Why do many children with ASD have an Intellectual Disability?
by Dr Giacomo Vivanti
Many individuals with Autism Spectrum Disorder (ASD) have Intellectual Disability (that is, below average I.Q. and poor adaptive functioning). What is the nature of this association? Data published from a recent study at the Olga Tennison Autism Research Centre (OTARC), Intellectual development in autism spectrum disorders, provide new insight into this complex issue.
The scientific community has given little attention to this question for decades. Indeed, the prevalent view in the field is that Intellectual Disability in ASD is an additional, unrelated condition that ‘happens’ to be present in some individuals with ASD, and is not seen as providing valuable information on the nature of autism.
Following this line of thought, most research in ASD conducted over the past decades, including research on treatment, has excluded individuals with ASD who have an Intellectual Disability, on the ground that their Intellectual Disability would confound the interpretation of results. As a consequence, we don’t have much knowledge on effective treatments for children with lower IQ (arguably the ones that are more in need of help) and we don’t know much about why Intellectual Disability occurs so often in ASD.
However, the data published in our study provide some new insight into this complex issue. Results from a longitudinal analysis of the intellectual development of 80 children with ASD indicate that the risk of developing an Intellectual Disability increases with the severity of ASD symptoms. In other words, those children who are more severely affected by ASD in early development are more likely to have a lower I.Q. later in life.
Why is this the case?
Recent research on brain plasticity indicates that brain organization in typical development is critically shaped by the child’s social learning experiences during early development. We propose that the presence of severe symptoms of ASD impedes this process, so that children who are more severely affected are those who are least able to appropriately engage in the social learning experiences that are crucial for normal intellectual development. Therefore, ASD and Intellectual Disability do not appear to be unrelated conditions. Rather, the presence of severe ASD symptoms might be a risk factor for developing Intellectual Disability. That is, the children with “ASD associated with Intellectual Disability” are in fact children whose ASD symptoms are so severe that these preclude them from processing the environmental inputs that ‘sculpt’ brain organization during early critical periods.
From this perspective, we argue that the practice of excluding children with Intellectual Disability in ASD research to study “pure autism unconfounded by Intellectual Disability” is ill considered. Rather, research should target those factors that place affected individuals at an increased risk of negative outcomes, such as the presence of an Intellectual Disability, and understanding the underlying causal mechanisms, to inform clinical practice, with the ultimate goal of fostering positive outcomes for all individuals with ASD.
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