adulthood in at least 20% of affected children. The mean onset of stuttering is 30 months. Although there is variability, early stuttering behaviours usually consist of word or syllable repetitions, while secondary behaviours such as tension, avoidance or escape behaviours are absent. Most young children are unaware of the interruptions in their speech. With young stutterers, disfluency may be episodic, and periods of stuttering are followed by periods of relatively decreased disfluency. Though the rate of early recovery is very high, with time a young person who stutters may transition from easy, relaxed repetition to more tense and effortful stuttering, including blocks and prolongations. Some propose that parental reactions may affect the development of a chronic stutter. Recommendations to "slow down", "take a breath", "say it again", etc., may increase the child's anxiety and fear, leading to more difficulties with speaking and, in the "cycle of stuttering," to yet more fear, anxiety and expectation of stuttering. With time secondary stuttering, including escape behaviours such as eye blinking and lip movements, may be used, as well as fear and avoidance of sounds, words, people, or speaking situations. Eventually, many become fully aware of their disorder and begin to identify themselves as stutterers. With this may come deeper frustration, embarrassment and shame. Other, rarer patterns of stuttering development have been described, including sudden onset with the child being unable to speak, despite attempts to do so. The child usually is unable to utter the first sound of a sentence, and shows high levels of awareness and frustration. Another variety also begins suddenly with frequent word and phrase repetition, and does not include the development of secondary stuttering behaviours. Neurogenic stuttering Some stuttering is also believed to be caused by neurophysiology. Neurogenic stuttering is a type of fluency disorder in which a person has difficulty in producing speech in a normal, smooth fashion. Individuals with fluency disorders may have speech that sounds fragmented or halting, with frequent interruptions and difficulty producing words without effort or struggle. Neurogenic stuttering typically appears following some sort of injury or disease to the central nervous system. Injuries to the brain and spinal cord, including cortex, subcortex, cerebellum, and even the neural pathway regions. Acquired stuttering In rare cases, stuttering may be acquired in adulthood as the result of a neurological event such as a head injury, tumour, stroke, or drug use. The stuttering has different characteristics from