Robertsonian and reciprocal translocations are the most common form of chromosome abnormality in humans, present in approximately one in 500 individuals. Couples where one partner carries a balanced translocation or other structural abnormality are at risk of having genetically unbalanced conceptions, which may result in failure to implant, miscarriage, or children with physical and/or mental disability.
At Unistel, a PGD test using commercially available FISH probes can be designed for all Robersonian translocations, most reciprocal translocations, as well as some inversions and complex chromosome rearrangements.
Translocation PGDs are more complex than aneuploidy screening. A work-up prior to the actual PGD is done on the parents’ DNA to verify the breakpoints and to ensure that the probes used will accurately distinguish between a balanced/normal embryo cell and an embryo cell carrying an unbalanced translocation.
FISH probes are used to track the chromosome segments involved in the translocation. The probes must go through a validation and selection process. Due to probe sensitivity, polymorphisms and the 3D nature of cells, not all probes are suitable for single cell analysis.
In collaboration with the UK laboratory, testing for translocations can also be carried out using array-CGH, to not only identify the presence or absence of translocations but also asess all of the chromosomes. Therefore, a-CGH covers not only translocation testing but aneuploidy testing too. A theoretical work-up of two weeks is required.
Translocation PGD can only distinguish between embryos that are balanced or unbalanced, therefore, it cannot distinguish between embryos which are chromosomally normal or carry the balanced translocation.
FISH probes successfully indicating a reciprocal translocation in a PGD work-up.
Please do not hesitate to contact the PGD Laboratory with any questions at +27 21 938 9213.