Delays in Motor Milestones Do Not Differ between Children with Autism Spectrum Disorder (ASD) with and without Co-Occurring Developmental Coordination Disorder (DCD) and Children with DCD Alone

Background: Motor symptoms in ASD have long been acknowledged by clinicians and documented using standardized motor assessments of gait, balance, and coordination (Ozonoff et al., 2008). Under DSM-5 guidelines (APA, 2013), Developmental Coordination Disorder (DCD) and Autism Spectrum Disorder (ASD) can be diagnosed as co-occurring (ASD+DCD). There is emerging literature demonstrating neurobiological (Caeyenberghs et al., 2016) and behavioral (Caçola et al., 2017) similarities and a high rate of co-occurrence (Miller et al., under review). However, the treated prevalence of ASD+DCD remains low, and the specific overlap between motor symptoms of ASD, DCD, and ASD+DCD is unknown.

Objectives: Our aim was to assess differences in developmental milestone acquisition among patients with ASD, DCD, and ASD+DCD in a local children’s hospital network. We expected that all three groups would have delayed gross and fine motor skills. We hypothesized that the ASD and ASD+DCD groups would have greater delay in age of acquisition for language than the DCD-only group, but the groups would not differ in age of acquisition for fine motor skills, activities of daily living (ADL), or gross motor skills.

Methods: We retrospectively evaluated electronic medical record (EMR) from 1994 to 2018 for patients who were 0-21 years old at the time of first chart entry, with a diagnosis of DCD or ASD+DCD. The number of patients since 1994 was 6,003 (ASD = 5,520, DCD = 424, ASD+DCD = 59). We conducted preliminary analysis on a subset of charts (2007-2018), with a total sample size of 2,239 (ASD = 2010, DCD = 205, ASD+DCD = 24). We collected data using a REDCap form including primary and co-occurring diagnoses, age in months at which patients met developmental milestones, and demographics as part of a larger study.

Results: We used multivariate analysis of variance to test diagnostic group (ASD, DCD, ASD+DCD) differences in age of developmental milestone acquisition (Table 1). Patients did not differ in age of acquisition for either gross motor or fine motor/ADL skills. The DCD group had an average age of language acquisition 12.36 months earlier than the ASD group.

Conclusions: The lack of group differences in age of acquisition for gross and fine motor skills supports our hypothesis that motor problems are profound in ASD. For many children, these likely warrant a co-occurring DCD diagnosis. This may lead to more targeted interventions for delayed or impaired motor skills greatly improving outcomes and quality of life (Blauw-Hospers & Hadders-Algra, 2005). Motor delays were similar between the ASD and DCD group, but the DCD group did not exhibit language delays. The link between ASD and DCD appears specifically rooted in motor skills, rather than reflecting global developmental delays. Missing information in the EMR limited our sample size, particularly for the ASD+DCD group where the treated prevalence was already quite low. This study highlights the need to clarify overlap versus independent presentation of motor symptoms in these two disorders.