Stability of sex chromosome mosaicism

In individuals with sex chromosome mosaicism the proportions of cell lines have been reported to change over time; however, purported changes have failed to show a consistent decrease or increase in any given cell line, normal or abnormal. We, therefore, investigated three mosaic individuals: two 45,X/46,X,i(Xq) and one 45,X/46,XX. We first initiated studies which verified that the proportion of various cell lines can be reliably (reproducibly) quantitated in lymphocytes of mosaic individuals, data which surprisingly were heretofore unavailable. Having established the ability to quantitate sex chromosome mosaicism, we initiated longitudinal studies. No significant differences in proportions of mosaic cell lines were observed in the three individuals studied over various time intervals. This stability was observed in individuals with high as well as lower proportions of 45,X cells. Further studies over longer periods and with other subjects are continuing, but our preliminary studies suggest mosaicism shows longitudinal stability, at least in adults. The practical clinical significance is that mosaicism can be reproducibly quantitated from a single lymphocyte culture, indicating that a single blood sample will generally suffice for most clinical studies.