ABSTRACT
Preimplantation genetic diagnosis (PGD) for single-gene disorders is based on the testing of oocytes or embryos to preselect and transfer only normal embryos back to the patient to achieve an unaffected pregnancy and the birth of a healthy child. As in PGD for chromosomal disorders, it is performed by testing either single blastomeres removed from eight-cell preimplantation embryos or a number of cells from blastocysts, or by testing female gametes by the removal and genetic analysis of the first and second polar bodies (PB1 and PB2). However, the latter approach cannot be applied for testing paternally derived abnormalities or for gender determination, which can be detected only by genetic analysis of single cells removed from the cleavingor blastocyst-stage embryo. Therefore, the two methods are complementary, and their application is dependent upon the PGD objectives in the individual patient.
