In the past, stuttering has been viewed and treated as a single disorder, but a series of University of Illinois studies is helping change that.
One study, entering its fifth year, is shedding light on different types of stuttering. Another is looking at variations in the structure of the brains of people who stutter.
Now, the UI researchers are turning their attention to the role genetics may play in making someone susceptible to stuttering.
"The most likely scenario is that there are one or more genes that contribute, they have a major effect, and a number of other genes that have a smaller effect," UI speech and hearing science Professor Nicoline Ambrose said recently.
Ambrose and UI Professor Ehud Yairi, working with researchers at the University of Chicago, have examined chromosomes in DNA extracted from blood samples of people who stutter and identified possible locations of genes that may affect stuttering. The results were published this spring in the American Journal of Human Genetics.
Yairi said previous studies of stuttering in twins and families provided a statistical basis for thinking stuttering has a genetic, as well as environmental, component.
"There was a justification to move into genetic biology," he said.
The next step is to look more closely at the interesting chromosomal sites and, eventually, to identify specific genes.
Among other things, they found that the locations differed among males and females. That jibes with something stuttering researchers had found already, before genetic testing arrived – that males tended to exhibit stuttering more than females and that females tended to have a better chance of recovering naturally, Yairi said.
He said there are indications as well that more than one general combination of genetic factors may influence stuttering, and that the specific combination involved influences where someone falls in subcategories of stuttering – those who recover naturally at a young age and persistent stutterers who are affected through adulthood, for instance.
The study is part of a nearly $2 million program funded by the National Institutes of Health's National Institute on Deafness and Other Communication Disorders, and headed by University of Chicago Professor Nancy Cox and Ambrose. The international project also involves researchers in Sweden and Israel.
Meanwhile, the UI researchers are in the fifth year of a five-year $4 million program to illuminate subcategories of stuttering and examine such factors as language and motor skills, temperament and personality, and stuttering within families. Yairi got the project started before "retiring" and turning it over to Ambrose, who serves as principal investigator.
In conjunction with the stuttering subtypes study, Kenneth Watkin, a UI professor who specializes in medical imaging, and former UI graduate student Soo Eun Chang, now at the National Institutes of Health, used magnetic resonance imaging to examine the brains of people who stutter.
The researchers have imaged the brains of volunteers ranging from kids to folks 60 and older who stutter persistently.
Yairi and Watkin said a small sample of the latter appears to show differences in the fibers connecting the left and right sides of the brain.
"We really need to explore this more fully," Watkin said. "It's an exciting time for us. The technology continues to grow and we can continue to ask more and more refined questions."
The UI researchers are looking for more people willing to participate in the studies – those 60 and older and kids who stutter, in particular – although Ambrose said that with a number of ongoing projects they can use a pool of potential participants of any age.
Those interested in participating can contact Ambrose at nambrose[AT]uiuc.edu or 244-2559 or Yairi at 244-2547.