Although the etiology of stuttering is not fully understood, there is strong evidence to suggest that it emerges from a combination of constitutional and environmental factors. Geneticists have found indications that a susceptibility to stuttering may be inherited and that it is most likely to occur in boys.1,2,3 Further support for inheritance comes from twin studies that have demonstrated a higher concordance for stuttering among both members of identical twin pairs than fraternal twin pairs.4,5 Congenital brain damage is also suspected to be a predisposing factor in some cases.1 For a large number of children who stutter, however, there is neither family history of the disorder nor clear evidence of brain damage.
Brain imaging studies conducted in many laboratories throughout the world indicate that adults who stutter show distinct anomalies in brain function.6,7,8 In contrast with normal speakers, individuals who stutter show deactivation of left-hemisphere sensorimotor centers and over-activation of homologous right-hemisphere structures during both stuttered and nonstuttered speech. The essential defect is hypothesized to be a lack of sensorimotor integration necessary to regulate the rapid movements of fluent speech. Both temporary fluency (induced through singing or choral reading) and more permanent fluency (as a result of behavioral treatments) appear to normalize the activation patterns.9 The onset of stuttering is typically during the period of intense speech and language development as the child is progressing from 2-word utterances to the use of complex sentences, generally between the ages of 2 to 5 but sometimes as early as 18 months. The child's efforts at learning to talk and the normal stresses of growing up may be the immediate precipitants of the brief repetitions, hesitations, and sound prolongations that characterize early stuttering as well as normal disfluency*. These first signs of stuttering gradually diminish and then disappear in most children, but some children continue to stutter. In fact, they may begin to exhibit longer and more physically tense speech behaviors as they respond to their speaking difficulties with embarrassment, fear, or frustration. If referral to a speech-language pathologist for parent counseling and treatment is made before the child has developed a serious social and emotional response to stuttering, prognosis for recovery is good.10,11,12
*The term 'disfluency' means a hesitation, interruption, or disruption in speech. It may be normal or, as in the case of stuttering, it may be abnormal.
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