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Gene therapy is really complicated both scientifically and ethically. But it also has the potential to do some amazing things - like treating life threatening diseases in babies before they are even born.

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This episode of SciShow is brought to you by the American Society of Gene and Cell Therapy. [♪ INTRO].

Gene therapy is probably one of the most mind-boggling developments in the last few decades of medicine. The fact that we can treat certain diseases by changing someone's genetic makeup seems like it should be straight out of a sci-fi book.

In fact, when I was a kid, it was. But it can also be a little misunderstood. One of the most common misconceptions about gene therapy is the idea that it will someday be used to create what people call “designer babies” — essentially, kids who have their traits chosen before birth.

Things like intelligence or eye color, or even whether or not they're gonna go bald later in life. The truth is, most gene therapy research right now doesn't involve modifying fetal cells at all. And even when it does, researchers are looking to prevent or treat genetic disorders — not customize DNA just because they can.

In some ways, it's just like every other kind of medicine. And in others… it is very, very different. But one way or another, fetal gene editing could be a big part of the future of medicine — a future that may be here faster than you think.

There are a few different types of gene therapy, but the best-studied ones involve viruses. The basic idea is that scientists take a virus — called a vector — and remove the parts that cause disease. Then, they insert bundles of information for the vector to deliver instead.

That information usually takes the form of instructions, telling the body to produce something like a protein that it's naturally lacking. For example, those with hemophilia don't have enough of a specific blood-clotting protein. So the gene to treat it would tell their cells to start making those protein molecules.

Over the last few years, there have been an increasing number of successful gene therapy tests in both lab animals and humans. But treating a disease after someone is born can still come with some complications. Some treatments come with risks, others aren't thorough enough, and, for some conditions, there just aren't useful treatments at all.

So the idea behind fetal gene therapy is to prevent these diseases before someone is born. It might involve treating an embryo directly, or treating a fetus by injecting vectors into something like the amniotic fluid. But whatever the method, most researchers agree that these treatments shouldn't be used for just anything.

In the late 1990s, the UK's Gene Therapy Advisory Committee published two criteria that any fetal treatments worth considering should meet. First, they should have a clear advantage over other treatments, like transplants or postnatal therapy. And secondly, they should be used for life-threatening diseases with no suitable treatment.

In other words, the heart behind this is to help people to be as healthy as possible, just like other types of medicine — not to, say, genetically engineer an X-Man. The general consensus of other ethics committees has been along the same lines. Still, even with guidelines in place, most of these therapies are currently too risky to try in human fetuses, so research has mostly been confined to animal models.

Pregnant people can get blood and tissue tests to determine if their child is likely to have a genetic disease — including cystic fibrosis, hemophilia, and sickle cell anemia. But there are not many immediate options if those tests are positive. We are making progress, though.

In 2018, a promising study in Nature Medicine showed how fetal gene therapy could treat an illness in mice that is similar to Gaucher's disease in humans. Gaucher's is an inherited disorder that causes an enzyme deficiency — specifically, for an enzyme called glucocerebrosidase. Without healthy levels of it, waste builds up in the body, which can lead to all kinds of trouble.

Often, this disease can be treated by getting weekly enzyme injections, but a certain type of Gaucher's — type 2 — isn't treatable. In this type, there isn't enough glucocerebrosidase in the brain. And because of the blood-brain barrier that filters out most molecules, the enzyme injections don't work.

The disease is often fatal, and by the time a baby is born, a lot of the damage has already been done. So researchers have been looking into how to treat it using fetal gene therapy. In the 2018 experiment, scientists injected the brains of fetal mice with vectors full of instructions to make that missing enzyme — and it seemed to help!

The mice had relatively normal enzyme activity, although they did tend to weigh less and didn't perform as well on movement tests. A follow-up experiment seemed to be even more encouraging. In it, researchers injected the vectors into the bloodstream instead of the brain.

The mice were only allowed to be kept alive for 55 days for ethical reasons, but during that time, they didn't seem to be any different from regular mice. The team also showed that this vector-injecting method worked on larger animal fetuses, like macaques. The study was so successful that some scientists argue we are ready to start clinical trials of this method in humans.

But others disagree, pointing out that success in pre-clinical studies doesn't always equal success in clinical trials. So they think we need to keep researching. Because that's the thing about fetal gene therapy: It's really complicated, both scientifically and ethically.

After all, as soon as you start clinical trials — treating human embryos or fetuses that will develop into full-grown kids — you're dealing with a person's life. And that's not something to be taken lightly. We have done trials on fetuses before, but only using methods that were heavily studied and shown to be safe.

Like, in another 2018 study, published in The New England Journal of Medicine, researchers used fetal gene therapy to prevent XLHED — an inherited disorder that impairs sweat glands — in three babies. The kids were around a year and a half old when the paper was published, and seemed to be doing okay. The key was that the researchers were using extensively tested methods, and also got permission from their hospital's ethics committee.

That's very different from the news that broke just a few months later, when it came out that a Chinese researcher had altered human embryos using CRISPR, a newer gene-editing technique. This trial violated most of the accepted ethical guidelines. For one, it was done to reduce the babies' chances of contracting HIV, and there are much less risky ways to do that.

The scientist also didn't get permission from a committee, and, most importantly, the method he used isn't established as safe. CRISPR has done great in the lab, but it's also been shown to cause occasional, accidental mutations. Thankfully, the kids are healthy so far, but that doesn't mean they always will be.

So, let's just say there's a reason we have these guidelines. In the future, there will likely be a time when we can safely edit an embryo's genome in all kinds of different ways. But even when that day comes, there will be other things to think about, too.

Like, what would the consequences be if someone's edited genes were passed to their offspring? Or if the edited gene mutated over the course of someone's life? And then there are even messier questions, like how far is too far when it comes to gene editing, and if this science is interfering with evolution… or if it matters if it is.

The most we can say is that, right now, fetal gene therapy is really only intended for necessary treatments. The next steps are to continue the animal tests scientists have already started, to really understand how this science works and what the risks are. Because at the end of the day, when these experiments are approved for more frequent clinical trials in humans, we want to make sure they are as safe as possible.

If you're interested in keeping up with the latest research, you should check out the new patient education portal from the American Society of Gene and Cell Therapy. It's a super comprehensive resource for everything you've ever wanted to know about the different types of gene therapy, how they work, and both past and ongoing research into all kinds of treatments. And it is completely free.

To check it out for yourself, just head over to, or follow the link in the description below.