FLUORESCENCE IN-SITU HYBRIDIZATION WITH A CHROMOSOME 21-SPECIFIC COSMID CONTIG - 1-DAY DETECTION OF TRISOMY-21 IN UNCULTURED MESENCHYMAL CHORIONIC VILLUS CELLS

We present a modified, fast trisomy 21 detection assay using fluoresce nce in situ hybridization (FISH) on uncultured mesenchymal chorionic v illus cells. The whole test takes about 24 h. We used a cosmid contig as a probe and modified an in situ sample preparation method first des cribed by Klinger et al. (1992). The assay saves time and cost of cult ure in comparison with a previously described trisomy 21 detection FIS H assay (Bryndorf et al., 1993). A small blind clinical study comparin g the modified and the previously described FISH assays using mesenchy mal chorionic villus cells showed comparable results and concordance w ith conventional cytogenetic analysis. The frequency of nuclei with th ree hybridization signals from samples disomic for chromosome 21 range d from 0 to 8 per cent with both assays, while trisomic samples had 60 -80 and 54-90 per cent of the mesenchymal nuclei with three signals in the modified and previously described assays, respectively. Normal (d isomic) and trisomic mesenchymal chorionic villus samples can be disti nguished clearly and rapidly without culture in the modified assay.