ABSTRACT
Down syndrome and fragile X syndrome are the two most common genetic causes of mental retardation (Dykens, Hodapp, & Finucane, 2000). Each syndrome is associated with pervasive impairments in many domains of psychological and behavioral functioning (Chapman & Hesketh, 2000; Hagerman, 1999; Mazzocco, 2000; Rozien, 1997). The program of research described in this chapter is designed to further specify the similarities and differences in the behavioral phenotypes of the two syndromes, with special attention given to language learning and use and the domains of functioning that support language (e.g., cognition, theory of mind). Such cross-syndrome comparisons provide clinically useful information about areas of relative strength and weakness and, thus, the appropriateness of syndrome-specific programs of assessment and intervention. These comparisons also can be theoretically interesting because they help to specify the behavioral consequences of particular genetic variations. They also help to identify relationships between the various dimensions of language learning and use and other dimensions of psychological and behavioral functioning. In this chapter, we present some of our preliminary findings and discuss some of their implications for theory and practice. We also discuss some of the strengths and limitations of the approach we have taken.
