Two of the holy grails of medicine - stem cell technology and precision gene therapy - have been united for the first time in humans, say scientists.
It means patients with a genetic disease could, one day, be treated with their own cells. A study in Nature corrected a mutation in stem cells made from a patient with a liver disease.
At the moment, stem cells created from a patient with a genetic illness cannot be used to cure the disease as those cells would also contain the corrupted genetic code.
Researchers said this was a "critical step" towards devising treatments, but safety tests were still needed.
Scientists at the Wellcome Trust Sanger Institute and the University of Cambridge were working on cirrhotic liver disease. It is caused by a change to a single pair of letters, out of the six billion which make up the genetic code. As a result, a protein which protects the body from damage, antitrypsin, cannot escape from the liver where it is made.
The illness is one of the most common genetic diseases, affecting one in 2,000 people in Europe. The only solution is a liver transplant, but this requires a lifetime of drugs to prevent organ rejection.
The research group took a skin cell from a patient and converted it to a stem cell. A molecular scalpel was used to cut out the single mutation and insert the right letter - correcting the genetic fault. The stem cells were then turned into liver cells. One of the lead researchers, Prof. David Lomas, said: "They functioned beautifully with normal secretion and function". When the cells were placed into mice, they were still working correctly six weeks later.
Lomas said if this could be developed into a therapy it would be preferable to liver transplant as the patient would not need to take immunosuppressant drugs. He told the BBC that the technique was "ridiculously hard," yet "the potential is enormous, but only time will tell".
Further animal studies and human clinical trials would be needed before any treatment as "the key thing is safety". For example, concerns have been raised about "induced" stem cells being prone to expressing cancer causing genes.
Prof. Robin Ali, from University College London and the Medical Research Council's stem cell translational research committee, said: "It's very interesting. Most gene therapy is not correcting the gene, it's introducing a new copy of the gene, what's exciting is that this corrects. The big problem with individualised medicine is the cost - that is one of the major barriers."