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We talk a lot about CRISPR and "designer babies" but the science of editing genes is varied and complex. This month, an adult man received billions of gene-editing viruses via an IV in an effort to treat a rare disease.

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Last week was a pretty big deal for the future of medicine.

For the first time ever, researchers injected someone with tools that would edit his DNA, hopefully curing his genetic disease. If it works, it’ll be a huge step toward treating some of the world’s most debilitating genetic diseases.

But despite the connections being made in some places, this isn’t ushering in the age of designer babies. On November 13th, a man named Brian Madeux received billions of carefully-designed, gene-editing viruses via an IV. Madeux has Hunter syndrome, which means he’s missing an essential enzyme for breaking down certain kinds of large sugar molecules.

Instead, these sugars accumulate in his cells, causing them to swell, and making his tissues and organs grow to abnormal sizes. Hunter syndrome can lead to all sorts of problems, including less mobility, vision and hearing loss, brain degeneration, and heart disease. And like many rare genetic diseases, it has no cure.

Patients can get enzyme boosts to ease their symptoms, but they’re incredibly expensive, and the enzyme levels drop off quickly. Gene editing — if it works — would be a much more effective treatment. The idea is almost exactly what it sounds like: you take a patient’s genes, and you edit them, usually with the goal of fixing a mutation or curing a disease.

Researchers have been trying to cure diseases this way since 1989, but in the last few years, gene editing techniques have gotten much more accurate and reliable. There are already some approved treatments that involve taking the patient’s cells out of their body, modifying their genes, then putting the cells back in. With Madeux, researchers are doing something new: the tools to edit his DNA were injected directly into his blood to then go modify cells elsewhere in his body — in this case, his liver.

While most of the gene editing research you hear about these days uses a tool called CRISPR, this treatment uses a system known as zinc-finger nucleases. It’s a slightly older method that’s harder to design and make, but it also has a good track record. Zinc-finger nucleases consist of two essential parts—a DNA-clipping enzyme, and a section that binds directly with the part of the genome you want to cut.

To edit genes, scientists design a pair of these DNA clippers that cut both halves of the DNA strand. If the bit of DNA they want to add is designed to match the sequences at those broken ends, then when the cells go to repair the break, they’ll sometimes include the new gene. For Madeux’s treatment, the blueprints for these gene-editing tools were packaged in modified viruses, which, you know, infect cells — the way that viruses do.

Then, all the team needed to do was put them in a plain old IV. If all goes according to plan, Madeux’s liver will transform into a mini manufacturing plant for the enzyme he lacks. According to the researchers, if the gene gets into 1% of his liver cells successfully, he’ll make enough of the enzyme to treat his condition.

But that’s a big if. Gene therapy trials are known to be risky. People have died when the viruses used in other types of gene therapy treatments sent their immune systems into overdrive.

And that’s not the only potential complication. Sometimes the introduced genes land in the wrong spots and cause cancer. And if the gene is activated in the wrong cell type, it can cause other issues.

The new treatment is designed to avoid putting the gene in the wrong place very often, and there’s a fail-safe that’s supposed to prevent the insert from working in any non-liver cells. But there’s always a chance something could go wrong, and if it does, there’s no going back. They won’t be able to un-edit his cells.

That’s the risk—and reward—of what Madeux signed up for, and it may take several months before we know whether the experiment succeeded. Even if things do go smoothly, though, the therapy isn’t necessarily going to cure him completely or indefinitely. This genetic editing should help with most of the symptoms, but the enzyme probably won’t be able to cross the specialized barrier that protects the brain, which means it won’t be able to prevent brain damage.

It also can’t reverse the damage the disease has already caused over the past 44 years of his life. And the therapy should work for at least several years, but how long it remains effective depends on the age and type of cells that incorporate the new gene. The ultimate goal, though, isn’t to treat adults like Madeux and the other volunteers in this study—it’s to develop a safe enough protocol to use in children or even infants.

That way, they’d be spared the syndrome’s worst effects. And if this treatment works, researchers will also be a lot closer to developing similar gene therapies for other types of diseases. But one thing this research will not get us closer to is some dystopian future where we’re genetically engineering our children to have extra fingers or whatever.

Whenever there’s a new development in gene therapy, there’s a lot of talk about the risks of babies with edited genes, or how to draw the line between editing an embryo’s genes to eliminate a disease and custom-designing a person. And those are real ethical problems that we’ll need to solve before we start using gene editing to change someone’s genome before they’re born. But research like this, where scientists are trying to treat a disease in a living person, is totally different.

The changes to Madeux’s DNA won’t be happening in any of the cells destined to become sperm, so there’s no way for him to pass them on. This is a pretty big leap for gene therapy, especially if it works without serious complications. But it’s not designing babies.

Alright, I’ve got an EXCITING ANNOUNCEMENT for you. The SciShow team and I were talking about a common problem that many of us have. When people ask us what we want for Christmas or for our birthdays, often, we won't know what to say and then they’ll get frustrated and we’ll get frustrated and it’s like “I just wanted to do a nice thing for you and you’re being so stubborn!” But I don’t know!

I don’t care about stuff that much. But I was thinking, you know, there are a few things that I would like to get or that I’ve bought for myself of that people have gotten me that I loved because I love the world and the universe and understanding things and the existence of life and doing experiments on my proteins -- that kind of thing. So, we’ve put together a collection of artifacts of this universe.

We got a limited number of each of these things and we’ve put up at a store called SciShowFinds. These SciShow Finds are curated by me, they are things that I know I would love to get in my stocking. It's a very small list, just six cool things with varying price points.

And I did my best to only include one science book, It was very hard to pick, but I picked the one that had the most impact on me of all the books that I read this year. It's called "What is Life" and it makes an extremely compelling case that biology is like a chemical inevitability. And, along the way, you learn a whole lot about chemistry, and it’s great, because -- you might end up googling things every once in awhile to make sure you know what the author’s talking about -- but at the end of the book, you will understand chemistry in a whole new way.

We're probably going to add new we find them...throughout the year, and the new ones will replace these old ones, so these products are only around for a limited time. You're bound to have friends or family who would love these Mars Socks, trilobite fossils, or this Space Shuttle lapel pin. And, if not, you might want to get them for yourself or just send that link over to somebody who’s saying to you, “what do you want for Christmas?” and it’s like, “Just anything from this website, Ma.

You’ll be getting me socks that I’ll actually appreciate this time.” And know that when you buy from, or you send that link to somebody else, you are also supporting SciShow. So, thank you for doing that. And I know what you’re thinking, “Can I get that cool SciShow hoodie at

You can’t. You can’t. This is just for staff.