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.
The present study examines (1) the prevalence of learning difficulties; (2) correlates and predictors of academic achievement; and (3) explores IQ minus academic achievement distributions across different Noonan Syndrome spectrum and related genetic variants (NSSD). IQ, academic achievement, executive function, and attention performance-based and/or caregiver-rated measures were completed across two samples of youth with Noonan Syndrome, spectrum, and related disorders (NSSD; n = 123) and unaffected youth (n = 172). Youth with NSSD had significantly lower scores on all academic achievement measures than the unaffected group with large effects. Executive skills (e.g., processing speed, working memory, inhibitory control) were significant predictors of academic skills in addition to whether a participant has NSSD, and together they accounted for ~1/3-1/2 of the variability in academic scores. Exploratory analyses revealed significantly skewed IQ-Achievement distributions in the SOS1 and Other Variant groups, but not PTPN11 group, as compared to the unaffected youth. Between one fifth and one half of youth with NSSD are estimated to meet criteria for Specific Learning Disorder. Clinicians and educational settings should conduct rigorous, frequent screening of academic difficulties of youth with NSSD to intervene as early as feasible with appropriate services. Executive skills, especially working memory, processing speed, and cognitive flexibility, play a contributory role to difficulties with academics in NSSD, and should also be supported with targeted interventions.
