Longitudinal tracking of vocabulary development in children with neurodevelopmental and genetic disorders using Communicative Development Inventories (CDIs)

MacArthur-Bates Communicative Development Inventories (CDIs) are widely used to assess early language development and identify language delay in children, including those with neurodevelopmental and genetic conditions. This vignette reviews studies that used repeated CDI assessments to track expressive vocabulary growth over time. We identified 13 longitudinal studies including participants with autism, Down syndrome, Williams syndrome, and other rare genetic conditions. The results show that, across different conditions, expressive vocabulary development was delayed and highly heterogeneous, but few studies included more than two time points, hence limiting inferences about non-linear trajectories, plateaus, or regression. The review highlights both the potential and current limitations of CDI-based longitudinal data and underscores the need for harmonised, multi-timepoint study designs in order to better characterise expressive language development in atypical populations.