Hearing impairment is the most frequently occurring sensorineural defect in humans. The sense of hearing originates in the cochlea, a structure in the inner ear. Information about timing, frequency, and intensity of sounds is transmitted from the hair cells in the cochlea to the brain via spiral ganglion neurons by converting sound waves into nerve impulses. Any disruptions in this sensory pathway could result in auditory neuropathy and hearing impairment.
Causes
Auditory neuropathy is a type of hearing impairment caused by a defect in the hair cells and/or their synapses (synaptopathy) or the spiral ganglion neurons (neuropathy). It can affect people of all ages, from birth (congenital) through adulthood (acquired or age–related). Genetically inherited auditory neuropathy can be either isolated or associated with a systemic neurodegenerative disorder such as Charcot-Marie-Tooth disease or Friedreich’s ataxia.
Diagnosis
Auditory neuropathy can be diagnosed using hearing tests such as auditory brainstem response (ABR) and otoacoustic emissions (OAE). Auditory neuropathy is defined by an abnormal ABR reading together with a normal OAE reading. An abnormal ABR reading can be the result of damage to the auditory nerve pathway, including the inner hair cells, their connection to the nerve (synapses), and/or the nerve itself (spiral ganglion neurons).
Why We Care
Cochlear implants are currently the standard of care for hearing impairment. However, cochlear implant performance relies on healthy spiral ganglion neurons. Therefore, knowledge of the exact site of dysfunction (i.e., whether the patient suffers from synaptopathy or neuropathy) would aid in assessing the benefit of this treatment for patients. There are currently no available clinical tests that can distinguish between cochlear synaptopathy and neuropathy, but molecular genetic diagnosis can. Our long-term goal is to identify genes that are involved in congenital and age-related cochlear synaptopathy and/or neuropathy. Identification of these genes will improve the clinical diagnosis and our understanding of the molecular mechanisms that regulate the innervation of the cochlea and that cause cochlear neuropathy.
Our lab is interested in understanding the cellular and molecular mechanisms underlying peripheral auditory neuropathy. We utilize transgenic mouse models and a variety of cutting edge molecular, microscopic, and physiological approaches to understand cochlear neurogenesis, and neuropathy associated with congenital and age related hearing impairment.
OUR TEAM
We are currently open to STUDENT ROTATION and we also are offering a
POSTDOCTORAL POSITION at the Stanford University School of Medicine.
PUBLICATIONS
Sundaresan S, Kong JH, Fang Q, Salles F, Wangsawihardja F, Ricci AJ, Mustapha M. Thyroid hormone is required for pruning, functioning and long-term maintenance of afferent inner hair cell synapses. Eur J Neurosci. 2015 Sep 19. doi:10.1111/ejn.13081. PubMed PMID: 26386265.
Fang Q, Indzhykulian AA, Mustapha M, Riordan GP, Dolan DF, Friedman TB, Belyantseva IA, Frolenkov GI, Camper SA, Bird JE. The 133-kDa N-terminal domain enables myosin 15 to maintain mechanotransducing stereocilia and is essential for hearing. Elife. 2015 Aug 24;4. doi: 10.7554/eLife.08627. PubMed PMID: 26302205.
Calton MA, Lee D, Sundaresan S, Mendus D, Leu R, Wangsawihardja F, Johnson KR, Mustapha M. A lack of immune system genes causes loss in high frequency hearing but does not disrupt cochlear synapse maturation in mice. PLoS One. 2014 May 7;9(5):e94549. doi: 10.1371/journal.pone.0094549. eCollection 2014. PubMed PMID: 24804771; PMCID: PMC4012943.
Mendus D, Sundaresan S, Grillet N, Wangsawihardja F, Leu R, Müller U, Jones SM, Mustapha M. Thrombospondins 1 and 2 are important for afferent synapse formation and function in the inner ear. Eur J Neurosci. 2014 Apr;39(8):1256-67. doi: 10.1111/ejn.12486. Epub 2014 Jan 27. PubMed PMID: 24460873; PMC4132060.