title: Genetic and environmental influences underlying the relationship between autistic traits and temperament and character dimensions in adulthood.
abstract: BACKGROUND
  In recent years, several twin studies adopted a dimensional approach to Autism Spectrum Disorders (ASD) and estimated the contribution of genetic and environmental influences to variation in autistic traits. However, no study was performed on adults over 18 years of age and all but two studies were based on parent or teacher ratings. Also, the genetic and environmental contributions to the interplay between autistic traits and adult personality dimensions have not been investigated.
  
  
  METHODS
  A sample of 266 complete twin pairs (30% males, mean age 40 ± 12 years) drawn from the population-based Italian Twin Register was administered the Autism-Spectrum Quotient, Temperament and Character Inventory (TCI-125), and General Health Questionnaire (GHQ-12). Genetic structural equation modelling was performed with the Mx program. Estimates were adjusted for gender, age, and GHQ-12 score.
  
  
  RESULTS
  Genetic factors accounted for 44% and 20%-49% of individual differences in autistic traits and TCI dimensions, respectively. Unshared environmental factors explained the remaining proportion of variance. Consistently with the notion of a personality profile in ASD characterised by obsessive temperament, autistic traits showed significant phenotypic correlations with several TCI dimensions (positive: HA; negative: NS, RD, SD, C). Genetic and unshared environmental correlations between AQ and these TCI dimensions were significant. The degree of genetic overlap was generally greater than the degree of environmental overlap.
  
  
  CONCLUSIONS
  Despite some limitations, this study suggests that genetic factors contribute substantially to individual differences in autistic traits in adults, with unshared environmental influences also playing an important role. It also suggests that autistic traits and the majority of temperament and character dimensions share common genetic and environmental aetiological factors.
authors.affiliation: Mental Health Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy. Electronic address: angelo.picardi@iss.it.
authors.forename: Angelo
authors.initials: A
authors.lastname: Picardi
authors.affiliation: Genetic Epidemiology Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy.
authors.forename: Corrado
authors.initials: C
authors.lastname: Fagnani
authors.affiliation: Genetic Epidemiology Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Medda
authors.affiliation: Genetic Epidemiology Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy.
authors.forename: Virgilia
authors.initials: V
authors.lastname: Toccaceli
authors.affiliation: DISM, InterUniversity Center for Behavioural Neurosciences (ICBN), University of Udine, Udine, Italy; IRCCS "E. Medea" Scientific Institute, UDGEE, Udine, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Brambilla
authors.affiliation: Genetic Epidemiology Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Stazi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001321:Autistic Disorder / Q000453:epidemiology* / Q000523:psychology*; D002648:Child; D005260:Female; D006801:Humans; D007206:Individuality; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D010551:Personality; D011569:Psychiatric Status Rating Scales; D012931:Social Environment; D013694:Temperament; D014427:Twins