title: A prospective study of autistic-like traits in unaffected siblings of probands with autism spectrum disorder.
abstract: BACKGROUND
  The presence of autistic-like traits in relatives of individuals with autism spectrum disorder (ASD) is well recognized, but, to our knowledge, the emergence of these traits early in development has not been studied.
  
  
  OBJECTIVE
  To prospectively investigate the emergence of autistic-like traits in unaffected (no ASD diagnosis) infant siblings of probands diagnosed as having ASD.
  
  
  METHODS
  Two groups of children unaffected with ASD were assessed prospectively-siblings of probands diagnosed as having ASD (high risk [HR]) and control subjects with no family history of ASD (low risk [LR]). Scores on a measure of autistic-like traits at 12 months of age were used in a cluster analysis of the entire sample.
  
  
  METHODS
  A prospective study of infant siblings of probands with ASD from 3 diagnostic centers in Canada.
  
  
  METHODS
  The study included 170 HR and 90 LR children, none of whom was diagnosed as having ASD at age 3 years.
  
  
  METHODS
  The Autism Observation Scale for Infants was used to measure autistic-like traits and derive clusters at 12 months of age. Clusters were compared on ASD symptoms, cognitive abilities, and social-emotional difficulties at age 3 years.
  
  
  RESULTS
  Two clusters were identified. Cluster 1 (n = 37; 14.2% of total sample) had significantly higher levels of autistic-like traits compared with cluster 2. Within cluster 1, 33 children came from the siblings (19.4% of HR group) and only 4 came from the control subjects (4.5% of LR group). At age 3 years, children from cluster 1 had more social-communication impairment (effect size > 0.70; P < .001), lower cognitive abilities (effect size = -0.59; P < .005), and more internalizing problems (effect size = 0.55; P = .01). Compared with control subjects, HR siblings had a relative risk of 4.3 (95% CI,1.6-11.9) for membership in cluster 1.
  
  
  CONCLUSIONS
  Study findings suggest the emergence of autistic-like traits resembling a broader autism phenotype by 12 months of age in approximately 19% of HR siblings who did not meet ASD diagnostic criteria at age 3 years.
authors.affiliation: Offord Centre for Child Studies and McMaster Children's Hospital, McMaster University, Ontario, Canada.
authors.forename: Stelios
authors.initials: S
authors.lastname: Georgiades
authors.forename: Peter
authors.initials: P
authors.lastname: Szatmari
authors.forename: Lonnie
authors.initials: L
authors.lastname: Zwaigenbaum
authors.forename: Susan
authors.initials: S
authors.lastname: Bryson
authors.forename: Jessica
authors.initials: J
authors.lastname: Brian
authors.forename: Wendy
authors.initials: W
authors.lastname: Roberts
authors.forename: Isabel
authors.initials: I
authors.lastname: Smith
authors.forename: Tracy
authors.initials: T
authors.lastname: Vaillancourt
authors.forename: Caroline
authors.initials: C
authors.lastname: Roncadin
authors.forename: Nancy
authors.initials: N
authors.lastname: Garon
mesh_terms: D001321:Autistic Disorder / Q000453:epidemiology / Q000235:genetics / Q000523:psychology*; D002170:Canada / Q000453:epidemiology; D002675:Child, Preschool; D016000:Cluster Analysis; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D018730:Infant Behavior / Q000523:psychology*; D008297:Male; D011446:Prospective Studies; D011569:Psychiatric Status Rating Scales; D012306:Risk; D035781:Siblings / Q000523:psychology*