Gene therapy is an experimental medical procedure that attempts to correct a genetic mutation (missing or changed genes) so that properly functioning genes are restored in cells. When gene therapy works, the correct instructions for building proteins (chemicals that direct and control chemical reactions in the body) become available to cells again, and the body returns to normal or healthier functioning.

Scientists began discussing the possibility of this method of curing disease in the 1960s. In 1970, American physician Stanfield Rogers of the Oak Ridge National Laboratory in Tennessee attempted to use gene therapy to treat two sisters who suffered from a genetic disorder. called argininemia. With this genetic disorder, the body lacks an enzyme (a type of protein) called arginase. People with this disorder may have seizures and mental decline. Rogers tried to treat the sisters by using a virus to deliver the healthy gene into their cells. In this case, gene therapy was unsuccessful.

In 1977, scientists were able to use gene therapy techniques to introduce a gene into mammalian cells. American physician W. French Anderson conducted one of the first human gene therapy studies in 1990 on a four-year-old girl with a rare genetic disorder of the immune system called severe combined immunodeficiency (SCID). The immune system fights infections from bacteria and viruses, and the disorder made it difficult for her body to stay healthy. Anderson and her team genetically altered her white blood cells and then returned them to her body. The new white blood cells strengthened the girl’s immune system and enabled her to survive.

Another setback for gene therapy occurred in 1999. An eighteen-year-old patient named Jesse Gelsinger participated in a gene therapy trial for a genetic disease called ornithine transcarboxylase deficiency (OTCD). This rare disease prevents the liver from breaking down ammonia, which can build up in the body and become toxic. Gelsinger died of organ failure four days after starting treatment. The researchers believe that his immune system reacted to the virus that carried the new gene into his cells.

In 2000, French researcher Alain Fischer was able to cure children of a similar type of immune system disorder. Fischer used retroviruses as gene carriers. Retroviruses are a type of virus that uses ribonucleic acid (RNA) as its genetic material, rather than DNA. Retroviruses produce an enzyme (a protein that controls a biochemical reaction) that builds DNA on an RNA strand. The best known of these retroviruses is the human immunodeficiency virus (HIV), the virus responsible for acquired immunodeficiency syndrome (AIDS). Fischer inserted a retrovirus carrying the normal gene into the children’s blood stem cells. Several months later, two of the children in the trial developed a leukemia-like disease (a type of cancer that begins in the cells that make blood cells). As a result, the US Food and Drug Administration (FDA) stopped the use of retroviruses in the United States.

Although research in this field has moved slowly, it has still advanced. In 2003, the first officially licensed gene therapy became available in China. Several types of gene therapy are awaiting approval from the US Food and Drug Administration.