title: Sex differences in the association between infant markers and later autistic traits.
abstract: BACKGROUND
  Although it is well established that the prevalence of autism spectrum disorder (ASD) is higher in males than females, there is relatively little understanding of the underlying mechanisms and their developmental time course. Sex-specific protective or risk factors have often been invoked to explain these differences, but such factors are yet to be identified.
  
  
  METHODS
  We take a developmental approach, using a prospective sample of 104 infants at high and low familial risk for ASD, to characterise sex differences in infant markers known to predict emerging autism symptoms. We examine three markers previously shown to be associated with later autistic social-communication symptoms: the Autism Observation Scale for Infants (AOSI) total score, attention disengagement speed and gaze following behaviour. Our aim was to test whether sex differences were already present in these markers at 1 year of age, which would suggest sex-specific mechanisms of risk or protection.
  
  
  RESULTS
  While no sex differences were found in any of the three markers investigated, we found sex differences in their relationship to 3-year autism traits; all three markers significantly predicted later autism traits only in the boys.
  
  
  CONCLUSIONS
  Previously identified 'early autism markers' were associated with later autism symptoms only in boys. This suggests that there may be additional moderating risk or protective factors which remain to be identified. Our findings have important implications for prospective studies in terms of directly testing for the moderating effect of sex on emerging autistic traits.
authors.affiliation: Biostatistics Department, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.
authors.forename: Rachael
authors.initials: R
authors.lastname: Bedford
authors.affiliation: Centre for Brain and Cognitive Development, Birkbeck College, University of London, London, UK.
authors.forename: Emily J H
authors.initials: EJ
authors.lastname: Jones
authors.affiliation: Centre for Brain and Cognitive Development, Birkbeck College, University of London, London, UK.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Johnson
authors.affiliation: Biostatistics Department, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Pickles
authors.affiliation: Psychology Department, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.
authors.forename: Tony
authors.initials: T
authors.lastname: Charman
authors.affiliation: Centre for Brain and Cognitive Development, Birkbeck College, University of London, London, UK.
authors.forename: Teodora
authors.initials: T
authors.lastname: Gliga
mesh_terms: D001288:Attention / Q000502:physiology; D000067877:Autism Spectrum Disorder / Q000175:diagnosis* / Q000473:pathology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D007223:Infant; D008297:Male; D010641:Phenotype; D012307:Risk Factors; D012720:Severity of Illness Index; D012737:Sex Factors; D035781:Siblings; D011795:Surveys and Questionnaires; D014741:Video Recording
keywords: Autism; Differential liability; High risk; Infants; Sex difference