People have probably stuttered as long as humans have been able to speak. There's even an ancient Egyptian hieroglyph for stuttering.
Now scientists say they know why â€” at least some of the time. A report published online by the New England Journal of Medicine documents the first genes strongly linked to stuttering.
That may begin to lessen some of the misunderstandings and social stigma of stuttering.
The newly discovered gene mutations account for something like 9 percent of stuttering, the researchers say. That may not sound like much, but it's far more than accounted for so far by genes linked to other behavioral disorders, such as schizophrenia, depression or obsessive-compulsive disorder.
In The Family
And scientists think there are more stuttering genes to be discovered. After all, stuttering often runs in families.
Studies of families and twins show that the heritability of stuttering is "high to moderately high," says Dennis Drayna of the National Institute on Deafness and Other Communication Disorders, senior author of the new study. It's less heritable than tallness, but considerably more heritable than cholesterol level.
Drayna says most people â€” and many experts â€” probably don't think of stuttering as a genetic or inherited disorder.
"If you look at the literature on speculations about the cause of this disorder, what you see are things that are remarkably reminiscent of the causes of psychiatric disease in the 19th century," Drayna says. "Bad parenting. Overanxious mothers. There was never a whit of evidence to support these suggestions. But it's convenient to blame the parents, right?"
Stuttering Genes Linked To Rare Disorders
The researchers started their search for stuttering genes with a large Pakistani family, because one team member is a Pakistani specialist. They zeroed in on a portion of chromosome 12 as the likely place for stuttering mutations in this family. Closer analysis led them to a surprise.
The stuttering mutations clustered in three genes that are among the most-studied in all genetics. That's because they're involved with a large family of rare and usually fatal metabolic disorders known as lysosomal storage diseases. They include Tay-Sachs, Gaucher's disease, Hurler syndrome and Hunter syndrome.
"This was really quite a surprise," Drayna says. "We thought, 'Oh, it can't be this.' But in fact, it was."
So why don't these stuttering mutations wreak more metabolic havoc? Drayna and his colleagues don't know. Perhaps, they think, the mutations just gum up the workings of specific cells in the brain that govern speech.
Figuring that out could yield some big insights. "We believe we will learn a lot of important new things about the structures and functions inside the brain that give us the unique capability of speech," the NIH scientist says.
Wherever that research leads, specialists hope that finding stuttering genes will lead to better therapies. If stuttering mutations cause a missing or defective enzyme, for instance, maybe doctors will be able to replace it, as they already can with other lysosomal storage diseases.
For Many, Genetic Findings Are Liberating
But the very news that there is a genetic basis for much stuttering comes as a huge relief to many.
"Knowing that it has biological causes and that three genes have been found is pretty exciting," says Jane Fraser, president of the Stuttering Foundation of America.
Her father, Malcolm Fraser, a successful businessman, started the foundation in 1947 because of his own struggles with stuttering. The initial "F" of his own name gave him particular problems.
"One of the things that always worried him," Jane Fraser says, "was that he simply wasn't working hard enough. That if he just tried harder, he could keep himself from stuttering. Knowing that it has biological causes would lift a tremendous burden of guilt. I'm sure of it."
Kristin Chmela knows what she's talking about. She's worked a lifetime to overcome her own stuttering, and she can now, nearly all the time. She's also a certified "fluency therapist" in Long Grove, Ill., who treats other people who stutter.
"To be able to say that there is this truth, this biological cause of the problem, is pretty profound," Chmela says. "I think this is going to have a lot of implications, just psychologically, for a lot of my clients."