The First Gene Therapy to Cure a Fatal Brain Disease

Gene therapy has now been used to cure a fatal brain disease called adrenoleukodystrophy (ALD), a genetic disorder that occurs in approximately one in 20,000 boys. Even more startling is that the vectors used to deliver the normal form of the ALD gene to the boy's cells are disabled viruses similar to the AIDS virus, called lentiviruses.

In the new technique, hematopoietic (blood-forming) stem cells are removed from the patient's bone marrow and exposed to lentiviruses that contain normal copies of the ALD gene. (Lentiviruses are used because like the AIDS virus, they are better than most other viruses at inserting genes into cells.) The stem cells are then returned to the patient's bone marrow, where they grow and multiply.

Now for the really interesting part. Some of the corrected stem cells make their way to the brain, where (apparently because of the environment there) they develop into neural supporting cells called glial cells, correcting the original defect in glial cell formation.

The timing of treatment is critical, however. It takes about a year between initial diagnosis and the time the treatment is effective. Unfortunately, ALD can progress so fast that patients who already have obvious symptoms of the disease may not be able to be saved. The best candidates for a cure are patients who (by virtue of hereditary history) are thought to be at risk for the disease, and whose only signs of the disease so far are changes in their brain scans.