Sister chromatid exchange and lymphocyte proliferation in a Down syndrome mosaic

The number of SCE was compared in the normal and trisomic cell lines of a trisomy 21 mosaic case. It was found that in the trisomic cells the SCE-frequency was twice as high as in the normal cells. The mitoses with high numbers of SCE (above 10) were increased 4-5 fold. Differential chromatid staining also allowed us to determine the mitotic cycle of the mitoses. The percentage of mitoses from the fourth or a later mitotic cycle was significantly higher in the trisomic cell line than in the normal one. From this result, it can be concluded that the cell cycle time was distinctly shortened in the cells with trisomy 21.