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Mutation’s inside role in deafness

U. SHEFFIELD (UK) — A mutation of a specific microRNA appears to prevent development of the auditory sensory hair cells in the inner ear, leading to hearing loss and deafness.

The cells are essential for encoding sound as electrical signals that are then sent to the brain. Researchers are hopeful the discovery could provide the basis for treating progressive hearing loss and deafness.

Details of the work, based on studies of mice, are reported in the Proceedings of the National Academy of Sciences.

Mice do not normally hear until about 12 days after birth. Prior to this age their immature hair cells must execute a precise genetic program that regulates the development of distinct types of sensory hair cell, namely inner and outer hair cells.

Researchers at the University of Sheffield and the Wellcome Trust Sanger Institute found that in a strain of mice called diminuendo—which carry a single base mutation in the miR-96 gene—hair cell development is arrested around birth.

The study shows that miR-96 normally regulates hair cell development by influencing the expression of many different genes associated with a wide range of developmental processes at a specific stage. The researchers discovered that the mutation hinders the development not only of the mechanically sensitive hair bundle on the cell apex but also the synaptic structures at the base that govern transfer of electrical information to the sensory nerves.

These new findings suggest that miR-96 is a master regulator responsible for coordinating the development of the sensory cells that are vital to hearing.

Since the mutation in miR-96 is known to cause human deafness and microRNA molecules can be targeted by drugs, the work also raises new opportunities for developing treatments to treat hearing loss.

“Progressive hearing loss affects a large proportion of the human population, including new born and young children,” says Walter Marcotti, a biomedical scientists at Sheffield. “Despite the relevance of this problem, very little is currently known regarding the genetic basis of progressive hearing loss. Our research has provided new and exciting results that further our understanding of auditory development as well as possible molecular targets for the development of future therapies.”

The work was supported by the Royal National Institute for Deaf People, the Wellcome Trust, and the University of Sheffield.

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