Gene therapy dilemma: Treatment that halts brain disease can also cause cancer

Rare and fatal, the genetic disease known as cerebral adrenoleukodystrophy (ALD) devastates the brain in young boys. A mutation on the X chromosome leads to a buildup of fats that damage the insulation around nerve cells, leading to seizures, blindness, and often death by age 20. Now, a new study finds a promising treatment for the condition carries a substantial risk of cancer.

Two years ago, U.S. regulators approved a gene therapy that can halt ALD. But there were concerns that the treatment could cause cancer. A study published today in The New England Journal of Medicine (NEJM) confirms those fears, finding that 10% of the boys in two of its trials have since developed blood cancer, most likely as a result of the virus used to ferry a therapeutic gene into their cells.

The find poses a difficult choice for parents: Opt for the gene therapy, for which its manufacturer, bluebird bio, charges $3 million, or try an older and also risky treatment. “This disease can go very quickly and you have to stop the progression,” says...