THE PHENOMENON of chromosome mosaicism, the presence of two or more chromosome lines in one individual, has been found to account for a number of previously unexplained unusual clinical observations. A large number of intersex cases, whose etiology was previously unknown, has been found to be caused by an XX/XY, XY/XO, or analogous type of mosaic pattern.1 Some atypical and mild cases of Turner's syndrome and other chromosomal syndromes have been similarly explained by the finding of an admixture of normal and aneuploid cells in the affected individuals.1 The extent of clinical involvement in these types of cases has been generally assumed to be a function of the number of aneuploid cells and their distribution throughout the body.
Theoretically, it would appear possible that predominant unilateral aneuploidy could cause asymmetry and marked clinical involvement of only one side of the body. However, most reported cases of mosaicism appear
HOOK EB, YUNIS JJ. Congenital Asymmetry Associated with Trisomy 18 Mosaicism. Am J Dis Child. 1965;110(5):551–555. doi:10.1001/archpedi.1965.02090030575011
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