Expressive morphosyntax in boys with Fragile X syndrome with and without autism spectrum disorder.

Background: Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability, and the most common single gene disorder associated with autism. Language impairments in this disorder are well documented, but the nature and extent of syntactic impairments are still unclear.

Aims: To compare the performance of boys with FXS with and without autism spectrum disorder on measures of verb (VM) and noun (NM) morphosyntax with that of typically developing boys of similar non-verbal mental ages.