Dr. Kahn and his colleagues studied cerebral cavernous malformations as part of a larger effort to understand the development and function of blood vessels.

These brain defects occur in as many as one in 100 people, most of whom have no known genetic abnormality. Most learn they have the condition when they have a brain M.R.I. for something unrelated, like a blow to the head.

Some experience a symptom, like a seizure, because the bubble is leaking blood, or a stroke because it bursts. (An aneurysm is similar, but it forms in an artery.)

The only treatment is surgery, assuming the malformation is in an accessible area of the brain.

Up to 20 percent of patients have a family history of this brain defect, and in them the disease is much more aggressive.

They may have a few of these malformations — or thousands. Even babies can have strokes when the blood-filled bubbles burst.

Three genes have been linked to the disorder, and Dr. Kahn and his colleagues tried to figure out what these mutations really do. The scientists were able to mimic the condition in mice by deleting a gene that is mutated in many patients.

A year ago, the scientists moved to a new building, and something unexpected happened. The experimental mice stopped developing the brain malformations.