Mitochondrial Replacement Techniques:

Mitochondria are cellular structures that play a critical role in producing energy. While the majority of a cell’s DNA is found in the nucleus, mitochondria also contain a small amount of DNA that is inherited only from the mother. Inherited mitochondrial DNA (mtDNA) diseases result from failures of the mitochondria due to mutated, pathogenic mtDNA. A woman who carries mutated, pathogenic mtDNA may be at risk for passing on mtDNA disease to her children.

Mitochondrial replacement techniques (MRT) are a set of techniques designed to prevent the transmission of mitochondrial DNA (mtDNA) disease from mother to child. Each year in the United States, there are an estimated 778 births among women at risk for transmitting mtDNA disease. MRT could allow prospective mothers the opportunity to have a genetically related child with a significantly reduced risk of passing on pathogenic mtDNA.

Children born as a result of MRT would have genetic material from three individuals—nuclear DNA from each of the intended parents and mitochondrial DNA from a second woman (the oocyte provider). For intended parents and oocyte providers participating in an MRT clinical investigation, there would need to be discussion and agreement during the informed consent process about the social involvement, if any, of the oocyte or sperm provider with the future child and his or her family.

The committee recommended that initial clinical investigations be limited to the transfer of male embryos. This limitation reduces the risk of any uncertain consequences of MRT from being passed on to future generations since males do not pass down their mitochondrial DNA to offspring. Under certain conditions, as outlined in the report, transfer of female embryos created through MRT could be considered in the future.

MRT involves replacement of whole, intact, and naturally occurring mitochondrial DNA (via replacement of mitochondria). This represents a very different type of genetic change compared to modifying nuclear DNA, which would likely involve editing rather than replacing chromosomes.