A missing chunk of DNA – called Δ32 mutation —is 32 base pairs long and smack in the middle of the CCR5 gene, might be the most studied mutation in human history. The spontaneous deletion, which arose thousands of years ago, has a striking relationship with one of the worst human diseases: HIV/AIDS. People who inherit this mutation from both of their parents are naturally immune. last year, a Chinese scientist named He Jiankui used Crispr to try to endow two human embryos with the Δ32 mutation and immunity to HIV. Megan Molteni writes in Wired that last week, it emerged that fertility clinics around the world have been seeking He’s advice on offering a CCR5 Crispr edit as a service to prospective parents. Now, new research is suggesting that such a procedure might actually be an early death sentence.