Gene Therapy Gene therapy refers to the process of changing human genetic material to repair or compensate for the effects of a mutation or abnormality. For example, a gene therapy for a single gene disorder might aim to replace the mutated copy of the gene with a normal one. Because gene therapy aims to alter only some cells in an individual (those affected by the genetic condition), and because it seeks primarily to relieve the suffering of disease, there are generally less ethical objections.   The challenge facing genetic medicines is daunting. First, they must somehow deliver their genetic payload into enough cells to do some good. Retroviruses seemed well suited for this task, because these kinds of viruses normally infect cells by copying part of their DNA into the genetic code of a host cell. Most early trials of genetic medicines therefore co-opted retroviruses, replacing their harmful parts with genes intended to help treat a disease, such as cystic fibrosis or brain cancer. But viral drugs can take effect only if they can slip past the multilayered defenses of the human immune system. First comes an onslaught of antibodies soon after any familiar virus is detected in the bloodstream. These antibodies quickly bind up the virus and can also cause side effects such as inflammation. Viral particles that make it to target cells face a second obstacle: a tough membrane shielding the cell's DNA from attackers. Finally, those retroviruses that are lucky enough to make it past the immune defenses and to infect cells do so in an unpredictable manner; they typically will insert the therapeutic gene at a random position in the cell's DNA. The new gene might interrupt an important sequence, actually harming the cell. Even in the best case, new genes often end up in dormant stretches of DNA where they do not get switched on frequently enough to make much of a difference to the patient. Research in gene therapy is moving forward, and there are many promising new approaches being investigated. They are all theoretical or experimental at this time, and have not been proven clinically. While the future will likely bring some successful ways of treating disease by fixing mutated genes or compensating for their dysfunction, the lesson of years of research is that it is extremely difficult to alter human genetic information, even in very limited ways.   The current state of technology makes gene therapy still an evolving hope for the future. This does not mean that the ethical questions raised by genetic engineering and gene therapy are not worth discussing. Rather, we are fortunate to have the opportunity to explore these issues and, hopefully, form thoughtful policies and beliefs regarding gene therapy and genetic engineering, before technology makes these procedures a reality. However, it is also important to remain calm and informed about the difference between science fiction and science fact.