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Unknown risks: Mitochondrial replacement therapy is built on principles borrowed from IVF (above) and cloning

A bit like "Nazi", the E-word, eugenics, is prone to febrile over-use in discussions and debates; and it can be a reliable indicator that the user is losing his grip and the argument. But a report last spring from the Human Fertilisation and Embryology Authority (HFEA) has triggered a rash of worldwide criticism and an outbreak of the E-word — all directed at the HFEA and the British government. 

The report concerned the complex processes of mitochondrial genetic medicine, and it concluded: "Our advice to Government, set out in this report, is that there is general support for permitting mitochondria replacement in the UK." And not just the usual Luddite suspects, pro-life ideologues and Christian fundamentalists, but mainstream, progressive scientific journals, clinical academics and the lay media have all lined up to stress the dangers of the HFEA's recommendations. 

What's going on? In summary, it's a strikingly combustible combination we've seen often before in the UK: some quite brilliant medical science, ethical boundaries stretched or broken, and some quite shocking misinformation.

Every cell in the body contains tiny elements (organelles) called mitochondria. They are responsible for generating energy in the cell: necessary for viability itself, and for the execution of any specialised function-forceful contraction, if the mitochondria are in a muscle cell, electrical impulse generation in a nerve cell, and so on. Surprisingly, and uniquely among the different types of organelle within cells, mitochondria contain not just the enzymes and other molecules necessary for their energy-producing function, but also a certain number of genes. There are only a few dozen mitochondrial genes (compared to around 20,000 in the nucleus) but, just like nuclear genes, defects in them can cause devastating (though rare) diseases. 

Trying to fix or repair gene mutations in "ordinary" nuclear genes presents enormous technical difficulties, but the specific circumstances of mitochondrial genes open up their associated diseases to therapeutic possibilities. During reproduction, half of the new person's nuclear genes come from the mother (in the egg), and half from the father. But the egg also contains all of the new individual's mitochondrial genetic material; none derives from the sperm. So it is impossible to inherit a mitochondrial genetic disease from a father: these disorders may only be maternally transmitted. Modern medicine's technical ability to manipulate and control human fertilisation in the laboratory — in vitro fertilisation (IVF) — presents tantalising therapeutic avenues in relation to mitochondrial gene disorders. 

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