PGD in Italy: 1PB Testing

Limitations

 

  • Preconception genetic diagnosis by 1PB testing only provides information about the maternal genotype; it cannot be used in cases of paternally derived autosomal dominant disorders.

  • Preimplantation HLA matching (Verlinsky et al., 2001; Fiorentino et al., 2004, 2005; Van de Velde et al., 2004), to conceive a healthy child who could become a future umbilical cord blood donor of hematopoietic stem cells for the treatment of existing affected sibling, would be not possible.

  • To perform an indirect linkage analysis-based diagnosis, a family pedigree must be obtained and DNA from family members (existing children of the couples, maternal parents or DNA obtained from previous prenatal investigations) should be tested to determine which allele combination is associated with the maternal mutation. Hence, the technique will not be applicable for de novo mutations and in those cases where relatives are unavailable or unwilling to cooperate.

  • The high rate of heterozygosity found in 1PBs (56.2% and 61.1%, for CF and ?-thalassemia genes, respectively) greatly reduces the number of oocytes available for selection because no assertion on the status of the corresponding oocytes could be made. The probability of a crossing over occurrence is a function of the distance of the gene from the centromere. Since βT and CF genes are located in the telomeric region of their chromosomes, the reported high recombination rates were widely expected. However, a more centromeric location of other genes (e.g. DMD, SMN1, ATRX, PMP22, etc.) could result in a lower recombination rate, providing a greater number of oocytes available for ICSI.

  • A poor ovarian response to hormonal hyperstimulation, is also known to have a major impact on the number of the retrievable oocytes and, consequently, on the number of oocytes available for analysis, reducing the chance of finding mutation-free oocytes to be fertilised. Therefore, several IVF cycles may be necessary to obtain a pregnancy and a live birth.

  • The achievement of a high fertilization rate also represents a critical factor, and the consequences of a delayed ICSI on fertilization rate should be evaluated.




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