DALLAS -- With age comes wisdom, gray hair and hearing loss.

Nearly 22 million U.S. adults age 71 or older have hearing loss, according to the Hearing Loss Association of America, but it can manifest in men and women differently.

A new study by researchers at the University of Texas at Dallas and the State University of New York at Buffalo might give us more insight as to why.

The study, which was co-authored by Bohua Hu, a professor of speech, language and hearing at UTD, suggests that a missing gene causes earlier onset hearing loss in female mice, but has no change on males.

An unexpected finding

Hearing loss can be caused by many factors besides aging, including loud noises, head trauma and even certain drugs used in cancer treatments.

The researchers were looking into how to prevent drug-induced hearing loss when they stumbled upon a different discovery.

Researchers thought removing a gene called Slc16a5 could help protect ear function. This gene encodes a protein that ferries molecules into sensory cells in the ear, Hu said, where they can damage hearing.

By removing the function of the transport protein, researchers could prevent drug molecules from reaching delicate parts of the ear in the first place, he said.

But while monitoring mice that lacked the gene, researchers noticed something unusual: Female mice showed early onset hearing loss and had lost sensory hair cells, while male mice maintained their sense of hearing and had a normal number of hair cells.

Sensory hair cells act as a type of audio transducer, Hu said. When you hear a noise, sound waves are hitting the eardrum and causing it to vibrate.

“Sensory hair cells convert that mechanical vibration to neural activity, then send that neural activity to the brain,” he said, essentially helping your brain interpret sound.

Researchers ran tests to figure out the cause of this difference between male and female mice. They discovered the missing protein changed the behavior of genes that respond to estrogen, which is a sex-related hormone believed to have protective effects on the inner ear and ear function. This may help explain the underlying biological reason as to why hearing loss presents differently in males and females.

In the short term, Hu said, the findings could help doctors diagnose patients with early, unexplained hearing loss, since checking for gene mutations might explain why. Gene therapy to help treat hearing loss is a longer-term goal, he said.

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Niamh Ordner is a science reporting fellow at The Dallas Morning News. Her fellowship is supported by the University of Texas at Dallas. The News makes all editorial decisions.