How? I mean the way every drug for example is tested for safety, they give it to people (healthy volunteers) in escalating doses, and watch them for adverse effects.
Rarely, it happens that a drug that was expected to be safe based on animal testing turns out to be dangerous in humans, and healthy volunteers die. It’s a tragedy, it happens rarely, but it happens, and safety trials are still the best way to start the process of clinical trials for new drugs. For some treatments, such as gene therapy, it’s not ethical to ask a volunteer to just try it to see if it’s safe. So they look for sick people, who are consenting to risking a new treatment with unproven safety, because their other choice is to not be treated.
This is how it’s always done. I wonder what you mean when you say the treatment should be tested for safety before giving it to patients.

Edit: this was a personalized experimental treatment developed specifically for this girl, on the parents’ initiative. The clinical team did test for antibodies against the virus before injecting the AAV into the csf. Lots of shady and wrong things on the research side, I’m not protecting them, just disagreeing with the previous comment that this tragedy would have been prevented by a simple test.

Turns out they did on both mice and primates, and the side effect is also evaluated:

Another potential concern, however, emerged about 1 month before Mei was treated: the final conclusions of a primate toxicology study conducted at PriMed. The company’s report, dated 17 February 2025, concluded all four monkeys that received the therapy, whether at low or high doses, developed moderate to severe liver damage.

However, the ethics board did not review the safety report:

An ethics panel at Xinhua Hospital in China approved a gene-editing trial, but had not reviewed primate data suggesting safety concerns. Another hospital panel later concluded the experimental treatment was “definitely related” to Mei’s death.

Even worse, the brain development data from the primate study is entirely unconvincing:

But four of the experts Science asked to assess this figure, including one of the original reviewers of the Nature manuscript, expressed concerns about how well the primate proof-of-concept study was conducted. The submitted paper had no control samples to show the stain was selectively highlighting the gene editor. “It’s completely unconvincing,” says David Sanders, a biochemist at Purdue University who has studied gene therapy. “One can’t have the confidence that one isn’t mostly looking at background staining.”

I mean… the researchers lied to the parents about the risks. How are parents supposed to make an informed decision with false information.

…Qiu and his team downplayed the trial’s risks in describing them to the parents, overlooked safety signals in animal studies, and proceeded even though success was unlikely. “This shouldn’t have gone to trial,” says Steven Gray of the University of Texas Southwestern Medical Center… … “Learning the reality of these missing safeguards has fundamentally changed how we now view the entire project,” says the father… “We did not realize how unusual and dangerous many of the arrangements were.

Yupppp, which is what IMO made this whole thing extra tragic. The disease wasn't even that bad to begin with... definitely didn't necessitate literally doing the very first in-brain gene editing (which is why they needed much higher viral dose... which caused the death)

I have no clue where the family coughed up the $800K though. They don't seem to be the particularly rich type based on what the news report was saying, but maybe the parents did hide some information...?

Maybe yes, maybe no, but they definitely can make you die from immune reponse though.

Yes but it might kill you

Nah, genes only define (among other factors) how likely you are to suffer it.

Wouldn’t that be nice? No more med combos!

Not currently and this would be very difficult. These disorders are linked to the physical and chemical structure of the brain. The physical structure in particular develops as you become an adult and it would be fairly difficult to reverse once this happens. Shaping the formation process in younger people would be much easier.

The chemistry component might be easier to alter but then why not just use a safer and more reversible chemical approach for that?

Plus a lot of depression is highly linked to the environment you are in. I know it was for me. Changing to a healthier environment is the best cure for most people, though there are some for whom it won't work.