Genetic contributions to stuttering: the current evidence

Psychedelics in developmental stuttering to modulate brain functioning: a new therapeutic perspective?

Developmental stuttering (DS) is a neurodevelopmental speech-motor disorder characterized by symptoms such as blocks, repetitions, and prolongations. Persistent DS often has a significant negative impact on quality of life, and interventions for it have limited efficacy. Herein, we briefly review existing research on the neurophysiological underpinnings of DS -specifically, brain metabolic and default mode/social-cognitive networks (DMN/SCN) anomalies- arguing that psychedelic compounds might be considered and investigated (e.g., in randomized clinical trials) for treatment of DS. The neural background of DS is likely to be heterogeneous, and some contribution from genetically determinants of metabolic deficiencies in the basal ganglia and speech-motor cortical regions are thought to play a role in appearance of DS symptoms, which possibly results in a cascade of events contributing to impairments in speech-motor execution. In persistent DS, the difficulties of speech are often linked to a series of associated aspects such as social anxiety and social avoidance. In this context, the SCN and DMN (also influencing a series of fronto-parietal, somato-motor, and attentional networks) may have a role in worsening dysfluencies. Interestingly, brain metabolism and SCN/DMN connectivity can be modified by psychedelics, which have been shown to improve clinical evidence of some psychiatric conditions (e.g., depression, post-traumatic stress disorder, etc.) associated with psychological constructs such as rumination and social anxiety, which also tend to be present in persistent DS. To date, while there have been no controlled trials on the effects of psychedelics in DS, anecdotal evidence suggests that these agents may have beneficial effects on stuttering and its associated characteristics. We suggest that psychedelics warrant investigation in DS.

Erasmus clinical model of the onset and development of stuttering 2.0

A clinical, evidence-based model to inform clients and their parents about the nature of stuttering is indispensable for the field. In this paper, we propose the Erasmus Clinical Model of Stuttering 2.0 for children who stutter and their parents, and adult clients. It provides an up-to-date, clinical model summary of current insights into the genetic, neurological, motoric, linguistic, sensory, temperamental, psychological and social factors (be it causal, eliciting, or maintaining) related to stuttering. First a review is presented of current insights in these factors, and of six scientific theories or models that have inspired the development of our current clinical model. Following this, we will propose the model, which has proven to be useful in clinical practice. The proposed Erasmus Clinical Model of Stuttering visualizes the onset and course of stuttering, and includes scales for stuttering severity and impact, to be completed by the (parent of) the person who stutters. The pathway of the model towards stuttering onset is based on predisposing and mediating factors. In most children with an onset of stuttering, stuttering is transient, but if stuttering continues, its severity and impact vary widely. The model includes the circle of Engel (1977), which visualizes unique interactions of relevant biological, psychological, and social factors that determine the speaker's experience of stuttering severity and its impact. Discussing these factors and their interaction with an individual client can feed into therapeutic targets. The model is supplemented by a lifeline casus.

Awareness and Knowledge of Stuttering among Malaysian School-Aged Children: An Exploratory Study

INTRODUCTION

Knowledge and awareness of stuttering are closely associated with attitudes toward stuttering. Few studies have been conducted on the knowledge and awareness of school-aged children, and none have been conducted in Malaysia. This study aimed to: (a) determine knowledge and awareness of stuttering among Malaysian school-aged children, and (b) determine whether there are differences between age group, gender, and people who stutter (PWS) exposure groups.

METHODS

A cross-sectional study was conducted among 192 Malay school-aged children (mean age = 9.47, SD = 1.781) recruited via email and social media platforms. They completed a Malay version of the questionnaire devised by van Borsel et al. (1999) on various aspects of stuttering, including prevalence, onset, gender distribution, occurrence in different cultures, cause, treatment, intelligence, and heredity of stuttering. The χ2 test of independence was performed to compare the distributions of survey responses by age group, gender, and PWS exposure group.

RESULTS

Around half of the school-aged children had met a person who stutters, but certain aspects of their knowledge were limited. Knowledge also differed according to age and gender. Girls were more knowledgeable about stuttering than boys. Regarding stuttering treatment, younger children had more positive attitudes than older children. Participants who did not know a PWS were more likely to consult their family doctor rather than a speech-language pathologist in relation to stuttering.

CONCLUSION

Knowledge and awareness of stuttering among Malaysian school-aged children were limited. Findings of this study could be used to develop a stuttering awareness program specific to children to increase their knowledge and awareness about stuttering.

Therapeutic potential of robots for people who stutter: a preliminary study

Introduction

Growing anecdotal evidence suggests the feasibility of robotic intervention for people who suffer from disorders related to state anxiety. Few studies have been conducted on utilizing robots for persons who stutter (PWS). The present study examines the feasibility of using a robot for speech therapy for PWS.

Methods

We prepared four settings (i.e., interviews with unfamiliar persons, interviews with unfamiliar communication robots, reading sentences aloud with a tandem robot that can utter the same words as a user by repeating the user's voice after a short delay, and reading sentences aloud while being alone). We assessed the potential of the robots as both interlocutors and practice partners in training with delayed auditory feedback (DAF) for PWS. Moreover, we assessed the relationship between the trait of stuttering and the participants' affinity to the robots.

Results

Eleven PWS participated in the study. Eight (72.7%) participants had fewer stuttering-related psychological symptoms when they communicated with robots than when they communicated with humans. Spearman's rank correlation analysis revealed that there was a significant negative correlation between the Modified Erickson Communication Attitude scale (S-24) and the difference between the scores for stuttering-related psychological symptoms pertaining to the communication robot and humans (p < 0.01). Six participants (54.5%) had fewer stuttering-related psychological symptoms when they read aloud with the tandem robot than when they read aloud alone. There were significant positive correlations between S-24 and the differences between the scores for stuttering-related psychological symptoms when reading aloud with the tandem robot and those when reading aloud alone (p < 0.01).

Discussion

The communication robot and tandem utterance robot can sometimes be burdensome, although both robots were always easier to talk to for PWS in this preliminary study. The participants with positive speech-related attitudes were more inclined to decrease stuttering-related psychological symptoms when communicating with CommU than when communicating with humans. The participants whose speech-related attitudes were negative were more inclined to show a decrease in stuttering-related psychological symptoms when reading aloud with the tandem robot. Further studies are needed to provide more detailed information.

Predictors of public attitudes in Saudi Arabia toward people who stutter

PURPOSE

The Public Opinion Survey of Human Attributes-Stuttering (POSHA-S) was used to measure the attitudes of the general population in Saudi Arabia toward people who stutter (PWS) and to identify the predictors of the overall stuttering score (OSS).

METHOD

A total of 404 adults from Saudi Arabia (16.8% male and 83.2% female) completed an online POSHA-S questionnaire.

RESULTS

The attitudes of adults in Saudi Arabia were similar to those of other samples worldwide. Working status, income, and multilingualism were substantial predictors of the OSS.

CONCLUSION

Saudi adults have positive impressions, beliefs, and self-reactions to PWS. However, their knowledge of stuttering tends to be limited. Therefore, campaigns conducted to raise awareness of stuttering should adopt the most widely used sources of knowledge in the Saudi Arabian community (i.e., the Internet and social media). Sociodemographic variables predictive of positive versus negative OSS include working status and multilingualism. Unpredictive variables, that do not predict positive versus negative OSS, include age, gender, education, parental status, health, abilities, and income.

Stuttering associated with a pathogenic variant in the chaperone protein cyclophilin 40

Stuttering is a common speech disorder that interrupts speech fluency and tends to cluster in families. Typically, stuttering is characterized by speech sounds, words or syllables which may be repeated or prolonged and speech that may be further interrupted by hesitations or 'blocks'. Rare variants in a small number of genes encoding lysosomal pathway proteins have been linked to stuttering. We studied a large four-generation family in which persistent stuttering was inherited in an autosomal dominant manner with disruption of the cortico-basal-ganglia-thalamo-cortical network found on imaging. Exome sequencing of three affected family members revealed the PPID c.808C>T (p.Pro270Ser) variant that segregated with stuttering in the family. We generated a Ppid p.Pro270Ser knock-in mouse model and performed ex vivo imaging to assess for brain changes. Diffusion-weighted MRI in the mouse revealed significant microstructural changes in the left corticospinal tract, as previously implicated in stuttering. Quantitative susceptibility mapping also detected changes in cortico-striatal-thalamo-cortical loop tissue composition, consistent with findings in affected family members. This is the first report to implicate a chaperone protein in the pathogenesis of stuttering. The humanized Ppid murine model recapitulates network findings observed in affected family members.

New insights into the genetics of stuttering

This scientific commentary refers to ‘Stuttering associated with a pathogenic variant in the chaperone protein cyclophilin 40’ by Morgan et al. (https://doi.org/10.1093/brain/awad314).

Comparing the beliefs regarding biological or psychological causalities toward stereotyped perception of people who stutter

Purpose

Developmental stuttering is a fluency disorder that may be caused by neurological, genetic, or familial factors. However, a general perception that stuttering is caused by psychological problems could lead to negative attitudes toward stuttering, causing prejudice or discrimination against people who stutter (PWS). Thus, our study aimed to investigate whether certain beliefs in etiology of stuttering are related to the negative perception of stuttering.

Methods

A web-based survey of 413 native Japanese adults, aged 20-69, who did not suffer from stuttering, schizophrenia, or depression, was conducted in August 2021. The participants were recruited through the Web monitor panel. Participants were divided into three uniform groups based on their response to a 27-item questionnaire about their implicit belief regarding the etiology of stuttering: belief in the biological model (stuttering-biological group), belief in the psychological model (stuttering-psychological group), and the control group (those who responded to perception of healthy adult males). Participants were also asked to respond to 25 items of semantic differential scales about perception of stuttering or healthy adult males. Responses were summarized into several factors by factor analysis, and factor scores were compared among the three groups. The stuttering-biological group had the fewest participants, comprising 80 individuals. Overall, a total of 240 participants, 80 from each group, were included in the analysis.

Results

Some pairs of stereotypes included in semantic differential scales revealed differences between the groups; PWS, irrespective of the participants of the biological or psychological group, were considered as having negative stereotyping properties such as being "tense," "anxious," or "afraid." Additionally, three concepts from the factor analysis of these 25 items were analyzed using an analysis of variance, and significant differences were found; the mean factor score of the "danger" stereotype was lower in the stuttering-biological group compared to the stuttering-psychological group.

Conclusion

Although the simplification of the biological model is not recommended, anti-stigma campaigns to educate people that stuttering is caused by multidimensional factors, not just psychological ones, could change the general public's negative perceptions of stuttering.

Stuttering as a spectrum disorder: A hypothesis

Childhood-onset fluency disorder, commonly referred to as stuttering, affects over 70 million adults worldwide. While stuttering predominantly initiates during childhood and is more prevalent in males, it presents consistent symptoms during conversational speech. Despite these common clinical manifestations, evidence suggests that stuttering, may arise from different etiologies, emphasizing the need for personalized therapy approaches. Current research models often regard the stuttering population as a singular, homogenous group, potentially overlooking the inherent heterogeneity. This perspective consolidates both historical and recent observations to emphasize that stuttering is a heterogeneous condition with diverse causes. As such, it is crucial that both therapeutic research and clinical practices consider the potential for varied etiologies leading to stuttering. Recognizing stuttering as a spectrum disorder embraces its inherent variability, allowing for a more nuanced categorization of individuals based on the underlying causes. This perspective aligns with the principles of precision medicine, advocating for tailored treatments for distinct subgroups of people who stutter, ultimately leading to personalized therapeutic approaches.

[Stuttering in Children: Review and Referral Criteria]

Stuttering is a speech fluency disorder, in which people know perfectly well the message they want to convey, even though their speech is characterized by changes in rhythm, repetitions, prolongations, pauses and blocks, and may also be associated with states of anxiety or emotional tension. Up to one in every six children, typically between two and five years old, experience a period of transitory speech disfluency, with usual spontaneous recovery before reaching school age, with a prevalence rate of stuttering of up to 1% of the adult population, and a higher incidence rate in males (4:1). In Portugal, it is estimated that stuttering affects around 100 thousand people, acquiring importance due to its frequency and association with lower self-esteem, anxiety and social isolation, with negative impact on people's ability to communicate and on their well-being and social interactions. The aim of this article is to highlight the complexity of the diagnostic and therapeutic approach of stuttering in pediatrics, with a particular focus on differentiating between normal speech disfluencies and childhood-onset fluency disorder (stuttering) and referral criteria, in order to raise awareness and facilitate early detection of these cases.

Factors Associated With Symptoms of Anxiety and Depression in Children Who Stutter

PURPOSE

Children and adolescents who stutter may be at risk of elevated anxiety and depression symptoms, although studies have indicated variability in reported internalizing symptoms in this population. This study considers the association between anxiety and depression symptoms and stuttering, as well as child, family, and contextual factors that may affect this association.

METHOD

Thirty-five school-age children who stutter completed the Revised Children's Anxiety and Depression Scale-Short Version. We fitted regression models to examine the association between anxiety and depression symptoms with bullying, stuttering severity, family history of adverse mental health, and age in children who stutter.

RESULTS

Family history of adverse mental health was found to significantly predict anxiety and depression scores. Age also predicted depression scores, with older children reporting higher scores.

CONCLUSIONS

Family history of adverse mental health is associated with higher self-reported internalizing symptoms in children who stutter. The interaction between child, family, and contextual factors may change with age, and this requires further exploration in larger, longitudinal studies. The association between bullying and anxiety scores indicates the importance of anti-bullying initiatives in promoting psychosocial development in school-age children who stutter. This study also highlights the contribution of known risk factors for mental health, such as family history, to variability in symptom reporting.

Effects of Binaural Beat Stimulation in Adults with Stuttering

In recent decades, several studies have demonstrated a link between stuttering and abnormal electroencephalographic (EEG) β-power in cortex. Effects of exposure to binaural stimuli were studied in adults with stuttering (AWS, n = 6) and fluent participants (n = 6) using EEG, ECG, and speech analysis. During standard reading tasks without stimulation, in controls but not in the AWS group, EEG β-power was significantly higher in the left hemisphere than in the right hemisphere. After stimulation, the power of the β-band in AWS participants in the left hemisphere increased 1.54-fold. The average β-band power within the left frontotemporal area and temporoparietal junction of the cortex after stimulation in AWS participants shows an increase by 1.65-fold and 1.72-fold, respectively. The rate of disfluency dropped significantly immediately after stimulation (median 74.70% of the baseline). Similarly, the speech rate significantly increased immediately after stimulation (median 133.15%). We show for the first time that auditory binaural beat stimulation can improve speech fluency in AWS, and its effect is proportional to boost in EEG β-band power in left frontotemporal and temporoparietal junction of cortex. Changes in β-power were detected immediately after exposure and persisted for 10 min. Additionally, these effects were accompanied by a reduction in stress levels.

Fostering Positive Stuttering Identities Using Stutter-Affirming Therapy

PURPOSE

School-age children and adolescents frequently have difficulty developing positive identities around their stuttering. Many students experience both physical and social consequences from stuttering. The great lengths that speakers go to try to hide their stuttering and to speak fluently increase their difficulty. As long as school-age children who stutter try to identify as fluent speakers, they will have difficulty lessening the negative impact of stuttering on their lives. Fortunately, many people who stutter also report positive stuttering experiences. Speech-language pathologists can use these positive experiences to help school-age children grow more comfortable with stuttering. They can also help school-age children reduce some of the speaking effort and social stigma that leads them to try to conceal their stuttering in the first place. To accomplish both these goals, I propose a stutter-affirming therapy.

METHOD

This clinical focus article summarizes previous research about identity development in stuttering. I discuss a therapy approach I call stutter-affirming therapy. In elucidating this approach, I discuss practical ways that speech-language pathologists can use to help school-age children develop positive stuttering identities through easier speaking and stuttering. I ground these examples in a case study of a 12-year-old boy who stutters.

DISCUSSION

stutter-affirming therapy focuses on conditioning the speaker's reaction to stuttering in ways that move toward and embrace stuttering (stutterphilic reactions) rather than in ways that move away from and reject stuttering (stutterphobic reactions). Speech-language pathologists can help school-age children who stutter foster positive stuttering identities using the three priorities of stutter-affirming therapy. First, reject fluency by reducing stutterphobic and increasing stutterphilic reactions to stuttering. Second, value stuttering by discovering what speakers gain from it. Third, create an environment in which it is easier to stutter through education, advocacy, disclosure, and voluntary stuttering.

Social anxiety disorder in adolescents who stutter: A risk for school refusal

BACKGROUND

Stuttering is a childhood-onset fluency disorder. Part of the counseling for middle and high school students with persistent stuttering is related to school refusal. Anxiety disorders are known to contribute to school refusal. However, it is not known whether social anxiety disorder (SAD) is a factor in school refusal among adolescents who stutter.

METHODS

In our first study, we examined the relationship between school refusal and SAD in 84 middle and high school students who stutter; 26% of the 84 students were in the school refusal group and the remaining 74% were in the school attendance group. The second study examined whether SAD was associated with 10 factors related to speech and stuttering frequency using the Japanese version of the Liebowitz Social Anxiety Scale for Children and Adolescents to determine the presence of SAD. Of the 84 students in the first study, 40 participated in the second study.

RESULTS

The school refusal group of adolescents who stutter had significantly higher rates of SAD than the school attendance group. Fifty percent of adolescents who stutter met the criteria for SAD. Moreover, adolescents who stutter with SAD had significantly higher scores on the items "When speaking in public, do you experience tremors in your limbs?" and "After you stutter, do you have negative thoughts about yourself?" than the adolescents who stutter without SAD.

CONCLUSIONS

When examining adolescents who stutter, checking for comorbid SAD may lead to better support. Moreover, noticing their repetitive negative thinking, nervousness, and trembling during speech may help to resolve SAD.

The Expansion of the Spectrum in Stuttering Disorders to a Novel ARMC Gene Family (ARMC3)

Stuttering is a common neurodevelopment speech disorder that negatively affects the socio-psychological dimensions of people with disability. It displays many attributes of a complex genetic trait, and a few genetic loci have been identified through linkage studies. Stuttering is highly variable regarding its phenotypes and molecular etiology. However, all stutters have some common features, including blocks in speech, prolongation, and repetition of sounds, syllables, and words. The involuntary actions associated with stuttering often involve increased eye blinking, tremors of the lips or jaws, head jerks, clenched fists, perspiration, and cardiovascular changes. In the present study, we recruited a consanguineous Pakistani family showing an autosomal recessive mode of inheritance. The exome sequencing identified a homozygous splice site variant in ARMC3 (Armadillo Repeat Containing 3) in a consanguineous Pashtun family of Pakistani origin as the underlying genetic cause of non-syndromic stuttering. The homozygous splice site variant (NM_173081.5:c.916 + 1G > A) segregated with the stuttering phenotype in this family. The splice change leading to the skipping of exon-8 is a loss of function (LoF) variant, which is predicted to undergo NMD (Nonsense mediated decay). Here, we report ARMC3 as a novel candidate gene causing the stuttering phenotype. ARMC3 may lead to neurodevelopmental disorders, including stuttering in humans.

Association between stuttering and psychosocial complications in Saudi Arabian individuals: A pilot study

Background

Stuttering is a multifaceted speech disorder that affects the interpersonal communication. It has a significant psychosocial impact on individuals who stutter and on their families. Stuttering is associated with substantial psychosocial morbidity, including social or generalized anxiety, stigmatization or discrimination, impaired self-image, and poor quality of life. Psychosocial morbidity, such as the one reported among stuttering individuals, may provoke suicidal ideation that varies with gender, age, geographic region, and psychosocial reality. The present research aimed to determine the association between stuttering and psychosocial complications in Saudi Arabian individuals.

Materials and Methods

This study targeted a total of 107 male patients with stuttering. Only 59 of them fulfilled both inclusion and exclusion criteria. The researchers formulated a valid questionnaire to obtain quantifiable data for analysis. The questionnaire consisted of 76 questions spanning various domains. Following the data collection, a quantitative analysis was carried out.

Results

A total of 79.5% of the participants were adolescents or young adults between the ages of 16 and 26. Among them, 17.8% had a later onset of stuttering. The age of onset tended to be higher than 5 years, with over 80% of respondents reporting an age of onset in the last 5 years of their age. Among the participants, 57.6% reported a positive family history of stuttering.

Conclusions

The present study reports that patients who stutter (PWS) are at a higher risk of developing negative thoughts leading to suicidal attempts due to social anxiety and depression. Therefore, future studies should be designed to establish the relationship between stuttering and suicidal thoughts in order to establish policies that may improve the quality of life of those who stutter.

Stuttering, family history and counselling: A contemporary database

BACKGROUND

Information about genetic influence is useful to when counselling parents or caregivers who have infants and children at risk for stuttering. Yet, the most comprehensive family aggregate database to inform that counselling is nearly four decades old (Andrews et al., 1983). Consequently, the present study was designed to provide a contemporary exploration of the relationship between stuttering and family history.

METHODS

Data were sourced from the Australian Stuttering Research Centre, comprising 739 participants who presented for assessment, treatment, or investigation of stuttering. Reported family history data were acquired from pedigrees collected during assessment. We sought to establish the relation of the following variables to family history of stuttering: incidence, proband sex, parent sex, stuttering severity, age, reported age of stuttering onset, and impact of stuttering. Data were analysed with chi-square tests for independence, logistic and linear regression models.

RESULTS

Results were broadly consistent with existing data, but the following findings were novel. Males and females who stutter have the same increased odds of having a father who stutters relative to a mother who stutters. Males had later stuttering onset than females, with genetic involvement in this effect. There was a greater impact of stuttering for females than males with a family history of stuttering.

CONCLUSION

These findings have clinical applications. Speech-language pathologists may have infant or child clients known to them who are at risk of beginning to stutter. Information from the present study can be applied to counselling parents or caregivers of such children about stuttering and family history.

The Complexity of Stuttering Behavior in Adults and Adolescents: Relationship to Age, Severity, Mental Health, Impact of Stuttering, and Behavioral Treatment Outcome

PURPOSE

This study investigated the complexity of stuttering behavior. It described and classified the complexity of stuttering behavior in relation to age, behavioral treatment outcomes, stuttering severity, anxiety-related mental health, impact of stuttering, and gender.

METHOD

For this study, a taxonomy was developed-LBDL-C7-which was based on the Lidcombe Behavioral Data Language of stuttering. It was used by five experienced judges to analyze the complexity of stuttering behavior for 84 adults and adolescents before and after speech restructuring treatment. Data were 3,100 stuttering moments, which were analyzed with nominal logistic regression.

RESULTS

The complexity of stuttering behavior appears not to change as a result of treatment, but it does appear to change with advancing age. Complexity of stuttering behavior was found to be independently associated with clinician stuttering severity scores but not with percentage of syllables stuttered or self-reported stuttering severity. Complexity of stuttering behavior was not associated with gender, anxiety, or impact of stuttering.

CONCLUSION

Clinical and research applications of these findings are discussed.

The disabling nature of hope in discovering a biological explanation of stuttering

Discovering developmental stuttering's biological explanation has been an enduring concern. Novel advances in genomics and neuroscience are making it possible to isolate and pinpoint genetic and brain differences implicated in stuttering. This is giving rise to a hope that, in the future, dysfluency could be better managed if stuttering's biological basis could be better understood. Concurrent to this, there is another hope rising: a hope of a future where differing fluencies would not be viewed through a reductive lens of biology and associated pathologies. The central aim of this paper is to edge out ethical implications of novel research into stuttering's biological explanation. In doing so, the paper proposes to look beyond the bifurcation sketched by the medical and social model of disability. The paper demonstrates how the scientific hope of discovering stuttering's biological explanation acts as an accessory of disablement due to the language of 'lack' and 'deficit' employed in reporting scientific findings and proposes participatory research with people who stutter as an antidote to manage this disablement.

Epilepsy and Diagnostic Dilemmas: The Role of Language and Speech-Related Seizures

Although the impact of epilepsy on expressive language is heavily discussed, researched, and scientifically grounded, a limited volume of research points in the opposite direction. What about the causal relationship between disorder-related language activities and epileptic seizures? What are the possible diagnostic dilemmas that experts in the field of speech-language pathology, neurology, and related fields face? How far has research gone in investigating psychogenic nonepileptic seizures, the misdiagnosis of which can be a thorny issue for clinicians and a detrimental factor for the patients’ health? In order to address these questions, the study at hand focuses on a common, ever-intensified (by the COVID-19 pandemic) speech disorder—stuttering, and explores the pathophysiological and psychogenic background of the phenomenon. It also looks at the role of stuttering as a contributing factor to the appearance of epileptic seizures, in the hope of drawing attention to the complexity and importance of precise detection of stuttering-induced epilepsy, as a specific subcategory of language-induced epilepsy.

Stuttering and the social model

Stuttering has traditionally been thought of as a defect located within an individual. As such, stuttering is caused by pathology, leading to impaired communication and reduced quality of life. Research from this medical tradition has looked to understand the etiology of stuttering to develop curative therapeutic approaches. From this frame, professionals and academics are experts and holders of knowledge; people who stutter the recipients of this expertise. The social model emerged from within the disability rights movement and offers a counter narrative. It sees the way society is structured as disabling rather than physical impairment itself. Disability is experienced when a person is unable to participate fully in society through a mismatch between their body and the environment around them; thus, disability becomes a dynamic process, not an inherent characteristic. The social model highlights society's norms and values, and, in the case of stuttering, demonstrates how society is designed for, and expects, fluent speakers. From this frame, people who stutter are the experts of their experience and holders of knowledge; professionals and academics are their allies, collaborators, and advocates for social change. This theoretical framework poses challenging questions of the foundational theories upon which stuttering therapy is historically rooted. They call into question the hierarchical structures, power dynamics and even purpose of stuttering therapy and research. In this discussion paper, we will explore the social model of disability and its implications for stuttering therapy and research. We discuss the benefits of a social model approach as well as its limitations.

Structural insights into how GlcNAc-1-phosphotransferase directs lysosomal protein transport

GlcNAc-1-phosphotransferase catalyzes the initial step in the formation of the mannose-6-phosphate tag that labels ∼60 lysosomal proteins for transport. Mutations in GlcNAc-1-phosphotransferase are known to cause lysosomal storage disorders such as mucolipidoses. However, the molecular mechanism of GlcNAc-1-phosphotransferase activity remains unclear. Mammalian GlcNAc-1-phosphotransferases are α2β2γ2 hexamers in which the core catalytic α- and β-subunits are derived from the GNPTAB (N-acetylglucosamine-1-phosphate transferase subunits alpha and beta) gene. Here, we present the cryo-electron microscopy structure of the Drosophila melanogaster GNPTAB homolog, DmGNPTAB. We identified four conserved regions located far apart in the sequence that fold into the catalytic domain, which exhibits structural similarity to that of the UDP–glucose glycoprotein glucosyltransferase. Comparison with UDP–glucose glycoprotein glucosyltransferase also revealed a putative donor substrate-binding site, and the functional requirements of critical residues in human GNPTAB were validated using GNPTAB-knockout cells. Finally, we show that DmGNPTAB forms a homodimer that is evolutionarily conserved and that perturbing the dimer interface undermines the maturation and activity of human GNPTAB. These results provide important insights into GlcNAc-1-phosphotransferase function and related diseases.

Phenome risk classification enables phenotypic imputation and gene discovery in developmental stuttering

Developmental stuttering is a speech disorder characterized by disruption in the forward movement of speech. This disruption includes part-word and single-syllable repetitions, prolongations, and involuntary tension that blocks syllables and words, and the disorder has a life-time prevalence of 6-12%. Within Vanderbilt's electronic health record (EHR)-linked biorepository (BioVU), only 142 individuals out of 92,762 participants (0.15%) are identified with diagnostic ICD9/10 codes, suggesting a large portion of people who stutter do not have a record of diagnosis within the EHR. To identify individuals affected by stuttering within our EHR, we built a PheCode-driven Gini impurity-based classification and regression tree model, PheML, by using comorbidities enriched in individuals affected by stuttering as predicting features and imputing stuttering status as the outcome variable. Applying PheML in BioVU identified 9,239 genotyped affected individuals (a clinical prevalence of ∼10%) for downstream genetic analysis. Ancestry-stratified GWAS of PheML-imputed affected individuals and matched control individuals identified rs12613255, a variant near CYRIA on chromosome 2 (B = 0.323; p value = 1.31 × 10-8) in European-ancestry analysis and rs7837758 (B = 0.518; p value = 5.07 × 10-8), an intronic variant found within the ZMAT4 gene on chromosome 8, in African-ancestry analysis. Polygenic-risk prediction and concordance analysis in an independent clinically ascertained sample of developmental stuttering cases validate our GWAS findings in PheML-imputed affected and control individuals and demonstrate the clinical relevance of our population-based analysis for stuttering risk.

Population-based genetic effects for developmental stuttering

Despite a lifetime prevalence of at least 5%, developmental stuttering, characterized by prolongations, blocks, and repetitions of speech sounds, remains a largely idiopathic speech disorder. Family, twin, and segregation studies overwhelmingly support a strong genetic influence on stuttering risk; however, its complex mode of inheritance combined with thus-far underpowered genetic studies contribute to the challenge of identifying and reproducing genes implicated in developmental stuttering susceptibility. We conducted a trans-ancestry genome-wide association study (GWAS) and meta-analysis of developmental stuttering in two primary datasets: The International Stuttering Project comprising 1,345 clinically ascertained cases from multiple global sites and 6,759 matched population controls from the biobank at Vanderbilt University Medical Center (VUMC), and 785 self-reported stuttering cases and 7,572 controls ascertained from The National Longitudinal Study of Adolescent to Adult Health (Add Health). Meta-analysis of these genome-wide association studies identified a genome-wide significant (GWS) signal for clinically reported developmental stuttering in the general population: a protective variant in the intronic or genic upstream region of SSUH2 (rs113284510, protective allele frequency = 7.49%, Z = -5.576, p = 2.46 × 10^-8) that acts as an expression quantitative trait locus (eQTL) in esophagus-muscularis tissue by reducing its gene expression. In addition, we identified 15 loci reaching suggestive significance (p < 5 × 10^-6). This foundational population-based genetic study of a common speech disorder reports the findings of a clinically ascertained study of developmental stuttering and highlights the need for further research.

Psychological characteristics of early stuttering

PURPOSE

The purpose of this study was to use psychological measures of pre-schoolers who stutter and their parents to inform causal theory development and influence clinical practices. This was done using data from a substantive clinical cohort of children who received early stuttering treatment.

METHOD

The cohort (N = 427) comprised parents and their children who were treated with the Lidcombe Program, the Westmead Program, and the Oakville Program. The study incorporated demographic information, stuttering severity, and child and parent psychological measures prior to treatment.

RESULT

The cohort revealed nothing unusual about behavioural and emotional functioning, or the temperaments, of pre-school children that would influence treatment, be targeted during treatment, or influence causal theory development. However, a third of parents were experiencing moderate to high life stressors at the time of seeking treatment, and half the parents failed first-stage screening for Anankastic Personality Disorder.

CONCLUSION

The present results are consistent with a number of previous reports that showed that the population of pre-schoolers who stutter have no unusual psychological profiles. Hence, these results suggest that the association between mental health and stuttering later in life is a consequence of the disorder rather than being a part of its cause. The finding of the life stress of parents who seek stuttering treatment for pre-school children has potential clinical importance and warrants further investigation. Further psychological research is required about parents of pre-school children who stutter, because half the parents in the cohort failed the screener for Anankastic Personality Disorder. This is of interest because a previous study associated screening failure for another personality disorder (Impulsive Personality Disorder) with treatment dropout for early childhood stuttering.

Elevated iron concentration in putamen and cortical speech motor network in developmental stuttering

Theoretical accounts of developmental stuttering implicate dysfunctional cortico-striatal-thalamo-cortical motor loops through the putamen. However, the analysis of conventional MRI brain scans in individuals who stutter has failed to yield strong support for this theory in terms of reliable differences in the structure or function of the basal ganglia. Here, we performed quantitative mapping of brain tissue, which can be used to measure iron content alongside markers sensitive to myelin and thereby offers particular sensitivity to the measurement of iron-rich structures such as the basal ganglia. Analysis of these quantitative maps in 41 men and women who stutter and 32 individuals who are typically fluent revealed significant group differences in maps of R2*, indicative of higher iron content in individuals who stutter in the left putamen and in left hemisphere cortical regions important for speech motor control. Higher iron levels in brain tissue in individuals who stutter could reflect elevated dopamine levels or lysosomal dysfunction, both of which are implicated in stuttering. This study represents the first use of these quantitative measures in developmental stuttering and provides new evidence of microstructural differences in the basal ganglia and connected frontal cortical regions.

Atypical development of Broca's area in a large family with inherited stuttering

Developmental stuttering is a condition of speech dysfluency, characterized by pauses, blocks, prolongations and sound or syllable repetitions. It affects around 1% of the population, with potential detrimental effects on mental health and long-term employment. Accumulating evidence points to a genetic aetiology, yet gene-brain associations remain poorly understood due to a lack of MRI studies in affected families. Here we report the first neuroimaging study of developmental stuttering in a family with autosomal dominant inheritance of persistent stuttering. We studied a four-generation family, 16 family members were included in genotyping analysis. T1-weighted and diffusion-weighted MRI scans were conducted on seven family members (six male; aged 9-63 years) with two age and sex matched controls without stuttering (n = 14). Using Freesurfer, we analysed cortical morphology (cortical thickness, surface area and local gyrification index) and basal ganglia volumes. White matter integrity in key speech and language tracts (i.e. frontal aslant tract and arcuate fasciculus) was also analysed using MRtrix and probabilistic tractography. We identified a significant age by group interaction effect for cortical thickness in the left hemisphere pars opercularis (Broca's area). In affected family members this region failed to follow the typical trajectory of age-related thinning observed in controls. Surface area analysis revealed the middle frontal gyrus region was reduced bilaterally in the family (all cortical morphometry significance levels set at a vertex-wise threshold of P < 0.01, corrected for multiple comparisons). Both the left and right globus pallidus were larger in the family than in the control group (left P = 0.017; right P = 0.037), and a larger right globus pallidus was associated with more severe stuttering (rho = 0.86, P = 0.01). No white matter differences were identified. Genotyping identified novel loci on chromosomes 1 and 4 that map with the stuttering phenotype. Our findings denote disruption within the cortico-basal ganglia-thalamo-cortical network. The lack of typical development of these structures reflects the anatomical basis of the abnormal inhibitory control network between Broca's area and the striatum underpinning stuttering in these individuals. This is the first evidence of a neural phenotype in a family with an autosomal dominantly inherited stuttering.

IFNAR1 gene mutation may contribute to developmental stuttering in the Chinese population

BACKGROUND

Developmental stuttering is the most common form of stuttering without apparent neurogenic or psychogenic impairment. Recently, whole-exome sequencing (WES) has been suggested to be a promising approach to study Mendelian disorders.

METHODS

Here, we describe an application of WES to identify a gene potentially responsible for persistent developmental stuttering (PDS) by sequencing DNA samples from 10 independent PDS families and 11 sporadic cases. Sanger sequencing was performed for verification with samples obtained from 73 additional patients with sporadic cases.

RESULTS

We first searched for cosegregating variants/candidate genes in a Chinese family (Family 0) by sequencing DNA obtained from 3 affected members and 3 controls. Next, we sequenced DNA samples obtained from 9 additional Chinese families (Families 1-9) with stuttering to verify the identified candidate genes. Intriguingly, we found that two missense variants (Leu552Pro and Lys428Gln) of interferon-alpha/beta receptor 1 (IFNAR1) cosegregated with stuttering in three independent families (Families 0, 5 and 9). Moreover, we found two additional mutations (Gly301Glu and Pro335del) in the IFNAR1 gene in 4 patients with sporadic cases by using WES or Sanger sequencing. Further receptor mutagenesis and cell signaling studies revealed that these IFNAR1 variants may impair the activity of type I IFN signaling.

CONCLUSION

Our data indicate that IFNAR1 might be a potential pathogenic gene of PDS in the Chinese population.

Neuroanatomical anomalies associated with rare AP4E1 mutations in people who stutter

Developmental stuttering is a common speech disorder with strong genetic underpinnings. Recently, stuttering has been associated with mutations in genes involved in lysosomal enzyme trafficking. However, how these mutations affect the brains of people who stutter remains largely unknown. In this study, we compared grey matter volume and white matter fractional anisotropy between a unique group of seven subjects who stutter and carry the same rare heterozygous AP4E1 coding mutations and seven unrelated controls without such variants. The carriers of the AP4E1 mutations are members of a large Cameroonian family in which the association between AP4E1 and persistent stuttering was previously identified. Compared to controls, mutation carriers showed reduced grey matter volume in the thalamus, visual areas and the posterior cingulate cortex. Moreover, reduced fractional anisotropy was observed in the corpus callosum, consistent with the results of previous neuroimaging studies of people who stutter with unknown genetic backgrounds. Analysis of gene expression data showed that these structural differences appeared at the locations in which expression of AP4E1 is relatively high. Moreover, the pattern of grey matter volume differences was significantly associated with AP4E1 expression across the left supratentorial regions. This spatial congruency further supports the connection between AP4E1 mutations and the observed structural differences.

Performance of Bimanual Finger Coordination Tasks in Speakers Who Stutter

Stuttering is a neurodevelopmental speech disorder characterized by the symptoms of speech repetition, prolongation, and blocking. Stuttering-related dysfluency can be transiently alleviated by providing an external timing signal such as a metronome or the voice of another person. Therefore, the existence of a core motor timing deficit in stuttering has been speculated. If this is the case, then motoric behaviors other than speech should be disrupted in stuttering. This study examined motoric performance on four complex bimanual tasks in 37 adults who stutter and 31 fluent controls. Two tasks utilized bimanual rotation to examine motor dexterity, and two tasks used the bimanual mirror and parallel tapping movements to examine timing control ability. Video-based analyses were conducted to determine performance accuracy and speed. The results showed that individuals who stutter performed worse than fluent speakers on tapping tasks but not on bimanual rotation tasks. These results suggest stuttering is associated with timing control for general motor behavior.

Stuttering: A Disorder of Energy Supply to Neurons?

Stuttering is a disorder characterized by intermittent loss of volitional control of speech movements. This hypothesis and theory article focuses on the proposal that stuttering may be related to an impairment of the energy supply to neurons. Findings from electroencephalography (EEG), brain imaging, genetics, and biochemistry are reviewed: (1) Analyses of the EEG spectra at rest have repeatedly reported reduced power in the beta band, which is compatible with indications of reduced metabolism. (2) Studies of the absolute level of regional cerebral blood flow (rCBF) show conflicting findings, with two studies reporting reduced rCBF in the frontal lobe, and two studies, based on a different method, reporting no group differences. This contradiction has not yet been resolved. (3) The pattern of reduction in the studies reporting reduced rCBF corresponds to the regional pattern of the glycolytic index (GI; Vaishnavi et al., 2010). High regional GI indicates high reliance on non-oxidative metabolism, i.e., glycolysis. (4) Variants of the gene ARNT2 have been associated with stuttering. This gene is primarily expressed in the brain, with a pattern roughly corresponding to the pattern of regional GI. A central function of the ARNT2 protein is to act as one part of a sensor system indicating low levels of oxygen in brain tissue and to activate appropriate responses, including activation of glycolysis. (5) It has been established that genes related to the functions of the lysosomes are implicated in some cases of stuttering. It is possible that these gene variants result in a reduced peak rate of energy supply to neurons. (6) Lastly, there are indications of interactions between the metabolic system and the dopamine system: for example, it is known that acute hypoxia results in an elevated tonic level of dopamine in the synapses. Will mild chronic limitations of energy supply also result in elevated levels of dopamine? The indications of such interaction effects suggest that the metabolic theory of stuttering should be explored in parallel with the exploration of the dopaminergic theory.

Association Between Gray Matter Volume Variations and Energy Utilization in the Brain: Implications for Developmental Stuttering

Purpose The biological mechanisms underlying developmental stuttering remain unclear. In a previous investigation, we showed that there is significant spatial correspondence between regional gray matter structural anomalies and the expression of genes linked to energy metabolism. In the current study, we sought to further examine the relationship between structural anomalies in the brain in children with persistent stuttering and brain regional energy metabolism. Method High-resolution structural MRI scans were acquired from 26 persistent stuttering and 44 typically developing children. Voxel-based morphometry was used to quantify the between-group gray matter volume (GMV) differences across the whole brain. Group differences in GMV were then compared with published values for the pattern of glucose metabolism measured via F18 fluorodeoxyglucose uptake in the brains of 29 healthy volunteers using positron emission tomography. Results A significant positive correlation between GMV differences and F18 fluorodeoxyglucose uptake was found in the left hemisphere (ρ = .36, p < .01), where speech-motor and language processing are typically localized. No such correlation was observed in the right hemisphere (ρ = .05, p = .70). Conclusions Corroborating our previous gene expression studies, the results of the current study suggest a potential connection between energy metabolism and stuttering. Brain regions with high energy utilization may be particularly vulnerable to anatomical changes associated with stuttering. Such changes may be further exacerbated when there are sharp increases in brain energy utilization, which coincides with the developmental period of rapid speech/language acquisition and the onset of stuttering during childhood. Supplemental Material https://doi.org/10.23641/asha.14110454.

Evaluation of recurrent GNPTAB, GNPTG, and NAGPA variants associated with stuttering

Stuttering is a childhood-onset fluency disorder, intertwined with physiological, emotional, and anxiety factors. The present study was designed to evaluate the recurrence of the reported mutations among three previously implicated (GNPTAB, GNPTG, NAGPA) candidate genes, in persons with stuttering from south India. Mutation screening was performed among 64 probands on 12 specific exons, by Sanger sequencing. A total of 12 variants were identified, which included five nonsynonymous, five synonymous, and two noncoding variants. Three unrelated probands harbored heterozygous missense variants at conserved coding positions across species (p. Glu1200Lys in GNPTAB, p. Ile268Leu in GNPTG and p. Arg44Pro in NAGPA). Of these, only one variant (p. Glu1200Lys in GNPTAB) cosegregated with the affected status while p. Ile268Leu in GNPTG gene was found to be a rare de novo variant. Although this study identified some previously reported variants that have been claimed to have a role in stuttering, we confirmed only one of these to be a likely causal de novo variant (p.Ile268Leu) in the GNPTG gene at an allele frequency of 0.8% (1/128) in the families with stuttering.

Dissociated Development of Speech and Limb Sensorimotor Learning in Stuttering: Speech Auditory-motor Learning is Impaired in Both Children and Adults Who Stutter

Stuttering is a neurodevelopmental disorder of speech fluency. Various experimental paradigms have demonstrated that affected individuals show limitations in sensorimotor control and learning. However, controversy exists regarding two core aspects of this perspective. First, it has been claimed that sensorimotor learning limitations are detectable only in adults who stutter (after years of coping with the disorder) but not during childhood close to the onset of stuttering. Second, it remains unclear whether stuttering individuals' sensorimotor learning limitations affect only speech movements or also unrelated effector systems involved in nonspeech movements. We report data from separate experiments investigating speech auditory-motor learning (N = 60) and limb visuomotor learning (N = 84) in both children and adults who stutter versus matched nonstuttering individuals. Both children and adults who stutter showed statistically significant limitations in speech auditory-motor adaptation with formant-shifted feedback. This limitation was more profound in children than in adults and in younger children versus older children. Between-group differences in the adaptation of reach movements performed with rotated visual feedback were subtle but statistically significant for adults. In children, even the nonstuttering groups showed limited visuomotor adaptation just like their stuttering peers. We conclude that sensorimotor learning is impaired in individuals who stutter, and that the ability for speech auditory-motor learning-which was already adult-like in 3-6 year-old typically developing children-is severely compromised in young children near the onset of stuttering. Thus, motor learning limitations may play an important role in the fundamental mechanisms contributing to the onset of this speech disorder.

Streptococcal Infection as a Major Historical Cause of Stuttering: Data, Mechanisms, and Current Importance

Stuttering is one of the most well-known speech disorders, but the underlying neurological mechanisms are debated. In addition to genetic factors, there are also major non-genetic contributions. It is here proposed that infection with group A beta-hemolytic streptococcus (GAS) was a major underlying cause of stuttering until the mid-1900s when penicillin was introduced in 1943. The main mechanism proposed is an autoimmune reaction from tonsillitis, targeting specific molecules, for example within the basal ganglia. It is here also proposed that GAS infections may have continued to cause stuttering to some extent, to the present date, though more rarely. If so, early diagnosis of such cases would be of importance. Childhood cases with sudden onset of stuttering after throat infection may be particularly important to assess for possible GAS infection. The support for this hypothesis primarily comes from three lines of argument. First, medical record data from the 1930s strongly indicates that there was one type of medical event in particular that preceded the onset of childhood stuttering with unexpected frequency: diseases related to GAS throat infections. In particular, this included tonsillitis and scarlet fever, but also rheumatic fever. Rheumatic fever is a childhood autoimmune sequela of GAS infection, which was a relatively widespread medical problem until the early 1960s. Second, available reports of changes of the childhood prevalence of stuttering indicate striking parallels between stuttering and the incidence of rheumatic fever, with: (1) decline from the early 1900s; (2) marked decline from the introduction of penicillin in the mid 1940s; and (3) reaching a more stable level in the 1960s. The correlations between the data for stuttering and rheumatic fever after the introduction of penicillin are very high, at about 0.95. Third, there are established biological mechanisms linking GAS tonsillitis to immunological effects on the brain. Also, a small number of more recent case reports have provided further support for the hypothesis linking stuttering to GAS infection. Overall, it is proposed that the available data provides strong evidence for the hypothesis that GAS infection was a major cause of stuttering until the mid-1900s, interacting with genetic predisposition.

Trait perspective-taking and need for cognition in the formation of stereotypes about people who stutter

People who stutter (PWS) suffer from stereotypes portraying them as timid and anxious, which may affect their relationships and careers. One of the mechanisms for this stereotyping is the anchoring and adjustment heuristic, whereby individuals make judgements about PWS by using previous experiences for the initial judgement and then adjust accordingly. In the current study (n = 309) we replicate previous findings that individuals stereotype PWS by anchoring to experiences with episodic stuttering and adjusting toward typical non-stuttering individuals, although insufficiently. We extend this finding by testing whether trait perspective-taking and need for cognition moderate this relationship. The results show that trait perspective-taking decreases stereotyping of non-PWS, while having no effect on PWS stereotyping. However, need for cognition exhibited no consistent moderating effect on stereotyping.

Linking Lysosomal Enzyme Targeting Genes and Energy Metabolism with Altered Gray Matter Volume in Children with Persistent Stuttering

Developmental stuttering is a childhood onset neurodevelopmental disorder with an unclear etiology. Subtle changes in brain structure and function are present in both children and adults who stutter. It is a highly heritable disorder, and 12-20% of stuttering cases may carry a mutation in one of four genes involved in intracellular trafficking. To better understand the relationship between genetics and neuroanatomical changes, we used gene expression data from the Allen Institute for Brain Science and voxel-based morphometry to investigate the spatial correspondence between gene expression patterns and differences in gray matter volume between children with persistent stuttering (n = 26, and 87 scans) and their fluent peers (n = 44, and 139 scans). We found that the expression patterns of two stuttering-related genes (GNPTG and NAGPA) from the Allen Institute data exhibited a strong positive spatial correlation with the magnitude of between-group gray matter volume differences. Additional gene set enrichment analyses revealed that genes whose expression was highly correlated with the gray matter volume differences were enriched for glycolysis and oxidative metabolism in mitochondria. Because our current study did not examine the participants' genomes, these results cannot establish the direct association between genetic mutations and gray matter volume differences in stuttering. However, our results support further study of the involvement of lysosomal enzyme targeting genes, as well as energy metabolism in stuttering. Future studies assessing variations of these genes in the participants' genomes may lead to increased understanding of the biological mechanisms of the observed spatial relationship between gene expression and gray matter volume.

Psychological correlates of biological and non-biological explanations for stuttering

Purpose: This study examined whether people who stutter would associate biological and non-biological explanations of stuttering with the endorsement of stereotypes about people who stutter, prognostic expectations for the reduction of stuttering, feelings of guilt, self-blame, and shame about stuttering, and agency for speech modification.Method: This was a cross-sectional study including 372 adults who stutter. Participants completed a web survey with scales that measured their agreement with biological and non-biological models of stuttering; their endorsement of common stereotypes for people who stutter; prognostic expectations for reduced stuttering; feelings of guilt, self-blame, and shame about stuttering; and feelings of agency in their ability to modify their speech.Result: Biological explanations for stuttering were significantly correlated with reduced stereotype endorsement about people who stutter, lower prognostic expectations for reducing stuttering, and reduced feelings of guilt and self-blame regarding stuttering. Non-biological explanations for stuttering were significantly correlated with increased endorsement of negative stereotypes about people who stutter, increased prognostic expectations for reducing stuttering, and increased feelings of guilt, self-blame, and shame about stuttering.Conclusion: It is concluded that the implications of biological framing of stuttering among people who stutter are complex and should be well thought out by professionals. Explaining stuttering as biological, but responsive to personal and environmental influences, may lead to reduced guilt and self-blame, while at the same time fostering feelings of agency for speech modification.

Genetic pathways involved in human speech disorders

Rare genetic variants that disrupt speech development provide entry points for deciphering the neurobiological foundations of key human capacities. The value of this approach is illustrated by FOXP2, a transcription factor gene that was implicated in speech apraxia, and subsequently investigated using human cell-based systems and animal models. Advances in next-generation sequencing, coupled to de novo paradigms, facilitated discovery of etiological variants in additional genes in speech disorder cohorts. As for other neurodevelopmental syndromes, gene-driven studies show blurring of boundaries between diagnostic categories, with some risk genes shared across speech disorders, intellectual disability and autism. Convergent evidence hints at involvement of regulatory genes co-expressed in early human brain development, suggesting that etiological pathways could be amenable for investigation in emerging neural models such as cerebral organoids.

A systematic review of interventions for adults who stutter

PURPOSE

To examine the effectiveness of (i) face to face interventions (ii) models of service delivery and (iii) psychological treatments combined with speech-focused interventions for adults who stutter.

METHODS

Five electronic databases and three clinical trial registries were searched. Systematic reviews, randomised controlled trials (RCTs) and studies that applied an intervention with adults who stutter were included. Pharmaceutical interventions were excluded. Primary outcomes included a measure of stuttering severity. Risk of bias assessment was conducted on included studies and overall quality of the evidence was graded.

RESULTS

Five RCTS, four registered trials and three systematic reviews met inclusion criteria. Intervention approaches included speech restructuring programs (e.g. Camperdown Program) and transcranial direct current stimulation (tDCS). One study investigated cognitive behaviour therapy (CBT) alongside speech restructuring. Overall, studies were classified low risk of bias and good quality. Speech restructuring was included in all but one study (tDCS study) and had the most evidence i.e. supported by the greatest number of RCTs. On average, stuttering frequency was reduced by 50-57 % using speech restructuring approaches. No study reduced stuttering to the same level as community controls who don't stutter. The study on tDCS reduced stuttering frequency by 22-27 %. Speech restructuring delivered via telehealth was non-inferior to face-to-face intervention. One study reported CBT was an effective adjunct to speech restructuring interventions.

CONCLUSION

Speech restructuring interventions were found to reduce stuttering in adults, however degree and maintenance of fluency varied. The body of evidence surrounding tDCS and psychological interventions is limited. Replication studies should be considered.

Involvement of the Cortico-Basal Ganglia-Thalamocortical Loop in Developmental Stuttering

Stuttering is a complex neurodevelopmental disorder that has to date eluded a clear explication of its pathophysiological bases. In this review, we utilize the Directions Into Velocities of Articulators (DIVA) neurocomputational modeling framework to mechanistically interpret relevant findings from the behavioral and neurological literatures on stuttering. Within this theoretical framework, we propose that the primary impairment underlying stuttering behavior is malfunction in the cortico-basal ganglia-thalamocortical (hereafter, cortico-BG) loop that is responsible for initiating speech motor programs. This theoretical perspective predicts three possible loci of impaired neural processing within the cortico-BG loop that could lead to stuttering behaviors: impairment within the basal ganglia proper; impairment of axonal projections between cerebral cortex, basal ganglia, and thalamus; and impairment in cortical processing. These theoretical perspectives are presented in detail, followed by a review of empirical data that make reference to these three possibilities. We also highlight any differences that are present in the literature based on examining adults versus children, which give important insights into potential core deficits associated with stuttering versus compensatory changes that occur in the brain as a result of having stuttered for many years in the case of adults who stutter. We conclude with outstanding questions in the field and promising areas for future studies that have the potential to further advance mechanistic understanding of neural deficits underlying persistent developmental stuttering.

Neurofilament-lysosomal genetic intersections in the cortical network of stuttering

The neurobiological underpinnings of stuttering, a speech disorder characterized by disrupted speech fluency, remain unclear. While recent developments in the field have afforded researchers the ability to pinpoint several genetic profiles associated with stuttering, how these specific genetic backgrounds impact neuronal circuits and how they generate or facilitate the emergence of stuttered speech remains unknown. In this study, we identified the large-scale cortical network that characterizes stuttering using functional connectivity MRI and graph theory. We performed a spatial similarity analysis that examines whether the topology of the stuttering cortical network intersects with genetic expression levels of previously reported genes for stuttering from the protein-coding transcriptome data of the Allen Human Brain Atlas. We found that GNPTG - a gene involved in the mannose-6-phosphate lysosomal targeting pathways - was significantly co-localized with the stuttering cortical network. An enrichment analysis demonstrated that the genes identified with the stuttering cortical network shared a significantly overrepresented biological functionality of Neurofilament Cytoskeleton Organization (NEFH, NEFL and INA). The relationship between lysosomal pathways, cytoskeleton organization, and stuttering, was investigated by comparing the genetic interactome between GNPTG and the neurofilament genes implicated in the current study. We found that genes of the interactome network, including CDK5, SNCA, and ACTB, act as functional links between lysosomal and neurofilament genes. These findings support the notion that stuttering is due to a lysosomal dysfunction, which has deleterious effects on the neurofilament organization of the speech neuronal circuits. They help to elucidate the intriguing, unsolved link between lysosomal mutations and the presence of stuttering.

Human GNPTAB stuttering mutations engineered into mice cause vocalization deficits and astrocyte pathology in the corpus callosum

Stuttering is a common neurodevelopmental disorder that has been associated with mutations in genes involved in intracellular trafficking. However, the cellular mechanisms leading to stuttering remain unknown. Engineering a mutation in N-acetylglucosamine-1-phosphate transferase subunits α and β (GNPTAB) found in humans who stutter into the mouse Gnptab gene resulted in deficits in the flow of ultrasonic vocalizations similar to speech deficits of humans who stutter. Here we show that other human stuttering mutations introduced into this mouse gene, Gnptab Ser321Gly and Ala455Ser, produce the same vocalization deficit in 8-day-old pup isolation calls and do not affect other nonvocal behaviors. Immunohistochemistry showed a marked decrease in staining of astrocytes, particularly in the corpus callosum of the Gnptab Ser321Gly homozygote mice compared to wild-type littermates, while the staining of cerebellar Purkinje cells, oligodendrocytes, microglial cells, and dopaminergic neurons was not significantly different. Diffusion tensor imaging also detected deficits in the corpus callosum of the Gnptab Ser321Gly mice. Using a range of cell type-specific Cre-drivers and a Gnptab conditional knockout line, we found that only astrocyte-specific Gnptab-deficient mice displayed a similar vocalization deficit. These data suggest that vocalization defects in mice carrying human stuttering mutations in Gnptab derive from abnormalities in astrocytes, particularly in the corpus callosum, and provide support for hypotheses that focus on deficits in interhemispheric communication in stuttering.

Genetic factors and therapy outcomes in persistent developmental stuttering

PURPOSE

We investigated whether outcomes of therapy for persistent developmental stuttering differ in individuals who carry a mutation in one of the known genes associated with stuttering compared to individuals without such mutations.

METHOD

We studied outcomes of an intensive fluency shaping-based therapy program in individuals with persistent developmental stuttering. We evaluated a cohort of 51 stuttering individuals with who carried a mutation in either the GNPTAB, GNPTG, NAGPA, or AP4E1 gene. We compared therapy outcomes in these individuals with outcomes in 51 individuals matched for age, gender, and ethnicity, who stutter and underwent the same therapy program, and did not carry a mutation in any of these genes. Fluency pre- and post-therapy was evaluated using blinded observer-based quantitative stuttering dysfluency measures (Dysfluent Words Score, DWS), and by subjects' self-reported measures of struggle, avoidance and expectancy behavior associated with speaking (Perceptions of Stuttering Inventory, PSI). The difference between pre- and post-therapy fluency scores was taken as the measure of near-term therapy efficacy.

RESULTS

Comparison of fluency measures showed a strong effect of therapy overall. Mutation carriers achieved significantly less resolution in PSI following therapy, with PSI scores showing significantly less improvement in individuals who carry a mutation (p = 0.0157, RR = 1.75, OR = 2.92) while the group difference in DWS between carriers and non-carriers was statistically not significant in the present study, the trend observed in the results warrants further research focused on this important issue.

CONCLUSIONS

These results suggest stuttering is more resistant to therapy in individuals who carry a mutation in one of the genes known to be associated with stuttering.

Genetic epidemiology of stuttering among school children in the state of Tamil Nadu, India

PURPOSE

Stuttering is a fluency disorder with a worldwide prevalence of 1%. Reports on the epidemiology of stuttering in India are limited. Our primary goal was to examine the prevalence of the disorder among school children. The study also aimed to examine risk factors associated with severity and the impact of parental consanguinity in stuttering.

METHOD

Children from 97 schools in the State of Tamil Nadu, India were screened. Extensive speech characterization, epidemiological details and three-generational pedigrees were collected for 180 probands. The genetic basis of stuttering was examined using the analysis of genealogical index of families (GIF), kinship group and sibling recurrence risk (SRR) measures. Regression analysis and chi-square tests were performed to test the association of risk factors with severity of the disorder.

RESULTS

Among the 74,544 school children screened, the prevalence of stuttering was found to be 0.46%. Pedigree analysis revealed a positive family history in 101 (56%) probands; overall familial incidence was 11%. We observed an overall male-favored sex ratio (4:1). Familial aggregation (GIF = 442.60, p-value <0.001) and sibling recurrence risk ratio (K_s = 0.197, SD = 0.041) was high among consanguineous families. Severity of stuttering was strongly associated with gender and moderately associated with age at onset.

CONCLUSION

The prevalence of stuttering in Tamil Nadu is estimated for the first time in this study. High familial incidence, familial aggregation and sibling recurrence risk ratio point to the presence of a genetic basis. Familial aggregation was high among consanguineous families although consanguinity did not seem to play a role in severity.

Relationship between serum homovanillic acid, DRD2 C957T (rs6277), and hDAT A559V (rs28364997) polymorphisms and developmental stuttering

The involvement of the brain dopamine system in the pathophysiology of developmental stuttering has been previously suggested. In the present study, we aimed to investigate the relationship between developmental stuttering in children and the levels of serum homovanillic acid (HVA), dopamine D2 receptor (DRD2) C957T (rs6277), and solute carrier family 6 member 3 (SLC6A3) human dopamine transporter (hDAT) A559V (rs28364997) single-nucleotide polymorphisms. In a case-control study, serum level of HVA, DRD2 C957T, and DAT A559V were compared between 85 children who stuttered (CWS) and 85 age- and sex-matched children who did not stutter (CWNS). Although serum level of HVA was higher among the CWS (median = 25.50 ng/mL) than that in the CWNS (median = 17.40 ng/mL), the difference between the two groups was not significant (p = 0.43). No significant correlation was observed between age and the level of HVA among all the participants (r = -0.15, p = 0.06), nor was there any correlation among the CWS (r = -0.19, p = 0.14) or among the CWNS (r = -0.13, p = 0.27) according to the Spearman correlation coefficient. On the other hand, there was a significant negative correlation between age from stuttering onset and the serum level of HVA among the CWS group (r = -0.32, p = 0.01). The Spearman correlation coefficient did not indicate any significant correlation between stuttering severity and HVA in CWS (r = -0.06, p = 0.59). The mutant allele of hDAT A559V was observed neither in the CWS nor in the controls. The allele frequencies of DRD2 C957T were not significantly different between the CWS and the CWNS; however, the frequency of the TT genotype was significantly higher among the CWS (p = 0.02), which was associated with 2.25-fold susceptibility to stuttering (OR = 2.25, 95% CI = 1.03 to 4.90, p = 0.04). Our findings suggest that the serum level of HVA might be a biomarker for dopaminergic involvement in the pathogenesis of stuttering. Moreover, the present study indicates that the DRD2 C957T polymorphism might be a risk factor for the development of stuttering among Iranian Kurdish population.

Functional and Neuroanatomical Bases of Developmental Stuttering: Current Insights

Affecting 5% of all preschool-aged children and 1% of the general population, developmental stuttering-also called childhood-onset fluency disorder-is a complex, multifactorial neurodevelopmental disorder characterized by frequent disruption of the fluent flow of speech. Over the past two decades, neuroimaging studies of both children and adults who stutter have begun to provide significant insights into the neurobiological bases of stuttering. This review highlights convergent findings from this body of literature with a focus on functional and structural neuroimaging results that are supported by theoretically driven neurocomputational models of speech production. Updated views on possible mechanisms of stuttering onset and persistence, and perspectives on promising areas for future research into the mechanisms of stuttering, are discussed.