Similarity in monozygotic twins regarding vocal performance and acoustic features and their possible clinical relevance

Auditory similarities in voices of monozygotic twins have already been desc ribed in the literature. However, is there a clinical relevance! Thus, the present study was designed to identify parameters of vocal performance and acoustic features which are significantly more similar in monozygotic twins than in non-related persons. In our hypothesis, comparable prerequisites f or an increased vocal load in a profession or in an artistic education of t he voice could be due to these similarities. We compared intra-pair differe nces with data from a control group. Moreover,we examined the correlation o f intra-pair differences with the age of the monozygotic twins. A greater d ifference in older twin pairs than in younger pairs could show the effect o f an exogene influence. In addition to the few phoniatric studies in twins in the literature, we used current methods for acoustic analysis. We examin ed seven parameters of vocal performance and three acoustic features in 31 monozygotic twin pairs (median age 36 years, range 18-75 years) and compare d them with 30 control group pairs, which consisted of non-related persons of the same age and sex, newly combined from the group of monozygotic twins ("statistical twins"). We found significant differences in seven of ten pa rameters (vocal range, highest and lowest vocal fundamental frequency,funda mental speaking frequency, maximum voice intensity, number of partials, vib rate of intensity; U-test by Mann-Whitney). No correlation of the differenc es of the identical twins with age was found in the examined parameters. Th e voices of identical twins are significantly more similar than those of no n-related persons regarding the above mentioned features. Thus, the suitabi lity of the voices of monozygotic twins for professions with a high demand on voice is comparable. Results of the group comparison correlate largely w ith the literature. The missing correlation with age could be due to the fa ct that the environmental effects were not measurable, and/or the developme nt of the voice is more influenced by genetic effects.