Fragile X syndrome is a recently identified X-linked disorder resulting in mental retardation and characteristic physical, cognitive, and behavioral features. Although data are now accumulating regarding the psychological functioning of fragile X males, previous research has focused almost exclusively on the genetic aspects and physical features of the disorder. As a result, the data are quite limited on the intellectual, adaptive, and behavioral functioning of boys and men with fragile X syndrome, and many questions remain about the development of fragile X males in virtually all areas of functioning.

In addition, the research reports on fragile X syndrome are found largely in the genetics literature, and less accessible to parents, educators, and health professionals who seek guidance with the daily management and education of these individuals. Given this need, and the relative newness of the disorder, this chapter will begin with a brief overview of fragile X syndrome, including its genetic features and enigmas and its physical phenotype. Data on the prevalence of fragile X syndrome, and the intellectual, adaptive, and behavioral functioning of fragile X males will then be presented. These findings will be discussed in relation to the two-group approach in mental retardation, the trajectory of intelligence, and the interplay between genetics and the environment.

Overview of fragile X syndrome

Genetic features

The chromosomal abnormality associated with fragile X syndrome was initially identified in 1969 by Lubs, who observed a pinched or constricted end on the X chromosomes of mentally retarded males in a large pedigree that followed an X-linked inheritance pattern.