The Co-Occurrence of Autistic and Dyspraxic Symptomatology in the General Population

Background:  21-100% of individuals with an Autism Spectrum Disorder (ASD) present with motor abnormalities similar to that seen in dyspraxia (Gowen & Hamilton, 2012), indicating motor impairment as a potential diagnostic symptom in ASD. Individuals with dyspraxia (Creavin et al., 2014) and those with ASD (Anketell et al., 2013; Coulter et al., 2013) are more likely to have poor stereopsis. Stereopsis, or depth perception, may play a fundamental role in motor coordination activities such as navigation/object avoidance, reaching, grasping and object manipulation. To date, no systematic study has investigated the relationship between autistic traits (such as social difficulties) and reduced motor ability (increased 'clumsiness') in the general adult population and whether poor stereopsis may contribute to this association.

Objectives:  To determine whether autistic and dyspraxic characteristics co-occur in a large, typical population-based sample and if poor stereopsis plays a role in this relationship.

Methods:  Three validated questionnaires – the Stereopsis Screening Inventory (Coren & Hakstian, 1996), the Adult Developmental Coordination Disorder Checklist (Kirby, Edwards, Sugden, & Rosenblum, 2010), and the Autism-Spectrum Quotient (Baron-Cohen et al, 2001) - were used to explore whether stereopsis was correlated with dyspraxic symptomology (clumsiness) and/or autistic traits. 650 participants completed the questionnaires. 290 cases were missing a response for at least one item; missing data was imputed using random forest modelling. Factor analysis was used to determine whether clumsiness and autistic traits shared the same underlying basis (stereopsis).

Results:  Preliminary analyses showed that both stereopsis (r = 0.29, p < 0.001) and clumsiness (r = 0.64, p < 0.001) correlated with autistic traits and with each another (r = 0.27, p < 0.001). An exploratory factor analysis (EFA) on all items from all screening measures revealed ten underlying factors. Factors were largely composed of items from a single scale, indicating that any co-occurrence of poor stereopsis, clumsiness and autistic traits cannot be attributed to a single underlying mechanism.

However, when the factor scores from the EFA were correlated with one another, it was found that stereopsis correlated with social skills (r = -0.22, p < 0.001) and isolation due to motor proficiency (r = 0.27, p < 0.001). As stereopsis became worse, social skills decreased and isolation due to motor proficiency increased. Interestingly, social skills showed a negative correlation with isolation due to motor proficiency (r = -0.43, p < 0.001). These results indicate that isolation due to motor proficiency mediates the relationship between stereopsis and social skills.

Conclusions:  Although autistic and dyspraxic characteristics co-occur in the general adult population, they are independent of one another and do not share the same underlying mechanism. However, there is a relationship between reduced stereopsis and poor social skills that is mediated by motor ability. This is in line with the literature indicating that motor skill proficiency plays a role in the development of social communication skills. Determining the specific aspects of motor skill acquisition that are affected by poor stereopsis could inform social skill interventions for individuals with ASD.