"It can be [an] auditory or tactile or visual trigger -- and it's a system- or body-wide response, with different muscular responses through the body," said Hallett. "A patient with startle syndrome continues to have an exaggerated response even as the surprise ends."
There is no cure for the startle syndrome, but scientists say they understand it: Gene mutations work to prevent a chemical communication between nerves that calm the body down. Both the GABA and the glycine receptors work as "breaks" to the nervous system, but people with hyperekplexia can't get the signals from glycine.
"The glycine system acts like a break, and the [mutated] gene stops the system from working," said Thomas.
Doctors have discovered some of the genetic mutations that cause the condition.
Rita Shiang of the Department of Human and Molecular Genetics at Virginia Commonwealth University in Richmond, Va., part of the team that discovered the first gene associated with hyperekplexia in 1993, said she's not surprised scientists haven't found a cure yet.
"It's very hard to come up with a treatment [after finding a gene]," she said. "It takes a long time to figure out what's going on.
"People are always asking why you [would] study a rare disorder," she said. "But the more you know about these pathways, the more you understand about common disorders."
For the moment, many people with hyperekplexia can be treated with a very common drug: clonazepam, a member of the class of drugs called benzodiazepines that includes Valium.
Hallett said clonazepam works by increasing the effects of an alternative "breaking system" within the body: the GABA receptors.
Thomas said drinking [moderate amounts] of alcohol also can decrease symptoms.
"In the U.K., if [affected] people go out to a football game, they have to have a couple of drinks beforehand so they're not jumping all over the place," he said.
Unfortunately for Snyder, such drugs haven't worked. But she found networking with others has been therapeutic because hyperekplexia is so isolating.
"It can happen anywhere and everywhere. It's a scary thing to leave the house," said Snyder. "For the most part, I try to avoid going into public unless I have someone who I trust."