title: The co-occurrence of autistic and ADHD dimensions in adults: an etiological study in 17,770 twins.
abstract: Autism spectrum disorder (ASD) and attention deficit/hyperactivity disorder (ADHD) often occur together. To obtain more insight in potential causes for the co-occurrence, this study examined the genetic and environmental etiology of the association between specific ASD and ADHD disorder dimensions. Self-reported data on ASD dimensions social and communication difficulties (ASDsc), and repetitive and restricted behavior and interests (ASDr), and ADHD dimensions inattention (IA), and hyperactivity/impulsivity (HI) were assessed in a community sample of 17,770 adult Swedish twins. Phenotypic, genetic and environmental associations between disorder dimensions were examined in a multivariate model, accounting for sex differences. ASDr showed the strongest associations with IA and HI in both sexes (r(p) 0.33 to 0.40). ASDsc also correlated moderately with IA (females r(p) 0.29 and males r(p) 0.35) but only modestly with HI (females r(p) 0.17 and males r(p) 0.20). Genetic correlations ranged from 0.22 to 0.64 and were strongest between ASDr and IA and HI. Sex differences were virtually absent. The ASDr dimension (reflecting restricted, repetitive and stereotyped patterns of behavior, interests and activities) showed the strongest association with dimensions of ADHD, on a phenotypic, genetic and environmental level. This study opens new avenues for molecular genetic research. As our findings demonstrated that genetic overlap between disorders is dimension-specific, future gene-finding studies on psychiatric comorbidity should focus on carefully selected genetically related dimensions of disorders.
authors.affiliation: Department of Functional Genomics, Complex Trait Genetics, Center for Neurogenomics and Cognitive Research (CNCR), VU University Amsterdam, Amsterdam, The Netherlands.
authors.forename: T J C
authors.initials: TJ
authors.lastname: Polderman
authors.affiliation: Department of Life, Health and Chemical Sciences, Faculty of Science, The Open University, Milton Keynes, UK.
authors.forename: R A
authors.initials: RA
authors.lastname: Hoekstra
authors.affiliation: 1] Department of Functional Genomics, Complex Trait Genetics, Center for Neurogenomics and Cognitive Research (CNCR), VU University Amsterdam, Amsterdam, The Netherlands [2] Department of Complex Trait Genetics, Clinical Genetics, VU Medical Center, Amsterdam, The Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: Posthuma
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Larsson
mesh_terms: D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000235:genetics*; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis* / Q000235:genetics*; D015897:Comorbidity; D004200:Diseases in Twins / Q000175:diagnosis* / Q000235:genetics*; D044127:Epigenesis, Genetic / Q000235:genetics; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010641:Phenotype; D012737:Sex Factors; D013548:Sweden; D055815:Young Adult