A mitochondrion
Professor Nigel Brown FSB, President of the Society for General Microbiology, is writing an article each month for The Bridge, a local magazine delivered to every home in the villages of Corsley and Chapmanslade in Wiltshire.
There have been many comments in the news over recent weeks about so-called ‘three-parent babies’. This rather alarmist description is better expressed as ‘mitochondrial donation’ and it has been the subject of debate in Parliament, where it was agreed that it should be permitted in the UK to prevent mitochondrial disease. The UK is the first country in the world to allow this.
So what are mitochondria and what is mitochondrial disease? Mitochondria provide the energy (called ATP) for every cell in your body. There are many hundreds of them in most cells and they are particularly important in muscle, the brain and liver, the organs that consume most energy. Mitochondrial disease happens when the mitochondria do not function properly and such diseases may result in poor growth, loss of muscle coordination, loss of sight, seizures, heart and liver disease, and neurological problems. About 1 in 4,000 children suffer from such diseases.
So why is mitochondrial donation important? Most of your genetic material comes from both your father and mother and is found in the nucleus of every cell in your body. At conception the nucleus of the sperm fuses with the nucleus of the egg to create the nucleus of the first cell, which will divide many times to form a foetus. If there is a faulty gene from one parent, the chances are that the other parent has provided a functioning gene that allows your cells to work as normal. However, a small amount of genetic material is also found in the mitochondria and this is mainly concerned with energy generation. When the egg and sperm fuse at conception mitochondria come only from the egg – that is, from the mother. This means that if there is a faulty gene in the mitochondria there is no compensating functional gene from the father.
Mitochondrial donation is a way in which women who have a faulty mitochondrial gene can still give birth to healthy babies. An egg cell is taken from a woman who has normal mitochondria and the nucleus of the egg is removed, and replaced with the nucleus from the biological mother. This is then fertilised with a sperm from the father and the fertilised egg is implanted in the mother’s womb. (This is in-vitro fertilisation or IVF, a standard procedure these days for couples who have difficulty conceiving). The majority of the genes (over 70,000) are in the nucleus and come from the father and the mother as normal. However, the small number of genes present in mitochondria (37) are effectively donated by another woman – hence the tabloid description of ‘three-parent babies’.
Although the procedures are complex, the medical science behind them is relatively straight forward. The concerns are ethical and social. A number of opponents of the technique have claimed that it is ‘playing God’ and others have raised issues about the nature of an individual. Proponents have pointed out the number of children who could be saved from debilitating illness. This was an important discussion that has polarised views and has raised issues about ‘designer babies’.
The Society of Biology is sponsoring these articles in 2015 through our regional grant scheme, which supports locally focussed activity. This is the second of a series of articles that will focus on the life sciences – health, agriculture and biotechnology