New advances in human embryology: implications of the preimplantation diagnosis of genetic disease.

The diagnosis of genetic disease in preimplantation embryos is discussed. The typing of spermatozoa may be feasible for factors such as the presence of an X and Y chromosome. Embryos might be typed by non-invasive methods, by assessing their uptake of metabolites although the widest opportunities may arise by the use of invasive methods which involve the removal of one or a small number of cells. The methods of diagnosis are discussed, including enzyme assays and the use of DNA probes, preliminary results with human embryos are presented and the difficulties related to these techniques are debated. The low rate of implantation of replaced embryos will mean that many embryos will have to be diagnosed, and certain embryological factors such as the high incidence of chromosomal imbalance and the problems of 'imprinting' might obscure certain diagnoses. The advantages and disadvantages of the method are discussed.