Parental reports on early language and motor milestones in fragile X syndrome with and without autism spectrum disorders

Objective: This study examined features of early language and motor milestones in children with fragile X syndrome (FXS) and contrasted these features with a diagnosis of Autism Spectrum Disorder (ASD) later in life in these children. Methods: We retrospectively examined parental report of age of onset for walking and first words for primarily boys with FXS, both with ASD (FXS + ASD) and FXS-only. The diagnosis of ASD was established by DSM-IV criteria, which were complemented by the ADOS. The age of onset was analyzed as a continuous and categorical variable, which were compared to the upper limit of typically developing children. Results: Individuals with FXS-only are more delayed in the onset of first words than first walks. The finding represents a pattern suggesting a continuum as robustly demonstrated in individuals with FXS + ASD vs. FXS-only. Conclusion: Our results support validity of FXS + ASD co-morbidity as a distinct phenotype in individuals with FXS.