A normal claudin-9 gene produces a protein that protects the sensory cells in the ear. There are at least 24 genes in the claudin family, with the claudin-9 protein being part of a large complex. When that gene is mutated, it fails to produce the normal claudin-9 protein. The result is an improper distribution of potassium in the inner ear, which then floods the wrong part of the sensory cells, killing most and leaving the remaining ones functionally defective.
Research with deaf mice
Using deaf mice, the scientists identified the deafness-causing defect in the claudin-9 gene. Mice are used as research models because mouse and human auditory genetics are very similar. Mice have turned out to be very accurate models in research into human hearing, providing knowledge of how the auditory organs work. The scientists have started screening people with hearing impairment to see if some have the mutation in claudin-9, and the results are expected to show defective genes in some cases.