USH1C

The USH1C gene carries the instructions for the production of a protein called harmonin. Harmonin has the ability to bind to many other proteins in cell membranes and coordinates their activities. Harmonin sometimes acts as a bridge linking proteins in the cell membrane to those in the cytoskeleton, the internal framework that supports the cell.

Research suggests that harmonin plays a role in the development and maintenance of hairlike projections called stereocilia. Stereocilia line the inner ear and bend in response to sound waves. This bending motion is critical for converting sound waves to nerve impulses, an essential process for normal hearing. In the inner ear, protein complexes organized by harmonin probably act as connectors that link stereocilia into a bundle. This protein complex likely helps regulate the transmission of sound waves.

Harmonin is also made in specialized cells called photoreceptors. These cells detect and transfer light energy to the light-sensitive tissue at the back of the eye (the retina). The function of the harmonin-protein complex in the retina is not well understood, but it is thought to be important in the development and function of photoreceptor cells.

nonsyndromic deafness - caused by mutations in the USH1C gene

At least one mutation in the USH1C gene causes a form of nonsyndromic deafness (hearing loss without related signs and symptoms affecting other parts of the body) called DFNB18. This mutation changes a single DNA building block (nucleotide), which disrupts the instructions for producing harmonin. The abnormal version of harmonin causes defects in the stereocilia, leading to hearing loss and problems with balance.

Usher syndrome - caused by mutations in the USH1C gene

At least 10 USH1C mutations that cause Usher syndrome type 1C have been identified. One mutation is a common cause of Usher syndrome type 1C in the Acadian population of Louisiana. This mutation changes a single DNA building block (nucleotide) in the USH1C gene, replacing the nucleotide guanine with the nucleotide adenosine at position 216 (written as 216G>A). In other populations, some USH1C mutations insert or delete small amounts of DNA in the gene. Additional mutations disrupt how genetic information from the USH1C gene is spliced together to make a blueprint for producing harmonin. A lack of functional harmonin impairs the normal development of the stereocilia and the retina, leading to the signs and symptoms of Usher syndrome.