With gene-editing technology, scientists can remove harmful genes from a person's DNA and replace them with genes that function properly. CC0 Creative Commons

Scientists are editing genes inside a living person for the first time, in an attempt to help a man with a debilitating metabolic disorder.

The AP reported today that researchers at UCSF Benioff Children’s Hospital Oakland dripped new genes into the patient that will replace mutated ones causing his illness, known as Hunter syndrome. The experiment relies on a gene-editing technology that, while controversial, holds the potential for curing serious conditions by removing damaging genes and replacing them with properly functioning ones.

According to the U.S. National Library of Medicine, Hunter syndrome is a progressive disorder that is linked to the absence of a certain enzyme, because a genetic mutation prevents the body from producing it. Without that enzyme, certain tissues throughout the body become enlarged, including on the face, the vocal cords and in the patient’s airway, which constricts breathing. The disorder could lead to fluid buildup in the brain, thickened skin, skin growths and other issues that lead to complications like hearing and vision loss, recurring infections and heart problems.

The AP notes that Hunter syndrome patients can be treated with the missing enzyme on a weekly basis but it won’t stop damage to their brains, or reverse damage that has already been caused, and is a costly avenue.

“I’m willing to take that risk” of being the first person to try out the new treatment, Brian Madeux, 44, told the AP. “Hopefully it will help me and other people.” He also told that publication, “I’ve been waiting for this my whole life, something that can potentially cure me.”.

The experts will need to test the therapy on other adults first but, if successful, eventually the treatment may be used on significantly younger patients who have not experienced as much tissue damage.

Although CRISPR has become almost synonymous with the phrase “gene-editing tool” in public consciousness, the AP reported that this attempt is using a different tool that relies on proteins called zinc finger nucleases that bind to DNA and allow scientists to target a specific location in the genome. They are supposed to cut out the original, harmful gene and replace it with a new, disease-free one. In the case of the treatment for Madeux, the new gene will have his body make the enzyme that he is currently lacking.

The IV therapy that he received this week pumped him full of that clean gene and the proteins that will insert them into his DNA.

There are different forms of gene therapy, but the kinds that involve editing a person’s DNA have been controversial because of the potential for something to go wrong and people’s worries about how they will be used in the future.

Scientists have been concerned about whether changing one element of DNA could trigger other unforeseen changes that are potentially detrimental. And at least one study has suggested that editing genes with CRISPR could cause many unpredictable genetic mutations, based on an analysis of small changes found in the genomes of mice that had been treated with gene therapy to cure their blindness. The idea for critics is that even though we are constantly learning more about human genetics, we do not have a full enough understanding to predict all the ways DNA could behave once we start tweaking genes.

Another criticism of advanced gene-editing technology is that it could be used on embryos and fetuses to make “designer babies,” with parents choosing their children’s hair and eye color, for example. Others focus on the devastating genetic diseases and birth defects that could be essentially erased while a baby is still developing.

Earlier this year, American scientists used CRISPR to delete disease-causing genetic mutations from human embryos, the first time that had been done in the U.S. The researchers then let the embryos develop for a few days, to watch their progress, before terminating them.