Intellectual development in young children with autism spectrum disorders: A longitudinal study

Intelligence profiles in autism have been characterized by great variability. The questions of how autistic children's intelligence changes over time, and what factors influence these changes deserve study as part of efforts to document child autism profiles, but also because the relationship between intellectual functioning and children's background characteristics is poorly understood, particularly in a longitudinal context. A total of 39 autistic children and 39 age-matched neurotypical children (5-9 years old) completed two IQ assessments at preschool age and up to 4 years later. Repeated-measures analyses assessed longitudinal changes in the children's verbal (VIQ), performance (PIQ), and full-scale IQ (FSIQ) at group level. We further sought to identify clusters with distinct profiles in each group by adopting an unsupervised K-means clustering approach, and detect possible between-subgroup differences in terms of children's socioeconomic status and autism severity. The largest cluster in the autistic group was composed of children whose PIQ significantly dropped at follow-up, while the second largest cluster improved in all quotients; the smallest cluster, wherein children had more highly educated mothers than the rest of the clusters, was characterized by large improvement in VIQ. For the neurotypical children, there was a two-cluster division; the majority of them improved in the three quotients, while very few dropped in PIQ at follow-up. The relation between socioeconomic status and IQ changes was significant for both groups. The findings demonstrate both the complexity of intelligence changes in autism and the need to view this complexity through the lens of the children's socioeconomic diversity. The development of autistic children's intellectual skills is characterized by great variability which remains poorly understood. In the current study, we investigated the developmental trajectories of verbal IQ, performance IQ, and full-scale IQ scores of autistic children who were first assessed on their intellectual functioning skills at preschool age and were followed-up at the age of 9. Results showed distinct profiles of IQ changes in the autistic group which were significantly affected by the children's socioeconomic background. The study demonstrates that a dimensional perspective to IQ in autism that takes into consideration children's socioeconomic background might better inform our understanding of how their intelligence develops over time.