The human elastin gene (ELN) is responsible for the generation of elastic fibres in the extracellular matrix of connective tissue throughout the body, including the vocal folds. Individuals with Supravalvular aortic stenosis (SVAS) and Williams syndrome (WS) lack one normal ELN allele due to heterozygous ELN abnormalities, resulting in a haploinsufficiency. We measured perceptual and acoustic characteristics of voice quality in individuals with SVAS and WS to investigate the consequences to vocal function secondary to ELN haploinsufficiency. Results indicated that the voice quality of individuals with SVAS/WS was rated as significantly more abnormal, rough, and hoarse compared to normal controls, and that adults with SVAS/WS were rated as significantly lower in pitch. Acoustic measures indicated that individuals with SVAS/WS produced greater instability of fundamental frequency during phonation (as reflected via increased pitch sigma and increased jitter). These findings support the possibility that heterozygous ELN abnormalities negatively influence vocal fold biomechanics and the resulting sound produced by the vibrating glottis. (Contains 4 tables and 4 figures.)