Relative efficiency of FISH on metaphase and interphase nuclei from non-mosaic trisomic or triploid fibroblast cultures

Chromosome specific probes that are used in interphase fluorescence in situ hybridization (FISH) analysis are usually tested on disomic control samples. When used for preimplantation or prenatal diagnosis the aim is to detect aneuploidy, most frequently trisomy. In this study, skin fibroblast cultures from non-mosaic trisomic and triploid fetuses were analysed by FISH to assess probe efficiency regarding interphase detection of trisomy. Skin fibroblast cultures were used because they are considered to be stable in culture. FISH experiments were performed using centromeric probes for chromosomes X, Y, 18 and locus specific probes for chromosomes 13 and 21. In metaphase nuclei, the expected signals were found in 100% of at least 30 metaphases counted on each sample and this also confirmed non-mosaicism in agreement with conventional karyotyping of the fetuses. On interphase nuclei, however, only 80-89% of nuclei per population displayed the expected signals for autosomal probes and 90% for probes for the sex chromosomes. For each probe, a range of percentages was obtained that can be regarded as indicative of non-mosaic trisomy in uncultured specimens. In the case of prenatal samples, the expected presence of maternal cells may lead to a lowering of the threshold for a trisomic diagnosis. In the case of preimplantation diagnosis, the accuracy can be improved by the use of two probes per chromosome or by the analysis of two cells from each embryo.