Preimplantation genetic diagnosis is a technology that performs prenatal diagnosis. It can identify whether a particular embryo carries a gene for a particular disease. It is used to detect problems with specific genes or chromosomes in the embryo.
Preimplantation Genetic Diagnosis
Preimplantation genetic diagnosis techniques can detect genetic defects in embryos that are created by in vitro fertilization before they are implanted in the mother's womb. This diagnosis is indicated when one or both the parents have a genetic abnormality or mutation. Testing is performed on the embryo to determine whether it also carries the mutation. Parents can then decide not to have the embryo implanted and can opt for another that's free of the genetic mutation.
Preimplantation genetic diagnosis thus preempts the need for procedures such as amniocentesis and the need for termination of a pregnancy that's already ongoing. PGD allows couples at risk of passing genetic defects to have children who are free of these defects.
The Procedure for Preimplantation Genetic Diagnosis
Preimplantation genetic diagnosis technology uses in vitro fertilization of a woman's egg with a man's sperm to obtain an embryo which is allowed to develop in the laboratory for three days, until it reaches an eight-cell stage. One cell is removed from the embryo and tested for the genetic condition in consideration.
The tests can determine whether the embryo is free of the genetic condition by the sixth day and such an embryo, if healthy, can be implanted in the woman's womb to develop into a child. The testing doesn't affect the embryo adversely and it develops as a normal untested embryo would.
Preimplantation Genetic Haplotyping
While preimplantation genetic diagnosis is used to identify single gene defects, preimplantation genetic haplotyping is used to identify more than 6,000 gene defects. Preimplantation genetic haplotyping is an advanced and extended type of preimplantation genetic diagnosis technique.
It takes a single cell from an in vitro fertilized embryo and identifies many genetic disorders, even when the disorder is not known. It screens for a wider number of genetic disorders than PGD.
The Procedure of Preimplantation Genetic Haplotyping
A cell is taken from an embryo that's three days old and one that's reached the eight-cell stage. This cell is amplified a million times in the laboratory. The haplotyping identifies faulty genes in the embryo's parents and existent siblings and searches for the same faults in the cell of the embryo. If the embryo is a carrier for the genetic condition or has the genetic condition, it's not used for implantation in the mother's womb. However, if it's healthy, it's implanted to develop into a child.
Since preimplantation genetic haplotyping can test for diseases even if the specific mutation is not known, more embryos can be used for implantation. If scientists could determine that a certain mutation could be passed on only to male embryos, they would discard the male embryos and only use female embryos for implantation in the mother's womb. By using PGH technology, scientists can pinpoint which of the embryos would be carrying a certain mutation, and only those embryos would have to be discarded. The rest, even if they're male, could be used for implantation to develop as healthy children.