title: The broader autism phenotype in infancy: when does it emerge?
abstract: OBJECTIVE
  This study had 3 goals, which were to examine the following: the frequency of atypical development, consistent with the broader autism phenotype, in high-risk infant siblings of children with autism spectrum disorder (ASD); the age at which atypical development is first evident; and which developmental domains are affected.
  
  
  METHODS
  A prospective longitudinal design was used to compare 294 high-risk infants and 116 low-risk infants. Participants were tested at 6, 12, 18, 24, and 36 months of age. At the final visit, outcome was classified as ASD, Typical Development (TD), or Non-TD (defined as elevated Autism Diagnostic Observation Schedule [ADOS] score, low Mullen Scale scores, or both).
  
  
  RESULTS
  Of the high-risk group, 28% were classified as Non-TD at 36 months of age. Growth curve models demonstrated that the Non-TD group could not be distinguished from the other groups at 6 months of age, but differed significantly from the Low-Risk TD group by 12 months on multiple measures. The Non-TD group demonstrated atypical development in cognitive, motor, language, and social domains, with differences particularly prominent in the social-communication domain.
  
  
  CONCLUSIONS
  These results demonstrate that features of atypical development, consistent with the broader autism phenotype, are detectable by the first birthday and affect development in multiple domains. This highlights the necessity for close developmental surveillance of infant siblings of children with ASD, along with implementation of appropriate interventions as needed.
authors.affiliation: University of California-Davis. Electronic address: sally.ozonoff@ucdmc.ucdavis.edu.
authors.forename: Sally
authors.initials: S
authors.lastname: Ozonoff
authors.affiliation: University of California-Davis.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Young
authors.affiliation: University of California-Davis.
authors.forename: Ashleigh
authors.initials: A
authors.lastname: Belding
authors.affiliation: University of California-Davis.
authors.forename: Monique
authors.initials: M
authors.lastname: Hill
authors.affiliation: University of California-Davis.
authors.forename: Alesha
authors.initials: A
authors.lastname: Hill
authors.affiliation: University of California-Los Angeles.
authors.forename: Ted
authors.initials: T
authors.lastname: Hutman
authors.affiliation: University of California-Los Angeles.
authors.forename: Scott
authors.initials: S
authors.lastname: Johnson
authors.affiliation: University of California-Davis.
authors.forename: Meghan
authors.initials: M
authors.lastname: Miller
authors.affiliation: University of California-Davis.
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Rogers
authors.affiliation: Purdue University.
authors.forename: A J
authors.initials: AJ
authors.lastname: Schwichtenberg
authors.affiliation: University of California-Davis.
authors.forename: Marybeth
authors.initials: M
authors.lastname: Steinfeld
authors.affiliation: University of California-Davis.
authors.forename: Ana-Maria
authors.initials: AM
authors.lastname: Iosif
mesh_terms: D000367:Age Factors; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis* / Q000235:genetics*; D002675:Child, Preschool; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D008297:Male; D010641:Phenotype; D035781:Siblings
keywords: autism spectrum disorder; broader autism phenotype; infancy; siblings; social-communication