Genome-wide analyses of ADHD identify 27 risk loci, refine the genetic architecture and implicate several cognitive domains.

Attention-deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder with a major genetic component. Here, we present a genome-wide association study meta-analysis of ADHD comprising 38,691 individuals with ADHD and 186,843 controls. We identified 27 genome-wide significant loci, highlighting 76 potential risk genes enriched among genes expressed particularly in early brain development. Overall, ADHD genetic risk was associated with several brain-specific neuronal subtypes and midbrain dopaminergic neurons. In exome-sequencing data from 17,896 individuals, we identified an increased load of rare protein-truncating variants in ADHD for a set of risk genes enriched with probable causal common variants, potentially implicating SORCS3 in ADHD by both common and rare variants. Bivariate Gaussian mixture modeling estimated that 84-98% of ADHD-influencing variants are shared with other psychiatric disorders. In addition, common-variant ADHD risk was associated with impaired complex cognition such as verbal reasoning and a range of executive functions, including attention.

[Diagnosis, rehabilitation and development of disability 2000-2019 in Iceland].

INTRODUCTION: The disability assessment standard based on medically recognized illnesses or disabilities was introduced in Iceland 1999. The aim of this study is to examine the development of Social Insurance Administration (Tryggingastofnun ríkisins, TR) rulings regarding rehabilitation and disability pensions over a twenty-year period, since its introduction. MATERIAL AND METHODS: All registered diagnoses in the medical certificates of TR due to the approved rehabilitation or disability pension were examined in the period 2000-2019. The gender distribution and age distribution of these applicants and the number development during the period are described. At the same time, costs as a percentage of government expenditure are examined. RESULTS: The number of younger rehabilitation pensioners has increased rapidly in recent years, at the same time as the relative increase in disability pensioners has slowed slightly. Mental and musculoskeletal disorders are by far the most common types of illness leading to disability. Mental illnesses differ in terms of age distribution and increase over time. The proportion of individuals aged 18-66 with a 75% disability assessment has increased by a third during the period, from about 6% to 8%. The gender distribution of disability pensioners remains similar, with women accounting for 62% in total. Women are much more likely to receive disability pension due to musculoskeletal disorders than men and men are somewhat more likely to suffer from mental illness. The relative development of central government expenditure on total payments to rehabilitation and pensioners continues to grow as a proportion of central government expenditure. CONCLUSION: The number of rehabilitation pensioners has increased significantly since 2018, at the same time as the number of disability pensioners has decreased and there are indications that rehabilitation results in a lower number of new disability pensioners. Mental and musculoskeletal disorders are by far the most common types of illness leading to disability. A slightly lower proportion of disabled people have psychiatric diagnosis as a first diagnosis in the period 2000-2019 compared to those with a valid disability assessment in 2005, but the proportion of musculoskeletal disorders is slightly higher. Nevertheless, mental illnesses differ in age distribution and increase over time.

Identification of genetic overlap and novel risk loci for attention-deficit/hyperactivity disorder and bipolar disorder.

Differential diagnosis between childhood onset attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder (BD) remains a challenge, mainly due to overlapping symptoms and high rates of comorbidity. Despite this, genetic correlation reported for these disorders is low and non-significant. Here we aimed to better characterize the genetic architecture of these disorders utilizing recent large genome-wide association studies (GWAS). We analyzed independent GWAS summary statistics for ADHD (19,099 cases and 34,194 controls) and BD (20,352 cases and 31,358 controls) applying the conditional/conjunctional false discovery rate (condFDR/conjFDR) statistical framework that increases the power to detect novel phenotype-specific and shared loci by leveraging the combined power of two GWAS. We observed cross-trait polygenic enrichment for ADHD conditioned on associations with BD, and vice versa. Leveraging this enrichment, we identified 19 novel ADHD risk loci and 40 novel BD risk loci at condFDR <0.05. Further, we identified five loci jointly associated with ADHD and BD (conjFDR < 0.05). Interestingly, these five loci show concordant directions of effect for ADHD and BD. These results highlight a shared underlying genetic risk for ADHD and BD which may help to explain the high comorbidity rates and difficulties in differentiating between ADHD and BD in the clinic. Improving our understanding of the underlying genetic architecture of these disorders may aid in the development of novel stratification tools to help reduce these diagnostic difficulties.

Identification of Genetic Loci Shared Between Attention-Deficit/Hyperactivity Disorder, Intelligence, and Educational Attainment.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that is consistently associated with lower levels of educational attainment. A recent large genome-wide association study identified common gene variants associated with ADHD, but most of the genetic architecture remains unknown. METHODS: We analyzed independent genome-wide association study summary statistics for ADHD (19,099 cases and 34,194 controls), educational attainment (N = 842,499), and general intelligence (N = 269,867) using a conditional/conjunctional false discovery rate (FDR) statistical framework that increases power of discovery by conditioning the FDR on overlapping associations. The genetic variants identified were characterized in terms of function, expression, and biological processes. RESULTS: We identified 58 linkage disequilibrium-independent ADHD-associated loci (conditional FDR < 0.01), of which 30 were shared between ADHD and educational attainment or general intelligence (conjunctional FDR < 0.01) and 46 were novel risk loci for ADHD. CONCLUSIONS: These results expand on previous genetic and epidemiological studies and support the hypothesis of a shared genetic basis between these phenotypes. Although the clinical utility of the identified loci remains to be determined, they can be used as resources to guide future studies aiming to disentangle the complex etiologies of ADHD, educational attainment, and general intelligence.

Attention-deficit hyperactivity disorder shares copy number variant risk with schizophrenia and autism spectrum disorder.

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable common childhood-onset neurodevelopmental disorder. Some rare copy number variations (CNVs) affect multiple neurodevelopmental disorders such as intellectual disability, autism spectrum disorders (ASD), schizophrenia and ADHD. The aim of this study is to determine to what extent ADHD shares high risk CNV alleles with schizophrenia and ASD. We compiled 19 neuropsychiatric CNVs and test 14, with sufficient power, for association with ADHD in Icelandic and Norwegian samples. Eight associate with ADHD; deletions at 2p16.3 (NRXN1), 15q11.2, 15q13.3 (BP4 & BP4.5-BP5) and 22q11.21, and duplications at 1q21.1 distal, 16p11.2 proximal, 16p13.11 and 22q11.21. Six of the CNVs have not been associated with ADHD before. As a group, the 19 CNVs associate with ADHD (OR = 2.43, P = 1.6 × 10-21), even when comorbid ASD and schizophrenia are excluded from the sample. These results highlight the pleiotropic effect of the neuropsychiatric CNVs and add evidence for ADHD, ASD and schizophrenia being related neurodevelopmental disorders rather than distinct entities.

Discovery of the first genome-wide significant risk loci for attention deficit/hyperactivity disorder.

Attention deficit/hyperactivity disorder (ADHD) is a highly heritable childhood behavioral disorder affecting 5% of children and 2.5% of adults. Common genetic variants contribute substantially to ADHD susceptibility, but no variants have been robustly associated with ADHD. We report a genome-wide association meta-analysis of 20,183 individuals diagnosed with ADHD and 35,191 controls that identifies variants surpassing genome-wide significance in 12 independent loci, finding important new information about the underlying biology of ADHD. Associations are enriched in evolutionarily constrained genomic regions and loss-of-function intolerant genes and around brain-expressed regulatory marks. Analyses of three replication studies: a cohort of individuals diagnosed with ADHD, a self-reported ADHD sample and a meta-analysis of quantitative measures of ADHD symptoms in the population, support these findings while highlighting study-specific differences on genetic overlap with educational attainment. Strong concordance with GWAS of quantitative population measures of ADHD symptoms supports that clinical diagnosis of ADHD is an extreme expression of continuous heritable traits.

Reproductive fitness and genetic risk of psychiatric disorders in the general population.

The persistence of common, heritable psychiatric disorders that reduce reproductive fitness is an evolutionary paradox. Here, we investigate the selection pressures on sequence variants that predispose to schizophrenia, autism, bipolar disorder, major depression and attention deficit hyperactivity disorder (ADHD) using genomic data from 150,656 Icelanders, excluding those diagnosed with these psychiatric diseases. Polygenic risk of autism and ADHD is associated with number of children. Higher polygenic risk of autism is associated with fewer children and older age at first child whereas higher polygenic risk of ADHD is associated with having more children. We find no evidence for a selective advantage of a high polygenic risk of schizophrenia or bipolar disorder. Rare copy-number variants conferring moderate to high risk of psychiatric illness are associated with having fewer children and are under stronger negative selection pressure than common sequence variants.

Electroencephalography as a clinical tool for diagnosing and monitoring attention deficit hyperactivity disorder: a cross-sectional study.

OBJECTIVES: The aim of this study was to develop and test, for the first time, a multivariate diagnostic classifier of attention deficit hyperactivity disorder (ADHD) based on EEG coherence measures and chronological age. SETTING: The participants were recruited in two specialised centres and three schools in Reykjavik. PARTICIPANTS: The data are from a large cross-sectional cohort of 310 patients with ADHD and 351 controls, covering an age range from 5.8 to 14 years. ADHD was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders fourth edition (DSM-IV) criteria using the K-SADS-PL semistructured interview. Participants in the control group were reported to be free of any mental or developmental disorders by their parents and had a score of less than 1.5 SDs above the age-appropriate norm on the ADHD Rating Scale-IV. Other than moderate or severe intellectual disability, no additional exclusion criteria were applied in order that the cohort reflected the typical cross section of patients with ADHD. RESULTS: Diagnostic classifiers were developed using statistical pattern recognition for the entire age range and for specific age ranges and were tested using cross-validation and by application to a separate cohort of recordings not used in the development process. The age-specific classification approach was more accurate (76% accuracy in the independent test cohort; 81% cross-validation accuracy) than the age-independent version (76%; 73%). Chronological age was found to be an important classification feature. CONCLUSIONS: The novel application of EEG-based classification methods presented here can offer significant benefit to the clinician by improving both the accuracy of initial diagnosis and ongoing monitoring of children and adolescents with ADHD. The most accurate possible diagnosis at a single point in time can be obtained by the age-specific classifiers, but the age-independent classifiers are also useful as they enable longitudinal monitoring of brain function.

Psychiatric disorders in an urban sample of preschool children.

BACKGROUND: To increase limited epidemiological knowledge of early childhood psychopathology, a study of prevalence estimates and demographic correlates of psychiatric disorders was conducted in a sample of preschool children. METHODS: In a two-stage study, parents of 339 children aged 4-6 years who came for a medical check-up at three primary care centres in Reykjavik were invited to participate. First, the participants were screened with Brigance Screens and the Strengths and Difficulties Questionnaire (SDQ) for parents and teachers. Subsequently, the children were tested with a short version of Wechsler Preschool and Primary Scales of Intelligence - Revised and their parents were interviewed with the Schedule for Affective Disorders and Schizophrenia for School Aged Children Present and Lifetime Version. Weighted prevalence estimates were calculated and logistic regression was used to analyse the association between risk factors and psychiatric disorders. RESULTS: Of those invited to participate, 317 (93.5%) were included in the screening and of those, 131 received a full diagnostic assessment. The final study sample included 151 girls (47.6%) and 166 boys (52.4%) who represented 11.6% of the total birth cohort in Reykjavik. Weighted prevalence of DSM-IV psychiatric disorders was 10.1% (95% CI 6.7-13.5%) and 57/317 or 18.0% (95% CI 13.8-22.2%), including elimination disorders. Anxiety disorders (5.7%) and attention deficit hyperactivity disorder (3.8%) were the most common disorders in this preschool sample. Poor physical health of parents and higher education was associated with DSM-IV psychiatric disorders of the children. SDQ Total Difficulties score was associated with male gender and poor physical health of parents. CONCLUSIONS: This study indicates that psychiatric disorders in preschool children are common and may be correlated with parental health factors.

Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis.

BACKGROUND: Large, rare chromosomal deletions and duplications known as copy number variants (CNVs) have been implicated in neurodevelopmental disorders similar to attention-deficit hyperactivity disorder (ADHD). We aimed to establish whether burden of CNVs was increased in ADHD, and to investigate whether identified CNVs were enriched for loci previously identified in autism and schizophrenia. METHODS: We undertook a genome-wide analysis of CNVs in 410 children with ADHD and 1156 unrelated ethnically matched controls from the 1958 British Birth Cohort. Children of white UK origin, aged 5-17 years, who met diagnostic criteria for ADHD or hyperkinetic disorder, but not schizophrenia and autism, were recruited from community child psychiatry and paediatric outpatient clinics. Single nucleotide polymorphisms (SNPs) were genotyped in the ADHD and control groups with two arrays; CNV analysis was limited to SNPs common to both arrays and included only samples with high-quality data. CNVs in the ADHD group were validated with comparative genomic hybridisation. We assessed the genome-wide burden of large (>500 kb), rare (<1% population frequency) CNVs according to the average number of CNVs per sample, with significance assessed via permutation. Locus-specific tests of association were undertaken for test regions defined for all identified CNVs and for 20 loci implicated in autism or schizophrenia. Findings were replicated in 825 Icelandic patients with ADHD and 35,243 Icelandic controls. FINDINGS: Data for full analyses were available for 366 children with ADHD and 1047 controls. 57 large, rare CNVs were identified in children with ADHD and 78 in controls, showing a significantly increased rate of CNVs in ADHD (0·156 vs 0·075; p=8·9×10(-5)). This increased rate of CNVs was particularly high in those with intellectual disability (0·424; p=2·0×10(-6)), although there was also a significant excess in cases with no such disability (0·125, p=0·0077). An excess of chromosome 16p13.11 duplications was noted in the ADHD group (p=0·0008 after correction for multiple testing), a finding that was replicated in the Icelandic sample (p=0·031). CNVs identified in our ADHD cohort were significantly enriched for loci previously reported in both autism (p=0·0095) and schizophrenia (p=0·010). INTERPRETATION: Our findings provide genetic evidence of an increased rate of large CNVs in individuals with ADHD and suggest that ADHD is not purely a social construct. FUNDING: Action Research; Baily Thomas Charitable Trust; Wellcome Trust; UK Medical Research Council; European Union.

[The frequency of some factors in pregnancy and delivery for Icelandic children with ADHD]. / Islensk börn med ofvirkniröskun--lýsing á nokkrum thattum í medgöngu og faedingu.

OBJECTIVE: ADHD is a well known psychiatric disorder that begins in childhood and frequently persists into adulthood. In the last decade numerous studies have shown the importance of genetic factors in the etiology of ADHD. However other etiological factors seem to be involved. The aim of this study was to examine the frequency of some possible etiological factors for ADHD in Icelandic children diagnosed with ADHD. The study is descriptive. MATERIALS AND METHODS: The participants were 196 children referred for suspected ADHD to the outpatient unit of the Department of Child and Adolescent Psychiatry, Landspitali University Hospital during a 2 year period 1998-1999. The participants had either ICD-10 or DSM-IV hyperkinetic disorder and/or ADHD and the information was obtained from patient case notes. Information provided by parents in a questionnaire concerning health in pregnancy and the perinatal period was retrospectively analysed. RESULTS: The main results show statistically significant increased risk for ADHD associated with several factors such as low birthweight, young age of the mother at the time of the child's birth and Caesarean section, compared with reference groups such as mean values in all of the community. Other factors such as birthweight, alcohol or tobacco use in pregnancy, use of medication in pregnancy or vacuum extraction did not show statistically significant association with ADHD. CONCLUSION: The results indicate as some studies from other countries have suggested that an association exists between a number of factors in pregnancy, delivery and perinatal period and ADHD, even though there is still not enough evidence to confirm definite etiological factors.

Validity of self-report and informant rating scales of adult ADHD symptoms in comparison with a semistructured diagnostic interview.

In a study of ADHD symptoms in the relatives of probands diagnosed with ADHD, the validity of self-reported and informant-reported symptoms in childhood and adulthood was investigated with a semistructured diagnostic interview, the Schedule for Affective Disorders and Schizophrenia for School-Age Children (K-SADS) adapted for adults, as a criterion. The participating relatives were 80 women and 46 men aged 17 to 77. Rating scales based on the Diagnostic and Statistical Manual of Mental Disorders (4th ed.) were completed by participants and informants. Internal consistency of the scales and interrater reliabilities of the diagnostic interview were satisfactory. Correlations between ratings across sources of information supported convergent and divergent validity. Self-report scales and informant scales predicted interview-based diagnoses in childhood and adulthood with adequate sensitivities and specificities. It was concluded that the rating scales have good psychometric properties, at least in at-risk populations.