Bleed no more

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Medical researchers in England and the U.S. have just reported their successful treatment of six hemophilia-B patients using gene therapy a major breakthrough in the treatment of the disease.

Hemophilia-B, the second most common type of hemophilia, is a type of hereditary bleeding disorder that affects only males due to its linkage to the X-chromosome. The gene defect leads to the absence of an essential blood clotting factor known as factor IX. In the current study, published in The New England Journal of Medicine, researchers used a specific virus (adenovirus chosen because it would not provoke an immune response) to convey the intact gene for the clotting factor into their patients liver cells. The missing factor IX is normally synthesized in the liver, and the gene delivered there by the virus was, in this study, able to replace the defective gene.

Twenty-two months after the treatment, five out of the six patients had continued to produce their own clotting factor, although only four patients had levels sufficient to discontinue other treatments. ACSH s Dr. Ross notes that, Even though the gene therapy led to only a 2 percent production of the clotting factor compared to normal levels, that is enough to reduce bleeding risk and allow patients to live a fairly normal life without frequent infusions of donated serum clotting factor.

Risks, however, remain, since patients undergoing this treatment cannot be injected with the same virus another time, as their immune systems will now be primed to attack it. Nevertheless, given the initial success rate of this preliminary trial, the researchers as well as the scientific community at large are optimistic.

Gene therapy, the method of replacing a person s defective gene with an intact version of it, has for some time been a theoretically enticing idea. However, over the course of 20 years of research, researchers have had little success actually implementing the method. Though Dr. Ross agrees that the results of this study are a major breakthrough, he, like others, thinks that they need to be replicated in a larger group of patients. The success of gene therapy in this instance, he says, suggests the possibility of similar treatments for other genetic diseases. It s very good news.