Gene therapy shows promise against blood-clotting disease

Gene therapy has freed 10 men from nearly all symptoms of hemophilia for a year so far, in a study that fuels hopes that a one-time treatment can give long-lasting help and perhaps even cure the blood disease.

Hemophilia almost always strikes males and is caused by lack of a gene that makes a protein needed for blood to clot. Small cuts or bruises can be life-threatening, and many people need treatments once or more a week to prevent serious bleeding.

The therapy supplies the missing gene, using a virus that’s been modified so it won’t cause illness but ferries the DNA instructions to liver cells, which use them to make the clotting factor. The treatment is given through an IV.

In a study published Wednesday by the New England Journal of Medicine, all 10 men given the therapy now make clotting factor in the normal range. Bleeding episodes were reduced from about one a month before gene therapy to less than one a year. Nine of the 10 no longer need clotting factor treatments, and the 10th needs far...