Is the resulting phenotype of an embryo with balanced X autosome translocation obtained by means of preimplantation genetic diagnosis linked to the X inactivation pattern

Capsule:
In female balanced X-autosome translocation, normal/balanced female embryos obtained after a preimplantation genetic diagnosis procedure and transferred have a potential risk of clinical abnormalities owing to the uncertain outcome of X inactivation.

Authors:
Fatma Ferfouri, Ph.D., Izabel Bernicot, Ph.D., Anouck Schneider, Pharm.D., Emmanuelle Haquet, Ph.D., Bernard Hédon, M.D., Tal Anahory, M.D., Ph.D.

Volume 105, Issue 4, Pages 1035-1046

Abstract:

Objective:
To examine if a balanced female embryo with X-autosome translocation could, during its subsequent development, express an abnormal phenotype.

Design:
Preimplantation genetic diagnosis (PGD) analysis on two female carriers with maternal inherited X-autosome translocations.

Setting:
Infertility center and genetic laboratory in a public hospital.

Patient(s):
Two female patients carriers undergoing PGD for a balanced X-autosome translocations: patient 1 with 46,X,t(X;2)(q27;p15) and patient 2 with 46,X,t(X;22)(q28;q12.3).

Intervention(s):
PGD for balanced X-autosome translocations.

Main Outcome Measure(s):
PGD outcomes, fluorescence in situ hybridization in biopsied embryos and meiotic segregation patterns analysis of embryos providing from X-autosome translocation carriers.

Result(s):
Controlled ovarian stimulation facilitated retrieval of a correct number of oocytes. One balanced embryo per patient was transferred and one developed, but the patient miscarried after 6 weeks of amenorrhea. In X-autosome translocation carriers, balanced Y-bearing embryos are most often phenotypically normal and viable. An ambiguous phenotype exists in balanced X-bearing embryos owing to the X inactivation mechanism. In 46,XX embryos issued from an alternate segregation, der(X) may be inactivated and partially spread transcriptional silencing into a translocated autosomal segment. Thus, the structural unbalanced genotype could be turned into a viable functional balanced one. It is relevant that a discontinuous silencing is observed with a partial and unpredictable inactivation of autosomal regions. Consequently, the resulting phenotype remains a mystery and is considered to be at risk of being an abnormal phenotype in the field of PGD.

Conclusion(s):

It is necessary to be cautious regarding to PGD management for this type of translocation, particularly in transferred female embryos.

  • Anneleen

    Dear authors, I have read your research article with a lot of interest. I am myself a woman with a balanced translocation involving an X and an autosome (46,XX,t(X;19)(q13.3;q13.41)) and I am considering PGD. According to my genetician, my potential male progeny with a balanced translocation would have a close to 100% probability of being sterile (hence being phenotypically abnormal). In her view, the probability of my potential female progeny with a balanced translocation would have a relatively small chance of being phenotypically abnormal, given that I am myself phenotypically normal. As a result, she is recommending to transfer only female embryos (balanced or normal, if we cannot distinguish them). To me it seems her conclusions run counter to the conclusions of your paper. Would you agree? Or am I worrying too much? Many thanks already for your views.

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