Poor Movement Skill in the Broader Autism Phenotype: Identification and Stability Over Time

Background: Previous research has reported movement difficulties in children diagnosed with autism spectrum disorders (ASD) as well as in their younger siblings, who are at increased risk of developing ASD. Early motor abilities can affect the development of other domains, including language and communication (Iverson, 2010), which are core areas of difficulty in ASD. Understanding the stability of motor assessments over infancy and the early years could therefore help in identifying those most at risk of ASD-related difficulties later in development.

Objectives: One aim of the current study was to assess motor abilities in the younger siblings of individuals diagnosed with autism, once they had reached school age. Previous research has focused on younger children and infant siblings, or on older children with a diagnosis of ASD. A second objective was to assess how well early measures of motor ability used in studies of younger siblings related to assessments more commonly used in clinical settings and motor development research.

Methods: Twenty younger siblings of individuals diagnosed with autism were visited at the age of 5-7 years (mean = 6 years, 2 months) and their motor development was assessed through a standardised measure (the Movement ABC-2: MABC) and parental reports (the Vineland Adaptive Behavior Scales: VABS). These data were compared to those collected from two earlier visits, at mean ages of 9 and 40 months, through parental reports and a direct assessment, the Mullen Scales of Early Learning (MSEL).

Results: On the MABC, 3 of the 20 children had significant movement difficulties (falling at or below the 5^th percentile), with a further 4 children having borderline movement difficulties (6^th - 15^th percentiles). Using these same criteria, 5 children had significant movement problems based on a motor composite score from the VABS. In addition, analyses of the VABS raw scores for gross and fine motor skills revealed significant correlations with the Manual Dexterity scale on the MABC (ps < .01).

Inspection of the infant data revealed that those children with significant movement difficulties on the MABC had movement problems highlighted on either the VABS or the MSEL during at least one of the earlier visits. This was also the case for 3 of the 4 children with borderline movement difficulties at 5-7 years. As in our previous research (Leonard et al., 2011), gross and fine motor scores on parental report and direct assessment were well correlated during infancy and early childhood (ps < .05).

Conclusions: Significant movement difficulties were present in 35% of a group at increased risk of developing ASD. A further 20% had difficulties with at least one area of motor ability measured by the MABC. In the majority of these cases, motor problems had been highlighted earlier in development either by parental report or direct assessment. These data build on previous research that has found poor motor skills in infant siblings by highlighting the stability of these difficulties into early childhood. Future analyses will assess the impact of motor problems on the development of other domains and ASD-related symptoms.