Dennis Drayna giving a keynote presentation at the BSA conference 2006.

Genetics - how stammering can run in families
Dennis Drayna, Keynote speaker at BSA's 2006 conference
National Institute on Deafness and Other Communication Disorders
National Institutes of Health

"Understanding the underlying causes of stuttering will be a tremendous aid in designing new and better therapies. Even before this point, having good genetic markers for stuttering could help with stuttering diagnosis, identifying those that stutter because of genetic factors. These could help identify individuals at risk in families, and help get early intervention started in those who need it most. It's an exciting time in stuttering research. We have good reason to hope for better understanding of this age-old problem within the coming few years," Dr Drayna told the Stuttering Foundation of America.

He has led two recent studies in genetics, looking at large families where stammering is more common than usual. Studies of large family clusters in Pakistan have identified a specific location for a gene on chromosome 12 that seems to be an important contributor to stuttering in this population. Of particular interest will be what the gene codes for, and how it acts, both in stutterers and in normally fluent individuals.

Studies in Cameroon, West Africa, identified a family of 100 individuals, 45 of whom stutter. Further studies have identified another four large families, of whom almost half stutter. All the families found so far come from a single region in Cameroon's northwest province, suggesting there might be some common inherited factor at work in these families.

"Even though most stuttering doesn't seem to occur in such large family groups, finding the cause of stuttering in these families may provide important clues to the identity of other causes of this puzzling disorder," said Dr. Drayna.

In a recent presentation to the American Speech-Language-Hearing Association, he said that severity does not cluster in families. "In other words, if you have a family member who stutters, you are more likely to stutter. However, if you have a family member who stutters severely, his or her severity does not put you at additional risk for stuttering nor does it relate to the severity of your own stuttering."

He also highlighted another interesting finding that suggested that genetic transmission of stuttering affects females almost as frequently as males, and that the male-to-female ratio is much higher, probably 7 or 8 males for every 1 female, for individuals with no family history of stuttering.

Despite this genetic evidence, however, Dr. Drayna cautioned that most human medical problems are a combination of genes and "something else," such as environment or learning. Also, geneticists who study stuttering are almost certain that there are many genes that contribute to stuttering rather than one particular gene having most responsibility. For example, there are over 100 genes that cause deafness.

Reference:
Riaz, N., Steinberg S., Ahmad, J., Pluzhnikov, A., Raizuddin, S., Cox, N., and D. Drayna. Genomewide significant linkage to stuttering on chromosome 12. American Journal of Human Genetics. 76:647-651 (2005)

Acknowledgements: This article was gratefully compiled from reports on the Stuttering Foundation of America website. For a list of articles and the full text, go to: www.stutteringhelp.org/Default.aspx?tabid=35

From the Autumn 2006 edition of Speaking Out, page 11

See also: Research links: genetics