UW tackling growing trend of hearing loss
Seattle Times medical reporter
As a teenager, Hoffman cranked up his dad's hi-fi headphones to listen to Bill Haley and the Comets, Elvis and Little Richard. As an Air Force radar technician, his ears often went unprotected as thundering Phantom fighters streaked past on the runway each day.
Now Hoffman is paying for those years, with what doctors suspect is noise-induced hearing loss. He misses snatches of conversations. He strains to keep up in meetings. He can't hear the birds in his back yard.
"I've pretty well accepted what I have," says Hoffman, 56, a hospital electronics technician from Puyallup. "I'm just hopeful it won't get any worse."
The research ranges from the genetics of hearing loss to a major focus on regrowing crucial "hair cells" of the inner ear.
But of special interest are a species of tiny finches, known for their intricate, beautiful songs and ability to regrow hair cells - and thus regain hearing once it is lost.
Determining how the birds regrow those cells may show a way to do the same in humans.
"I would expect that restoration of hearing in humans is possible," says Dr. Edwin Rubel, known worldwide for his work at the UW's Virginia Merrill Bloedel Hearing Research Center. "It's just a question of when."
About 28 million Americans, or one in 10, have reduced hearing; 80 percent of those suffer irreversible hearing loss. The disability costs an estimated $56 billion annually in medical care and lost productivity in the United States.
Baby boomers, in particular, are losing their hearing in increasing numbers; among people between ages 46 and 64, hearing problems have increased a whopping 26 percent in recent years.
Even among people between 18 and 45, the rate has increased 17 percent. Damage from noise is a major offender, the cause of about half of all hearing loss in the U.S.
"It seems everything in our society is noisy. People think that if sound isn't big enough to shake the body, it's not good," says Dr. George Gates, director of the Bloedel Center. "We should all say, whoa, quiet down."
Researchers at the center have become significant players in the quest to develop treatments for hearing and balance problems. They have produced more than 80 studies on how we hear and how that sense is destroyed.
The center is named for the hearing-impaired wife of timber magnate Prentice Bloedel. The couple, now deceased, established a $5 million endowment in 1989 and donated another $2 million in 1991.
Birds offer hints to recovery
The human ear holds 15,000 hair cells, which in turn stimulate nerve cells that send signals to the brain. The hair cells are vulnerable to damage from noise, certain antibiotics, disease and the aging process.
UW scientists think finding a way to regenerate those cells - not possible now - could prove one of the biggest boons to the hard of hearing since the hearing aid.
The music of birds is helping to find the way.
In a small lab in the Bloedel Center's basement, Dr. Sarah Woolley sits very still, listening to the staccato songs and calls of two Bengalese finches as they flit back and forth in their cage. One, a beautiful mottled white, sings at the top of his lungs to the other, a pale brown. Like all the laboratory birds, both were born in captivity and have always lived with other birds.
"There it is - his song," whispers Woolley.
Each Bengalese finch learns its song from its father, then alters it slightly to make it unique. It becomes that bird's song for life; it never changes, and the bird never learns another.
Researchers painlessly destroy finches' hair cells with an overdose of an antibiotic. With the cells gone, the birds cannot hear the notes of their own songs, which soon deteriorate into little more than noise bursts.
But the birds' hair cells regrow completely in about four weeks, and the birds rediscover their songs.
Woolley pores over sound graphs of a bird's song, analyzing every syllable, or series of notes, as it rebuilds to perfection. When the song is restored, she uses electrodes to examine how cells in the bird's brain stem respond to sounds. Then she euthanizes the bird and studies the cells under a microscope.
The most significant finding: The regenerated hair cells function just as well as the originals. The birds not only hear again, they understand the sound.
But the research has offered a surprise: Finches with restored hearing not only relearn their own songs, they learn additional notes and syllables from other finches in the lab and add to their songs.
This gives researchers hope that if human cells could be stimulated to regrow, people who have been deaf for much of their lives could learn language.
"It could reopen a critical period of learning," Woolley says.
Imagining total quiet
Don Hoffman never dreamed the blasts of noise he endured as a youth would damage the delicate hair cells in his ear.
Doctors say other events in Hoffman's adulthood likely added to the damage: regular use of a circular saw that reverberated in a warehouse and a severe head cold that lasted for weeks.
He was 36 when he first noticed he had trouble hearing on the telephone with his left ear. "It was like people were talking in a muffled tone. Everything was at reduced volume."
Tests showed a 40 percent loss in his left ear, mostly in the frequency range of normal conversation. He was fitted with his first hearing aid.
As a manager for a scientific-products company, he worried about being able to understand in business meetings. He learned to sit with his right ear toward those who are speaking.
"If someone was talking and looking away, it was very difficult. It still is today," Hoffman says.
Hoffman's hearing has continued to decline over the years, to about 70 percent loss in his left ear and about 40 percent loss in his right.
He copes with state-of-the-art hearing aids with directional microphones. But restaurants, cars, and other noisy environments pose a challenge. On the telephone, some words escape him. He always repeats numbers because he can't distinguish between two and three. Sometimes he amuses his friends with his misunderstandings.
"Not so long ago, we were riding along I-5 and I asked my car-pool friends if they were really talking about sea-lion pie," Hoffman said, laughing. "They cracked up. They were talking about Key lime pie."
But Hoffman worries that his speech comprehension is getting worse, and he misses more and more bits of normal conversation.
"I like to be part of the conversation, rather than just a listener," he says. "And I don't want to appear standoffish and snobbish."
His wife has suggested he might want to consider learning sign language. The prospect does not sit well. And while he knows research can take years, he is encouraged by the work at the UW.
"To have hearing loss is one thing," he says. "To not have hearing at all is something else. I can't imagine walking around in total quiet."
Hair-cell research grows
Back in 1986, no one knew any animal could restore its own hearing. Dr. Ed Rubel, a neurobiologist at UW, was trying to understand the basics of hearing loss when, in an experiment with a chicken, he accidentally discovered that hair cells regrew after they had been destroyed with an overdose of an antibiotic.
"Nature was trying to tell us something," Rubel says. "It proves once again that progress often is made when we don't get the result you expect."
The same discovery was made by University of Pennsylvania scientists about the same time, and interest in hair-cell regeneration boomed. Now 20 to 30 labs worldwide are pursuing the topic; the UW has produced about half the findings.
Rubel and his colleagues are taking several approaches to restoring hair cells:
• Naturally occurring growth factors, biochemical substances, are used to stimulate division in cells that normally surround and support hair cells. These support cells then must be induced to become hair cells. The UW scientists have accomplished cell division in mice and rats in the balance organs of the inner ear, but not in the cochlea, which is concerned with hearing.
• Transdifferentiation attempts to induce support cells to convert directly to hair cells without having to divide. This has been accomplished in birds and frogs.
• The genes of the inner ear that prevent cell division are silenced. Scientists at the UW and the Fred Hutchinson Cancer Research Center accomplished this in mice cochlea, causing support cells, but not hair cells, to proliferate.
Rubel says it may be 10 or 20 years before scientists discover how to cause human hair cells to regenerate. But he has no doubt it will happen.
"The most important thing is that we have opened this field of research," he says. "Before that, no one was asking the question whether this could be done."
Warren King can be reached at 206-464-2247, or at firstname.lastname@example.org.