PGD and PCD not as successful as hoped

A new study warns couples about the limitations of certain types of preconception diagnosis used to identify eggs that are free of genetic disease. These tests assess the genetic make up of mitochondrial DNA in supporting cells as evidence of what may be occurring in the eggs. These tests are done prior to in vitro fertilization in hopes of finding an egg with good DNA.

Preimplantation genetic diagnosis (PGD) and preconception diagnosis (PCD) are tests which have been very useful and reassuring to couples who know they have a genetic mutation in their family. “PGD and PCD represent alternatives to conventional prenatal diagnosis for couples who have a high risk of giving birth to a child affected with a serious genetic disorder. . . and can prevent the anxiety associated with a prenatal diagnosis procedure and the optional termination of the pregnancy,” explained Dr. Julie Steffann from the Universite Paris-Descartes and Hopital Necker-Enfants Malades in Paris.

These procedures look at supporting cells created from the embryo. The assumption is that the genetic make up of these so-called polar bodies will reflect the genetic make up of the embryo. They are looking in particular at mitochondrial DNA. If the polar bodies are good, the embryo is good and is given a green light for implantation.

Unfortunately, the doctors have found that there are variations within the mitochondrial DNA. What doctors look for is mutant load which may indicate how risky it is for the embryo to carry the genetic mutation. Clinicians want to select eggs with low mutant loads. These doctors found that there is a poor correlation between the mutant load of mitochondrial DNA in an egg and that of its polar body. The mutant loads may not be the same.

The only option is to look for completely mutation free embryos, not ones with a low mutation load.

Source: Cell Press, Medical News Today