Clinical heterogeneity among children with neurodevelopmental disorders reflects diversity in strengths and needs that can have important implications for therapeutic management. Until recently, research into comorbidities contributing to such diversity has tended to reflect the clinical divide between neuromotor and developmental-behavioral disciplines. However, over the past 10 to 15 years there has been greater recognition that risk of mental health and neurobehavioral disorders is shared across the broad continuum of developmental medicine, including cerebral palsy (CP).
Recognizing that functional impairments associated with CP often extend well beyond the motor system, Christensen et al. report rates of autism spectrum disorders (ASD) in this patient population, from a US-based surveillance system (the ‘Autism and Developmental Disabilities Monitoring Network’). This study is particularly timely as rates of ASD are reported to be increasing in the general population although there is little evidence that ASD rates are specifically increasing among children with CP. Indeed, the reported rate of 6.9% is very similar compared to estimates from the same surveillance system and geographic regions 2 years earlier. That said, the ASD rates in children with CP remain elevated compared to general population rates, consistent with epidemiological research in other areas of the world.
Does this observation shed new light on potential shared causative mechanisms between the two disorders? It is increasingly clear that there are multiple etiological pathways to ASD. Scherer et al. recently reported that whole genome sequencing could increase the etiological yield of genetic testing to as high as 50% in children with ASD, albeit with many different de novo and rare inherited variants identified. Cerebral palsy is also characterized by both clinical and etiological heterogeneity. Specific genetic variants that have an impact on both motor and social-communication (and/or general intellectual development) may contribute to shared liability to the two disorders. However, there are already clear examples of factors that are not primarily genetic (e.g. preterm birth) that increase the risk of both disorders. Thus, there is likely to be a myriad of factors underlying the co-occurrence of ASD and CP. The relative contribution of genetically-influenced developmental versus injury-related processes in the co-occurrence of ASD and CP remains an interesting question for future work. Another question is, do ASD and CP co-occur across the clinical continuum of each disorder, or mainly in association with intellectual disability? This issue should also be addressed in future research, perhaps through further stratification of population samples.
What are the clinical implications, particularly in regard to the need for intensified surveillance and/or screening for signs of ASD in children with CP? There are a few issues to consider. First, while ASD screening and diagnostic tools have been extensively evaluated in the pediatric population, further validation in special populations such as children with CP is needed, particularly in the presence of features (e.g. sensory impairments, motor deficits limiting use of gestures such as pointing) that may complicate differential diagnosis. Second, recent studies have indicated a roughly 3 to 4-fold increase in a range of emotional and behavioral disorders (including attention-deficit–hyperactivity disorder, depression, anxiety etc.) among children with CP compared to similar-aged peers. Given that recent population prevalence estimates of ASD are as high as 2%, the relative elevation in ASD rates in children with CP appears to be in line with other emotional-behavioral comorbidities. This argues for a more general emphasis on mental health in clinical follow-up of school-aged children with CP rather than an exclusive focus on specific diagnoses such as ASD.
However, assessment of early social-communication and play behaviors serves not only to identify the risk of ASD, but also to open dialogue and service planning aimed at optimizing function in these domains. Indeed, developmental surveillance that aims to identify not only specific comorbid diagnoses such as ASD, but opportunities to enhance function and participation offers the potential to benefit all children with neurodevelopmental disorders.