PGD for Chromosome Translocation
Reciprocal translocations (an exchange of two terminal
segments from different chromosomes) and Robertsonian
translocations have been reported to occur in one in every
500 live births.
Carriers of these balanced translocations
are generally phenotypically normal, as there is no net loss
of genetic material, but may be detected when the couple
presents with infertility or recurrent pregnancy loss.
addition, balanced translocations may be discovered when
there is a phenotypically-abnormal offspring arising from
the production of genetically-unbalanced gametes (Kanavakis,
2002; Braude, et al., 2002).
A member of a couple may carry a balanced translocation.
This increases the risk for a pregnancy with an unbalanced
chromosome complement, which can cause birth defects, mental
retardation, and/or miscarriage.
The primary aim of PGD for translocation determination is to
improve live birth rates by either reducing the risk of
recurrent spontaneous abortions or to improve pregnancy rate
in infertile couples (e.g., after failed IVF attempts).
Success rates reported from three large centers (two in the
United States, one in Italy) report an overall pregnancy
rate of 29% per oocyte retrieval, increasing to 38% when
calculated per embryo transfer.
Braude et al. (2002)
indicate in a review of the published, peer-reviewed,
scientific literature that there is insufficient evidence
supporting the use of PGD for the detection of chromosomal
translocations as a method to improve live birth rates; or
to reduce the risk of pregnancy loss in women of advanced
maternal age (age 35 or older), in women with repeat IVF
failures, or in women with recurrent spontaneous abortions.