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Motor impairment should be a “Specifier” for autism spectrum disorder

In a recent Letter to the Editor, responding to Bhat’s (2021) claim that there is a “need to recognise motor impairments as one of the diagnostic criteria or specifiers of ASD” (p. 202), Bishop et al. (2022) initiated a very fruitful discussion regarding whether current evidence supports inclusion of motor impairments within the diagnostic criterion for autism spectrum disorder (ASD). In their original work, Bhat (2020) based their claim on their reports of the high prevalence of motor impairment observed in a large sample of children (n = 13,887) using a screening measure for Development Coordination Disorder (DCD), the DCD-Q. We agree with Bishop and colleague’s expressed position that there is currently not enough evidence to support the inclusion of motor impairment within the “core criteria” that constitute a diagnosis of ASD—motor impairments are neither specific nor universal to individuals diagnosed with ASD. However, we argue that there is evidence for motor impairments to be considered as prevalent and functionally impactful as other domains recognized as “specifiers” to an ASD diagnosis (i.e., intellectual impairment and language impairment). We provide a brief overview of this evidence below. Previous studies have reported atypical spontaneous movements early in infancy (e.g., Einspieler et al., 2014), delays in early motor milestones (e.g., Bolton et al., 2012; Reynolds et al., 2021), and fine and gross motor difficulties in infants at elevated likelihood for autism between 6 and 36 months (e.g., Iverson et al., 2019; Landa et al., 2013; Licari et al., 2021a). In addition to Bhat’s evidence utilizing the DCD-Q (Bhat, 2020, 2021), studies of autistic children have also demonstrated high prevalence rates of motor impairment utilizing both broader measures of adaptive functioning (e.g., Licari et al., 2019; Reynolds et al., 2021) and gold-standard objective assessments of motor proficiency (e.g., Dewey et al., 2007; Green et al., 2009). While Bishop and colleagues suggest that motor delays and impairments may be better explained by “autistic behaviors,” “lack of interest,” “lack of motivation,” “social demands” or “intellectual impairments,” we argue that observations of motor impairments emerging early in life, persisting throughout childhood, and measured across different methods and assessments, demonstrates otherwise. Given that motor impairment has been described since the earliest conceptualizations of autism and continues to be highlighted as a highly prevalent domain that clearly sits alongside the autism phenotype, it is time for these challenges to be recognized early and supported. Motor impairment is currently recognized as an “associated feature” in the DSM-5, however poor recognition and a lack of skilled expertise in evaluating these difficulties during a diagnostic evaluation has resulted in motor impairment being overlooked during the diagnostic evaluation process. Our previous findings have shown that, unfortunately, only 1% of children at the time of an ASD diagnosis have their motor impairments clinically recognized (Licari et al., 2019), well below what would be expected based on broader prevalence estimates. As mentioned by Bishop and colleagues, motor impairment can only be “specified” within the current diagnostic framework if associated with another neurodevelopmental disorder such as DCD. A diagnosis of DCD is not currently recommended until 5 years of age, to account for natural variability that exists in the attainment of motor skills, however this often means that a critical therapeutic window to support the early development of motor skills is likely to be missed. On average, children receive a diagnosis of ASD on or before 5 years of age, and additional diagnostic evaluations for co-occurring conditions like DCD, given inadequate recognition and support for this diagnosis (Licari et al., 2021b), places additional financial and time costs on clinicians and families. Notwithstanding this evidence, we would like to emphasize that the use of the DCD-Q to support Bhat’s claim is not without some limitations. Despite its widespread use across clinical and research contexts, the DCD-Q has received limited psychometric evaluation, often with inadequate latent variable modeling approaches. Further, several DCD-Q items may conflate different processes that contribute to an assessment of motor abilities, and a low score (denoting impairment) may be due to factors unrelated to genuine motor deficits or developmental coordination difficulties (e.g., visual impairment). As a result, the construct validity of the DCD-Q is currently unclear. Given that the DCD-Q was only designed to be used as a screening measure (i.e., to identify those “at risk”), there is a clear need for new informant instruments measuring motor proficiency that are developed and validated based on the gold standard principles of measurement development (such as the National Received: 29 August 2022 Accepted: 7 September 2022