Exploring genetic and environmental effects in dysphonia: a twin study

PURPOSE To explore the existence of genetic effects as well as the interaction between potential genetic effects and a voice-demanding occupation on dysphonia. METHOD One thousand seven hundred and twenty-eight Finnish twins (555 male; 1,173 female) born between 1961 and 1989 completed a questionnaire concerning vocal symptoms and occupation. The zygosity determination resulted in 125 monozygotic and 108 dizygotic full twin pairs. A composite variable called dysphonia was formed by summing 6 vocal symptoms based on the results of a factor analysis. Twin model fitting was used to explore the contribution of genetic and environmental effects on the dysphonia variable. RESULTS Individual differences in dysphonia were explained by genetic effects (35%) and nonshared environmental effects (65%). Shared environmental effects were estimated at 0%. Also, the authors found that for the participants who worked in voice-demanding occupations, the causes of dysphonia were more environmental, whereas the etiology of the symptoms was more strongly affected by genes in the participants with less voice-demanding occupations. However, this gene-environment interaction was not statistically significant. CONCLUSION Both genetic and environmental factors have an impact on the etiology of voice problems. Environmental factors, either independently or interacting with genetic factors, seem to play the key role, especially if the person has a voice-demanding occupation.