The use of DNA probes in preimplantation and prenatal diagnosis.

DNA probes are now widely used for prenatal diagnosis, but the prospect of preimplantation diagnosis of genetic disorders requires the development of sensitive genetic tests that can be performed on small numbers of cells removed from a preimplantation-stage pre-embryo. The sensitivity of molecular tests can now be increased by specifically amplifying the target DNA with the polymerase chain reaction. In situ hybridisation with chromosome-specific DNA probes to repeated sequences also permits the detection of particular numerical chromosome aberrations or the distinction of male and female pre-embryos when only a few interphase nuclei are available. We have used in situ hybridisation to a Y chromosome-specific DNA probe to sex preimplantation-stage pre-embryos and to sex fetuses from samples of chorionic villus cells, amniotic fluid cells, and fetal blood. These two approaches (amplification of target DNA and in situ hybridisation) provide suitable tests for improving prenatal diagnosis particularly when few cells are available and they offer the possibility of tests suitable for preimplantation diagnosis.