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Mutated ion channel linked to progressive hearing loss
  
By Birgit Hofmann

It is now well known that genes play a major role in hearing loss, often by affecting cells in the inner ear that receive sound. A new study suggests that an inherited, progressive form of hearing loss called DFNA2 may be caused by genetic alterations not only in the inner ear but also in nerve cells in the brainstem that receive auditory signals.

Scientists from the Center for Molecular Neurobiology at the Universität Hamburg, and the Institut Pasteur in Paris report that DFNA2 may be related to defects in an ion channel that is present in the sensory hair cells of the ear and in the region of the brainstem associated with hearing. Their paper appears in the current issue of the Proceedings of the National Academy of Sciences.

In earlier studies, mutations in the potassium channel gene KCNQ4, a ‘channel’ that permits ions to go through a cell’s membrane, have been linked to DFNA2. To find out more about the role and location of KCNQ4, the researchers studied the auditory system of mice. Most surprisingly, they could show that KCNQ4, while being absent from most other brain regions, is expressed in several nuclei of the central auditory pathway in the brainstem, and for the first time, an ion channel is shown to be specifically expressed in a sensory pathway.

The study also shows KCNQ4 is situated at the lower membrane of the sensory (outer hair) cells, where potassium exits the cell. The research team concluded that a breakdown of KCNQ4 function may result in an eventual degeneration of the hair cells due to a chronic potassium overload.

By showing that gene mutations and molecular factors may be responsible for hereditary deafness in mice, the researchers hope to have come closer to understanding progressive hearing loss in humans.

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Kharkovets, T. et al. KCNQ4, a K+ channel mutated in a form of dominant deafness, is expressed in the inner ear and the central auditory pathway. Proc Natl Acad Sci USA 97, 4333-4338 (April 11, 2000).
 

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