Gene therapy is a new technology wherein a defective gene is replaced or supplemented with a normal gene. Such a technique would theoretically work for any disease caused by a single defective allele. The new gene is inserted into a cell in the affected tissue. For the gene therapy to be permanent, the cells that receive the replacement gene must be ones that multiply throughout the patient's life time so that the transplanted gene can be replicated and continuously expressed.

Gene therapy can be performed using recombinant DNA technology to insert the gene into the patient's body. Often, a retrovirus (one that contains the enzyme reverse transcriptase to change viral RNA to DNA) is used to carry the gene to the patient's cells.Currently, only about 1% of inserted genes reach their target cells. Those that reach their target cells may work inefficiently or produce insufficient protein so that the therapy may not work efficiently. To date, the number of patients receiving gene therapy treatments has increased dramatically, but no official cures have occurred.

The most promising trials underway in humans include those attempting to cure Severe Combined Immune Deficiency Syndrome (SCID). Untreated, SCID is normally lethal at an early age. Some bone marrow cells are removed from the patient, the normal gene is inserted by use of a retrovirus, and then returned by injection into the bone marrow of the upper arm. Infants treated with this method have remained healthy into early adulthood!

1. Should we treat human sperm or eggs in hope of correcting genetic defects in future generations? Such treatments currently are currently done in mice to create mice having human diseases for use in controlled studies.

2. Should we tamper with defective human genes in body cells, even when the resulting disease is life-threatening? Some argue that such treatments could lead to the practice of eugenics, which are deliperate attempts to control the genetic makeup of the human population.

3. Others state that gene therapies are fundamentally no different than the use of conventional medical treatments used to save lives (use of medicines or organ transplants).