Mitochondria, as all of those studying biology know are the ‘batteries’ of the cell providing the majority of energy from respiration. When mitochondria become faulty there are a range of problems from muscle weakness, heart disease and early dementia. About 1 in 200 babies born will have mitochondrial disorders. Doctors have tried to rectify these by injecting donor mitochondria into faulty cells but this has not been successful as they are so small and easily damaged.
Mitochondria are probably the remnants of a symbiotic relationship with bacteria. They were probably bacteria that were engulfed by cells; these cells then had a massive evolutionary advantage being able to generate 15 times as much ATP [the energy currency of a cell]. Mitochondria are the same size as bacteria, also contain circular DNA, have bacterial type ribosomes and enzymes and have a double membrane like bacteria.
Mitochondria are outside the nucleus and are not involved in fertilisation of the sperm and egg nuclei. Mitochondria are solely inherited from the mother – the egg cell mitochondria present in the cytoplasm will form the foetal mitochondria. Doctors have recently developed techniques to prevent mothers passing on mitochondrial diseases to their children. In this new technique the nucleus from an embryo will be placed into a donor egg cell with normal mitochondria that has had its nucleus removed. The nucleus will contain genetic information from the parents – mother and father and the enucleated egg cell [egg cell without a nucleus] from a third person. The newly formed embryo will thus have genetic information from the original two parents and genetic mitochondrial information from the donor –‘three parents.’ This will cause a genetic change which will be passed down the line to other generations. This affects what the HFEA describes as the germ line.
HFEA [The Human Fertilisation and Embryology Authority] has launched a public consultation on the ethics of this new IVF technique to decide whether to make it legal for women carriers of mitochondrial disease to be allowed to have mitochondrial replacement therapy. For more information and to register your view go to http://mitochondria.hfea.gov.uk/mitochondria
Ethical scenario of the week [taken from HFEA website]
Martin and Jane have a five year old daughter with mitochondrial disease. Her symptoms are severe and her doctors say that they will get worse as she grows up.
Like many mothers whose children have genetically inherited disorders, Jane feels a sense of responsibility for her daughter’s problems. She hadn’t known when she was pregnant that she carried unhealthy mitochondria.
Recently, Jane and Martin have been talking about the possibility of having another baby. Jane began to research mitochondria replacement and wanted to explore these options in greater detail, but Martin had concerns.
He was not only worried about how it might affect Jane and any resulting children, but also because it would mean that, if their next child was a daughter, she would no longer be passing on her mother’s mitochondrial DNA. Martin was concerned that altering the germ line in this way is tampering with nature.
Martin suggested adoption. However, Jane said she wanted her own children rather than adopt. Jane’s view was that it was worth going through the treatment to ensure their children were healthy.