Gene Therapy for Hemophilics

Scientists reported that an experimental gene-replacement procedure appears to improve blood clotting in hemophiliacs without triggering complications. Researchers injected patients with a healthy gene to stimulate production of a blood-clotting protein. Just three patients participated in the experiment.

About 5,000 Americans suffer from hemophilia B. They produce insufficient levels of a clotting protein known as Factor IX. As a result, blood leaks into their joints. Many patients are disabled by age 30.

Researchers believe hemophilia B is suitable for gene therapy because the factor IX gene is small and a healthy copy can be easily substituted. Also, levels of factor IX as low as 1 percent of normal can improve blood clotting, so the new gene does not have to work perfectly to be effective.

Researchers injected a healthy factor IX gene into the patients' thigh muscles. The gene had been incorporated into a low dose of a simple virus that has never been associated with human disease. As the virus spread, it copied the healthy gene into the patients' cells. Tthe healthy gene was producing effective levels of factor IX in two patients within 12 weeks. Their reliance on clotting medication was reduced 50 percent and 80 percent. The third patient showed no improvement.