Daniel Choo

The molecular mechanisms dictating the morphogenesis and differentiation of the mammalian inner ear are largely unknown. To better elucidate the normal development of this organ, two approaches were taken. First, the membranous labyrinths of mouse inner ears ranging from 10.25 to 17 d postcoitum (dpc) were filled with paint to reveal their gross development. Particular attention was focused on the developing utricle, saccule, and cochlea. Second, we used bone morphogenetic protein 4 (BMP4) and lunatic fringe (Fng) as molecular markers to identify the origin of the sensory structures. Our data showed that BMP4 was an early marker for the superior, lateral, and posterior cristae, whereas Fng served as an early marker for the macula utriculi, macula sacculi, and the sensory portion of the cochlea. The posterior crista was the first organ to appear at 11.5 dpc and was followed by the superior crista, the lateral crista, and the macula utriculi at 12 dpc. The macula sacculi and the cochlea were present at 12 dpc but became distinguishable from each other by 13 dpc. Based on the gene expression patterns, the anterior and lateral cristae may share a common origin. Similarly, three sensory organs, the macula utriculi, macula sacculi, and cochlea, seem to arise from a single region of the otocyst.

OBJECTIVE: To medically and audiologically characterize a population of children diagnosed as having auditory neuropathy (AN). STUDY DESIGN: Retrospective medical chart review. SETTING/SUBJECTS: We identified 22 patients from a pediatric otology clinic in a tertiary care pediatric hospital setting. RESULTS: A genetic factor in AN is suggested by our identification of 3 families with 2 affected children and 2 other children with family histories that were positive for hearing loss. Clinical features common among our population included a history of hyperbilirubinemia (n = 11 [50%]), prematurity (n = 10 [45%]), ototoxic drug exposure (n = 9 [41%]), family history of hearing loss (n = 8 [36%]), neonatal ventilator dependence (n = 8 [36%]), and cerebral palsy (n = 2 [9%]). Full clinical and audiological data were available for 18 of the 22 children, including otoacoustic emissions, auditory brainstem responses with cochlear microphonics, and age-appropriate audiometric findings. Significantly, 9 of these 18 patients showed improvement in behavioral thresholds over time, indicating that a subset of children with AN may recover useful hearing levels. Also significant was the success of cochlear implantation in 4 children. CONCLUSIONS: Management of AN in children requires serial clinical and audiometric evaluations, with a prominent role for behavioral testing. Prematurity, genetics, and hyperbilirubinemia appear to be significant factors in the development of AN; hyperbilirubinemia can be associated with spontaneous improvement of hearing thresholds. For those children not benefiting from amplification or FM systems, cochlear implantation remains a potentially successful method of habilitation.

Intratympanic instillation of Depo-Medrol (80 mg/cc), dexamethasone ophthalmic solution (1 mg/cc), or dexamethasone intravenous (4 mg/cc) solution produces improvement of cochlear function in certain patients with Meniere's disease, autoimmune inner ear disease and sudden sensorineural deafness. Tinnitus improved in 47%, most often in patients with Meniere's disease (9 of 15; 60%). The SRT improvement of greater than 10 dB or SD greater than 15% was documented in 41% (average improvement in SRT: 15 dB; SD: 24%). Patients with tinnitus and bilateral sensorineural hearing loss (i.e., presbycusis) did not benefit from the treatment. Prior to treatment with intratympanic medication, laser assisted tympanostomy with middle ear exploration, using otoendoscopy to determine the status of the round window niche and remove mucosal folds, helps in making the round window membrane accessible to local application of drops. Placing Gelfoam into the round window niche under direct vision, and using a Venturi Bobbin tube in the tympanic membrane, appears to be a satisfactory method for delivering medication to the inner ear fluids. The medication can be injected by the physician through the tube into the middle ear, or the patient can perform self-treatment at home, placing medication in the external auditory canal. A double-blind, cross-over study in patients with Meniere's disease is now in progress with Institutional Review Board (IRB) approval, which will be reported at a later date. This preliminary study has shown that intratympanic steroids may affect the symptoms of hearing loss and tinnitus in patients with various inner ear problems. Patients with Meniere's disease appear to respond in the highest percentage of cases. Hopefully, additional research will suggest the appropriate drugs which can be used to treat inner ear disease. Direct application of the drug to the round window membrane may increase the concentration in the inner ear fluids, thus avoiding the systemic effects.

The Otx1 and Otx2 genes are two murine orthologues of the Orthodenticle (Otd) gene in Drosophila. In the developing mouse embryo, both Otx genes are expressed in the rostral head region and in certain sense organs such as the inner ear. Previous studies have shown that mice lacking Otx1 display abnormal patterning of the brain, whereas embryos lacking Otx2 develop without heads. In this study, we examined, at different developmental stages, the inner ears of mice lacking both Otx1 and Otx2 genes. In wild-type inner ears, Otx1, but not Otx2, was expressed in the lateral canal and ampulla, as well as part of the utricle. Ventral to the mid-level of the presumptive utricle, Otx1 and Otx2 were co-expressed, in regions such as the saccule and cochlea. Paint-filled membranous labyrinths of Otx1-/- mutants showed an absence of the lateral semicircular canal, lateral ampulla, utriculosaccular duct and cochleosaccular duct, and a poorly defined hook (the proximal part) of the cochlea. Defects in the shape of the saccule and cochlea were variable in Otx1-/- mice and were much more severe in an Otx1-/-;Otx2(+/)- background. Histological and in situ hybridization experiments of both Otx1-/- and Otx1-/-;Otx2(+/)- mutants revealed that the lateral crista was absent. In addition, the maculae of the utricle and saccule were partially fused. In mutant mice in which both copies of the Otx1 gene were replaced with a human Otx2 cDNA (hOtx2(1)/ hOtx2(1)), most of the defects associated with Otx1-/- mutants were rescued. However, within the inner ear, hOtx2 expression failed to rescue the lateral canal and ampulla phenotypes, and only variable rescues were observed in regions where both Otx1 and Otx2 are normally expressed. These results suggest that both Otx genes play important and differing roles in the morphogenesis of the mouse inner ear and the development of its sensory organs.

BACKGROUND AND OBJECTIVE: Congenital cytomegalovirus (cCMV) infection remains a leading cause of childhood hearing loss. Currently universal CMV screening at birth does not exist in the United States. An alternative approach could be testing infants who do not pass their newborn hearing screening (NHS) for cCMV. This study was undertaken to evaluate whether a targeted approach will identify infants with CMV-related sensorineural hearing loss (SNHL). METHODS: Infants born at 7 US medical centers received NHS and were also screened for cCMV while in the newborn nursery. Infants who tested positive for CMV received further diagnostic audiologic evaluations to identify or confirm hearing loss. RESULTS: Between 2007 and 2012, 99 945 newborns were screened for both hearing impairment and cCMV. Overall, 7.0% of CMV-positive infants did not pass NHS compared with 0.9% of CMV-negative infants (P < .0001). Among the cCMV infants who failed NHS, diagnostic testing confirmed that 65% had SNHL. In addition, 3.6% of CMV-infected infants who passed their NHS had SNHL confirmed by further evaluation during early infancy. NHS in this cohort identified 57% of all CMV-related SNHL that occurred in the neonatal period. CONCLUSIONS: A targeted CMV approach that tests newborns who fail their NHS identified the majority of infants with CMV-related SNHL at birth. However, 43% of the infants with CMV-related SNHL in the neonatal period and cCMV infants who are at risk for late onset SNHL were not identified by NHS.