Preimplantation Genetic Testing

Thousands of different single gene mutations, cancer predisposition genes, and now multi-factorial diseases can be screened in the early human embryo before transfer during an IVF cycle1. Having multiple cells to work with removes some of the potential issues that surrounded early attempts at single cell biopsy including reductions in allele drop-out (ADO) and preferential amplification (PA). Allele drop-out arises in the early stages of amplification by polymerase chain reaction (PCR), where one allele of a heterozygote is not primed and products for this allele are not created. 

In a heterozygote cell, this means that one allele will be missed which can lead to misdiagnosis as a homozygous embryo2. Preferential amplification is similar to ADO except that some product is made for one allele while more product is made for the other allele. Again, depending on the down-stream method of analysis chosen, this can lead to errant results and potential misdiagnosis. Dreesen’s and colleagues have published a thorough review of misdiagnosis during PGT-M (PGD), and Warren and colleagues have shown how using the PG-Seq™ kit with TSE lessens or eliminates the issues of PA and ADO.