Relationship Between Intellectual Disability and Behavioral Comorbidity in Children With Fragile X Syndrome

Purpose: Fragile X syndrome (FXS) presents with variable cognitive and neurobehavioral abnormalities. We recently reported clinically relevant behavioral subtypes in children with FXS based on a latent class analysis (LCA), which suggested an association between level of intellectual disability (ID) and frequency of co-occurring behavioral conditions. The present study further investigated ID-behavioral comorbidity associations in the same subject sample. Methods: We analyzed the large (1,072 males, 338 females) pediatric FORWARD clinic-based natural history study database, using multiple statistical techniques including chi-square analyses, polyserial correlations, regression analyses, and LCA. Results: We demonstrated that frequency of irritability/agitation, aggression, and self-injury (IAAS), autism spectrum disorder (ASD), hypersensitivity and, to lesser extent, perseverative behavior (OCD-like) are a function of ID level across the range of FXS clinical severity. With exception of IAAS, these associations were further supported by correlations between ID levels and scales shown to represent the aforementioned behavioral comorbidities. Conclusion: The ID-behavioral comorbidity associations reported here could help in the identification and management of problematic behaviors in individuals with FXS and other ID-associated disorders.