Hearing Research

Researchers Fighting the Effects of Noise

By Yishane Lee

The cornerstone of Hearing Health Foundation, ever since its founding in 1958 as the Deafness Research Foundation, has been funding early-career researchers who bring innovative thinking to hearing and balance research. HHF’s Emerging Research Grants (ERG) are awarded to the most promising scientists in the field, with many going on to earn prestigious National Institutes of Health backing.

HHF is always proud to see ERG grantees thrive in their careers and research. Most recently, two ERG scientists funded in the mid-1990s have made headlines, each for treatments for noise-induced hearing loss (NIHL).

1996 and 1997 ERG scientist John Oghalai, M.D., of the University of Southern California, coauthored a study showing promise for preventing NIHL. Published May 7, 2018, in the Proceedings of the National Academy of Sciences, Oghalai and team used miniature optics to examine the mouse cochlea after exposure to extremely loud noise, and found that in addition to immediate hair cell death, a fluid buildup in the inner ear over several hours eventually led to nerve cell loss. The fluid buildup, or endolymph hydrops, contributes to synaptopathy, or damage to the auditory nerve cell synapse. In a USC News press release, Oghalai described the excess fluid as a feeling of fullness and ringing in the ear that a person may experience after attending a loud concert.

Because the extra fluid showed a high concentration of potassium, the team saw a method to re-balance the fluids that naturally occur in the inner ear by injecting a salt (sodium) and sugar solution into the middle ear three hours after exposure. Nerve cell loss was reduced by 45 to 64 percent, which may help preserve hearing. The researchers see applications for this treatment for military service members who experience blast trauma as well as for people who have Ménière’s disease, the hearing and balance condition that is associated with inner ear fluid buildup.

Images from the cochleae of guinea pigs show the presence of more hair cells in animals treated with a short interfering RNA that interrupts a gene upregulated after damage (right; control on left). Inner and outer hair cells (IHC and OHC) are labeled in green, stereocilia in yellow, and nuclei in blue. Arrowheads indicate ectopic hair cells. Credit:    The Scientist    via    Molecular Therapy   .

Images from the cochleae of guinea pigs show the presence of more hair cells in animals treated with a short interfering RNA that interrupts a gene upregulated after damage (right; control on left). Inner and outer hair cells (IHC and OHC) are labeled in green, stereocilia in yellow, and nuclei in blue. Arrowheads indicate ectopic hair cells. Credit: The Scientist via Molecular Therapy.

1996 ERG scientist Richard Kopke, M.D., FACS, of the Hough Ear Institute in Oklahoma, spent more than 20 years serving with the U.S. Army, becoming well aware of the dangers of NIHL for service members. In a paper in Molecular Therapy, published online in March 2018, Kopke and colleagues used “small interfering RNAs” (siRNAs) to block the activity of the Notch signaling pathway gene Hes1 that itself blocks hair cell differentiation in developing supporting cells and may contribute to the failure of hair cells to regenerate after injury.

These siRNAs were delivered using nanoparticles directly injected to the cochleae of live, adult guinea pigs. Kopke’s team had previously shown using siRNAs to block Hes1 to be effective in regenerating hair cells in cultured mouse cochlea. In the current study, the 24-hour, sustained-release of siRNAs through nanoparticles three days after deafening resulted in the recovery of some hearing ability, measured using auditory brainstem responses, at three weeks and continuing to nine weeks, when the study ended. Compared with the control mice, the RNA-injected mice showed less overall hair cell loss and early signs of immature hair cell development, which the authors say may signal hair cell regeneration. Hearing loss caused by noise, chemotherapy drugs, or aging that damages or kills hair cells are all targets for this potential treatment.

In an article in The Scientist, HHF’s Hearing Restoration Project consortium member Jennifer Stone, Ph.D., who was not involved in the paper, echoed the study authors in saying further research should work to determine which cells are turning into hair cells, and whether the observed hair cell development is truly new hair cells and not the repair of damaged hair cells. Kopke and team plan to test the treatment using longer periods between deafening and injection, while also modifying dose and delivery.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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Stenting to Relieve One Specific Cause of Pulsatile Tinnitus

By Jayne Wallace for the Weill Cornell Medicine Brain and Spine Center

The Centers for Disease Control and Prevention estimates that 15 percent of the U.S. population, or 48 million people, have some type of tinnitus, hearing a ringing or buzzing in the absence of an external sound source.

Pulsatile tinnitus, in contrast, usually has a sound source. In these cases, affecting fewer than 10 percent of tinnitus patients, sounds are caused by turbulence in the blood flow around the ear. And among these cases, intracranial hypertension comprises about 8 percent of cases. This is when narrowing in one of the large veins in the brain causes a disturbance in the blood flow, leading to the pulsatile tinnitus.

Dural arteriovenous fistula, MRA showed only subtle alterations as a result of atypical flows in the right transverse sinus (arrow). Photo courtesy of Deutsches Ärzteblatt International.

Dural arteriovenous fistula, MRA showed only subtle alterations as a result of atypical flows in the right transverse sinus (arrow). Photo courtesy of Deutsches Ärzteblatt International.

“Traditionally there has been no good treatment for many of these patients who are told to learn to live with it,” says Athos Patsalides, M.D., an interventional neuroradiologist at New York City’s Weill Cornell Medicine Brain and Spine Center, where he also serves as an associate professor of radiology in neurological surgery.

Till now, available treatments—medication or more complicated surgery—were either ineffective or produced side effects and other problems just as bad or worse. “That’s why we started the clinical trials for venous sinus stenting, a minimally invasive procedure that is very effective in alleviating the narrowing in the vein,” says Patsalides, who pioneered the use of VSS to treat patients with idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri because the symptoms tend to mirror those of a brain tumor.

“Many IIH patients suffer from vision loss, headaches, and pulsatile tinnitus, and I saw a pattern with patients experiencing resolution of the pulsatile tinnitus immediately after VSS,” Patsalides says.

This led to the possibility of using VSS for selected patients with pulsatile tinnitus. After the Food and Drug Administration approved the clinical trial, it began in May 2016 and has an estimated completion date of January 2021.

“In the stenting procedure, with the patient under general anesthesia, we insert a tiny, soft catheter into a vein located in the upper part of the leg and thread it up to the affected vein in the brain,” Patsalides says.

A self-expanding stent is deployed into the narrowed segment of the vein, relieving the stenosis, restoring normal blood flow, and reducing or eliminating the pulsatile tinnitus. “Happily, the patient is typically discharged from the hospital within 24 to 48 hours,” he says.

To learn more, see weillcornellbrainandspine.org. Hearing Health Foundation notes that the trial is ongoing, and that the procedure is potentially able to address only one specific cause of pulsatile tinnitus and should not be taken as a solution for other forms of tinnitus, which often has no known cause.

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A Clinical Trial for a New Drug to Protect Hearing

By Yishane Lee

The U.S. Food and Drug Administration (FDA) has approved a novel drug to protect against ototoxicity (harmfulness to hearing) due to the use of aminoglycoside antibiotics to treat severe infections. The FDA approval paves the way for a Phase I clinical trial to test whether the drug, found to be significantly protective in animals, is safe for humans.

Mature lateral line hair cells from larval zebrafish (shown with the neuromast sensory organ enlarged) serve as a platform for studying drugs and genes that modulate hair cell susceptibility to ototoxic agents.  

Mature lateral line hair cells from larval zebrafish (shown with the neuromast sensory organ enlarged) serve as a platform for studying drugs and genes that modulate hair cell susceptibility to ototoxic agents.  

The drug, ORC-13661, was developed by University of Washington professors Edwin Rubel, Ph.D., and David Raible, Ph.D., who are members of Hearing Health Foundation’s Scientific Advisory Board and Hearing Restoration Project, respectively, and Fred Hutchinson Cancer Research Center scientist Julian Simons, Ph.D. “While this program was not directly funded by HHF, both David and I have definitely been supported by HHF for a long time,” Rubel says. “This is a drug to prevent hearing loss that we've developed over the past 15-plus years.”

Rubel points out the drug’s two main features: “It is a brand new drug with a composition of matter patent, not one that is used for other medical purposes and being repurposed; and it is the first drug that was developed, from the get-go, to protect hair cells from ototoxic injury.”

After screening libraries of potential chemicals to see which stopped hair cell death in zebrafish lateral line system, Rubel, Raible, and team identified the best candidate and then boosted its effectiveness by tweaking its chemical structure; results were published in the Journal of Medicinal Chemistry in January 2018.

Rubel adds, “Toxicity studies in zebrafish, rats, and dogs required by the FDA show superior safety and nearly 100 percent hearing protection at all frequencies.” If the Phase I trial shows the drug is safe for humans, the next step is to test its efficacy among patients using aminoglycosides.

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Hearing—With Difficulty Understanding: Life With Auditory Processing Disorder

By Lauren McGrath

This April, Hearing Health Foundation (HHF) draws your attention to Auditory Processing Disorder (APD), a condition that causes impairments in sound localization—the ability to identify sound sources—and has been closely linked to autism. April 4 is recognized as APD Awareness Day in some regions of the U.S. and April is Autism Awareness Month nationwide.

APD occurs when the central nervous system has difficulty processing verbal or auditory information, specifically in noisy, social environments. Individuals with APD do not necessarily have a diagnosed hearing loss; in fact, many have normal audiogram results. With APD and typical hearing, the inner ear properly sends signals to the brain, but, once received, the brain fails to interpret and analyze these sounds accurately, resulting in jumbled messages.

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In the U.S., it is estimated five percent of school-age children, or 2.5 million children, have APD. Individuals with APD are often unable to hear sounds as words and have learning problems, including difficulty in reading, spelling, and language comprehension. It is vital to review the symptoms, demographics, and treatments of APD, should you suspect it in yourself or a loved one.

Individuals with APD have trouble distinguishing between words or syllables that sound alike (auditory discrimination) and recalling what they heard (poor auditory memory). They show delayed responses to verbal requests and instructions and will often ask someone to repeat what has been said. APD is commonly misdiagnosed as ADD/ADHD, dyslexia, or hearing loss.

Demographically, APD is a common secondary diagnosis for children with autism; most children diagnosed with autism have auditory processing disorders or auditory difficulties. HHF Emerging Research Grants (ERG) recipient Elizabeth McCullagh, Ph.D.’s 2017 published work in The Journal of Comparative Neurology examines the strong connection between Fragile X Syndrome (FXS), the most common genetic form of autism, and difficulties with sound localization.

Additionally, APD is prevalent in individuals with neurological problems, including those who have experienced head injuries or strokes. Older adults, who are more susceptible to some cognitive decline, are also at greater risk for APD.

Military veterans who have been repeatedly exposed to blasts are another community disproportionately affected by APD. An estimated 15% of all returning military personnel live with APD. HHF’s ERG recipient Edward Bartlett, Ph.D., explains that the changes to the central auditory system may account for the behavioral issues that veterans experience, such as problems with memory, learning, communication, and emotional regulation.

Retired U.S. Army Colonel John Dillard of HHF’s Board of Directors remarks, “It is truly unfortunate that our veterans, after making such honorable sacrifices, are forced to live with APD, often alongside tinnitus and/or hearing loss. I am hopeful that future scientific advancements will better the lives of veterans and all Americans.”

There are no cures for APD, but there are many treatments that aim to improve the effectiveness of everyday communication. These include environmental modifications, addressing functional deficits, and improving listening and spoken language comprehension. Pursuing treatment for APD as early as possible is imperative, McCullagh explains, because hearing is vital to social and educational interactions. “Those with APD often develop issues with language development, hearing in noise, and sound localization. Risks associated include not being able to participate in noisy environments which can often result in depression and anxiety.”

Much more research of APD is needed to improve the accuracy of methodologies for diagnosis and to determine the best interventions for each child or adult. Even though there are available strategies to treat APD, researchers, including those funded by HHF, largely through the generosity of the Royal Arch Masons Research Assistance, are hard at work finding alternative treatments that will improve the lives of those with APD.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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Moving Toward a Future Free of Drug-Induced Hearing Loss

By Erik Robinson

A new special publication orchestrated by five of the nation’s leading hearing experts compiles the latest research into hearing loss caused by drugs and solvents—how it occurs, how to treat it, and how to prevent it.

HHF Council of Scientific Trustees member Peter Steyger, Ph.D., and colleagues produced a special  Frontiers in Cellular Neuroscience  publication on the topic of ototoxicity.

HHF Council of Scientific Trustees member Peter Steyger, Ph.D., and colleagues produced a special Frontiers in Cellular Neuroscience publication on the topic of ototoxicity.

The compilation was published online as a special research topic by the journal Frontiers in Cellular Neuroscience on March 5, 2018. It includes both original research and focused reviews. The Pharmaceutical Interventions for Hearing Loss Working Group organized the effort at the behest of the Department of Defense (DoD) Hearing Center of Excellence.

“We’re trying to elevate ways for the human population to avoid losing this important sensation for experiencing and communicating with the world around us,” says coauthor Peter Steyger, Ph.D., a professor of otolaryngology/head and neck surgery in the Oregon Health & Science University (OHSU) School of Medicine, and a member of Hearing Health Foundation’s Council of Scientific Trustees.

“Ototoxicity is a threat to hearing at any age and hearing loss remains a significant side effect of chemotherapy. This review highlights how far we’ve come in understanding that threat and provides us with a roadmap for developing more effective ways to recognize and address the problem,” adds coauthor Jian Zuo, Ph.D., of the department of developmental neurobiology at St. Jude Children’s Research Hospital in Memphis, Tennessee.

In people, hearing cells don’t regenerate so the loss is irreversible. That’s why it is crucial to understand the mechanisms that affect hearing and how to prevent loss of hearing, Steyger says. The introductory editorial, “Moving Toward a Future Free of Ototoxicity,” highlights the latest scientific research exploring how certain pharmaceuticals damage the inner ear while others can protect it. It also highlights the need for better monitoring and detection of hearing loss over time, especially among patients being treated with antibiotics.

Steyger, who lost hearing as a child after being treated with antibiotics for meningitis when 14 months old, noted that hearing loss affects a surprisingly large proportion of the population—rising from an estimated 1 in 500 newborns to as many as half of all people age 75 or older. The research encapsulated in the new e-book includes 23 scientific articles from 93 authors and represents the state of the science in both prevention and treatment of ototoxicity hearing loss. (The e-book is available to all, free of charge.)

“This compilation will help to propel our knowledge forward and underscore the need to better understand the dangers of ototoxicity. The DoD Hearing Center of Excellence is honored to host and mobilize this important effort,” says coauthor Carlos Esquivel, M.D., a neurotologist and chief medical officer in the Clinical Care, Rehabilitation, and Restoration Branch of the DoD Hearing Center of Excellence at Joint Base San Antonio in Texas.

In addition to Steyger, Zuo, and Esquivel, the publication’s editors include Lisa Cunningham, Ph.D., of the National Institute on Deafness and Other Communication Disorders, and Kelly Watts, Au.D., of the DoD Hearing Center of Excellence.

This originally appeared in OHSU News and was republished with permission. 

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Mapping Better Hearing

By Vicky Chan

Hearing Health Foundation (HHF) is grateful to the many individuals and organizations who have empowered groundbreaking hearing loss research in the last 60 years. A new interactive map displays every institution in the U.S. where HHF has been fortunate to fund groundbreaking research, yielding outstanding advancements in hearing and balance science. The map also indicates the rates of hearing loss in each state, signaling that additional work is urgently needed.

The colors—light yellow, yellow, green, teal, blue, and purple—represent the rates of hearing loss in each state. The calculations are based off 2015 U.S. Census Data, using estimates from the well-known prevalence of hearing loss among specific demographics. At the lowest end of the range in light yellow, hearing loss affects 13.71% of Colorado’s population. The highest rate was found in Missouri, purple, where the prevalence measured 20.15%. The mean for all states was 18.16%. The numbers signal the significance of hearing loss research.

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Nearly all of the institutions on the map represent recipients of the Emerging Research Grants (ERG) who have carried out investigations related to tinnitus, hyperacusis, Ménière's disease, Usher syndrome, hearing loss in children, Central Auditory Processing Disorder, and strial atrophy.

A few institutions are home to the work of the Hearing Restoration Project’s (HRP) domestic consortium members, who focus on investigating hair cell regeneration as a cure for hearing loss and tinnitus. They conduct research at Baylor College of Medicine, Harvard Medical School, Oregon Health & Science University, Stanford University, Stowers Institute, University of Maryland, University of Michigan, University of Southern California, University of Washington, and Washington University.

By mid-year, the institutions corresponding to HHF’s newly formed Ménière's Disease Grants (MDG) program will be added to the map.

HHF envisions a world in which no one lives with hearing loss and tinnitus—until this is realized, we’ll do everything we can to put more innovative hearing loss research on the map.

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2018: Hear's to You

By Nadine Dehgan

From every one of us at Hearing Health Foundation (HHF)—scientists, staff, and volunteers—thank you for your support in 2017 and best wishes for 2018.

Because of folks like you, 2017 was an incredible year in which HHF:

  • Increased funding for Hearing Restoration Project & Emerging Research Grants by 35%
  • Launched Ménière's Disease Grants program to better understand & treat this condition
  • Began to fund critical Ototoxic Drug Research so cancer survivors won't have to live with hearing loss as a result of their life-saving treatments
  • Advocated for universal newborn hearing screenings, resulting in the passage of the Early Hearing Detection and Intervention Act
  • Endorsed the Over-the-Counter Hearing Aid Act, which will provide a more affordable and accessible treatment option for adults with mild to moderate hearing loss
  • Created Faces of Hearing Loss to show that hearing and balance disorders affect all of us
  • Received Top Ratings from all Charity Watchdogs including Consumer Reports and BBB

With hearts full of gratitude, we look forward to the work to be done in 2018—HHF’s 60th anniversary year.

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With your help, HHF will continue to fund groundbreaking discoveries for the tens of millions of Americans with hearing loss and tinnitus—among whom is Ethan, 6, born with bilateral (in both ears) hearing loss and fortunate to receive early intervention.

Ethan is a first-grader who loves his sisters, soccer, reading, math, and martial arts. Until a cure for hearing loss is realized, he will be dependent on hearing aids or other treatments.

New scientific findings in 2018—empowered by you—can change the future of hearing loss for Ethan and so many others. I look forward to updating you on progress made.

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Gaining Better Clarity of Neural Networks

By Pranav Parikh

The ear, just like any other organ in the human body, uses nerves to function properly. One of the most vital nerves that the ear uses is the cochlear nerve, which connects the inner ear to the brain, or more specifically to the tonotopically-based regions of the cochlear nuclear complex located in the brainstem. This nerve shares the same shape and design of most nerves in the body, with dendrites absorbing information from various sources, sending the signal down the axon of the nerve through action potentials, and terminating the signal in a synapse so the message can be spread. In order to allow for this process to occur expediently, the nerve encounters a process known as myelination (providing a myelin sheath to propagate a signal faster). This is done through a glial cell known as an oligodendrocyte. Oligodendrocytes form a layer of lipid (fat) and protein around the axon to provide insulation, thereby allowing for signals to be sent to the brain more efficiently.

The immunoreactivity of Olig2 was detected during postnatal day (PND) 0 to 7, which became weaker after PND 10. Before PND 7, the majority of Olig2-expressing cells were found within the modiolus at the basal cochlear turn, while a few cells were located peripherally to the DIC-PCTZ and in close proximity to the spiral lamina at the basal cochlea turn. After PND 7, Olig2-expressing cells were fully overlapped with the DIC-PCTZ within modiolus at the spiral lamina in the basal cochlea.

The immunoreactivity of Olig2 was detected during postnatal day (PND) 0 to 7, which became weaker after PND 10. Before PND 7, the majority of Olig2-expressing cells were found within the modiolus at the basal cochlear turn, while a few cells were located peripherally to the DIC-PCTZ and in close proximity to the spiral lamina at the basal cochlea turn. After PND 7, Olig2-expressing cells were fully overlapped with the DIC-PCTZ within modiolus at the spiral lamina in the basal cochlea.

A team of scientists led by Dr. Zhengqing Hu, funded by Hearing Health Foundation through its Emerging Research Grants program (2010 & 2011) was able to analyze oligodendrocyte protein expression in the cochlear nerve of postnatal mice. Through the use of Differential Interference Contrast (DIC) microscopy, they were able to investigate the cochlear nerve at staggered postnatal days, meaning the period following birth.

Their findings indicate oligodendrocytes are found to migrate along with the transition zone between the central and peripheral nervous systems. As the fetus develops after birth, and myelination occurs in the nerves connecting to the brain, the oligodendrocyte protein marker Oligo2 was observed. This could mean loss of hearing function could be connected to unmyelinated axons. There are many other neurodegenerative autoimmune diseases, such as multiple sclerosis, caused by demyelination, and hearing loss could potentially be added to that list. Dr. Hu’s work improves clarity of the neural network connecting the inner ear and the brain.

Zhengqing Hu, M.D., Ph.D. , is a 2010 and 2011 Emerging Research Grants recipient. Hu's research was published by Otolaryngology-Head and Neck Surgery on July 11, 2017.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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Researcher Discovers Gene Mutation Related to Usher Syndrome Type 3

By Pranav Parikh

Usher syndrome type 3 is an inherited disease in which an individual is born with typical hearing and develops hearing loss in the stages of early childhood. They will most likely develop complete hearing loss by the time they are an adult. Though cases of Usher syndrome type 3 (and its subtypes) are quite infrequent, representing 2 percent of total Usher syndrome cases, the onset symptoms have damaging and often irreversible consequences that severely disrupt the lives of those living with the condition. There is currently no cure for the disease, but cochlear implants have seen some success in providing partial hearing function in patients.

A 3D model of the HARS enzyme, including the catalytic site (where the reaction occurs) and the anticodon site (the part that starts protein synthesis through RNA transcription).

A 3D model of the HARS enzyme, including the catalytic site (where the reaction occurs) and the anticodon site (the part that starts protein synthesis through RNA transcription).

Susan Robey-Bond, Ph.D., a 2012 Emerging Research Grants scientist, and her team at the University of Vermont College of Medicine were able to isolate a mechanism involved in the development of Usher syndrome. Histidyl-tRNA synthetase is an enzyme that is instrumental in protein synthesis. This enzyme, given the acronym HARS, is thought to be involved in the presentation of Usher syndrome type 3B in patients. The early symptoms of temporary hearing and vision loss, hallucinations, and sometimes sudden fatal buildup of fluid in the lungs may be triggered by a fever-causing illness. The hearing and vision loss are eventually severe and permanent.

A graphical representation depicting temperature variation between the wild-type and mutant version of the HARS enzyme .

A graphical representation depicting temperature variation between the wild-type and mutant version of the HARS enzyme.

Usher syndrome type 3B is autosomal recessive, meaning children of parents carrying the gene but who do not display symptoms have a likelihood of developing the disease. It is caused by a USH3B mutation, which substitutes a serine amino acid for a tyrosine amino acid in HARS. The team studying the biochemical properties of the gene compared the Y454S mutation in the HARS enzyme with its wild-type (non-mutated) form and found similar functional biochemical characteristics, as stated in the researchers’ recent paper in Biochemistry.

The amino acid activation, aminoacylation, and tRNA binding functions were all consistent between the mutation and wild-type genes. In later analysis, though, the team found that at an elevated temperature the Y454S substitution was less stable than the wild-type. More specifically, cells from patients containing the Y454S mutation displayed lower levels of protein synthesis, which could explain the onset of deafness these patients experience. How these proteins are implicated in the hearing processes will eventually help develop cures or better treatments for Usher syndrome.

Susan Robey-Bond, Ph.D., was a 2012 Emerging Research Grants recipient. For more, see her Biochemistry paper:, “The Usher Syndrome Type IIIB Histidyl-tRNA Synthetase Mutation Confers Temperature Sensitivity.”

Empower groundbreaking research toward better treatments and cures for Usher syndrome. If you are able, please make a contribution today.

 
 
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Early Detection Improved Vocabulary Scores in Kids with Hearing Loss

By Molly Walker

Children with hearing loss in both ears had improved vocabulary skills if they met all of the Early Hearing Detection and Intervention guidelines, a small cross-sectional study found.

Those children with bilateral hearing loss who met all three components of the Early Hearing Detection and Intervention guidelines (hearing screening by 1 month, diagnosis of hearing loss by 3 months and intervention by 6 months) had significantly higher vocabulary quotients, reported Christine Yoshinaga-Itano, PhD, of the University of Colorado Boulder, writing in Pediatrics.

The authors added that recent research reported better language outcomes for children born in areas of the country during years where universal newborn hearing screening programs were implemented, and that these children also experienced long-term benefits in reading ability. The authors said that studies in the U.S. also reported better language outcomes for children whose hearing loss was identified early, who received hearing aids earlier or who began intervention services earlier. But those studies were limited in geographic scope or contained outdated definitions of "early" hearing loss.

"To date, no studies have reported vocabulary or other language outcomes of children meeting all three components of the [Early Hearing Detection and Intervention] guidelines," they wrote.

Researchers examined a cohort of 448 children with bilateral prelingual hearing loss between 8 and 39 months of age (mean 25.3 months), who participated in the National Early Childhood Assessment Project -- a large multistate study. About 80% of children had no additional disabilities that interfered with their language capabilities, while over half of the children with additional disabilities reported cognitive impairment. Expressive vocabulary was measured with the MacArthur-Bates Communicative Development Inventories.

While meeting all three components of the Early Hearing Detection and Intervention guidelines was a primary variable, the authors identified five other independent predictor variables into the analysis:

  • Chronological age
  • Disability status
  • Mother's level of education
  • Degree of loss
  • Adult who is deaf/hard of hearing

They wrote that the overall model was significantly predictive, with the combination of the six factors explaining 41% of the variance in vocabulary outcomes. Higher vocabulary quotients were predicted by higher maternal levels of education, lesser degrees of hearing loss and the presence of a parent who was deaf/or hard of hearing, in addition to the absence of additional disabilities, the authors said. But even after controlling for these factors, meeting all three components of the Early Hearing Detection and Intervention guidelines had "a meaningful impact" on vocabulary outcomes.

The authors also said that mean vocabulary quotients decreased as a child's chronological age increased, and this gap was greater for older children. They argued that this complements previous findings, where children with hearing loss fail to acquire vocabulary at the pace of hearing children.

Overall, the mean vocabulary quotient was 74.4. For children without disabilities, the mean vocabulary quotient was 77.6, and for those with additional disabilities, it was 59.8.

Even those children without additional disabilities who met the guidelines had a mean vocabulary quotient of 82, which the authors noted was "considerably less" than the expected mean of 100. They added that 37% of this subgroup had vocabulary quotients below the 10th percentile (<75).

"Although this percentage is substantially better than for those who did not meet [Early Hearing Detection and Intervention] guidelines ... it points to the importance of identifying additional factors that may lead to improved vocabulary outcomes," they wrote.

Limitations to the study included that only expressive vocabulary was examined and the authors recommended that future studies consider additional language components. Other limitations included that disability status was determined by parent, with the potential for misclassification.

The authors said that the results of their study emphasize the importance of pediatricians and other medical professionals to help identify children with hearing loss at a younger age, adding that "only one-half to two-thirds of children met the guidelines" across participating states.

This article was republished with permission from MedPageToday

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