Clinical application of preimplantation genetic diagnosis for translocations in couples with recurrent miscarriages
2006
Ozawa, N.(National Center for Child Health and Development, Tokyo (Japan))
Balanced carriers of chromosome structural abnormalities, although phenotypically normal, may present with reduced fertility, recurrent miscarriages, or offspring with an abnormal phenotype. While balanced translocations are found in 0.35% of neonatal population, they occur in 1.4% of IVF patients with implantation failure and 2% of patients with recurrent miscarriages. At meiosis 1, translocated chromosomes are paired with their corresponding normal chromosomes and form a quadrivalent (in the case of reciprocal translocation) or a trivalent (in the case of Robertsonian translocation). The unbalanced gametes are produced through malsegregation of these unique complexes. The occurrence risk of the unbalanced gametes depends on the number and the breakpoints of the chromosomes involved in translocation, and the extent of the genetic imbalance resulting from abnormal segregation could determine the viability of the gamete or the conception. Recently, PGD (preimplantation genetic diagnosis) has been performed worldwide for translocation carriers in order to select embryos with no genetic imbalance and increase their pregnancy and delivery rates. Although there is a possibility of successful natural outcome in many translocation carriers, the introduction of PGD into ART is expected to improve reproductive performance of these couples.
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