What is preimplantation genetic diagnosis?
Preimplantation genetic diagnosis (PGD) is a technique for testing embryos created by in vitro fertilization (IVF) for specific genetic disorders. The techniques enable couples with a particular inherited condition in their family to avoid passing it on to their children. There are some genetic disorders that we can diagnose on preimplantation embryos (autosomal dominant, recessive or sex-linked inherited disorders, or chromosomal disorders). The process helps potential parents prevent the birth of a child with a serious genetic condition. PGD is used when a couple has a known risk of passing on a genetic abnormality and diagnostic testing is performed on an embryo to determine if it has also inherited the abnormality.
Numerous diseases and disorders classified as chromosomal disorders, single gene defects and sex-linked disorders can be tested for through a technique called pre-implantation genetic diagnosis (PGD).
Process of PGD
PGD involves the use of assisted reproductive technology (ART). Eggs are obtained and fertilised through in vitro fertilisation (IVF). Once fertilised, the embryos develop for 5-6 days and then a number of cells are removed from each embryo. The genetic material (DNA or chromosomes) within these cells of the embryo is then tested for the genetic or chromosomal abnormality. An unaffected embryo is then transferred to the woman’s uterus to implant. If successful, the procedure will result in pregnancy and the child should not be affected by the condition for which it was tested.
WHO can use preimplantation genetic diagnosis?
These are the following specific genetic disorder that we can use PGD for testing preimplantation embryos. Couples generally considered for PGD include:
- Carriers of a serious autosomal recessive condition: For carriers of an autosomal recessive condition, there is a 1 in 4 (25%) risk of each pregnancy delivering an affected child. Thalassemia is an example of the disease in this group.
- Carriers of a serious autosomal dominant condition: For carriers of an autosomal dominant condition, there is a 1 in 2 (50%) risk of each pregnancy delivering an affected child. Myotonic dystrophy, Marfan syndrome and neurofibromatosis are the examples of the disease in this group.
- Couples with a family history of serious sex-linked disorders: Couples with a family history of a sex-linked disorder have a 1 in 4 (25%) risk of each pregnancy delivering an affected child (half of all male children). Hemophilia A is an example of the disease in this group.
- Couples with inherited translocation disorders in their chromosomes.
Therefore, PGD may be recommended if:
- you or your partner has a family history of a serious genetic condition and/or
- you and your partner already have a child with a serious genetic condition and/or
- you and your partner have had a number of pregnancy terminations because your baby had a serious genetic condition.
- You have the recurrent pregnancy loss with known abnormal karyotyping.
Which conditions can be diagnosed using preimplantation genetic diagnosis?
PGD is available for two broad categories of conditions including:
- Single gene defects for which PGD testing is available.
- Chromosomal abnormalities, including inversions, deletions, aneuploidy (an abnormal number of chromosomes), and translocations (where a piece of one chromosome either becomes attached to another chromosome or swaps places with a segment from another chromosome).