RNA-Seq Analysis of Allele-Specific Expression in the Mouse Cochlea

Objectives:

Age-related hearing impairment or presbycusis is one of the most common sensory abnormalities in the world. Mouse models have been widely used in studies of hearing loss to separate genetic and environmental influences. We will describe novel cis- and trans-regulation and dominance patterns in gene expression levels from cochlea of mice.

Methods:

Next-generation sequencing (RNA-Seq) data has been acquired from cochlea of three F1 mouse hybrid strains (n = 4) from parental strains C57BL/6J, DBA/2J, C3H/HeJ.

Results:

An analysis of allele-specific expression will be reported and novel transcripts, isoforms, cis and trans-regulation, long non-coding RNAs, and dominance patterns will be discussed in relation to known genes.

Conclusions:

This will help to elucidate mechanisms and better understand the genetic backdrop of age related hearing impairment.

FVB/NJ mice demonstrate a youthful sensitivity to noise-induced hearing loss and provide a useful genetic model for the study of neural hearing loss

The hybrid mouse diversity panel (HMDP), a panel of 100 strains, has been employed in genome wide association studies (GWAS) to study complex traits in mice. Hearing is a complex trait and the CBA/CaJ mouse strain is a widely used model for age-related hearing loss (ARHI) and noise induced hearing loss (NIHL). The CBA/CaJ strain's youthful sensitivity to noise and limited age-related loss led us to attempt to identify additional strains segregating a similar phenotype for our panel. FVB/NJ is part of the HMDP and has been previously described as having a similar ARHI phenotype to CBA/CaJ. For these reasons, we have studied the FVB/NJ mouse for ARHI and NIHL phenotypes in hopes of incorporating its phenotype into HMDP studies. We demonstrate that FVB/NJ exhibits ARHI at an earlier age than CBA/CaJ and young FVB/NJ mice are vulnerable to NIHL up until 10 to 12 weeks. This suggests that FVB/NJ may be used as an additional genetic model for neural forms of progressive hearing loss and for the study of youthful sensitivity to noise.

Surgical management of endolymphatic sac tumors

Objective To review the cumulative experience of surgical management of endolymphatic sac tumors (ELSTs) in the literature. To review the experience with ELST management at a tertiary referral-based otology-neurotology practice and present our approach to management. Study Design Retrospective patient review at a referral-based otology-neurotology practice. Methods A review of all available records from the House Clinic of patients with ELSTs was performed. Presentation, diagnostic workup, microsurgical approach, and outcomes were reviewed. Literature review using MEDLINE of studies reporting surgical outcomes of patients with ELSTs was also performed. Results Retrospective chart review revealed 18 patients with ELSTs who underwent surgical management. Grouping of these patients provides surgical outcomes on the largest group of mostly non-von Hippel-Lindau patients with ELSTs in the literature. Patients most commonly presented with sensorineural hearing loss, tinnitus, and dizziness. A majority of patients presented with large tumors exhibiting significant destruction of surrounding structures including the cochlea, vestibule, and internal auditory canal. Patients underwent microsurgical resection with the intent of complete resection. Conclusions Although the extensive nature of ELSTs at time of diagnosis often precludes hearing preservation, complete microsurgical resection can be achieved safely with preservation of facial function in the majority of cases.

Outcomes following Semicircular Canal Plugging

Objectives:

1) Examine audiometric outcomes following semicircular canal plugging for either superior semicircular canal dehiscence syndrome or refractory positional vertigo. 2) Review symptom control rates and complication rates for canal plugging procedures.

Methods:

Retrospective chart review at a private neurotologic tertiary referral center. Patients undergoing semicircular canal plugging for superior semicircular canal dehiscence syndrome or refractory positional vertigo from January 1, 2007, to December 31, 2012, were included. Pre- and postoperative audiometry, operative findings, and clinical symptoms were assessed through chart review. Acoustic reflex testing, vestibular testing, and canal dehiscence size were examined in superior canal dehiscence patients.

Results:

A total of 28 patients underwent a canal plugging procedure during the study period: 24 superior canal dehiscence syndrome patients and 4 posterior canal occlusion patients. Postoperative air conduction pure-tone averages were 22.5 and 13.0 dB for these two groups, respectively, compared to their preoperative values of 21.1 and 11.0 dB. The average pre- and postoperative word-recognition scores for the entire cohort were 96.2% and 94.0%. Vestibular evoked myogenic potential data showed reduced thresholds in 7 canal dehiscence patients. The average size of the canal dehiscence, based on preoperative radiological measurements, was 3.4 mm. Surgical complications were limited to one temporary facial weakness (Grade 2). Complete symptom improvement was noted in 35.7% of all patients, while 16.7% of canal dehiscence patients reported no change in symptoms.

Conclusions:

Semicircular canal plugging procedures are associated with excellent hearing outcomes and may reduce preoperative symptoms in patients with canal dehiscence and refractory positional vertigo.

Functional variants of MIF, INFG and TFNA genes are not associated with disease susceptibility or hearing loss progression in patients with Ménière's disease

Variability in acute immune response genes could determine susceptibility or prognosis for Ménière's disease (MD). The cytokines tumor necrosis factor α (TNFα), macrophage migration inhibitory factor (MIF) and interferon γ (INFγ) are proinflammatory cytokines of the innate immune response. These cytokines mediate inflammation and have been previously associated with the inflammatory process in several autoimmune diseases. We investigated the association between functional allelic variants of MIF (rs35688089), IFNG (rs2234688) and TNFA (rs1800629) in patients with MD. In addition to testing these variants for an association with disease, we also tested for an association with clinical aspects of disease progression, such as persistence of vertigo and the sensorineural hearing loss. A total of 580 patients with diagnosis of definite MD, according to the diagnostic scale of the American Academy of Otolaryngology-Head and Neck Surgery, and 552 healthy controls were included. DNA samples from a set of 291 American patients were used to confirm the results obtained in the MIF gene in our Spanish cohort. Although we found a significant association with the allele containing five repeats of CATT within the MIF gene in patients with MD in the Spanish cohort [corrected p = 0.008, OR = 0.69 (95 % CI, 0.54-0.88)], this finding could not be replicated in the American set. Moreover, no genetic associations for variants in either the TNFA or IFNG genes and MD were found. These results support the conclusion that functional variants of MIF, INFG, and TFNA genes are not associated with disease susceptibility or hearing loss progression in patients with MD.

Hybrid mouse diversity panel: a panel of inbred mouse strains suitable for analysis of complex genetic traits

We have developed an association-based approach using classical inbred strains of mice in which we correct for population structure, which is very extensive in mice, using an efficient mixed-model algorithm. Our approach includes inbred parental strains as well as recombinant inbred strains in order to capture loci with effect sizes typical of complex traits in mice (in the range of 5% of total trait variance). Over the last few years, we have typed the hybrid mouse diversity panel (HMDP) strains for a variety of clinical traits as well as intermediate phenotypes and have shown that the HMDP has sufficient power to map genes for highly complex traits with resolution that is in most cases less than a megabase. In this essay, we review our experience with the HMDP, describe various ongoing projects, and discuss how the HMDP may fit into the larger picture of common diseases and different approaches.

Evolution in the management of facial nerve schwannoma

OBJECTIVE

To design a treatment algorithm based on experience with facial nerve schwannomas (FNS) over a 30-year period.

STUDY DESIGN

Retrospective chart review.

METHOD

Seventy-nine patients with facial nerve schwannomas seen from 1979 through 2009 at a tertiary referral private otologic practice were categorized by treatment modality. Interventions included surgical resection with grafting, bony decompression, observation, or stereotactic radiation. Outcome measures included House-Brackmann facial nerve grade before and after intervention as well as change in facial nerve grade, tumor size, involved segments of nerve, time to intervention.

RESULTS

Thirty-seven patients (46.8%) ultimately underwent surgical excision with grafting or primary anastomosis, 21 (26.6%) underwent bony decompression alone, 15 (19.0%) were managed with observation only, and 6 (7.6%) had stereotactic radiation. Through 1995, 85% of cases had surgical resection and none had observation only. Of the 52 patients seen after 1995, 27% had surgical resection and grafting, 33% had bony decompression, 29% were managed with observation alone, and 11% had radiotherapy. Facial nerve grade was maintained or improved over the follow-up period (mean time = 3.9 years) in 78.9% of the decompression group and 100% of the observation and radiation groups compared to 54.8% of the resection group (P ≤ .012).

CONCLUSIONS

Surgical resection and grafting, once widely accepted and practiced, has in many cases given way to observation, bony decompression, or stereotactic radiation. A wide armamentarium of options is available to the neurotologist treating facial nerve schwannomas with the ability to preserve facial function for a longer period of time.

Avoiding Disaster at the Skull Base: Case Studies in 3D

Program Description: Disaster awaits unprepared surgeons at the skull base. Multiple routine surgeries in otolaryngology are in close proximity to the skull base. Potential risks of endoscopic sinus surgery include cerebrospinal fluid leak, loss of olfaction, penetrating brain injury, visual loss, hemorrhage from the internal carotid artery, and loss of trigeminal sensory and motor function. Potential risks of temporal bone and lateral approaches include vascular injuries of the sigmoid sinus, jugular bulb, and internal carotid artery; injury to cranial nerves 7-12; cerebrospinal fluid leak, intra- and extradural hemorrhage; and brain trauma. A thorough understanding of skull base anatomy is essential for avoiding such complications during routine surgical procedures. In this miniseminar, case studies will be used to demonstrate potential risks of standard surgical procedures relative to the skull base. Important anatomical landmarks and relationships will be presented in 3D using cadaveric dissections and intraoperative photographs. Strategies to avoid skull base complications will be discussed with an emphasis on everyday surgical procedures.

Educational Objectives: 1) Understand key anatomical relationships at the skull base. 2) Relate skull base anatomy to anterior and lateral skull base approaches. 3) Apply anatomical knowledge to avoid surgical complications.

GRM7 variants confer susceptibility to age-related hearing impairment

Age-related hearing impairment (ARHI), or presbycusis, is the most prevalent sensory impairment in the elderly. ARHI is a complex disease caused by an interaction between environmental and genetic factors. Here we describe the results of the first whole genome association study for ARHI. The study was performed using 846 cases and 846 controls selected from 3434 individuals collected by eight centers in six European countries. DNA pools for cases and controls were allelotyped on the Affymetrix 500K GeneChip for each center separately. The 252 top-ranked single nucleotide polymorphisms (SNPs) identified in a non-Finnish European sample group (1332 samples) and the 177 top-ranked SNPs from a Finnish sample group (360 samples) were confirmed using individual genotyping. Subsequently, the 23 most interesting SNPs were individually genotyped in an independent European replication group (138 samples). This resulted in the identification of a highly significant and replicated SNP located in GRM7, the gene encoding metabotropic glutamate receptor type 7. Also in the Finnish sample group, two GRM7 SNPs were significant, albeit in a different region of the gene. As the Finnish are genetically distinct from the rest of the European population, this may be due to allelic heterogeneity. We performed histochemical studies in human and mouse and showed that mGluR7 is expressed in hair cells and in spiral ganglion cells of the inner ear. Together these data indicate that common alleles of GRM7 contribute to an individual's risk of developing ARHI, possibly through a mechanism of altered susceptibility to glutamate excitotoxicity.

Mapping of genetic modifiers of Eya1 ( bor/bor ) in CAST/EiJ and BALB/cJ that suppress cochlear aplasia and associated deafness

Mice homozygous for the hypomorphic allele Eya1 ( bor ) exhibit cochlear aplasia, with associated deafness, and renal hypoplasia, similar to Branchio-Oto-Renal syndrome (BOR) in humans. Although much is known about the genetics of the disease, little is known about the factors that modify its phenotypic expression. We have recently detailed two modifier loci (Mead1 and Mead2) in a C3HeB/FeJ-Eya1 ( bor/+ ) x C57BL/6 J intercross that suppress the ear-related phenotypes in our hypomorphic mutants. In this study we report corroborating evidence for our initial finding with the identification of two modifier loci mapping to the same region in CAST/EiJ and BALB/cJ. Furthermore, we describe an additional locus (Mead3) on chromosome 19 in CAST/EiJ, within which the previously cloned suppressor Nxf1 resides. The suppression effect on cochlear coiling was studied on congenic line(s) for each protective allele. The penetrance and suppressor strength of these alleles vary by strain and locus. Eya1 ( bor/bor ) hypomorphs, when homozygous for each of the three protective alleles (CAST/EiJ, C57BL/6 J, or BALB/cJ) at the Mead1 or Mead2 locus, exhibit completely penetrant suppression of cochlear agenesis. At the Mead1 locus, the C57BL/6 J and BALB/cJ alleles have comparable strengths. At the Mead2 locus, the C57BL/6 J and CAST/EiJ alleles have comparable strengths. In contrast, mice with genotype Eya1 ( bor/bor )Mead3(CAST/CAST) exhibit incomplete penetrance (50%) and a wide range of cochlear coiling (1/4-1(1/2) turns). The identification of these additional modifier alleles could provide crucial clues for evaluating the candidate genes.

Management of Cerebrospinal Fluid Leaks After Acoustic Tumor Removal

Objective:

To present a logical algorithm for management of postoperative cerebrospinal fluid (CSF) leak that occurs after acoustic tumor removal, and to describe a method for eustachian tube resection.

Clinical Presentation:

We present an algorithm in the form of a flow chart, describe middle fossa craniotomy for eustachian tube resection, and present three cases in which this technique was used.

Technique:

For CSF leak, pressure dressing at the wound and bed rest for the patient are advised; lumbar drain is indicated if the leak does not resolve. Occasionally, wound exploration is required. CSF rhinorrhea is treated first with a lumbar drain. If this approach is unsuccessful, the choice of treatment depends on the patient's hearing status. If a patient has no hearing, we perform a blind sac closure of the ear canal and pack the eustachian tube. If a patient has hearing, wound reexploration and lumbar drainage are advised. When conservative and initial surgical procedures for resolving CSF leak fail, we perform a middle fossa craniotomy to identify, divide, and remove a segmental portion of the cartilaginous eustachian tube and then cauterize and occlude both ends.

Conclusion:

At centers where surgical removal of acoustic tumors is frequently performed, a logical protocol should be in place for treatment of postoperative CSF leak. The leak location and the patient's hearing status are factors in determining the appropriate treatment method. Middle fossa craniotomy for resection of the eustachian tube is a safe, definitive management option for treatment of recalcitrant CSF rhinorrhea that occurs after acoustic tumor surgery.

Lung adenocarcinoma invasion in TGFbetaRII-deficient cells is mediated by CCL5/RANTES

Recently, we identified a lung adenocarcinoma signature that segregated tumors into three clades distinguished by histological invasiveness. Among the genes differentially expressed was the type II transforming growth factor-beta receptor (TGFbetaRII), which was lower in adenocarcinoma mixed subtype and solid invasive subtype tumors compared with bronchioloalveolar carcinoma. We used a tumor cell invasion system to identify the chemokine CCL5 (RANTES, regulated on activation, normal T-cell expressed and presumably secreted) as a potential downstream mediator of TGF-beta signaling important for lung adenocarcinoma invasion. We specifically hypothesized that RANTES is required for lung cancer invasion and progression in TGFbetaRII-repressed cells. We examined invasion in TGFbetaRII-deficient cells treated with two inhibitors of RANTES activity, Met-RANTES and a CCR5 receptor-blocking antibody. Both treatments blocked invasion induced by TGFbetaRII knockdown. In addition, we examined the clinical relevance of the RANTES-CCR5 pathway by establishing an association of RANTES and CCR5 immunostaining with invasion and outcome in human lung adenocarcinoma specimens. Moderate or high expression of both RANTES and CCR5 was associated with an increased risk for death, P=0.014 and 0.002, respectively. In conclusion, our studies indicate RANTES signaling is required for invasion in TGFbetaRII-deficient cells and suggest a role for CCR5 inhibition in lung adenocarcinoma prevention and treatment.

Surgical management of skull base chondroblastoma

OBJECTIVES

Chondroblastoma is a rare tumor accounting for 1% of primary bone tumors. Chondroblastoma involving the skull base is exceedingly rare with approximately 60 cases reported. We reviewed our experience with chondroblastoma of the skull base with an emphasis on current lateral skull base approaches and long-term tumor control.

STUDY DESIGN AND SETTING

A retrospective case review at a tertiary neurotology private practice group was performed over a 20-year period. Five patients were identified with skull base chondroblastoma. All patients underwent surgical intervention, and success of surgery was determined by disease-free status at last follow-up. Mean follow-up time was 5.8 years.

RESULTS

Two patients underwent gross tumor removal as primary therapy. One patient underwent partial tumor removal at an outside institution, and follow-up magnetic resonance imaging demonstrated rapid growth of residual tumor. This patient was successfully treated with gross total removal of residual tumor with an infratemporal craniotomy approach. Near total tumor removal was performed in two patients because of intimate involvement of vital structures. At last follow-up, no patient had radiographic evidence of tumor recurrence. There were no significant postoperative complications.

CONCLUSIONS

Gross total or near total resection of skull base chondroblastomas through lateral skull base approaches results in long-term tumor control and low complication rates.

Hearing preservation surgery for neurofibromatosis Type 2–related vestibular schwannoma in pediatric patients

OBJECT

The authors reviewed the proportion of pediatric patients with neurofibromatosis Type 2 (NF2) in whom hearing was preserved after middle fossa resection of vestibular schwannoma (VS).

METHODS

In this retrospective chart review the authors examined the cases of 35 children with NF2 who had undergone middle fossa resection (47 surgeries) between 1992 and 2004 in a neurotological tertiary care center. Surgical outcome was assessed using pure-tone average (PTA) thresholds obtained before and immediately after resection. Speech discrimination scores (SDSs) and pre- and postfacial nerve grades were also recorded. In 55% of surgeries, hearing of less than or equal to 70 dB PTA was maintained postoperatively. The American Academy of Otolaryngology-Head and Neck Surgery Class A hearing (PTA < or = 30 dB and SDS > or = 70%) was preserved in 47.7%. Facial nerve function was good (House-Brackmann Grades I or II) in 81% of the patients. Twelve patients had bilateral middle fossa resections; in nine (75%) of these patients hearing was maintained postoperatively in both ears.

CONCLUSIONS

More than half of the children with NF2 in the authors' cohort experienced hearing preservation after middle fossa resection was performed for VS. The authors recommend this approach for preserving hearing in children with NF2.

Effect of ciprodex on graft healing in tympanoplasty

The present study was conducted to evaluate whether the administration of ciprofloxacin 0.3%/dexamethasone 0.1% (Ciprodex)-soaked gelfoam during tympanoplasty has adverse effects on graft healing. Records of patients who had undergone tympanoplasty with Ciprodex-soaked gelfoam packing placed in the middle and external ear canal were reviewed. The time to heal for each patient and the number of postoperative perforations/complications were recorded. Sixty-four charts met the inclusion criteria. Most procedures were primary type I tympanoplasties with temporalis fascia grafts. Healing of the tympanic membrane was documented in 95.3% of patients, and mean time to healing was 49 d. Two patients who underwent revision tympanoplasty failed to exhibit healing at any visit after surgery. Postoperative complications were infrequent. Patients with Ciprodex-soaked gelfoam packing placed during tympanoplasty showed an overall rate of healing of 95%. Although this study is limited by its retrospective design, the data suggest that the use of Ciprodex during tympanoplasty has no detrimental effect on postoperative graft healing.

Controversies in building a management algorithm for vestibular schwannomas

PURPOSE OF REVIEW

The present review examines the various mainstream treatment options, benefits and risks, and controversies involved in developing a management algorithm for treatment of vestibular schwannoma.

RECENT FINDINGS

Advances in microsurgery and radiosurgery have made tremendous contributions to management of vestibular schwannoma; however, considerable controversy still exists. The auditory and facial nerve functional outcomes have improved with use of intraoperative monitoring for vestibular schwannoma removal and with lower radiosurgery doses; however, risks to the facial and auditory nerves still exist. Observing vestibular schwannomas for growth with serial magnetic resonance imaging is an increasingly popular option for small vestibular schwannomas that allows patients to enjoy hearing and facial function.

SUMMARY

The risks and benefits of each treatment option must be weighed for each patient, and management decisions regarding vestibular schwannomas should be individualized for each patient depending on tumor anatomy, patient preferences, and symptoms.

Identification of two major loci that suppress hearing loss and cochlear dysmorphogenesis in Eya1bor/bor mice

The Eya1(bor) mutant hypomorph contains an intracisternal A particle insertion in intron 7 of the Eya1 gene that results in a 50% reduction in wild-type mRNA levels. The homozygous mutants have middle and inner ear defects and variable kidney abnormalities. The severity of the disorder is affected by genetic background. In contrast to complete deafness and cochlear agenesis in the C3HeB/FeJ strain, F2 Eya1(bor/bor) mutants from an intercross between C3HeB/FeJ-Eya1(bor/+) and C57BL/6J showed variable auditory brain-stem responses and cochlear coiling. In this study, using these F2 Eya1(bor/bor) mutants, we have identified two major loci, Mead1 (modifier of Eya1-associated deafness 1) and Mead2, that are responsible for suppression of the original phenotypes. We have narrowed these two loci to 5.4 and 4.4 cM, respectively, in congenic lines. Quantitative PCR demonstrated that this modifying effect did not result from an increase in wild-type Eya1 mRNA, suggesting Mead1 and Mead2 are interacting directly or indirectly with Eya1 during inner ear development.

Genetics of hearing loss: Allelism and modifier genes produce a phenotypic continuum

Recent genetic and genomic studies have greatly advanced our knowledge of the structure and function of genes involved in hearing loss. We are starting to recognize, however, that many of these genes do not appear to follow traditional Mendelian expression patterns and are subject to the effects of allelism and modifier genes. This review presents two genes illustrative of this concept that have varied expression pattern such that they may produce either syndromic or nonsyndromic hearing loss. One of these genes, cadherin 23, produces a spectrum of phenotypic traits, including presbycusis, nonsyndromic prelingual hearing loss (DFNB12), and syndromic hearing loss as part of Usher syndrome (Usher 1D). Missense mutations in CDH23 have been associated with presbycusis and DFNB12, whereas null alleles cause the majority of Usher 1D. Modifier gene products that interact with cadherin 23 also affect the phenotypic spectrum. Similarly, allelsim in the gene encoding wolframin (WFS1) causes either a nonsyndromic dominant low-frequency hearing loss (DFNA6/14/38) or Wolfram syndrome. Missense mutations within a defined region are associated with DFNA6/14/38, while more severe mutations spanning WFS1 are found in Wolfram syndrome patients. The phenotypic spectrum of Wolfram syndrome is also hypothesized to be influenced by modifier genes products. These studies provide increasing evidence for the importance of modifier genes in elucidating the functional pathways of primary hearing loss genes. Characterizing modifier genes may result in better treatment options for patients with hearing loss and define new diagnostic and therapeutic targets.