Auditory outcome after cochlear implantation in patients with congenital nonsyndromic hearing loss: influence of the GJB2 status

The congenital hearing phenotype in GJB2 in Queensland, Australia: V37I and mild hearing loss predominates

GJB2 was originally identified in severe, non-syndromic sensorineural hearing loss (SNHL), but was subsequently associated with mild and moderate SNHL. Given the increasing utilisation of genetic testing pre-conceptually, prenatally, and neonatally, it is crucial to understand genotype-phenotype correlations. This study evaluated the nature and frequency of GJB2 variants in an Australian paediatric population with varying degrees of SNHL ascertained through newborn hearing screening. Audiograms from individuals with GJB2 variants and/or a GJB6 deletion (GJB6-D13S11830) were retrospectively reviewed (n = 127). Two-thirds were biallelic (homozygous/compound heterozygous) for pathogenic/likely pathogenic variants of GJB2 and/or GJB6 (n = 80). The most frequent variant was c.109 G > A, followed by c.35delG and c.101 T > C. Compared to biallelic carriage of other GJB2 variants, c.109 G > A positive individuals (homozygous/compound heterozygous) were more likely to have mild HL at their initial and latest audiograms (p = 0.0004). Biallelic carriage of c.35delG was associated with moderately-severe or greater SNHL at both initial and latest audiograms (p = 0.007). The c.101 T > C variant presented with milder SNHL and U-shaped audiograms (p = 0.02). In this agnostically identified cohort, mild SNHL predominated in GJB2/GJB6 carriers in contrast to previous studies targeting individuals with significant loss. Consequently, c.109 G > A, associated with milder phenotypes, was the most frequent. This study provides valuable data to support prognostic confidence in genetic counselling.

Cochlear Health and Cochlear-implant Function

The cochlear implant (CI) is widely considered to be one of the most innovative and successful neuroprosthetic treatments developed to date. Although outcomes vary, CIs are able to effectively improve hearing in nearly all recipients and can substantially improve speech understanding and quality of life for patients with significant hearing loss. A wealth of research has focused on underlying factors that contribute to success with a CI, and recent evidence suggests that the overall health of the cochlea could potentially play a larger role than previously recognized. This article defines and reviews attributes of cochlear health and describes procedures to evaluate cochlear health in humans and animal models in order to examine the effects of cochlear health on performance with a CI. Lastly, we describe how future biologic approaches can be used to preserve and/or enhance cochlear health in order to maximize performance for individual CI recipients.

Does size of the cochlear nerve affect postoperative auditory performance in pediatric cochlear implant patients with normal cochlear nerves?

Introduction

Cochlear implantation is an effective treatment method for severe to profound hearing loss. Many factors that may influence cochlear implantation success have been explained in previous studies. Apart from those, minor differences in size of normal cochlear nerves may affect postoperative performance.

Objective

To investigate whether the minor differences in cochlear nerve size in normal cochlear nerves affect postoperative cochlear implant performance.

Methods

30 pediatric prelingually deaf patients who were treated with cochlear implantation were included in this study. From the reconstructed parasagittal magnetic resonance images, the diameter and cross-sectional area of the cochlear nerve on the ipsilateral and contralateral side were measured. Auditory evaluations were performed 1, 3, 6 and 12 months following the first fitting. All the analysis was performed by using EARS®, evaluation of auditory responses to speech tool. Correlation between cochlear nerve diameter, cross-sectional area and postoperative auditory perception was analyzed to determine whether variation in cochlear nerve size contributes to postoperative auditory performance.

Results

The mean diameter of the cochlear nerve on the ipsilateral side was 718.4 μm (504.5 − 904.3 μm) and mean cross sectional area was 0.015 cm² (0.012 − 0.018 cm²). On the contralateral side the mean cochlear nerve diameter was 714.4 μm (502.6 − 951.4 μm) and mean cross sectional area was 0.014 cm² (0.011 − 0.019 cm²). The correlation between the diameter and cross-sectional area of the ipsilateral and contralateral cochlear nerve revealed no significance. Mean score at first month monosyllable-trochee-polysyllable test, MTP1, was 0.17 (0.08 − 0.33), at 6th month with 6 words test, 6th month MTP6 was 0.72 (0.39 − 1.0), at 6th month with 12 words, 6th month MTP 12 was 0.46 (0.17 − 0.75) and at 12th month with 12 words, 12th month MTP12 was 0.73 (0.25 − 1.0). There was no correlation between the monosyllable-trochee-polysyllable test, values at any time with the diameter of the ipsilateral cochlear nerve. However, the first month MTP, 6th month MTP6 and 12th month MTP12 correlated with the cross-sectional area of the ipsilateral cochlear nerve.

Conclusion

Measuring the cross sectional area of the normal- appearing cochlear nerve may give important prognostic knowledge on cochlear implant outcomes. In patients with a larger cross sectional area the auditory performance was better and faster. Although normal appearing, slight differences on cross sectional area of the cochlear nerve may affect performance. Measuring the size of the cochlear nerve on parasagittal magnetic resonance images may provide beneficial information on the postoperative rehabilitation process.

Development of in-house genetic screening for pediatric hearing loss

OBJECTIVES

To evaluate the efficiency of in-house genetic testing for mutations causing the most common types of inherited, nonsyndromic, sensorineural hearing loss (SNHL).

METHODS

Retrospective cohort study of 200 patients at a single, pediatric medical center with suspected or confirmed hearing loss who underwent either send out vs in-house genetic testing for mutations in GJB2/GJB6, SLC26A4, and MTRNR1. Primary outcome measure was the difference in mean turnaround time for send-out vs in-house genetic testing. Additional outcomes included associations between audiometric findings and genetic test results.

RESULTS

One hundred four send-out tests were performed between October 2010 and June 2014, and 100 in-house tests were performed between November 2014 and November 2016. The mean turnaround time for send-out testing was 53.7 days. The mean turnaround time for in-house testing was 18.9 days. This difference was statistically significant (P < .001). The largest component of turnaround time was the amount of time elapsed between receipt of specimen in the lab and final test result. These intervals were 47.0 and 18.3 days for send-out and in-house tests, respectively. Notably, the longest turnaround time for in-house testing (43 days) was less than the average turnaround time for send-out testing. In addition, we identified two simple audiometric parameters (ie, bilateral newborn hearing screen referral and audiometry showing symmetric SNHL) that may increase diagnostic yield of genetic testing.

CONCLUSIONS

The development of in-house genetic testing programs for inherited SNHL can significantly reduce testing turnaround times. Newborn hearing screening and audiometry results can help clinicians identify patients most likely to benefit from genetic testing.

LEVEL OF EVIDENCE

IV.

Glendonald Auditory Screening Procedure (GASP): clinical markers of the development of auditory recognition and comprehension abilities in children using cochlear implants

PURPOSE

To verify the influence of the age of implantation in the development of closed-set auditory recognition and auditory comprehension abilities in children using unilateral cochlear implants (CI), comparing distinct groups and determining clinical markers.

METHODS

Participants were 180 children operated and activated until 36 months of age and who used a CI for at least 60 months. Abilities of auditory recognition in closed-set and auditory comprehension were analyzed through the GASP Tests 5 and 6. The influence of age of implantation was investigated with three groups of children: implanted before 18 months (G1), between 19 and 24 months (G2) and between 25 and 36 months of age (G3).

RESULTS

There was no statistically significant difference when comparing the three groups. Children progressively developed auditory abilities, presenting auditory recognition ability together at approximately 41±4 months of CI use and auditory comprehension at 53±4 months.

CONCLUSION

There was no correlation between hearing performance and age of implantation for children implanted before 36 months of age. For the abilities of auditory recognition and comprehension, the clinical marker was 41±4 and 53±4 months of auditory age, respectively. Therefore, it is expected that, around 60 months of CI use, children implanted during the sensitive period can understand speech without the aid of orofacial reading, reaching the most complex hearing abilities.

Long Term Speech Perception Outcomes of Cochlear Implantation in Gap Junction Protein Beta 2 Related Hearing Loss

BACKGROUND AND OBJECTIVES

The mutation of the gap junction protein beta 2 (GJB2) gene is the predominant cause of autosomal recessive non-syndromic hearing loss. The purpose of this study was to evaluate the speech perception outcome after cochlear implantation according to the presence of a GJB2 mutation.

SUBJECTS AND METHODS

During the period from March 2004 to February 2005, 38 patients underwent cochlear implantation at Asan Medical Center. Genetic factors and speech perception were evaluated in all subjects, and the patients were grouped according to the presence of a GJB2 mutation. The two groups were carefully matched according to the age at cochlear implantation. We analyzed four mutations in the GJB2 gene: 35delG, 167delT, 235delC, and E114G. Speech perception outcomes were measured using the open set, 1 and 2 syllables, the comprehension test, the Meaningful Auditory Integration Scale, the categories of auditory performance, and the Speech Intelligibility Rating scores. The evaluations were performed before the operation, 6 and 12 months thereafter, and then annually up to nine years after cochlear implantation.

RESULTS

Fifteen patients had bi-allelic GJB2 mutations (11 with E114G and 4 with 235delC), whereas the remaining 23 had wild type alleles. For the age-matched analysis, 14 patients were selected and divided into two groups of 7 subjects each: GJB2 mutation and no mutation (i.e., deafness of unknown origin). Overall, all patients showed improvement of speech perception outcome after cochlear implantation. There was no difference in the improvement between patients with and without GJB2 mutations at the 5-year and 9-year follow up. The pattern of improvement throughout the duration of the follow-up also showed no difference between the two groups.

CONCLUSIONS

Similar outcomes of speech perception are expected after cochlear implantation in pediatric patients with or without GJB2 mutation.

Residual Hearing in DFNB1 Deafness and Its Clinical Implication in a Korean Population

Introduction

The contribution of Gap junction beta-2 protein (GJB2) to the genetic load of deafness and its mutation spectra vary among different ethnic groups.

Objective

In this study, the mutation spectrum and audiologic features of patients with GJB2 mutations were evaluated with a specific focus on residual hearing.

Methods

An initial cohort of 588 subjects from 304 families with varying degrees of hearing loss were collected at the otolaryngology clinics of Seoul National University Hospital and Seoul National University Bundang Hospital from September 2010 through January 2014. GJB2 sequencing was carried out for 130 probands with sporadic or autosomal recessive non syndromic hearing loss. The audiograms were evaluated in the GJB2 mutants.

Results

Of the 130 subjects, 22 (16.9%) were found to carry at least one mutant allele of GJB2. The c.235delC mutation was shown to have the most common allele frequency (39.0%) among GJB2 mutations, followed by p.R143W (26.8%) and p.V37I (9.8%). Among those probands without the p.V37I allele in a trans configuration who showed some degree of residual hearing, the mean air conduction thresholds at 250 and 500 Hz were 57 dB HL and 77.8 dB HL, respectively. The c.235delC mutation showed a particularly wide spectrum of hearing loss, from mild to profound and significantly better hearing thresholds at 250 Hz and 2k Hz than in the non-p.V37I and non-235delC nonsyndromic hearing loss and deafness 1(DFNB1) subjects.

Conclusion

Despite its reputation as the cause of severe to profound deafness, c.235delC, the most frequent DFNB1 mutation in our cohort, caused a wide range of hearing loss with some residual hearing in low frequencies. This finding can be of paramount help for prediction of low frequency hearing thresholds in very young DFNB1 patients and highlights the importance of soft surgery for cochlear implantation in these patients.

Whole-exome sequencing and its impact in hereditary hearing loss

Next-generation sequencing (NGS) technologies have played a central role in the genetic revolution. These technologies, especially whole-exome sequencing, have become the primary tool of geneticists to identify the causative DNA variants in Mendelian disorders, including hereditary deafness. Current research estimates that 1% of all human genes have a function in hearing. To date, mutations in over 80 genes have been reported to cause nonsyndromic hearing loss (NSHL). Strikingly, more than a quarter of all known genes related to NSHL were discovered in the past 5 years via NGS technologies. In this article, we review recent developments in the usage of NGS for hereditary deafness, with an emphasis on whole-exome sequencing.