MST on unfertilised human oocytes that have abnormal mtDNA
PNT on fertilised oocytes that have abnormal mtDNA
Studies on human embryonic stem (ES) cells derived from blastocysts that are heteroplasmic for abnormal mtDNA and blastocysts created through MST and PNT, where the oocytes had abnormal mtDNA19
Similar experiments using induced pluripotent stem (iPS) cells derived from patients carrying different mtDNA mutations20
Further studies on the mtDNA carryover in a non-human primate model into the possible heteroplasmy of tissues in the fetus. The possibility of carryover of even a small percentage of abnormal mtDNA, means that any girls born from MST or PNT should be considered at risk of transmitting the disease to their offspring
Further studies on vitrifying zygotes created through PNT
Much of the information on mtDNA copy number, replication and the bottleneck has been obtained from studying mouse and other animal embryos. Further research on mitochondrial biology in early human embryos, and in the germline in particular, is encouraged and should be supported by research funding agencies.
Further work is required to develop reliable assays for mitochondrial disease caused by mutations in nuclear DNA, especially as PGD may be the preferred alternative for those who wish to prevent transmission of such diseases without having to consider prenatal diagnosis and possible termination of an affected pregnancy.
Conclusions This section summarises the conclusions made in the report.
19 ES cells have a low number of mitochondria that do not need to function. Differentiated cells derived from the ES cells, such as muscle, can have high numbers of mitochondria. These can be put in conditions requiring oxidative phosphorylation. It is also possible to derive primordial germ cells in vitro to explore aspects of the mitochondrial bottleneck and whether certain abnormal mtDNA have a replication advantage.
It is not possible for iPS cells to provide information on mitochondrial behaviour in the early embryo. Page 22 of 45