Potential errors with rapid analysis techniques: partial duplication 21q resulting from a paternal paracentric...

We report on partial duplication 21q resulting from a paternal insertion identified during prenatal diagnosis. While performing interphase fluorescence in situ hybridization (I-FISH), we were able to identify 3 signals of the LSI 21 Spectrum Orange probe with chorionic villus sampling. Using standard cytogenetic analysis, I-FISH and GTG banding, structural aberrations in 21q in the parents and in the fetus could not be reliably determined. Applying metaphase fluorescence in situ hybridization (M-FISH), we identified a recombinant chromosome 21 carrying an interstitial duplication of the Down syndrome critical region inherited from the father. Both data from our analysis and published literature recommend the use of rapid testing methods such as I-FISH and standard cytogenetic analysis in prenatal diagnosis. It became obvious that I-FISH would not detect such a particular aberration. Thus, karyotyping, I-FISH and M-FISH should be performed in all Down syndrome cases.