A study of the genetic and environmental etiology of stuttering in a selected twin sample

Stuttering is a developmental disorder of speech production that usually emerges in childhood. In this study, a large population-based twin sample from the Australian Twin Registry (1567 pairs and 634 singles aged 17-29 years) was screened to identify twin pairs in which one or both members reported themselves to be affected by stuttering. Telephone interview-based diagnoses were obtained for 457 of these individuals (self-reported affected cases, cotwins, and controls) to determine whether the self-report was correct. To correct for ascertainment bias we carried out a bivariate analysis of the final diagnosis in the selected sample with the screening item in the full sample, using the categorical raw data option of Mx 1.47c. After correcting for ascertainment bias, approximately 70% (95% confidence interval: 39-86%) of the variance in liability to stuttering was found to be attributable to additive genetic effects, with the remainder due to nonshared environmental effects.

The genetic basis of persistence and recovery in stuttering

Although past research has provided evidence of a genetic component to the transmission of susceptibility to stuttering, the relationship between the genetic component to stuttering and persistence and recovery in the disorder has remained unclear. In an attempt to characterize this relationship, the immediate and extended families of 66 stuttering children were investigated to determine frequencies of cases of persistent and recovered stuttering. Pedigree analysis and segregation analysis were used to examine patterns of transmission. The following questions were investigated: 1. Is there a sex effect in recovery from stuttering? Here, we sought to test the hypothesis that females are more likely to recover than males, leading to the change in sex ratio from approximately 2:1 males to females close to onset of the disorder, to 4 or 5:1 in adulthood. 2. Is persistence/recovery in stuttering transmitted in families? If recovery/ persistence appears to be transmitted, (a) are recovered and persistent stuttering independent disorders?; (b) is recovery a genetically milder form of persistent stuttering?; or (c) is persistence/recovery transmitted independent of the primary susceptibility to stuttering? Results indicated sharply different sex ratios of persistent versus recovered stutterers in that recovery among females is more frequent than among males. It was found that recovery or persistence is indeed transmitted, and further, that recovery does not appear to be a genetically milder form of stuttering, nor do the two types of stuttering appear to be genetically independent disorders. Data are most consistent with the hypothesis that persistent and recovered stuttering possess a common genetic etiology, and that persistence is, in part, due to additional genetic factors. Segregation analyses supported these conclusions and provided statistical evidence for both a single major locus and polygenic component for persistent and recovered stuttering.

Genetics of stuttering: a critical review

The fact that stuttering runs in families has been documented over a long period and has led to speculations and research about the role of a genetic component to this disorder. Although the genetic factor cannot be proved by familial aggregation and twin studies alone, such research has continued to provide support for a relationship between stuttering and genetics. The purposes of this article are to review and critique the research in this area. The article first assesses research methodologies that have been employed in familial studies of stuttering. It proceeds to review and critique incidence, twin, and aggregation studies. In addition, it includes sections on subgroups, genetic models of stuttering, and implications for future research as well as for clinical work. With a focus on improved methodology and recent findings, a current perspective on our knowledge of the genetic component to stuttering is provided. Among other conclusions, the article emphasizes that failure to consider epidemiologic factors has probably biased previous results regarding the genetics of stuttering. New preliminary data also appear to provide evidence that spontaneous recovery and chronicity are influenced by genetic factors. Generally, however, the review of incidence and twin studies, as well as of evidence for the various inheritance models, confirms previous conclusions about the interaction between genetic and environmental factors in stuttering.

Stuttering may be a type of action dystonia

We observed abnormal involuntary movements, involving principally the facial and neck muscles, in 23 patients with stuttering. These movements were similar to involuntary movements seen in distinct dystonic syndromes. There was a history of stuttering in the first degree relatives of six patients. The association of stuttering with degenerative neurologic disorders and focal brain lesions, cerebral blood flow changes in patients with developmental stuttering, its occurrence as a side effect of centrally acting drugs, induction and alleviation of stuttering by mechanical perturbation, or by electrical stimulation of the thalamus, a strong genetic predisposition with male preponderance, and the statistically significant occurrence of stuttering in the family history of patients with idiopathic torsion dystonia suggest an organic basis for developmental stuttering. These findings and the reported similarities between the involuntary movements associated with stuttering and dystonic involuntary movements support the hypothesis that stuttering is a form of segmental or focal action dystonia.

Predictive factors of persistence and recovery: pathways of childhood stuttering

This article presents broad preliminary findings from a longitudinal study of stuttering pertaining to differentiation of developmental paths of childhood stuttering, as well as possible early prediction of High Risk, Low Risk, and No Risk for chronic stuttering. More than 100 preschool children who stutter have been closely followed for several years from near the onset of stuttering using a multiple data collection system, with 45 nonstuttering children serving as controls. Thirty-two stuttering and 32 control subjects who have progressed through several stages of the investigation were identified for the present indepth analyses. They represent four subgroups: I. Persistent Stuttering; II. Late Recovery; III. Early Recovery; IV. Control. Comparative data for the groups with special reference to differences in frequency of disfluency, acoustic features, phonologic skills, language development, nonverbal skills, and genetics are presented. The results suggest several promising predictors of recovery and chronicity.

Immune disorders and handedness in dyslexic boys and their relatives

Thirty dyslexic and 30 control boys aged 7-11 years were compared for frequency of immune disorders and handedness as well as for family history of immune disorders and learning disabilities (dyslexia and stuttering). They were also compared for neurological status and for history of speech and language difficulties. There were no significant differences between the two groups in the frequency of immune disorders and in handedness. The results showed significantly more dyslexic boys with soft neurological signs and signs of speech and language disorders. The frequency of dyslexia was significantly higher in the relatives of the dyslexic boys. Also significantly more mothers of the dyslexic boys reported difficulties during pregnancy and complications at delivery. The results are discussed in terms of Geschwind's hypothesis and neuromaturational delay as possible determinants of developmental dyslexia.

Stuttering as a phenotype for behavioral genetics research

Stuttering is a broad behavioral phenotype with an adult prevalence of 0.7-1.0%. Family, twin, and segregation studies all indicate that stuttering has a large genetic component to its etiology. The relatively simple phenotype, the early onset, and the apparent rarity of phenocopies of adult stuttering all make stuttering a promising model for the study of the genetics of broad behavioral phenotypes.

Familial relationship between Gilles de la Tourette's syndrome, attention deficit disorder, learning disabilities, speech disorders, and stuttering

OBJECTIVE

This study examined the familial relationship between Gilles de la Tourette's syndrome (GTS) and attention deficit disorder (ADD), learning problems, speech disorders, and stuttering.

METHOD

This family study consisted of 338 first degree relatives of 85 GTS probands and 113 controls. All available relatives were personally assessed using structured interviews, and family history information was collected from all family members. Best-estimate diagnoses were assigned for GTS, ADD, learning problems, speech disorders, and stuttering. Analyses examined whether ADD, learning problems, speech disorders, and stuttering by themselves represent genetically variant expressions of GTS.

RESULTS

There was no evidence that ADD, learning problems, speech disorders, or stuttering represent variant expressions of GTS. However, relatives with GTS were at increased risk for ADD regardless of the ADD diagnosis of the GTS proband.

CONCLUSIONS

ADD, learning problems, stuttering, and speech problems by themselves are not variant forms of GTS. However, GTS and ADD may be etiologically related in some persons. There may be two types of individuals with GTS and ADD: ones in whom ADD is independent of GTS, and others in whom ADD is secondary to occurrence of GTS.

Genetic aspects of early childhood stuttering

Although stuttering has long been acknowledged as a familial disorder, the nature of a genetic component remains unclear. Most previous data used in genetic studies were obtained primarily from adults who stutter and may be biased in several respects. The purpose of this investigation was to quantify the frequency of stuttering in relatives of preschool-age children who stutter, and who were first seen close to the onset of the disorder. Detailed pedigrees (family trees), including first-, second-, and third-degree relatives, were obtained from parents of 69 children who stuttered. We found, as have previous studies, that more male than female relatives ever stuttered, but that female subjects who stuttered had more female relatives who ever stuttered than did male subjects. In order to identify the genetic model most consistent with the observed patterns of stuttering transmission, we conducted segregation analyses. Results from these analyses suggest that transmission of a single major genetic locus increasing the liability to stuttering best accounts for the transmission of stuttering in families of preschool-age children who stutter.

A new sampling strategy for linkage studies in psychoses

Linkage between stuttering and manic-depression has been postulated to account for the reported association between these conditions, in three large pedigrees. This finding permits a novel and potentially more productive sampling strategy to be used in future linkage studies.

Genetic aspects of idiopathic speech and language disorders

At the outset of this article, we posed the question of whether or not the current evidence from genetic studies of DLD and stuttering indicate that it would be fruitful to conduct studies aimed at determining the gene location for each of these disorders. As we pointed out, because these are behavioral development disorders, phenotypic variations and changes in characteristics through the life span pose problems when attempting to determine who is and is not affected. Further, because these disorders can be either idiopathic or secondary to a variety of causes, any genetic study must rule out or take account of cases secondary to other factors. Few studies conducted thus far have taken these problems into account, and the results must be considered tentative. Given these reservations, the results certainly point to a genetic component in both disorders, although the data collected thus far on DLD suggest a mendelian form of transmission. If further more intensive studies continue to support this model for DLD, linkage studies on this disorder are likely to be productive.

A case-control study of idiopathic torsion dystonia

A study of 71 patients with idiopathic torsion dystonia (ITD) and 71 matched controls was performed to investigate the range of possible clinical expression of ITD and the role of environmental factors in the development of the disease. A family history of tremor and stuttering were the only factors significantly associated with ITD. No associated environmental factor was identified.

For better or for worse: left-handedness, pathology, and talent

Geschwind and his colleagues have hypothesized that left-handedness may be a marker for anomalous dominance and is associated with certain immune disorders, learning disorders, and special talents. The few relevant studies done to date have yielded somewhat mixed findings, and little had been done to study the relationship of relevant findings to the definition of handedness employed in a given study. The present study assessed the association between handedness and a variety of disorders, talents, and skills in subjects and their parents and siblings. Results showed that mathematical, artistic, and musical talents varied systematically as a function of handedness. Verbal skills, stuttering, and asthma were also significant discriminators in some discriminant function analyses, and certain variations in the definition of handedness produced systematic variations in results. Finally, certain disorders, particularly eczema, stuttering, and epilepsy, in the parents were related to handedness in their offspring.

Postulated genetic linkage between manic-depression and stuttering

We record pedigrees of three families in which stuttering and bipolar illnesses are found. An association between the two conditions is demonstrated, and linkage analysis suggests that the respective genes could occur at linked loci. The implications of this finding are noted.

A controlled study of Tourette syndrome. I. Attention-deficit disorder, learning disorders, and school problems

Tourette syndrome (TS) is a common, hereditary, neurobehavioral disorder of childhood. To determine the frequency of various behavioral manifestations, we have compared 47 random normal controls to 246 patients with TS, 17 with attention-deficit disorder (ADD), and 15 with ADD secondary to a TS gene (ADD 2(0) TS). All subjects were examined prospectively with a 425-item questionnaire based on the Diagnostic Interview Schedule and the Diagnostic and Statistical Manual of Mental Disorders (DSM III). The TS patients were divided into grade 1 (too mild to treat [17.5%]), grade 2 (requiring treatment [58.9%]), and grade 3 (severe [23.6%]). Patients in all three grades of TS were significantly different from controls for DSM III symptoms of inattention, impulsivity, and hyperactivity. Sixty-two percent of TS patients had ADD, compared with 6.3% of controls; and 48.8% had ADD with hyperactivity (ADDH), compared with 4.2% of controls. In the majority of TS patients, the natural history of the disease was to start with ADDH and 2.4 years later develop motor and vocal tics. Among TS patients, 39% had previously received medication for ADDH or behavior problems, compared with 2% of the controls. Although stimulants can occasionally exacerbate tics, there was no evidence that stimulants cause TS and they are often a valuable adjunct to the treatment of TS. It is estimated that 10%-30% of ADDH is due to or associated with the presence of a TS gene. TS patients had a significantly increased frequency of (1) attending classes for the educationally handicapped, (2) placement in classes for the severely emotionally disturbed, (3) attending any special classes, (4) severe test anxiety, (5) stuttering, (6) letter, number, or word reversal, (7) reading very slowly, and (8) poor retention of material read. A reading-problem score (dyslexia) greater than or equal to 3 was present in 26.8% of TS patients, compared with 4.2% of controls. Number reversal, word reversal, and poor retention were significant even for the TS patients with tics too mild to treat. The multiple ways in which TS impacts school performance, as well as potential remedies, are discussed.

Family history of children with developmental language disorders

The present study shows the increased incidence of language-related disorders among family members of children with language disorders. The family histories of 74 children with developmental language disorders and 36 normal children were compared. The children with language disorders had significantly more family members who reported speech, stuttering, reading, and language disorders than the normal control group.

Some environmental factors and hypotheses for stuttering in families with several stutterers

Individuals in families with several stutterers (five or more) and individuals in families with no stutterers were the basis of a broad study designed to elucidate both genetic and nongenetic factors relevant to stuttering. In order to examine both nongenetic hypotheses regarding the etiology of stuttering as well as environmental factors possibly predisposing to stuttering, data were collected using two structured case-history interviews and four self-report inventories. We were unable to identify prenatal, developmental, or medical factors that distinguish stutterers from their nonstuttering family members. Further, we found no evidence of (a) anxiety levels differing among stutterers, their nonstuttering family members, and nonstuttering controls; (b) familial attitudes toward speech differing between nonstuttering family members and those of nonstuttering controls; or (c) ratings of parental behavior or children's traits which distinguished stutterers from nonstuttering family members.

Language and the young stutterer: a new look at old theories and findings

The major theories and research approaches as to the etiology and development of stuttering are reviewed from a historical perspective. Findings are drawn from different sources indicating that language deficits are an initial contributing factor and a continuing component of this disorder. Those subsets of children which constitute high-risk groups are identified. It is suggested that researchers begin investigating the underlying organic bases of stuttering and its relationship to stages of language development. Finally, clinicians are encouraged to employ a therapy program that is concerned with all areas of language, rather than emphasizing treating only the symptoms of stuttering behavior.

Recovery and persistence of stuttering among relatives of stutterers

Recovery and persistence of stuttering were examined in the first-degree relatives of a large group of adult persistent stutters. The percentage of recovered individuals reported in these families supports the hypothesis that recovered and persistent stuttering are not independent disorders. Sex and type of relative were significant variables in the distributions of recovery and persistence of stuttering. Handedness in male subjects and birth order did not distinguish between recovered and persistent stutterers. Female recovered stutterers had significantly earlier ages of stuttering onset than the other groups (male recovered stutterers and male and female persistent stutterers). Female recovered stutterers also tended to recover earlier than male recovered stutterers, and the durations of stuttering symptoms were similar in both sexes.

The onset of stuttering in two- and three-year-old children: a preliminary report

Data on the onset of stuttering in 22 children 2 and 3 years of age were obtained through systematic parent interviews using a coded questionnaire. All children were reported to have begun stuttering prior to 36 months of age. The results indicated more similar sex distribution and greater diversity in manner of onset than was reported in past investigations. Most parents perceived early stuttering to be associated with some degree of tensions and force. The length of syllable and word repetition as reported appeared to be above the average for normally disfluent children of similar ages. Directions for future research of early childhood stuttering and clinical implications of the data are discussed.

Genetic influences on learning disabilities and speech and language disorders

This paper is a comprehensive review of known examples of genetically influenced learning disabilities (LDs) and speech and language disorders (SLDs). The review is divided between 2 broad classes of studies: (a) those which begin with an LD or SLD phenotype that appears to be familial and attempt to learn more about the specifics of genetic transmission, if any; and (b) those which begin with a group of individuals, all of whom share a given documented genetic risk factor, to see if it leads to a specific LD or SLD. Included in the first category are familial dyslexia, stuttering, and other speech and language disorders. In the second category are included sex chromosome anomalies, treated PKU, and minor autosomal anomalies. Issues of definition, variability, and developmental changes in the cognitive phenotype are discussed throughout. The implications of this work for our understanding of cognitive development and its bases in brain development and genetics are also discussed.

Language onset and concomitant speech and language problems in subgroups of stutterers and their siblings

Time of language onset and frequencies of speech and language problems were examined in stutterers and their nonstuttering siblings. These families were grouped according to six characteristics of the index stutterer: sex, recovery or persistence of stuttering, and positive or negative family history of stuttering. Stutterers and their nonstuttering same-sex siblings were found to be distributed identically in early, average, and late categories of language onset. Comparisons of six subgroups of stutterers and their respective nonstuttering siblings showed no significant differences in the number of their reported articulation problems. Stutterers who were reported to be late talkers did not differ from their nonstuttering siblings in the frequency of their articulation problems, but these two groups had significantly higher frequencies of articulation problems than did stutterers who were early or average talkers and their siblings.

Genetic strategies for the analysis of childhood behavioral traits

Genetic strategies appropriate for the analysis of childhood behavioral traits are reviewed. The problem of etiologic heterogeneity is discussed, and suggestions for minimizing its effect are offered. Two traits, stuttering and Tourette syndrome, are given as examples to illustrate methodologies useful for the genetic analysis of childhood disorders. In both examples, it is shown that the disorder clusters in families, that it is vertically transmitted, and that the transmission is sex-modified. Several genetic models can explain the pattern of transmission, although cultural hypotheses also should be considered. Hence, additional analyses need to be attempted to help clarify the modes of transmission and the factors involved.

Analysis of the sibship patterns of stutterers

Analyses of birth rank, age separation, and the frequency of stutterers in birth ranks before and after the proband were undertaken for the purpose of verifying or disproving conjectures made by other authors on possible relationships between family structures and stuttering. Results based on data drawn from over 300 sibships, showed (a) stutterers were randomly distributed among the birth ranks, (b) the age separation of the siblings was independent of stuttering status, and (c) the frequency of stutterers in birth ranks before the proband and the frequency of stutterers in birth ranks after the proband were not significantly different.

Concordance for stuttering in monozygotic and dizygotic twin pairs

The role of genetic factors in the etiology of stuttering was investigated in 30 pairs of same-sex twins, each pair containing at least one stutterer. Care was taken to ensure maximum accuracy in zygosity classification and objectivity in stuttering diagnosis. Zygosity classification was made independently of stuttering diagnosis. Pair-wise concordance for stuttering was significantly higher in identical twins (63%) than in fraternal same-sex twins (19%). The estimated risk of stuttering in the monozygotic (MZ) co-twin of a stutterer was .77, and .32 in the dizygotic (DZ) co-twin of a stutterer. The findings strongly suggest the operation of genetic factors in stuttering. However, the presence of as many as six pairs of identical twins who were discordant for stuttering underlines the importance of the interaction of genetic and environmental factors in the etiology of this disorder.

Intrapair similarity in frequency of disfluency in monozygotic and dizygotic twin pairs containing stutterers

It is known that concordance for stuttering is higher in monozygotic (MZ) than in dizygotic (DZ) twins. Evidence for genetic contribution to the frequency of speech disruption in stutterers was examined in 17 pairs of MZ and 13 pairs of DZ twins, each pair containing at least one stutterer. Intraclass correlations and analyses of variance indicated positive evidence for a genetic contribution to the overall frequency of disfluency in speech and to the frequency of certain types of speech disruption (blocked and prolonged sounds). There was little evidence for genetic influence on other types of speech disruption (various types of repetitions and interjections) In those disfluency types for which genetic predictions were confirmed, evidence of excessive dissimilarity in DZ cotwins suggests that a simple, additive gene-environment model is unlikely to be appropriate for disfluency frequency data.

Vertical transmission of susceptibility to stuttering with sex-modified expression

Stuttering is not usually considered genetic, although it has long been known to be familial. Data collected on 2035 relatives of 397 unrelated adult stutterers confirm and quantify the strong familial concentration. Our analytic approach to these family data, one that does not require specification of a genetic hypothesis, shows that stuttering among relatives occurs in a pattern indicating vertical transmission of a susceptibility to stuttering with sex-modified expression. Although simple Mendelian hypotheses are not sufficient to explain the observed pattern of stuttering in families, more complex genetic models can explain the pattern. In the past, such evidence has been considered sufficient, because it does not preclude the possibility of cultural transmission. However, certain cultural transmission hypotheses previously proposed for stuttering are excluded by these data. The findings in this study support a growing opinion among speech pathologists that most stuttering is a genetically inherited neurologic disorder.

Familial stuttering patterns are not related to one measure of severity

The possibility of a genetic component to the severity of stuttering was investigated using data on 184 adult stutters and their families. Frequency of stuttering during a pre-treatment oral reading task was used as the severity measure for each of the index cases. Information on whether or not a relative ever stuttered was obtained on all first degree relatives. The family data variables, including sex and exact relationship, combined with birthdate and sex of index case were used in three types of analyses: multiple regressions, AID regressions, and stepwise regressions. None of the variables tested, including stuttering among first degree relatives, was a predictor of severity of stuttering in the index case. We conclude that this measure of severity is not related to the genetic factors which predispose to stuttering.

Hereditary factors in stammering

A pedigree from Hazaribagh District of Bihar (india) with 12 stammerers spread over five generations was analysed for the mode of inheritance of stuttering. A predisposition seems to be a prerequisite for its occurrence. The relative roles of heredity an environment in the expression of stammering were evaluated. Transmission appears to be by a dominant autosomal. Variable expressivity, incomplete penetrance as well as partial sex-limitation as other causes have also been considered.

Prevalence of stuttering

The prevalence of stuttering in a university population was 2.1%; 3.4% were former stutterers. More men than women stuttered. Right handed female stutterers were less likely to have "lost" their stutter than were right handed males. Stutterers, past stutterers, and questionable stutterers all had a family history of stuttering. The significant prevalence of stuttering, the increased prevalence among males, the lack of a decline of this disorder over the past few decades despite the increased number of speech clinicians and data concerning handedness, emphasise the need to investigate organic causes of stuttering.

A reexamination of the role of heredity in stuttering

In the light of recent breakthrough in the study of schizophrenia indicating a far stronger genetic factor than has been previously suspected, the role of heredity in stuttering is critically reexamined. Present knowledge of the role of heredity in stuttering springs from four principal data sources: (1) studies of familial incidence; (2) spontaneous recovery studies; (3) twin studies; and (4) studies of parental disfluency. It is hypothesized that the 4:1 sex ratio in stuttering may be the product of selective genetic factors. Critical examination of earlier and more recent studies leads to substantial evidence that a familial predisopsing factor exists in about 25% cases of stuttering.

Stuttering and tics in twins

A total of 63 twin pairs (22 MZ and 41 DZ), with one or both members affected by not organic stuttering and/or tics, have been drawn out of the Mendel Institute's twin file. Concordance of stuttering was observed in 10:12 MZ, but only in 2:19 DZ twin pairs; concordance of tics in 6:10 MZ and in 2:22 DZ twin pairs. Stuttering did not come out significantly associated either with other disturbances of language or with an IQ under the average; almost always it was possible to find out a precipitating factor. Significant relations between stuttering and tics could not be stated. Sex ratio, obtained regarding any affected subject separately, clearly turned in favour of males both in stuttering (32:12) and in tics (27:12). Stutterers and left-handers incidence in the families of stuttering subjects appeared significant in comparison with families of subjects with tics.

Psychosocial study of stammering in Egyptian children

Stammering has been defined as an interruption in the normal rhythm of speech of such a frequency and abnormality as to attract attention, interfere with communication or cause distress to a stammerer or his audience (Bloodstein, 1960).

Auditory feedback as a major factor in stuttering

This paper summarizes theories of DAF reaction and related research, and explores another hypothesis relating stuttering behavior and DAF reaction. The hypothesis stresses both internal and external feedback disruptions due to physiological characteristics of individuals. It also proposes that anxiety and its concomitant physiological factors act as catalysts to feedback disruptions.

Recovery from stuttering in a junior and senior high school population

Recovery from stuttering was studied in the Tuscaloosa, Alabama junior and senior high schools. Of 5054 students interviewed, 119 active stutterers were observed and another 68 students reported recovery from stuttering. This one-third recovery rate for the total population, while contrasting with a four-fifths recovery rate reported in a college student study varied from less than one-third in the junior high group to approximately one-half in the high school population. Familial incidence of stuttering was negatively related to recovery from stuttering. A positive relationship was found between parental identification of stuttering and the stutterer’s receiving speech therapy. No relationships were observed among recovery and stuttering severity, participation in therapy, and the nature of initial disfluencies.

Stuttering and its disappearance

Spontaneous recovery was found in four-fifths of all stuttering cases. Data were obtained from 5138 students at the University of California, Berkeley and Los Angeles, of whom 147 had at some time been definitely categorized as stutterers. Severity was the most important factor related to probability of recovery. For those who had never been worse than mild, seven-eights recovered, while for those who had ever been severe, only one-half recovered. When severity was held constant, enrollment in public school therapy had no effect, positive or negative, upon the probability of eventual recovery. The fact that fewer of those who received public school therapy had recovered was primarily attributable to the finding that the severe were more likely to be enrolled.

Parent, teacher, or speech clinician diagnosis of stuttering was significantly related to assignment to public school therapy, while self-diagnosis was inversely related. Those who began with blocking and became severe were more likely to have continued as stutterers, while those who began with syllable repetition were more likely to have recovered. Although familial incidence was higher in stutterers than in normal controls, it did not distinguish those who continued to stutter from those in whom the problem had disappeared.