Rapid prenatal diagnosis of Down syndrome using quantitative fluorescence in situ hybridization on interphase nuclei

Presently, conventional cytogenetic analysis of metaphase chromosomes remains the reference approach in prenatal diagnosis. However, this method is labor-intensive and time-consuming. The first step toward the rapid identification of aneuploidies is achieved by interphase fluorescence in situ hybridization (FISH) with centromeric or locus-specific probes. Spot counting using this type of probes is a reliable approach, but is very time-consuming with some technical and biological limitations. In this study, we present a new FISH method using image cytometry for the detection of trisomy 21 within interphase nuclei.

The method is based on a comparative quantitation of the fluorescence signals emitted by whole chromosome 21 and 22 painting probes cohybridized on interphase nuclei. The chromosomal imbalance was determined with an automated image cytometer by detecting an abnormal ratio of both fluorescence emissions when compared with the ratio obtained in normal cells.

Ten blood samples and twenty amniotic fluids were analyzed. Results from FISH and standard cytogenetics were compared and 100% correlation was achieved.

This method, which enables an easy detection of chromosomal imbalances without a need for metaphase preparations, can be applied to the diagnosis of trisomy 21 and extended to other disorders with chromosomal imbalances. Compared to other interphase FISH techniques, it avoids spot-scoring difficulties.