Prevalence of Motor Impairment in Autism Spectrum Disorder: Analysis of a Population-Based Cohort
Objectives: The present study examined the prevalence of motor impairment at time of diagnosis in a large cohort of children with ASD, and to investigate the relationship between motor impairment and core features of the ASD phenotype.
Methods: Vineland Adaptive Behavior Scale (VABS) motor scores were examined in a sub-cohort of children aged ≤ 6 years from the Western Australian Autism Register (N = 2084; 81.2% males, 18.8% females). Motor scores were compared to other domains within the VABS (communication, daily living socialization), across DSM criteria, intellectual level, age and gender.
Results: A total of 35.4% of children scored in the low range on the motor skill subdomain of the VABS, and a further 43.7% in the moderately low range (combined total of 79.1%). This frequency was slightly lower than the other VABS subdomains, with 79.1% scoring in the low and 17.7% in the moderately low ranges for social skills (combined total of 96.8%), 62.3% scoring in the low and 29.3% in the moderately low ranges for daily living (combined total of 91.6%), and 65.7% scoring in the low and 24.9% moderately low ranges for communication (combined total of 90.6%). Whilst the prevalence of poor motor scores was high, motor impairment was only reported as a comorbid condition by diagnosing clinicians in 1.34% of the sample. Motor scores were lower in children diagnosed with ASD at a later age (p<0.001), and children with intellectual impairment (37.7% of the sample) had motor scores lower than those without (p<0.001). Examination of motor scores based on diagnostic criteria from the DSM revealed that those cases meeting the diagnostic criteria for impairments in non-verbal behaviour (i.e., body postures and gestures) and restricted and repetitive behaviours (i.e., motor stereotypies) displayed lower motor scores than those without.
Conclusions: The prevalence of motor impairment found in this large cohort was at least as common as one current diagnostic specifier. This highlights the need for further consideration of motor impairment within diagnostic evaluation for ASD.
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