BOSTON Three genes linked to a rare metabolic disorder may also cause some cases of stuttering, researchers said on Wednesday in a finding that could lead to a new treatment for the speech condition.
Two of the genes are used by brain cells as part of a waste recycling process, the researchers reported in the New England Journal of Medicine. A third has no other known role.
"This is the first study to pinpoint specific gene mutations as the potential cause of stuttering, a disorder that affects 3 million Americans," Dr. James Battey, director of the National Institute on Deafness and Other Communication Disorders, said in a statement.
About 5 percent of preschoolers and 1 percent of adults stutter or stammer.
Researchers at the NIDCD, part of the U.S. National Institutes of Health, studied 123 Pakistani people with and without stuttering, including 46 from a family heavily affected by the condition. Then they compared their DNA to more than 500 people from the United States and Britain, half who stuttered and half who did not.
None of the people who did not stutter had the genetic mutations.
Doctors have known for years that genetics play a role in stuttering, a speech disorder in which a person repeats or prolongs sounds, syllables, or words.
Therapies include strategies as reducing anxiety, regulating breathing and rate of speech, and using electronic devices to help improve fluency. However, the study supports the idea that biological differences in the brain underlie stuttering.
This study may explain about 9 percent of cases.
Simon Fisher of Oxford University said many questions remain about how a waste disposal gene might translate into a stutter. "The task of connecting the dots between genes and stuttering is just beginning," he wrote in a commentary.
Two of the genes are involved in disorders called mucolipidosis II and mucolipidosis III, in which waste accumulates in cells, causing joint, heart, liver, speech and other problems.
But the volunteers in the study who stuttered were not ill because they only had one defective copy of the genes.
"ML disorders are recessive," geneticist Dennis Drayna of NIDCD, who led the study, said in a statement.
"You need to have two copies of a defective gene in order to get the disease. Nearly all of the unrelated individuals in our study who stuttered had only one copy of the mutation," he said.
(Editing by Maggie Fox and Eric Walsh)