Is Autism Left-Handed? Exploring Abnormal Lateralization in Handedness and Language Among Individuals with ASD.

Background:  Language and fine-motor function are typically lateralized to the left hemisphere. Neurologic lateralization during brain development underlies handedness and communication asymmetry. Atypical lateralization of these functions has been observed in individuals with autism spectrum disorder (ASD) and other neurodevelopmental disorders. Recently, a study of handedness in individuals with ASD reported a lower handedness score than typically developing (TD) children. Limited research has suggested a small effect of handedness on language, in that right-handed children had better language scores than non-right-handed subjects.

Objectives:  The current study aims to explore the difference in handedness quotient between individuals with ASD vs. TD. In addition, this study investigates the association between handedness and language function among individuals with ASD. Finally, the association between handedness and communication is explored separately for different facets of a handedness assessment. Handedness is measured utilizing the Edinburgh inventory, which measures the degree of dominance of an individual’s right or left hand based on eye, hand and foot laterality.

Methods:  Thirty children diagnosed with ASD and seventeen TD children ages 8-18 years old underwent testing for handedness utilizing the Edinburgh Handedness Laterality quotient. Communicative function was assessed with the Vineland Adaptive Behavior Scales – Second Edition, Communication Domain (VABS-CD). Linear regression analysis was performed to explore the correlation between Edinburgh handedness quotient and communication scores. A t-test comparison of VABS-CD communication scores between right-handed and left handed and ambidextrous/undifferentiated individuals with ASD was completed for each item in the Edinburgh scale as well as global Laterality Quotient.

Results:  The difference in handedness quotient between individuals with ASD (median 88) and TD (median 100) did not reach significance (p=0.319). There is no significant correlation between handedness quotient and VABS-CD scores (r²=0.1, p=0.109) Furthermore, there was no significant difference between VABS-CD communication scores among individuals with ASD who are right-handed vs. those that are left handed and ambidextrous/ undifferentiated (p=0.702). No differences emerged even when communication scores were compared based on laterality of each item on Edinburgh handedness quotient scale (lowest p-value was 0.201).

Conclusions:  This study failed to replicate the reported association between handedness and communication function among individuals with ASD. Studies controlling for non-verbal intellectual quotient are necessary to explore whether individual differences in cognition may account for discrepant results. Further studies investigating the inter-relation between abnormal lateralization of communication and motor function may inform the neurobiologic basis of autism and other neurodevelopmental disorders.