Sex differences in attention Deficit Hyperactivity Disorder: candidate genetic and endocrine mechanisms

Methylphenidate enhances implicit learning in healthy adults

BACKGROUND AND PURPOSE

One limiting factor in the development of pharmacological interventions to enhance cognition is the absence of biomarkers that can be used in healthy volunteers to screen novel compounds. Drug discovery has tended to rely heavily on explicit measures of cognition, but these are typically insensitive to cognition-enhancing effects in healthy volunteers. This study investigated whether a novel battery of implicit cognition measures is sensitive to the effects of methylphenidate (Ritalin) in healthy volunteers.

EXPERIMENTAL APPROACH

Eighty healthy volunteers were randomised to receive either a single (10 mg) dose of methylphenidate or matched placebo. Participants completed a battery of tasks measuring implicit cognition (location priming, contextual cueing, implicit task switching). The effect of methylphenidate on standard, explicit measures of cognition was also assessed.

KEY RESULTS

Methylphenidate enhanced implicit learning on the location priming task and the implicit task-switching task. In line with previous work, we found that these effects were greater in male volunteers. There was no evidence for improved learning in any of the explicit measures.

CONCLUSION AND IMPLICATIONS

These results demonstrate that implicit measures of cognition are sensitive to pharmacological interventions in healthy volunteers. As such, implicit cognition measures may be a useful way of screening and tracking cognitive effects of novel agents in experimental medicine studies.

Sex-specific differences in mitochondria biogenesis, morphology, respiratory function, and ROS homeostasis in young mouse heart and brain

Sex-specific differences in mitochondrial function and free radical homeostasis are reported in the context of aging but not well-established in pathogeneses occurring early in life. Here, we examine if sex disparity in mitochondria function, morphology, and redox status starts early and hence can be implicated in sexual dimorphism in cardiac as well as neurological disorders prevalent at young age. Although mitochondrial activity in the heart did not significantly vary between sexes, female brain exhibited enhanced respiration and higher reserve capacity. This was associated with lower H₂O₂ production in female cardiac and brain tissues. Using transmission electron microscopy, we found that the number of female cardiac mitochondria is moderately greater (117 ± 3%, P = 0.049, N = 4) than male's, which increased significantly for cortical mitochondria (134 ± 4%, P = 0.001, N = 4). However, male's cardiac mitochondria exhibited fragmented, circular, and smaller mitochondria relative to female's mitochondria, while no morphologic sex-dependent differences were observed in cortical mitochondria. No sex differences were detected in Nox2 and Nox4 proteins or O₂-consuming/H₂O₂-producing activities in brain homogenate or synaptosomes. However, a strong trend of increased EPR-detected NOX superoxide in male synaptosomes hinted at higher superoxide dismutase activity in female brains, which was confirmed by two independent protocols. We also provide direct evidence that respiring mitochondria generally produce an order-of-magnitude lower reactive oxygen species (ROS) proportions than currently estimated. Our results indicate that sex differences in mitochondrial biogenesis, bioenergetics, and morphology may start at young age and that sex-dependent SOD capacity may be responsible for differences in ROS homeostasis in heart and brain.

Evidence of sexual dimorphism of HTR1B gene on major adult ADHD comorbidities

Attention-deficit/hyperactivity disorder (ADHD) is a very common psychiatric disorder across the life cycle and frequently presents comorbidities. Since ADHD is highly heritable, several studies have focused in the underlying genetic factors involved in its etiology. One of the major challenges in this search is the phenotypic heterogeneity, which could be partly attributable to the sexual dimorphism frequently seen in psychiatric disorders. Taking into account the well-known sexual dimorphic effect observed in serotonergic system characteristics, we differentially tested the influence of HTR1B SNPs (rs11568817, rs130058, rs6296 and rs13212041) on ADHD susceptibility and on its major comorbidities according to sex. The sample comprised 564 adults with ADHD diagnosed according to DSM-IV criteria and 635 controls. There was no association of any HTR1B SNPs tested in relation to ADHD susceptibility. As for the comorbidities evaluated, after correction for multiple tests, significant associations were observed for both rs11568817 and rs130058 with substance use disorders (P_corr = 0.009 and P_corr = 0.018, respectively) and for rs11568817 with nicotine dependence (P_corr = 0.025) in men with ADHD. In women with ADHD, the same rs11568817 was associated with generalized anxiety disorder (P_corr = 0.031). The observed effects of rs11568817 G allele presence conferring risk to either substance use disorders or generalized anxiety disorder according to sex, suggest an overall scenario where a higher transcriptional activity of HTR1B, resulting from the presence of this allele, is related to externalizing behaviors in men and internalizing behaviors in women. These results are consistent with and expand previous evidence of sexual dimorphism of the serotoninergic system.

PCBs and measures of attention and impulsivity on a continuous performance task of young adults

The present study examines the relationship between current body burden of persistent PCBs and attention and impulsivity in 140 Akwesasne Mohawk young adults aged 17 to 21 whose environment has been contaminated by industrial effluent. Attention and impulsivity were measured by errors of omission, errors of commission, and patterns of reaction time responses on the Conners Continuous Performance Test. The PCB measure was the sum of those persistent PCB congeners detected in 50% of the participants. After adjusting for multiple covariates, regression analyses showed a significant positive relationship between PCB levels and omission scores, but only for males.

Pilot study indicate role of preferentially transmitted monoamine oxidase gene variants in behavioral problems of male ADHD probands

Background

Attention deficit hyperactivity disorder (ADHD) is an etiologically complex childhood onset neurobehavioral disorder characterized by age-inappropriate inattention, hyperactivity, and impulsivity. Symptom severity varies widely and boys are diagnosed more frequently than girls. ADHD probands were reported to have abnormal transmissions of dopamine, serotonin, and/or noradrenaline. Monoamine oxidase A (MAOA) and B (MAOB), mitochondrial outer membrane bound two isoenzymes, mediate degradation of these neurotransmitters and thus regulating their circulating levels. Case-control analyses in different populations, including Indians, suggested involvement of MAOA and MAOB genes in the etiology of ADHD. Due to high heritability rate of ADHD, we tested familial transmission of MAOA and MAOB variants to ADHD probands in 190 nuclear families having ADHD probands from Indo-Caucasoid ethnicity.

Methods

Subjects were recruited following the Diagnostic and Statistical Manual of Mental Disorders-4th edition (DSM-IV). Appropriate scales were used for measuring the behavioral traits in probands. Genotyping was performed through PCR-based amplification of target sites followed by DNA-sequencing and/or gel-electrophoresis. Data obtained were analyzed by family based statistical methods.

Results

Out of 58 variants present in the analyzed sites only 15 were found to be polymorphic (30 bp-uVNTR, rs5906883, rs1465107, rs1465108, rs5905809, rs5906957, rs6323, rs1137070 from MAOA and rs4824562, rs56220155, rs2283728, rs2283727, rs3027441, rs6324, rs3027440 from MAOB). Statistically significant maternal transmission of alleles to male probands was observed for MAOA rs5905809 ‘G’ (p = 0.04), rs5906957 ‘A’ (p = 0.04), rs6323 ‘G’ (p = 0.0001) and MAOB rs56220155 ‘A’ (p = 0.002), rs2283728 ‘C’ (p = 0.0008), rs2283727 ‘C’ (p = 0.0008), rs3027441 ‘T’ (p = 0.003), rs6324 ‘C’ (p = 0.003), rs3027440 ‘T’ (p = 0.0002). Significantly preferential maternal transmissions of different haplotype combinations to male probands were also noticed (p < 0.05), while female probands did not reveal such transmission bias. Behavioral traits of male probands exhibited significant association with gene variants. Age of the mother at pregnancy also revealed association with risk variants of male probands.

Conclusions

It may be inferred that the MAOA and MAOB variants may contribute to the etiology of ADHD in the Indo-Caucasoid population and could be responsible for higher occurrence of ADHD in the boys.

Electronic supplementary material

The online version of this article (10.1186/s12881-017-0469-5) contains supplementary material, which is available to authorized users.

Attention-Deficit/Hyperactivity Disorder: A Historical Neuropsychological Perspective

The behavior patterns of hyperactivity, impulsivity and inattention that would ultimately become recognized as Attention-Deficit Hyperactivity Disorder (ADHD) have been described for centuries. Nevertheless, in the past 35 years, advances in diagnostic methods, identification of biomarkers, and treatments have advanced at an exponential rate. ADHD is now recognized as the most common behavioral disorder of childhood, with risks extending well into adulthood for both males and females, leading to its identification as a significant public health issue. This historical neuropsychological review of ADHD emphasizes scientific highlights in the past 35 years related to ADHD, including the evolution of the diagnosis (from Hyperkinetic Reaction of Childhood to ADHD), influential theories (executive functions, cognitive-energetic, delay aversion), landmark treatment studies (Multimodal Treatment of ADHD [MTA] and Preschool ADHD Treatment Study [PATS]), and advances in brain mapping techniques (anatomic, functional, and resting state magnetic resonance imaging, diffusion tensor imaging). The review concludes by highlighting the challenges of studying and treating a heterogeneous neurodevelopmental disorder like ADHD, with emphasis on associated disorders and conditions (learning disabilities, sluggish cognitive tempo), special populations (girls, preschoolers, adults), and recommendations for scientific inquiry in the next 35 years. Neuropsychologists are well positioned to address the clinical and research challenges of the next generation of studies, especially involving advances in understanding the sexual dimor.phism, full developmental course, and dynamic risks associated with ADHD. (JINS, 2017, 23, 916-929).

Offspring neuroimmune consequences of maternal malnutrition: Potential mechanism for behavioral impairments that underlie metabolic and neurodevelopmental disorders

Maternal malnutrition significantly increases offspring risk for both metabolic and neurodevelopmental disorders. Animal models of maternal malnutrition have identified behavioral changes in the adult offspring related to executive function and reward processing. Together, these changes in executive and reward-based behaviors likely contribute to the etiology of both metabolic and neurodevelopmental disorders associated with maternal malnutrition. Concomitant with the behavioral effects, maternal malnutrition alters offspring expression of reward-related molecules and inflammatory signals in brain pathways that control executive function and reward. Neuroimmune pathways and microglial interactions in these specific brain circuits, either in early development or later in adulthood, could directly contribute to the maternal malnutrition-induced behavioral phenotypes. Understanding these mechanisms will help advance treatment strategies for metabolic and neurodevelopmental disorders, especially noninvasive dietary supplementation interventions.

Effect of exposure to polycyclic aromatic hydrocarbons on basal ganglia and attention-deficit hyperactivity disorder symptoms in primary school children

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) have been proposed as environmental risk factors for attention deficit hyperactivity disorder (ADHD). The effects of these pollutants on brain structures potentially involved in the pathophysiology of ADHD are unknown.

OBJECTIVE

The aim of this study was to investigate the effects of PAHs on basal ganglia volumes and ADHD symptoms in school children.

METHODS

We conducted an imaging study in 242 children aged 8-12years, recruited through a set of representative schools of the city of Barcelona, Spain. Indoor and outdoor PAHs and benzo[a]pyrene (BPA) levels were assessed in the school environment, one year before the MRI assessment. Whole-brain volumes and basal ganglia volumes (caudate nucleus, globus pallidus, putamen) were derived from structural MRI scans using automated tissue segmentation. ADHD symptoms (ADHD/DSM-IV Scales, American Psychiatric Association 2002) were reported by teachers, and inattentiveness was evaluated with standard error of hit reaction time in the attention network computer-based test.

RESULTS

Total PAHs and BPA were associated with caudate nucleus volume (CNV) (i.e., an interquartile range increase in BPA outdoor level (67pg/m³) and indoor level (76pg/m³) was significantly linked to a decrease in CNV (mm³) (β=-150.6, 95% CI [-259.1, -42.1], p=0.007, and β=-122.4, 95% CI [-232.9, -11.8], p=0.030 respectively) independently of intracranial volume, age, sex, maternal education and socioeconomic vulnerability index at home). ADHD symptoms and inattentiveness increased in children with higher exposure to BPA, but these associations were not statistically significant.

CONCLUSIONS

Exposure to PAHs, and in particular to BPA, is associated with subclinical changes on the caudate nucleus, even below the legislated annual target levels established in the European Union. The behavioral consequences of this induced brain change were not identified in this study, but given the caudate nucleus involvement in many crucial cognitive and behavior processes, this volume reduction is concerning for the children's neurodevelopment.

Attention deficit hyperactivity disorder (ADHD) in phenotypically similar neurogenetic conditions: Turner syndrome and the RASopathies

Background

ADHD (attention deficit hyperactivity disorder) is a common neurodevelopmental disorder. There has been extensive clinical and basic research in the field of ADHD over the past 20 years, but the mechanisms underlying ADHD risk are multifactorial, complex and heterogeneous and, as yet, are poorly defined. In this review, we argue that one approach to address this challenge is to study well-defined disorders to provide insights into potential biological pathways that may be involved in idiopathic ADHD.

Main body

To address this premise, we selected two neurogenetic conditions that are associated with significantly increased ADHD risk: Turner syndrome and the RASopathies (of which Noonan syndrome and neurofibromatosis type 1 are the best-defined with regard to ADHD-related phenotypes). These syndromes were chosen for two main reasons: first, because intellectual functioning is relatively preserved, and second, because they are strikingly phenotypically similar but are etiologically distinct. We review the cognitive, behavioural, neural and cellular phenotypes associated with these conditions and examine their relevance as a model for idiopathic ADHD.

Conclusion

We conclude by discussing current and future opportunities in the clinical and basic research of these conditions, which, in turn, may shed light upon the biological pathways underlying idiopathic ADHD.

A schizophrenia relevant 5-Choice Serial Reaction Time Task for mice assessing broad monitoring, distractibility and impulsivity

The 5-Choice Serial Reaction Time Task (5-CSRTT) is an automated test for rodents allowing the assessment of multiple cognitive measures. Originally designed to assess cognitive deficits relevant to attention deficit hyperactivity disorder, it has been widely used in the investigation of neural systems of attention. In the current study, we have set up a modified version, which reduced the training phase to only 8-9 days with minimal food deprivation and without single-housing. Furthermore, based on evidence that patients with schizophrenia are more impaired in broad monitoring abilities than in sustained attention, we successfully developed a protocol replicating the Spatial Attentional Resource Allocation Task (SARAT), used in humans to assess broad monitoring. During this task, when the target appeared at a single pre-cued location, mice selectively responded faster. Instead, increasing the number of validly cued locations proportionately decreased accuracy. We then validated a protocol which is relevant for neuropsychiatric disorders in which additional irrelevant pre-cue lights selectively disrupted attention (distractibility). Finally, we improved previously used protocols changing inter-trial intervals from 5 to 7 s by randomly presenting this shift only in 20% of the trials. This resulted in a selective effect on premature responses (impulsivity), with important implications for schizophrenia as well as for other mental disorders. Therefore, this revised 5-CSRTT reduced training and stress on the animals while selectively measuring different cognitive functions with translational validity to schizophrenia and other psychiatric disorders.

Association of Y-linked variants with impulsivity and aggression in boys with attention-deficit/hyperactivity disorder of Chinese Han descent

Y chromosome plays important role in brain function and may help to explain the sex difference in attention-deficit/hyperactivity disorder (ADHD). A total of 857 boys with ADHD and 574 male controls were genotyped for 14 Y-linked markers. Analyses for both dichotomous phenotype and quantitative traits and the interaction effects with MAOA were performed. The results indicated significant association of four markers (M88, M95, M175, and M119) with inhibition function and aggression in boys with ADHD. Positive interaction effects with MAOA were also detected. In conclusion, some Y-linked variants may be associated with the impulsivity and aggression in boys with ADHD.

Potential short-term neurobehavioral alterations in children associated with a peak pesticide spray season: The Mother's Day flower harvest in Ecuador

BACKGROUND

Exposures to cholinesterase inhibitor pesticides (e.g. organophosphates) have been associated with children's neurobehavioral alterations, including attention deficit and impulsivity. Animal studies have observed transient alterations in neurobehavioral performance in relation to cholinesterase inhibitor pesticide exposures; however, limited evidence exists regarding transient effects in humans.

METHODS

We estimated the associations between neurobehavioral performance and time after Mother's Day flower harvest (the end of a heightened pesticide usage period) among 308 4-to 9-year-old children living in floricultural communities in Ecuador in 2008 who participated in the ESPINA study. Children's neurobehavior was examined once (NEPSY-II: 11 subtests covering 5 domains), between 63 and 100days (SD: 10.8days) after Mother's Day harvest (blood acetylcholinesterase activity levels can take 82days to normalize after irreversible inhibition with organophosphates).

RESULTS

The mean (SD) neurobehavioral scaled scores across domains ranged from 6.6 (2.4) to 9.9 (3.3); higher values reflect greater performance. Children examined sooner after Mother's Day had lower neurobehavioral scores than children examined later, in the domains of (score difference per 10.8days, 95%CI): Attention/Inhibitory Control (0.38, 0.10-0.65), Visuospatial Processing (0.60, 0.25-0.95) and Sensorimotor (0.43, 0.10-0.77). Scores were higher with longer time post-harvest among girls (vs. boys) in Attention/Inhibitory Control.

CONCLUSIONS

Our findings, although cross-sectional, are among the first in non-worker children to suggest that a peak pesticide use period may transiently affect neurobehavioral performance, as children examined sooner after the flower harvest had lower neurobehavioral performance than children examined later. Studies assessing pre- and post-exposure measures are needed.

Polymorphisms of STS gene and SULT2A1 gene and neurosteroid levels in Han Chinese boys with attention-deficit/hyperactivity disorder: an exploratory investigation

This study examined the relationships among polymorphisms of the STS gene and SULT2A1 gene, dehydroepiandrosterone (DHEA) and its sulfated form (DHEA-S), and characteristics of attention-deficit/hyperactivity disorder (ADHD). We used cheek swabs to obtain the genomic DNA of 200 ADHD male probands (mean age: 8.7 years), 192 patients’ mothers and 157 patients’ fathers. Three SNPs in the STS gene (rs6639786, rs2270112, and rs17268988) and one SNP in the SULT2A1 gene (rs182420) were genotyped. Saliva samples were collected from the ADHD patients to analyze DHEA and DHEA-S levels. The behavioral symptoms were evaluated with the Swanson, Nolan, and Pelham, and Version IV Scale for ADHD (SNAP-IV), and the neuropsychological function was assessed using the Conners’ Continuous Performance Tests (CPT). We found the C allele of rs2270112 within the STS gene to be over-transmitted in males with ADHD. Polymorphisms of rs182420 within the SULT2A1 gene were not associated with ADHD. In addition, the C allele carriers of rs2270112 demonstrated significantly higher DHEA-S levels than the G allele carriers. Levels of DHEA were positively correlated with attention as measured by the CPT. These findings support a potential role in the underlying biological pathogenesis of ADHD with regard to STS polymorphisms and neurosteroid levels.

Utilization of Stimulants and Atomoxetine for Attention-Deficit/Hyperactivity Disorder among 5.4 Million Children Using Population-Based Longitudinal Data

Use of stimulants to treat attention-deficit/hyperactivity disorder (ADHD) has increased over the past two decades and varies substantially between countries. The objective of this multinational population-based study was to examine utilization of ADHD drugs (stimulants and atomoxetine) including comedication with other psychotropic drugs in the entire child population in the five Nordic countries. We included longitudinal data on dispensed ADHD drugs from five Nordic prescription registers during 2008-2012, which in 2012 comprised 48,296 individuals among 5.42 million inhabitants aged 0-17 years. Prevalence of filling ≥1 prescriptions of ADHD drugs among children aged 6-17 years increased during 2008-2012 from 5.9 to 11.2 and 19.4 to 31.0 per 1000 girls and boys, respectively. Prevalence by country showed that Iceland, Finland and Sweden had a steady increase during the study period, while in Norway the prevalence was quite stable and in Denmark it levelled off from 2010. Use in preschoolers (aged 0-5 years) was rare. Iceland had much higher prevalence and incidence than the other Nordic countries. The incidence of ADHD drug use increased during the study period, from 4.0 to 4.9 and from 1.5 to 2.3 per 1000 boys and girls, respectively. The increasing number of new users levelled off somewhat after 2010. Comedication with other psychotropic drugs was more common among girls (33.9%) than boys (27.0%) and was mainly melatonin, followed by antidepressants and antipsychotics. Overall prevalence of ADHD drug use increased among Nordic girls and boys aged 6-17 years, whereas the incidence increased slightly during 2008-2010 but levelled off through 2012. The substantial differences in ADHD drug use across the Nordic countries and high degree of comedication with other psychotropic drugs underscore the importance of close monitoring of treatment for ADHD among children.

Potential role of pre- and postnatal testosterone levels in attention-deficit/hyperactivity disorder: is there a sex difference?

OBJECTIVE

Both prenatal testosterone (T) exposure and postnatal T levels have been associated with developing neural circuitry and behavioral systems. This study examined the potential correlation between pre- and postnatal T levels and behavioral and neurocognitive profiles of children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

Two hundred ADHD patients with a mean age of 8.7±2.0 years (158 boys and 42 girls) were recruited. The ratio of the length of the right index finger (2D) to that of the right ring finger (4D) (2D/4D ratio) served as a surrogate of prenatal T exposure, and postnatal T was determined using salivary T concentration. Behavioral symptoms were evaluated using the Swanson, Nolan, and Pelham - Version IV Scale for ADHD (SNAP-IV). Neurocognitive function was assessed using the Wechsler Intelligence Scale for Children - Fourth Edition (WISC-IV) and Conners' Continuous Performance Test (CPT).

RESULTS

Lower 2D/4D ratios were associated with comorbid disruptive behavior disorders (t=2.15, P=0.033) in all participants. Among the boys with ADHD, neither 2D/4D ratios nor salivary T levels were associated with behavioral symptoms or neurocognitive function. Among the girls with ADHD, the salivary T level was positively correlated with the Perceptual Reasoning Index of the WISC-IV (r=0.48, P=0.001) and the Confidence Index (r=0.37, P=0.017) and Omission Errors of the CPT (r=0.62, P<0.001).

CONCLUSION

Findings suggest that a higher prenatal T exposure is associated with a greater risk of developing disruptive behavior disorders, and T may exert differential neurocognitive effects between boys and girls with ADHD. However, the neurobiological mechanisms of T involved in the pathogenesis of ADHD warrant further investigation.

Associations between corpus callosum size and ADHD symptoms in older adults: The PATH through life study

Neuroimaging studies of attention-deficit/hyperactivity disorder (ADHD) have revealed deviations of the corpus callosum in children and adolescents. However, little is known about the link between callosal morphology and symptoms of inattention or hyperactivity in adulthood, especially later in life. Here, we investigated in a large population-based sample of 280 adults (150 males, 130 females) in their late sixties and early seventies whether ADHD symptoms correlate with callosal thickness. In addition, we tested for significant sex interactions, which were followed by correlation analyses stratified by sex. Within males, there were significant negative correlations with respect to inattention and hyperactivity in various callosal regions, including the anterior third, anterior and posterior midbody, isthmus, and splenium. A thinner corpus callosum may be associated with fewer fibers or less myelination of fibers. Thus, the observed negative correlations suggest impaired inter-hemispheric communication channels necessary to sustain motor control and attention, which may contribute to symptoms of hyperactivity, impulsivity and/or inattention. Interestingly, within females, callosal thickness was positively related to hyperactivity in a small area within the rostral body, suggesting a sexually dimorphic neurobiology of ADHD symptoms. Altogether, the present results may reflect a lasting relationship between callosal morphology and ADHD symptoms throughout life.

Exploratory study to evaluate plasma vasopressin and apelin-13 levels in children with attention-deficit hyperactivity disorder

AIM

Vasopressin exerts robust influences on social communication and behavior in humans. Apelin is a relatively novel neuropeptide that could counteract vasopressin's actions and has been shown to be closely related with a broad range of physiological functions. Abnormalities in vasopressin and apelin have been detected in a variety of psychiatric disorders, but their relation to attention-deficit hyperactivity disorder (ADHD) is unknown. In the present study, we explored the plasma levels of vasopressin and apelin-13 in children with ADHD.

METHODS

Thirty-four children with ADHD and 36 healthy controls were enrolled in this study. The severity of ADHD symptoms was assessed via Conners' Parent Rating Scale and Conners' Teacher Rating Scale. Plasma levels of vasopressin and apelin-13 were measured using commercial enzyme-linked immunosorbent assay kits.

RESULTS

The mean plasma apelin-13 levels were significantly higher in male children with ADHD than in male control subjects; no significant difference was found between the groups for plasma apelin-13 levels in girls or in the entire subject cohort. Plasma vasopressin levels did not show any significant differences between groups. There were no significant correlations between plasma levels of these neuropeptides and scores for Conners' Parent Rating Scale and Conners' Teacher Rating Scale.

CONCLUSION

Our results suggest a sex-specific association between plasma apelin-13 levels and ADHD. Apelin-13 may play a role in the etiopathogenesis of ADHD either with a direct impact on the apelin receptor or via its opposing effect on the vasopressinergic system.

Monoamine oxidase B gene variants associated with attention deficit hyperactivity disorder in the Indo-Caucasoid population from West Bengal

Background

Attention deficit hyperactivity disorder (ADHD) is characterized by symptoms of inattention, excessive motor activity and impulsivity detected mostly during childhood. These traits are known to be controlled by monoamine neurotransmitters, chiefly dopamine, serotonin and norepinephrine. Monoamine oxidase A (MAOA) and B (MAOB), two isoenzymes bound to the outer membrane of mitochondria, are involved in the degradation of monoamines and were explored for association with ADHD in different ethnic groups. In the present study, few exonic as well as intronic MAOB variants were analyzed in ADHD probands (N = 150) and ethnically matched controls (N = 150) recruited following the Diagnostic and Statistical Manual for Mental Disorders-4^th edition (DSM-IV). Appropriate scales were used for measuring the behavioural attributes. Gene variants were analyzed by amplification of target sites followed by DNA sequencing and data obtained were analyzed by population based statistical methods.

Results

Out of 34 variants present in the analyzed sites, only seven functional variants, rs4824562, rs56220155, rs2283728, rs2283727, rs3027441, rs6324 and rs3027440, were found to be polymorphic. rs2283728 ‘C’ (P = 3.45e-006) and rs3027440 ‘T’ (P = 0.02) alleles showed higher frequencies in ADHD probands as compared to controls. rs56220155 ‘A’ (P = 0.04) allele and ‘GA’ (P = 0.04) genotype showed higher frequencies in the male and female ADHD probands respectively as compared to sex-matched controls. Analysis of pairwise linkage disequilibrium revealed striking differences between probands and controls. Haplotype analysis revealed significantly higher occurrence of different haplotypes in the ADHD probands while some haplotypes were detected in the controls only. Higher scores for conduct problems were found to be associated with rs56220155 ‘A’ (P = 0.05) allele in the male ADHD probands. Multifactor dimensionality reduction analysis showed independent as well as interactive effects of polymorphic variants which were more robust in the male probands.

Conclusions

Since all the polymorphic variants analyzed were functional, it may be inferred that MAOB gene variants are contributing to the etiology of ADHD in the Indo-Caucasoid population from eastern India which merits further in depth analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0401-6) contains supplementary material, which is available to authorized users.

Moving towards causality in attention-deficit hyperactivity disorder: overview of neural and genetic mechanisms

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by developmentally inappropriate levels of inattention and hyperactivity or impulsivity. The heterogeneity of its clinical manifestations and the differential responses to treatment and varied prognoses have long suggested myriad underlying causes. Over the past decade, clinical and basic research efforts have uncovered many behavioural and neurobiological alterations associated with ADHD, from genes to higher order neural networks. Here, we review the neurobiology of ADHD by focusing on neural circuits implicated in the disorder and discuss how abnormalities in circuitry relate to symptom presentation and treatment. We summarise the literature on genetic variants that are potentially related to the development of ADHD, and how these, in turn, might affect circuit function and relevant behaviours. Whether these underlying neurobiological factors are causally related to symptom presentation remains unresolved. Therefore, we assess efforts aimed at disentangling issues of causality, and showcase the shifting research landscape towards endophenotype refinement in clinical and preclinical settings. Furthermore, we review approaches being developed to understand the neurobiological underpinnings of this complex disorder, including the use of animal models, neuromodulation, and pharmacoimaging studies.

Sex and Gender Differences in Central Nervous System-Related Disorders

There are important sex differences in the brain that seem to arise from biology as well as psychosocial influences. Sex differences in several aspects of human behavior and cognition have been reported. Gonadal sex steroids or genes found on sex chromosomes influence sex differences in neuroanatomy, neurochemistry and neuronal structure, and connectivity. There has been some resistance to accept that sex differences in the human brain exist and have biological relevance; however, a few years ago, it has been recommended by the USA National Institute of Mental Health to incorporate sex as a variable in experimental and clinical neurological and psychiatric studies. We here review the clinical literature on sex differences in pain and neurological and psychiatric diseases, with the aim to further stimulate interest in sexual dimorphisms in the brain and brain diseases, possibly encouraging more research in the field of the implications of sex differences for treating these conditions.

Testosterone and Androgen Receptor Sensitivity in Relation to Hyperactivity Symptoms in Boys with Autism Spectrum Disorders

INTRODUCTION

Autism spectrum disorders (ASD) and hyperactivity symptoms exhibit an incidence that is male-biased. Thus androgen activity can be considered a plausible biological risk factor for these disorders. However, there is insufficient information about the association between increased androgen activity and hyperactivity symptoms in children with ASD.

METHODS

In the present study, the relationship between parameters of androgenicity (plasmatic testosterone levels and androgen receptor sensitivity) and hyperactivity in 60 boys (age 3-15) with ASD is investigated. Given well documented differences in parent and trained examiners ratings of symptom severity, we employed a standardized parent`s questionnaire (Nisonger Child Behavior Rating Form) as well as a direct examiner`s rating (Autism diagnostic observation schedule) for assessment of hyperactivity symptoms.

RESULTS

Although it was found there was no significant association between actual plasmatic testosterone levels and hyperactivity symptoms, the number of CAG triplets was significantly negatively correlated with hyperactivity symptoms (R2 = 0.118, p = 0.007) in the sample, indicating increased androgen receptor sensitivity in association with hyperactivity symptoms. Direct trained examiner´s assessment appeared to be a relevant method for evaluating of behavioral problems in the investigation of biological underpinnings of these problems in our study.

CONCLUSIONS

A potential ASD subtype characterized by increased rates of hyperactivity symptoms might have distinct etiopathogenesis and require a specific behavioral and pharmacological approach. We propose an increase of androgen receptor sensitivity as a biomarker for a specific ASD subtype accompanied with hyperactivity symptoms. Findings are discussed in terms of their implications for practice and future research.

Genetic dissection of neural circuits underlying sexually dimorphic social behaviours

The unique hormonal, genetic and epigenetic environments of males and females during development and adulthood shape the neural circuitry of the brain. These differences in neural circuitry result in sex-typical displays of social behaviours such as mating and aggression. Like other neural circuits, those underlying sex-typical social behaviours weave through complex brain regions that control a variety of diverse behaviours. For this reason, the functional dissection of neural circuits underlying sex-typical social behaviours has proved to be difficult. However, molecularly discrete neuronal subpopulations can be identified in the heterogeneous brain regions that control sex-typical social behaviours. In addition, the actions of oestrogens and androgens produce sex differences in gene expression within these brain regions, thereby highlighting the neuronal subpopulations most likely to control sexually dimorphic social behaviours. These conditions permit the implementation of innovative genetic approaches that, in mammals, are most highly advanced in the laboratory mouse. Such approaches have greatly advanced our understanding of the functional significance of sexually dimorphic neural circuits in the brain. In this review, we discuss the neural circuitry of sex-typical social behaviours in mice while highlighting the genetic technical innovations that have advanced the field.

Testosterone in relation to behavioral problems in pre-pubertal boys with autism spectrum disorders

Autism spectrum disorders (ASD) are neurodevelopmental conditions characterized by impairment in social communication and presence of stereotyped/restricted behaviors. Children with ASD very often demonstrate co-morbid psychiatric problems, problems known to be affected by testosterone in neurotypical populations. However, there are few reports investigating relationships between testosterone and psychiatric conditions in children with ASD. The aim of this study was to determine the relationship between plasmatic levels of testosterone and behavioral/emotional problems in pre-pubertal boys with ASD. The study sample consisted of 31 pre-pubertal boys (ages 3-10) with ASD. Parents completed the Nisonger Child Behavior Rating Form (NCBRF) to assess specific behavioral/emotional problems as observed in the previous 2 months. Plasmatic testosterone levels were determined in boys according to standardized procedures. It was found that there were positive correlations between testosterone levels and the conduct problems subscale (p=0.034, rs=0.382) of NCBRF and also between testosterone levels and the hyperactive subscale (p=0.025, rs=0.402) of NCBRF. Findings in this study are in line with research conducted in the neurotypical population. This is the first large study investigating testosterone and emotional/behavioral problems in ASD and warrants further research in this field in order to clarify the etiopathogenesis of psychiatric co-morbidities and improve their treatment.

Perinatal exposure to endocrine disruptors: sex, timing and behavioral endpoints

Of the approximately 85,000 chemicals in use, 1000 have been identified as having the ability to disrupt normal endocrine function. Exposure to endocrine disrupting chemicals (EDCs) during critical period in brain differentiation (prenatal and neonatal life) via the mother can alter the course of the development of sexually dimorphic behaviors. Bisphenol A (BPA) is a very high volume chemical used in plastic, resins and other products, and virtually everyone examined has detectable BPA. BPA has estrogenic activity and is one of the most studied EDCs. We review evidence from studies in rodents using dose levels relevant to human exposure. BPA alters behavior and eliminates or in some cases reverses sexually dimorphic behaviors observed in unexposed animals.

Elucidating X chromosome influences on Attention Deficit Hyperactivity Disorder and executive function

OBJECTIVE

To identify distinct behavioral and cognitive profiles associated with ADHD in Turner syndrome (TS), relative to idiopathic ADHD and neurotypical controls, in order to elucidate X-linked influences contributing to ADHD.

METHODS

We used a multilevel-model approach to compare 49 girls with TS to 37 neurotypical females, aged 5-12, on established measures of behavior (BASC-2) and neurocognitive function (NEPSY). We further compared girls with TS to BASC-2 and NEPSY age-matched reference data obtained from children with idiopathic ADHD.

RESULTS

Within the TS group, 51% scored at or above the "at-risk" range for ADHD-associated behaviors on the BASC-2 (TS/+ADHD). The BASC-2 behavioral profile in this TS/+ADHD-subgroup was comparable to a reference group of boys with ADHD with respect to attentional problems and hyperactivity. However, the TS/+ADHD-subgroup had significantly higher hyperactivity scores relative to a reference sample of girls with ADHD (p = 0.016). The behavioral profile in TS was associated with significantly lower attention and executive function scores on the NEPSY relative to neurotypical controls (p = 0.015); but was comparable to scores from a reference sample of children with idiopathic ADHD. Deficits in attention and executive function were not observed in girls with TS having low levels of ADHD-associated behavior (TS/-ADHD).

CONCLUSIONS

ADHD-associated behavioral and cognitive problems in TS are prevalent and comparable in severity to those found in children with idiopathic ADHD. The ADHD phenotype in TS also appears relatively independent of cognitive features typically associated with TS, like visuospatial weaknesses. These findings suggest that X-linked haploinsufficiency and downstream biological effects contribute to increased risk for ADHD.

Gender Differences in the Behavioral Symptoms and Neuropsychological Performance of Patients with Attention-Deficit/Hyperactivity Disorder Treated with Methylphenidate: A Two-Year Follow-up Study

OBJECTIVE

This study investigated the gender differences in behavioral symptoms, as rated by various informants, and in neuropsychological performance, among patients with attention-deficit/hyperactivity disorder (ADHD) treated with methylphenidate during 24 months in a clinical setting.

METHODS

Study participants comprised 128 boys (mean age: 13.2±2.4 years) and 26 girls (mean age: 12.8±1.0 years) with ADHD. All patients were prescribed short-acting oral methylphenidate, taken two or three times daily; each dose ranged between 0.3 and 1.0 mg/kg. At the baseline and 6, 12, 18, and 24 months later, behavioral symptoms were evaluated using the parent and teacher forms of the Swanson, Nolan, and Pelham Version IV (SNAP-IV) scale for ADHD and the ADHD Rating Scale (completed by a child psychiatrist). In addition, neuropsychological function was assessed using the Test of Variables of Attention (TOVA) at each interval.

RESULTS

Although both the boys and girls exhibited a significant decrease in the ADHD symptoms observed by parents and clinicians, the girls improved more than the boys did. Based on the teacher reports, neither the boys nor the girls exhibited significant decreases in ADHD symptoms. The symptoms rated by teachers were more severe in the boys than in the girls throughout the first 12 months; however, the gender difference lessened after 12 months. Based on the TOVA assessment, a composite score (containing response time, response time variability, and ADHD score obtained using the TOVA) did not indicate differences between genders. However, another composite score (containing omission errors, commission errors, and response sensitivity) suggested significant improvement only in the boys.

CONCLUSIONS

The results suggested that according to a longitudinal follow-up, behavioral and neuropsychological changes among patients with ADHD might differ between genders. Gathering multidimensional information from patients with ADHD is essential in determining how gender modifies the functional outcome of ADHD.

Biological factors underlying sex differences in neurological disorders

The prevalence, age of onset, pathophysiology, and symptomatology of many neurological and neuropsychiatric conditions differ significantly between males and females. Females suffer more from mood disorders such as depression and anxiety, whereas males are more susceptible to deficits in the dopamine system including Parkinson's disease (PD), attention-deficit hyperactivity disorder (ADHD), schizophrenia, and autism spectrum disorders (ASD). Until recently, these sex differences have been explained solely by the neuroprotective actions of sex hormones in females. Emerging evidence however indicates that the sex chromosome genes (i.e. X- and Y-linked genes) also contribute to brain sex differences. In particular, the Y-chromosome gene, SRY (Sex-determining Region on the Y chromosome) is an interesting candidate as it is expressed in dopamine-abundant brain regions, where it regulates dopamine biosynthesis and dopamine-mediated functions such as voluntary movement in males. Furthermore, SRY expression is dysregulated in a toxin-induced model of PD, suggesting a role for SRY in the pathogenesis of dopamine cells. Taken together, these studies highlight the importance of understanding the interplay between sex-specific hormones and sex-specific genes in healthy and diseased brain. In particular, better understanding of regulation and function of SRY in the male brain could provide entirely novel and important insights into genetic factors involved in the susceptibility of men to neurological disorders, as well as development of novel sex-specific therapies.

Sex differences in myelin-associated protein levels within and density of projections between the orbital frontal cortex and dorsal striatum of adult rats: implications for inhibitory control

Impulsive actions and decisions often lead to undesirable outcomes. Lesion and neuroimaging studies have revealed that the orbital frontal cortex (OFC) and dorsal striatum (dSTR) play key roles in inhibitory control. It has been proposed that greater OFC input into the dSTR reflects enhanced top-down cognitive control and less impulsive responding. We previously reported a sex difference in inhibitory control, such that female rats make fewer impulsive errors than do male rats. The goal of the present study was to investigate differences in the OFC and dSTR of young adult male and female rats. In Experiment 1, we measured levels of two myelin-associated proteins, myelin basic protein (MBP) and myelin proteolipid protein (PLP), in the OFC and dSTR. Western blot data revealed that females had significantly higher levels of both MBP and PLP in the OFC but similar levels in the dSTR as compared to males. In Experiment 2, we infused the anterograde tracer, biotinylated dextran amine (BDA), into the OFC and measured the density of BDA in the dSTR. BDA was visualized using histochemistry followed by light microscopy imaging and densitometry analysis. Density of BDA in the dSTR was significantly greater in females as compared to males indicating that the projections from the OFC to dSTR may be greater in females as compared to males. Our results suggest a potential neuroanatomical sex difference that may contribute to the reported differences in inhibitory control levels of male and female rats.

Comparison of the validity of the use of the spontaneously hypertensive rat as a model of attention deficit hyperactivity disorder in males and females

The spontaneously hypertensive rat (SHR) is a commonly used and well-studied rodent model of attention deficit hyperactivity disorder (ADHD). Sex differences in the cognitive symptoms of ADHD are reported. However, the female SHR rat is much less studied than its male counterpart. The goal of the current study was to assess the validity of the SHR rodent model of ADHD by examining attentional performance, inhibitory control, and hyperactivity in both male and female SHR rats. Adult SHR and control Wistar-Kyoto rats were trained on the 5-choice serial reaction time task, a self-paced test of attention and inhibitory control. This task requires animals to identify the location of a brief light stimulus among five possible locations under several challenging conditions. Analyses of percent correct revealed that attentional performance in SHR females was not significantly different from control females, whereas attentional performance in SHR males was significantly different from control males. Analyses of the number of premature responses revealed that SHR rats made more inhibitory control errors than did control rats and that this decrease in inhibitory control was present in both SHR males and females. Analyses of activity in the open field revealed that SHR rats were more hyperactive than were control rats and that this increased hyperactivity was present in both SHR males and females. The current findings have implications for the study of sex differences in ADHD and for the use of SHR rats as a model of ADHD in females.

Interactions between MAOA and SYP polymorphisms were associated with symptoms of attention-deficit/hyperactivity disorder in Chinese Han subjects

As candidate genes of attention--deficit/hyperactivity disorder (ADHD), monoamine oxidase A (MAOA), and synaptophysin (SYP) are both on the X chromosome, and have been suggested to be associated with the predominantly inattentive subtype (ADHD-I). The present study is to investigate the potential gene-gene interaction (G × G) between rs5905859 of MAOA and rs5906754 of SYP for ADHD in Chinese Han subjects. For family-based association study, 177 female trios were included. For case-control study, 1,462 probands and 807 normal controls were recruited. The ADHD Rating Scale-IV (ADHD-RS-IV) was used to evaluate ADHD symptoms. Pedigree-based generalized multifactor dimensionality reduction (PGMDR) for female ADHD trios indicated significant gene interaction effect of rs5905859 and rs5906754. Generalized multifactor dimensionality reduction (GMDR) indicated potential gene-gene interplay on ADHD RS-IV scores in female ADHD-I. No associations were observed in male subjects in case-control analysis. In conclusion, our findings suggested that the interaction of MAOA and SYP may be involved in the genetic mechanism of ADHD-I subtype and predict ADHD symptoms.