Motor Stereotypies in Autism and Rett Syndrome:Difference and Similarities

Background: Rett Syndrome (RS) and Autistic Disorder (AD) share many phenotypic features, one of them stereotypies, defined as repetitive, rhythmical, patterned, purposeless movements like hand flapping.  Our previous research showed that, in addition to their signature hand-washing stereotypies, girls with RS have many others, some overlapping those of children with AD. The neurologic basis of stereotypies is poorly understood, even in RS despite its known genetic basis.

Objectives: Our goal is detailed description and comparison of the motor stereotypies of AD and RS, hoping to advance understanding of their pathophysiology and management.  Our first step was to detail similarities and differences in the frequency, topography, and variety of stereotypies which might provide clues to their underlying circuitry.  The second was to determine whether specific stereotypies, besides the signature hand stereotypies of RS, characterize one or the other disorder and thus may help early diagnosis.

Methods:   Twenty girls with RS recruited in Portugal were videotaped during a neurologic examination. All had MECP2 mutations and NVIQs < 70; 9 could walk independently.  Mean chronologic age was 60 months (range 36-96). Twenty American children (11 boys, 9 girls) with AD were matched for chronological age and NVIQ (mean age 68 months, range 33-98).  Our preliminary research found no influence of gender on stereotypies. All AD children underwent comprehensive behavioral and neurological evaluations, were ambulatory, and none had a frank neurologic disorder.  They were videotaped during a standardized play session.  In both groups the 5 minute video segment selected for scoring of each stereotypy was the most representative of that child.  Coding included frequency, variety, and body parts affected with particular attention to the hands.  Significance was set at p<0.05

Results:  Stereotypies were continuous in half the children with RS (50% vs.15% in AD).  Stereotypies were infrequent (at most 2 during 5 minutes) in 35% of children with AD (5% in RS).  All hand stereotypies in RS children were midline, compared to 30% in AD.  Stereotypies with hands together (e.g., “washing,” clapping, clenching) characterized RS (60%) rather than AD (10%).  Hand to mouth or to face was also more prevalent in RS (65% vs.15%).  Fewer stereotypies in RS girls with sufficient hand use involved an object (30% vs. 60%).  There was no difference between groups in rocking, stereotypic gaits (RS girls able to walk), variety, complexity, or dystonic features of the stereotypies.

Conclusions: The neurologic origin of RS stereotypies is taken for granted whereas it remains controversial in AD, despite strong overlaps between them.  Useful differences in RS include their quasi-continuousness, the signature involvement of joined hands in the midline, and frequent touching of mouth and face.  Compulsive perseverative use of objects points to AD and suggests orbitofronto-striato-thalamo-cortical circuitry rather than a more strongly subcortical basis for the more elementary movements in RS.  Recent animal and human research suggests that stereotypies may denote reversible dysfunction rather than fixed damage in both.  Advanced imaging will be required to help resolve these differences which may have important implications for future pharmacologic management.