PREIMPLANTATION GENETIC DIAGNOSIS - CURRENT STATUS AND NEW DEVELOPMENTS

Preimplantation genetic diagnosis (PGD) is a very early form of prenat al diagnosis aimed at eliminating embryos carrying serious genetic dis eases before implantation, To this end, two major technologies are in use: the polymerase chain reaction (PCR) for monogenic deseases and fl uorescent in-situ hybridization (FISH) for chromosomal aberrations, In this review, a number of problems arising from the use of these techn ologies, as well as their possible solutions and new developments, are discussed, Concerning PCR, the phenomenon of allelic drop-out, as wel l as methods to reduce this problem, such as fluorescent PCR, are desc ribed, The advantages and disadvantages of sperm separation by flow cy tometry as an adjunct to sex determination for the avoidance of X-link ed disease are discussed, The application of FISH for aneuploidy detec tion is commented upon and the advances in cell recycling, in which PC R and FISH are combined, are analysed, Finally, diseases for which PGD is currently possible are summarized.