Purpose: Recently, Simberg et al. (2009) found genetic effects on a composite variable consisting of 6 vocal symptom items measuring dysphonia. The purpose of the present study was to determine genetic and environmental effects on the individual vocal symptoms in a population-based sample of Finnish twins.
Method: The sample comprised 1,728 twins (125 monozygotic and 108 dizygotic twin pairs) born between 1961 and 1989, who completed a questionnaire concerning 6 vocal symptoms. Values for additive genetic, dominant genetic, shared environmental, and nonshared environmental components were computed separately for all symptoms. Multivariate analyses to determine genetic and environmental associations between the vocal symptoms were also performed.
Results: Variance was explained by significant additive genetic effects (27%) in only one of the vocal symptoms, namely, voice gets low or hoarse, whereas the variance of one of the vocal symptoms, voice gets strained or tires, could be explained by nonshared environmental influence alone. Multivariate analyses showed that the correlations for most of the symptom combinations were significant.
Conclusions: Both genetic and environmental components influence vocal symptoms. Genetic and environmental influences seem to be differently balanced in different vocal symptoms. Genetic effects are moderate, whereas environmental effects seem to be the most important factor contributing to the presence of vocal symptoms.