Stuttering: incidence and causes

Abstract

Definition Stuttering, or stammering as it is also referred to, is a devel-opmental speech disorder, which usually appears in chil-dren between the ages of 3 and 8 years. More often than not it remits before puberty, but it can persist into adult life. 1 Stuttering is characterized by involuntary syllable repeti-tions, syllable prolongations, or interruptions (blocks) in the smooth flow of speech. There may sometimes be difficulty in differentiating infants who definitely stutter from those who show the dysfluency often seen in infancy as a normal stage of speech development. However, the two are distinct. 2 The overall frequency of dysfluency, the proportion and duration of dysfluency types, and the associated behaviours not directly related to speech such as eye, head, and body move-ments, can help to distinguish between the two. 3 There has certainly been controversy over the exact definition of stut-tering when selecting participants for research studies. 4 Wingate 5 criticized Yairi and coworkers 6–8 for not being strict enough in their selection of affected children and for including those who were classified as having stutter-like dysfluencies, especially whole-word repetitions. However, Yairi and colleagues 9 refuted these claims, stating that although syllable repetitions are the most common compo-nent of stuttering, whole-word repetitions do occur in stut-tering and therefore this is not a criteria for exclusion. In fact, whole-word repetitions seem to be more common when the onset of stuttering is early in life. 10 Incidence of stuttering It is usually accepted that the overall incidence of stuttering is about 1%, but in the preschool and school populations it is around 4%, and at all ages seems to be more common among males than females. About 80% of those who stutter will out-grow their disability, but there is no way of guaranteeing that this will happen. 11 Young 12 concluded that the 80% recovery rate is an overestimate as retrospective studies are not likely to yield verifiable data. According to recent American reports, stuttering affects more than 15% of children in the age range of 4 to 6 years, dropping to 1 to 2% among adults. 14 A study of stuttering in a university population in Boston, USA, found prevalence to be 2.1%. 11 Also, 3.4% of those questioned had previously experi-enced a problem with stuttering. More males than females stuttered and right-handed females who stuttered were less likely to have lost their stutter than were right-handed males. All had a family history of stuttering and, at that time, there was no evidence of a decline of the disorder over the previous few decades in spite of an increased number of speech clinics in the area. In 1984 no decreasing trend was reported. 13 In a survey of children in junior and senior schools in Alabama, USA, twice as many black students had speech disor-ders, such as stuttering and articulatory problems, as white students, 15 and among 793 adults in the UK with significant learning disorders, 6.3% were dysfluent for no definite rea-son. These included examples of stuttering, cluttering, and atypical dysfluencies – the first group being the largest. 16 Another study involved 9930 pupils from 150 schools for children with hearing impairments. Only 12 of these children were said to stutter: three in the oral mode only, six in manual communication only with effortless repetition using sign lan-guage, and three in both modes. Of those dysfluent in the manual mode, only one child was reported to repeat the first syllable and show perseverations and incoordinate manipula-tions. There was also blocking on some signs with difficulty in continuing through the block. One child had weakness in motor skills, which caused signs to be jerky and hesitant, and another child was described as beginning a sign and then stopping and repeating it. The findings, although intriguing, are open to criticism: those on manual dysfluency were not based on any particular standard and the language level of the children was not given so that some of the results may have been within the normal limits of a child in the early stages of language learning, or be due to other neuromotor deficits. 17