves as a key target in many psychostimulants drugs. DAT1 gene methylation has been considered an epigenetic marker in ADHD. The identification of G-rich sequence motifs potential to form G-quadruplexes is correlated with functionally important genomic regions. Herein, biophysical and biochemical techniques are employed to investigate the structural polymorphism along with the effect of cytosine methylation on a 26-nt G-rich sequence present in the promoter region of the DAT1 gene. The gel electrophoresis, circular dichroism spectroscopy, and UV-thermal melting data are well correlated and conclude the formation of a parallel (bimolecular), as well as antiparallel (tetramolecular) G-quadruplex in Na⁺ solution. Interestingly, the existence of uni-, bi-, tri-, and tetramolecular quadruplex structures in K⁺ solution exhibited only the parallel type G-quadruplex. The results demonstrate that in presence of either cation (Na⁺ or K⁺) the cytosine methylation reserved the structural topologies unaltered. However, methylation lowers the thermal stability of G-quadruplexes and the duplex structures, as well. These findings provide insights to understand the regulatory mechanisms underlying the formation of the G-quadruplex structure induced by DNA methylation.

Epigenetic Analysis of the Dopamine Transporter Gene DAT1 with a Focus on Personality Traits in Athletes

Human phenotypes (traits) are determined by the selective use of a person's unique genotype (DNA sequence), following exposure to environmental stimuli, such as exercise. Inducing profound changes in epigenetics may be an underlying factor of the beneficial effects of exercise. This study aimed to investigate the association between methylation in the promoter region of the DAT1 gene and personality traits measured by the NEO-FFI questionnaire in a group of athletes. The study group included 163 athletes, and the control group consisted of 232 non-athletes. The obtained results show several significant differences between the studied groups of subjects. The Extraversion scale and the Conscientiousness scale results of the NEO-FFI are significantly higher in the group of athletes compared to controls. The total methylation and the number of methylated islands in the promoter region of the DAT1 gene are higher in the study group. Pearson's linear correlation between the total methylation, the number of methylated islands and the NEO-FFI shows significant results for the Extraversion and Agreeability scales. The total methylation and the number of methylated islands in the promoter region of the DAT1 gene are higher in the study group. Pearson's linear correlation between the total methylation, the number of methylated islands and the NEO-FFI shows significant results for the Extraversion and Agreeability scales. Our analysis of the methylation status of individual CpG sites revealed a new direction of research into the biological aspects of regulating dopamine release and personality traits in people practicing sports.

Can Epigenetics Predict Drug Efficiency in Mental Disorders?

Psychiatric disorders affect millions of individuals and their families worldwide, and the costs to society are substantial and are expected to rise due to a lack of effective treatments. Personalized medicine-customized treatment tailored to the individual-offers a solution. Although most mental diseases are influenced by genetic and environmental factors, finding genetic biomarkers that predict treatment efficacy has been challenging. This review highlights the potential of epigenetics as a tool for predicting treatment efficacy and personalizing medicine for psychiatric disorders. We examine previous studies that have attempted to predict treatment efficacy through epigenetics, provide an experimental model, and note the potential challenges at each stage. While the field is still in its infancy, epigenetics holds promise as a predictive tool by examining individual patients' epigenetic profiles in conjunction with other indicators. However, further research is needed, including additional studies, replication, validation, and application beyond clinical settings.

Methylation Dynamics on 5'-UTR of DAT1 Gene as a Bio-Marker to Recognize Therapy Success in ADHD Children

Attention-deficit/hyperactivity disorder (ADHD), a neuropsychiatric condition characterized by inattention, hyperactivity, and impulsivity, afflicts 5% of children worldwide. Each ADHD patient presents with individual cognitive and motivational peculiarities. Furthermore, choice of appropriate therapy is still up to clinicians, who express somewhat qualitative advice on whether a child is being successfully cured or not: it would be more appropriate to use an objective biomarker to indicate whether a treatment led to benefits or not. The aim of our work is to search for such clinical biomarkers. We recruited 60 ADHD kids; psychopathological scales were administered at recruitment and after six weeks of therapy. Out of such a cohort of ADHD children, we rigorously extracted two specific subgroups; regardless of the initial severity of their disease, we compared those who obtained the largest improvement (ΔCGAS > 5) vs. those who were still characterized by a severe condition (CGAS < 40). After such a therapy, methylation levels of DNA extracted from buccal swabs were measured in the 5'-UTR of the DAT1 gene. CpGs 3 and 5 displayed, in relation to the other CpGs, a particular symmetrical pattern; for "improving" ADHD children, they were methylated together with CpG 2 and CpG 6; instead, for "severe" ADHD children, they accompanied a methylated CpG 1. These specific patterns of methylation could be used as objective molecular biomarkers of successful cures, establishing if a certain therapy is akin to a given patient (personalized medicine). Present data support the use of post-therapy molecular data obtained with non-invasive techniques.

Network pharmacology, molecular docking, and experimental validation to explore the potential mechanism of Long Mu Qing Xin mixture for the treatment of attention deficit hyperactivity disorder

Background: Long Mu Qing Xin Mixture (LMQXM) has shown potentially positive effects in alleviating attention deficit hyperactivity disorder (ADHD); however, the action mechanism is still not fully understood. This study aimed to predict the potential mechanism of LMQXM for ADHD using network pharmacology and molecular docking, which were then validated using animal experiments.

Methods: Network pharmacology and molecular docking techniques were used to predict the core targets and potential pathways of LMQXMQ for ADHD, and KEGG pathway enrichment analysis revealed the potential significance of dopamine (DA) and cyclic adenosine monophosphate (cAMP) signaling pathways. To verify the hypothesis, we conducted an animal experiment. In the animal experiment, the young spontaneously hypertensive rats (SHRs) were randomly divided into the model group (SHR), the methylphenidate hydrochloride group (MPH, 4.22 mg/kg), and 3 LMQXM groups (low-dose (LD) group, 5.28 ml/kg; medium-dose (MD) group, 10.56 ml/kg; and high-dose (HD) group, 21.12 ml/kg), and administered by gavage for 4 weeks; the WKY rats were set as the control group. The open field test and Morris water maze test were used to evaluate the behavioral performance of rats, high performance liquid chromatography mass spectrometry (LC-MS) was used to analyze DA levels in the prefrontal cortex (PFC) and striatum of rats, ELISA was used to detect cAMP concentrations in the PFC and striatum, and immunohistochemistry and qPCR were used to analyze positive cell expression and mRNA expression for indicators related to DA and cAMP pathways.

Results: The results showed that beta-sitosterol, stigmasterol, rhynchophylline, baicalein, and formononetin might be key components of LMQXM for ADHD and that these components bind well to the core targets, DA receptors (DRD1 and DRD2). Furthermore, LMQXM might act through the DA and cAMP signaling pathways. In the animal experiment, we found that MPH and LMQXM-MD controlled hyperactivity and improved learning and memory in SHRs, while LMQXM-HD only controlled hyperactivity in SHRs; meanwhile, MPH and LMQXM-MD upregulated DA and cAMP levels, mean optical density (MOD) of cAMP, and MOD and mRNA expression of DRD1 and PKA in the prefrontal cortex (PFC) and striatum of SHRs, while LMQXM-LD and LMQXM-HD upregulated DA and cAMP levels in the striatum, MOD of cAMP in the PFC, and mRNA expression of PKA in the PFC. However, we did not find a significant regulatory effect of LMQXM on DRD2.

Conclusion: To sum up, this study demonstrated that LMQXM may increase DA levels mainly by activating the cAMP/PKA signaling pathway through DRD1, thereby controlling the behavioral disorders of SHRs, which is most effective at moderate doses, and this may be a key mechanism for LMQXM in the treatment of ADHD.

Epigenetics and ADHD

There is robust evidence of genetic susceptibility to Attention-Deficit Hyperactivity Disorder (ADHD); however, there still remains significant variability that is not attributable to genetic factors. The emerging field of epigenetics is beginning to reveal how genotypic expression can be mediated by an array of variables including external environmental exposure, inter-individual developmental variation, and by the genome itself. Epigenetic modification plays a central role in neurobiological and developmental processes, and disturbances to these processes can have implications for a range of mental health problems. Although the field is still in its early days, this chapter will discuss the current standing of epigenetic research into ADHD. Firstly, key relevant epigenetic processes will be discussed. This will be followed by an overview of the key findings to date investigating the role of epigenetics in ADHD. Human studies have included the theory-driven approach of candidate-gene studies (CGS), as well as the increasingly popular exploratory approach of epigenome-wide association studies (EWAS). Overall, the findings are heterogeneous. However, it is possible that with more longitudinal studies and better characterised cohorts, both predictive and protective links between epigenetic processes and ADHD will be revealed.

The Role of Epigenetics in the Pathogenesis and Potential Treatment of Attention Deficit Hyperactivity Disorder

There is increasing evidence that dysregulated epigenetic mechanisms of gene expression are involved in the pathogenesis of attention deficit hyperactivity disorder (ADHD). This review presents a comprehensive summary of the current state of research on the role of epigenetics in the pathogenesis of ADHD. The potential role of epigenetic drugs in the treatment of ADHD is also reviewed. Several studies suggest that there are epigenetic abnormalities in preclinical models of ADHD and in ADHD patients. Regarding DNA methylation, many studies have reported DNA hypermethylation. There is evidence that there is increased histone deacetylation in ADHD patients. Abnormalities in the expression of microRNAs (miRNAs) in ADHD patients have also been found. Some currently used drugs for treating ADHD, in addition to their more well-established mechanisms of action, have been shown to alter epigenetic mechanisms of gene expression. Clinical trials of epigenetic drugs in patients with ADHD report favorable results. These data suggest that abnormal epigenetic mechanisms of gene expression may be involved in the pathogenesis of ADHD. Drugs acting on epigenetic mechanisms may be a potential new class of drugs for treating ADHD.

Prenatal risk factors and genetic causes of ADHD in children

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) is a common disease among children; it affected 5-7% of the population in 2015. ADHD is a multifactorial disease, and its etiology is still not clearly understood.

DATA SOURCES

This narrative review has been done by searching the PubMed and Embase databases using attention deficit/hyperactivity disorder, ADHD, risk factors; genetics; pediatrics; psychiatrics as keywords.

RESULTS

ADHD is considered to be a hereditary disorder in which genes play the fundamental role in the pathogenesis; however, findings from genetic-environmental studies support the hypothesis that genetic factors can exert effects on an individual's condition by determining his/her responses to environmental exposures, especially those during the prenatal stage.

CONCLUSION

ADHD is considered as a hereditary disorder in which genes and prenatal risk factors play fundamental roles in the pathogenesis.

Children’s ADHD and Dysregulation Problems, DAT1 Genotype and Methylation, and their Interplay with Family Environment

Background

International literature has underlined the complex interplay between genetic and environmental variables in shaping children’s emotional-behavioral functioning.

Objective

This study aimed to explore the dynamic relationship between children’s Dopamine Transporter (DAT1) genotype and methylation, and maternal and paternal affective environment, on children’s Attention Deficit Hyperactivity Disorder (ADHD) problems and dysregulation problems.

Method

In a community sample of 76 families with school-aged children, we assessed children’s DAT1 genotype and methylation, their own ADHD problems and dysregulation profile (CBCL 6–18 DP), and maternal and paternal psychopathological risk, parenting stress, and marital adjustment. Hierarchical regressions were carried out to verify the possible moderation of children’s genotype on the relationship between children’s methylation and psychopathological risk, parental environment and children’s methylation, and parental environment and children’s psychopathological risk.

Results

The levels of methylation at M1 CpG significantly predicted ADHD problems among children with 10/10 genotype, whereas high levels of methylation at M6 CpG predicted low ADHD problems for children with 9/x genotype. High levels of methylation at M3 CpG were associated with high scores of CBCL DP. DAT1 genotype moderated the relationship between maternal and paternal variables with children’s methylation and psychopathological risk. The scores of maternal and paternal Dyadic Adjustment Scale showed indirect effects on children’s methylation and psychopathological risk in relation to those exerted by risk factors.

Conclusion

Our study has supported the emerging evidence on the complex nature of children’s emotional-behavioral functioning and the associated risk and protective factors, with important implications for the planning of preventive programs.

Developmental exposure to methylmercury and ADHD, a literature review of epigenetic studies

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects the competence of academic performance and social wellness in children and adults. The causes of ADHD are unclear. Both genetic and environmental factors contribute to the development of ADHD. The behavioral impairments in ADHD are associated with epigenetic changes in genes that are important for neurodevelopment. Among environmental causes of ADHD, the neurotoxin methylmercury (MeHg) is associated with an increased risk for ADHD. Developing children are susceptible to neurotoxic effects of prenatal MeHg exposure. Human epidemiology studies have shown that prenatal MeHg exposure could invoke epigenetic changes in genes that are involved in ADHD. In addition, the pathogenesis of ADHD involves dopaminergic system, which is a target of developmental MeHg exposure. MeHg-induced alterations in the dopaminergic system have a profound impact on behavioral functions in adults. As a trace level of MeHg (around nM) can induce long-lasting behavioral alterations, potential mechanisms of MeHg-induced functional changes in the dopaminergic system may involve epigenetic mechanisms. Here, we review the relevant evidence on developmental MeHg exposures and the risk for ADHD. We also point out research gaps in understanding environmental causes of ADHD.

Influence of DAT1 Promotor Methylation on Sports Performance

In the mammalian genome, DNA methylation is an epigenetic mechanism involving the transfer of a methyl group onto the C5 position of the cytosine to form 5-methylcytosine. DNA methylation regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factors (TFs) to DNA. As there are still many questions concerning the role of methylation in creating personality, we concentrated on searching for such associations. The research group was 100 sports male subjects (mean age = 22.88, SD = 6.35), whereas the control group included 239 healthy male volunteers matched for age (mean age = 21.69, SD = 3.39), both of European origin. The methods used in our research were as follows: DNA isolation, methylation-specific PCR, sequencing chromatophores, all conducted according to the manufacturer’s procedure. To evaluate personality traits, the NEO Five-Factor Personality Inventory (NEO-FFI) and STAI Inventory were used. We observed the existence of a statistically significant correlation for all the aspects of personality covered and CpG islands’ methylation. Nonetheless, we think that the tested group and the number of tested promotor islands in the DAT1 gene are still too small to make explicit conclusions, so it needs further profound analysis.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

DNA methylation signature as a biomarker of major neuropsychiatric disorders

DNA methylation is a broadly-investigated epigenetic modification that has been considered as a heritable and reversible change. Previous findings have indicated that DNA methylation regulates gene expression in the central nervous system (CNS). Also, disturbance of DNA methylation patterns has been associated with destructive consequences that lead to human brain diseases such as neuropsychiatric disorders (NPDs). In this review, we comprehensively discuss the mechanism and function of DNA methylation and its most recent associations with the pathology of NPDs-including major depressive disorder (MDD), schizophrenia (SZ), autism spectrum disorder (ASD), bipolar disorder (BD), and attention/deficit hyperactivity disorder (ADHD). We also discuss how heterogeneous findings demand further investigations. Finally, based on the recent studies we conclude that DNA methylation status may have implications in clinical diagnostics and therapeutics as a potential epigenetic biomarker of NPDs.

Association between COMT methylation and response to treatment in children with ADHD

BACKGROUND

COMT had been considered a promising candidate gene in pharmacogenetic studies in ADHD; yet the findings from these studies have been inconsistent. Part of these inconsistencies could be related to epigenetic mechanisms (including DNA methylation). Here we investigated the role of genetic variants of the COMT gene on the methylation levels of CpG sites in the same gene and explored the effect of methylation on methylphenidate (MPH) and placebo (PBO) response in children with ADHD.

METHODS

Two hundred and thirty children with ADHD (6-12 years) participated in a randomized, double-blind, placebo-controlled crossover trial with MPH. Univariate analysis was performed to examine the associations between genotypes in the COMT gene and DNA methylation in the same genetic loci. Association between the DNA methylation of 11 CpG sites and PBO/MPH responses were then assessed using spearman's correlation analysis in 212 children. Multiple linear regression analyses were performed to test the interaction between these factors while accounting for sex.

RESULTS

Associations were observed between specific genetic variants and methylation level of cg20709110. Homozygous genotypes of GG (rs6269), CC (rs4633), GG (rs4818), Val/Val (rs4680) and the haplotype (ACCVal/GCGVal) were significantly associated with higher level of methylation. This CpG showed a significant correlation with placebo response (r = -0.15, P = 0.045) according to the teachers' evaluation, and a close-to significance correlation with response to MPH according to parents' evaluation (r = -0.134, p = 0.051). Regression analysis showed that in the model including rs4818, sex and DNA methylation of cg20709110 contributed significantly to treatment response.

CONCLUSIONS

These preliminary results could provide evidence for the effect of genetic variations on methylation level and the involvement of the epigenetic variation of COMT loci in modulating the response to treatment in ADHD.

TRIAL REGISTRATION

clinicaltrials.gov, number NCT00483106.

DAT1 and Its Psychological Correlates in Children with Avoidant/Restrictive Food Intake Disorder: A Cross-Sectional Pilot Study

International research has underlined the role played by children’s and maternal psychopathological symptoms on the onset of avoidant/restrictive food intake disorder (ARFID) in early childhood. No study has considered the possible interplay between children’s dopamine transporter (DAT1) genotype and methylation, dysregulation problems and maternal psychopathological risk. This study aimed to investigate the complex relationship between these variables, considering the possible mediation role played by children’s DAT1 methylation on the relationship between mothers’ psychopathological risk and children’s dysregulation problems, moderated by children’s DAT1 genotype. Our sample consisted of 94 early children and their mothers, divided into four subgroups, based on children’s ARFID subtypes (irritable/impulsive (I/I), sensory food aversions (SFA), post-traumatic feeding disorders subtypes (PTFD), and a non-clinical group (NC)). We addressed children’s dysregulation problems and maternal psychopathological risk, and collected children’s DNA through buccal swabs. Results showed that children’s 9/x genotype was associated with PTFD and NC groups, whereas the 10/10 genotype was associated with the SFA group, with large effect size. There were significant large differences in the study groups on children’s DAT1 total methylation, children’s dysregulation problems, and maternal psychopathological risk. Children’s DAT1 methylation did not mediate the relationship between mother’s psychopathological risk and children’s dysregulation problems, but there was a significant large direct effect. Children’s 9/x genotype moderated the relationship between maternal psychopathological risk and children’s DAT1 methylation but, respectively, with a large and small effect. Our pilot study suggested that the relationship between children’s DAT1 genotype and methylation, dysregulation problems, and maternal psychopathological risk has a crucial contribution to ARFID.

Association of norepinephrine transporter methylation with in vivo NET expression and hyperactivity-impulsivity symptoms in ADHD measured with PET

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder with a robust genetic influence. The norepinephrine transporter (NET) is of particular interest as it is one of the main targets in treatment of the disorder. As ADHD is a complex and polygenetic condition, the possible regulation by epigenetic processes has received increased attention. We sought to determine possible differences in NET promoter DNA methylation between patients with ADHD and healthy controls. DNA methylation levels in the promoter region of the NET were determined in 23 adult patients with ADHD and 23 healthy controls. A subgroup of 18 patients with ADHD and 18 healthy controls underwent positron emission tomography (PET) with the radioligand (S,S)-[¹⁸F]FMeNER-D₂ to quantify the NET in several brain areas in vivo. Analyses revealed significant differences in NET methylation levels at several cytosine-phosphate-guanine (CpG) sites between groups. A defined segment of the NET promoter ("region 1") was hypermethylated in patients in comparison with controls. In ADHD patients, a negative correlation between methylation of a CpG site in this region and NET distribution in the thalamus, locus coeruleus, and the raphe nuclei was detected. Furthermore, methylation of several sites in region 1 was negatively associated with the severity of hyperactivity-impulsivity symptoms. Our results point to an epigenetic dysregulation in ADHD, possibly due to a compensatory mechanisms or additional factors involved in transcriptional processing.

Emotional-Behavioral Regulation, Temperament and Parent-Child Interactions Are Associated with Dopamine Transporter Allelic Polymorphism in Early Childhood: A Pilot Study

International research has highlighted the role played by individual genetic polymorphism, children’s emotional-behavioral functioning, and quality of parent–child feeding interaction in shaping children’s development. Few studies have focused on the dopamine transporter (DAT1) gene in these processes. In a community sample of 81 families with young children aged between 19 and 28 months (37 males and 44 females), this pilot study aimed to explore possible relationships between children’s DAT1 genotype (9/x: 9/9, 9/19 contrasted to 10/10), their own psychological profiles, parental psychopathological risk, and the quality of mother–child and father–child feeding interactions. Children’s DAT1 genotype was assessed collecting DNA through buccal; children’s temperament and emotional-behavioral regulation, and parental psychopathological risk were assessed, respectively, through report-form and self-report instruments; then, dyadic exchanges were videotaped during a mealtime, and coded based on the Scala di Valutazione dell′Interazione Alimentare (SVIA). Results showed significant differences in the variables under study based on children’s DAT1 genotype, with a higher risk associated with the 10/10. Our findings have provided preliminary new evidence on the relationship between a different child’s polymorphisms, their own emotional-behavioral functioning, and the quality of the family environment, with important implications for the planning of more targeted prevention programs.

Association between DNA methylation and ADHD symptoms from birth to school age: a prospective meta-analysis

Attention-deficit and hyperactivity disorder (ADHD) is a common childhood disorder with a substantial genetic component. However, the extent to which epigenetic mechanisms play a role in the etiology of the disorder is unknown. We performed epigenome-wide association studies (EWAS) within the Pregnancy And Childhood Epigenetics (PACE) Consortium to identify DNA methylation sites associated with ADHD symptoms at two methylation assessment periods: birth and school age. We examined associations of both DNA methylation in cord blood with repeatedly assessed ADHD symptoms (age 4-15 years) in 2477 children from 5 cohorts and of DNA methylation at school age with concurrent ADHD symptoms (age 7-11 years) in 2374 children from 9 cohorts, with 3 cohorts participating at both timepoints. CpGs identified with nominal significance (p < 0.05) in either of the EWAS were correlated between timepoints (ρ = 0.30), suggesting overlap in associations; however, top signals were very different. At birth, we identified nine CpGs that predicted later ADHD symptoms (p < 1 × 10^-7), including ERC2 and CREB5. Peripheral blood DNA methylation at one of these CpGs (cg01271805 in the promoter region of ERC2, which regulates neurotransmitter release) was previously associated with brain methylation. Another (cg25520701) lies within the gene body of CREB5, which previously was associated with neurite outgrowth and an ADHD diagnosis. In contrast, at school age, no CpGs were associated with ADHD with p < 1 × 10^-7. In conclusion, we found evidence in this study that DNA methylation at birth is associated with ADHD. Future studies are needed to confirm the utility of methylation variation as biomarker and its involvement in causal pathways.

DNA methylation biomarkers of future health outcomes in children

Biomarkers which predict future health outcomes are key to the goals of precision health. Such biomarkers do not have to be involved in the causal pathway of a disease, and their performance is best assessed using statistical tests of clinical performance and evaluation of net health impact. DNA methylation is the most commonly studied epigenetic process and represents a potential biomarker of future health outcomes. We review 25 studies in non-oncological paediatric conditions where DNA methylation biomarkers of future health outcomes are assessed. Whilst a number of positive findings have been described, the body of evidence is severely limited by issues with outcome measures, tissue-specific samples, accounting for sample cell type heterogeneity, lack of appropriate statistical testing, small effect sizes, limited validation, and no assessment of net health impact. Future studies should concentrate on careful study design to overcome these issues, and integration of DNA methylation data with other 'omic', clinical, and environmental data to generate the most clinically useful biomarkers of paediatric disease.

Methylation of the dopamine transporter gene in blood is associated with striatal dopamine transporter availability in ADHD: A preliminary study

Dopamine transporters (DAT) are implicated in the pathogenesis and treatment of attention-deficit hyperactivity disorder (ADHD) and are upregulated by chronic treatment with methylphenidate, commonly prescribed for ADHD. Methylation of the DAT1 gene in brain and blood has been associated with DAT expression in rodents' brains. Here we tested the association between methylation of the DAT1 promoter derived from blood and DAT availability in the striatum of unmedicated ADHD adult participants and in that of healthy age-matched controls (HC) using Positron Emission Tomography (PET) and [¹¹ C]cocaine. Results showed no between-group differences in DAT1 promoter methylation or striatal DAT availability. However, the degree of methylation in the promoter region of DAT1 correlated negatively with DAT availability in caudate in ADHD participants only. DAT availability in VS correlated with inattention scores in ADHD participants. We verified in a postmortem cohort with ADHD diagnosis and without, that DAT1 promoter methylation in peripheral blood correlated positively with DAT1 promoter methylation extracted from substantia nigra (SN) in both groups. In the cohort without ADHD diagnosis, DAT1 gene expression in SN further correlated positively with DAT protein expression in caudate; however, the sample size of the cohort with ADHD was insufficient to investigate DAT1 and DAT expression levels. Overall, these findings suggest that peripheral DAT1 promoter methylation may be predictive of striatal DAT availability in adults with ADHD. Due to the small sample size, more work is needed to validate whether DAT1 methylation in blood predicts DAT1 methylation in SN in ADHD and controls.

Parent SNAP-IV rating of attention-deficit/hyperactivity disorder: accuracy in a clinical sample of ADHD, validity, and reliability in a Brazilian sample

OBJECTIVE

To investigate the psychometric properties of the short or multimodal treatment study version of the Swanson, Nolan, and Pelham, Version IV (SNAP-IV) scale, which measures attention-deficit/hyperactivity disorder and oppositional defiant disorder symptoms.

METHODS

Participants were 765 parents of children from 4 to 16 years old (641 non-attention-deficit/hyperactivity disorder and 124 attention-deficit/hyperactivity disorder children) from Belo Horizonte, Brazil, who reported sociodemographic characteristics and answered the SNAP-IV. Parents of the clinical sample also underwent the K-SADS-PL interview.

RESULTS

Age was significantly associated with SNAP-IV hyperactivity-impulsivity problems (r=-0.14), but not with inattention or oppositional defiant disorder. Sex was a significant influence on attention-deficit/hyperactivity disorder and oppositional defiant disorder severity (all p<0.001), with boys showing higher scores in the full sample, but not within the attention-deficit/hyperactivity disorder group. Exploratory and confirmatory factor analysis supports a three-factor structure of the SNAP-IV scale. Moderate-to-strong correlations were found between SNAP-IV and K-SADS-PL measures. All SNAP-IV scales showed very high internal consistency coefficients (all above 0.91). SNAP-IV inattention scores were the most predictive of attention-deficit/hyperactivity disorder diagnosis (AUC: 0.877 for the averaging rating method and the raw sum method, and 0.874 for the symptom presence/absence method).

CONCLUSION

The parent SNAP-IV showed good psychometric properties in a Brazilian school and clinical sample.

Epigenome-wide Association Study of Attention-Deficit/Hyperactivity Disorder Symptoms in Adults

BACKGROUND

Previous studies have reported associations between attention-deficit/hyperactivity disorder symptoms and DNA methylation in children. We report the first epigenome-wide association study meta-analysis of adult attention-deficit/hyperactivity disorder symptoms, based on peripheral blood DNA methylation (Infinium HumanMethylation450K array) in three population-based adult cohorts.

METHODS

An epigenome-wide association study was performed in the Netherlands Twin Register (N = 2258, mean age 37 years), Dunedin Multidisciplinary Health and Development Study (N = 800, age 38 years), and Environmental Risk Longitudinal Twin Study (N = 1631, age 18 years), and results were combined through meta-analysis (total sample size N = 4689). Region-based analyses accounting for the correlation between nearby methylation sites were also performed.

RESULTS

One epigenome-wide significant differentially methylated position was detected in the Dunedin study, but meta-analysis did not detect differentially methylated positions that were robustly associated across cohorts. In region-based analyses, six significant differentially methylation regions (DMRs) were identified in the Netherlands Twin Register, 19 in the Dunedin study, and none in the Environmental Risk Longitudinal Twin Study. Of these DMRs, 92% were associated with methylation quantitative trait loci, and 68% showed moderate to large blood-brain correlations for DNA methylation levels. DMRs included six nonoverlapping DMRs (three in the Netherlands Twin Register, three in the Dunedin study) in the major histocompatibility complex, which were associated with expression of genes in the major histocompatibility complex, including C4A and C4B, previously implicated in schizophrenia.

CONCLUSIONS

Our findings point at new candidate loci involved in immune and neuronal functions that await further replication. Our work also illustrates the need for further research to examine to what extent epigenetic associations with psychiatric traits depend on characteristics such as age, comorbidities, exposures, and genetic background.

Children's DAT1 Polymorphism Moderates the Relationship Between Parents' Psychological Profiles, Children's DAT Methylation, and Their Emotional/Behavioral Functioning in a Normative Sample

Parental psychopathological risk is considered as one of the most crucial features associated with epigenetic modifications in offspring, which in turn are thought to be related to their emotional/behavioral profiles. The dopamine active transporter (DAT) gene is suggested to play a significant role in affective/behavioral regulation. On the basis of the previous literature, we aimed at verifying whether children’s DAT1 polymorphisms moderated the relationship between parents’ psychological profiles, children’s emotional/behavioral functioning, and DAT1 methylation in a normative sample of 79 families with school-age children (Ntot = 237). Children’s biological samples were collected through buccal swabs, while Symptom Check-List-90 item Revised, Adult Self Report, and Child Behavior Check-List/6–18 was administered to assess parental and children’s psychological functioning. We found that higher maternal externalizing problems predicted the following: higher levels of children’s DAT1 methylation at M1, but only among children with 10/10 genotype; higher levels of methylation at M2 among children with 10/10 genotype; while lower levels for children with a 9-repeat allele. There was also a positive relationship between fathers’ externalizing problems and children’s externalizing problems, only for children with a 9-repeat allele. Our findings support emerging evidence of the complex interplay between genetic and environmental factors in shaping children’ emotional/behavioral functioning, contributing to the knowledge of risk variables for a child’s development and psychological well-being.

Impact of adult attention deficit hyperactivity disorder and medication status on sleep/wake behavior and molecular circadian rhythms

Attention deficit hyperactivity disorder (ADHD) is a common neuropsychiatric condition that has been strongly associated with changes in sleep and circadian rhythms. Circadian rhythms are near 24-h cycles that are primarily generated by an endogenous circadian timekeeping system, encoded at the molecular level by a panel of clock genes. Stimulant and non-stimulant medication used in the management of ADHD has been shown to potentially impact on circadian processes and their behavioral outputs. In the current study, we have analyzed circadian rhythms in daily activity and sleep, and the circadian gene expression in a cohort of healthy controls (N = 22), ADHD participants not using ADHD-medication (N = 17), and participants with ADHD and current use of ADHD medication (N = 17). Rhythms of sleep/wake behavior were assessed via wrist-worn actigraphy, whilst rhythms of circadian gene expression were assessed ex-vivo in primary human-derived dermal fibroblast cultures. Behavioral data indicate that patients with ADHD using ADHD-medication have lower relative amplitudes of diurnal activity rhythms, lower sleep efficiency, more nocturnal activity but not more nocturnal wakenings than both controls and ADHD participants without medication. At the molecular level, there were alterations in the expression of PER2 and CRY1 between ADHD individuals with no medication compared to medicated ADHD patients or controls, whilst CLOCK expression was altered in patients with ADHD and current medication. Analysis of fibroblasts transfected with a BMAL1:luc reporter showed changes in the timing of the peak expression across the three groups. Taken together, these data support the contention that both ADHD and medication status impact on circadian processes.

Epigenetics and ADHD: Toward an Integrative Approach of the Disorder Pathogenesis

OBJECTIVE

Epigenetic hypothesis is one of the research pathways used to explain the complex etiology of neurodevelopmental disorders. This review highlights the findings of recent studies in the field of epigenetics in ADHD.

METHODS

An electronic literature search using Medline.

RESULTS

In the Gene × Environment interaction model, several clinical, genetic and molecular arguments support the epigenetic hypothesis in ADHD etiology. Environmental ADHD risk factors including toxic, nutritional factors and stressful life events lead to changes in DNA methylation and in histone modification levels. One critical CpG site located in the promoter of the DRD4 gene exhibited a specific pattern in ADHD children. A methylome wide exploration of DNA showed decreased methylation in vasoactive intestinal peptide receptor 2 gene, which was not replicated by further research.

CONCLUSION

Current data require consolidation and could lead to the identification of biomarkers and the introduction of new modalities of treatment.

[Genetics and epigenetics of attention deficit hyperactivity disorder]

Molecular genetic studies of attention deficit hyperactivity disorder (ADHD) have demonstrated the involvement of multiple genes in the etiology of ADHD. A polygenic hypothesis of the etiopathogenesis was formulated without clear knowledge of common mechanisms of ADHD development. Twin, family and adoption studies have established the heritability of 70-80% for ADHD. Association studies have shown the relationship between ADHD and genes of dopaminergic (DRD4, DRD5, SLC6A3), serotoninergic (HTR1B, 5-HTTLPR), glutamatergic (mGluR, NDRG2) systems, metabolic pathways (SLC2A3, SLC6A4, CDH13, CFOD1, GFOD1), membrane proteins (KChIP1, ITGA1, SNAP-25) as well as tumour-suppressor (NDRG2, NF1) and cytokine genes. The marked comorbidity of ADHD with other psychiatric disorders and shared genetic risk factors were determined. Studies of a role of copy number variations (CNVs) provided more promising evidence that suggested the possible involvement of retroelements as the unifying factors of disease etiopathogenesis. Transposons, which are sensitive to stress, may cause CNVs and are key regulators of brain development and functioning. The dysregulation of transposons is thought to be important in changes in tuning of gene regulatory pathways and epigenetic regulation of neurons in ADHD that may be a common principle underlying the heterogeneous nature of ADHD. Research on noncoding RNAs will help to confirm the hypothesis and develop diagnostic algorithms of examination of ADHD patients as an important step in the implementation of personalized medicine in psychiatry.

Effects of Interaction Between DRD4 Methylation and Prenatal Maternal Stress on Methylphenidate-Induced Changes in Continuous Performance Test Performance in Youth with Attention-Deficit/Hyperactivity Disorder

OBJECTIVES

Environmental factors may interact with genetic factors via the epigenetic process, and this interaction can contribute to inter-individual variability in the treatment response. The purpose of this study was to investigate the interaction effects between dopamine receptor D4 (DRD4) methylation and prenatal maternal stress on the methylphenidate (MPH) response of youth with attention-deficit/hyperactivity disorder (ADHD).

METHODS

This study was an 8-week open-label trial of MPH that included 74 ADHD youth. We investigated the associations between MPH treatment response, which was defined as a score ≤2 on the Clinical Global Impressions-Improvement (CGI-I) scale, and the methylation of 28 cytosine-guanine dinucleotide (CpG) sites of DRD4. Additionally, the interaction effects between DRD4 methylation and prenatal maternal stress on changes in Continuous Performance Test (CPT) scores after MPH treatment were investigated.

RESULTS

Although there were no significant sites that showed significant association with treatment response, there was a significant interaction effect of the methylation of CpG7 and prenatal maternal stress on changes in omission errors of the CPT following treatment (p = 0.0001).

CONCLUSIONS

The present findings indicate that the interaction between methylation of CpG7 of DRD4 and prenatal maternal stress may be predictive of the treatment response to MPH in youth with ADHD.

Annual Research Review: DNA methylation as a mediator in the association between risk exposure and child and adolescent psychopathology

BACKGROUND

DNA methylation (DNAm) is a potential mechanism for propagating the effects of environmental exposures on child and adolescent mental health. In recent years, this field has experienced steady growth.

METHODS

We provide a strategic review of the current child and adolescent literature to evaluate evidence for a mediating role of DNAm in the link between environmental risks and psychopathological outcomes, with a focus on internalising and externalising difficulties.

RESULTS

Based on the studies presented, we conclude that there is preliminary evidence to support that (a) environmental factors, such as diet, neurotoxic exposures and stress, influence offspring DNAm, and that (b) variability in DNAm, in turn, is associated with child and adolescent psychopathology. Overall, very few studies have examined DNAm in relation to both exposures and outcomes, and almost all analyses have been correlational in nature.

CONCLUSIONS

DNAm holds potential as a biomarker indexing both environmental risk exposure and vulnerability for child psychopathology. However, the extent to which it may represent a causal mediator is not clear. In future, collection of prospective risk exposure, DNAm and outcomes - as well as functional characterisation of epigenetic findings - will assist in determining the role of DNAm in the link between risk exposure and psychopathology.

The dopamine transporter role in psychiatric phenotypes

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

Methylation changes and pathways affected in preterm birth: a role for SLC6A3 in neurodevelopment

AIM

To analyze whether preterm newborns show differences in methylation patterns in comparison to full-term newborns in white blood cells.

PATIENTS & METHODS

Anthropometrical, biochemical features and methylation levels of preterm newborns (n = 24) and full-term newborns (n = 22) recruited in La Paz University Hospital (Spain) were assessed at 12 months of gestational age, whereas Bayley Scale of Infant Development was evaluated at 24/36 months.

RESULTS

From all the statistically significant CpGs, methylation levels of cg00997378 (SLC6A3 gene) showed the highest differences (p < 0.0001), being associated with prematurity risk factors.

CONCLUSION

SLC6A3 methylation, previously related to attention-deficit/hyperactivity disorder, neuronal function and behavior, might be a potential epigenetic biomarker with value in the early diagnosis and management of neurodevelopmental diseases in newborns.

[Diagnosis and treatment of cognitive impairment in adults with attention deficit hyperactivity disorder]

AIM

To qualify cognitive impairment in adults with attention deficit hyperactivity disorder (ADHD) and evaluate the efficacy of memoplant in the treatment of this pathology.

MATERIAL AND METHODS

The authors present the results of the clinical, psychological and electroencephalographic examination of 40 patients with ADHD, aged from 18 to 45 years. All patients received memoplant in dose of 240 mg a day for 8 weeks.

RESULTS AND CONCLUSION

Adult patients with ADHD were characterized by both subjective and objective disorders of memory and attention. The results of the electroencephalographic study suggested the dysfunction of the frontal-thalamic regulatory system and the lack of non-specific activation of the reticular formation. After treatment, clinical improvement was observed in 24 patients (60.0%). Repeated psychological and neuropsychological examinations showed a reduction of inattention and improvement of memory performance.

DNA Methylation at the DAT Promoter and Risk for Psychopathology: Intergenerational Transmission between School-Age Youths and Their Parents in a Community Sample

BACKGROUND

The effect of gene polymorphisms and promoter methylation, associated with maladaptive developmental outcomes, vary depending on environmental factors (e.g., parental psychopathology). Most studies have focused on 0- to 5-year-old children, adolescents, or adults, whereas there is dearth of research on school-age youths and pre-adolescents.

METHODS

In a sample of 21 families recruited at schools, we addressed parents' psychopathological symptoms (through SCL-90-R); offspring emotional-behavioral functioning (through CBCL-6-18); dopamine transporter gene (DAT1) for epigenetic status of the 5'-untranslated region (UTR) and for genotype, i.e., variable number of tandem repeats polymorphism at the 3'-UTR. Possible associations were explored between bio-genetic and psychological characteristics within the same individual and between triplets of children, mothers, and fathers.

RESULTS

DAT methylation of CpG at positions M1, M6, and M7 in mothers was correlated with maternal (phobic) anxiety, whereas in fathers' position M6 was related to paternal depression, anxiety, hostility, psychoticism, and higher Global Severity Index (GSI). No significant correlations were found between maternal and offspring DAT methylation. Significant correlations were found between fathers' methylation at CpG M1 and children's methylation at CpG M6. Linear regressions showed that mothers and fathers' GSI predicted children's methylation at CpG sites M2, M3, and M6, whereas fathers' GSI predicted children's methylation at CpG sites, particularly M1, M2, and M6. Moreover, offspring methylation of DAT at CpG M2 predicted somatic complaint, internalizing and attention problems; methylation of DAT at CpG M6 predicted withdraw.

CONCLUSION

This study may have important clinical implication for the prevention and treatment of emotional-behavioral difficulties in children, as it adds to previous knowledge about the role of genetic and environmental factors in predicting psychopathological symptoms within non-clinical populations.

Prenatal Alcohol Exposure in Rodents As a Promising Model for the Study of ADHD Molecular Basis

A physiological parallelism, or even a causal effect relationship, can be deducted from the analysis of the main characteristics of the “Alcohol Related Neurodevelopmental Disorders” (ARND), derived from prenatal alcohol exposure (PAE), and the behavioral performance in the Attention-deficit/hyperactivity disorder (ADHD). These two clinically distinct disease entities, exhibits many common features. They affect neurological shared pathways, and also related neurotransmitter systems. We briefly review here these parallelisms, with their common and uncommon characteristics, and with an emphasis in the subjacent molecular mechanisms of the behavioral manifestations, that lead us to propose that PAE in rats can be considered as a suitable model for the study of ADHD.