Infant Motor Skill and ASD

Background: Emerging theoretical and empirical work suggests that infant motor skill is a characteristic of a prodromal period for autism spectrum disorder (ASD) and developmental vulnerability in infants with an older sibling with ASD (High-risk, HR infants). However, few studies have focused on the first year of life—when delays are proposed to be first evident. Further, little research has addressed this question for HR infants for whom developmental delays have been observed.

Objectives:   (1) Examine the presence of motor delays in HR infants relative to infants with no family history of ASD (Low-risk, LR infants). (2) Examine the presence of motor delays in infants later identified with ASD. (3) Examine the relation between infant motor skill and concurrent ASD symptomatology.

Methods:   Our sample included 104 HR infants and 55 LR infants assessed at 6 months of age as part of an ongoing longitudinal study. Older sibling’s ASD was confirmed using the Autism Diagnostic Observation Schedule (ADOS) and clinical judgment. We assessed infant motor skill using the standardized Peabody Developmental Motor Scales (PDMS). Motivated by previous work, we used the Stationary gross motor subscale and two fine motor subscales (Grasping and Visual-motor Integration, VMI). To assess autism symptomatology at 6 months, we administered the Autism Observation Scale for infants (AOSI). To date, a subset of 74 infants (49 HR, 25 LR) have reached a 24-month follow-up session and these infants were divided into one of two groups based on whether they met our ASD criteria (ADOS score for ASD and clinical judgment). This resulted in 11 infants with ASD (all from HR group) and 63 infants without ASD (No Diagnosis, ND group). Due to unequal sample sizes, we performed non-parametric tests for all analyses (the pattern of results is unchanged using parametric alternatives).

Results:   We found that the HR infants scored lower than LR infants on the Stationary scale (z=2.76, p=.006) and both fine motor scales (Grasping: z=2.52, p=.012; VMI: z=2.03, p=.043) (Figure 1). A subset of infants had AOSI scores available (HR: n=74, HR: n=45) to test relations between infant motor skill and concurrent autism symptomatology. Overall, the HR group had higher AOSI scores (mean = 7.80, SD = 3.76) than the LR group (mean = 5.67, SD = 3.02), indicating greater ASD symptomatology in the HR group (z=3.13, p=.002). Within the HR group, AOSI scores significantly related to PDMS stationary (rho=-.333, p=.004) and grasping scores (rho=-.284, p=.014). Finally, we found motor delays in infants later identified with ASD relative to those without ASD. The ASD group scored lower than the ND group on the PDMS stationary scale (z=2.62, p=.009) and both fine motor scales (Grasping: z=2.97, p=.003; VMI: z=2.42, p=.016)(Figure 2).

Conclusions:  Our findings provide evidence supporting infant motor skill as an area of developmental vulnerability in HR infants and an early indicator of ASD. In combination this points to the importance of considering motor skill when characterizing a putative prodromal period for ASD and developmental monitoring of HR infants.