The data is compatible with polygenetic inheritance models and inconsistent with non-genetic forms of transmission such as learning by mimicry. The location of stuttered dysfluencies is not random. This is usually at the beginning of sentences and phrases. Certain maneuvers promote fluency in stutterers, such as singing, loud broadband noise during speech production, repetitive reading of the same passage, and speaking in cadence to a metronome. Thus far we have discussed developmental stuttering.
Some fluent individuals develop neurologic compromise and become stutterers.
Developmental stuttering is primarily a word-initiation phenomenon. The fragmentation of a word, prolongation of a sound at the beginning of a word or other word-type disruption, are hallmark features of developmental stuttering. These word-disruptions primarily occur at the beginning of sentences or phrases. The location of dysfluencies in developmental stutterers is different from the location of dysfluencies in individuals with acquired stuttering. The onset of stuttering in previously fluent adults, without history of any stuttering during childhood, is usually seen in neurologic disease, but also can occur in psychogenic disturbances.