Although there is considerable variability, most individuals with Down syndrome have mental retardation and speech and language deficits, particularly in language production and syntax and poor speech intelligibility. This article describes research findings in the language and communication development of individuals with Down syndrome, first briefly describing the physical and cognitive phenotype of Down syndrome, and two communication related domains-hearing and oral motor skills. Next, we describe language development in Down syndrome, focusing on communication behaviors in the prelinguistic period, then the development of language in children and adolescents, and finally language development in adults and the aging period. We describe language development in individuals with Down syndrome across four domains: phonology, semantics, syntax, and pragmatics. Wethen suggest strategies for intervention and directions for research relating to individuals with Down syndrome.

Boys with FXS and DS have distinctive language profiles. Although both groups demonstrated syntactic delays, boys with DS showed greater delays.

Boys with FXS and boys with DS differed in receptive language levels, demonstrating unique language profiles for each syndrome. Language comprehension appears to be an important area to target in assessment and intervention for both populations.

This study examined the language development of 55 preschool-age children adopted from China who had resided in their permanent homes for approximately 2 years or longer. Slightly over 5% of the children scored below average on 2 or more measures from a battery of standardized speech-language tests normed on monolingual English speakers. However, the vast majority scored within or well above the average range on 2 or more measures. Contrary to other reports on the language development of internationally adopted children, the results suggest that "second first language" acquisition proceeds rapidly in the majority of preschool-age children adopted as infants and toddlers. For the children in the sample who scored below average, results indicated that they were among the children who had been exposed to English for the least amount of time. The results of this study demonstrate both the robustness of the language system in the majority of adopted children from China as well as slower growth in a small subset of lower performers in the 1st years after adoption.

Boys with fragile X syndrome with (n = 49) and without (n = 33) characteristics of autism spectrum disorder, boys with Down syndrome (39), and typically developing boys (n = 41) were compared on standardized measures of receptive vocabulary, expressive vocabulary, and speech administered annually over 4 years. Three major findings emerged. Boys with fragile X without autism spectrum disorder did not differ from the younger typically developing boys in receptive and expressive vocabulary and speech production when compared at similar levels of nonverbal cognitive skills. Boys with fragile X without autism spectrum disorder and typically developing boys had higher receptive vocabulary and speech production than did boys with Down syndrome. There were mixed patterns of results for the boys with fragile X and characteristics of autism spectrum disorder.