Researchers have discovered a gene linked to stuttering, a speech disorder that afflicts an estimated one million adults worldwide. Scientists believe the finding raises hope that a drug might someday be developed to treat this disabling condition.
Researchers say the speech impediment appears to stem from a defect in the gene that regulates the way brain cells break down and recycle waste products. This abnormality interferes with the brain's ability to process speech.
Stuttering causes sufferers to get stuck repeating or prolonging sounds, syllables or words that interrupt the normal flow of speech.
Experts say most children who stutter seem to magically outgrow the disorder.
But for people who continue to stutter into adulthood, researcher Dennis Drayna of the US National Institute on Deafness and Other Communicable Disorders says stuttering can be profoundly disabling.
"I think in some cases it is hardly even viewed as a legitimate disorder," said Drayna. "You know people just dismiss it all the time when in fact it's a clear biological disorder that has very big influences on affected individuals."
Stuttering's cause has long been a mystery, but it has frequently been diagnosed as a psychological problem. Treatments have included strategies to reduce anxiety and stress, and the use of breathing exercises.
But stuttering tends to run in families, a fact that prompted Drayna and colleagues to search for a genetic link.
They homed in on a single gene, known as GNPTAB, which was defective in 46 members of a large Pakistani family. The abnormal gene also was found in 77 unrelated Pakistanis with the speech impediment.
In addition, the researchers found the same dysfunctional gene in a group of American and British stutterers.
Drayna says the GNPTAB gene is present in all higher-order animals and contributes to humans' unique ability to communicate.
"We're not the biggest. We're not the strongest. We're not the fastest. We don't have the best senses of vision or hearing. What it is, is our ability to communicate so we can form groups in communities and do much larger things than we could ever do as individual organisms," he added. "So when you destroy an individual's ability to communicate, you have really destroyed one of the most important aspects that we have as a species."
In addition to the abnormal GNPTAB gene, Drayna's research team discovered that several other defective genes associated with GNPTAB were also shared by the stutterers.
These genes are involved in a number of inherited metabolic disorders, including Tay Sachs, a rare, incurable and usually fatal disease that causes the destruction of nerve cells in young children.
Drayna says therapies to replace enzymes that cause the diseases have been developed to treat half a dozen of these metabolic disorders. He is hopeful there could eventually be a similar treatment for stuttering.
But in a published commentary on the research, Simon Fisher, a speech and language researcher at the Wellcome Trust Center for Human Genetics at Oxford University cautions that before researchers can develop a drug therapy for stuttering, they will need to learn much more about the precise biochemical mechanism of the disorder.
Fisher notes that not every stutterer in the Drayna study had the defective gene, meaning there must be a number of other genes tied to stuttering.
"What we can't say that this is a recessive or a dominant form," said Fisher. "All that we can say is that by carrying this particular variant, you have a greater chance of being a stutterer."
An article on the discovery of a gene associated with stuttering, and the commentary by Simon Fisher, are published this week in the New England Journal of Medicine.