Op-Ed

A baby dressed in a shirt, diapers, and cap, floats mid-air.

Last week, US scientists edited a human embryo for the first time. That’s just the beginning.

The first step is a no-brainer. Say you are one of the tens of thousands of people with Huntington’s disease, a terrible, hereditary neurodegenerative disorder caused by a mutation in the HTT gene. The diseased version of the gene makes an abnormally long protein that becomes toxic in your neurons, eventually killing them. Symptoms usually appear in your 30s or 40s as small twitching movements, a lack of coordination, and depression. In the coming years, the spasms will grow. It will be increasingly difficult to walk, talk, and think. Within 20 years, you will most likely be dead. You are resigned to your fate, but you and your partner would very much like to have kids, and you have no interest in passing this particular legacy to your child.

Today, your best bet is a procedure called preimplantation genetic diagnosis (PGD), in which embryos produced through in vitro fertilization (IVF) are screened for the unwanted gene. PGD has been a game changer for many...