CHAMPAIGN, Ill. -- Genetics appears to be a principal factor in the development and persistence of stuttering, say researchers at the University of Illinois and the University of Chicago.
The likelihood a child will begin to stutter and the likelihood of continuing depend a lot on the family tree and the child's gender, the researchers report in an article in this month's issue of the Journal of Speech and Hearing Research.
After surveying the extended families of 66 children who stuttered, then analyzing the findings against models of how genetically based traits are passed on, the researchers concluded "there is something genetic underlying the transmission of stuttering in general, and that most people who stutter have that factor," said Nicoline Ambrose, a research associate with the Stuttering Research Project at the U. of I. and the lead author of the article. They further concluded that "people who persist in stuttering have additional genetic factors that are prompting them to persist," Ambrose said, "and those factors are much more common in males than females." About 2.5 million Americans stutter.
Their models suggest that susceptibility to stuttering results from the large influence of one gene, combined with the smaller effect from a small group of other genes, Ambrose said. "It's not saying there is a single stuttering gene," Ambrose noted, "but there is a gene that has a big effect on the transmission of susceptibility to stuttering." The next phase of their research, supported by the National Institutes of Health, will involve DNA testing that they hope will lead to identifying that gene, she said.
Co-authors of the article are Nancy Cox, a geneticist at the U. of C. School of Medicine, and Ehud Yairi, a U. of I. professor of speech and hearing science and principal investigator for the decade-long Stuttering Research Project. Supported by NIH grants since 1989, the project is one of the few long-term studies of children who begin to stutter, having collected data on more than 150 children so far. The project has examined numerous areas, such as speech, language, and emotional and cognitive development.
Researchers long have known that stuttering tends to run in families and that persistent stuttering is much more common in males than females, by a ratio of 4 or 5 to 1, said Yairi, a persistent stutterer himself. The common belief, however, has been that the family link came not from genes but from family attitudes, he said. It's been thought that parents with a family history of stuttering tend to overreact to a child's normal speech repetitions, causing a reaction that leads to real stuttering.
About five in every 100 children will begin to stutter at some point, most before age 5. About four of those five will stop within a few years, Yairi said. One, however, will become persistent, struggling with a disorder in which speech problems are "only the tip of the iceberg," he said. Finding clues as to which kids will persist -- the aim of the overall project -- will help to target them for early intervention. The genetic link "is so far the single strongest, consistent, reliable predictor that we have," Yairi said.