Rather than aiming specifically at avoiding transmission of the mutation and thus disease prevention, PGD for mitochondrial heteroplasmy can only be aimed at risk reduction.
Centres that carry out PGD for mtDNA disorders should:
offer prenatal diagnosis or PGD as the first option for patients who have an identified mutation and a low to medium level of heteroplasmy
have appropriate experience and expertise in the diagnosis and management of mtDNA disorders, knowledge of the different mutations and the proportion of heteroplasmy likely to lead adult disease
provide appropriate experienced genetic counselling, in order to decide upon and document the threshold level of abnormal mtDNA measured at PGD above which embryos would not be replaced in order to minimise the risk of the child being affected with the disorder
be encouraged to consider single embryo transfer to enable follow up of the fate of the embryo transferred21
encourage patients to consider prenatal testing following PGD, to assess the consistency in levels of heteroplasmy
record the levels of abnormal mtDNA in the woman, the embryo (trophectoderm or cleavage stage biopsy) and in the subsequent child to assess the degree of correlation
MST and PNT have the potential to be used for all patients with mtDNA disorders, which may make them preferential to PGD in the future. In patients with homoplasmy or high levels of heteroplasmy, these are the only techniques that would make it possible for them to have a genetically related unaffected child.
There is currently insufficient evidence to recommend one transfer technique over the other.
21 Using single embryo transfer will require centres to have an effective cryopreservation programme in order to freeze the remaining suitable embryos that were not transferred. Page 23 of 45