Fluorescence in situ hybridization of chorionic interphase cells for prenatal screening of Down syndrome

Our purpose was to determine the usefulness and reliability of fluorescence in situ hybridization on interphase chorionic villi cells in the prenatal diagnosis of Down syndrome.

A total of 336 samples of chorionic villi were analysed by direct chromosome preparation and FISH with a DNA probe specific to chromosome 21. The samples were obtained as part of the routine obstetric investigation and management.

The sampling and direct karyotyping was successful in all cases. At least 50 cells were valuable by FISH in 331 of 336 samples. Both methods showed Down syndrome in 12 cases. The follow-up investigations showed that there was no false-negative or false-positive result following these procedures.

Based on these results and the fact that it is possible to analyse by interphase FISH at least ten times more cells than by conventional cytogenetic methods, and these cells originate from different tissues of chorionic villi, it is concluded that FISH increases the reliability of the diagnosis. Nevertheless, more data are needed for correct statistical analysis. Since this method is cheaper and gives diagnosis earlier than cell culture, the combination of direct chromosome preparation and FISH on chorionic villi is offered for prenatal Down syndrome screening.