Thursday, May 1, 2008

Gene Therapy: Struggling to Leave the Past Behind

Gene therapy is a relatively new method of treatment that involves replacing the defective allele of a gene with a functional one. The technique, originally thought to hold great potential for the treatment of genetic diseases, was at first greeted with excitement and enthusiasm. This enthusiasm continued to grow after the first successful administration of gene therapy in 1990, to improve the health of four-year old Ashanthi Desilva (born with severe combined immunodeficiency).

Since then, however, gene therapy has had its ups and downs, hitting rock bottom with the death of 19-year old Jesse Gelsinger in 1990. Gelsinger wasn’t in a life or death situation. He volunteered for the study because of a brush with death he had early in life due to a genetically inherited liver disease. He volunteered with the hopes that a cure would relieve others from suffering through some of the trials he had as a young boy. Gelsinger, however, wasn’t informed of some of the possible dangers of the treatment he was about to undergo—dangers that the scientists involved in the study were cognizant of. They neglected to tell him, and he died several days after treatment.

Since then, gene therapy has struggled to creep out from under the shadow of that dark incident. Continued successes, however, indicate that gene therapy may still have the opportunity to live up to its once heralded potential. One example is a study reported this week in the New England Journal of Medicine that describes successfully using gene therapy to restore vision in three young adults born with severe blindness.

The subjects suffer from a disease known as Leber congenital amaurosis (LCA), which usually leads to complete blindness by middle age and is thought to be caused by a mutation in a gene called retinal pigment epithelium 65 (RPE65). The gene encodes for a protein that converts vitamin A into a form that can be used by the rods and cones of the eye to make rhodopsin (a pigment that absorbs light).

The researchers injected one eye of each patient with a harmless virus carrying the healthy form of the RPE65 gene. After only two weeks, all of the participants reported improved vision in dimly lit environments. Within six weeks, some of the patients were able to read several lines of an eye chart or navigate an obstacle course—dramatic improvements over their previous levels of legal blindness. The researchers involved suggest that, due to the efficacy of this treatment, it could eventually be applied to other eye disorders, such as macular degeneration.

Every advance made in the use of gene therapy is a major one, as after the death of Jesse Gelsinger, many were quick to condemn the use of the procedure as unsafe and irresponsible. While the scientists involved in the Gelsinger debacle deserve those criticisms, the procedure itself holds great promise for understanding and ameliorating some of the worst afflictions humans face. Hopefully one day the number of lives improved and saved through the use of gene therapy will soften the sting of the egregious mistakes made in its early history.

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