Features of autism in Rett syndrome and severe mental retardation.

The team gave the Autism Behavior Checklist (ABC) to girls with Rett syndrome and to girls with severe mental retardation. They matched the groups for age and motor skills so the scores would not be swayed by those factors.

The goal was to see if Rett syndrome looks more "autistic" than plain severe MR once you hold development level steady.

Rett girls scored higher on only two ABC parts: Sensory and Relating. On the other four parts the two groups looked the same.

So Rett syndrome adds extra sensory and social quirks, but it does not show the full autism pattern seen in idiopathic ASD.

Donahoe et al. (2000) also used the ABC and found that kids with autism beat an MR-only group on every repetitive-behavior item. Reid et al. (2003) now shows Rett kids do NOT beat the MR group on those same items. The gap closes because Rett lacks the wide-ranging autism profile.

Kraijer (2000) warned that when you match MR groups you should use self-help and motor scores, not social scores. H et al. followed that tip, matching on motor level, so their Sensory/Relating gap is more believable.

Castañe et al. (1993) watched two Rett girls in analogue sessions and saw hand stereotypies pop off no matter what was happening around them. H et al.'s ABC data back this up: the Rett group did not outscore MR on the Body & Object Use subscale, meaning the stereotypies are present but not uniquely severe.

If you assess a girl who has both MR and odd sensory or social reactions, do not jump to an autism label. Check for Rett first; the ABC can help you spot the narrower pattern. Use the Sensory and Relating subscale jumps as red flags, but lean on genetic testing and history for the final call. This keeps diagnoses clean and guides you to Rett-specific supports like breathing exercises and hand-use programs instead of generic ASD packages.