Could mitochondrial diseases be eradicated for good?

Mitochondria are organelles that exist in every cell in the body. They make adenosine triphosphate (ATP) which is a source of energy needed for all biological processes. As well as this function, they contain genetic information (the nucleus of the cell also contains DNA). The genetic information is responsible for producing proteins, essential biological molecules. 

The two main functions of the mitochondria make it more susceptible to dangerous mutations in its DNA. As a result of mutations, mitochondrial diseases develop. What makes these so dangerous, is that the mutated mitochondrial DNA (mtDNA) will be passed on to a child. This is because mtDNA is inherited from the mother only, so there is no genetic variation occurring or a chance of not inheriting particular genes as with nuclear DNA.

Mitochondrial diseases affect the body in a number of ways but they can cause great physical and emotional stress on families. The body is mostly affected in areas where energy is needed most: the heart, brain and muscles. Symptoms can range from developmental delays to dementia and fainting to diabetes. 

Fortunately, new technologies are being explored which could cure these currently incurable diseases. The method is mitochondrial transfer and results in a “three-parent baby”.  In short, the nucleus from the mother’s egg cell is removed and placed inside the egg cell of a donor. This means that the mother’s nuclear DNA is involved in fertilisation but the mitochondrial DNA comes from an outside donor. This new egg cell fuses with a sperm cell from the father to form a zygote (which develops into a baby). 

Mitochondrial Transfer (Photo Credit: the Guardian)

This technology has already been used and in 2016, the first “three parent baby” was born with the help of Dr. John Zhang and the New Hope Fertility Center. Dr. Zhang has been criticised for not considering the ethical concerns attached to mitochondrial transfer and for ignoring the scientific community. The fast development of new technology makes it more difficult to discuss ethics, especially when medicine could alleviate pain in people’s lives. 

Dr. Zhang and the “three parent baby” (Photo Credit: Nature)

The main concerns: 

  • Mutant mitochondrion could be accidentally carried from the mother. This technology is still new and developing so there will be some doubt about its efficiency. If damaged mitochondria are still in the new egg cell, then the percentage of damaged DNA would be small. A small amount of mutated mitochondrial DNA will not cause the child to have a disease, but they may carry this onto their own children or develop a disorder later in life. Something like this must be regulated for a long period of time to ensure the transfer has been effective. The reason this is a cause for concern, is that by the time the “three- parent” child has developed a mitochondrial disease, they may have already had children who will inherit the damaged DNA. The decision to have children knowing that they may inherit a disease, is up to the parent but they may not know that they carry damaged DNA. A physician (such as Dr. Zhang) must ensure the family are aware that the treatment decreases the risk of developing a mitochondrial disease but does not always cure it, before continuing.
  • There have not been enough clinical trials to know the true side effects on the child. Tests have been done on cell culture and primates (close relatives to humans) but there is still ambiguity around its effect on the health of the child. The Nuffield Council on Bioethics reported that the treatment should be proven to be safe before use. It would not be beneficial to have treatment for a life- saving disease, if it was not yet safe.  
  • There are many concerns about regulation of this technology. In the United States this technology is banned, in the UK it is limited but in Ukraine it is completely unregulated. This means that many will abuse this technology in many ways that we may not know of yet.
  • The development of CRISPR-Cas9, a cheap form of genetic engineering, makes it easier for people to abuse mitochondrial transfer techniques. 
  • There is a controversial question arising from these concerns: Should only males be born using mitochondrial transfer? Females born will carry the mitochondria onto their children, meaning this technique will have generational effects. However, a male will not because the mitochondrial DNA comes solely from the mother. This would eliminate the concern of side effects on generations to come.

These concerns are what fuelled the criticism for Dr. Zhang and many do not agree with what he has done. But he has helped a family who were struggling to have children who don’t suffer from mitochondrial diseases and the transfer has been successful so far. The child will need to be under observation to know the real effects, hopefully the technique will undergo more research so it can be widely accessed to eradicate mitochondrial disease.

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