title: Stability and change of IQ scores in preschool children diagnosed with autistic spectrum disorder.
abstract: OBJECTIVE
  To investigate cognitive development in preschool-age children diagnosed with Autistic Spectrum Disorder (ASD; N = 39) compared with that of children diagnosed with mental retardation (MR; N = 14) and normally developing children (NC; N = 36).
  
  
  METHODS
  In a prospective longitudinal study, cognitive development was tested at age 24 months (T1; SD = 6 months) and 43 months (T2; SD = 5).
  
  
  RESULTS
  Group IQ scores were stable between T1 and T2 as evidenced by high correlations (r = .81, P < .01) and consistency of average group scores. At the same time however, about a third of children with ASD showed an increase of cognitive scores of 15 points or more. This increase of IQ was correlated with lower scores at the early screening of autistic traits (ESAT) at T1, higher IQ level at T2 and higher expressive language skills at T2. Intensity of treatment was not related to IQ increase.
  
  
  CONCLUSIONS
  High correlations between cognitive scores in preschool children with ASD suggest that measurements of cognitive function are valid at this age. We found indications of both stability and change of IQ scores. Findings suggest that some children with ASD show catch-up intellectual development. To the best of our knowledge, this increase in IQ scores cannot be attributed to treatment effects.
authors.affiliation: Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, P.O. 85500, 3508 GA, Utrecht, The Netherlands. cdietz@umcutrecht.nl
authors.forename: Claudine
authors.initials: C
authors.lastname: Dietz
authors.forename: Sophie H N
authors.initials: SH
authors.lastname: Swinkels
authors.forename: Jan K
authors.initials: JK
authors.lastname: Buitelaar
authors.forename: Emma
authors.initials: E
authors.lastname: van Daalen
authors.forename: Herman
authors.initials: H
authors.lastname: van Engeland
mesh_terms: D001321:Autistic Disorder / Q000175:diagnosis* / Q000453:epidemiology*; D002675:Child, Preschool; D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D015995:Prevalence; D012720:Severity of Illness Index; D013997:Time Factors