Genes that cause stuttering identified

From The Times in the UK. Marilyn Monroe (pictured) was a well-known stutterer.

A set of genes that appears to raise the risk of stuttering has been identified, paving the way for completely new forms of treatment.

Three different genetic variants that are linked to the disorder, which affects about 1 per cent of the adult population in Britain, have been identified by an international team of scientists. The variants are thought to account for about 9 per cent of the genetic risk of stuttering.

Repeating or prolonging sounds, syllables or words tends to run in families, and scientists have long suspected a genetic component. Therapies focusing on strategies to reduce anxiety, regulate breathing and pace speech evenly have mixed success.

The findings suggest that in some cases] the condition could be the result of a glitch in the day-to-day process by which fats and carbohydrates are broken down in key regions of the brain.

Dennis Drayna, of the US National Institute on Deafness and Other Communication Disorders, who helped to lead the study, said: “For the first time we have pinpointed the cells and molecules that underline it.”

A genetic explanation for why some people stutter could help to tailor treatments. Dr Drayna said: “We have identified one subset of genes. In future, we could subdivide groups of individuals whose therapy could be better tuned to their genetic constitution.”

The results, published in the journal Nature, also point towards at least one potential cause for stuttering. Two of the genes identified, GNPTAB and GNPTG, are involved in breaking down and recycling important enzymes inside cells. The genes have been linked to two serious metabolic diseases known as mucolipidosis II and III, in which abnormal amounts of carbohydrates or fatty materials accumulate in cells, leading to skeletal deformities and severe learning disabilities. Records show that patients with mucolipidosis II are generally unable to speak, providing further evidence for a link between these genes and the ability to communicate.

Confirming the link would open up the possibility of developing pharmacological treatments for stuttering that would synthetically replace enzyme deficiencies that arise from the gene mutation.

Mucolipidosis patients have mutations on both copies of the genes, while in the study the individuals who stuttered only had a mutation on one copy of the genes and a normal version on their other copy. This could explain why people who stutter do not have any of the physical symptoms of mucolipidosis.

It is not clear why the mutation would specifically affect speech in the brain and leave other brain functions perfectly intact. The team is now looking in the mouse brain to see in which particular regions the gene is most expressed, which could provide clues about the role it plays in controlling speech.

Kate Watkins, a neuroscientist at the University of Oxford, who specialises in speech and language, said: “There have been a quite number of studies on stuttering and genetics but this is the first to actually find specific mutations.”