Left Handed Phenotype in Autism

Background: Traditionally expressive language is perceived as being housed in the anterior left hemisphere.  This is generally accepted to be the case in approximately 90% of right hand dominant individuals and approximately 60% of left handed individuals. Hemispheric specialization places paralinguistic aspects of communication in various locations in the right hemisphere.  Children with autism have a greater propensity for left handedness than the general population, with widespread language deficits in receptive language, expressive language, and the paralinguistics of communication.  

Objectives:  Investigate handedness as a variable of language development, and current language level pediatric autism patients.

Methods:  This retrospective investigation involved review of medical charts and available documentation for twenty-five children who received an outpatient evaluation for autism.

Results:  As has been consistently documented in the literature, this sample of children with autism included a greater number of males than females, at approximately 80% males. Second, as has been previously proposed, there is a higher rate of left handedness in children with autism when compared to the general population. Third, left handed children with autism had a more substantial history of language delay and persisting language deficits relative to right-handed children with autism.

Conclusions:  These results suggest that left handed children with autism and substantial language delay may be a neuropsychological differentiated subset of this heterogeneous disorder.  When considering the historical theories of early neural plasticity and dynamic localization, this pattern would suggest early abnormal left hemisphere development. In order to preserve the more fundamentally valuable aspect of expressive communication, as compared to paralinguistics, expressive language is re-localized in the right hemisphere, resulting in reduced efficiency of paralinguistics. This culminates in greater overall communication deficits, as has been seen in children with autism, especially those with left handedness as seen in this retrospective investigation.  Future investigation may involve imaging procedures to confirm localization. Modified treatment approaches may be considered.