US researchers have identified a genetic mutation responsible for the hearing loss that occurs with the condition Usher syndrome type I.
'In this study, researchers were able to pinpoint the gene which caused deafness in Usher syndrome type I as well as deafness that is not associated with the syndrome through the analysis of 57 humans from Pakistan and Turkey', said lead investigator Dr Zubair Ahmed, assistant professor of ophthalmology at Cincinnati Children's Hospital Medical Center and the University of Cincinnati.
Usher syndrome is a hereditary condition that causes both a loss of vision and hearing. Progressive degeneration of the retina, the light-sensitive part of the eye, leads to night blindness and loss of peripheral vision, while damage to the inner ear leads to deafness. The condition affects approximately one in every 25,000 people in developed countries.
Mutations in several genes, encoding structural proteins in sensory cells of the ear and eye, have previously been linked to Usher syndrome. In the current study, the authors determined that mutations in another gene, CIB2, were responsible for deafness in Usher syndrome type I and also non-syndromic deafness, where no other symptoms are associated with the loss of hearing.
The researchers established that the CIB2 protein localised to the tips of specialised structures in the sensory cells of the inner ear called mechanosensory stereocilia which are important for both hearing and balance.
At the tips of these mechanosensory stereocilia, where sound waves are converted into electrical signals, the calcium-binding protein CIB2 was found to interact with other proteins previously associated with Usher syndrome. Co-author of the study, Dr Gregory Frolenkov of the University of Kentucky, determined that the identified mutations in CIB2 changed its ability to bind calcium and disrupted the detection of sound by sensory cells of the inner ear.
Dr Ahmed stated: 'With this knowledge, we are one step closer to understanding the mechanism of mechanoelectrical transduction and possibly finding a genetic target to prevent non-syndromic deafness as well as Usher Syndrome type I'.
The study is published in the journal Nature Genetics.