Emotional disturbance in mental retardation: an investigation of differential diagnosis.

Doctors compared four groups of people with intellectual disability. One group had autism. The other three had psychosis, schizophrenia, or severe emotional problems.

They gave everyone the same tests for language, daily-living skills, and behavior. Then they asked which scores best told the groups apart.

Only the autism group had very low language and daily-living scores. The other three groups looked the same on every test.

In other words, low talking and low adaptive skills were the red flags for autism, not mood or odd beliefs.

Fink et al. (2014) seems to disagree. They found autistic kids read faces just fine once verbal ability is held still. The two studies clash until you see both point to language as the key variable. Handleman et al. (1980) used language level to split diagnoses; Elian removed it to test emotion skill. Same data, different lens.

Prigge et al. (2013) built on the 1980 finding. They showed that when autism traits and low adaptive skills occur together, severe behavior problems skyrocket. The pair of markers is more powerful than either alone.

Totsika et al. (2010) widened the age view. In adults over 50, autism plus ID looked no different from ID-only once adaptive level was counted out. Again, daily-living scores drive the picture, not the autism label itself.

When you assess an adult or child with ID and mood swings, run language and adaptive tests first. If both are sharply below IQ, think autism and refer for ADOS. If both are near IQ, look at trauma, anxiety, or psychosis instead. This one step keeps you from chasing the wrong diagnosis and guides you to the right supports.