VOCAL FUNDAMENTAL-FREQUENCY IN A TWIN SAMPLE - LOOKING FOR A GENETIC EFFECT

Many complex, quantitative traits are the result of genetic and environmental interactions. The production of the human voice is such a trait and therefore can be examined for the action of genetic factors. In this study, the twin method was utilized in order to test for the presence of a genetic component in vocal fundamental frequency (VFF). The voices of 122 adult twins from the Midwest Twin Register (University of Kansas) were analyzed for VFF. The twins read the first paragraph of the Rainbow Passage, and the resulting recording was analyzed for the vocal fundamental frequency by means of a specialized computer program. Zygosity of these twins was determined by their genotypic comparisons based upon 18 different genetic markers. Preliminary analysis of data resulted in computation of intraclass correlations. The high intraclass correlations (r = 0.621 for female and r = 0.845 for male twin pairs) reflect the high degree of familial resemblance of the twins compared to randomly matched pairs in the sample. After adjustment of the raw values of VFF for age and weight, these coefficients were lowered (r = 0.516 for females and r = 0.690 for males) but still remained significant. The application of the twin model to female twins (41 pairs of monozygotic and eight pairs of dizygotic) allowed comparisons of the correlation coefficients between both types of twins. For raw VFF data no differences were found (r = 0.609 for MZ twins and r = 0.669 for DZ twins). After adjustment for age and weight, the correlation coefficient for dizygotic twins became lower (r = 0.338) than that for monozygotic twins (r = 0.539). This difference between the monozygotic and dizygotic twins is suggestive of the important role of genetics in the production of voice. These results also suggest that the VFF may be a useful phenotype that can be utilized for the assessment of genetic involvement in voice production.