Government researchers have discovered the first genes linked to stuttering -- a complex of three mutated genes that may be responsible for one in every 11 stuttering cases, especially in people of Asian descent.
Studies of stuttering in both families and twins had long suggested that stuttering has a significant genetic component. But until now, scientists had not been able to identify specific genes that might cause the disorder.
The finding is important, experts said, because it shows that stuttering, which affects as many as 1% of all adults worldwide, is biological in origin and not the result of poor parenting, emotional distress or other nebulous factors that many physicians have cited as causes.
"We hear every day from parents worried that they have caused their child's stuttering," Jane Fraser, president of the Stuttering Foundation, said in a statement. "Parents don't cause stuttering, and this research could lift the burden of guilt from their shoulders."
Surprisingly, the newly identified genes play a role in clearing metabolic wastes out of brain cells, and when a person has two mutated copies of them, they cause a lethal disease.
Down the road, the research could help identify children who are likely to develop stuttering problems, allowing early initiation of treatments that can minimize or eliminate the problem.
Even further in the future, it could lead to new treatments to overcome the biological underpinnings of the disorder.
But those goals are still far away. "The task of connecting the dots between genes and stuttering is just beginning," wrote geneticist Simon E. Fisher of Oxford University in an editorial accompanying the report in the New England Journal of Medicine.
Stuttering is marked by the involuntary repetition or prolongation of sounds, syllables, words or phrases, as well as frequent pauses, impeding the fluency of speech. An estimated 5% of children develop stuttering between the ages of 3 and 6, but most either grow out of it or are successfully treated.
The problems can be exacerbated by stress and anxiety, but most researchers now believe that those are not the underlying causes.
Researchers estimate that about 50% to 70% of stuttering is genetic in origin, so there must be many other genes that play a role.
The lead author of the study, geneticist Dennis Drayna of the National Institute on Deafness and Other Communication Disorders, speculated that it might eventually be possible to screen at-risk children for the presence of the genes so that therapy can be initiated earlier.