Preimplantation Genetic Diagnostics
Preimplantation genetic diagnostics (PGD) makes it possible to screen the embryo for individual genetic defects that cause severe inherited disorders, or for changes in the number of chromosomes or structural chromosomal mutations. In the case of sex chromosome-linked conditions, it is possible to determine the gender of the embryo. The embryo may be tested for individual genetic defects if the genetic alteration caused by an inherited disorder carried by one or both parents is known. The identification of genetic defects is based on the replication of genetic material (PCR) and a subsequent analysis.
Structural chromosomal mutations include inter-chromosomal translocations. While balanced translocation carriers are healthy, unbalanced translocations may cause repeated miscarriages or severe damage to the child.
In preimplantation genetic diagnostics, one or two cells are collected from a three-day embryo with at least six cells and analyzed for the genetic defect or chromosomal mutation. Cells may also be collected from a blastocyst for analysis, if rapid analysis methods are available.
If an embryo is found that is healthy with regard to the genetic or chromosomal defect screened for, a single embryo is usually transferred into the uterus. The remaining embryos may be frozen.
Preimplantation genetic diagnostics can only be used to determine the presence of the targeted mutation in the embryo but not any other abnormalities that may be present.