The development of novel quantification assay for mitochondrial DNA heteroplasmy aimed at preimplantation genetic diagnosis of Leigh encephalopathy

Purpose: To perform preimplantation genetic diagnosis (PGD) of Leigh encephalopathy, we developed a rapid and reliable quantification assay for the percentage of T8993G mtDNA mutation and analyzed various specimens. Methods: We prepared the standard curve by measuring serial proportion of 8993T/G cloned plasmid DNA using real-time PCR, and measured (1) mutant DNA (known proportions by PCR-RFLP), (2) single lymphocytes from 46% mutant carrier, (3) 123 blastomeres from 20 abnormal embryos. Results: (1) These were within -5∼+6% error range, (2) mean 44.3%(11-70%), (3) Five embryos harbored T8993G mutation (4-22%). Embryos from same person indicated different degrees of heteroplasmy, and blastomeres from same embryo demonstrated limited dispersion of heteroplasmy (2-11%). Conclusions: (1) This method provides rapid and reliable PGD for Leigh encephalopathy. (2) The variable heteroplasmy with somatic mitosis was suggested. (3) T8993G mutation was existed in undeveloped embryo, and the bottleneck theory was supported. The limited heteroplasmy dispersion of blastomeres from same embryo also supported reliability of PGD for T8993G mutation.