How a Rare Brain Mutation Spread Across America

Of the three Bowlin sisters, Margaret, the middle one, was the first to show signs. She began having seizures as a toddler. Then the eldest, Bettina, had a brief and mysterious episode of weakness in her right hand. In 1986, as an adult, she had a two-week migraine that got so bad, she couldn’t hold food in her mouth or money in her right hand. The youngest, Susan, felt fine, but her parents still took her for an exam in 1989, when she was 19. A brain scan found abnormal clusters of blood vessels that, as it turned out, were in her sisters’ brains too. These malformations in the brain can be silent. But they can also leak or, worse, burst without warning, causing the seizures, migraines, and strokelike symptoms Bettina and Margaret experienced. If the bleeding in the brain gets bad enough, it can be deadly.

At the time, doctors could not tell the Bowlins exactly what was wrong, only that they suspected it ran in the family. The girls’ father, Jerry Bowlin, had the same malformations in his brain (though he had no symptoms), and he knew of an uncle with epilepsy. To understand his daughters’ afflictions, he began mapping out a family tree. Jerry asked around his family and, later, reconnected with long-lost cousins through Facebook, and he kept hearing more stories of seizures and strokelike illnesses. But even as the family tree filled out, the exact cause of these malformations remained elusive.

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