Ask the Experts; August 2008; Scientific American Magazine; by Arthur Nienhuis, James BeMiller; 1 Page(s)

Gene therapy is the addition of new genes to a patient¿s cells to replace missing or malfunctioning genes. Researchers typically use a virus to carry the genetic cargo into cells, because that is what viruses evolved to do with their own genetic material.

Doctors can perform the treatment, first tested in humans in 1990, inside or outside the body. In the former case, they may inject the gene-carrying virus directly into the region that has defective cells. This approach is useful in therapies for Parkinson's disease, for instance, in which only part of the brain must be targeted.