Stuttering linked to genetics, motor control
February 19th, 2011
05:14 PM ET

Stuttering linked to genetics, motor control

Jennifer McGuire remembers how, as a child, she would order only certain things at restaurants because they would be easier to say. McGuire, 30, has stuttered for as long as she can remember.

"Stuttering has colored my whole life," she said Saturday. "Only recently has it not been the first thing I think about when I get up in the morning and the last thing before I go to bed."

Stuttering typically starts around 2 to 4 years of age, after the stutterer already had learned language, which is why legendary psychoanalysist Sigmund Freud thought it had something to do with parenting or something else in the environment.

But scientists have found copious evidence that biological mechanisms in the brain can explain stuttering. They presented some of the more recent findings at the American Association for the Advancement of Science meeting in Washington, D.C.

Stuttering is the central issue in "The King's Speech," nominated for Oscars in 12 categories at next weekend's 83rd Annual Academy Awards. The film hits home for many people who have lived with a stutter.

About half of stutterers have a clear family history of this speech disorder, said Dennis Drayna of the National Institutes of Health. But Drayna thinks this is in an underestimate for the genetic influence.

Drayna's research on the genetics of stuttering has shown that genes that appear to be involved all control some aspect of cell metabolism. The mutations linked with it are also associated with genes for rare childhood diseases called mucolipidosis type 2 and type 3. Those who suffer type 2 typically don't live to the age of 10, those with type 3 live only into young adulthood. But it has been noted anecdotally that those who live to age 7 or 8 with type 2 often don't ever develop the ability to speak.

The brains of people who stutter seem to have particular signatures in function and structure. Luc De Nil of the University of Toronto and colleagues used functional magnetic resonance imaging to look at what's going on in the brains of children and adults who stutter. It seems that the speech-motor control region of the frontal cortex, the premotor cortex and the cerebellum are all involved, while there is an underactivation in the auditory cortex. There are also clear differences in stuttering adults and children in terms of brain anatomy: the gray matter cortex and white matter intercortical connections appear different in them. These underlying structural differences appear to explain at least some of the functional differences seen in these individuals. Moreover, patients who develop a stutter after a stroke often have lesions in the same areas of the brain implicated in stuttering, De Nil has found.

Stuttering also appears to be related to motor coordination. In an experiment with children, De Nil's group also found that children who stutter have more problems learning sequences of finger-tapping than those who do not have the speech disorder. Those who stutter have more difficulties with the timing of sequential movements.

This seems to be a problem in movements of the mouth and jaw, previous research has shown in people who stutter.

"We’ve been able to show that the discoordinations are present even when people who stutter speak fluently," he said.

It's possible that because motor coordination and stuttering are linked, the degree of a patient's motor deficiency may predict how well he or she will respond to stuttering treatment, De Nil said. This idea needs more research, however.

In as many as 75% to 80% of stuttering cases, a child will recover spontaneously from stuttering, and there's no clear reason why some do better than others, said Anne Smith, researcher at Purdue University. Parents should try to help their children immediately, rather than ignoring the problem, if they pick up on speech difficulties.

The most painful part of stuttering is blocking: When you open your mouth to try to say something and nothing comes out, she said. This can lead to a lot of stress. What stuttering does to a person’s self-confidence and freedom to speak is depicted well in "The King's Speech," De Nil said.

As for McGuire, she is now pregnant, and is paying close attention to the research regarding genetics and brain characteristics in stuttering. She finds it exciting.

"It would be great if my child ends up being a person who stutters, but is able to have it be less mysterious, and have access to effective therapies and an earlier stage in life."

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