The first people to be gene-edited - a pair of baby twin girls - may have been mutated in a way that shortens life expectancy, research suggests.

Professor He Jiankui shocked the world when he genetically altered the twins to try to give them protection against HIV, the BBC reported.

However, now a study in Nature Medicine shows people who naturally have the mutation - he was trying to recreate - were significantly more likely to die young.

Experts said Prof He's actions were "very dangerous" and "foolish".

Prof He was targeting a gene called CCR5. It is a set of genetic instructions that are important for how the immune system functions. They are also the doorway that human immunodeficiency virus (HIV) walks through to infect cells.

Mutations to CCR5 essentially lock the door and give people resistance to HIV. So, Prof He made embryos in an IVF clinic and then used gene-editing technologies on the twins to alter the CCR5 gene.

Resulting in girls - named Lulu and Nana - who were born last year.

The problem is CCR5 has a bigger role in the body than just making people vulnerable to HIV. It is active in the brain and in fighting off other infections, particularly flu.

The study, at the University of California, Berkeley, looked at nearly 410,000 people in the UK, among them those who had only the mutated version of CCR5 were 20 per cent more likely to die before they turned 78.

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