twins, bowing, EMG, breathiness, aging


Objectives: This study examined case histories, diagnostic features, and treatment response in two 79-year-old male monozygotic (identical) twins with vocal fold bowing, exploring both genetic and environmental factors.
Study Design: Case study.
Methods: DNA concordance was examined via cheek swab. Case histories, videostroboscopy, auditory- and visual-perceptual assessment, electromyography, acoustic measures, and Voice Handicap ratings were undertaken. Both twins underwent surgical intervention and subsequent voice therapy.
Results: Monozygosity was confirmed for DNA polymorphisms, with 10 of 10 concordance for STR DNA markers. For both twins, auditory and visual-perceptual assessments indicated severe bowing, hoarseness and breathiness, although Twin 1 was judged to be extremely severe. Differences in RMS amplitudes were observed for TA and LCA muscles, with smaller relative amplitudes observed for the Twin 1 versus Twin 2. No consistent voice improvement was observed following surgical intervention(s), despite improved mid-membranous vocal fold closure. Marked reductions in Voice Handicap Index total scores were observed following behavioral voice therapy, coinciding with increased mid-membranous and posterior laryngeal (interarytenoid) glottal closure. No substantive differences in acoustic measures were observed.
Conclusions: Vocal fold bowing was more severe for Twin 1 versus Twin 2 despite identical heritability factors. Overall voice improvement with treatment was greater for Twin 2 than Twin 1. Environmental factors might partially account for the differences observed between the twins, including variability in their responsiveness to behavioral voice therapy. Voice therapy was useful in improving mid-membranous and posterior laryngeal closure, although dysphonia remained severe in both cases.

Original Publication Citation

Tanner, K., Sauder, C., Thibeault, S., Dromey, C. & Smith, M.E. (2010). Vocal fold bowing in elderly male monozygotic twins: A case study. Journal of Voice, 24, 470-476.

Document Type

Peer-Reviewed Article

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David O. McKay School of Education


Communication Disorders