Motor Development and Its Relation to Cognitive and Language Development in Young Children At High Risk for ASD

Background:  Motor abnormalities have been documented in children with autism spectrum disorders (ASD) from infancy into adulthood.  In typical development, self-experience (self-generated action) is linked to social and language abilities.  Early motor delay could interfere with the type of self-experience needed for healthy development in non-motor domains.  Three prospective longitudinal studies of ASD have reported disruption in early motor development in 6-month-olds, with preliminary evidence that early delay in postural control is related to social and communication impairment, including ASD at 36 months.  Also, motor impairments are reportedly associated with social and communication impairments in older children with ASD.

Objectives:  

1. Determine rate of motor delay at 14, 24, and 36 months in siblings of children with ASD (sibs-A) with and without ASD outcome diagnosis (made at 36 months).
2. Determine whether children with ASD who exhibit motor delay have comparable language and non-verbal cognitive functioning as children with ASD whose motor development is within normal limits.

Methods:  A prospective, longitudinal study of development was conducted involving younger siblings of children with ASD (sibs-A; n=204).  Children were tested at 14, 24, and 36 months.  At each age, the Mullen Scales of Early Learning was administered.  Criterion for motor delay: Scoring >1.5 sd below the test mean on the Mullen Fine or Gross motor scale (Only the Fine Motor scale was administered at 36 months).  Outcome diagnosis of ASD (n=52) was established at age 36 months based on expert clinical judgment and meeting ADOS criteria for ASD or autism. 

Results:  The proportion of sibs-A with motor delay increased with age in the ASD group, but not in the non-ASD sibs-A, as shown below. 

Age	14 months		24 months		36 months
Group	ASD	Non-ASD	ASD	Non-ASD	ASD	Non-ASD
Proportion with delay	19%	20%	45%	11%	63%	11%

Next, the ASD group was separated into two subgroups: No Motor Delay and Motor Delay.  At 14 months, the ASD Motor Delay group scored significantly lower on the Mullen Visual Reception scale compared to the No Motor Delay group (p=.027).  Mean Visual Reception T score for both groups was within a standard deviation of the mean, indicating average nonverbal cognitive ability.  At 24 and 36 months, the ASD Motor Delay group scored significantly lower than the No Motor Delay group on the Visual Reception and both language scales (p’s<.001).

Conclusions:  Motor delay increasingly becomes evident as children with ASD near the third birthday. Early in the second year of life, motor delay could not be attributed to nonverbal cognitive delay because nonverbal cognitive scores were within normal limits.  Nonetheless, at subsequent ages, the Motor Delay ASD group was comprehensively impaired, and by 36 months, scored ~2 standard deviations below the No Motor Delay ASD group.  Results indicate that early intervention for children with ASD should address motor functioning.  Motor demands of speech targets (e.g., phonetic structure and motoric complexity) and of actions required for gesture or play activities should be carefully examined and modified according to children’s motor abilities.