Depletion of mitochondrial DNA in leucocytes harbouring the 3243A->G mtDNA mutation

Abstract

Background: The 3243ARG MTTL1 mutation is the most common heteroplasmic mitochondrial DNA (mtDNA) mutation associated with disease. Previous studies have shown that the percentage of mutated mtDNA decreases in blood as patients get older, but the mechanisms behind this remain unclear. Objectives and method: To understand the dynamics of the process and the underlying mechanisms, an accurate fluorescent assay was established for 3243ARG heteroplasmy and the amount of mtDNA in blood with real-time polymerase chain reaction was determined. The amount of mutated and wild-type mtDNA was measured at two time points in 11 subjects. Results: The percentage of mutated mtDNA decreases exponentially during life, and peripheral blood leucocytes in patients harbouring 3243ARG are profoundly depleted of mtDNA. Conclusions: A similar decrease in mtDNA has been seen in other mitochondrial disorders, and in 3243ARG cell lines in culture, indicating that depletion of mtDNA may be a common secondary phenomenon in several mitochondrial diseases. Depletion of mtDNA is not always due to mutation of a nuclear gene involved in mtDNA maintenance.

Novel mitochondrial tRNAIlem.4282A>G gene mutation leads to chronic progressive external ophthalmoplegia plus phenotype

“…A convenient short PCR amplicon was designed (164 bp) for a mutation-specific restriction fragment length polymorphism (RFLP) by mismatch inclusion at the very 3′ end of the reverse primer, which digested the PCR product accordingly (figure 2B,C). Other primer pairs were generated to exclude that the mismatch at the 3′ end introduced a PCR-inflicted amplification bias and dilutions for accurate LFC amplification were performed 13. Alternative PCR amplicons of the region surrounding the mutation were compared by semiquantitative sequencing electropherograms and suggested unaffected PCR bias.…”

Universal heteroplasmy of human mitochondrial DNA

“…Rapid turnover of blood cells can lead to the loss of mtDNA mutations during life, either through selection against a particular mutation (35) or simply by genetic drift (36). On the other hand, the loss of mutations is much less likely in a post mitotic tissue such as the skeletal muscle, where the replication of mtDNA can lead to an increase in mutation load during life within individual cells and the tissue as a whole, even from very low levels of heteroplasmy (31).…”

Gimap3 Regulates Tissue-Specific Mitochondrial DNA Segregation

“…In humans carrying the A3243G MELAS mutation, there is depletion of mtDNA independent of heteroplasmy level and age, which might be a secondary effect of the mutation and a driver for selection of wild type mtDNA [16]. However, the mechanism that leads to a decreased copy number and drives selection for the wild type mtDNA remains unknown.…”