Stuttering and Genetics

Feb 24 2011 Published by under Brain & Behavior

Ever since the release of the award-winning movie The King's Speech, there has been a lot of discussion about stuttering in the media.

The movie is the fictionalized story of the struggle of King George VI - "Bertie" to his family - to overcome his stuttering with speech therapy.  That summary doesn't make it sound particularly interesting, but I found the story to be quite engaging. By the end I was rooting for Bertie to make it through his big speech.

It's estimated that almost 1% of adults stutter, just like Bertie. After decades of research, the underlying causes are only beginning to be understood.

At this past week's annual meeting of the American Association for the Advancement of Science (AAAS) in Washington DC, there was a symposium that focused on recent developments in cross-disciplinary stuttering research.  The most interesting study discussed in that session looked at how genetics may contribute to the speech disorder.

NIH geneticist Dennis Drayna and his colleagues have been studying closely-related families in Pakistan. They discovered three mutations associated with stuttering in those families. The three affected genes - GNPTAB, GNPTG, and NAGPA - are involved in directing glycoproteins to the lysosomes. Lysosomes are tiny organelles inside the cell that break down waste material and cellular debris. If the proper glycoproteins don't end up in the lysosomes, carbohydrates and fatty materials can build up to toxic levels in the body's cells.

It was already known that some mutations in GNPTAB and GNPTG cause mucolipidosis, a disease that affects both neurological and physical development.  In its severest form, mucolipidosis causes mental retardation and skeletal deformities. The people who carry the mutations in GNPTAB and GNPTG associated with stuttering don't have the severe neurological and physical problems associated with mucolipidosis.

It's not entirely clear how the mutations in genes involved in cellular metabolism might affect the development of the brain and cause speech problems, so there's still a lot of research to be done. But no matter what the mechanism is, finding these mutations provides support to the idea that the cause of stuttering is primarily physiological rather than behavioral or psychological.

But these genes are only a small part of the story.  Only about 6% of stutterers carry a mutation in GNPTAB, GNPTG or NAGPA.  Drayna's team and other research labs are searching for  additional associated mutations.  The hope is that the ongoing research into the genetics of stuttering will ultimately lead to new effective therapies.

Listen to the  AAAS Podcast on "The Mysteries of Stuttering" for more about the research presented at the symposium.

Additional reading:
• Michael Palin: "Stuttering: It's on everyone's lips now" Los Angeles Times (2011)

• Howell P. "Listen to the lessons of The King's Speech" Nature 470 (7) (2011) doi:10.1038/470007a

* Schenkman L. "First Gene Mutations Linked to Stuttering"  (Science NOW 2010)

• Willyard C. "Ancient Mutation to Blame for Stuttering" (Science NOW 2011)

• You can find more information about current research and resources for stutterers on the Stuttering Foundation of America's web site.   The National Institutes of Health also provides information on stuttering.

• Read the original research article: Kang C. et al. "Mutations in the Lysosomal Enzyme-Targeting Pathway and Persistent Stuttering" N Engl J Med 362:677-685 (2010)  doi: 10.1056/NEJMoa0902630 (free full text)

• Learn more about the research presented at the 2011 AAAS Meeting.

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