Replacing Faulty Mitochondria

Faults in mitochondria - the so-called powerhouse of a cell - are the cause of a number of human disorders.  Now, researchers in Oregon have demonstrated successful replacement of mitochondrial DNA in egg cells that then developed into healthy animals.

Mitochondria are passed down from mother to child, and errors in mitochondrial DNA (or mtDNA) can lead to a range of conditions, including heart failure, muscle weakness and blindness.  It's thought that these errors may affect as many as 1 in 200 children, though around 1 in 5000 show evidence of disease at birth.  There are currently no cures and present treatments only alleviate symptoms and delay disease progression.

An ideal solution would be to avoid inheriting damaged mtDNA at all.  To this end, Masahito Tachibana from the Oregon Health & Science University and colleagues have been researching ways to replace faulty mitochondria in human egg cells, or oocytes, with healthy ones from a donor. 

Using donated human oocytes, the researchers extracted genomic DNA - the general DNA makes you unique - and implanted this into an egg that has healthy mitochondria, but has had its own genomic DNA removed.  These eggs were then fertilized by IVF and allowed to form blastocysts - bundles of cells that could, potentially, go on to form a human embryo.  Around half of these cells fertilized normally, and went on to produce similar numbers of stem cells as other control cells that hadn't had the DNA transplant, but were fertilized in the same way.  This has been described as three-parent IVF, as the nuclear and mitochondrial DNA came from two different women.

The research on human cells stopped at this stage, but previous work has been carried out on eggs from macaque monkeys, transplanting the DNA in the same way.  These eggs were implanted in female macaques, and have now developed into fully healthy, three-year-old monkeys.

The researchers, writing in the journal Nature, now call for more research into the safety and efficacy of this type of research, so that we can move forward into clinical trials.