At least one baby has been born in the UK with the DNA of three people through a treatment designed to prevent mothers passing on harmful gene mutations. How it works: the nucleus of a fertilised egg is removed, minus the mother’s faulty mitochondria, then used to replace the nucleus of a healthy donor’s egg. The new egg is then inserted back into the mother. The result: a child with less risk of inheriting potentially fatal mutations, with the genetics of both parents and of the donor (about 0.2 per cent). These aren’t the only children in the world to be born this way. A Jordanian child was the first in 2016 through a US team working in Mexico. But the UK – specifically Newcastle – has staked itself out as the centre for this research, walking a fine line saving lives by taking control of genetics.