King's College London

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. Female-specific protective factors, or male-specific risk factors, have often been invoked to explain these differences, but such factors are yet to be identified. Methods: In order to characterise sex differences in infant markers known to predict emerging symptoms of autism we take a developmental approach using a prospective sample of 104 infants at high and low familial risk for ASD. We examined three markers previously shown to be associated with later autistic social-communication symptoms in this sample: the Autism Observation Scale for Infants (AOSI), attention disengagement and gaze following behaviour. Our aim was to test whether sex differences were already present in these markers at around one year of age or whether differences exist in the relationship between risk markers and later 3-year autism traits. Results: While no sex differences were found in any of the 3 markers investigated, suggesting that male and female infants express similar levels of risk, the makers significantly predicted later autism traits only in the boys. Conclusions: The results suggest that so-called ‘early autism markers’ may in fact only be markers in boys, and there may be other additional intervening factors acting in girls. This has important implications for prospective studies in terms of directly testing for the moderating effect of sex on emerging autistic traits.