Autism and Intellectual Disability: Ontario Services and Support

Prevalence and Assessment

The reported co-occurrence rate of intellectual disability in autism has changed over time as diagnostic practices have evolved. Earlier studies reported rates of 50-70%, but recent population-based studies using broader autism diagnostic criteria find rates of 30-40%. A 2021 meta-analysis by Postorino et al. confirmed a pooled prevalence of approximately 33% across 38 studies.

Cognitive assessment in autistic individuals requires instruments validated for this population. Standard IQ tests may underestimate abilities due to the influence of language delays, social demands of the testing situation, and attentional differences. Ontario clinicians increasingly use non-verbal IQ measures (e.g., Leiter-3) and adaptive behaviour assessments (Vineland-3) to provide a more accurate picture.

Ontario Services for Dual ASD-ID

In Ontario, individuals with dual ASD-ID can access services through multiple pathways. The Ontario Autism Program provides clinical services during childhood. Developmental Services Ontario (DSO) provides the gateway to adult developmental services including residential supports, day programs, and Passport funding for community participation.

Eligibility for adult developmental services requires a DSO application, which should be initiated at age 16 to allow processing time before the youth turns 18. The DSO assessment determines eligibility based on the intellectual disability, not the autism diagnosis — meaning that autistic individuals without ID do not qualify for adult developmental services, creating a significant service gap.

The Surrey Place Dual Diagnosis Program in Toronto and regional dual diagnosis justice programs serve individuals with complex co-occurring presentations. Community Networks of Specialized Care provide consultation and support for challenging situations across Ontario.