title: Autism Spectrum Disorder, Intellectual Disability, and Delayed Walking.
abstract: OBJECTIVE
  Delayed onset of independent walking is common in intellectual disability (ID). However, in children with autism spectrum disorders (ASD), delayed walking has not been reported as frequently, despite the high rate of concurrent ID in ASD. This study directly examined the relationship between delayed walking and severity of ID in children with ASD versus other non-ASD diagnoses.
  
  
  METHODS
  Participants were 1185 individuals (ASD, n = 903; non-ASD, n = 282) who received an assessment at age 4 to 12 years (6.89 ± 2.25) that yielded an estimate of nonverbal IQ (NVIQ) and retrospectively reported age of walking from the Autism Diagnostic Interview-Revised. The relationship between diagnostic group and delayed walking (defined as occurring at ≥16 months) as a function of NVIQ was explored using the Cox proportional hazards model.
  
  
  RESULTS
  Children with ASD were less likely to exhibit delayed walking than those with non-ASD diagnoses, and this difference was larger at lower levels of NVIQ (P = .002). For example, rates of delayed walking for ASD and non-ASD were 13% and 19%, respectively, in those with NVIQ >85 but 31% and 60% in children with NVIQ <70.
  
  
  CONCLUSIONS
  Although lower IQ scores were associated with increased rates of late walking in both ASD and non-ASD groups, children with low IQ were more likely to show delayed walking in the absence of ASD. This raises the possibility of separate etiological pathways to ID in children with and without ASD.
authors.affiliation: Department of Psychiatry, University of California, San Francisco, San Francisco, California; somer.bishop@ucsf.edu.
authors.forename: Somer L
authors.initials: SL
authors.lastname: Bishop
authors.affiliation: Pediatrics and Developmental Neuroscience Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland; and.
authors.forename: Audrey
authors.initials: A
authors.lastname: Thurm
authors.affiliation: Pediatrics and Developmental Neuroscience Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland; and.
authors.forename: Cristan
authors.initials: C
authors.lastname: Farmer
authors.affiliation: Weill Cornell Medical College, New York, New York.
authors.forename: Catherine
authors.initials: C
authors.lastname: Lord
mesh_terms: D000067877:Autism Spectrum Disorder / Q000150:complications / Q000175:diagnosis*; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000150:complications / Q000175:diagnosis*; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008607:Intellectual Disability / Q000150:complications / Q000175:diagnosis*; D007361:Intelligence Tests; D008297:Male; D012189:Retrospective Studies; D013997:Time Factors; D016138:Walking / Q000502:physiology*