Doctors made history recently when they used a technique called zinc-finger nucleases to cure a rare genetic disorder. Brian Madeux was diagnosed with Hunter syndrome, which is caused by the lack of a gene that is used to produce an enzyme that breaks down certain carbohydrates within the body. This leads to a build-up of carbohydrates in the body’s cells, causing numerous problems from hernias to eye infections and brain degeneration. While currently doctors are able to treat the condition by regularly injecting the missing enzyme into Madeux’s bloodstream in a procedure called gene boosting, the problem is the current procedure costs over $400,000 a year. And even if Madeux does receive regular doses of the missing enzyme, it does not reverse the damage that’s already been done, or any further deterioration to Madeux’s brain.

Dangamo Therapeutics have injected Madeux with harmless viruses carrying a package of gene-editing material in the hope to inject the missing gene in the right place in his DNA. This should give his liver the ability to produce the enzyme naturally. If successful, the new technique could be used to cure many dangerous and debilitating genetic disorders.