Genome-wide association study of persistent developmental stuttering

A genome-wide association study (GWAS) is an approach that involves scanning markers across complete sets of DNA, or genomes, of many people to indentify genetic variations associated with a particular disease. A GWAS uses unrelated individuals, and for the purposes of this study, only those who persistently stutter, to identify common genetic variants among these people when contrasted to the general population of matched ethnicity. Eighty-four affected subjects, ages 13 to 70 years, of northern European ancestry and 107 matched controls were investigated to identify replicable candidate genes that influence the risk of individuals to stutter. The results associated 10 significant candidate genes with persistent developmental stuttering. In addition, the pathways in which these genes function to potentially disrupt the fluent production of speech were investigated. Functional significance was found with relevance to three functional categories pertaining to neural development, neural function, and behavior. Many of the genes were also found to be implicated in other known neurological, behavioral, and speech and language disorders

Individual differences in auditory-motor integration revealed by speech fluency manipulations

A role for auditory feedback in maintaining fluency appears less specific than for pitch control, as one example, but delayed auditory feedback (DAF) clearly provides a potent manipulation of fluency. As most speakers are susceptible to DAF, we predicted DAF is particularly suited to identifying individual differences in auditory-motor integration. We conducted a series of studies to probe susceptibility to DAF-induced disfluency in 60 normally fluent speakers during conversation and oral reading. We further contrasted DAF effects on fluency with dual-task effects on fluency. During conversation and reading under DAF (250 ms delay), multivariate cluster classification indicated speakers show high, low or intermediate susceptibility to disfluency. In contrast, dual-task effects on fluency appeared bimodal with individuals showing high or low susceptibility. DAF susceptibility was not related to dual-task disfluency in 41/60 speakers, but the remaining speakers were disfluent under DAF & dual-task conditions. When the DAF paradigm was extended to adults who stutter, most were classified as highly susceptible. The findings provide compelling evidence that individual differences need to be considered in auditory-motor integration research. Fluency is influenced by both auditory feedback and cognitive factors related to attention, which can inform theories of normal and disordered speech

PlexinA polymorphisms mediate the developmental trajectory of human corpus callosum microstructure

PlexinA is a neuronal receptor protein that facilitates axon guidance during embryogenesis. This gene is associated with several neurological disorders including Alzheimer's disease, Parkinson's disease and autism. However, the effect of variants of PlexinA on brain structure remains unclear. We demonstrate that single nucleotide polymorphisms within the intron and 3'UTR segments of several human PlexinA genes alter the post-natal developmental trajectory of corpus callosum microstructure. This is the first demonstration that PLXNA mediation of a neuroanatomical traits can be detected in humans using in vivo neuroimaging techniques. This result should encourage future research that targets specific disease-related polymorphisms and their relevant neural pathways

The Role of Effortful Control in Stuttering: Replication Study

No Abstract Availabl

Individual Variability in Delayed Auditory Feedback Effects on Speech Fluency and Rate in Normally Fluent Adults

Purpose Delayed auditory feedback (DAF) is known to induce stuttering-like disfluencies (SLDs) and cause speech rate reductions in normally fluent adults, but the reason for speech disruptions is not fully known, and individual variation has not been well characterized. Studying individual variation in susceptibility to DAF may identify factors that predispose an individual to be more or less dependent on auditory feedback. Method Participants were 62 normally fluent adults. Each participant performed a spontaneous speech task in 250-ms DAF and amplified nondelayed auditory feedback (NAF) conditions. SLDs, other disfluencies (ODs), speech errors (SEs), and articulation rate (AR) were measured under each condition. Results In the DAF condition, SLDs and SEs significantly increased, and AR decreased. Sex had a limited effect in that men exhibited higher rates of ODs and faster AR than women. More important, parametric cluster analysis identified that 2- and 3-subgroup solutions reveal important variation that differentiates tendencies toward disfluency changes and rate reduction under DAF, which are theoretically and empirically preferred to a single-group solution. Conclusion Individual variability in response to DAF may be accounted for by subgroups of individuals. This suggests that certain normally fluent individuals could be more dependent on intact feedback to maintain fluency