ABSTRACT
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. Here we report the first preclinical studies on pronuclear transplantation (PNT). Surprisingly, techniques used in proof-of-concept studies involving abnormally fertilized human zygotes were not well tolerated by normally fertilized zygotes. We have therefore developed an alternative approach based on transplanting pronuclei shortly after completion of meiosis rather than shortly before the first mitotic division. This promotes efficient development to the blastocyst stage with no detectable effect on aneuploidy or gene expression. After optimization, mtDNA carryover was reduced to <2% in the majority (79%) of PNT blastocysts. The importance of reducing carryover to the lowest possible levels is highlighted by a progressive increase in heteroplasmy in a stem cell line derived from a PNT blastocyst with 4% mtDNA carryover. We conclude that PNT has the potential to reduce the risk of mtDNA disease, but it may not guarantee prevention.
Subject(s)
DNA, Mitochondrial/genetics , Mitochondrial Diseases/genetics , Mitochondrial Diseases/prevention & control , Mitochondrial Replacement Therapy/methods , Nuclear Transfer Techniques , Adult , Blastocyst/cytology , Blastocyst/metabolism , Cell Nucleus/genetics , Cell Nucleus/metabolism , Cytoplasm/genetics , Cytoplasm/metabolism , DNA, Mitochondrial/analysis , Female , Gene Expression Profiling , Humans , Male , Meiosis , Mitochondria/genetics , Mitochondria/metabolism , Mitochondrial Diseases/pathology , Stem Cells/cytology , Stem Cells/metabolism , Translational Research, Biomedical , Young Adult , Zygote/cytology , Zygote/metabolismABSTRACT
OBJECTIVE: To develop and assess a polymerase chain reaction (PCR)-based preimplantation genetic diagnosis (PGD) approach for detection of chromosomal imbalances in embryos. DESIGN: A prospective study of embryos derived from chromosome translocation carriers that have undergone PGD using a novel molecular-based approach. SETTING: A reference molecular genetics laboratory specialized in the provision of transport PGD services and a private IVF clinic. PATIENT(S): Twenty-seven couples carrying 12 different reciprocal translocations and 2 Robertsonian translocations. INTERVENTION(S): Preimplantation genetic diagnosis from chromosome translocation carriers on blastomeres biopsied from cleavage stage embryos. MAIN OUTCOME MEASURE(S): Embryo diagnosis rate, pregnancy rate (PR), implantation rate, take-home-baby rate. RESULT(S): Overall, 241/251 (96.0%) embryos were successfully diagnosed for chromosome rearrangements. Preimplantation genetic screening was included in the protocol of 12 couples, involving analysis of 90 embryos, 84 (93.3%) of which were successfully diagnosed and 53 (63.1%) showed aneuploidies. Embryos suitable for transfer were identified in 24 cycles. Eighteen couples achieved a clinical pregnancy (75.0% PR/embryo transfer), with a total of 31 embryos implanted (59.6% implantation rate). Ten patients (1 triplet, 1 twin, and 8 singleton pregnancies) have delivered 13 healthy babies, and the other patients (3 twins and 5 singletons) have currently ongoing pregnancies. CONCLUSION(S): The PCR-based PGD protocol for translocations has the potential to overcome several inherent limitations of fluorescence in situ hybridization-based tests, providing potential improvements in terms of test performance, automation, turnaround time, sensitivity, and reliability.
