(CNN) -- A new study brings researchers one step closer to unraveling a medical mystery that has perplexed scientists for thousands of years: What causes people to stutter?

Research appearing in Wednesday's New England Journal of Medicine reveals three genetic mutations in the brain cells of people who stutter. The cells are located in the part of the brain that controls speech, which suggests that genes could play a big role in the disorder.

"People have looked for a cause of stuttering for 5,000 years," said Dennis Drayna, a researcher at the National Institute on Deafness and Other Communication Disorders, and a co-author of the study. "Many, many things have been suggested as a cause of stuttering. None of them have turned out to be true. For the first time today, we know one of the causes of this disorder."

"These mutations affect a process inside cells that degrades things that the cells don't need anymore," said Drayna. "This process is called the garbage can, or more like the recycling bin, of the cell. When this process gets interrupted, the cell goes haywire, and that causes problems."

These problems, according to the study, may explain why some people stutter.

Stuttering, also referred to as stammering, is a disruption in the normal flow of speaking. For people with the disorder, speech comes out in fits and starts, certain syllables may be prolonged or repeated, and for some, stuttering is accompanied by involuntary facial tics.

Previous studies have suggested genetics as one possible explanation for stuttering, along with developmental delays and confused speech processing in the brain. But that knowledge can only go so far, said Drayna.

"Just knowing a disorder is genetic doesn't really help us understand that disorder at a level that, for instance, doctors would like to know," said Drayna. "Once we have genes, we know much more about the causes of the disorder."

Knowing the genetic underpinnings of the disorder could unlock even more genes associated with stuttering, which could lead to more specific diagnosis and treatment.

"People who are helped by one type of therapy might for instance be the people with mutations in one of these genes, whereas the people who are helped by another therapy are people with mutations in another gene that we've identified," said Drayna. "For the first time we can now begin to ask this kind of question, why do some therapies work well in some people and not well in others?"

Roughly 3 million people in the United States stutter, according to the National Institutes of Health. About 60 percent of those with the disorder have a family member who also stutters. The condition is most common among children, although about 1 percent of people carry the condition through adulthood, according to the Stuttering Foundation of America.

Michael Liben, 25, has stuttered for as long as he can remember, "since I began speaking," said Liben, a law student in New York. "I remember my middle school graduation. It was my job to lead the Pledge of Allegiance and it took me a while to get started, and it was probably the lengthiest Pledge of Allegiance in the history of America."

Liben said he suspected a genetic connection with his stuttering -- his mother Sindy Liben also stutters -- but what is most encouraging to Liben, and the stuttering community in general, is the study's confirmation of what they already knew: Stuttering is a problem with neither social nor emotional origins.

"It's just great news for people who stutter to know that it's a gene," said Tammy Flores, executive director of the National Stuttering Association. "It's not anything else. It's a gene."

Added Drayna: "An important point that's reinforced by our findings is that stuttering, at its basis, is a biological disorder. Even today, people seem to think stuttering might be an emotional disorder, or even a social disorder, and it's really very unlikely that either of those two things are true. I think the sooner that stuttering is recognized as a biological disorder, people can get down to using that understanding ... to better treat the disorder."

In an editorial appearing in the journal, Simon E. Fisher, an investigator into molecular mechanisms underlying speech and language, poses the questions that linger despite the discovery of "stuttering genes": Why would dysfunction in certain cells affect how one speaks? Are there other undiscovered genes associated with stuttering? Could this discovery help us to understand whether early stutterers will continue to stutter through adulthood?

"As with other neurodevelopmental disorders that affect speech, the task of connecting the dots between genes and stuttering is just beginning," said Fisher, a fellow at the Wellcome Trust Centre for Human Genetics at Oxford University.

Drayna emphasized that finding the genes for stuttering does not automatically mean a cure, but that better treatment and diagnosis is on the horizon. Groups like the National Stuttering Association are excited nonetheless.

"[Stuttering is] something that you will be able to identify," said Flores. "You will be able to couple that with speech therapy and support groups, and get help. It's very, very exciting to have all of this happening now."