Gene therapy, which aims to patch faulty genes with working DNA, has been a long time in development. The following are major milestones: 1972 - Researchers first suggest gene therapy as a treatment for genetic diseases but oppose its use in humans "for the foreseeable future", pending greater understanding of the technology. 1990 - A four-year-old girl with severe immunodeficiency became the first patient to undergo gene therapy in the United States.