Incidence of mosaic cell lines in vivo and malsegregation of chromosome 21in lymphocytes in vitro of trisomy 21 patients: detection by fluorescence in situ hybridization on binucleated lymphocytes

In order to detect aneuploidy in interphase human lymphocytes, both in vivo and in vitro, fluorescence in situ hybridization (FISH) was carried out on binucleated cells cytokinesis-blocked by cytochalasin B at the first mitos is after phytohemagglutinin stimulation. A pericentric chromosome-21-specif ic DNA probe prepared from yeast artificial chromosome clone 881D2 by the p olymerase chain reaction was employed. One thousand binucleated cells per i ndividual were scored from cultures from twelve trisomy 21 patients aged 0. 01-8.9 years (mean 4.3 years) and 20 normal children of similar age. Of tri somy 21 patients, increased frequencies of disomic cells in vivo (1.690+/-1 .070%) and cells containing six signals with nondisjunction (0.822+/-0.554% ) were found, compared with those of monosomic 21 cells in vivo (0.265+/- 0 .130%) and cells containing four signals with nondisjunction in normal chil dren (0.369+/-0.250%; P=0.000 and P=0.000, respectively). These results sho w that malsegregation of chromosome 21 occurs more often in trisomic 21 cel ls than in disomic cells from normal children. The frequency of nondisjunct ion was significantly higher than the loss of chromosome 21 in both culture d trisomic (0.822+/-0.554% vs 0.043+/-0.049%, P=0.000) and disomic (0.369+/ -0.250% vs 0.010+/-0.030%, P=0.000) cells. Comparisons of in vivo and in vi tro data on aneuploidy indicate that a cell selection mechanism may exist i n vivo. All these results show that FISH, with a chromosome-specific probe, on binucleated lymphocytes is a powerful tool for simultaneously detecting mosaic cell lines in vivo and malsegregation (loss and nondisjunction) of a corresponding chromosome in vitro in the same cell population.