title: Genetic heritability and shared environmental factors among twin pairs with autism.
abstract: BACKGROUND
  Autism is considered the most heritable of neurodevelopmental disorders, mainly because of the large difference in concordance rates between monozygotic and dizygotic twins.
  
  
  OBJECTIVE
  To provide rigorous quantitative estimates of genetic heritability of autism and the effects of shared environment.
  
  
  METHODS
  Twin pairs with at least 1 twin with an autism spectrum disorder (ASD) born between 1987 and 2004 were identified through the California Department of Developmental Services.
  
  
  METHODS
  Structured diagnostic assessments (Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule) were completed on 192 twin pairs. Concordance rates were calculated and parametric models were fitted for 2 definitions, 1 narrow (strict autism) and 1 broad (ASD).
  
  
  RESULTS
  For strict autism, probandwise concordance for male twins was 0.58 for 40 monozygotic pairs (95% confidence interval [CI], 0.42-0.74) and 0.21 for 31 dizygotic pairs (95% CI, 0.09-0.43); for female twins, the concordance was 0.60 for 7 monozygotic pairs (95% CI, 0.28-0.90) and 0.27 for 10 dizygotic pairs (95% CI, 0.09-0.69). For ASD, the probandwise concordance for male twins was 0.77 for 45 monozygotic pairs (95% CI, 0.65-0.86) and 0.31 for 45 dizygotic pairs (95% CI, 0.16-0.46); for female twins, the concordance was 0.50 for 9 monozygotic pairs (95% CI, 0.16-0.84) and 0.36 for 13 dizygotic pairs (95% CI, 0.11-0.60). A large proportion of the variance in liability can be explained by shared environmental factors (55%; 95% CI, 9%-81% for autism and 58%; 95% CI, 30%-80% for ASD) in addition to moderate genetic heritability (37%; 95% CI, 8%-84% for autism and 38%; 95% CI, 14%-67% for ASD).
  
  
  CONCLUSIONS
  Susceptibility to ASD has moderate genetic heritability and a substantial shared twin environmental component.
authors: Departmentof Psychiatry, Stanford UniversitySchool of Medicine, USA. joachimh@stanford.edu
authors: Joachim
authors: J
authors: Hallmayer
authors: Sue
authors: S
authors: Cleveland
authors: Andrea
authors: A
authors: Torres
authors: Jennifer
authors: J
authors: Phillips
authors: Brianne
authors: B
authors: Cohen
authors: Tiffany
authors: T
authors: Torigoe
authors: Janet
authors: J
authors: Miller
authors: Angie
authors: A
authors: Fedele
authors: Jack
authors: J
authors: Collins
authors: Karen
authors: K
authors: Smith
authors: Linda
authors: L
authors: Lotspeich
authors: Lisa A
authors: LA
authors: Croen
authors: Sally
authors: S
authors: Ozonoff
authors: Clara
authors: C
authors: Lajonchere
authors: Judith K
authors: JK
authors: Grether
authors: Neil
authors: N
authors: Risch
mesh_terms: D000293:Adolescent; D000328:Adult; D002140:California; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics; D016001:Confidence Intervals; D004777:Environment; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008423:Maternal Age; D008957:Models, Genetic; D018579:Patient Selection; D015995:Prevalence; D018570:Risk Assessment; D012737:Sex Factors; D012959:Socioeconomic Factors; D014430:Twins, Monozygotic / Q000706:statistics & numerical data*