Capturing Phenotypic Heterogeneity in Differentiated Sensory Processing Profiles: Non-Syndromic Autism and Fragile X Syndrome

Proficient sensory processing affords adaptive responses required for daily functioning. Sensory processing differences are common across neurodevelopmental disabilities (NDDs), including autism and fragile X syndrome (FXS), and, in some cases, associated with challenging behaviors. Although sensory processing differences are common in both autism and FXS, little is known about possible variation as a function of genetic etiology, or autism classification. This study characterized sensory processing features and examined associations between these features and challenging behavior in 102 male participants—non-syndromic autism ( n = 37), FXS-only ( n = 15), FXS + ASD ( n = 20), and neurotypical (NT) children ( n = 30). Autistic children demonstrated the highest levels of sensory processing differences; however, nuanced group differences were also identified. The autistic groups (autism and FXS + ASD) were similar on hypo-responsivity and sensory seeking, and the FXS groups (FXS-only and FXS + ASD) were similar on hyper-responsivity and sensory seeking. Within-group associations between sensory differences and challenging behavior were relatively similar across groups. Findings have implications for potential etiological mechanisms of sensory processing differences and associated functional consequences. Implications for diagnostic specificity and intervention are discussed. Lay Abstract Sensory processing differences are common in neurodevelopmental disabilities such as autism and fragile X syndrome (FXS). Sensory differences include extreme sensitivity to sensory experiences (hyper-responsivity), decreased sensitivity to sensory experiences (hypo-responsivity), and seeking out sensory experiences to an unexpected degree (sensory seeking). While more is known about sensory differences and challenging behaviors in autism, less is known about these patterns in children with FXS. This study examined the profiles of sensory processing differences and patterns of association between types of sensory response and challenging behavior in males between 24 and 69 months of age with FXS with and without co-occurring autism compared with young autistic males. Participant’s parents filled out questionnaires about sensory responses and challenging behaviors. Results showed that sensory hyper-responsivity is likely part of the broader behavioral profile of FXS, whereas hypo-responsivity is more indicative of autism. In addition, results demonstrated comparable associations between types of atypical sensory processing and ratings of challenging behaviors across groups. These findings contribute to our understanding of the similarities and differences between autism and FXS and have important implications for targeted assessment and intervention practices.