Stuttering is a neurodevelopmental disorder characterized by pauses and repeated sounds or words, which disrupt the normal flow of speech, causing great embarrassment for some sufferers. For 1 in 4 children who experience early stuttering, the condition persists as a lifelong speech problem, with as many as one percent of adults in the United States affected by stuttering.
It is believed stuttering stems from problems with the circuits in the brain which control speech, however, precisely how and where these problems occur is unknown.
Astrocytes’ key role in stuttering
Now, a study led by researchers at the NIH shows a loss of cells in the brain called astrocytes are associated with stuttering in mice. The team states their study in mice, engineered with a human gene mutation previously linked to stuttering, offers insights into the neurological deficits associated with stuttering. The study is published in the journal Proceedings of the National Academy of Sciences.
Previous studies show neuroimaging has identified differences in the brains of people who stutter compared to those who do not. The brain imaging studies of people who stutter are important, however, these imaging studies cannot decipher if the differences contribute to stuttering or are an effect of stuttering. The current study shows the loss of astrocytes in the corpus callosum, a part of the brain providing a bridge between the two hemispheres, is linked to stuttering in engineered mice.
The current study utilizes mice engineered with the human GNPTAB gene mutation, previously linked to stuttering. Results show a decrease in astrocytes, supportive brain cells which play a critical role in supporting nerve cells, in brain tissue in the animals with the genetic mutation compared to the mice without the mutation. Data findings show the loss of astrocytes was more pronounced in the corpus callosum, a brain region known to help to integrate signals for language between both hemispheres of the brain.
The lab states using advanced magnetic resonance imaging (MRI) methods, they detected reduced local volume of the corpus callosum in the mutant mice. These readings were in contrast to the normal diffusion tensor MRI values gained, providing further support for a defect in this brain region.
They go on to add experiments where GNPTAB gene was introduced into individual brain cell types, rather than the entire mouse, confirmed the vocalization defect is specific to astrocytes. This finding was confirmed by the fact the mice did not have a stutter when the mutation was engineered into other types of brain cells.
The team surmises their data shows mice carrying the human stuttering gene derive from abnormalities in astrocytes, particularly in the corpus callosum. For the future, the researchers state their findings could open the door to new therapeutic strategies for some people with persistent developmental stuttering by targeting associated molecular pathways and cells.
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