Preimplantation genetic diagnosis or screening (PGD/S) is an alternative to prenatal testing that allows parents at high risk of transmitting a genetic disease, to test, select and transfer to the uterus only genetically normal embryos. This ensures a child that is free from the specific genetic condition even before a clinical pregnancy has been established hence avoiding the scenario where a termination of pregnancy may be required.
PGD is also available for those patients who have had recurrent pregnancy losses due to unknown reasons as it has been found that most frequently these spontaneous abortions are due to numerical or structural chromosomal abnormalities. By screening embryos for a balanced genetic complement and only transferring those found to be normal, a full term pregnancy resulting in a healthy baby may be achieved.
This method of screening of embryos for the correct number of chromosomes is also an option for those patients who are of advanced maternal age (older than 35 years of age) and have experienced repeated IVF failures due to unknown underlying causes. The embryos are tested to determine that they have the 2 pairs of all 23 chromosomes and are not affected with aneuploidy diseases such as Down, Edward’s, Turner’s or Kleinfelter’s syndrome.
These syndromes are also commonly found in children of patients who are in consanguineous relationships (marriages between cousins) and so this testing can also be extended to patients in such situations.
The scope of PGD currently extends to include:
Single gene disorders – cystic fibrosis, Huntington’s disease, sickle cell anaemia, Tay Sachs disease
Gender selection of sex-linked diseases – Fragile X, haemophilia, Turner’s syndrome
Numerical chromosomal abnormalities – Down, Patau, aneuploidy testing
Structural chromosomal abnormalities – DMD, BMD, translocations
HLA matching – to produce a compatible healthy baby and its stem cells for transplantation to an existing affected child
