Expressive language during conversational speech in boys with fragile X syndrome.

We compared the expressive syntax and vocabulary skills of 35 boys with fragile X syndrome and 27 younger typically developing boys who were at similar nonverbal mental levels. During a conversational speech sample, the boys with fragile X syndrome used shorter, less complex utterances and produced fewer different words than did the typically developing boys after controlling for their nonverbal MA, speech intelligibility, and mother's education. The boys with fragile X used less complex noun phrases, verb phrases, and sentence structure, but did not use fewer questions and negations.