The second revolution in gene therapy that has cured Javier, a child with a lethal error in the X chromosome

A “small strand of blood in the poop.” This was the first sign, initially viewed as unimportant, that put Jesús Lunar and Cristina López on the trail that something was happening with their son’s health. Javier had been born on June 12, 2020, and before the discovery, which occurred a few days later, everything had been following the chaotic routines that new members of any family impose. Six months later, however, the doctors sat the couple down and gave them the news that was going to change their lives.

“We were told that Javier had Wiskott-Aldrich syndrome, a rare genetic disease that affects the immune system. At first we didn’t know how to react, it was hard for us to accept that it could be fatal. But then something in your head clicks. You tell yourself that you have to keep going and that everything that needs to be done will be done. And so it has been to this day,” says this computer programmer born in 1982.

Javier is almost five years old now and, apart from some minor...