Mitochondrial DNA (mtDNA) mutations are maternally inherited and are associated with a broad range of debilitating and fatal diseases. Reproductive technologies designed to uncouple the inheritance of mtDNA from nuclear DNA may enable affected women to have a genetically related child with a greatly reduced risk of mtDNA disease. To this end, we have performed preclinical studies on pronuclear transplantation (PNT). Surprisingly, techniques used in proof of concept studies involving abnormally fertilized human zygotes were not well tolerated when applied to those that undergo normal fertilisation. We have therefore developed an alternative approach based on transplanting pronuclei shortly after completion of meiosis rather than shortly before the first mitotic division. The modified procedure, known as early PNT (ePNT), promotes efficient development to the blastocyst stage with no detectable effect on aneuploidy or gene expression. Following further optimisation, mtDNA carryover was reduced to <2% in the majority (79%) of PNT blastocysts. However, we found that 1/5 hESC lines derived from PNT blastocysts showed a marked increase in heteroplasmy despite relatively low (4%) starting levels. While the relevance of this to development in vivo is unclear, the finding underscores the importance of reducing mtDNA carryover to the lowest possible levels. We propose that the new ePNT procedure has the potential to give rise to normal pregnancies with a reduced risk of mtDNA disease, but may need further modification to eliminate disease in all cases.
11 Jul 2016 - 11 Jul 2016