Longitudinal Profiles of Expressive Vocabulary, Syntax, and Pragmatic Language in Boys with Fragile X Syndrome or Down Syndrome

Fragile X syndrome (FXS) and Down syndrome (DS) are the two leading genetic causes of intellectual disability, and FXS is the most common known genetic condition associated with autism. Both FXS and DS are associated with significant language impairment, but little is known about expressive language across domains over time or the role of autism in language development in FXS