Combined use of cytogenetic analysis and FISH for the identification of two antenatal de novo markers as Robertsonian translocations involving the p arms.

In two prenatal cases, de novo nonmosaic bisatellited marker chromosomes were studied with the combined use of fluorescence in situ hybridization (FISH) with chromosome specific probes and cytogenetic heteromorphisms. The FISH studies showed that one of the small accessory chromosome could be a heterozygous 14/15 or 15/22 translocation involving the p arms of these chromosomes, the other showed only one hybridization spot with the classical satellite probe of chromosome 15. The analysis of heteromorphisms of the parental acrocentric chromosomes demonstrated that the two markers were Robertsonian translocations involving in the first case the p arms of the maternal 15 and 22 chromosomes and in the second case the p arms of the maternal 14 and 15 chromosomes.