to permit far more reliable visualisation and removal of the spindle, with all its associated chromosomes.
Safety of MST and PNT
The panel considered the following safety issues of the MST and PNT techniques: the carryover of mtDNA from the affected oocyte or zygote; the reagents used in the techniques; and the nuclear-mitochondrial interactions involved.
mtDNA carryover: Carryover of mtDNA from the affected oocyte or zygote might be expected with both techniques as the spindle or pronuclei are enclosed in a „karyoplast‟ during the manipulation technique, that contains nuclear DNA, cell membrane and a small amount of surrounding cytoplasm. In theory, carryover of abnormal mtDNA may be an issue if abnormal mtDNA is preferentially replicated and if there is a marked difference in segregation across tissues. However evidence presented to the panel was reassuring17. Carryover was usually considerably less than 2% of the total mtDNA in the reconstituted embryos from both MST and PNT, with MST appearing to have a lower carryover than PNT. In several cases the level was undetectable (although the sensitivity of the methods used would not have detected very low amounts). The evidence suggests that the likelihood of preferential replication of abnormal mtDNA and marked differences in segregation across tissues is remote. The maximum levels of carryover of mtDNA in MST and PNT is markedly less than the level of abnormal mtDNA in an embryo that may be accepted for transfer following PGD. Nevertheless, without evidence from the use of MST or PNT in humans, the possibility of carryover of even a small percentage of abnormal mtDNA, means that any girls born from these techniques should be considered to have a (theoretically) low risk of transmitting the disease to their offspring.
4.3.3 Reagents: To carry out the micromanipulation techniques in MST and PNT, it is necessary to use a number of reagents not used in conventional assisted conception or
17 Professor Doug Turnbull, Newcastle University, oral presentation to panel; Dr Mitalipov, Oregon University, oral presentation to panel. Page 18 of 45