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

Disentangling the trajectories of maternal depressive symptoms and partnership problems in the transition to parenthood and their impact on child adjustment difficulties

Maternal perinatal depression (PND) and partnership problems have been identified to influence the development of later child adjustment difficulties. However, PND and partnership problems are closely linked which makes it difficult to draw conclusions about the exact transmission pathways. The aim of the present study was to investigate to what extent PND symptoms and partnership problems influence each other longitudinally and to examine the influence of their trajectories on child adjustment difficulties at the age of three. Analyses were based on publicly available data from the German family panel "pairfam". N = 354 mothers were surveyed on depressive symptoms and partnership problems annually from pregnancy (T0) until child age three (T4). Child adjustment difficulties were assessed at age three. Results of latent change score modeling showed that partnership problems predicted change in PND symptoms at T0 and T3 while PND symptoms did not predict change in partnership problems. Child adjustment difficulties at age three were predicted by PND symptoms, but not by partnership problems. Partnership problems predicted externalizing, but not internalizing symptoms. Results underline the effects of family factors for the development of child adjustment difficulties and emphasize the importance of early interventions from pregnancy onwards.

Bioinformatic Evaluation of KLF13 Genetic Variant: Implications for Neurodevelopmental and Psychiatric Symptoms

The Krüppel-like factor (KLF) family represents a group of transcription factors (TFs) performing different biological processes that are crucial for proper neuronal function, including neuronal development, synaptic plasticity, and neuronal survival. As reported, genetic variants within the KLF family have been associated with a wide spectrum of neurodevelopmental and psychiatric symptoms. In a patient exhibiting attention deficit hyperactivity disorder (ADHD) combined with both neurodevelopmental and psychiatric symptoms, whole-exome sequencing (WES) analysis revealed a de novo heterozygous variant within the Krüppel-like factor 13 (KLF13) gene, which belongs to the KLF family and regulates axonal growth, development, and regeneration in mice. Moreover, in silico analyses pertaining to the likely pathogenic significance of the variant and the impact of the mutation on the KLF13 protein structure suggested a potential deleterious effect. In fact, the variant was localized in correspondence to the starting residue of the N-terminal domain of KLF13, essential for protein-protein interactions, DNA binding, and transcriptional activation or repression. This study aims to highlight the potential involvement of the KLF13 gene in neurodevelopmental and psychiatric disorders. Nevertheless, we cannot rule out that excluded variants, those undetectable by WES, or the polygenic risk may have contributed to the patient's phenotype given ADHD's high polygenic risk. However, further functional studies are required to validate its potential contribution to these disorders.

A Systematic Review and Meta-analysis of Parental Depression, Antidepressant Usage, Antisocial Personality Disorder, and Stress and Anxiety as Risk Factors for Attention-Deficit/Hyperactivity Disorder (ADHD) in Children

Poor parental mental health and stress have been associated with children's mental disorders, including attention-deficit/hyperactivity disorder (ADHD), through social, genetic, and neurobiological pathways. To determine the strength of the associations between parental mental health and child ADHD, we conducted a set of meta-analyses to examine the association of parent mental health indicators (e.g., parental depression, antidepressant usage, antisocial personality disorder, and stress and anxiety) with subsequent ADHD outcomes in children. Eligible ADHD outcomes included diagnosis or symptoms. Fifty-eight articles published from 1980 to 2019 were included. We calculated pooled effect sizes, accounting for each study's conditional variance, separately for test statistics based on ADHD as a dichotomous (e.g., diagnosis or clinical cutoffs) or continuous measurement (e.g., symptoms of ADHD subtypes of inattentiveness and hyperactivity/impulsivity). Parental stress and parental depression were significantly associated with increased risk for ADHD overall and both symptoms and diagnosis. Specifically, maternal stress and anxiety, maternal prenatal stress, maternal depression, maternal post-partum depression, and paternal depression were positively associated with ADHD. In addition, parental depression was associated with symptoms of ADHD inattentive and hyperactive/impulsive subtypes. Parental antisocial personality disorder was also positively associated with ADHD overall and specifically ADHD diagnosis. Prenatal antidepressant usage was associated with ADHD when measured dichotomously only. These findings raise the possibility that prevention strategies promoting parental mental health and addressing parental stress could have the potential for positive long-term impacts on child health, well-being, and behavioral outcomes.

Metabolomic Markers in Attention-Deficit/Hyperactivity Disorder (ADHD) among Children and Adolescents-A Systematic Review

Attention-Deficit/Hyperactivity Disorder (ADHD), characterized by clinical diversity, poses diagnostic challenges often reliant on subjective assessments. Metabolomics presents an objective approach, seeking biomarkers for precise diagnosis and targeted interventions. This review synthesizes existing metabolomic insights into ADHD, aiming to reveal biological mechanisms and diagnostic potentials. A thorough PubMed and Web of Knowledge search identified studies exploring blood/urine metabolites in ADHD-diagnosed or psychometrically assessed children and adolescents. Synthesis revealed intricate links between ADHD and altered amino acid metabolism, neurotransmitter dysregulation (especially dopamine and serotonin), oxidative stress, and the kynurenine pathway impacting neurotransmitter homeostasis. Sleep disturbance markers, notably in melatonin metabolism, and stress-induced kynurenine pathway activation emerged. Distinct metabolic signatures, notably in the kynurenine pathway, show promise as potential diagnostic markers. Despite limitations like participant heterogeneity, this review underscores the significance of integrated therapeutic approaches targeting amino acid metabolism, neurotransmitters, and stress pathways. While guiding future research, this overview of the metabolomic findings in ADHD suggests directions for precision diagnostics and personalized ADHD interventions.

Integrative multi-omics analysis of genomic, epigenomic, and metabolomics data leads to new insights for Attention-Deficit/Hyperactivity Disorder

The evolving field of multi-omics combines data and provides methods for simultaneous analysis across several omics levels. Here, we integrated genomics (transmitted and non-transmitted polygenic scores [PGSs]), epigenomics, and metabolomics data in a multi-omics framework to identify biomarkers for Attention-Deficit/Hyperactivity Disorder (ADHD) and investigated the connections among the three omics levels. We first trained single- and next multi-omics models to differentiate between cases and controls in 596 twins (cases = 14.8%) from the Netherlands Twin Register (NTR) demonstrating reasonable in-sample prediction through cross-validation. The multi-omics model selected 30 PGSs, 143 CpGs, and 90 metabolites. We confirmed previous associations of ADHD with glucocorticoid exposure and the transmembrane protein family TMEM, show that the DNA methylation of the MAD1L1 gene associated with ADHD has a relation with parental smoking behavior, and present novel findings including associations between indirect genetic effects and CpGs of the STAP2 gene. However, out-of-sample prediction in NTR participants (N = 258, cases = 14.3%) and in a clinical sample (N = 145, cases = 51%) did not perform well (range misclassification was [0.40, 0.57]). The results highlighted connections between omics levels, with the strongest connections between non-transmitted PGSs, CpGs, and amino acid levels and show that multi-omics designs considering interrelated omics levels can help unravel the complex biology underlying ADHD.

Gene Interaction of Dopaminergic Synaptic Pathway Genes in Attention-Deficit Hyperactivity Disorder: a Case-Control Study in Chinese Children

Attention-deficit hyperactivity disorder is a highly inherited neurodevelopmental disorder. Previous genetic research has linked ADHD to certain genes in the dopaminergic synaptic pathway. Nonetheless, research on this relationship has produced varying results across various populations. China is a multi-ethnic country with its own unique genetic characteristics. Therefore, such a population can provide useful information about the relationship between gene polymorphisms in dopaminergic synaptic pathways and ADHD. This study looked at the genetic profiles of 284 children in China's Xinjiang. In total, 142 ADHD children and 142 control subjects were enrolled. Following the extraction of DNA from oral mucosal cells, 13 SNPs for three candidate genes (SLC6A3, DRD2, and GRIN2B) in the dopaminergic synaptic pathway of ADHD were screened. Based on the results of single nucleotide polymorphism (SNP) analyses, we found that the DRD2 gene variants rs6277 and rs6275, and the SLC6A3 gene variant rs2652511, were significantly associated with ADHD in boys and girls, respectively, after adjusting for false discovery rate (FDR) in terms of allele frequencies. Furthermore, our generalized multifactorial downscaling approach identified a significant association between rs6275 and rs1012586. These findings suggest that DRD2 and SLC6A3 genes have a crucial role in ADHD susceptibility. Additionally, we observed that the interaction between GRIN2B and DRD2 genes may contribute to the susceptibility of Chinese children with ADHD.

Developmental antecedents of attention-deficit/hyperactivity disorder symptoms in middle childhood: The role of father-child interactions and children's emotional underregulation

The present study examined the influence of fathers' parenting quality during infancy on children's emotion regulation during toddlerhood and, subsequently, attention-deficit/hyperactivity disorder (ADHD) symptoms in middle childhood. Fathers and their 8-month-old infants (N = 124) were followed over time to obtain home observations of parenting quality at 8 and 24 months, laboratory observations of children's emotion regulation at 24 months, and teacher reports of children's ADHD symptoms at 7 years. A path analysis revealed that fathers' emotional disengagement in infancy and minimizing responses to children's distress in toddlerhood forecast children's development of ADHD symptoms in middle childhood. Further, a significant indirect effect was found such that fathers' parenting at 8 and 24 months predicted subsequent development of ADHD symptoms at age 7 through toddlers' difficulty regulating emotion. Implications of this study for early intervention and directions for future research are discussed.

DNA methylation is associated with prenatal exposure to sulfur dioxide and childhood attention-deficit hyperactivity disorder symptoms

Epigenetic influence plays a role in the association between exposure to air pollution and attention deficit hyperactivity disorder (ADHD); however, research regarding sulfur dioxide (SO₂) is scarce. Herein, we investigate the associations between prenatal SO₂ exposure and ADHD rating scale (ARS) at ages 4, 6 and 8 years repeatedly in a mother-child cohort (n = 329). Whole blood samples were obtained at ages 2 and 6 years, and genome-wide DNA methylation (DNAm) was analyzed for 51 children using the Illumina Infinium HumanMethylation BeadChip. We analyzed the associations between prenatal SO₂ exposure and DNAm levels at ages 2 and 6, and further investigated the association between the DNAm and ARS at ages 4, 6 and 8. Prenatal SO₂ exposure was associated with ADHD symptoms. From candidate gene analysis, DNAm levels at the 6 CpGs at age 2 were associated with prenatal SO₂ exposure levels. Of the 6 CpGs, cg07583420 (INS-IGF2) was persistently linked with ARS at ages 4, 6 and 8. Epigenome-wide analysis showed that DNAm at 6733 CpG sites were associated with prenatal SO₂ exposure, of which 58 CpGs involved in Notch signalling pathway were further associated with ARS at age 4, 6 and 8 years, persistently. DNAm at age 6 was not associated with prenatal SO₂ exposure. Changes in DNAm levels associated with prenatal SO₂ exposure during early childhood are associated with increases in ARS in later childhood.

Polygenic risk score for attention-deficit/hyperactivity disorder and brain functional networks segregation in a community-based sample

Neuroimaging studies suggest that brain development mechanisms might explain at least some behavioural and cognitive attention-deficit/hyperactivity disorder (ADHD) symptoms. However, the putative mechanisms by which genetic susceptibility factors influence clinical features via alterations of brain development remain largely unknown. Here, we set out to integrate genomics and connectomics tools by investigating the associations between an ADHD polygenic risk score (ADHD-PRS) and functional segregation of large-scale brain networks. With this aim, ADHD symptoms score, genetic and rs-fMRI (resting-state functional magnetic resonance image) data obtained in a longitudinal community-based cohort of 227 children and adolescents were analysed. A follow-up was conducted approximately 3 years after the baseline, with rs-fMRI scanning and ADHD likelihood assessment in both stages. We hypothesised a negative correlation between probable ADHD and the segregation of networks involved in executive functions, and a positive correlation with the default-mode network (DMN). Our findings suggest that ADHD-PRS is correlated with ADHD at baseline, but not at follow-up. Despite not surviving for multiple comparison correction, we found significant correlations between ADHD-PRS and segregation of cingulo-opercular networks and DMN at baseline. ADHD-PRS was negatively correlated with the segregation level of cingulo-opercular networks but positively correlated with the DMN segregation. These directions of associations corroborate the proposed counter-balanced role of attentional networks and DMN in attentional processes. However, the association between ADHD-PRS and brain networks functional segregation was not found at follow-up. Our results provide evidence for specific influences of genetic factors on development of attentional networks and DMN. We found significant correlations between polygenic risk score for ADHD (ADHD-PRS) and segregation of cingulo-opercular networks and default-mode network (DMN) at baseline. ADHD-PRS was negatively correlated with the segregation level of cingulo-opercular networks but positively correlated with the DMN segregation.

Epigenome-wide DNA methylation in externalizing behaviours: A review and combined analysis

DNA methylation (DNAm) is one of the most frequently studied epigenetic mechanisms facilitating the interplay of genomic and environmental factors, which can contribute to externalizing behaviours and related psychiatric disorders. Previous epigenome-wide association studies (EWAS) for externalizing behaviours have been limited in sample size, and, therefore, candidate genes and biomarkers with robust evidence are still lacking. We 1) performed a systematic literature review of EWAS of attention-deficit/hyperactivity disorder (ADHD)- and aggression-related behaviours conducted in peripheral tissue and cord blood and 2) combined the most strongly associated DNAm sites observed in individual studies (p < 10^-3) to identify candidate genes and biological systems for ADHD and aggressive behaviours. We observed enrichment for neuronal processes and neuronal cell marker genes for ADHD. Astrocyte and granulocytes cell markers among genes annotated to DNAm sites were relevant for both ADHD and aggression-related behaviours. Only 1 % of the most significant epigenetic findings for ADHD/ADHD symptoms were likely to be directly explained by genetic factors involved in ADHD. Finally, we discuss how the field would greatly benefit from larger sample sizes and harmonization of assessment instruments.

The role of DNA methylation in progression of neurological disorders and neurodegenerative diseases as well as the prospect of using DNA methylation inhibitors as therapeutic agents for such disorders

Genome-wide studies related to neurological disorders and neurodegenerative diseases have pointed to the role of epigenetic changes such as DNA methylation, histone modification, and noncoding RNAs. DNA methylation machinery controls the dynamic regulation of methylation patterns in discrete brain regions.

Objective

This review aims to describe the role of DNA methylation in inhibiting and progressing neurological and neurodegenerative disorders and therapeutic approaches.

Methods

A Systematic search of PubMed, Web of Science, and Cochrane Library was conducted for all qualified studies from 2000 to 2022.

Results

For the current need of time, we have focused on the DNA methylation role in neurological and neurodegenerative diseases and the expression of genes involved in neurodegeneration such as Alzheimer's, Depression, and Rett Syndrome. Finally, it appears that the various epigenetic changes do not occur separately and that DNA methylation and histone modification changes occur side by side and affect each other. We focused on the role of modification of DNA methylation in several genes associated with depression (NR3C1, NR3C2, CRHR1, SLC6A4, BDNF, and FKBP5), Rett syndrome (MECP2), Alzheimer's, depression (APP, BACE1, BIN1 or ANK1) and Parkinson's disease (SNCA), as well as the co-occurring modifications to histones and expression of non-coding RNAs. Understanding these epigenetic changes and their interactions will lead to better treatment strategies.

Conclusion

This review captures the state of understanding of the epigenetics of neurological and neurodegenerative diseases. With new epigenetic mechanisms and targets undoubtedly on the horizon, pharmacological modulation and regulation of epigenetic processes in the brain holds great promise for therapy.

Functional urination or defecation disorders may be warning signs of attention-deficit/hyperactivity disorder among children in rural China

BACKGROUND

This study was designed to investigate the prevalence of attention-deficit/hyperactivity disorder (ADHD) and its association with functional urination and defecation disorders among children in rural China.

METHODS

A cross-sectional study was conducted with children aged 6-18 in rural schools in southwest China using a survey questionnaire. The Swanson, Nolan, and Pelham Questionnaire-IV (SNAP-IV) was used to measure ADHD symptoms, and standardized questions about urination and defecation were used to measure lower urinary tract symptoms (LUTS) and functional defecation disorders (FDDs). The association of ADHD with LUTS and FDDs was analyzed by matched logistic regression after propensity score matching was performed to minimize the influence of potential confounders, including demographic characteristics.

RESULTS

A total of 17,279 participants were included in the analyses. The prevalence of ADHD was 2 % mainly among boys before age 12, after which it showed a decreasing trend with age, resulting in a concomitant reduction in gender differences. The risk of ADHD was positively associated with the presence of enuresis, holding maneuvers, intermittency, and encopresis, with encopresis having the strongest association (P = 0.001). The presence of holding maneuvers, intermittency, excessive volitional stool retention, and encopresis were associated with a higher risk of ADHD at 6-15 years-old, with intermittency exhibiting an increasingly positive association with ADHD risk across ages 6-15.

CONCLUSIONS

ADHD was associated with LUTS and FDDs, which highlights that functional urination and/or defecation disorders could serve as warning signs for ADHD that should trigger screening, especially in relatively backward regions with little ADHD awareness.

Neurobiological insights into twice-exceptionality: Circuits, cells, and molecules

Twice-exceptional learners face a unique set of challenges arising from the intersection of extraordinary talent and disability. Neurobiology research has the capacity to complement pedagogical research and provide support for twice-exceptional learners. Very few studies have attempted to specifically address the neurobiological underpinnings of twice-exceptionality. However, neurobiologists have built a broad base of knowledge in nervous system function spanning from the level of neural circuits to the molecular basis of behavior. It is known that distinct neural circuits mediate different neural functions, which suggests that 2e learning may result from enhancement in one circuit and disruption in another. Neural circuits are known to adapt and change in response to experience, a cellular process known as neuroplasticity. Plasticity is controlled by a bidirectional connection between the synapse, where neural signals are received, and the nucleus, where regulated gene expression can return to alter synaptic function. Complex molecular mechanisms compose this connection in distinct neural circuits, and genetic alterations in these mechanisms are associated with both memory enhancements and psychiatric disorder. Understanding the consequences of these changes at the molecular, cellular, and circuit levels will provide critical insights into the neurobiological bases of twice-exceptionality.

Effects of Methylphenidate on the Dopamine Transporter and Beyond

The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.

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.

[The Genetic Basis of ADHD - An Update]

The Genetic Basis of ADHD - An Update Abstract. Genetic risks play an important role in the etiology of attention-deficit/hyperactivity disorder (ADHD). This review presents the current state of knowledge concerning the genetic basis of the disorder. It discusses the results of twin- and family-based studies, linkage and association studies as well as recent findings resulting from Genome Wide Association Studies (GWAS). Furthermore, it elaborates on the relevance of polygenic risk scores, rare variants, and epigenetic alterations, especially in light of findings on genetic pleiotropy in the context of frequent psychiatric comorbidities in patients with ADHD.

Social Determinants of Health and ADHD Symptoms in Preschool-Age Children

OBJECTIVE

Attention-Deficit/Hyperactivity Disorder (ADHD) disproportionately affects socioeconomically disadvantaged children, but for unclear reasons. We examined the association between social determinants of health (SDH) and ADHD symptoms in a national sample of preschool-age children.

METHODS

We conducted exploratory factor analysis (EFA) and exploratory structural equation modeling (ESEM) with a sample of 7,565 preschool-age children from the 2016 National Survey of Children's Health, to examine the association between ADHD symptoms and SDH.

RESULTS

EFA indicated a one-factor structure for ADHD symptoms, and three factors for SDH (socioeconomic status, access to basic needs, and caregiver well-being). Independently, all three SDH were significantly associated with higher ADHD symptoms. However, in the ESEM model, only worse caregiver well-being (β = .39, p < .01) was significantly associated with ADHD symptoms, and fully mediated the relationship between SDH and ADHD symptoms.

CONCLUSION

Addressing caregiver well-being in preschoolers with ADHD symptoms could be an early intervention strategy.

Attention Deficit Hyperactivity Disorder and Bipolar Disorder: Diagnosis, Treatments, and Clinical Considerations: A Narrative Review

Attention-deficit Hyperactivity Disorder is one of the most common childhood mental health disorders, affecting about 5.6% of the population worldwide. Several studies have specifically shown a high prevalence of comorbid mood disorders, such as depression and bipolar disorder (BD), in those diagnosed with ADHD. Several common symptoms of ADHD are also found in BD, which are characterized by alternating periods of euthymia and mood disturbances. The inattention and impulsivity of ADHD can be seen in manic and hypomanic episodes of BD. Over the past decade, there has been an increased interest in research between the correlation of ADHD and pediatric bipolar disorder (PBD) in children. Some experts hypothesize that more children are comorbidly diagnosed with ADHD and PBD because of how many clinicians treat children with ADHD. Other factors, which may affect the dual diagnoses of ADHD and PBD, are overlapping diagnostic criteria for the two disorders, the inevitable biases seen when one disorder is diagnosed without the other, and related risk factors leading to prodromal relationships. By examining clinical trials, a better understanding of whether ADHD and PBD have a stepwise progression or if other factors influence these comorbidities, such as blurred lines of diagnostic criteria. Those with ADHD are also at an increased risk of impairment at work and in social settings. This manuscript explores both progression of this disease and its clinical connections to other disorders.

DNA Methylation in LIME1 and SPTBN2 Genes Is Associated with Attention Deficit in Children

DNA methylation levels are associated with neurodevelopment. Attention-deficit/hyperactivity disorder (ADHD), characterized by attention deficits, is a common neurodevelopmental disorder. We used methylation microarray and pyrosequencing to detect peripheral blood DNA methylation markers of ADHD. DNA methylation profiling data from the microarray assays identified potential differentially methylated CpG sites between 12 ADHD patients and 9 controls. Five candidate CpG sites (cg00446123, cg20513976, cg07922513, cg17096979, and cg02506324) in four genes (LIME1, KCNAB2, CAPN9, and SPTBN2) were further examined with pyrosequencing. The attention of patients were tested using the Conners’ Continuous Performance Test (CPT). In total, 126 ADHD patients with a mean age of 9.2 years (78.6% males) and 72 healthy control subjects with a mean age of 9.3 years (62.5% males) were recruited. When all participants were categorized by their CPT performance, the DNA methylation levels in LIME1 (cg00446123 and cg20513976) were found to be significantly higher and those in SPTBN2 (cg02506324) were significantly lower in children with worse CPT performance. Therefore, DNA methylation of two CpG sites in LIME1 and one CpG site in SPTBN2 is associated with attention deficits in children. DNA methylation biomarkers may assist in identifying attention deficits of children in clinical settings.

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.

DNA methylation associated with persistent ADHD suggests TARBP1 as novel candidate

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by age-inappropriate symptoms of inattention and/or hyperactivity and impulsivity. ADHD is highly prevalent in childhood and often persists into adulthood. Both genetic variants and environmental factors play a role in the onset and persistence of ADHD, and epigenetic changes, such as DNA methylation are considered as a link for their interplay. To investigate this, we studied DNA methylation in 37 candidate genes by performing targeted bisulfite sequencing of DNA isolated from whole blood of N = 88 individuals diagnosed with adult ADHD and N = 91 unaffected individuals (mean age 34.2 years). Differentially methylated sites were assessed by generalized linear models testing ADHD status and ADHD symptoms, accounting for a methylation-based smoking score, age, sex, and blood cell count. DNA methylation of single sites within DRD4 and KLDR1 was associated with adult ADHD status, and multiple DNA methylation sites within TARBP1 were associated with ADHD symptoms in adulthood and childhood. Awaiting replication, findings of this pilot study point to TARBP1 as a new candidate gene for ADHD symptoms. Our work also stresses the need for research to further examine the effects of environmental factors, such as nicotine exposure, on epigenetic modifications associated with psychiatric traits.

Maternal use of hormonal contraception and risk of childhood ADHD: a nationwide population-based cohort study

Although maternal use of hormones has been suspected of increasing the risk for childhood attention-deficit/hyperactivity disorder (ADHD), no study has examined hormonal contraception use in this context. We examined the association between maternal hormonal contraception use before or during pregnancy and ADHD risk in children. This nationwide population-based cohort study included 1,056,846 children born in Denmark between 1998 and 2014. Prescriptions for hormonal contraceptives redeemed by the mother was categorized as: no use, previous use (> 3 months before pregnancy), and recent use (≤ 3 months before or during pregnancy). Children were followed for ADHD, from birth until 31 December 2015. Cox proportional hazard models were used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). During 9,819,565 person-years of follow-up (median: 9.2), ADHD was diagnosed or a prescription for ADHD medication redeemed for 23,380 children (2.2%). The adjusted HR for ADHD was higher in children of mothers who had previously (HR 1.23; 95% CI 1.18-1.28) or recently (HR 1.30; 95% CI 1.24-1.37) used hormonal contraception than in those of mothers with no use. The highest estimates were seen for use of non-oral progestin products with HRs of 1.90 (95% CI 1.59-2.26) for previous use, 2.23 (95% CI 1.96-2.54) for recent use, and 3.10 (95% CI 1.62-5.91) for use during pregnancy. Maternal use of hormonal contraception was associated with an increased risk for ADHD in the offspring; more pronounced for non-oral progestin-only than other products.

Epigenome-wide association study of attention-deficit/hyperactivity disorder in adults

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder that often persists into adulthood. There is growing evidence that epigenetic dysregulation participates in ADHD. Given that only a limited number of epigenome-wide association studies (EWASs) of ADHD have been conducted so far and they have mainly focused on pediatric and population-based samples, we performed an EWAS in a clinical sample of adults with ADHD. We report one CpG site and four regions differentially methylated between patients and controls, which are located in or near genes previously involved in autoimmune diseases, cancer or neuroticism. Our sensitivity analyses indicate that smoking status is not responsible for these results and that polygenic risk burden for ADHD does not greatly impact the signatures identified. Additionally, we show an overlap of our EWAS findings with genetic signatures previously described for ADHD and with epigenetic signatures for smoking behavior and maternal smoking. These findings support a role of DNA methylation in ADHD and emphasize the need for additional efforts in larger samples to clarify the role of epigenetic mechanisms on ADHD across the lifespan.

Genome-Wide DNA Methylation Patterns in Persistent Attention-Deficit/Hyperactivity Disorder and in Association With Impulsive and Callous Traits

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that often persists into adulthood. ADHD and related personality traits, such as impulsivity and callousness, are caused by genetic and environmental factors and their interplay. Epigenetic modifications of DNA, including methylation, are thought to mediate between such factors and behavior and may behave as biomarkers for disorders. Here, we set out to study DNA methylation in persistent ADHD and related traits. We performed epigenome-wide association studies (EWASs) on peripheral whole blood from participants in the NeuroIMAGE study (age range 12-23 years). We compared participants with persistent ADHD (n = 35) with healthy controls (n = 19) and with participants with remittent ADHD (n = 19). Additionally, we performed EWASs of impulsive and callous traits derived from the Conners Parent Rating Scale and the Callous-Unemotional Inventory, respectively, across all participants. For every EWAS, the linear regression model analyzed included covariates for age, sex, smoking scores, and surrogate variables reflecting blood cell type composition and genetic background. We observed no epigenome-wide significant differences in single CpG site methylation between participants with persistent ADHD and healthy controls or participants with remittent ADHD. However, epigenome-wide analysis of differentially methylated regions provided significant findings showing that hypermethylated regions in the APOB and LPAR5 genes were associated with ADHD persistence compared to ADHD remittance (p = 1.68 * 10-24 and p = 9.06 * 10-7, respectively); both genes are involved in cholesterol signaling. Both findings appeared to be linked to genetic variation in cis. We found neither significant epigenome-wide single CpG sites nor regions associated with impulsive and callous traits; the top-hits from these analyses were annotated to genes involved in neurotransmitter release and the regulation of the biological clock. No link to genetic variation was observed for these findings, which thus might reflect environmental influences. In conclusion, in this pilot study with a small sample size, we observed several DNA-methylation-disorder/trait associations of potential significance for ADHD and the related behavioral traits. Although we do not wish to draw conclusions before replication in larger, independent samples, cholesterol signaling and metabolism may be of relevance for the onset and/or persistence of ADHD.

Large epigenome-wide association study of childhood ADHD identifies peripheral DNA methylation associated with disease and polygenic risk burden

Epigenetic variation in peripheral tissues is being widely studied as a molecular biomarker of complex disease and disease-related exposures. To date, few studies have examined differences in DNA methylation associated with attention-deficit hyperactivity disorder (ADHD). In this study, we profiled genetic and methylomic variation across the genome in saliva samples from children (age 7-12 years) with clinically established ADHD (N = 391) and nonpsychiatric controls (N = 213). We tested for differentially methylated positions (DMPs) associated with both ADHD diagnosis and ADHD polygenic risk score, by using linear regression models including smoking, medication effects, and other potential confounders in our statistical models. Our results support previously reported associations between ADHD and DNA methylation levels at sites annotated to VIPR2, and identify several novel disease-associated DMPs (p < 1e-5), although none of them were genome-wide significant. The two top-ranked, ADHD-associated DMPs (cg17478313 annotated to SLC7A8 and cg21609804 annotated to MARK2) are also significantly associated with nearby SNPs (p = 1.2e-46 and p = 2.07e-59), providing evidence that disease-associated DMPs are under genetic control. We also report a genome-wide significant association between ADHD polygenic risk and variable DNA methylation at a site annotated to the promoter of GART and SON (p = 6.71E-8). Finally, we show that ADHD-associated SNPs colocalize with SNPs associated with methylation levels in saliva. This is the first large-scale study of DNA methylation in children with ADHD. Our results represent novel epigenetic biomarkers for ADHD that may be useful for patient stratification, reinforce the importance of genetic effects on DNA methylation, and provide plausible molecular mechanisms for ADHD risk variants.

Integrated Analysis of microRNA and mRNA Expression Profiles: An Attempt to Disentangle the Complex Interaction Network in Attention Deficit Hyperactivity Disorder

Attention Deficit Hyperactivity Disorder (ADHD) is a childhood-onset neurodevelopmental disorder, whose etiology and pathogenesis are still largely unknown. In order to uncover novel regulatory networks and molecular pathways possibly related to ADHD, we performed an integrated miRNA and mRNA expression profiling analysis in peripheral blood samples of children with ADHD and age-matched typically developing (TD) children. The expression levels of 13 miRNAs were evaluated with microfluidic qPCR, and differentially expressed (DE) mRNAs were detected on an Illumina HiSeq 2500 genome analyzer. The miRNA targetome was identified using an integrated approach of validated and predicted interaction data extracted from seven different bioinformatic tools. Gene Ontology (GO) and pathway enrichment analyses were carried out. Results showed that six miRNAs (miR-652-3p, miR-942-5p, let-7b-5p, miR-181a-5p, miR-320a, and miR-148b-3p) and 560 genes were significantly DE in children with ADHD compared to TD subjects. After correction for multiple testing, only three miRNAs (miR-652-3p, miR-148b-3p, and miR-942-5p) remained significant. Genes known to be associated with ADHD (e.g., B4GALT2, SLC6A9 TLE1, ANK3, TRIO, TAF1, and SYNE1) were confirmed to be significantly DE in our study. Integrated miRNA and mRNA expression data identified critical key hubs involved in ADHD. Finally, the GO and pathway enrichment analyses of all DE genes showed their deep involvement in immune functions, reinforcing the hypothesis that an immune imbalance might contribute to the ADHD etiology. Despite the relatively small sample size, in this study we were able to build a complex miRNA-target interaction network in children with ADHD that might help in deciphering the disease pathogenesis. Validation in larger samples should be performed in order to possibly suggest novel therapeutic strategies for treating this complex disease.

DNA methylation of dopamine-related gene promoters is associated with line bisection deviation in healthy adults

Handedness and language lateralization are the most investigated phenotypes among functional hemispheric asymmetries, i.e. differences in function between the left and the right half of the human brain. Both phenotypes are left hemisphere-dominant, while investigations of the molecular factors underlying right hemisphere-dominant phenotypes are less prominent. In the classical line bisection task, healthy subjects typically show a leftward attentional bias due to a relative dominance of the right hemisphere for visuospatial attention. Based on findings of variations in dopamine-related genes affecting performance in the line bisection task, we first tested whether DNA methylation in non-neuronal tissue in the promoter regions of DBH, SLC6A3, and DRD2 are associated with line bisection deviation. We replicated the typical behavioral pattern and found an effect of DNA methylation in the DBH promoter region on line bisection deviation in right-aligned trials. A second exploratory analysis indicated that an overall DNA methylation profile of genes involved in dopamine function predicts line bisection performance in right-aligned trials. Genetic variation in dopamine-related genes has been linked to attention deficit hyperactivity disorder (ADHD), a neurodevelopmental trait associated with rightward attentional bias. Overall, our findings point towards epigenetic markers for functional hemispheric asymmetries in non-neuronal tissue not only for left hemisphere-dominant, but also for right hemisphere-dominant phenotypes.

Situating adult attention-deficit/hyperactivity disorder in the externalizing spectrum: Etiological, diagnostic, and treatment considerations

Adult attention-deficit/hyperactivity disorder (ADHD) has a population prevalence of 5%. However, its prevalence is much higher in mental health and substance use treatment settings. It is associated with significant physical and psychiatric morbidity, as well as social, occupational, and legal consequences. Adult ADHD is considered to be a part of the externalizing spectrum with which it shares both homotypic comorbidity and heterotypic continuity across the lifespan. This is attributable to a shared genetic basis, which interacts with environmental risk factors such as nutritional deficiencies and psychosocial adversity to bring about epigenetic changes. This is seen to result in a lag in brain maturation particularly in the areas of the brain related to executive functioning (top-down regulation) such as the prefrontal and cingulate cortices. This delay when coupled with impairments in reward processing, leads to a preference for immediate small rewards and is common to externalizing disorders. Adult ADHD is increasingly understood to not merely be associated with the classically described symptoms of hyperactivity, impulsivity and inattention, but also issues with motivation, emotional recognition and regulation, excessive mind wandering, and behavioral self-regulation. These symptoms are also observed in other disorders which overlap with the externalizing spectrum such as oppositional defiant disorder, conduct disorder, antisocial and borderline personality disorder. It is therefore important to develop both broad-based and specific interventions to be able to target these deficits which can reduce the burden and improve outcomes.

Salivary biomarkers for the diagnosis and monitoring of neurological diseases

Current research efforts on neurological diseases are focused on identifying novel disease biomarkers to aid in diagnosis, provide accurate prognostic information and monitor disease progression. With advances in detection and quantification methods in genomics, proteomics and metabolomics, saliva has emerged as a good source of samples for detection of disease biomarkers. Obtaining a sample of saliva offers multiple advantages over the currently tested biological fluids as it is a non-invasive, painless and simple procedure that does not require expert training or harbour undesirable side effects for the patients. Here, we review the existing literature on salivary biomarkers and examine their validity in diagnosing and monitoring neurodegenerative and neuropsychiatric disorders such as autism and Alzheimer's, Parkinson's and Huntington's disease. Based on the available research, amyloid beta peptide, tau protein, lactoferrin, alpha-synuclein, DJ-1 protein, chromogranin A, huntingtin protein, DNA methylation disruptions, and micro-RNA profiles provide display a reliable degree of consistency and validity as disease biomarkers.