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Psychiatric Causes of Intellectual Disabilities

Tammy Reynolds, B.A., C.E. Zupanick, Psy.D. & Mark Dombeck, Ph.D.

Autism Spectrum Disorder (ASD)

A leading cause of intellectual disabilities (ID, formerly mental retardation) is autism spectrum disorder (ASD). A person may be diagnosed with both ASD and an ID. ASD has two primary symptoms. First, people with ASD have trouble with communication and social interaction. Second, they demonstrate repetitive patterns of behaviors, interests, or activities. Some examples are repetitive speech, ritualized patterns of behavior, or fixation upon certain objects. Approximately 40% of people with ID will also have ASD. However, nearly 70% of people with ASD also have ID (reported in La Malfa, G., Lassi, S., Bertelli, M., & Placidi, G.F., (2004). See also http://www.cdc.gov). Thus, while ASD and ID share some similarities, they are not the same.

autism word collageAlthough similar, the two disorders are often difficult to tease apart. People with ASD might appear to meet the criteria for ID because their IQ scores are low. However, these low test scores may not reflect intelligence per se. Instead, the low scores might result from problems with test taking itself. These test-taking problems result from communication and social limitations. Since IQ testing relies on both of these abilities to some extent, IQ scores may be artificially low. Some children with ASD may have an average IQ. However, they cannot demonstrate their abilities because they cannot communicate their understanding of the testing protocols. In contrast, children with intellectual disabilities lack this intellectual capacity or understanding. Although the two conditions are distinct, they can and do frequently co-occur. More information about co-occurring disorders is found in the Diagnostic Section.