HEARING LOSS – A BRIEF HISTORY
Progress in Hair Cell Regeneration – January 2001
As most of our readers probably know, most hearing loss is caused by deterioration of the hair cells in the cochlea. The hair cells move in response to acoustic energy entering the ear, and stimulate the auditory nerve with information regarding the characteristics of the incoming sound. Drugs, heredity, or loud noises can damage or destroy the hair cells, resulting in hearing loss.
We have known for some time that some animals (including many birds) can spontaneously regenerate damaged hair cells, but regeneration has never been observed in mammals – until now. The August 26, 2000 Issue of the British medical Journal Lancet reported successful regeneration of hair cells in a postnatal rat cochlea by introducing a particular gene (Math1) to the cochlea. Researcher Wei-Qiang Gao (Genentech, San Francisco, CA,USA) points out, “It wasn’t just a few hair cells–we had several hundred, so it’s robust production”.
The next step in the investigation is to determine whether similar techniques can regenerate hair cells in mature rats. Success in these experiments would bode well for eventual hair cell regeneration in humans.
Another possibility to replace damaged hair cells is transplantation. Matthew Holley (University of Bristol, UK) and his colleagues have developed an “ear in a test tube”, in which they have successfully grown mouse hair cells. Future advances may allow growth and transplantation of human hair cells.
Hair Cell Regeneration Update from the House Ear Institute – August 2001
The House Ear Institute has been actively involved in the research on hair cell regeneration. They are pursuing two complementary strategies in hopes of understanding the regeneration process and how to induce it in humans. Here’s a link to an article describing their recent work. http://www.hei.org/research/projects/cmb/haircellchall.htm
- aGonda Department of Cell and Molecular Biology, House Ear Institute,
- bCenter for Basic Neuroscience, University of Texas Southwestern Medical Center,
- cDepartment of Cell and Neurobiology, University of Southern California Medical School,
24 September 2003; The sensory hair cells and supporting cells of the organ of Corti are generated by a precise program of coordinated cell division and differentiation. Since no regeneration occurs in the mature organ of Corti, loss of hair cells leads to deafness. To investigate the molecular basis of hair cell differentiation and their lack of regeneration, we have established a dissociated cell culture system in which sensory hair cells and supporting cells can be generated from mitotic precursors. By incorporating a Math1-GFP transgene expressed exclusively in hair cells, we have used this system to characterize the conditions required for the growth and differentiation of hair cells in culture. These conditions include a requirement for epidermal growth factor, as well as the presence of periotic mesenchymal cells. Lastly, we show that early postnatal cochlear tissue also contains cells that can divide and generate new sensory hair cells in vitro.
Europe Issues Patent on Hearing Loss Treatment – October 2003
Editor: Here’s more breaking news on hair cell regeneration. Sound Pharmaceuticals has been issued a European patent for its hair cell regeneration treatment. Note that this development is only part of the required solution, and it doesn’t mean that a treatment will be widely available next week. But I think it is a big step towards viable hair cell regeneration. Here’s the press release: Sound Pharmaceuticals, Inc. (SPI) announced that its patent “Method for the treatment of diseases or disorders of the inner ear” has issued in Europe, effective Oct. 1, 2003.
SPI has developed a novel strategy to stimulate auditory hair cell regeneration using proprietary cell cycle inhibition technology. Typically, auditory hair cells in mammals are not replaced when injured or lost. This results in permanent and often progressive sensorineural hearing a disease that affects over 30 million in the US. In non-mammals like birds, hair cell regeneration occurs through the spontaneous proliferation of the adjacent supporting cell. These newly proliferating supporting cells can go on to become replacement hair cells. However in mammals, auditory supporting cells do not proliferate or regenerate into hair cells even in the presence of growth factors.
SPI identified that p27Kip1, a cyclin dependent kinase inhibitor, prevents supporting cells from proliferating after embryogenesis. Compounds developed by SPI to inhibit p27Kip1 have been shown to stimulate supporting cell proliferation after drug or noise induced hair cell loss. “We are the only group that has demonstrated the ability to stimulate proliferative regeneration in the cochlea of mammals” says Dr. Jonathan Kil, President & CEO. “It is anticipated that this revolutionary technology will be critical in developing treatments to restore hearing in humans.”
Sound Pharmaceuticals, Inc. is a drug development company focused on treating hearing loss. To date, Sound Pharmaceuticals’ drug discovery program has identified targets for the prevention of hearing loss and for the improvement of hearing in individuals with hearing loss. For more information please visit http://www.soundpharmaceuticals.com
Transplantation of bone marrow stromal cells into the cochlea of chinchillas – 19 January 2004 – Volume 15 – Issue 1 – pp 1-4, Auditory and Vestibular Systems – Survival, migrational mobility and differentiation of autologous marrow cells in damaged cochlea suggest their potential as transplants for treatment of various degenerative inner ear diseases.
Promising Research on Hair Cell Regeneration – October 2004
Editor: For people interested in hearing loss “cures”, hair cell regeneration is the current best bet. It appears that virtually all animals except mammals regenerate hair cells on a routine basis. Dr. Edwin W. Rubel [Virginia Merrill Bloedel Professor of Hearing Science, Virginia Merrill Bloedel Hearing Research Center, Otolaryngology-Head and Neck Surgery, Physiology and Biophysics, Psychology (Adjunct)] and his colleagues are among the researchers on the forefront of this exciting technology. “Hearing Review” recently published an interview of Dr. Rubel along with a synopsis of the research status. Here’s one question and answer from the interview. The complete article is available at: http://www.hearingreview.com/Articles.ASP?articleid=H0410F01
Hearing Review: If hair cell regeneration is indeed possible, do you think this science will ever progress to a point where there will be full restoration of hair cells, or do you think that it’s far more likely we would see a partial restoration of hair cells in the inner ear?
Rubel: In my opinion, it’s not a question of if we will regenerate, restore, or protect hair cells, it’s a question of when. Because we now know that it’s possible, it’s only a matter of time until we can apply this science to humans. My best prediction is 10-20 years. I certainly hope to see it in my lifetime.
With respect to the degree of hair cell regeneration or restoration, my gut feeling is that it will all depend on what type of hearing loss a person has to begin with. One possibility for regeneration are people who have complete loss of hair cells due to some genetic anomaly, ototoxins, aminoglycosides, etc. In these cases, hearing care professionals may someday have a choice between recommending a cochlear implant versus an approach for growing enough hair cells where hearing aids could be used more effectively and provide much more acoustic information to that patient. As another example, you might see a patient who has a 50% loss of their outer hair cells. In this case, maybe we will be able to stimulate the regrowth and replacement of these “cochlear amplifier” cells.
Stem-cell researchers hope for deafness cure within 15 years – November 2004
Editor: “The Scotsman” is reporting on research at Sheffield University that may enable hearing restoration in the foreseeable future. Here are excerpts from the story. For the complete article, please point your browser to http://news.scotsman.com/uk.cfm?id=1346202004 SCIENTISTS hope that stem-cell research could lead to a cure for deafness in as little as ten years. Researchers from Sheffield University are using embryonic stem cells in efforts to grow new cells in the inner ear. Although in its early stages, the team from Sheffield University hopes it could lead to a cure for deafness in ten to 15 years. Dr Rivolta added that his team hoped to undertake the first tests on animals in two years. “It could then be possible to do human trials in three to four years, but that would depend on the animal trials.”
Stem cells could cure deafness in ten years.
Scientists at Britain’s Sheffield University are hoping that stem cell research could lead to a cure for deafness within ten years! Laboratory tests have demonstrated that embryonic stem cells have the capability to regrow in damaged areas; animal testing is planned within two years. Here’s the full story.
Survey and research on acute severe hearing disorders. Study on the expression of cells similar to internal ear stem cell after acute acoustic trauma using a nestin GFP rat. – 2005 Rats that co-expressed nestin and GFP (green fluorescent protein) were used to study whether the presence of cells similar to internal ear stem cell could be identified using nestin, a filament of an intermediate size, as a marker. In the cochlea of 4-week-old nestin-GRP rats, nestin-positive cells were observed only in spiral ganglion cells but not in the sensory epithelial cell layer comprising hair cells and supprt cells of Corti organ. A very small number of nestin-positive cells were observed inside the Corti organ in the cochlea of the rats loaded with band noise at 4 kHz and 125 dB for two hours. Cells similar to internal ear stem cell are deemed likely to differentiate to support cells or hair cells. Regeneration therapy of cochlea hair cells was suggested to be possible.
Stem Cells May Be Key To Deafness Cure – August 2006
In a dusty, cluttered lab at Stanford University, a team of young scientists is on a quest. Curing deafness is the goal, reports CBS News correspondent Elizabeth Kaledin, and Stefan Heller says stem cells hold the key. Heller and his entire team were recruited away from Harvard, and they’ve made a breakthrough discovery: They’ve found that stem cells have the capacity to regenerate in the inner ear. Full Story
Stem cell based therapy to restore nearly normal hearing Nov 2006 – hearing in humans. The current review focuses on stem cell-based therapy with particular emphasis to summarize …. restored hearing loss, which demonstrates their potential ….
First blood and bone stem cell research on deafness – December 2006 – Deafness Research UK is funding a new research programme that will be the first to try and develop a cure for deafness using stem cells taken from umbilical cord blood or bone marrow. This three-year project will be based in the Centre for Stem Cell Biology at the University of Sheffield and has been made possible by a £126,000 charitable donation from GlaxoSmithKline (GSK). It will be the first research to use these promising new lines of stem cells, which are less controversial than stem cells derived from human embryos, in the search for a cure for deafness. Full Story
COSM 2007: Triological Society – Stem Cell and Genetic Therapies for Hair Cell-Related Hearing Loss
Neil Segil, PhD, from the House Ear Institute, discussed the potential of hair cell regeneration with endogenous progenitor cells—specifically supporting cells. In mice, Dr. Segil’s team tested the capacity of cochlear supporting cells to divide and transdifferentiate by using green fluorescent markers expressed only in supporting cells in the inner ear. With the resulting purified supporting cells, the scientists discovered that the cells were still capable of self-division. And, although these cells normally wouldn’t actively divide, under the culture conditions in the lab, they did.
“If we keep these cells in culture for six days, some of the cells begin to differentiate as hair cells,” he said, adding that they have not yet identified the stimulus for the division. What they did determine is that self-division is age-dependent, in early cells. It is important, Dr. Segil said, to further test whether self-division can be stimulated in mature cells. In another study, Dr. Segil’s team is targeting one pathway that keeps cells next to each other from differentiating as the same cell type. They believe that supporting cells are being actively inhibited from becoming hair cells by this pathway. Additional projects look at cell differentiation to better understand the process by which the supporting cell differentiated state is maintained.
Tech Could End Deafness – February 2007
“We have a good chance of getting normal hearing back in normal ears,” said Richard Schmiedt, an otolaryngology professor at the Medical University of South Carolina. The stem-cell approach involves restoring the tiny “hair cells” in the ear that convert sound into electrical impulses. When the cells die, people permanently lose their hearing. Bringing back the cells through stem-cell transplants, along with a shock of electricity, could restore hearing, scientists say. At Stanford University, professor Stefan Heller, who discovered stem cells in the inner ear, believes they can be used to cure deafness in mice within five years. Heller and his colleagues are trying to learn from birds, which do not become deaf, the secret genetic recipe for warding off hearing loss. Full Story
The Miracle of Hair Cells and Prospects for Regrowth – June 2007
Here’s a great article that explains the structure and function of inner and outer hair cells and also looks at some of the research into regrowing these cells. If you’re interested in this topic, it’s very much worth the read! Full Story
Stem Cell Therapy Recovers Lost Hearing – June 2007
Stem cells injected into the inner ear survived in half of the injured rats, where they migrated away from the site of injection toward the injured region within the inner ear. These stem cells divided in the new environment and expressed several proteins necessary for hearing, suggesting tissue-specific differentiation. Further, transplanted cells that migrated to the damaged area of the inner ear displayed shape similar to that of cochlear fibrocytes. Importantly, transplanted rats exhibited faster recovery from hearing loss, particularly in the high frequency range, which is difficult to restore by natural regeneration. Stem cell migration into the damaged area of the inner ear improved hearing of high frequency sound (40 kHz) by 23% compared to natural recovery in untreated animals. Full Story
Genes In Human Inner Ear Cells Restored – June 2007
Dr. Jeffrey Holt, associate professor of neuroscience and otolaryngology at UVa, and his research team, including Dr. Bradley Kesser, an assistant professor of otolaryngology, targeted a gene known as KCNQ4, which causes genetic hearing loss in humans when mutated. They engineered a correct form of the gene and created a gene therapy delivery system that successfully transferred the KCNQ4 gene into human hair cells harvested from the inner ears of patients with hearing loss. “Our results show that gene therapy reagents are effective in human inner ear tissue. Taken together with the results from another group of scientists who showed that similar gene therapy compounds can produce new hair cells and restore hearing function in guinea pigs suggest that the future of gene therapy in the human inner ear is sound,” Holt said. Full Story
Researchers Develop New Method of Growing Hair Cells – November 2007 – Researchers at the University of Virginia have developed a new method of growing inner-ear hair cells that will aid research to help people regain their hearing. Dr. Jeffrey T. Corwin, a professor of neuroscience at the UVa Health System, and Dr. Zhengqing Hu, a neuroscience research assistant, have been growing cells from inner ears of chicken embryos. They hope to extend that knowledge to re-grow the inner-ear hair cells of humans. Mammals grow inner-ear hair cells only before they are born, unlike amphibians and birds, which can re-grow damaged or lost cells. These unique structures are lost over time as mammals age, or if they contract certain infections or undergo trauma. The loss of inner-ear hair cells results in hearing loss and balance impairment. Hu and Corwin’s process is able to grow chicken inner-ear hair cells in a laboratory setting. Full Story
Mesenchymal Stem Cell Transplantation Accelerates Hearing Recovery through the Repair of Injured Cochlear Fibrocytes – (American Journal of Pathology. 2007;171:214-226.) DOI: 10.2353/ajpath.2007.060948 – From the Laboratory of Auditory Disorders* and Division of Hearing and Balance Research, National Institute of Sensory Organs, and the Department of Plastic Surgery, National Tokyo Medical Center, Tokyo, Japan – Cochlear fibrocytes play important roles in normal hearing as well as in several types of sensorineural hearing loss attributable to inner ear homeostasis disorders. Recently, we developed a novel rat model of acute sensorineural hearing loss attributable to fibrocyte dysfunction induced by a mitochondrial toxin. In this model, we demonstrate active regeneration of the cochlear fibrocytes after severe focal apoptosis without any changes in the organ of Corti. To rescue the residual hearing loss, we transplanted mesenchymal stem cells into the lateral semicircular canal; a number of these stem cells were then detected in the injured area in the lateral wall. Rats with transplanted mesenchymal stem cells in the lateral wall demonstrated a significantly higher hearing recovery ratio than controls. The mesenchymal stem cells in the lateral wall also showed connexin 26 and connexin 30 immunostaining reminiscent of gap junctions between neighboring cells. These results indicate that reorganization of the cochlear fibrocytes leads to hearing recovery after acute sensorineural hearing loss in this model and suggest that mesenchymal stem cell transplantation into the inner ear may be a promising therapy for patients with sensorineural hearing loss attributable to degeneration of cochlear fibrocytes.
Directed differentiation of mouse cochlear neural progenitors in vitro- 18 June 2008 – Departments of 1Otolaryngology and 2Neurosurgery, 3Graduate Program in Neuroscience, 4Stem Cell Institute, and 5Bioengineering, University of Minnesota, Minneapolis, Minnesota – Multipotent cochlear neural progenitors (CNPs) in the organ of Corti hold the promise for cell replacement in degenerative hearing disorders. However, not much is known about the CNPs and the specific conditions for their differentiation. Here we isolate the CNPs from the postnatal day 1 organ of Corti in mice and demonstrate their capability to self-renew and to differentiate into hair cell-like and neuronal cell-like phenotypes under the guidance of sonic hedgehog (SHH), epidermal growth factor (EGF), retinoic acid (RA), and brain-derived neurotrophic factor (BDNF), herein termed SERB (abbreviation of SHH, EGF, RA, and BDNF) in an asymmetric or symmetric manner from clonal isolates. Differentiation of CNPs into hair cells by SERB was dependent on the ERK signaling pathway, whereas the differentiation of CNPs into neurons by SERB was not. This work develops a new in vitro methodology for the maintenance and self-regeneration of CNPs for future design of regenerative strategies for hearing disorders.
Novel approaches to treating sensorineural hearing loss. Auditory genetics and necessary factors for stem cell transplant. 2008 Aug;14(8):RA114-25. Sensorineural hearing loss is a chronic disease, with a serious impact on human communication and quality of life. Exposure to various factors can lead to irreversible hearing impairment, as the auditory epithelium in humans comprises terminally differentiated cells. By contrast, the inner ear of lower vertebrates and invertebrates shows regenerative capacity. Efforts to regenerate the damaged human inner ear may involve renewed cell proliferation, or transplanting cells that can differentiate into sensory cells. Literature review. Animal studies, in vitro studies, retrospective-cohort studies, community-based case-controls, clinical guidelines, and review articles. Embryonic stem cells, inner ear stem cells, and stem cells from other tissues (i.e., neural tissue, hematopoietic system) may be candidates for restoring the auditory epithelium.
Transcriptional regulation of p27kip1 is the primary determinant of terminal mitosis and the final number of postmitotic progenitors of hair and supporting cells. Basic helix-loop-helix transcription factor Math1 was found to be necessary and sufficient for the production of auditory hair cells. Notch signaling seems to play a major role in the regulation of Math1, through lateral inhibition. Brn3c, Gfi1, and Barhl1 are also specific transcription factors that have been implicated in hair cell maintenance and consequent survival. Evidence concerning development, maintenance, and regeneration of hair cells is still at an embryonic stage. Combined data, as attempted in the present study, will lead to a more successful management of deafness.
Sensory Cell Regeneration and Stem Cells: What We Have Already Achieved in the Management of Deafness – Otology & Neurotology: September 2008 – Volume 29 – Issue 6 – pp 758-768, doi: 10.1097/MAO.0b013e31817fdfad – There is an already exciting progress in the fields of sensory cell regeneration and SC research in an attempt to restore hearing or prevent deafness. However, further understanding of the underlying mechanisms of auditory genetics, continuing investigation of the human genome, refinement of the delivering techniques, and specification of the therapeutic strategies have to be developed before functional regeneration of the cochlea can be achieved in clinical practice.
Umbilical Stem Cells May Repair Damaged Cochlear Hair Cells – September 2008
According to an Italian research team publishing their findings in the current issue of Cell Transplantation (17:6), hearing loss due to cochlear damage may be repaired by transplantation of human umbilical cord hematopoietic stem cells (HSC) since they show that a small number migrated to the damaged cochlea and repaired sensory hair cells and neurons. For their study, the team used animal models in which permanent hearing loss had been induced by intense noise, chemical toxicity or both. Cochlear regeneration was only observed in animal groups that received HSC transplants. Researchers used sensitive tracing methods to determine if the transplanted cells were capable of migrating to the cochlea and evaluated whether the cells could contribute to regenerating neurons and sensory tissue in the cochlea. Full Story
Researchers Make in Vitro Inner Ear Hair Cells – November 2008
Iranian researchers managed to successfully extract bone marrow stem cells from rodents and produce in vitro inner ear hair cells. “In this two-year project, researchers cultured and produced inner ear hair cells, a procedure which is not commonly performed in other countries,” research team-leader, Mohammad Farhadi told the Iranian students news agency. Farhadi reported that injecting the resulted cells into deaf mice has successfully tackled hearing loss in them. Full Story
New Stem Cell Therapy May Lead To Treatment For Deafness – ScienceDaily (Mar. 23, 2009) — Deafness affects more than 250 million people worldwide. It typically involves the loss of sensory receptors, called hair cells, for their “tufts” of hair-like protrusions, and their associated neurons. The transplantation of stem cells that are capable of producing functional cell types might be a promising treatment for hearing impairment, but no human candidate cell type has been available to develop this technology. A new study led by Dr. Marcelo N. Rivolta of the University of Sheffield has successfully isolated human auditory stem cells from fetal cochleae (the auditory portion of the inner ear) and found they had the capacity to differentiate into sensory hair cells and neurons…”The results are the first in vitro renewable stem cell system derived from the human auditory organ and have the potential for a variety of applications, such as studying the development of human cochlear neurons and hair cells, as models for drug screening and helping to develop cell-based therapies for deafness,” say the authors.
Stem cells may help deaf people hear – April 2009 – Stem cells may help deaf people hear again, according to early stage research by British scientists. A team at the University of Sheffield said on Thursday they had discovered how to turn stem cells into ones that behave like sensory hair cells or auditory neurons, which could then be surgically inserted into the ear to restore lost hearing. Lead researcher Marcelo Rivolta said the approach, which is being tested on animals, held significant potential but was a long way from being offered to patients. Full Story
Hair Cell Regeneration – How It Works and What It Means for Audiologists – May 2009 – Twenty years have passed since the discovery of hair cell regeneration in birds (Corwin & Cotanche, 1988; Ryals & Rubel, 1988). The initial excitement caused by this discovery has been followed by steady progress in understanding the fundamental mechanisms that recently culminated in research evidence of hair cell regeneration in both the auditory and vestibular portions of the mammalian inner ear (Kawamoto et al., 2003; Izumikawa et al., 2005; Staecker et al., 2007). Clinical audiologists are faced with the responsibility of translating these basic science findings into potential patient application. They raise important questions: When will hair cell regeneration be a reality for my patients? What will be the measures of candidacy? What will the impact of hair cell regeneration be in my patients who use or are candidates for hearing aids or other amplification devices? Will hearing aids or cochlear implants continue to be needed in the face of hair cell regeneration? Full Story
Regrowing Hair Cells in the Human Cochlea – June 2009
More than 20 years ago, Douglas Cotanche, PhD, then at the Medical University of South Carolina and now affiliated with Children’s Hospital Boston, discovered that the hair cells within the chick cochlea were capable of a “significant amount of recovery and regeneration” following acoustic trauma.1 His unexpected discovery began a cascade of research on the question of whether hair cells within the human cochlea could someday achieve the same regenerative results. If and when this happens, many of the causes of hearing loss in humans, from noise to aging, can finally be resolved without the need for hearing aids or cochlear implants. Although steady progress has been made in understanding the mechanisms underlying hair cell regeneration, human subjects have yet to participate in clinical trials concerned with regrowing hair cells. Such trials may still be years away. Let’s look at a sampling of the research in 2008, which moves us ever closer to the goal of restoring hearing in this most natural way. Full Story
Can a Tiny Fish Save Your Ears? – August 2009
For many people, loss of hearing is irreversible. For scientists trying to figure out what can be done about that, one answer may lie-or swim, actually-in freshwater aquariums. About one of every 10 Americans suffers from hearing impairment, according to a survey conducted by the Better Hearing Institute, a nonprofit advocacy group. By far the most common cause of hearing loss is damage to the so-called hair cells in the inner ear as a result of excessive noise, certain illnesses and drugs, and simple aging. The problem is that once hair cells die, humans (like other mammals) aren’t able to grow new ones. In recent years, a research team at the University of Washington in Seattle has been working on finding a way to resolve that problem in experiments involving the zebrafish, a common aquarium denizen. The zebrafish, like many aquatic creatures, has clusters of hair cells running along the outside of its body that help sense vibrations in the water, working in a similar way to hair cells in the human inner ear. But unlike humans, zebrafish are able to regenerate their damaged hair cells. Researchers hope their work can unlock secrets to protect human hair cells from becoming damaged and to stimulate the cells to regenerate. Full Story
Cord Blood Stem Cells Repair Mouse Inner Ear – August 2009
Results: The authors found that HSC migrated and engrafted into the cochlea of the deaf mice and that the levels of engraftment correlated with both the severity of damage and the treatment dose. Analysis at 60 days post-treatment showed that the mice in the HSC treatment group had well-repaired cochlea with dramatic hair cell regrowth, while control mice showed no sign of repair or hair cell regeneration.
Conclusion: The study shows dramatic repair of cochlear damage in mice after intravenous infusion of cord blood HSC, suggesting a potential therapeutic strategy using cord blood stem cells in hearing rehabilitation therapies. Full Story
Regeneration of the mammalian inner ear sensory epithelium – Oct 2009 – …focus on ‘self-repair’ of the mammalian inner ear sensory epithelium, including recruiting the in-situ proliferation and differentiation of endogenous cells at the damaged site and the autologous transplantation
Stem Cells Cure Hearing Loss? – November 2009 – Chloe had to travel outside of the United States for stem cell treatment for her hearing disorder. Chloe’s hearing was tested two months after the procedure was completed on October 16, 2009. The results were spectacular. The left ear improved to 50% from 0%. The right ear gained almost complete hearing. http://repairstemcell.wordpress.com/2009/11/05/stem-cells-heal-hearing-loss/
(much thanks to hearinglossweb.com for compiling many of these articles!)
To find out if you are a candidate for stem cell therapy for your hearing disorder, contact me at email@example.com – The information is free and there is no obligation.