Vertical transmission of susceptibility to stuttering with sex-modified expression.

Abstract

Stuttering is not usually considered genetic, although it has long been known to be familial. Data collected on 2035 relatives of397 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 ofa 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.Stuttering is a readily identifiable disorder of speech characterized by frequent interruptions or blocks in the smooth transition from the production of one sound to the production of the subsequent sound. The primary defect in stuttering, the block, is manifest as a repetition or prolongation of a sound, or as a silent gap in speech (1, 2). A layman's recognition of these symptoms and judgement of the presence of stuttering correspond closely to a speech pathologist's. The block is believed to reflect a basic organic problem (1, 2). Aberrant laryngeal activity (3) and deviant vocal tract events (4) during a stuttering moment may be reflections of this basic organic problem. Secondary aspects of stuttering, such as the severity, are definitely exacerbated by stressful environments. Concomitant behaviors, such as grimaces, eye blinks, and shoulder jerks, may be present as the result of operant learning. About 5% of males and 2% offemales stutter for at least six months sometime during childhood (5), but many affected children recover before they become adults and the adult prevalence is not precisely known. Although stuttering is a common disorder, it has an unknown and probably complex etiology.The probable organic basis and the well-recognized tendency to "run in families" indicate that the etiology of stuttering may have a genetic component. Although there is no simple Mendelian pattern of inheritance, recent analyses have shown that the frequencies of relatives who stutter could be explained by genetic hypotheses. Both polygenic and single-major-locus models have been shown to be compatible with the data (5-9). However, compatibility with two quite different hypotheses cannot be considered strong evidence in favor ofa genetic etiology, nor do any analyses eliminate the possibility ofcultural inheritance. These considerations motivate the use of different analytic approaches. Methods are needed that are not based on etiologic hypotheses but will allow the testing of factors that migh...

Speech-motor and linguistic skills of young stutterers prior to onset

“…Though, initially all were viewed as nonstutterers, follow-up a year later revealed that 26 were then regarded as stutterers. This finding is consistent with the genetically based high-risk hypothesis that has been proposed over the years in relation to children o f stutterers (An drew and Harris, 1964; Van Praag and Janssen, 1980;Kidd, 1977;Kidd et al, 1981), O f those children who came to be seen as stutterers, 16 were male and 10 were female. This yielded a male-to-female ratio o f 1.6:1, which is larger than that found by Yairi (1983) in a younger group o f stuttering children (1.2:1) but smaller than the estimated 4:1 ratio among adult stut terers (Bloodstein, 1987).…”

Predictive factors of persistence and recovery: Pathways of childhood stuttering

“…These observations point to a genetic factor. Research by Howie (1981) and Kidd and associates at Yale (Kidd, 1980;Kidd, 1984;Kidd, Heimbuch, & Records, 1981) added much knowledge about the role of genetics in the transmission of susceptibility to stuttering. The Yale studies' findings were consistent with a polygenic multifactorial model of inheritance with a possible major locus, and with males having a higher susceptibility.…”

Genetic studies of stuttering in a founder population

“…When the monozygotic and dizygotic twin correlations are used to model the additive genetic and environmental components, both Andrews et al (1991) and Felsenfeld et al (2000) concluded that approximately 70% of the phenotypic variance is due to additive genetic effects and approximately 30% to non-shared effects. Several studies have shown a higher incidence of stuttering in first degree relatives (20-74%) than in the general population (1.3-42%) (Kidd, Heimbuch, & Records, 1981;Yairi, Ambrose, & Cox, 1996). Both the concordance of stuttering among monozygotic twin pairs and the familial aggregation of stuttering are consistent with a genetic component to stuttering.…”