Early and Persistent Motor Delay In the Broader Autism Phenotype: Evidence From a Prospective Study

Background:  

Prospective studies into infants at-risk of developing autism have found motor atypicalities between the ages of 6 and 24 months (e.g., Landa & Garrett-Mayer, 2006). These motor symptoms often precede the problems in social-communicative development associated with autism (Rogers, 2009).

Objectives:  

The aim of the analyses was to build a profile of motor development in infant siblings of children diagnosed with autism, determining whether motor atypicalities are part of the endophenotype of autism, and when interventions could be introduced.

Methods:  

Participants were 53 infants at high-risk of developing Autism Spectrum Disorder (ASD) and 50 low-risk infants, tested longitudinally at the ages of 6, 12-15 and 24 months. Eighteen of the high-risk infants were flagged for meeting criteria for ASD at 24 months, and analyses were conducted on the groups with and without these participants. Outcome measures were the gross and fine motor scales on the Mullen Scales of Early Learning (standardized task) and the Vineland Adaptive Behavior Scales (parental report) at the three age points.

Results:  

Strong correlations were found between measures of gross motor ability at all three age points (low-risk: rs > .5, ps < .01; high-risk: rs > .4, ps < .01), although fine motor skills were less consistent across the two measures over time. High-risk and low-risk groups differed significantly on both gross and fine motor scales at 6 months based on parental report, with high-risk infants still scoring lower on both scales at 12-15 months (all ps < .01). Infants only differed significantly on motor skills on the Mullen Scales of Early Learning from the age of 12-15 months.

Conclusions:  

Motor atypicalities were found as early as 6 months of age in infants at high-risk of developing ASD, over and above differences in other cognitive areas. These differences between low- and high-risk groups persisted over time, and were not changed substantially when infants who were later flagged for meeting ASD criteria were removed from the analyses. Taken together, these data suggest that motor difficulties may be part of the endophenotype of autism, and that focused intervention could begin as early as 6 months on the basis of motor markers. These interventions would have important effects not only on motor development, but also on other cognitive skills.