PGD, or preimplantation genetic diagnosis, is among the most advanced of contemporary diagnostic procedures used for testing genetic abnormalities. PGD is used when in vitro fertilization or IVF is chosen as the assisted reproductive technology (ART). Since the embryos are fertilized in vitro, there is a chance to test them before being implanted within the uterine tissue of the female patient. The embryos are usually tested for genetic disorders. These tests are conducted as a part of PGD screening or PGD testing. Despite its utility, preimplantation genetic diagnosis hasn’t been able to address some medical conditions and some probable risks.
Preimplantation Genetic Diagnosis Limitations
It should be noted that though highly-advanced, the PGD from of genetic analysis doesn’t have a 100% success rate. The two most commonly-observed genetic medical conditions that can be passed onto the child despite a PGD testing are:
- Chromosomal Translocations - Chromosomal translocations are genetic abnormalities wherein there is undesired fragmentation and linking between the chromosomes. These structurally-different chromosomes can lead to a host of genetic disorders. It is generally regarded that the error rate of PGD in its inability to detect chromosomal translocations can be as high as ten percent. Diseases caused by chromosomal translocations include cancer such as leukemia and infertility.
- Mosaic Down Syndrome - This syndrome is often referred to as Mosaic Down Syndrome. It is also a Trisomy (genetic abnormality) of the 21st chromosome. Children suffering from Mosaic Syndrome have 47 chromosomal groupings instead of the normal, 46 pairs. PGD is generally regarded as inadequate for diagnosing this condition.
Reasons Leading to Limitations of PGD
It should be noted that all the embryos aren’t analyzable during PGD testing. While some PGD specialists choose to eliminate all the untested embryos, some might proceed to implant them. Preimplantation genetic diagnosis is capable of testing only 11 of the 23 chromosome pairs that are found in the embryo. This means that every PGD tested embryo contains 12 chromosomes that may carry a genetic defect.
Various PGD techniques like FISH testing can only test for a few chromosomes in the fertilized embryo. Other PGD testing methods like PCR or Polymerase Chain Reaction testing too is prone to failing to recognize genetic defects precipitated by a single gene.
Others Risks of PGD: Developmental Arrest
Though not a common occurrence, there is a possibility that a damaged embryo might be unconsciously used by the PGD specialist. The damage to the embryo can take place during its in vitro fertilization or during the PGD testing itself. In either of the scenarios, the slightest of damage to the embryo can lead to severe developmental defects in the newborn.
PGD testing involves a biopsy of the embryo. If not done properly, the biopsy can delay the process of cell division within the developing embryo which can even compromise chances of a live birth.
Further, even if the development defects were induced by the PGD specialist or the attending team, there is very little that the parents can do in terms of identifying the real cause of damage to the embryo.