SEX-CHROMOSOME TETRASOMY AND PENTASOMY

Sex chromosome abnormalities occur in at least I in 400 births and inc lude the well-described 47,XXX, 47,XXY, 47,XYY, and 45,X karyotypes. T he addition of more than one extra X or Y chromosome occurs rarely, an d little information is available in the medical literature. Individua l case reports make up most of this body of knowledge, and all are bas ed on subjects who identified themselves postnatally. Many were ascert ained through screenings of institutions and hospitals; thus, there is no unbiased information on the natural history of poly X and Y karyot ypes. A direct relationship between the number of additional sex chrom osomes and the severity of the phenotype is generally assumed. The pur pose of this article is to summarize what is known about these conditi ons and to present 10 additional cases. The karyotypes include, 48,XXX X, 49,XXXXX, 48,XXYY, 48,XXXY, 49,XXXXY, 49,XXXYY, 48,XYYY, 49,XYYYY, and 49,XXYYY.