An Aid to Hearing
Gene Chip Pinpoints Cause of Hearing Loss
Pediatric otolaryngologist John Greinwald, MD, and research colleagues at Cincinnati Children's have developed a hearing gene chip that is now ready for clinical use. |
| 1987 The average age for diagnosing children with profound hearing loss is age 4. |
| 2007 Hearing loss is identified in the first months of life, and a customized gene chip developed at Cincinnati Children's can determine the precise genetic cause. |
The news came as a shock to Temple Parker. Her sons Kyle, then 7, and Caleb, 4, both had significant hearing loss.
"In hindsight, it makes sense," she says, looking back. "I had noticed things. It took Kyle longer to conceptualize. He was on an Individualized Education Plan (IEP) at school, and Caleb also was struggling. He was always asking me, 'What?' I'd get annoyed because he wasn't listening, but I didn't suspect hearing loss."
It's a common story, says otolaryngologist John Greinwald, MD. "If the hearing loss starts out mild, it's often missed. Later, people look back and recognize the signs."
Caleb's first-grade teacher, frustrated by his behavior in school, was the first to suggest he might be having trouble because he couldn't hear well. She advised Temple to have his hearing tested. Temple had her three sons tested at the same time. Kyle and Caleb both had hearing loss.
That was six years ago. The boys have worn hearing aids ever since. "I'm so thankful for the hearing aids. It puts them on an even playing field," Temple says.
Early Identification
Today, Kyle and Caleb would likely be diagnosed much sooner, thanks to mandatory hearing screening for newborns. Currently about 35 states require newborn hearing screens.
"Twenty years ago, the average age of diagnosis for a child with profound hearing loss was 4 years old," says Dr. Greinwald. "Ten years ago, it was 2. Now we're detecting hearing loss in the first months of life."
The newborn screen is a quick, painless test, usually performed in the hospital nursery before the baby goes home. If the test suggests hearing impairment, the next step is further testing by an audiologist, with more sophisticated technology, to confirm the hearing loss.
The Genetics of Hearing Loss
In most cases, hearing impairment in newborns is the result of damage to the inner ear, or cochlea – called sensorineural hearing loss. Sensorineural hearing loss is one of the most common birth defects, affecting two of every 1,000 newborns in the US. In Ohio, 450 to 500 children are diagnosed with a handicapping hearing loss every year.
Recent studies have shown that more than half the time, sensorineural hearing loss has an inherited or genetic basis, and scientists have succeeded in identifying the genes most often involved. "The study of the genes involved in hearing and deafness is crucial to our understanding and care of children with handicapping hearing loss," Dr. Greinwald says.
"If the hearing loss has a genetic component, we can attempt to predict the child's clinical course much earlier and start planning therapy sooner."
For most children, treatment includes hearing aids and speech and listening therapy. Ideally, the infant will be fitted with a hearing aid by age 3 to 6 months. Children who cannot be helped with hearing aids may be candidates for cochlear implantation, a surgery that can be performed on children as young as 1.
Introducing hearing aids, cochlear implant or sign language early, when the baby is developing communication and social skills, can have a big impact on the child's overall development.
For Kyle and Caleb, "as soon as they got their hearing aids, the difference was like night and day," their mother says. "They never take them off, except when they sleep. They value them so much."
Leadership in Gene Chip Technology
While genetic testing offers accurate diagnosis, the tests available in the past could screen just one gene at a time – a laborious and expensive approach.
Now, Dr. Greinwald and his research colleagues have developed a gene chip that can screen several genes at once, from a drop of blood.
After years of laboratory testing, the gene chip will be launched for clinical application at Cincinnati Children's Hospital Medical Center in late 2007. This firstgeneration gene chip tests for eight genes. "Based on our preliminary data, we think these are the genes that will be the most impactful in identifying hearing loss," says Dr. Greinwald. The chip – a glass sliver not much larger than a postage stamp – analyzes 23,000 DNA sequences on these genes. It takes a month to complete the analysis.
An improved gene chip is in the final stages of laboratory testing and will soon become available for clinical use. The second-generation chip tests 17 genes and can complete the analysis in less time.
This innovative use of gene chip technology has catapulted Cincinnati Children's to the forefront of gene-based diagnostics for hearing loss.
