DOI: 10.0000/JHSE.1000180 J Health Sci Educ Vol 4(2): 1-6 Autism Spectrum Disorder-Associated Behavior in Infants with Down Syndrome Hahn LJ 1,2* , Hamrick LR 3 , Kelleher BL 3 and Roberts JE 2 1 Department of Speech & Hearing Science, University of Illinois at Urbana-Champaign, USA 2 Department of Psychology, University of South Carolina; USA 3 Department of Psychological Sciences, Purdue University, USA Abbreviations: DS: Down syndrome, ASD: Autism Spectrum Disorder, TD: Typically Developing, nsASD: non-syndromic ASD, AOSI: Autism Observation Scale for Infants Background Autism spectrum disorder (ASD) is a common and lifelong disorder affecting 1:59 in the general population [1]. Early treatment of ASD leads to improved outcomes [2,3]; thus, early detection is critical. Examining ASD in neurogenetic syndromes at high risk for ASD, such as Down syndrome (DS), helps establish the shared phenomenology between disorders [4] and advance our understanding of the specific needs of children with neurogenetic syndromes. DS is caused by the presence of an overexpression of genes on chromosome 21 and is the most common genetic (chromosomal) abnormality associated with intellectual disability (affecting 1 in 691 individuals [5]). While not extensively researched, existing work suggests that ~20% (7- 42%) of children with DS meet diagnostic criteria for ASD [6- 8]. As such, ASD is highly expressed in DS at a rate much higher than the general population. The limited research is likely due to diagnostic challenges given the presence of intellectual disability because clinicians need to differentiate ASD-like behaviors from similar behaviors associated with intellectual disability [9,10] and a historical bias that the “social strengths” in DS represent a protective factor against ASD [11]. Also, many children with DS may not be eligible for ASD diagnostic tools depending on the level of their motor skills (e.g., the toddler module of the Autism Diagnostic Observation Schedule-2 requires a minimum mental age of 12 months and that the child is walking or “cruising” [12]). These challenges have led to reluctance in making a diagnosis of ASD in DS resulting in delays or misdiagnoses [10,11,13]. Whereas, the average age of diagnosis in non-syndromic ASD (nsASD) is 3-4 years [1]. Research identifying early signs of nsASD has primarily focused on developmental trajectories of infants with older siblings with nsASD suggesting that early behavioral signs include impaired visual attention [14], delays in language and gesture [15], and motor difficulties [16]. To date, no research has described signs of ASD in children with DS younger than 2 years-of-age with only a handful of studies conducted at preschool-age and older [17]. In a longitudinal study with 20 2-to-3-year-olds with DS, 15% (3 children) met ASD diagnostic criteria (mean age 34 months [17]. Diagnostic stability was high over time, and all three children with Abstract 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. Keywords: Down syndrome; Autism Spectrum Disorder; Infants