Comparing rates of psychiatric and behavior disorders in adolescents and young adults with severe intellectual disability with and without autism.

Burack et al. (2004) compared teens and young adults who had both autism and severe intellectual disability to peers with severe ID alone. They used the DASH-II checklist to count psychiatric and behavior problems in each group.

The design was quasi-experimental. Every autistic participant was matched to a non-autistic peer by age, sex, and IQ range.

The autism plus severe ID group showed about five times more clinically significant conditions than the ID-only group. They also scored higher on seven of thirteen DASH-II sub-scales, especially anxiety, mood, sleep, organic, and stereotypy/tic areas.

Garrison et al. (2025) extends the anxiety finding. They showed that autistic teens with ID can self-report anxiety when verbal and daily-living skills are strong enough. This gives you a practical way to track the anxiety that A et al. flagged.

Coffey et al. (2005) looked at sleep in autistic teens and young adults. Actigraphy caught problems in 80% of participants, while parent forms missed most. Together with A et al., the message is clear: screen sleep with objective tools, not just questionnaires.

Deserno et al. (2017) moves the story into adulthood. They found that autistic young adults without ID still have large gaps between IQ and daily-living skills, and bigger gaps link to more psychiatric issues. A et al. showed the severe-ID side; K et al. show the pattern continues up the ability spectrum.

If you work with autistic clients who have severe ID, plan for multiple co-occurring issues. Build broad screening into your intake: anxiety, mood, sleep, tics, and medical pain. Use actigraphy or sleep diaries for sleep, try self-report anxiety scales when language allows, and keep reassessing across adolescence and into adulthood. Early, wide, and repeated screening leads to faster referrals and better behavior plans.