Genes are the basic unit of heredity. They carry the chemical instructions that determine the form and function of each cell. Through gene therapy, doctors can provide a new set of instructions for treated cells. Every human cell has an estimated 50,000 to 100,000 genes. Genetic diseases result when a gene is defective or missing, causing affected cells to malfunction.
Gene therapy makes it possible to correct such defects in the function of cells.
Gene therapy is in the early stages of development but offers hope of treating or preventing genetic diseases that today are incurable. There are thousands of known genetic diseases. They include muscular dystrophy, cystic fibrosis, hemophilia, and some forms of cancer and cardiovascular disease. Doctors first used gene therapy as a treatment in 1990. Scientists at the National Institutes of Health in Bethesda, Maryland, inserted a normal human ADA gene into immune cells taken from the girl's body.