Frederick R. Rickles, M.D., chief of the division of hematology and oncology and professor of medicine at the University of Connecticut School of Medicine, points out that the replacement gene would not have to work perfectly to be beneficial. If you convert someone from less than 1 percent clotting factor, which defines severe hemophilia, to 5 percent, which is mild hemophilia . . . Gene therapy for hemophilia has yet to be tried in humans. Studies in the laboratory and in experimental animals involving factor VIII and IX genes seem to show that the technique works, but it's too soon to tell for sure. A person with hemophilia lacks one of the dozen or so factors that cause blood to clot.
Treatment consists of intravenous infusion of the missing factor and is now usually done at home.
When and how much antihemophilic factor patients need depends on the severity of their disease. In severe hemophilia, clotting factor activity is less than 1 percent of normal. Injury, surgery, or dental care can present significant problems requiring treatment. Spontaneous bleeding can require infusion of factor concentrate as often as several times a week in severe hemophilia. In mild hemophilia, factor activity ranges between 5 and 50 percent of normal.