Depending on how many copies of the abnormal allele are present in the polar bodies, we can determine whether the egg carries the normal allele or the abnormal allele. All eggs that carry the abnormal allele are eliminated. Because polar body biopsy only analyzes the maternal contribution of the DNA, this technique cannot determine whether the resulting embryo would be normal or a carrier of the disease. Therefore, blastomere biopsy may need to be performed as a second step. To further reduce the problems associated with ADO, and increase the accuracy of DNA tests, linked markers are also utilized.
Linked markers are segments of DNA that lie very close to the gene being studied.
By testing the linked markers, as well as the gene in question, we can confirm the results of the genetic testing and determine whether ADO has occurred. The third group of patients who can benefit from PGD are those with balanced translocations. Carriers of balanced translocations are healthy individuals, but have high miscarriage rates and are at increased risk for having children with unbalanced chromosome translocations, which result in an extra amount of one chromosome and a missing piece of another chromosome. Probes can be developed to detect these unusual chromosomal abnormalities, and can be used on cells taken from a blastomere biopsy. This procedure would greatly reduce the risk of having a child with a severe chromosomal problem, resulting from the translocation, and would also greatly reduce the miscarriage rate.