What Causes Stuttering?
Joseph Agan, visiting assistant professor of communication disorders in the College of Education and Health Professions, replies:
Developmental stuttering is characterized by an abnormally high frequency and/or duration of stoppages in the fluent, forward flow of speech. These disfluencies typically take the form of repetition of sounds, syllables or one-syllable words; prolongation of sounds (i.e., sssssip); or blocks of airflow or voicing in speech. Researchers estimate that a minute of speech involves between 10,000 to 15,000 neuromuscular events. It is amazing that most speakers are able to focus on what they are saying and not how they are saying it.
Developmental stuttering often emerges between the ages of two to five, when children’s spoken language skills become both increasingly linguistically complex and socially sophisticated. Of those children who stutter, about 75 percent will recover fluent speech without intervention within a few months of onset. An estimated 1 percent of the population develops a chronic or persistent fluency disorder that we typically think of as ‘stuttering’. Chronic stuttering evolves over time to include increased muscular tension and struggle. Stutterers learn escape and avoidance behaviors to avoid stuttering moments that result in negative social responses.
But what causes stuttering? Multiple factors may cause stuttering in children who have a neurophysiological predisposition for stuttering. Different constitutional factors may be present in people who become persistent stutterers. A dys-synchrony in the neural substrate for speech and language production is thought to affect children predisposed to stutter. In people who stutter chronically, researchers have proposed that a reactive temperament makes these individuals more likely to associate negative past speaking experiences with certain speaking situations. They then employ strategies that result in more frequent and severe stuttering episodes.
The physiological mechanisms suspected of being compromised in stuttering remain a mystery. However, evidence suggests that stuttering has a genetic basis. Recently, Denis Drayna of the National Stuttering Foundation and a researcher with the National Institute on Deafness and Other Communication Disorders has discovered three genes linked to stuttering. Mutations in two of the genes have been linked to a rare metabolic disorder. Stuttering may result from a glitch in the process of recycling cellular components in key areas of the brain essential for fluent speech. Understanding how these metabolic defects affect fluent speech could lead to new treatment approaches for stuttering.
More information on stuttering can be obtained from the National Stuttering Foundation Web site.