What are Sex Chromosomal Aneuploidies?
Sex chromosome aneuploidies (SCA) describe those conditions in which there is some variation among the normal euploidic sex chromosomes in male (XY) or female (XX) individuals. These variations are most often caused by non-disjunction of the 23rd sex chromosome pair during meiosis. Found in 1 in 400 live newborns, SCA are even more common than Down syndrome or fragile X syndrome. While SCA can include a variety of abnormalities of the sex chromosomes, by far the most commonly occurring SCA involve the deletion (45,X or partial X monosomy) or addition (47,XXY, 47,XYY, 47,XXX) of an X or Y chromosome. Of these conditions, only Turner syndrome, caused by the loss of all or part of an X chromosome, results in an easily identifiable physical phenotype. Subtle language, neuromotor, and learning difficulties have been identified in most forms of SCA, however. The neurodevelopmental effects of the 47XXY (Klinefelter syndrome) and 47XXX karyotypes are also investigated in light of these phenoty
