PRENATAL DETECTION OF CHROMOSOME ANEUPLOIDIES IN UNCULTURED CHORIONICVILLUS SAMPLES BY FISH

We developed a 1-d FISH assay for detection of numerical chromosome ab normalities in uncultured chorionic villus samples (CVS). Probes speci fic for chromosomes 13, 18, 21, X, and Y were used to determine ploidy by analysis of signal number in hybridized nuclei. Aneuploidy detecti on using this assay was directly compared with the results obtained by conventional cytogenetic analysis in a consecutive, clinical study of 2,709 CVS and placental samples. The FISH assay yielded discrete diff erences in the signal profiles between cytogenetically normal and abno rmal samples. On the basis of these results, we generated FISH-assay c utoff values that discriminated between karyotypically normal and aneu ploid samples. Samples with mosaicism and a single sample with possibl e heritable small chromosome X probe target were exceptions and showed poor agreement between FISH results and conventional cytogenetics. We conclude that the FISH assay may act as a more accurate and less labo r-demanding alternative to ''direct'' CVS analysis.