• Analysis of shared heritability in common disorders of the brain

      Anttila, Verneri; Bulik-Sullivan, Brendan; Finucane, Hilary K.; Walters, Raymond K.; Bras, Jose; Duncan, Laramie; Escott-Price, Valentina; Falcone, Guido J.; Gormley, Padhraig; Malik, Rainer; et al. (American Association for the Advancement of Science, 2018-06-22)
      Disorders of the brain can exhibit considerable epidemiological comorbidity and often share symptoms, provoking debate about their etiologic overlap. We quantified the genetic sharing of 25 brain disorders from genome-wide association studies of 265,218 patients and 784,643 control participants and assessed their relationship to 17 phenotypes from 1,191,588 individuals. Psychiatric disorders share common variant risk, whereas neurological disorders appear more distinct from one another and from the psychiatric disorders. We also identified significant sharing between disorders and a number of brain phenotypes, including cognitive measures. Further, we conducted simulations to explore how statistical power, diagnostic misclassification, and phenotypic heterogeneity affect genetic correlations. These results highlight the importance of common genetic variation as a risk factor for brain disorders and the value of heritability-based methods in understanding their etiology.
    • Attention-deficit hyperactivity disorder shares copy number variant risk with schizophrenia and autism spectrum disorder.

      Gudmundsson, Olafur O; Walters, G Bragi; Ingason, Andres; Johansson, Stefan; Zayats, Tetyana; Athanasiu, Lavinia; Sonderby, Ida Elken; Gustafsson, Omar; Nawaz, Muhammad S; Jonsson, Gudbjorn F; et al. (Nature Publishing Group, 2019-10-17)
      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.

      Demontis, Ditte; Walters, Raymond K; Martin, Joanna; Mattheisen, Manuel; Als, Thomas D; Agerbo, Esben; Baldursson, Gísli; Belliveau, Rich; Bybjerg-Grauholm, Jonas; Bækvad-Hansen, Marie; et al. (Nature Publishing Group, 2019-01-01)
      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.
    • Identification of Genetic Loci Shared Between Attention-Deficit/Hyperactivity Disorder, Intelligence, and Educational Attainment.

      O'Connell, Kevin S; Shadrin, Alexey; Smeland, Olav B; Bahrami, Shahram; Frei, Oleksandr; Bettella, Francesco; Krull, Florian; Fan, Chun C; Askeland, Ragna B; Knudsen, Gun Peggy S; et al. (Elsevier Science, 2019-11-29)
      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. Keywords: ADHD; Cognition; Genetic overlap; Mental health; Pleiotropy; Psychiatric disorder.