title: Autism Spectrum Disorders and Other Mental Health Problems: Exploring Etiological Overlaps and Phenotypic Causal Associations.
abstract: OBJECTIVE
  Recent studies have highlighted the impact of coexisting mental health problems in autism spectrum disorders (ASD). No twin studies to date have reported on individuals meeting diagnostic criteria of ASD. This twin study reports on the etiological overlap between the diagnosis of ASD and emotional symptoms, hyperactivity, and conduct problems measured with the Strengths and Difficulties Questionnaire.
  
  
  METHODS
  Genetic and environmental influences on the covariance between ASD and coexisting problems were estimated, in line with the correlated risks model prediction. Phenotypic causality models were also fitted to explore alternative explanations of comorbidity: namely, that coexisting problems are the result of or result in ASD symptoms; that they increase recognition of ASD; or that they arise due to an over-observation bias/confusion when differentiating between phenotypes.
  
  
  RESULTS
  More than 50% of twins with broad spectrum/ASD met the borderline/abnormal levels cut-off criteria for emotional symptoms or hyperactivity, and approximately 25% met these criteria for the 3 reported problems. In comparison, between 13% and 16% of unaffected twins scored above the cut-offs. The phenotypic correlation between ASD and emotional symptoms was explained entirely by genetic influences and accompanied by a moderate genetic correlation (0.42). The opposite was true for the overlap with conduct problems, as nonshared-environmental factors had the strongest impact. For hyperactivity, the best-fitting model suggested a unidirectional phenotypic influence of hyperactivity on ASD.
  
  
  CONCLUSIONS
  Our findings suggest a possible effect of hyperactivity on identification of ASD. The lack of genetic influences on conduct problems-ASD overlap further supports the genetic independence of these 2 phenotypes. Finally, the co-occurrence of emotional symptoms in ASD, compared to other co-occurring problems, is completely explained by common genetic effects.
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK. Electronic address: beata.b.tick@kcl.ac.uk.
authors.forename: Beata
authors.initials: B
authors.lastname: Tick
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Colvert
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK; IOPPN, King's College London.
authors.forename: Fiona
authors.initials: F
authors.lastname: McEwen
authors.affiliation: IOPPN, King's College London; South London and Maudsley National Health Service Foundation Trust (SLAM), Maudsley Hospital, London.
authors.forename: Catherine
authors.initials: C
authors.lastname: Stewart
authors.affiliation: IOPPN, King's College London.
authors.forename: Emma
authors.initials: E
authors.lastname: Woodhouse
authors.affiliation: South London and Maudsley National Health Service Foundation Trust (SLAM), Maudsley Hospital, London.
authors.forename: Nicola
authors.initials: N
authors.lastname: Gillan
authors.affiliation: IOPPN, King's College London.
authors.forename: Victoria
authors.initials: V
authors.lastname: Hallett
authors.affiliation: Clinical, Educational and Health Psychology, University College London.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Lietz
authors.affiliation: South London and Maudsley National Health Service Foundation Trust (SLAM), Maudsley Hospital, London.
authors.forename: Tracy
authors.initials: T
authors.lastname: Garnett
authors.affiliation: IOPPN, King's College London.
authors.forename: Emily
authors.initials: E
authors.lastname: Simonoff
authors.affiliation: Birkbeck, University of London.
authors.forename: Angelica
authors.initials: A
authors.lastname: Ronald
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK.
authors.forename: Patrick
authors.initials: P
authors.lastname: Bolton
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK.
authors.forename: Francesca
authors.initials: F
authors.lastname: Happé
authors.affiliation: Medical Research Council (MRC) Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience (IOPPN), King's College London, UK.
authors.forename: Frühling
authors.initials: F
authors.lastname: Rijsdijk
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000209:etiology; D000067877:Autism Spectrum Disorder / Q000209:etiology* / Q000523:psychology; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000209:etiology / Q000235:genetics; D015897:Comorbidity; D004644:Emotions; D005260:Female; D005824:Genetics, Behavioral; D006801:Humans; D008297:Male; D008603:Mental Health; D010641:Phenotype; D011595:Psychomotor Agitation / Q000209:etiology* / Q000235:genetics / Q000523:psychology; D014427:Twins / Q000235:genetics / Q000523:psychology
keywords: autism spectrum disorders; behavioral genetics; comorbidity; mental health