IVF based approaches towards the treatment and prevention of mitochondrial disease

Abstract

Mitochondria are strictly maternally inherited, with all paternal mitochondria being destroyed following fertilisation. Women known to be carriers of pathogenic mtDNA mutations are therefore at increased risk of conceiving affected children. These women are currently offered the following options to aid in genetic counselling: oocyte donation, prenatal genetic diagnosis (PND) or preimplantation genetic diagnosis (PGD). One of the aims of this thesis, was to examine the feasibility of PGD for mtDNA inherited disorders, with specific emphasis on answering the following questions: how accurately does the mutation load observed in the biopsied blastomeres reflect the mutation load in the remaining embryo, are those mutation loads initially observed in the biopsied blastomeres maintained throughout preimplantation embryonic development and do mutation loads observed in the inner cell mass reflect those mutation loads observed in the extra-embryonic trophectoderm cells? In my thesis, I have now been able to provide data towards answering each of these questions through the examination of mutation loads in oocytes, embryos and blastocysts obtained from mitochondrial patients undergoing fertility treatment. Techniques, which have been developed in my current laboratory, have facilitated the characterisation of a nuclear transfer technique known as pronuclear transfer (PNT). This is a method to prevent the transmission of mitochondrial DNA disease from mother to child (Craven et al, 2010). As part of the work for my thesis, I have examined the reproducibility of the PNT technique by assessing whether the procedure could be performed by different operators, whilst maintaining levels of efficiency, survival and developmental outcome. Experiments are now being performed to examine the feasibility of PNT in normally fertilised human zygotes, created from donated oocytes. As it is unlikely that egg collection will be possible from two independent donors on the same day, the final purpose of this study was to examine the potential and feasibility of vitrification of eggs or fertilised embryos at both the pronuclear (PN) and Metaphase II (MII) stage for the purpose of the PNT technique. In summary, my studies has examined the reliability of current methods to reduce the likelihood of having a child affected by a mitochondrial DNA disorder and new techniques currently being developed to prevent the transmission of defective mitochondrial DNA, altogether. I hope this will provide fresh hope for patients with mitochondrial DNA disease.