Cross-sectional evidence for a decrease in cognitive function with age in children with autism spectrum disorders?

Autism spectrum disorders (ASD) are associated with early disturbances in brain maturation processes and these interferences presumably have their consequences for the progressive emergence of cognitive deficits later in life, as expressed in intelligence profiles. In this study, we addressed the impact of age on cognitive functioning of 6- to 15-year-old children and adolescents with ASD. Intelligence profiles were measured by the Wechsler Intelligence Scale for Children and compared among four consecutive age cohorts (children aged 6.17-8.03 years, 8.04-9.61 years, and 9.68-11.50 years and adolescents aged 11.54-15.85 years) of 237 high-functioning boys with ASD. The results clearly demonstrated that the global intelligence level was lower in children aged 8 years and older, when compared with 6- and 7-year-old children with ASD. This is mostly due to the Freedom From Distractibility factor, suggesting that older children were less able to sustain their attention, they were more distractible, or had more graph motor difficulties. Moreover, an effect of age was also found with respect to the relatively poor performance on the subtest Comprehension when compared with other verbal comprehension subtests, indicating that specifically the impairments in verbal comprehension and social reasoning abilities were more profound in older children when compared with 6- and 7-year-old children with ASD. Findings of this cross-sectional study showed that it is relevant to take age into account when evaluating the impact of cognitive impairments on intelligence in children with ASD, because the impact of these developmental disorders might be different at different ages.