Longitudinal development of language and fine motor skills is correlated, but not coupled, in a childhood atypical cohort

BackgroundAutism is a behaviorally defined neurodevelopmental condition that is often associated with early developmental delays in language and motor domains. However, little is known about the complex dynamic processes that drive the co-development of such difficulties in children at-risk for atypical developmental trajectories. Using a longitudinal design, the aim of the present study was to model the parallel growth of language and motor skills in a cohort of infants at-risk for atypical development, and to explore differences between those who go on to receive a diagnosis and those who do not. MethodsReceptive and expressive language and fine motor skills were assessed at four measurement occasions in a group of 239 infants (122 girls and 117 boys, average age of 6 months at t1 and 36 months at t4) in the BASIS sample (Elsabbagh et al. 2013) consisting of infants with autistic siblings. Latent Growth Curve Analysis was applied to investigate the mutualistic coupling of longitudinal changes in these domains. ResultsOur results showed highly correlated slopes, suggesting that improvements in language go hand-in-hand with improvement in motor skills in the whole sample. We did not find compelling evidence for coupling between these skills, i.e. baseline scores in one domain were not associated with the rate of change in the other. Notably, we observed differences between children who would later go on to receive a diagnosis, compared to those who would not: Both the scores at baseline, as well as the rate of change, were more variable in the atypical group, suggesting the possibility of latent heterogeneity.ConclusionsGreater variability at baseline in the (later diagnosed) atypical group, combined with very strong correlations between the slopes, suggests that dynamic processes amplify small differences between individuals at 6 months result into large individual differences in autism symptomatology at 36 months. Our results also suggest that those children who go on to receive a diagnosis of atypical development at age three are not specifically characterized by stronger or weaker coupling between language and motor skills.