It is the most treasured and joyous sound for nearly every parent: their child's laughter. But for a rare number of children, laughter can signal a potentially devastating, even fatal future, and their parents will do anything to make the laughter stop.
"The giggling when he was young was such an endearing type of a giggle that we thought it was his normal giggling," Robin Dysart of San Antonio, Texas, said about son Keagan, who is now 9. "Until we realized he was giggling at inappropriate times. There wouldn't be anything to laugh about."
Karen Williams of Toronto noticed the same strange behavior in her son, Mateo, who is now 7.
"There's a forcedness to it," she said. "It almost looks like there's something else that's possessing the laughter."
They are called gelastic seizures, and appear as spontaneous, uncontrollable and often maniacal giggles or laughter. They are short and unpredictable. The cause: a rare form of epilepsy called Hypothalamic Hamartoma (HH) in which a non-cancerous lesion wreaks havoc in a highly sensitive area near the brain's stem. HH affects just on in one million children and, too often, the laughter goes undiagnosed.
The Dysarts have video of Keagan swimming. It looks innocent enough until you hear an odd giggle as the little boy struggles to stay above water.
"He's in his own little world, he's enjoying himself, and he's entertaining himself," Keagan's father, Chris Dysart, said he thought at that time.
Added his wife, Robin: "What's wrong with giggling?"
As each boy grew up, the strange giggling persisted. Some of Keagan's school teachers reprimanded him early on for his inappropriate laughter, according to his parents. Both families drifted in the medical wilderness looking for answers.
Finally, one neurologist told the Dysarts that Keagan's strange laughter wasn't funny at all but potentially dangerous. "I couldn't understand how they could call these seizures, at first," Robin Dysart said. "He's not convulsing, he's not on the floor, like everybody thinks of a seizure, like grand maul seizures, all these uncontrollable things. How can this be a seizure?"
Mateo's parents got even less information from their Canadian doctors.
"It's a child being a child," one doctor told them. Unsatisfied, Karen Williams hunted on the Internet for clues.
"And when you type in 'laughing episode,' anything to do with unexplained laughter, gelastic seizures came up. And when you typed in 'gelastic seizures,' benign brain tumor came up, and that's when the magnitude of it really hit us," Williams said.
Left untreated, the laughing seizures caused by HH can cause long-term behavioral and cognitive damage. Some children grow up so debilitated that they live with their parents. Some have even been institutionalized.
For Robin Dysart, tears would stream out of her as she contemplated Keagan's future.
"The thing that always scared me the most was just this stereotypical image of a homeless, crazy person that has that maniacal laugh and nobody accepts him," she said. "To be a parent of a child who's unaccepted; I can't explain it."
Keagan and Mateo were treated with anti-epileptic drugs. But it didn't stop the laughing. And both boys developed other kinds of seizures, such as tonic or panic seizures that occurred up to six times a day.
"He [struggled] everyday to hold it together," Williams said of Mateo, a hyper little boy who found sanctuary playing hockey and soccer.
Keagan always loved taking the school bus. He asked his father one day whether he could walk to the bus stop on his own. His parents would normally accompany him to the corner because of his seizures.
Moments after Keagan took off on his own, the phone rang: It was the school's transportation department. Keagan had seized and collapsed before getting on the bus.
"I had no clues what was going on," Chris Dysart said. "I tried to wake my son up, and he's not responding, I mean, not responding in the least bit. At that point, I was like, 'We've got to do something.'"
For years, little could be done to stop the laughing seizures, short of an invasive craniotomy. Fraught with danger, the brain is separated, carved open and the lesion, deep in the brain's center, cut out. The risks are every parent's nightmare: a possible loss of sight, uncontrollable urination, stroke and even death if the kidneys shut down.
"And that's what led us to want to explore new technologies to be able to get to these deep centers in the brain, without having to do traditional surgery," said Dr. Angus Wilfong, the medical director at the Comprehensive Epilepsy Program at Texas Children's Hospital in Houston.
Now there is hope. For the first time, in an experimental pilot program at Texas Children's Hospital, doctors are using real time MRI-guided lasers to destroy lesions that cause laughing seizures in epilepsy patients like Mateo and Keagan.
"So the new techniques, this MRI-guided laser ablation have increased our accuracy and our safety and our worry factor," said neurosurgeon Dr. Daniel Curry, who, along with Wilfong, is behind this potential breakthrough.
It's a journey to the center of the brain. With MRI imaging guiding their every move, doctors drill a small hole the size of a pencil into the child's skull inserting a laser probe and then guide it to the lesion. The lesion is destroyed in a matter of seconds and a lifetime of misery and suffering averted.
This Friday, "20/20's" cameras take you inside this amazing new surgery. "It's curing epilepsy at the speed of light. So, it really is a new world," Wilfong of Texas Children's Hospital said.
Keagan and Mateo underwent the surgery -- Keagan last year at age 8 and Mateo earlier this year at age 7. Today, both boys are seizure free, filled with real laughter, the kind parents don't want to stop.
"Robin and I were in the kitchen and then we hear this laughter," Chris Dysart remembered shortly after Keagan had the laser ablation surgery. "And Robin and I just kind of tensed up and froze. And we walk around into the living room, and he was laughing, like really laughing, at the TV show, and at appropriate times.
"And I think Robin and I just sat there in tears for about five, 10 minutes, because this was the first time we'd heard him laugh. And he wasn't having a seizure."
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