There are many theories and popular beliefs about the causes of stuttering. While researchers have made significant progress in identifying the conditions that are responsible for the onset of stuttering, the specific cause has not yet been established. The current thinking is that stuttering is a neurodevelopmental condition with multiple factors contributing to its onset.
Neurological studies find that there are differences in the activity that occurs in areas of the brain that support speech production in persons who are prone to stutter, compared to persons who do not stutter. These differences are detectable in the brains of young children, as stuttering begins. The precise nature of the differences is not yet known.
Factors that are thought to contribute or influence the onset and continuation of stuttering include genetics, language development and the environment. Researchers are also interested in how speech fluency is influenced by personality, temperament, behaviour, and other personal characteristics.
The relationship between genetics and stuttering has been of interest for years based on research showing that stuttering tends to run in families and that most persons who persist in stuttering are male. Not all genetically related members of the same family will stutter. Some stutter for a short time and recover, while others persist. A family history of stuttering is not essential for someone to begin to stutter, but it does present an increased risk.
Stuttering usually begins after children have been talking for some time. It emerges gradually or suddenly, and unexpectedly, as children begin to communicate using longer and more complex sentences. This suggests a relationship between language development and stuttering. The language skills of young children who stutter have been examined with varied results. While, some children present with language-related delays, others have advanced language skills; however, most are likely to have language skills that are within normal levels for their age. There is no evidence to support that bilingualism or multilingualism is a factor contributing to the onset of stuttering.
Environmental factors by themselves are unlikely to cause stuttering, but they may contribute in some way to exacerbate (i.e., make it temporarily more pronounced) and perpetuate stuttering. Like all humans, children and adults who stutter are subject to the influences and effects of surroundings, other people, circumstances, and life events. For example, it may be more difficult for persons prone to stutter to speak in situations where there is verbal competition or time pressure. Various combinations of environmental factors will contribute the frequency and severity of stuttering at specified times. There is no evidence to support that parenting style or family environments cause stuttering.
Research related to the causes of stuttering continues to guide professional efforts to develop effective treatments. Early intervention, before the age of 6 years, remains the best option for reducing, and even eliminating stuttering, preventing its long-term impacts. It may one day be possible to identify children who are at greater risk for continued stuttering closer to onset and to provide therapies that are better targeted to each child, reducing, or eliminating possible negative effects for children and parents soon after stuttering begins.