Feb. 10, 2010 -- Researchers with the National Institutes of Health (NIH) have identified three genes that may predispose people to stuttering -- a condition that affects 3 million Americans and 5% of young children.
Because stuttering tends to run in families, it has long been suspected that genes play a role in the speech disorder.
In unique genetic research involving families with clusters of persistent stutterers, investigators with the NIH's National Institute on Deafness and Other Communication Disorders (NIDCD) identified a likely location of gene variants associated with the disorder.
In their latest research, the researchers found specific gene mutations that appear to lead to stuttering.
The findings appear today online in the New England Journal of Medicine.
Jane Fraser, president of the support and education group Stuttering Foundation of America, calls the identification of a genetic component associated with the disorder a big step forward.
"For adults who stutter this is huge because it proves there is a biological reason for stuttering," she tells WebMD. "So many people who stutter feel extreme guilt and think that if they just tried harder they could get over it."
She adds that for many parents of children who stutter, the news will come as a relief.
"Every day we get calls from parents asking what caused their child's stuttering," she says. "What they are really asking is, 'Did I cause it?' We can now say with a lot more assurance that the answer is no."
Normal speech involves a series of coordinated muscle movements associated with breathing, voice production, and movement of the throat, palate, tongue, and lips. These muscle movements are controlled by the brain and monitored through the senses of hearing and touch.
This normal speech is disrupted in stutterers, but the cause of this disruption has not been understood.
While stuttering affects all ages, it most often occurs in young children who are still learning verbal communication.
Roughly one in 20 children has the condition. Young boys are twice as likely to stutter as young girls; older boys are three to four times more likely to stutter than older girls.
Most children eventually outgrow stuttering; about 1% of adults stutter.
Identifying Genetic Mutations
In the newly published study, NIDCD geneticist Dennis Drayna, PhD, and colleagues built on earlier work involving 46 Pakistani families with large numbers of persistent stutterers.
They identified mutations in a gene known as GNPTAB in the family members who stuttered and looked for these gene mutations in 46 stutterers from the original families and 77 Pakistani stutterers that were not members of these families.
The study also included close to 550 stutterers and non-stutterers living in the United States and the U.K.
The GNPTAB mutations were present in many of the stutterers but in none of the non-stutterers.
The study also confirmed that mutations in two other genes -- GNPTG and NAGPA -- were common in stutterers but not in the non-stutterers.
Further analysis led the researchers to estimate that about 9% of people who stutter and have a family history of the condition have mutations in one of the three genes.
"To put that in context, there are about 3 million people in the U.S. who stutter," Drayna tells WebMD. "If half of that is due to genetics, that's 1.5 million people, so it could be expected that 145,000 Americans who stutter have a mutation in one of these genes."
The researchers hope to conduct an even larger investigation of stutterers across the globe to better understand the prevalence of these genetic mutations.
And Drayna says unpublished work from his group makes him optimistic that other stuttering genes will be identified soon.
"We identified three in this paper, but it is clear there are more genes on other chromosomes to be found," he says. "We think there is really a lot of hope for future progress in understanding the genetic causes of this disorder."
NIDCD Director James F. Battey Jr., MD, PhD, tells WebMD that such an understanding could soon lead to tests that identify children whose stuttering will persist into adulthood.
It could also lead to earlier treatment by better identifying children who probably won't grow out of stuttering.
Fraser says early treatment is critical for children with a strong family history of the disorder.
"By early I mean 2 to 4 years of age," she says. "If your therapist tells you to come back when the child is older, go find another therapist."