Technique To Fix DNA Flaws Is Tested

Inspired by the body's own system for fixing genetic glitches, scientists at a company in California have made a molecular repair kit that corrects mutations in a cell's DNA. In experiments with human cells harboring mutations such as those that cause a fatal childhood disease, the new system fixed the broken genes in up to 20 percent of the tested cells. That is a level of efficiency hundreds of times better than previous experiments using other approaches, and one probably adequate to elicit a cure if the technique were to be used on an actual patient, the scientists reported yesterday. The team is only now beginning to assess the technique in live animals, a prerequisite for the human testing the company hopes to begin next year. But if it works as well in mice as it does in laboratory dishes, experts said, the approach could become a serious competitor to conventional gene therapy. That field, which attempts to force-feed healthy genes into cells hobbled by defective ones, has been plagued by failure for more than a decade and recently was found to cause leukemia in some patients. By contrast, the new system simply rewrites the small stretch of "misspelled" genetic code that is typically the reason a gene has gone bad. "This is the first time anyone has been able to precisely and with high efficiency edit the human genome," said study leader Michael Holmes, director of the gene modification group at Sangamo BioSciences Inc., of Richmond, Calif., which funded the study.