Genetic and Environmental Effects on Vocal Symptoms
Genetic and environmental components influence vocal symptoms, according to a study in the Journal of Speech, Language, and Hearing Research [doi:10.1044/1092-4388(2011/10-0188)]. Researchers conducted a study to determine genetic and environmental effects on the individual vocal symptoms measuring dysphonia in a population-based sample of Finnish twins.
In the study, 1,728 twins (125 identical and 108 fraternal pairs) born between 1961 and 1989 completed a questionnaire about six vocal symptoms. The researchers computed values for additive genetic, dominant genetic, shared environmental, and nonshared environmental components separately for all symptoms. They also performed multivariate analyses to determine genetic and environmental associations between the vocal symptoms.
In only one of the vocal symptoms—voice gets low or hoarse—variance was explained by significant additive genetic effects (27%). In another symptom—voice gets strained or tires—the variance could be explained by nonshared environmental influence alone. Multivariate analyses showed that the correlations for most of the symptom combinations were significant.
Researchers conclude that genetic and environmental influences seem to be differently balanced in different vocal symptoms and that genetic effects are moderate, whereas environmental effects seem to be the most important factor contributing to the presence of vocal symptoms.
Motor Sequencing Deficit and Speech Sound Disorder
A measure of motor sequencing deficit may be a potential endophenotype—a marker of familial risk—of speech sound disorder (SSD), according to a recent study in Psychiatric Genetics. Researchers identified SSD and measured motor sequencing during oral motor testing in multigenerational members of a family with evidence of a familial motor-based SSD.
Analyses revealed that in seven of the 10 family members with available data, SSD affectation status and motor sequencing status coincided. Linkage analysis revealed four regions of interest, primarily identified with the measure of motor sequencing ability. One region overlaps with a locus implicated in rapid alternating naming. The locus of one of the regions contains a locus implicated in dyslexia; the locus of another region borders on a gene known to affect the component traits of language impairment.
These results are consistent with a motor-based endophenotype of SSD that would be informative for genetic studies. The linkage results warrant follow-up in additional families and with fine mapping or next-generation approaches to gene identification. Search doi: 10.1097/YPG.0b013e328353ae92.
Novel Candidate Genes for Childhood Apraxia of Speech
A research study in Genetics in Medicine to identify new genes and genetic variations associated with childhood apraxia of speech suggests that several heterogeneous genomic pathways are associated with the disorder. Researchers used a comprehensive protocol that samples speech in challenging contexts to assess 24 participants who were suspected to have childhood apraxia of speech. All participants met clinical-research criteria for childhood apraxia of speech.
Array comparative genomic hybridization analyses—with increased coverage of genes and regions previously associated with childhood apraxia of speech—detected a total of 16 copy-number variations with potential consequences for speech-language development in 12 of the 24 participants. The copy-number variations occurred on 10 chromosomes, three of which had two to four candidate regions. Several participants were identified with copy-number variations in two to three regions. The findings suggest that different genes may be associated with this rare, severe, and persistent speech disorder. Search DOI: doi:10.1038/gim.2012.72.
Connexin Mutations in Progressive Sensorineural Hearing Loss
Genotype cannot be used to differentiate non-progressive from progressive hearing loss cases, according to a recent study in the Journal of Laryngology & Otology.
Given that mutations in the gap junction protein beta-2 gene are known to be responsible for mild to profound congenital and late-onset hearing loss, researchers investigated the molecular basis of progressive hearing loss compared with nonprogressive hearing loss. Following clinical evaluation, researchers performed genetic analysis on 72 patients with progressive sensorineural hearing loss.
The researchers established pathological genotypes in 16 patients (22.2%). Six different gap junction protein beta-2 gene mutations were detected in 15 patients; one specific mutation was responsible for 56% of the mutated alleles. Analyses revealed that similar pathological genotypes, occurring with similar frequencies, were responsible for progressive hearing loss, compared with reported genotypes for nonprogressive hearing loss. Thus, genotype cannot be used to differentiate nonprogressive from progressive hearing loss; in this study, patients both with and without an established pathological genotype had a similar clinical course.