Autism Spectrum Disorder-Associated Behaviour in Infants with Down Syndrome.

Background: Individuals with Down syndrome (DS) are at high risk for autism spectrum disorder (ASD) with ~20% of individuals meeting diagnostic criteria for ASD. Despite the high risk, there is no research documenting early signs of ASD in infants with DS or potential prodromal ASD-associated behaviors.

Aim: This preliminary case-control study described ASD-associated behaviors in infants with DS contrasted to typically developing (TD) infants.

Patients and methods: The Autism Observation Scale for Infants (AOSI) was used to describe ASD-related behaviors in 18 infants with DS (7-18 months) and 18 TD infants (9-14 months).

Results: Thirty nine percent (7 out of 18) of infants with DS in our sample were designated "at risk" for ASD on the AOSI with 100% of infants with DS demonstrating at least one feature of ASD. In contrast, only 11% (2 out of 18) of TD infants were designated "at risk" for ASD on the AOSI. Social and communication impairments appear to represent early signs of elevated ASD-associated behavior in infants with DS.

Conclusions: Early signs of ASD-associated behavior appear present and detectable in infants with DS. These early signs mirror findings of other populations at risk for ASD with social communication as the primary behavioral impairment to signal elevated risk for the emergence of ASD. This study contributes to the refinement of the DS behavioral phenotype and identifies important next steps to help improve the identification, diagnosis, and treatment of ASD in DS.