STRC

Researchers have identified STRC gene variants (also called mutations) in individuals with nonsyndromic hearing loss, which is loss of hearing that is not associated with other signs and symptoms. Variants in this gene cause a form of nonsyndromic hearing loss called DFNB16. This form of hearing loss can either be present before a child learns to speak (prelingual) or begin after a child learns to speak (postlingual). The hearing loss ranges from mild to profound and particularly affects the ability to hear high-frequency sounds.

The STRC gene variants that cause nonsyndromic hearing loss add a small amount of DNA to the STRC gene or delete DNA from the gene. In many cases, the variant deletes a piece of chromosome 15 that includes the entire STRC gene. Variants in this gene lead to the production of a nonfunctional version of stereocilin or prevent any of this protein from being produced. A loss of functional stereocilin likely alters the structure of stereocilia, preventing them from connecting to one another. As a result, certain auditory functions are impaired, which leads to hearing loss in people with DFNB16.

Deafness-infertility syndrome is a condition caused by a deletion of genetic material on the long (q) arm of chromosome 15. This condition is characterized by the combination of hearing loss and difficulty conceiving children (a condition called infertility).

The chromosomal region that is typically deleted contains multiple genes, including the STRC gene. People with this condition have the deletion in both copies of chromosome 15 in each cell. As a result of the deletion, no stereocilin protein is produced. A lack of stereocilin likely interferes with the normal function of stereocilia and impairs certain auditory functions, resulting in hearing loss in people with deafness-infertility syndrome. 

The loss of another gene, CATSPER2, in the same region of chromosome 15 results in the impaired movement of sperm. This causes the infertility seen in people with deafness-infertility syndrome. Researchers are working to determine how the loss of additional genes in the deleted region affects people with deafness-infertility syndrome.