Genes linked to stuttering found

Three genes that play a part in the development of stuttering have been identified, which may lead to new forms of treatment.

Stuttering is a speech disorder in which a person repeats or prolongs sounds, syllables, or words, disrupting the normal flow of speech. It can severely hinder communication and a person's quality of life. Most children who stutter will outgrow stuttering, although many do not; roughly 1% 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. The latest study of volunteers in Pakistan, the US and England found three genes that could be a source of stuttering. Previous studies have indicated that mutations in two of these genes are in other rare metabolic disorders involving brain mechanisms.

These genes play a part in breaking down and recycling cellular components, a normal day to day activity in all higher animals. Two of them have already been tied to two serious metabolic diseases (ML disorders) that can ultimately cause joint, skeletal system, heart, liver, and other health problems as well as developmental problems in the brain. They are also known to cause problems with speech.

But for the disease to occur, the individual has to inherit copies from both parents, according to study leader Dr Drayna: "ML disorders are recessive. 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. Also, with stuttering, the protein is still made, but it's not made exactly right. With ML diseases, the proteins typically aren't made at all. Still, there are a few complexities remaining to be understood, and we'd like to learn more about them."

The researchers estimate that roughly 9% of people who stutter possess mutations in one of the three genes. Among the next steps, they are conducting a worldwide epidemiological study to better determine the percentage of people who carry one or more of these mutations. They are also conducting biochemical studies to determine specifically how the mutations affect the enzymes. A long-term goal is to use these findings to determine how this metabolic defect affects structures within the brain that are essential for fluent speech.

The study is reported in the online edition of the New England Journal of Medicine and carried out at the National Institutes of Health.

This article was published on Thu 11 February 2010