Chinese scientist He Jiankui genetically mutated twins born last year to be resistant to HIV infection through the CRISPR-Cas9 gene-editing technology — however, according to an analysis released June 3 by UC Berkeley researchers in the journal Nature Medicine, this mutation also comes with a 21 percent increase in mortality later in life.

According to Michael Eisen, a campus professor of genetics, after scientists noticed certain groups of sex workers showing resistance to HIV infection, they discovered the CCR5-∆32 gene mutation in 1996. The mutation interferes with the HIV virus’s ability to bind to the host cell’s surface.

“Beyond the many ethical issues involved with the CRISPR babies, the fact is that, right now, with current knowledge, it is still very dangerous to try to introduce mutations without knowing the full effect of what those mutations do,” said UC Berkeley professor of integrative biology Rasmus Nielsen in a UC Berkeley press release. “In this case, it is probably not a mutation that most people would want to have. You are actually, on average, worse off having it.”

After He’s experiment on the twins was publicized, Nielsen and postdoctoral fellow Xinzhu Wei decided to study the specific mutation He induced, the CCR5-∆32 mutation. To do this, they analyzed more than 400,000 sample genomes and medical records from a British database called the UK Biobank.

Previous studies on the CCR5-∆32 mutation revealed that people with this mutation are four times more likely to die after an influenza infection. Nielsen and Wei’s study shows that having two mutated copies of the gene will significantly increase the chance that a person will die between ages 41 and 78.

“People shouldn’t have been doing this in the first place, but this study shows that anyone who thinks there are only benefits to having this mutation are clearly wrong,” Eisen said.