Emotional and behavioral outcomes among youths with mental disorders during the first Covid lockdown and school closures in England: a large clinical population study using health care record integrated surveys.

PURPOSE: Emotional and behavioral problems in children and young people (CYP) have increased over the pandemic. Those with pre-existing mental disorders are more vulnerable but have been understudied. We investigated emotional and behavioral outcomes in this population; differences across diagnostic groups; and social, educational, and clinical determinants. METHODS: We invited 5386 caregivers and CYP (aged 5-17) under child mental health services pre-pandemic to complete an online survey on CYP's emotional/behavioral symptoms and pandemic-related circumstances, and integrated responses with clinicodemographic information extracted from electronic health records. We compared four parent-rated outcomes (total emotional/behavioral scores and emotional/behavioral changes as compared to before the pandemic) across the three most common diagnostic groups in our population (Attention Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD) and emotional disorders (EmD)). We then estimated the association of clinicodemographic and pandemic-related characteristics with emotional/behavioral outcomes. RESULTS: A total of 1741 parents (32.3%) completed the survey. Parents of CYP with ADHD or ASD reported more behavioral difficulties (t(591) = 5.618 (0.001); t(663) = 6.527 (0.001)); greater emotional deterioration (t(591) = 2.592 (0.009); t(664) = 4.670 (< 0.001); and greater behavioral deterioration (t(594) = 4.529 (< 0.001); t(664) = 5.082 (< 0.001)) as compared to the EmD group. Those with ASD and EmD showed more emotional difficulties than ADHD (t(891) = - 4.431 (< 0.001); t(590) = - 3.254 (0.001)). Across diagnoses, poor parental mental health and challenges with education were most strongly associated with worse outcomes. CONCLUSIONS: Within our clinical population, CYP with ADHD/ASD were the most adversely affected during lockdown. Enhancing clinical service provision that tackles parental stress and supports education may help mitigate the impact of future restrictions.

Remote assessment of ADHD in children and adolescents: recommendations from the European ADHD Guidelines Group following the clinical experience during the COVID-19 pandemic.

The COVID-19 pandemic led ADHD services to modify the clinical practice to reduce in-person contact as much as possible to minimise viral spread. This had far-reaching effects on day-to-day clinical practice as remote assessments were widely adopted. Despite the attenuation of the acute threat from COVID, many clinical services are retaining some remote practices. The lack of clear evidence-based guidance about the most appropriate way to conduct remote assessments meant that these changes were typically implemented in a localised, ad hoc, and un-coordinated way. Here, the European ADHD Guidelines Group (EAGG) discusses the strengths and weaknesses of remote assessment methods of children and adolescents with ADHD in a narrative review based on available data and expert opinions to highlight key recommendations for future studies and clinical practice. We conclude that going forward, despite remote working in clinical services functioning adequately during the pandemic, all required components of ADHD assessment should still be completed following national/international guidelines; however, the process may need adaptation. Social restrictions, including changes in education provision, can either mask or exacerbate features associated with ADHD and therefore assessment should carefully chart symptom profile and impairment prior to, as well as during an ongoing pandemic. While remote assessments are valuable in allowing clinical services to continue despite restrictions and may have benefits for routine care in the post-pandemic world, particular attention must be paid to those who may be at high risk but not be able to use/access remote technologies and prioritize these groups for conventional face-to-face assessments.

A white paper on a neurodevelopmental framework for drug discovery in autism and other neurodevelopmental disorders.

In the last decade there has been a revolution in terms of genetic findings in neurodevelopmental disorders (NDDs), with many discoveries critical for understanding their aetiology and pathophysiology. Clinical trials in single-gene disorders such as fragile X syndrome highlight the challenges of investigating new drug targets in NDDs. Incorporating a developmental perspective into the process of drug development for NDDs could help to overcome some of the current difficulties in identifying and testing new treatments. This paper provides a summary of the proceedings of the 'New Frontiers Meeting' on neurodevelopmental disorders organised by the European College of Neuropsychopharmacology in conjunction with the Innovative Medicines Initiative-sponsored AIMS-2-TRIALS consortium. It brought together experts in developmental genetics, autism, NDDs, and clinical trials from academia and industry, regulators, patient and family associations, and other stakeholders. The meeting sought to provide a platform for focused communication on scientific insights, challenges, and methodologies that might be applicable to the development of CNS treatments from a neurodevelopmental perspective. Multidisciplinary translational consortia to develop basic and clinical research in parallel could be pivotal to advance knowledge in the field. Although implementation of clinical trials for NDDs in paediatric populations is widely acknowledged as essential, safety concerns should guide each aspect of their design. Industry and academia should join forces to improve knowledge of the biology of brain development, identify the optimal timing of interventions, and translate these findings into new drugs, allowing for the needs of users and families, with support from regulatory agencies.

Is there an increased risk of perinatal mental disorder in women with gestational diabetes? A systematic review and meta-analysis.

AIM: Gestational diabetes (GDM) and mental disorder are common perinatal morbidities and are associated with adverse maternal and child outcomes. While there is a relationship between type 2 diabetes and mental disorder, the relationship between GDM and mental disorder has been less studied. We conducted a systematic review and meta-analysis of the prevalence of mental disorders in women with GDM and their risk for mental disorders compared with women without GDM. METHODS: Published, peer-reviewed literature measuring prevalence and/or odds of GDM and perinatal mental disorders was reviewed systematically. Risk of bias was assessed using a checklist. Two independent reviewers were involved. Analyses were grouped by stage of peripartum, i.e. antepartum at the time of GDM diagnosis and after diagnosis, and in the postpartum. RESULTS: Sixty-two studies were included. There was an increased risk of depressive symptoms in the antenatal period around the time of diagnosis of GDM [odds ratio (OR) 2.08; 95% confidence interval (CI) 1.42, 3.05] and in the postnatal period (OR 1.59; 95% CI 1.26, 2.00). CONCLUSIONS: Given the potential relationship between GDM and perinatal mental disorders, integration of physical and mental healthcare in women experiencing GDM and mental disorders could improve short- and long-term outcomes for women and their children.

Disentangling the autism-anxiety overlap: fMRI of reward processing in a community-based longitudinal study.

Up to 40% of youth with autism spectrum disorder (ASD) also suffer from anxiety, and this comorbidity is linked with significant functional impairment. However, the mechanisms of this overlap are poorly understood. We investigated the interplay between ASD traits and anxiety during reward processing, known to be affected in ASD, in a community sample of 1472 adolescents (mean age=14.4 years) who performed a modified monetary incentive delay task as part of the Imagen project. Blood-oxygen-level dependent (BOLD) responses to reward anticipation and feedback were compared using a 2x2 analysis of variance test (ASD traits: low/high; anxiety symptoms: low/high), controlling for plausible covariates. In addition, we used a longitudinal design to assess whether neural responses during reward processing predicted anxiety at 2-year follow-up. High ASD traits were associated with reduced BOLD responses in dorsal prefrontal regions during reward anticipation and negative feedback. Participants with high anxiety symptoms showed increased lateral prefrontal responses during anticipation, but decreased responses following feedback. Interaction effects revealed that youth with combined ASD traits and anxiety, relative to other youth, showed high right insula activation when anticipating reward, and low right-sided caudate, putamen, medial and lateral prefrontal activations during negative feedback (all clusters PFWE<0.05). BOLD activation patterns in the right dorsal cingulate and right medial frontal gyrus predicted new-onset anxiety in participants with high but not low ASD traits. Our results reveal both quantitatively enhanced and qualitatively distinct neural correlates underlying the comorbidity between ASD traits and anxiety. Specific neural responses during reward processing may represent a risk factor for developing anxiety in ASD youth.

Predicting the diagnosis of autism in adults using the Autism-Spectrum Quotient (AQ) questionnaire.

BACKGROUND: Many adults with autism spectrum disorder (ASD) remain undiagnosed. Specialist assessment clinics enable the detection of these cases, but such services are often overstretched. It has been proposed that unnecessary referrals to these services could be reduced by prioritizing individuals who score highly on the Autism-Spectrum Quotient (AQ), a self-report questionnaire measure of autistic traits. However, the ability of the AQ to predict who will go on to receive a diagnosis of ASD in adults is unclear. METHOD: We studied 476 adults, seen consecutively at a national ASD diagnostic referral service for suspected ASD. We tested AQ scores as predictors of ASD diagnosis made by expert clinicians according to International Classification of Diseases (ICD)-10 criteria, informed by the Autism Diagnostic Observation Schedule-Generic (ADOS-G) and Autism Diagnostic Interview-Revised (ADI-R) assessments. RESULTS: Of the participants, 73% received a clinical diagnosis of ASD. Self-report AQ scores did not significantly predict receipt of a diagnosis. While AQ scores provided high sensitivity of 0.77 [95% confidence interval (CI) 0.72-0.82] and positive predictive value of 0.76 (95% CI 0.70-0.80), the specificity of 0.29 (95% CI 0.20-0.38) and negative predictive value of 0.36 (95% CI 0.22-0.40) were low. Thus, 64% of those who scored below the AQ cut-off were 'false negatives' who did in fact have ASD. Co-morbidity data revealed that generalized anxiety disorder may 'mimic' ASD and inflate AQ scores, leading to false positives. CONCLUSIONS: The AQ's utility for screening referrals was limited in this sample. Recommendations supporting the AQ's role in the assessment of adult ASD, e.g. UK NICE guidelines, may need to be reconsidered.

Comparison of parental estimate of developmental age with measured IQ in children with neurodevelopmental disorders.

BACKGROUND: Formal IQ tests are an important part of the diagnostic and needs-based assessment process for children with neurodevelopmental disorders. However, resources for such assessments are not always available. It has been suggested that parental estimates of their child's developmental age could serve as a proxy IQ when formal measures are unavailable. METHOD: Parental estimates of their child's developmental age were converted to a developmental quotient (DQ) in 197 children with Autism Spectrum Disorder (ASD) aged 4-9 years, and 108 children with ADHD and intellectual disability (ADHD + ID) aged 7-15 years. Formal IQ assessments were then conducted. Parents completed the Social Communication Questionnaire ((SCQ), a measure of autism symptomatology) and a demographic questionnaire. RESULTS: In the ASD sample, 58% of parent estimates were within 15 points (i.e. one standard deviation) of the child's measured IQ score. Lower measured IQ and lower SCQ total score predicted higher parental accuracy. In the ADHD + ID sample, 74% of parental estimates were within 15 points of measured IQ. In this group, higher child IQ predicted greater parental accuracy. Parents in the ADHD + ID group were more likely to overestimate children's ability level than parents in the ASD group. CONCLUSIONS: In this study, the majority of parents of children with ADHD and ID were able to estimate their child's intellectual ability level with some accuracy. Parents of children with ASD were less accurate, but this may be because these parents were focussing more on children's level of adaptive functioning, which is known to be typically lower than cognitive ability in ASD.

Elephants in Pyjamas: Testing the Weak Central Coherence Account of Autism Spectrum Disorders Using a Syntactic Disambiguation Task.

According to the weak central coherence (CC) account individuals with autism spectrum disorders (ASD) exhibit enhanced local processing and weak part-whole integration. CC was investigated in the verbal domain. Adolescents, recruited using a 2 (ASD status) by 2 (language impairment status) design, completed an aural forced choice comprehension task involving syntactically ambiguous sentences. Half the picture targets depicted the least plausible interpretation, resulting in longer RTs across groups. These were assumed to reflect local processing. There was no ASD by plausibility interaction and consequently little evidence for weak CC in the verbal domain when conceptualised as enhanced local processing. Furthermore, there was little evidence that the processing of syntactically ambiguous sentences differed as a function of ASD or language-impairment status.

Adolescent eating disorder behaviours and cognitions: gender-specific effects of child, maternal and family risk factors.

BACKGROUND: Eating disorder behaviours begin in adolescence. Few longitudinal studies have investigated childhood risk and protective FACTORS. AIMS: To investigate the prevalence of eating disorder behaviours and cognitions and associated childhood psychological, physical and parental risk factors among a cohort of 14-year-old children. METHOD: Data were collected from 6140 boys and girls aged 14 years. Gender-stratified models were used to estimate prospective associations between childhood body dissatisfaction, body mass index (BMI), self-esteem, maternal eating disorder and family economic disadvantage on adolescent eating disorder behaviours and cognitions. RESULTS: Childhood body dissatisfaction strongly predicted eating disorder cognitions in girls, but only in interaction with BMI in boys. Higher self-esteem had a protective effect, particularly in boys. Maternal eating disorder predicted body dissatisfaction and weight/shape concern in adolescent girls and dieting in boys. CONCLUSIONS: Risk factors for eating disorder behaviours and cognitions vary according to gender. Prevention strategies should be gender-specific and target modifiable predictors in childhood and early adolescence.

IQ in children with autism spectrum disorders: data from the Special Needs and Autism Project (SNAP).

BACKGROUND: Autism spectrum disorder (ASD) was once considered to be highly associated with intellectual disability and to show a characteristic IQ profile, with strengths in performance over verbal abilities and a distinctive pattern of 'peaks' and 'troughs' at the subtest level. However, there are few data from epidemiological studies. METHOD: Comprehensive clinical assessments were conducted with 156 children aged 10-14 years [mean (s.d.)=11.7 (0.9)], seen as part of an epidemiological study (81 childhood autism, 75 other ASD). A sample weighting procedure enabled us to estimate characteristics of the total ASD population. RESULTS: Of the 75 children with ASD, 55% had an intellectual disability (IQ<70) but only 16% had moderate to severe intellectual disability (IQ<50); 28% had average intelligence (115>IQ>85) but only 3% were of above average intelligence (IQ>115). There was some evidence for a clinically significant Performance/Verbal IQ (PIQ/VIQ) discrepancy but discrepant verbal versus performance skills were not associated with a particular pattern of symptoms, as has been reported previously. There was mixed evidence of a characteristic subtest profile: whereas some previously reported patterns were supported (e.g. poor Comprehension), others were not (e.g. no 'peak' in Block Design). Adaptive skills were significantly lower than IQ and were associated with severity of early social impairment and also IQ. CONCLUSIONS: In this epidemiological sample, ASD was less strongly associated with intellectual disability than traditionally held and there was only limited evidence of a distinctive IQ profile. Adaptive outcome was significantly impaired even for those children of average intelligence.

Defining the cognitive phenotype of autism.

Although much progress has been made in determining the cognitive profile of strengths and weaknesses that characterise individuals with autism spectrum disorders (ASDs), there remain a number of outstanding questions. These include how universal strengths and deficits are; whether cognitive subgroups exist; and how cognition is associated with core autistic behaviours, as well as associated psychopathology. Several methodological factors have contributed to these limitations in our knowledge, including: small sample sizes, a focus on single domains of cognition, and an absence of comprehensive behavioural phenotypic information. To attempt to overcome some of these limitations, we assessed a wide range of cognitive domains in a large sample (N=100) of 14- to 16-year-old adolescents with ASDs who had been rigorously behaviourally characterised. In this review, we will use examples of some initial findings in the domains of perceptual processing, emotion processing and memory, both to outline different approaches we have taken to data analysis and to highlight the considerable challenges to better defining the cognitive phenotype(s) of ASDs. Enhanced knowledge of the cognitive phenotype may contribute to our understanding of the complex links between genes, brain and behaviour, as well as inform approaches to remediation.

European guidelines on managing adverse effects of medication for ADHD.

The safety of ADHD medications is not fully known. Concerns have arisen about both a lack of contemporary-standard information about medications first licensed several decades ago, and signals of possible harm arising from more recently developed medications. These relate to both relatively minor adverse effects and extremely serious issues such as sudden cardiac death and suicidality. A guidelines group of the European Network for Hyperkinetic Disorders (EUNETHYDIS) has therefore reviewed the literature, recruited renowned clinical subspecialists and consulted as a group to examine these concerns. Some of the effects examined appeared to be minimal in impact or difficult to distinguish from risk to untreated populations. However, several areas require further study to allow a more precise understanding of these risks.

Non-word repetition in adolescents with specific language impairment and autism plus language impairments: a qualitative analysis.

UNLABELLED: Non-word repetition (NWR) was investigated in adolescents with typical development, Specific Language Impairment (SLI) and Autism Plus language Impairment (ALI) (n=17, 13, 16, and mean age 14;4, 15;4, 14;8 respectively). The study evaluated the hypothesis that poor NWR performance in both groups indicates an overlapping language phenotype (Kjelgaard & Tager-Flusberg, 2001). Performance was investigated both quantitatively, e.g. overall error rates, and qualitatively, e.g. effect of length on repetition, proportion of errors affecting phonological structure, and proportion of consonant substitutions involving manner changes. Findings were consistent with previous research (Whitehouse, Barry, & Bishop, 2008) demonstrating a greater effect of length in the SLI group than the ALI group, which may be due to greater short-term memory limitations. In addition, an automated count of phoneme errors identified poorer performance in the SLI group than the ALI group. These findings indicate differences in the language profiles of individuals with SLI and ALI, but do not rule out a partial overlap. Errors affecting phonological structure were relatively frequent, accounting for around 40% of phonemic errors, but less frequent than straight Consonant-for-Consonant or vowel-for-vowel substitutions. It is proposed that these two different types of errors may reflect separate contributory mechanisms. Around 50% of consonant substitutions in the clinical groups involved manner changes, suggesting poor auditory-perceptual encoding. From a clinical perspective algorithms which automatically count phoneme errors may enhance sensitivity of NWR as a diagnostic marker of language impairment. LEARNING OUTCOMES: Readers will be able to (1) describe and evaluate the hypothesis that there is a phenotypic overlap between SLI and Autism Spectrum Disorders (2) describe differences in the NWR performance of adolescents with SLI and ALI, and discuss whether these differences support or refute the phenotypic overlap hypothesis, and (3) understand how computational algorithms such as the Levenshtein Distance may be used to analyse NWR data.

Sentence repetition in adolescents with specific language impairments and autism: an investigation of complex syntax.

BACKGROUND: Recent studies have indicated that many children with autism spectrum disorders present with language difficulties that are similar to those of children with specific language impairments, leading some to argue for similar structural deficits in these two disorders. AIMS: Repetition of sentences involving long-distance dependencies was used to investigate complex syntax in these groups. METHODS & PROCEDURES: Adolescents with specific language impairments (mean age = 15;3, n = 14) and autism spectrum disorders plus language impairment (autism plus language impairment; mean age = 14;8, n = 16) were recruited alongside typically developing adolescents (mean age = 14;4, n = 17). They were required to repeat sentences containing relative clauses that varied in syntactic complexity. OUTCOMES & RESULTS: The adolescents with specific language impairments presented with greater syntactic difficulties than the adolescents with autism plus language impairment, as manifested by higher error rates on the more complex object relative clauses, and a greater tendency to make syntactic changes during repetition. CONCLUSIONS & IMPLICATIONS: Adolescents with specific language impairments may have more severe syntactic difficulties than adolescents with autism plus language impairment, possibly due to their short-term memory limitations.

Measles vaccination and antibody response in autism spectrum disorders.

OBJECTIVE: To test the hypothesis that measles vaccination was involved in the pathogenesis of autism spectrum disorders (ASD) as evidenced by signs of a persistent measles infection or abnormally persistent immune response shown by circulating measles virus or raised antibody titres in children with ASD who had been vaccinated against measles, mumps and rubella (MMR) compared with controls. DESIGN: Case-control study, community based. METHODS: A community sample of vaccinated children aged 10-12 years in the UK with ASD (n = 98) and two control groups of similar age, one with special educational needs but no ASD (n = 52) and one typically developing group (n = 90), were tested for measles virus and antibody response to measles in the serum. RESULTS: No difference was found between cases and controls for measles antibody response. There was no dose-response relationship between autism symptoms and antibody concentrations. Measles virus nucleic acid was amplified by reverse transcriptase-PCR in peripheral blood mononuclear cells from one patient with autism and two typically developing children. There was no evidence of a differential response to measles virus or the measles component of the MMR in children with ASD, with or without regression, and controls who had either one or two doses of MMR. Only one child from the control group had clinical symptoms of possible enterocolitis. CONCLUSION: No association between measles vaccination and ASD was shown.

In utero characterisation of fetal growth by ultrasound scanning in the rabbit.

Fetal development is an important factor influencing the susceptibility of adults to metabolic diseases. In order to study the influence of fetal growth on further development in animal models like the rabbit, methods of measurement of fetal and placental size and viability must be established and validated. In this study, 42 New Zealand does bred naturally (N=12) or transferred with in vivo produced embryos (2, 4 or 6 embryos/doe) have been scanned every 2-3 days with a 7.5 MHz transabdominal probe from Day 7 post-coitum until term to measure fetal and placental growth. Vesicle, placental, fetal length and head size have thus been determined according to number of fetuses and time. In late gestation, the fetuses that were transferred in limited numbers to the uterus of does were significantly larger than their natural breeding counterparts probably due to reduced litter size.

Parental views about services for children attending schools for the emotionally and behaviourally disturbed (EBD): a qualitative analysis.

AIM: This study examines the views of parents of children attending schools for the emotionally and behaviourally disturbed (EBD). The study aims to gain an understanding of the journey through the educational system taken by these children and to explore their families' experience of services along the way. METHODS: Thirty parents of 25 children attending primary and secondary EBD schools in three South London boroughs took part in focus group discussions. Parents were asked about their experiences of services, including educational, health and social services, as well as how they thought services should be improved. RESULTS: Qualitative analysis identified a complex web of individual, professional and organizational factors which contributed to social exclusion of children with EBD problems and their families. These factors included children receiving inadequate education because of long periods of exclusion or inappropriate placements whilst waiting for a statement of special educational needs. Parents also felt personally socially excluded because of lack of childcare provision out of school hours. Many parents felt that their children did not fit into services and were constantly being passed on to other professionals. The analysis identified aspects of services that promote social inclusion and provide support to families, including acceptance of children into EBD schools, help from voluntary organizations and support from other parents with children with EBD problems. Parents particularly stressed the value of working in collaboration with professionals to achieve shared goals. CONCLUSION: EBD schools provide a valuable resource for parents. However parents often lack emotional and practical support in coping with their children's complex needs. Agencies need to improve communication and joint working to provide effective services for these families.

Assessment of genetic and environmental influences on differential ratings of within-family experiences and relationships in twins.

BACKGROUND: Although there is evidence that genetic factors influence individual differences in environmental risk exposure, there are few findings on genetic effects on differential parenting. The present study sought to examine this issue. METHODS: The sample comprised 1,117 pairs of like-sex male and female twins, aged 8-16 years, and their parents, recruited from the school population of Virginia. Differential ratings of the within-family experiences were provided by the Twin Inventory of Relationships and Experiences (TIRE). RESULTS: Dimensions describing the within-family environment based on differential ratings contrasting the twins with one another, were influenced, to an approximately equal extent, by both genetic and environmental factors. CONCLUSIONS: The findings suggest that genetic differences between like-sex siblings lead them to experience their family environment differently, but also that environmental influences significantly affect interactions within the family.

Child psychiatric symptoms and psychosocial impairment: relationship and prognostic significance.

BACKGROUND: Relatively little is known about the relationships between psychiatric symptoms, diagnosis and psychosocial impairment. AIMS: To examine these contemporaneous relationships and prognostic significance in a large general population sample. METHOD: Symptoms of major depression, conduct and oppositional defiant disorders were assessed by interview in two waves of the Virginia Twin Study of Adolescent behavioural Development (2800 children aged 8-16 years). RESULTS: Many children below the DSM-III-R diagnostic threshold, especially for depression, had symptom-related impairment, whereas many children reaching the symptom threshold for conduct and oppositional defiant disorders were little impaired. Impairment score was linearly related to symptom count, with no evidence of any additional impairment at the diagnostic threshold. For depression, only symptoms predicted later symptoms and diagnosis. For conduct and oppositional defiant disorders, impairment was additionally predictive of later symptoms and diagnosis. CONCLUSIONS: Impairment, in addition to symptoms, is important for both nosology and prognosis.

Association study of a dopamine transporter polymorphism and attention deficit hyperactivity disorder in UK and Turkish samples.

Molecular genetic studies in attention deficit hyperactivity disorder (ADHD) have focussed on candidate genes within the dopamine system, which is thought to be the main site of action of stimulant drugs, the primary pharmacological treatment of the disorder. Of particular interest are findings with the dopamine transporter gene (DAT1), since stimulant drugs interact directly with the transporter protein. To date, there have been eight published association studies of ADHD with a 480 base-pair allele of a variable number tandem repeat (VNTR) polymorphism in the 3'-untranslated region of the gene, five that support an association and three against. We have analysed the same VNTR marker in a dataset of UK Caucasian children and an independent dataset of Turkish Caucasian children with DSM-IV ADHD, using the transmission disequilibrium test (TDT). Results from the UK (chi(2) = 8.97, P = 0.001, OR = 1.95), but not the Turkish sample (chi(2) = 0.93, P = 0.34) support association and linkage between genetic variation at the DAT1 locus and ADHD. When considered alongside evidence from other published reports, there is only modest evidence for the association, consistent with a very small main effect for the 480-bp allele (chi(2) = 3.45, P = 0.06, OR = 1.15), however we find significant evidence of heterogeneity between the combined dataset (chi(2) = 22.64, df = 8, P = 0.004).