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Parsing Heterogeneity in the Emerging Autism Phenotype: Effects of Familial Risk for Autism Spectrum Disorder


Autism spectrum disorder (ASD) is a heterogeneous, highly heritable neurodevelopmental disability. Evidence suggests individuals with ASD who are at high familial risk for autism (i.e., those from multiplex families containing two or more ASD-affected children), exhibit distinct clinical characteristics from individuals with ASD from simplex families. The aim of the present study was to examine the effects of familial risk for autism on the emerging autism phenotype among infants and toddlers showing signs of ASD. Participants (N = 137) were 12- to 36-month-olds referred to two larger autism intervention studies due to autism concerns. Overall, simplex children showing signs of ASD demonstrated more severe cognitive delays, were more likely to present with expressive language delays, and had more severe autism symptoms than multiplex children with emerging ASD symptoms. This study is among the first to examine the effects of familial risk for autism among infants and toddlers showing early symptoms of ASD, and demonstrates that simplex-multiplex differences are present in the first years of life and before autism symptoms fully emerge.

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