Newborn hearing screening--a silent revolution.
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Ear↗
Biomedical subjects
Walter E Nance
Publications and source records attributed to Walter E Nance.
Does universal newborn hearing screening identify all children with GJB2 (Connexin 26) deafness? Penetrance of GJB2 deafness.
OBJECTIVE: Deafness is the most common neurosensory defect at birth, and GJB2 (connexin 26) mutations are the most frequent genetic cause of hearing loss in many populations. The hearing loss caused by GJB2 mutations is usually congenital in onset and moderate to profound in degree. Considerable phenotypic variation has been noted however, including two anecdotal cases of apparent non penetrance at birth. The objective of this study is to document nine additional children with two pathogenic GJB2 mutations who had non penetrance of hearing loss at birth. DESIGN: Subjects were identified through a national repository which includes deaf probands ascertained primarily from the United States through the Annual Survey of Deaf and Hard of Hearing Children and Youth conducted at the Research Institute at Gallaudet University. The hearing of each of these children had been screened at birth using standard audiologic techniques. Parents were interviewed and available medical records were reviewed. Testing for GJB2 mutations was performed by PCR and sequencing of the entire coding exon in all nine individuals. RESULTS: Using parent interviews and medical records, we documented that all nine children passed newborn audiologic hearing screening. The age at which the hearing loss was subsequently identified in these nine children ranged from 12-60 mo. Of these nine children, 3 were compound heterozygotes and six were homozygous for the 35delG mutation in the GJB2 gene. CONCLUSION: These nine cases demonstrate that current newborn hearing screening does not identify all infants with two GJB2 mutations. These cases suggest that the frequency of non penetrance at birth is approximately 3.8% or higher. It is important to consider connexin deafness in any child with recessive nonsyndromic hearing loss as well as simplex cases with no history of other affected family members even when the newborn hearing screening results were within the normal range.
Audiometry, Evoked Response↗
Education in the genetics of hearing loss: a survey of early hearing detection and intervention programs.
PURPOSE: Permanent hearing loss at birth or in early childhood is common and has many genetic and environmental causes. Advances in the identification and characterization of genetic forms, combined with the early identification of children through the implementation of state-based Early Hearing Detection and Intervention programs suggests the need for education about the causes of hearing loss among professionals who work in these programs. METHODS: An online survey was directed to state program coordinators of Early Hearing Detection and Intervention programs to identify gaps in knowledge about the genetic causes of hearing loss and to assess interest in continuing education on this topic. RESULTS: The study identified clear gaps in respondents' knowledge about genetic causes of hearing loss. Twenty percent of respondents indicated that they had received no training in genetics. When asked to rate their knowledge about the genetics of hearing loss, most rated their knowledge as "not adequate." Respondents expressed interest in genetics training through several modalities, including a distance learning format. CONCLUSION: This study provides documentation of the need for education of health care professionals involved in the early identification of hearing loss. Suggestions for suitable educational formats based on respondent needs and interests are provided.
Data Collection↗
Importance of congenital cytomegalovirus infections as a cause for pre-lingual hearing loss.
BACKGROUND: No large population based studies of newborn hearing screening have reported the population frequency of more than one specific form of deafness. OBJECTIVES: To combine available data on the overall incidence of pre-lingual deafness with estimates for specific causes to gain insight into age-related changes in the prevalence of the major causes of pre-lingual deafness. STUDY DESIGN: The incidence of deafness in England was adjusted for the exclusion of unilateral losses to obtain an overall estimate of 1.86 per 1000 births in the United States. Longitudinal data were used to estimate that the prevalence rises to 2.70 per 1000 at age 4. The genetic component was estimated sentinel phenotype analysis, and studies of single entities were integrated to estimate the prevalence of specific causes. RESULTS AND CONCLUSIONS: Congenital CMV infections and connexin mutations are the two major causes of deafness at birth, while causes for enlarged vestibular aqueduct along with congenital CMV infection are the major causes of pre-lingual hearing loss that is not expressed at birth. By molecular screening tests on newborn blood spots for four known causes, 60% of the infants who develop late onset pre-lingual hearing loss could be identified at birth.
Cytomegalovirus Infections↗
Characterization of Usher syndrome type I gene mutations in an Usher syndrome patient population.
Usher syndrome type I (USH1), the most severe form of this syndrome, is characterized by profound congenital sensorineural deafness, vestibular dysfunction, and retinitis pigmentosa. At least seven USH1 loci, USH1A-G, have been mapped to the chromosome regions 14q32, 11q13.5, 11p15, 10q21-q22, 21q21, 10q21-q22, and 17q24-25, respectively. Mutations in five genes, including MYO7A, USH1C, CDH23, PCDH15 and SANS, have been shown to be the cause of Usher syndrome type 1B, type 1C, type 1D, type 1F and type 1G, respectively. In the present study, we carried out a systematic mutation screening of these genes in USH1 patients from USA and from UK. We identified a total of 27 different mutations; of these, 19 are novel, including nine missense, two nonsense, four deletions, one insertion and three splicing defects. Approximatelly 35-39% of the observed mutations involved the USH1B and USH1D genes, followed by 11% for USH1F and 7% for USH1C in non-Acadian alleles and 7% for USH1G. Two of the 12 MYO7A mutations, R666X and IVS40-1G > T accounted for 38% of the mutations at that locus. A 193delC mutation accounted for 26% of CDH23 (USH1D) mutations, confirming its high frequency. The most common PCDH15 (USH1F) mutation in this study, 5601-5603delAAC, accounts for 33% of mutant alleles. Interestingly, a novel SANS mutation, W38X, was observed only in the USA cohort. The present study suggests that mutations in MYO7A and CDH23 are the two major components of causes for USH1, while PCDH15, USH1C, and SANS are less frequent causes.
Abnormalities, Multiple↗
Audiological features of GJB2 (connexin 26) deafness.
OBJECTIVE: The aim of the present study was to characterize audiological profiles in patients with GJB2 deafness DESIGN: We screened DNA from 399 individuals with nonsyndromic deafness for mutations in the connexin 26 gene (GJB2) by sequence analysis. A total of 77 (19%) of these deaf individuals were biallelic GJB2 mutations (either homozygous or compound heterozygous mutations) (GJB2 deafness). Using the audiological classification criteria of genetic deafness proposed by the European Workshop on Genetic Hearing Loss, we analyzed audiograms of these patients to characterize audiological features of the GJB2 deafness. In addition, we reviewed audiological data of 411 deafness cases from the literature providing details of audiological data (including 157 with GJB2 deafness). RESULTS: All categories of hearing loss severity were found, with significant differences in the findings from GJB2 cases: 1 (4.5%) of 22 individuals with mild hearing loss, 10 (13.3%) of 75 with moderate loss, 14 (14.9%) of 94 with severe loss, and 52 (25%) of 208 with profound deafness (Chi-square test, 3 df, p = 0.016). 81.6% of patients with GJB2 mutations had severe to profound loss, 18.4% with mild to moderate loss (Chi-square test, p = 0.014). The 235delC mutation was always associated with profound deafness. The main audiogram shapes found were residual/sloping (72.7%) and flat (23.4%). There were no differences in the severity and audiogram shapes of the hearing impairment between homozygous and compound heterozygous GJB2 deafness (Chi-square test, p > 0.05). CONCLUSIONS: Our study shows that the probability of finding biallelic GJB2 mutations increases with the severity of hearing loss. Audiograms associated with GJB2 deafness were usually nonspecific. Patients with unknown causes of severe or profound hearing loss should be routinely tested for GJB2 mutations, but due to the variability in hearing loss, individuals with lesser degrees of hearing loss should not be precluded from testing.
Adolescent↗
Superficial siderosis: a potentially important cause of genetic as well as non-genetic deafness.
Superficial siderosis is an important disease that is increasingly being recognized as a cause of sensorineural hearing loss. Hemosiderin, resulting from repeated episodes of subarachnoid bleeding, is deposited preferentially on the surface of the eighth nerve, cerebellum, and brain stem as a consequence of glial catabolism of ferritin within those structures. This deposition eventually results in destruction and demyelination within the central nervous system, leading to the cardinal clinical findings of superficial siderosis: hearing loss, ataxia, and myelopathy. This mechanism may contribute to the pathogenesis of several forms of genetic deafness, and should be considered as a diagnostic possibility in cases of late onset deafness even in the absence of an overt history of subarachnoid bleeding.
Adult↗
Relevance of connexin deafness (DFNB1) to human evolution.
The connexins are the subunits of a family of proteins that form gap junctions, allowing ions and small molecules to move between adjacent cells. At least four connexins are expressed in the ear, and, although there are known mutations at >100 loci that can cause deafness, those involving DFNB1, in the interval 13q11-q12 containing the GJB2 and GJB6 genes coding for connexins 26 and 30, are the most frequent cause of recessive deafness in many populations. We have suggested that the combined effects of relaxed selection and linguistic homogamy can explain the high frequency of connexin deafness and may have doubled its incidence in this country during the past 200 years. In this report, we show by computer simulation that assortative mating, in fact, can accelerate dramatically the genetic response to relaxed selection. Along with the effects of gene drift and consanguinity, assortative mating also may have played a key role in the joint evolution and accelerated fixation of genes for speech after they first appeared in Homo sapiens 100,000-150,000 years ago.
Animals↗
Prevalence and evolutionary origins of the del(GJB6-D13S1830) mutation in the DFNB1 locus in hearing-impaired subjects: a multicenter study.
Mutations in GJB2, the gene encoding connexin-26 at the DFNB1 locus on 13q12, are found in as many as 50% of subjects with autosomal recessive, nonsyndromic prelingual hearing impairment. However, genetic diagnosis is complicated by the fact that 10%-50% of affected subjects with GJB2 mutations carry only one mutant allele. Recently, a deletion truncating the GJB6 gene (encoding connexin-30), near GJB2 on 13q12, was shown to be the accompanying mutation in approximately 50% of these deaf GJB2 heterozygotes in a cohort of Spanish patients, thus becoming second only to 35delG at GJB2 as the most frequent mutation causing prelingual hearing impairment in Spain. Here, we present data from a multicenter study in nine countries that shows that the deletion is present in most of the screened populations, with higher frequencies in France, Spain, and Israel, where the percentages of unexplained GJB2 heterozygotes fell to 16.0%-20.9% after screening for the del(GJB6-D13S1830) mutation. Our results also suggest that additional mutations remain to be identified, either in DFNB1 or in other unlinked genes involved in epistatic interactions with GJB2. Analysis of haplotypes associated with the deletion revealed a founder effect in Ashkenazi Jews and also suggested a common founder for countries in Western Europe. These results have important implications for the diagnosis and counseling of families with DFNB1 deafness.
Connexin 26↗
Evidence of a founder effect for the 235delC mutation of GJB2 (connexin 26) in east Asians.
Mutations in the GJB2 gene encoding connexin 26 (Cx26) are a major cause of autosomal recessive and sporadic cases of congenital deafness in most populations. The 235delC mutation of GJB2 is the most frequent known mutation in some east Asian populations, with a carrier frequency of approximately 1%. In order to study the origin of 235delC among east Asians, we analyzed single-nucleotide polymorphisms (SNPs) within the coding region of GJB2 and flanking the 235delC mutation. We observed significant linkage disequilibrium between 235delC and five linked polymorphic markers, suggesting that 235delC arose from a common founder. The detection of 235delC only in east Asians, but not in Caucasians, and the small chromosomal interval of the shared haplotype suggest that 235delC is an ancient mutation that arose after the divergence of Mongoloids and Caucasians. Similarly, the finding that this mutation appears on a single haplotype provides no support for the possibility that recurrent mutation is the explanation for the high frequency of the allele.
Asian People↗
Chudley-McCullough syndrome: expanded phenotype and review of the literature.
Chudley-McCullough syndrome is an autosomal recessive condition characterized by profound sensorineural deafness, hydrocephalus secondary to obstruction of the foramen of Monro, and other structural abnormalities of the brain. We describe a family including two brothers and a sister with this condition. Each has profound sensorineural deafness that was either congenital or rapidly progressive in infancy and asymmetric dilatation of the lateral ventricles secondary to obstruction of the foramen of Monro. They also have additional brain abnormalities, including arachnoid cyst, partial agenesis of the corpus callosum, and abnormalities in the migration of cerebellar cells. This report is the fourth description of this condition within four years, suggesting Chudley-McCullough may not be as rare as once assumed. We, therefore, recommend an audiological assessment for all children with hydrocephalus, especially those with obstruction of the foramen of Monro.
Adolescent↗
Prestin, a cochlear motor protein, is defective in non-syndromic hearing loss.
Prestin, a membrane protein that is highly and almost exclusively expressed in the outer hair cells (OHCs) of the cochlea, is a motor protein which senses membrane potential and drives rapid length changes in OHCs. Surprisingly, prestin is a member of a gene family, solute carrier (SLC) family 26, that encodes anion transporters and related proteins. Of nine known human genes in this family, three (SLC26A2, SLC26A3 and SLC26A4) are associated with different human hereditary diseases. The restricted expression of prestin in OHCs, and its proposed function as a mechanical amplifier, make it a strong candidate gene for human deafness. Here we report the cloning and characterization of four splicing isoforms for the human prestin gene (SLC26A5a, b, c and d). SLC26A5a is the predominant form of prestin whereas the others showed limited distribution associated with certain developmental stages. Based on the functional importance of prestin we screened for possible mutations involving the prestin gene in a group of deaf probands. We have identified a 5'-UTR splice acceptor mutation (IVS2-2A>G) in exon 3 of the prestin gene, which is responsible for recessive non-syndromic deafness in two unrelated families. In addition, a high frequency of heterozygosity for the same mutation was observed in these subjects, suggesting the possibility of semi-dominant influence of the mutation in causing hearing loss. Finally, the observation of this mutation only in the Caucasian probands indicated an association with a specific ethnic background. This study thereby reveals an essential function of prestin in human auditory processing.
Alternative Splicing↗
The genetics of deafness.
Deafness is an etiologically heterogeneous trait with many known genetic and environmental causes. Genetic factors account for at least half of all cases of profound congenital deafness, and can be classified by the mode of inheritance and the presence or absence of characteristic clinical features that may permit the diagnosis of a specific form of syndromic deafness. The identification of more than 120 independent genes for deafness has provided profound new insights into the pathophysiology of hearing, as well as many unexpected surprises. Although a large number of genes can clearly cause deafness, recessive mutations at a single locus, GJB2 or Connexin 26, account for more than half of all genetic cases in some, but not all populations. The high frequency may well be related to the greatly improved social, educational, and economic circumstances of the deaf that began with the introduction of sign language 300-400 years ago, along with a high frequency of marriages among the deaf in many countries. Similar mechanisms may account for the rapid fixation of genes for speech after the first mutations appeared 50,000-100,000 years ago. Molecular studies have shown that mutations involving several different loci may be the cause for the same form of syndromic deafness. Even within a single locus, different mutations can have profoundly different effects, leading to a different pattern of inheritance in some cases, or isolated hearing loss without the characteristic syndromic features in others. Most cases of genetic deafness result from mutations at a single locus, but an increasing number of examples are being recognized in which recessive mutations at two loci are involved. For example, digenic interactions are now known to be an important cause of deafness in individuals who carry a single mutation at the Connexin 26 locus along with a deletion involving the functionally related Connexin 30 locus. This mechanism complicates genetic evaluation and counseling, but provides a satisfying explanation for Connexin 26 heterozygotes who, for previously unknown reasons, are deaf. A specific genetic diagnosis can sometimes be of great clinical importance, as in the case of the mitochondrial A1555G mutation which causes gene carriers to be exquisitely sensitive to the ototoxic effects of aminoglycosides. This potentially preventable genetic-environmental interaction was the most common cause of genetic deafness in countries where these antibiotics were used indiscriminately in the past. Advances in genetic knowledge along with the use of cochlear implants have posed unique ethical dilemmas for society as well as the deaf community. Since most deaf children are born to hearing parents, it seems likely that deaf culture, and intermarriages among those born with deafness will recede during this century. Will future critics view this as one of the medical triumphs of the 21(st) Century, or as an egregious example of cultural genocide? On the other hand, genetics can provide empowering knowledge to the deaf community that for the first time can allow many deaf couples to know whether their children will be hearing or deaf even before they are conceived.
Biotinidase Deficiency↗
Human reproductive cloning.
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Bioethical Issues↗
The prevalence of connexin 26 ( GJB2) mutations in the Chinese population.
Mutations in GJB2, encoding gap junction beta 2 protein (connexin 26), are responsible for the commonest form of non-syndromic recessive deafness in many populations. It has been reported recently that the most common 35delG mutation in GJB2 is exceptionally low in Japanese and Korean populations, but another deletion, 235delC, is relatively frequent. Since the Chinese constitute approximately one fifth of the global population, the frequency of GJB2 mutations in the population has important implications for understanding worldwide causes of genetic deafness. To determine whether GJB2 mutations are an important cause of deafness in Chinese, we conducted mutation screening for GJB2 in 118 deaf Chinese probands, including 60 from simplex and 58 from multiplex families with non-syndromic deafness, and 150 normal hearing Chinese controls. Four mutations, including 235delC, 299-300delAT, V37I, and 35delG, were found in the patients. Thirty-nine percent of the probands had a GJB2mutation. Of the 118 probands, 19 carried two definitely pathogenic mutations: three among the 58 multiplex cases (5.2%) and 16 among the 60 simplex cases (26.7%). Twenty-seven probands (22.9%) were found to carry only single GJB2 mutations. None of them had mutations in exon 1 of GJB2 and or the 342-kb deletion of GJB6. The 235delC mutation was the most prevalent mutation (20.3% of alleles), accounting for 81% of the pathologic alleles in multiplex cases and 67% in simplex cases. Analysis of the affected haplotypes in the patients with the homozygous 235delC mutation yielded evidence for a single origin of the mutation. The carrier frequency of the 235delC mutation in control subjects with normal hearing was 1.3%. The 35delG mutation was only noted as a heterozygous change in two simplex cases (1.2% of alleles). These results indicated that mutations in GJB2 are a major cause of inherited and sporadic congenital deafness in the Chinese population. The 235delC mutation, rather than 35delG, is the most common mutation found in the Chinese deaf population. Our data support the view that specific combinations of GJB2 mutation exist in different populations.
Alleles↗
Mutations in the alternatively spliced exons of USH1C cause non-syndromic recessive deafness.
We have recently shown that USH1C underlies Usher syndrome type 1c (USH1C), an USH1 subtype characterized by profound deafness, retinitis pigmentosa, and vestibular dysfunction. USH1C encodes a PDZ-domain-containing protein, harmonin. Eight different Ush1c transcripts were identified in the mouse inner ear. Moreover, transcripts containing seven alternatively spliced exons (A-F, G/G) were found to be expressed in the inner ear, but not in the eye. These findings suggested that mutations involving USH1C might also be the cause of DFNB18, a form of non-syndromic deafness, which maps to a chromosomal region that includes USH1C. We screened 32 Chinese multiplex families with non-syndromic recessive deafness for USH1C mutations. In one family, congenital profound deafness without RP was associated with a C to G transversion in the alternatively spliced exon D, predicting an arginine to proline substitution at codon 608 in the proline-, serine- and threonine-rich region of harmonin. We also screened 320 deaf probands from other ethnic background and found three who were heterozygous for changes in the alternately spliced exons including Gly431Val in exon B, Arg620Leu and Arg636Cys in exon D. None of these mutations were detected in DNA from 200 control subjects with normal hearing including 110 Chinese. We also screened 121 non-Acadian probands with type 1 Usher syndrome. None carried any mutations in these exons of USH1C. Our findings show that USH1C mutations can also cause non-syndromic deafness and that some harmonin isoforms are specifically required for inner ear function.
Adaptor Proteins, Signal Transducing↗
Otoancorin, an inner ear protein restricted to the interface between the apical surface of sensory epithelia and their overlying acellular gels, is defective in autosomal recessive deafness DFNB22.
A 3,673-bp murine cDNA predicted to encode a glycosylphosphatidylinositol-anchored protein of 1,088 amino acids was isolated during a study aimed at identifying transcripts specifically expressed in the inner ear. This inner ear-specific protein, otoancorin, shares weak homology with megakaryocyte potentiating factor/mesothelin precursor. Otoancorin is located at the interface between the apical surface of the inner ear sensory epithelia and their overlying acellular gels. In the cochlea, otoancorin is detected at two attachment zones of the tectorial membrane, a permanent one along the top of the spiral limbus and a transient one on the surface of the developing greater epithelial ridge. In the vestibule, otoancorin is present on the apical surface of nonsensory cells, where they contact the otoconial membranes and cupulae. The identification of the mutation (IVS12+2T>C) in the corresponding gene OTOA in one consanguineous Palestinian family affected by nonsyndromic recessive deafness DFNB22 assigns an essential function to otoancorin. We propose that otoancorin ensures the attachment of the inner ear acellular gels to the apical surface of the underlying nonsensory cells.
Amino Acid Sequence↗
Frequency and distribution of GJB2 (connexin 26) and GJB6 (connexin 30) mutations in a large North American repository of deaf probands.
PURPOSE: Profound hearing loss occurs with a frequency of 1 in 1000 live births, half of which is genetic in etiology. The past decade has witnessed rapid advances in determining the pathogenesis of both syndromic and nonsyndromic deafness. The most significant clinical finding to date has been the discovery that mutations of GJB2 at the DFNB1 locus are the major cause of profound prelingual deafness in many countries. 1 More recently, GJB2 mutations have been shown to cause deafness when present with a deletion of the GJB6 gene. We report on the prevalence of GJB2 and GJB6 mutations in a large North American Repository of DNA from deaf probands and document the profound effects of familial ethnicity and parental mating types on the frequency of these mutations in the population. METHODS: Deaf probands were ascertained through the Annual Survey of Deaf and Hard of Hearing Children and Youth, conducted at the Research Institute of Gallaudet University. Educational, etiologic, and audiologic information was collected after obtaining informed consent. DNA studies were performed for the GJB2 and GJB6 loci by sequencing and PCR methods. RESULTS: GJB2 mutations accounted for 22.2% of deafness in the overall sample but differed significantly among Asians, African-Americans and Hispanics and for probands from deaf by deaf and deaf by hearing matings, as well as probands from simplex and multiplex sibships of hearing parents. In our sample, the overall incidence of GJB2/GJB6 deafness was 2.57%. CONCLUSION: GJB2 mutations account for a large proportion of deafness in the US, with certain mutations having a high ethnic predilection. Heterozygotes at the GJB2 locus should be screened for the GJB6 deletion as a cause of deafness. Molecular testing for GJB2 and GJB6 should be offered to all patients with nonsyndromic hearing loss.
Alleles↗