For the first time ever, scientists have attempted to cure a person’s disease by editing a gene inside the body in a bid to permanently alter the patient’s DNA. Forty-four-year-old Brian Madeux, who has a metabolic disease called Hunter syndrome, was the subject of the first such experiment in California on Monday, the Associated Press reports. Scientists used an IV to inject Madeux with billions of copies of a corrective gene and a genetic tool to cut his DNA in a specific spot. “We cut your DNA, open it up, insert a gene, stitch it back up. Invisible mending,” Sandy Macrae, president of Sangamo Therapeutics, the California company testing the method, told the Associated Press. Scientists have edited people’s genes in the past, but that work involved altering cells inside a lab and then returning them to the body, whereas the latest experiment was performed inside a person’s body. The results of such gene editing won’t be clear until tests are done in three months, and experts say the risks of such irreversible gene tinkering are still not entirely clear.