Nearly all the patients with Sturge-Weber syndrome or port-wine stains had the mutation in affected areas of the skin or brain. Researchers almost never found the mutation on visibly normal skin or in people with neither the birthmark nor the syndrome.
The mutation is in the GNAQ gene, which makes a protein that is critical for cell signaling.
Researchers think that when the mutation happens very early in a baby's development, it may lead to the more severe Sturge-Weber syndrome. When it happens later, it causes port-wine stains, which can be disfiguring but usually don't lead to more extensive health issues.
Now that they have identified the mutation, doctors can start to look for drugs that will treat some of the problems it causes. Current treatments for Sturge-Weber aim to control symptoms, but don't always do the job.
"In half or more of the patients, their seizures are not fully or well-controlled," Comi said. "We have low-dose aspirin to try to prevent strokes. We're able to help the children, but we're certainly not able to prevent all the neurologic and ophthalmologic consequences of the condition."
Perhaps the most immediate consequence of the discovery may be that it lessens the guilt felt by many parents who believe they somehow caused their children's condition by passing it to them genetically.
"For some parents, it's going to be a huge relief," Ball said. "It's a huge lodestone that people carry for a while."
Ball said she didn't really feel the weight of her own guilt lift until recently, when she heard the news of the discovery.
"I didn't know if I had caused it," she said. "But I always felt that if I had caused it, then it was my responsibility to make it right."