A case of infantile autism associated with Down's syndrome.

Doctors wrote about one child who had both Down's syndrome and autism. This was rare in 1979. The paper is a single case study.

They described the child's behaviors and how the two conditions looked together.

The child showed clear signs of both conditions. Autism can hide inside Down's syndrome if you are not looking for it.

The authors warned that autism is easy to miss when Down's is already known.

Schwichtenberg et al. (2013) later tested a larger group and found about 1 in 5 kids with Down's also meet autism cut-offs. Ding et al. (2017) saw the same pattern in 674 youths.

Godfrey et al. (2019) showed these kids have their own symptom mix. They have equal social and repetitive scores, unlike typical autism where social scores are worse.

Johnson et al. (2009) proved the autism signs are bigger than what you would expect from low IQ alone. Together these papers turn one rare case into a common screening rule.

Always screen for autism when you see a child with Down's syndrome. Use the SCQ or ADI-R and watch for extra stereotypy, repetitive talk, over-activity, and self-injury. These kids need the same ABA plans as any autistic learner, but expect milder social gaps and adjust peer goals.