There is no known cause for stuttering. Theories about the causes of stuttering can be divided into three categories.
Stuttering could possibly be inherited, and 50% to 70% of all stutterers are related to another stutterer. 8 9 While having a stutterer in the family does not automatically create another stutterer, it has been shown to create "stuttering potential" or a "stuttering predisposition." This inherited genetic factor may cause the speech pathways in the brain to be less efficient, making it difficult for the stutterer to meet fluency demands and get his or her words out quickly. Genetics may also influence the temperament of some stutterers, which makes them react negatively to their own early stuttering behavior. In a 1999 study conducted jointly between U.S. and Australian researchers, hundreds of twins who stuttered were examined, with significant differences in concordance rates for stuttering being found between identical and fraternal twin pairs. Scientists are also working to identify the "stuttering genes", largely through the Stuttering Research Project at the University of Illinois.