By STEPHANIE NANO, Associated Press Writer Stephanie Nano, Associated Press Writer – 11 mins ago
NEW YORK – Why people stutter has long been a medical mystery, with the condition blamed over the years on emotional problems, overbearing parents and browbeating teachers. Now, for the first time, scientists have found genes that could explain some cases of stuttering.
"In terms of mythbusters, this is really an important step forward," said Jane Fraser, president of the Stuttering Foundation.
Researchers taking part in a government-funded study discovered mutations in three genes that appear to cause the speech problem in some people. Stuttering tends to run in families, and previous research suggested a genetic connection. But until now, researchers had not been able to pinpoint any culprit genes.
Dennis Drayna, a geneticist and senior author of the study, said he hopes the results help convince doubters that stuttering "is almost certainly a biological problem."
The research — released Wednesday by the New England Journal of Medicine — also points to a possible enzyme treatment for stuttering someday.
Without a known cause, stuttering has been attributed to such things as nervousness, lack of intelligence, stress or bad parenting. Stutterers were told it was all in their heads. Fraser said parents contact her group worried they have done something to cause their children's stuttering. Were they too strict? Too attentive? Didn't pay enough attention?
The gene discovery should lift that guilt, she said.
Drayna and other experts said that while stress and anxiety can make stuttering worse, they do not cause it. "It really is not an emotional disorder. It doesn't come from your interactions with other people," he said.
Stuttering usually starts in children as they are learning to talk. Most youngsters lose their stutter as their brain develops. For some, the stuttering persists. An estimated 3 million Americans stutter. Treatments include speech therapy and electronic devices.
"This is a very difficult disorder to study," said Drayna, who is with the National Institute on Deafness and Other Communication Disorders. "You can't study it in cells in a dish. You can't study it in a test tube. You can only study it in awake humans."
To find the genes, Drayna and others first looked at a large, inbred Pakistani family with many members who stuttered, and discovered a mutation on chromosome 12. Then they found the same mutation and two other mutated genes in a group of nearly 400 other people from Pakistan, the U.S. and England who stutter.
They didn't find the mutations in a similar group of people who don't stutter, except in one Pakistani volunteer.
The researchers estimate that the three gene variants account for 9 percent of all stuttering cases. But they are looking for other stuttering genes. In fact, between 50 percent and 70 percent of stuttering cases are thought to have a genetic component, Drayna said.
"The task of connecting the dots between genes and stuttering is just beginning," Simon E. Fisher of England's Oxford University wrote in an accompanying editorial.
The three implicated genes normally help run the "recycling bin" where cells of the body send their garbage. The mutations apparently interfere with that, affecting brain cells that control speech.
"People had suggested all sorts of causes for stuttering over the years. An inherited disorder of cell metabolism was never on anyone's list," Drayna said.
Two of the stuttering genes have previously been tied to rare diseases that can occur when the cell's recycling bin malfunctions.
Other related disorders are now being treated by replacing a missing enzyme, and that could eventually be a treatment method for some kinds of stuttering, the researchers said.
Kristin Chmela, a speech therapist from suburban Chicago who specializes in treating stuttering, said she was teased and bullied for her own stuttering while growing up, and "there were lots of days where I was afraid to go to school."
She said she is looking forward to sharing the gene discovery with those she treats: "It's going to be very interesting to see the reaction on some of their faces."
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On the Net:
New England Journal: http://www.nejm.org
Stuttering Foundation: http://www.stutteringhelp.org
Genes Behind Stuttering Found
posted: 10 February 2010 05:00 pm ET
Stuttering may have genetic underpinnings, according to a new study. For the first time, scientists have identified specific genetic alterations that they believe play a key role in giving rise to the speech disorder.
These alterations, or mutations, are located on three particular genes, and are thought to cause a glitch in the way cells dispose of cellular "garbage."
"For hundreds of years, the cause of stuttering has remained a mystery for researchers and health care professionals alike, not to mention people who stutter and their families," said Dr. James F. Battey, Jr., director of the National Institute on Deafness and Other Communication Disorders (NIDCD), the organization that led the study. "This is the first study to pinpoint specific gene mutations as the potential cause of stuttering," and might lead to an expansion in treatment options, he said.
The results were published online Feb. 10 in the New England Journal of Medicine.
Stuttering is a speech disorder in which a person repeats or prolongs sounds, syllables, or words, disrupting the normal flow of speech. The result can severely hinder communication. Most children who stutter outgrow it, although many do not; roughly 1 percent of adults stutter worldwide. Current therapies for adults who stutter have focused on such strategies as reducing anxiety, regulating breathing and rate of speech, and using electronic devices to help improve fluency.
Stuttering tends to run in families, and researchers have long suspected a genetic component. Previous studies of a group of families from Pakistan pointed to chromosome 12 as a site that may be involved in the disorder. (A chromosome is a long sequence of DNA that contains many genes.)
In the current study, researchers took a closer look at this chromosome. They identified mutations in a gene known as GNPTAB in the affected family members. The GNPTAB gene is carried by all higher animals, and gives cells instructions for making an enzyme that assists in breaking down and recycling cellular components.
They then analyzed the genes of 123 Pakistani individuals who stutter — 46 from the original families and 77 who are unrelated — as well as 96 unrelated Pakistanis who don't stutter, and who served as controls. Individuals from the United States and England also took part in the study, 270 who stutter and 276 who don't. The researchers found some individuals who stutter possessed the same mutation as that found in the large Pakistani family.
The scientists then looked at two other genes which are closely tied to the role of GNPTAB. They found individuals who stuttered showed mutations in these genes while control groups did not.
Several of the newly identified "stuttering genes" are thought to contribute to certain metabolic disorders. People with these disorders cannot properly break down cell waste, causing deposits to build up in their cells. These deposits can ultimately cause health problems in the body's joints, skeletal system, heart and liver, as well as developmental problems in the brain. They are also known to cause problems with speech.
So why don't people who stutter also have these metabolic disorders? For many of these metabolic diseases, a person needs to have two defective copies of a gene, said study author Dennis Drayna, a geneticist with the NIDCD. But in the current study, nearly all of the unrelated individuals who stuttered had only one copy of the mutated gene, he said.
The findings open new research avenues into possible treatments for stuttering. For example, current treatment methods for some metabolic disorders involve injecting a manufactured enzyme into a person's bloodstream to replace the missing enzyme. The researchers wonder if enzyme replacement therapy might be a possible method for treating some types of stuttering in the future.
Right now, about 9 percent of people who stutter are known to possess mutations in one of the three genes, the researchers say. Next, they plan to conduct a worldwide study to better determine the number of people who carry these mutations. A long-term goal is to better understand how metabolic defects may affect structures within the brain that are essential for fluent speech.
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