Mitochondria and its DNA
Mitochondria (singular – mitochondrion) are organelles, or small components of a cell, whose function is to provide energy for the cell. They produce adenosine triphosphate (ATP), which allows the cell to carry out functions that require energy. This may include muscle cells that need energy to contract, or skin cells that need energy to grow and multiply.
Interestingly, mitochondria have their own DNA (a molecule that can be used to pass down information to make things in your body like proteins), called mitochondrial DNA or mtDNA, which contains the genetic information that is used to make ATP. The problem is that mtDNA can only be inherited from your mother, and not from your father.
In fertilisation, the egg cell from the mother contains a lot of mitochondria needed for cell division. The sperm cells from the father contains a lot of mitochondria in their tails to be able to move and swim towards the egg cell, but since the tail of the sperm does not enter the egg cell, no paternal mitochondrial DNA is passed down to the offspring.
The problem with this is that if there are any problems with the mother’s mitochondrial DNA, this too will be passed down in the offspring. In nuclear DNA (hereditary information that comes from both parents), when the mother has a recessive allele that can cause disease, for example, sickle-cell disease, the child does not get the disease if the father’s DNA has a “healthy” version of the allele. But since no paternal mtDNA transmission occurs, if the mother has a problem with the mitochondria, so will the child.
When there is a problem with the mitochondria, which can occur as a result of mutations in mtDNA, this can be passed down to the offspring, and so the question of how to stop this faulty mitochondrial DNA from being passed down is posed. This is where spindle transfer and pronuclear transfer come in.
Spindle Transfer
Spindle transfer, coined “three-way IVF” by the media, is a process which can be done before IVF to produce offspring without mitochondrial disease. This process involves taking the nucleus of the egg cell from the mother with compromised mitochondria and inserting it into an “empty” donor egg cell with healthy mitochondria and no nucleus, which stops the unhealthy mitochondrial DNA from being passed on when it is fertilised with sperm from the father. This has been successfully done on monkeys, but not in humans as the potential risks are unknown.
Pronuclear Transfer
A similar process to spindle transfer, pronuclear transfer involves taking the nucleus of a fertilised embryo with the defective mitochondria and transfering it into donor eggs with healthy mitochondria. This has been done in humans, through research done at Newcastle University (and funded by Muscular Dystrophy Campaign). This is amazing technology, since mitochondrial diseases affect around 3,500 people in the UK. However, it has not yet been permitted for treatment as they alter the mtDNA of the egg/embryo.
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| Source: DailyMail |
Ethics
The ethical problem with this, is of course, the mixing of some DNA from another parent. There aren’t any studies available to show any long term risks and if it can be considered safe. My opinion is that if this technology can stop further generations from developing mitochondrial diseases, it is essentially eradicating this kind of disease.
It is cost effective as well because the child will not develop a mitochondrial disease which may cost a lot to manage, and it will be a great source of medical research. To me, this is medicine at its best. If we can eliminate genetic disorders, then future generations will definitely benefit.
The colour of the baby’s eyes or hair isn’t affected by this technology because nuclear DNA from the mother is still kept the same. It is only the DNA from the mitochondria, the energy factories of the cells, that is changed. Your child would still be yours. Although some may say that mtDNA plays a huge part because it determines whether you will get a disease or not, mitochondria only contains DNA to be able to make the ATP, the energy currency molecule, it does not determine whether your child is genetically yours, because that is determined by the nuclear DNA.
Designer Baby?
Some people say that babies born from pronuclear transfer or spindle transfer are designer babies, though this is wrong because a designer baby refers to a baby whose genetic makeup (nuclear DNA) has been selected or changed by using genetic engineering to add or delete genes in the chromosomes, whereas this technology uses a donor’s mtDNA to eliminate mitochondrial disease in the offspring.
But the issue remains: is it ethical to alter the mtDNA of an embryo? Let me know what your thoughts are in the comments section below!
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