Gene therapy is the name applied to the treatment of inherited diseases by corrective genetic engineering of the dysfunctional genes. It is part of a broader field called genetic medicine, which involves the screening, diagnosis, prevention and treatment of hereditary conditions in humans. The results of genetic screening can pinpoint a potential problem to which gene therapy can sometimes offer a solution. Genetic defects are significant in the total field of medicine, with up to 15 out of every 100 newborn infants having a hereditary disorder of greater or lesser severity. More than 2000 genetically distinct inherited defects have been classified so far, including diabetes, cystic fibrosis, haemophilia, sickle-call anemia, phenylketonuria, Down syndrome and cancer. By the end of 1993, techniques involving gene therapy had been approved for use on such diseases as severe combined immune deficiency (SCID), familial hypercholesterolemia, cystic fibrosis, and Gaucher's disease. Many protocols are being developed...