Response inhibition in children and adolescents with fragile X syndrome

Limited knowledge exists on the high degree of overlap, such as in executive functioning, between fragile X syndrome (FXS) and autism. We aimed to better understand the shared response inhibition difficulties and the underlying neurocognitive mechanisms in individuals with FXS and autism. Children and adolescents with (1) FXS (n = 29), (2) a positive autism screening (hereafter: autism group) (n = 28), or (3) neurotypical development (n = 25) were recruited. To assess response inhibition abilities, we used a go/no-go task and the auditory attention + response set inhibition subtask of the NEPSY-II. To compare the amount of cognitive effort that is elicited during response inhibition, we investigated the pupil response during the go/no-go task. Children and adolescents with FXS showed more difficulties with inhibiting responses compared to the autism and neurotypical groups across the different response inhibition tasks. The autism and neurotypical groups did not differ in performance on the tasks. Pupillometric analysis showed subtle, but significant differences in pupil size between the FXS and both other groups. The autism and neurotypical groups did not differ in pupil size. Children and adolescents with FXS have difficulties with inhibiting their responses compared to the neurotypical and autism group, even when a task is relatively simple. This may reflect reduced cognitive effort in FXS, as indicated by reduced pupil dilation. Future research should explore other executive functions in FXS at behavioral and physiological measurement levels, to identify neurocognitive mechanisms across domains.