Sex chromosomal abnormalities. Etiology, phenotypic expression, and the role of lyonization

Individuals with sex chromosomal abnormalities have significantly better chances of leading normal lives than individuals with autosomal abnormalities. This is due, in part, to the role of lyonization in the genetic inactivation of X chromosomes. In contrast to earlier studies contaminated with subject ascertainment bias, prospective studies of individuals with SCA generally indicate a relatively normal profile with respect to overall intellectual capacity and psychopathology. Although some SCAs affect neuromotor, speech, language, cognitive and emotional development to some degree, it is noteworthy that none of the effects necessarily occurs and that some of the deficits are amenable to corrective intervention. Results from prospective studies also indicate significant genotype-environment interactions that can have important implications for intervention.