Causes of deafness identified

Published: Thursday 15 March 2007

according to the Encyclopedia of Deafness and Hearing Disorders (second edition), roughly 0.1 per cent of the world's population is deaf. Scientists of University of Illinois, usa, in a study, have identified a molecular cause of the problem.

The researchers said that within the cochlea of the inner ear, sound waves cause the basilar membrane to vibrate. These vibrations stimulate hair cells, which trigger nerve impulses transmitted to the brain. They also found that mutations in a protein called espin can cause floppiness in tiny bundles of protein filaments, impairing the passage of vibrations and resulting in deafness. Filamentous actin (f-actin) is a rod-like protein that provides a structural framework in living cells. f-actin is organised into bundles by espin, a linker protein found in sensory cells, including cochlear hair cells.Genetic mutations in espin's f-actin binding sites are linked to deafness in mice and human beings.

"We found the structure of the bundles changes dramatically when normal espin is replaced with espin mutants that cause deafness," says Gerard Wong, a professor of materials science and engineering, physics and bioengineering at the University of Illinois at Urbana-Champaign.

"The interior structure of the bundles changes from a rigid, hexagonal array of uniformly twisted filaments to a liquid crystalline arrangement of filaments. The rigidity of these bundles is essential for hearing," says Wong. High resolution x-ray diffraction experiments allowed the researchers to solve the structure of various espin-actin bundles. Wong also says he has high hopes from this finding. Changing gene expression to turn on the transcription of just a fraction of normal espin could potentially salvage some hearing.

"We have identified a mechanism to potentially rescue this particular kind of pathology," says Wong. "Even so, this is really the first step. This work has relevance to not just human hearing, but also to artificial sensors."

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