Protein Contributes to Deaf-Blindness

Usher syndrome protein causes deafness and blindness

(RxWiki News) The discovery of a new role for a protein that mutates in a common genetic disorder that leaves individuals deaf and blind could explain the cause of the most severe cases of the disorder.

The protein called harmonin can lead to Usher syndrome, the most common disorder that affects both sight and hearing. It is best known for sensing sounds in the inner ear, but it has another just as important role. Four out of every 100,000 babies born in the United States will be affected

"Try vitamin A supplements to slow progression of Usher syndrome."

Amy Lee, senior study author and University of Iowa associate professor in the departments of molecular physiology and biophysics, otolaryngology-head and neck surgery, and neurology, said  most existing research has primarily focused on the input end of inner hair cells in the same spot where sound waves produce motion of the stereocilia, located on the tips of hair cells.

She said new research suggests that a protein called harmonin appears to control the signal output of cells at the opposite end of the inner hair cells. There they may play a role in the transmission of sound information to the brain by mediating movement, which activates the cells and initiates the transmission of sound information.

Researchers also found that harmonin is important for regulating calcium channels at the hair cell synapse Previous studies showed that too many or too few calcium channels could cause deafness in mice, demonstrating that the number of channels are important for normal hearing.

Lee said harmonin appears to control precisely how many channels are available. She believes that with Usher syndrome there are too many calcium channels available, which causes abnormal signaling at the synapses. Lee said it might eventually be possible to alter the interaction between harmonin and the calcium channels in a way that aids Usher syndrome patients.

The protein also is expressed in the eye's retina, but it is not yet known how that contributes to blindness in Usher syndrome.

The research was published in Nature Neuroscience.

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Review Date: 
August 24, 2011