This is a landmark introduction to the facts and hopes of gene therapy: an exciting, albeit controversial, technique that could bring about a new age in medical treatment. Modern medicine has had relatively little to offer children with disorders such as thalassemia and severe combined immune deficiency. Many of these young patients still face repeated hospitalizations and, often, an early death. In gene therapy, a child with life-threatening genetic disease caused by a defect in a single gene will he treated with the gene's normal counterpart. Successful development of somatic cell gene...