RAPID DETECTION OF NUMERICAL ABERRATIONS OF CHROMOSOME-13, CHROMOSOME-18 AND CHROMOSOME-21 IN CHORIONIC MESENCHYMAL CELLS

We have devised and evaluated a rapid screening method for the detecti on of numerical aberrations of chromosomes 13, 18 and 21 in chorionic villus cells. We used non-radioactive in situ hybridization (ISH) with three chromosome-specific probes on overnight-attached mesenchymal ce lls from chorionic villi. A blind study was performed of 47 karyotypic ally normal samples, one triploid sample, two samples trisomic for chr omosome 21, and two samples from a fetus with putative mosaicism (46/4 7,+21). All samples were hybridized with the chromosome 18- and 21-spe cific probes. Thirty samples were additionally hybridized with the chr omosome 13-specific probe. The test could be completed within 3-4 days of sampling. In samples disomic with respect to the probed chromosome s, an average of 2 per cent (range 0-9 per cent) had three hybridizati on signals. By contrast, in the samples trisomic for the probed chromo some(s), 57 per cent (chromosome 13), 51 per cent (chromosome 18), and an average of 74 per cent (55-86 per cent) (chromosome 21) of the nuc lei exhibited three signals. In the putative mosaic samples, the numbe r of nuclei with three chromosome 21-specific signals ranged from 41 t o 69 per cent. We conclude that this technique rapidly and clearly dis tinguishes between normal and trisomic/triploid samples, and consequen tly may be of use in future prenatal diagnosis.