Comorbid Down Syndrome and ASD: Differential Social Affect in ASD Symptoms

Background: Little is known about the ASD symptom profile of children with comorbid Down syndrome and ASD (DS+ASD). Whereas previous literature suggests limited social impairments in individuals with DS-only (Fidler, 2005), recent research demonstrates an estimated 20% of the DS population has ASD (DiGuiseppi et al., 2010). The limited research available suggests children with DS+ASD have fewer social impairments than in ASD but similar communication impairments; however, social functioning has largely been assessed using parent-report (Warner et al., 2017) or in very small samples (n=3; Hepburn et al., 2008). Elucidating differences in ASD symptoms for those with ASD and a comorbid genetic syndrome can further our understanding of the nature and etiology of ASD in these children. Identifying ASD symptom profiles of children with comorbid DS+ASD early in development is critical to informing early identification and intervention.

Objectives: The goal of this study is to assess ASD symptom profiles within and between clinical samples of children with ASD, DS, and DS+ASD.

Methods: Participants included 93 children (59 males; Mean age= 60.43 months) with ASD (n=43), DS (n=38), and DS+ASD (n=12). Data were compiled from a larger study completed at the University of Colorado School of Medicine/Colorado State University (DiGuiseppi et al., 2010) and from the National Database for Autism Research. ASD symptoms were assessed using the ADOS Module 1 and scores were converted to severity scores using the algorithm described by Gotham and colleagues (2007). A 3x2 mixed-model ANOVA with one between subjects factor (diagnostic group: DS, ASD, DS+ASD) and one within subjects factor (ADOS scale: social-affect (SA) and restricted, repetitive behaviors (RRBs)) was completed to examine if SA and RRBs are differentially impacted in the DS+ASD group compared to the other two groups.

Results: A significant group-by-scale interaction was revealed (F [2, 86] = 5.33, p < 0.001 using a Greenhouse-Geisser adjustment); each group presented with unique profiles. Specifically, the DS+ASD group had a profile unlike either the DS or ASD in isolation groups. Compared to those with ASD, SA in DS+ASD was significantly less impaired; in contrast, RRBs were similar across ASD and DS+ASD. Compared to those with DS, SA and RRBs were significantly more impaired in the DS+ASD group.

Conclusions: Results suggest ASD symptom profiles for children with DS+ASD are not similar to those with either ASD or DS in isolation. Specifically, whereas the DS+ASD group presents with RRBs similar to those with ASD, SA is less impacted and may act as a protective factor within this group. Given prior research suggesting social abilities are a relative strength for those with DS, investigation of the contribution of reciprocal social interaction and communication to overall social affect within this group is important. Discrepancies within social affect, characteristic to ASD, have important implications for both early identification and intervention. As early intervention has been shown to alter developmental trajectories and improve lifetime outcomes for children with ASD (Orinstein et al., 2014), it will be important to investigate whether these interventions will have similar benefits for those with DS+ASD.