National Institutes of Health (NIH) researchers have uncovered the DNA “fingerprint,” associated with enlarged vestibular aqueducts (EVA). Clinical audiologists know EVA to be an inherited form of hearing impairment that often has a progressive form of sensorineural hearing loss.
Most children with EVA pass newborn hearing tests, but begin to lose their hearing in the first few months or years of their lives. While children with EVA gradually lose their hearing, the pattern is unpredictable, with abrupt drops interspersed with episodes of brief recovery. In addition, hearing loss is often the only sign of EVA.
According to the article on published on the NIH website, the DNA variants lie near a known EVA-linked gene called SLC26A4. The connection between this gene and EVA had evaded scientists until now. Their discovery may improve methods for diagnosing EVA and may lead to new ways to restore SLC26A4 function and preserve hearing in those with the condition. The study appeared August 4, 2017, in the Journal of Medical Genetics.
Laboratory chief of Deafness and Other Communication Disorders Molecular Biology and Genetics section at NIH and study leader, Dr. Andrew Griffith, said, “Now that we’ve found this fingerprint—which we’ve been seeking for quite some time—we can use it to help identify the cause of hearing loss in children with EVA. We now have a genetic method that can inform the outcome of clinical progression and be used for testing in siblings to determine their chance of developing EVA.”
The vestibular aqueduct is a small channel that extends from the cochlea toward the brain, and serves as a conduit for the electrostatic fluid that fills the cochlea. People with EVA have an enlarged channel, but scientists do not believe that the malformation itself causes hearing loss. Rather, it appears that both the structural anomaly and hearing loss are secondary to another defect.
The causes of EVA are complex and not fully understood, but a breakthrough came in 1997, when mutations in SLC26A4 were first linked to the condition. About half of EVA cases are caused by defects in this gene, which codes for a type of protein called an ion channel. Hearing loss in these patients likely stems from disturbances in ion balances necessary for maintaining healthy cells and transmitting sound signals to the brain. The other half of EVA patients lack evidence of SLC26A4 mutations, suggesting that other genetic or environmental factors are involved.
To learn more about EVA and its genetic fingerprints, readers are encouraged to visit the two links above.
*featured image courtesy wikimedia commons