BEIJING-A genetic mutation that a Chinese scientist tried to create in twin girls born last year, in the hope of protecting them against HIV, has been found to raise the risk of an early death.

He Jiankui at the Southern University of Science and Technology in Shenzhen sparked an international outcry in November when he announced the birth of twin girls, Lulu and Nana, after he edited the DNA in their embryos. The procedure was meant to mimic a natural mutation that protects about 10% of northern Europeans from HIV infection. But in new research, scientists in the US found that the mutation is linked to shorter life expectancy. By the age of 74, the death rate was on average 26% higher in Britons who carried mutations in both copies of the gene, compared with those who had mutations in only one copy or neither.

He targeted a gene called CCR5 which makes a protein that protrudes from the surface of immune cells. While scientists are unclear exactly what the CCR5 protein does, the HIV virus latches on to it to enter and infect cells. A natural mutation called delta 32 disables the protein and so prevents HIV from getting inside cells. While He failed to replicate the natural mutation, he instead appeared to introduce different mutations which disabled a single copy of the CCR5 gene in one of the girls and both copies of the gene in the other. A preliminary Chinese government investigation released in January found that in performing what is called germline genome editing, where genetic changes are made that can be passed on from generation to generation, He had sidestepped regulations and oversight and had used fake ethical review documents in pursuit of “personal fame”.