Hearing

An Introduction & Practical Guide

James Tysome, Rahul Kanegaonkar

• Publisher: CRC Press
• Year: 2015
• ISBN:
  9780429586002
• Edition: 1
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

Hearing is essential for normal communication. We are able to localise sound with surprising accuracy and can detect time differences as small as the time it takes for sound to pass from the mouth of one person to the ear of another. However, hearing loss is underdiagnosed, poorly understood and a common cause of social isolation. Hearing: An Intro

III

HEARING LOSS AND REHABILITATION

■ Genetics of hearing impairment

Dirk Kunst

■ External ear

Nick Saunders

■ Eustachian tube dysfunction

Holger H. Sudhoff

■ Acute otitis media and otitis media with effusion

Mahmood F. Bhutta

■ Retraction pockets and perforations

Peter Monksfield

■ Cholesteatoma

Thomas P.C. Martin

■ Otosclerosis

Jeremy Lavy

■ Ossiculoplasty

Simon Lloyd

■ Bone-anchored hearing aids

Philip J. Clamp

■ Middle ear implants

Neil Donnelly

■ Presbyacusis

Ruth V. Lloyd

■ Sudden sensorineural hearing loss

William P.L. Hellier

■ Noise-induced hearing loss

Stephen Broomfield

■ Autoimmune inner ear hearing loss

Bruno Kenway & James R. Tysome

■ Cochlear implantation

Maarten de Wolf & Richard Irving

■ Tumours of the cerebellopontine angle

Patrick Axon

■ Ototoxicity

Aaron Trinidade & James R. Tysome

■ Auditory brainstem implants

Simon R.M. Freeman

■ Hearing aids

Sarah Yorke-Smith & Elizabeth Hough

■ Hearing therapy

Elizabeth Hough & Sarah Yorke-Smith

■ Hearing habilitation in children

Victoria H. Parfect & Sarah Yorke-Smith

■ Hearing rehabilitation in adults

Sarah Yorke-Smith & Elizabeth Hough

■ Additional support for patients with hearing loss

Elizabeth Hough & Sarah Yorke-Smith

■ Tinnitus

David M. Baguley

■ Hyperacusis

Don J. McFerran

■ Auditory processing disorder

Nicholas A. Quinn & Richard K. Gurgel

■ Future therapies

Mahmood F. Bhutta

6

GENETICS OF HEARING IMPAIRMENT

Dirk Kunst

Contents

Introduction

Genetic description of hearing impairment

Genetic testing

Clinical description of hearing impairment

Results of cochlear implantation

Conclusion

References

INTRODUCTION

The identification of genes that contribute to hearing and balance is helping to elucidate the molecular biology of the inner ear. In time, this research will lead to treatment strategies that prevent or stop the progression of hearing impairment: for example, by gene therapy. For this reason, it is important to keep abreast of new developments in the field of molecular biology of the inner ear.

Approximately 1 in 1,000 neonates are severely hearing impaired, with bilateral hearing thresholds of ≥80 dB. In at least half of these cases, the cause is inherited. The mode of inheritance can be autosomal recessive (70–80% of patients), autosomal dominant (20–30%) or X-linked (1–2%); mitochondrial inherited sensorineural hearing impairment (SNHI) has also been described. In approximately 70% of hereditary cases, no other stigmata related to SNHI can be recognized; these types of hearing impairment are classified as non-syndromic. The above mentioned data are mostly related to profound early childhood hearing impairment (pre-lingual phase). However, in the majority of patients with autosomal dominantly inherited hearing impairment, the age of onset is usually after early childhood (post-lingual phase). The prevalence of post-lingual SNHI in western Europe, with an average hearing threshold of >25 dB, is approximately 1% in young adults, about 10% up to the age of 60 years and almost 50% at 80 years. The degree to which hereditary causes contribute to hereditary post-lingual hearing impairment, and the prevalence of the different modes of inheritance, are unknown. Age-related hearing impairment is considered to be multifactorial, and is the result of both genetic and environmental factors.¹,²

GENETIC DESCRIPTION OF HEARING IMPAIRMENT

The disease genes causing SNHI are expressed throughout the whole cochlea. The pathomechanisms of hearing impairment depend on the mutated gene and, therefore, on the function of the encoded protein in the inner ear. In addition, the type of mutation can play a role in terms of dominant and recessive mutations.

The locus on the chromosome that harbours a gene involved in non-syndromic autosomal dominant hearing impairment is specified by the prefix ‘DFNA’. Non-syndromic autosomal recessive hearing impairment carries the prefix ‘DFNB’, while X-linked forms of non-syndromic hearing impairment are prefixed by ‘DFNX’. About 64 DFNA, 101 DFNB and five DFNX loci are known. Many more loci are likely to be identified in the future. Approximately 30 genes for autosomal dominant, 55 genes for autosomal recessive and three for X-linked hearing impairment have been identified. There are more than 400 syndromes with hearing impairment as a feature and in many of these the associated gene has been identified. Much of these data are available via the Hereditary Hearing Loss website (http://hereditary-hearingloss.org).

GENETIC TESTING

Multiple technologies are available to identify the genetic defect underlying a clinically diagnosed hereditary hearing impairment. For example, linkage analysis can be used to confirm the inheritance of a disease allele in affected family members. Moreover, selected gene tests can confirm a genetic mutation as a cause of hearing impairment in an individual or family. Next generation sequencing techniques can be used to sequence a large panel of genes or the complete exome (whole exome sequencing) in a single experiment. Although whole exome sequencing has only recently been introduced into clinical practice, it is more efficient and cheaper than consecutive single gene sequencing.

CLINICAL DESCRIPTION OF HEARING IMPAIRMENT

In order to give an adequate clinical description of hearing impairment, several characteristics should be taken into account. These include age of onset, rate of progression, audiogram shape and severity. A tool to characterise different types of hearing impairment, based on pure tone audiograms, is the age-related typical audiogram (ARTA) method. This type of audio profiling reveals a comprehensive phenotype presentation in hearing impairment. If the genotype in a family is known, the corresponding ARTA can be used for counselling purposes. An ARTA can also help in predicting the gene ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Contributors
• Abbreviations
• SECTION I Basic science of hearing
• SECTION II Assessment of hearing
• SECTION III Hearing loss and rehabilitation