Amanda Dimachkie Nunnally, PhD, Postdoctoral Research Scholar, UC Davis Mind Institute


Individuals with Down syndrome are diagnosed with autism at a much higher rate than the general population, with prevalence estimates ranging from 16-42% in Down syndrome compared to 1.9% in the general population. There is still much to be understood about the presentation of autism symptoms in individuals with Down syndrome, as some of the core characteristics of autism may overlap with intellectual disability. Individuals with Down syndrome and co-occurring autism tend to have more severe rigid and repetitive behaviors and greater challenges with social communication than do individuals with Down syndrome alone. However, the degree to which symptoms can be attributed to each condition remains understudied.  

In a recent study published in Brain Science, Researchers at UC Davis Mind Institute explored the presence and presentation of autism characteristics in 83 individuals with Down syndrome, aged between 6 and 23 years. They found that 37% of our sample met criteria for a diagnosis of autism using the Autism Diagnostic Observation Schedule 2 (ADOS-2), consistent with what prior studies have reported. Next, we explored which skills on the ADOS-2 differentiated individuals in our sample who met autism classification from those who did not. Skills such as eye gaze, use of gestures, quality of social overtures and rapport were more impaired in individuals with Down syndrome who met autism classification compared to those who did not. This finding is consistent with the notion that while individuals with Down syndrome may experience difficulties in social communication, individuals with both Down syndrome and autism experience more substantial difficulties in this area. Lastly, upon examining whether the two groups differed in language and cognitive abilities, they discovered that individuals with Down syndrome who met classification for autism demonstrated more limited language skills, particularly expressive grammar, than those with Down syndrome alone.  

Altogether, their findings confirm earlier studies reporting higher rates of co-occurring autism in individuals with Down syndrome. They also confirm more severe impairments on specific social measures and language skills in individuals with Down syndrome who met classification for autism compared to those who did not. Additionally, for individuals in our sample with more limited language skills, the presence of restricted and repetitive behaviors no longer differentiated individuals with Down syndrome who classified for autism from those who did not. This suggests shared characteristics between autism and Down syndrome. The findings presented in this study build upon earlier studies by examining the presentation of autism characteristics in individuals with Down syndrome using the largest sample to date, describing for the first time the profile of symptoms in these individuals, and establishing a role for expressive language in the emergence of autism symptoms. Their findings demonstrate the need for more research exploring the complexities of diagnosing autism in individuals with Down syndrome, particularly the relationship between language and the presentation of autism characteristics.  

infographic alt text: summarizes findings from a study of 83 people with Down syndrome age 6-23.  37% of participants met diagnostic criteria for autism.  Many traits overlap, and people with both diagnoses had more impaired eye gaze, gesture, expressive language, and social skills.  The findings help in understanding the profile of autistic traits in people with Down Syndrome and the role of language in various traits.