The neurological glitches behind stuttering: Causes and arising treatments

Including President Joe Biden, Emily Blunt, and James Earl Jones, stuttering affects over 70 million people, including 3 million Americans. Denoted by continuous interruptions in the starting and timing of syllabi, stuttering can have dramatic effects. About five percent of children stutter, but approximately 80 percent recover from stuttering by the time they reach adulthood, resulting in one percent of the world’s adult population being stutterers according to a 2004 study in PLoS Biology. Additionally, with adults, there are four times as many male stutterers as female stutterers. While scientists are still not certain on the exact causes of stuttering, there are new theories behind stuttering’s origin, such as issues in brain circuitry, excess dopamine absorption, and even genetic inheritance. 

The default mode network… seems to interrupt the signals between the areas of the brain that take part in formulating movements and attention to tasks.

One section of the brain’s circuit system that may be unique in those who stutter is the default mode network. The default mode network, which is involved in analyzing the past and contemplating the future, seems to interrupt the signals between the areas of the brain that take part in formulating movements and attention to tasks. Literally, the brain interrupts its own signals, and this is translated into interruptions in speech patterns. 

There may also be a genetic connection to stuttering. Researchers investigated a region of chromosome 12 in those who stutter, and a mutation found in the GNPTAB gene may be connected to stuttering. Investigating a largely inbred family, a 2011 study by Dennis Drayna and Changsoo Kang found that a single mutation in the coding sequence of the GNPTAB gene resulted in the insertion of a positively charged lysine amino acid in place of a negatively charged glutamic acid component. Since an analysis of the GNPTAB protein in all other species revealed that glutamic acid was present, it was inferred that this small change has substantial effects on the functionality of the protein. When investigating other individuals, the same mutation was common in other stutterers and was not present in non-stuttering control subjects. Mutations in the GNPTAB gene have been linked to diseases that cause degeneration of bodily tissue, including the brain. In severe mutations, individuals do not live long and never develop the ability to speak. It is hypothesized that a smaller mutation in the GNPTAB gene may lead to issues in speech development, but further studies are needed to test the biochemical functionality of the mutated enzymes and determine if these result in stuttering.

Another arising theory behind the cause of stuttering is excess dopamine activity in the basal ganglia, a complex network in the brain that is involved in the control of movement. Stuttering has overlapping symptoms to Tourette’s syndrome, a movement disorder where individuals experience an involuntary expression of actions and vocal sounds. Tourette’s syndrome has been associated with excess dopamine and therefore has been treated with antidopaminergic drugs such as olanzapine and risperidone, according to a 2014 study in Hospital Pharmacy and a 2018 study in Psychiatry and Neurological Sciences. Antidopaminergic drugs suppress dopamine receptors’ ability to absorb dopamine and have also been implemented in treating some individuals that stutter. So far, results have been strongly positive for reducing stuttering. However, there are also issues with olanzapine and its possible role in inducing stuttering in individuals reported in a case study from the Ankara Numune Training and Research Hospital in Turkey. A new drug, ecopipam, appears to suppress D1 dopamine receptors, which may relieve some of the harsher side effects of the other antidopaminergics. In a research study of 10 volunteers, ecopipam appeared to be effective in lowering the number of syllabi stuttered in the volunteers, with an average decrease of nine percent of syllabi mispronounced before and after taking the drug for eight weeks. However, much more testing is required to verify the effects of ecopipam on stuttering.

Overall, stuttering is still not very well understood, but research is in the works to improve the livelihoods of those affected by the condition. New therapies and drugs are being investigated and show positive results, so it may not be long until stuttering is a glitch of the past.

Hospital Pharmacy in SAGE Journals (2014). DOI: 10.1310/hpj4903-242.

Journal of Neurodevelopmental Disorders (2011). DOI:  10.1007/s11689-011-9090-7

Journal of Psychiatry and Neurological Sciences (2018). DOI: 10.5350/DAJPN2018310410

PLoS Biology (2004). DOI: 10.1371/journal.pbio.0020046