Cochlear implantation for progressive hearing loss caused by an A8296G mutation in mitochondrial DNA

Mitochondrial DNA mutations such as A3243G or A1555G are widely reported to cause hearing loss, but few reports exist on the A8296G mutation, which can also cause hearing loss. This report presents the case of a patient with the A8296G mutation and severe bilateral sensorineural hearing loss (SNHL) that progressed over two decades. The patient had no history of diabetes, but did have a family history of SNHL in her father and maternal grandmother. She was first diagnosed with SNHL at 45 years of age, and an A8296G mutation was found. The hearing threshold in the low-frequency range of the right ear was preserved at diagnosis, but eventually declined resulting in severe bilateral hearing loss by the age of 66 years, and cochlear implantation (CI) was performed in the left ear. The hearing threshold three months after CI was 25-45 dB HL, and the phoneme speech discrimination score in the left ear improved from 20% without CI to 74% with CI. SNHL patients with the A8295G mutation are good candidates for treatment with CI.

Targeted Next-Generation Sequencing in Children With Bilateral Sensorineural Hearing Loss: Diagnostic Yield and Predictors of a Genetic Cause

OBJECTIVE

To investigate the diagnostic yield of targeted next-generation sequencing using hearing loss panels and to identify patient-related factors that are associated with a definite genetic cause.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

PATIENTS

Children with congenital or late-onset, bilateral sensorineural hearing loss.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

The number of patients with a definite genetic diagnosis.

RESULTS

We report on 238 patients with hearing loss: 130 were male and 108 were female. About 55% had congenital hearing loss. A genetic cause was identified in 94 of the patients (39.5%), with 72.3% of these showing nonsyndromic and 27.6% showing syndromic hearing loss. The diagnostic yield was highest among North African patients (66.7%). A multiple linear regression model shows that profound hearing loss, family history of hearing loss, congenital hearing loss, and North African ethnicity are significantly related to identifying a genetic cause.

CONCLUSIONS

Targeted next-generation sequencing using a panel of hearing loss genes identified a genetic diagnosis in almost 40% of children with bilateral sensorineural hearing loss. We describe the predictors of a genetic diagnosis, and this information may be used during genetic counseling.

Association of Genetic Diagnoses for Childhood-Onset Hearing Loss With Cochlear Implant Outcomes

Importance

In the US, most childhood-onset bilateral sensorineural hearing loss is genetic, with more than 120 genes and thousands of different alleles known. Primary treatments are hearing aids and cochlear implants. Genetic diagnosis can inform progression of hearing loss, indicate potential syndromic features, and suggest best timing for individualized treatment.

Objective

To identify the genetic causes of childhood-onset hearing loss and characterize severity, progression, and cochlear implant success associated with genotype in a single large clinical cohort.

Design, Setting, and Participants

This cross-sectional analysis (genomics) and retrospective cohort analysis (audiological measures) were conducted from 2019 to 2022 at the otolaryngology and audiology clinics of Seattle Children's Hospital and the University of Washington and included 449 children from 406 families with bilateral sensorineural hearing loss with an onset younger than 18 years. Data were analyzed between January and June 2022.

Main Outcomes and Measures

Genetic diagnoses based on genomic sequencing and structural variant analysis of the DNA of participants; severity and progression of hearing loss as measured by audiologic testing; and cochlear implant success as measured by pediatric and adult speech perception tests. Hearing thresholds and speech perception scores were evaluated with respect to age at implant, months since implant, and genotype using a multivariate analysis of variance and covariance.

Results

Of 406 participants, 208 (51%) were female, 17 (4%) were African/African American, 32 (8%) were East Asian, 219 (54%) were European, 53 (13%) were Latino/Admixed American, and 16 (4%) were South Asian. Genomic analysis yielded genetic diagnoses for 210 of 406 families (52%), including 55 of 82 multiplex families (67%) and 155 of 324 singleton families (48%). Rates of genetic diagnosis were similar for children of all ancestries. Causal variants occurred in 43 different genes, with each child (with 1 exception) having causative variant(s) in only 1 gene. Hearing loss severity, affected frequencies, and progression varied by gene and, for some genes, by genotype within gene. For children with causative mutations in MYO6, OTOA, SLC26A4, TMPRSS3, or severe loss-of-function variants in GJB2, hearing loss was progressive, with losses of more than 10 dB per decade. For all children with cochlear implants, outcomes of adult speech perception tests were greater than preimplanted levels. Yet the degree of success varied substantially by genotype. Adjusting for age at implant and interval since implant, speech perception was highest for children with hearing loss due to MITF or TMPRSS3.

Conclusions and Relevance

The results of this cross-sectional study suggest that genetic diagnosis is now sufficiently advanced to enable its integration into precision medical care for childhood-onset hearing loss.

Genetics of Hearing Impairment in North-Eastern Romania-A Cost-Effective Improved Diagnosis and Literature Review

Background: We have investigated the main genetic causes for non-syndromic hearing impairment (NSHI) in the hearing impairment individuals from the North-Eastern Romania and proposed a cost-effective diagnosis protocol. Methods: MLPA followed by Sanger Sequencing were used for all 291 patients included in this study. Results: MLPA revealed abnormal results in 141 cases (48.45%): 57 (40.5%) were c.35delG homozygous, 26 (18.44%) were c.35delG heterozygous, 14 (9.93%) were compound heterozygous and 16 (11.35%) had other types of variants. The entire coding region of GJB2 was sequenced and out of 150 patients with normal results at MLPA, 29.33% had abnormal results: variants in heterozygous state: c.71G>A (28%), c.457G>A (20%), c.269T>C (12%), c.109G>A (12%), c.100A>T (12%), c.551G>C (8%). Out of 26 patients with c.35delG in heterozygous state, 38.46% were in fact compound heterozygous. Conclusions: We identified two variants: c.109G>A and c.100A>T that have not been reported in any study from Romania. MLPA is an inexpensive, rapid and reliable technique that could be a cost-effective diagnosis method, useful for patients with hearing impairment. It can be adaptable for the mutation spectrum in every population and followed by Sanger sequencing can provide a genetic diagnosis for patients with different degrees of hearing impairment.

A novel autosomal recessive GJB2-associated disorder: Ichthyosis follicularis, bilateral severe sensorineural hearing loss, and punctate palmoplantar keratoderma

Ichthyosis follicularis, a distinct cutaneous entity reported in combination with atrichia, and photophobia has been associated with mutations in MBTPS2. We sought the genetic cause of a novel syndrome of ichthyosis follicularis, bilateral severe sensorineural hearing loss and punctate palmoplantar keratoderma in two families. We performed whole exome sequencing on three patients from two families. The pathogenicity and consequences of mutations were studied in the Xenopus oocyte expression system and by molecular modeling analysis. Compound heterozygous mutations in the GJB2 gene were discovered: a pathogenic c.526A>G; p.Asn176Asp, and a common frameshift mutation, c.35delG; p.Gly12Valfs*2. The p.Asn176Asp missense mutation was demonstrated to significantly reduce the cell-cell gap junction channel activity and increase the nonjunctional hemichannel activity in the Xenopus oocyte expression system. Molecular modeling analyses of the mutant Cx26 protein revealed significant changes in the structural characteristics and electrostatic potential of the Cx26, either in hemichannel or gap junction conformation. Thus, association of a new syndrome of an autosomal recessive disorder of ichthyosis follicularis, bilateral severe sensorineural hearing loss and punctate palmoplantar keratoderma with mutations in GJB2, expands the phenotypic spectrum of the GJB2-associated disorders. The findings attest to the complexity of the clinical consequences of different mutations in GJB2.

A novel CHST3 allele associated with spondyloepiphyseal dysplasia and hearing loss in Pakistani kindred

Skeletal dysplasias (SDs) are highly heterogeneous disorders composed of 40 clinical sub-types that are part of 456 well-delineated syndromes in humans. Here, we enrolled consanguineous kindred from a remote area of Sindh province of Pakistan, with 14 affected individuals suffering with short stature, kyphoscoliosis, joint dislocations, clubfoot, heart valve anomalies and progressive bilateral mixed hearing loss. To identify pathogenic variants in this family, whole exome sequencing (WES) was performed in one affected and one normal individual, which revealed a novel transversion mutation (c.802G>T; p.Glu268*) in CHST3 associated with the phenotype. CHST3 encodes a chondroitin 6-O-sulfotransferase-1 (C6ST-1) enzyme that is essential for the sulfation of proteoglycans found in cartilages. Previously, mutations in CHST3 have largely been reported in sporadic cases of SD, primarily with severe spinal abnormalities, joint dislocations, joint contractures, and clubfoot. Clinical and radiological examination of the affected individuals in this family provides new insights into phenotypic spectrum of CHST3 alleles and disease progression with age.

Congenital cytomegalovirus infection - a common cause of hearing loss of unknown aetiology

AIM

The aim of this study was to investigate the role of congenital cytomegalovirus (CMV) infection as a cause of various types of sensorineural hearing loss (SNHL) in a group of nonsyndromic children with otherwise unknown aetiology of hearing loss. Furthermore, the occurrence of combined congenital CMV infection and connexin 26 (Cx26) mutations was investigated.

METHODS

The dried blood spot (DBS) cards of 45 children with various degrees of hearing deficits and 46 children with severe/profound hearing loss were tested for CMV DNA with polymerase chain reaction (PCR) technique. The DBS cards of the 46 children with severe/profound hearing loss were also analysed for Cx26 mutations.

RESULTS

Of the 45 children with various degrees of hearing loss, nine were positive for CMV DNA (20%). The nine children represented severe/profound, mild and unilateral hearing loss. From the 46 children with severe/profound hearing loss, nine of 46 (20%) were positive for CMV DNA. In addition, three of the CMV DNA-positive children were carriers of mutations of Cx26.

CONCLUSION

Congenital CMV infection is a high risk factor in hearing impairment among children.

Genotype-phenotype correlation in DFNB8/10 families with TMPRSS3 mutations

In the present study, genotype–phenotype correlations in eight Dutch DFNB8/10 families with compound heterozygous mutations in TMPRSS3 were addressed. We compared the phenotypes of the families by focusing on the mutation data. The compound heterozygous variants in the TMPRSS3 gene in the present families included one novel variant, p.Val199Met, and four previously described pathogenic variants, p.Ala306Thr, p.Thr70fs, p.Ala138Glu, and p.Cys107Xfs. In addition, the p.Ala426Thr variant, which had previously been reported as a possible polymorphism, was found in one family. All affected family members reported progressive bilateral hearing impairment, with variable onset ages and progression rates. In general, the hearing impairment affected the high frequencies first, and sooner or later, depending on the mutation, the low frequencies started to deteriorate, which eventually resulted in a flat audiogram configuration. The ski-slope audiogram configuration is suggestive for the involvement of TMPRSS3. Our data suggest that not only the protein truncating mutation p.T70fs has a severe effect but also the amino acid substitutions p.Ala306Thr and p.Val199Met. A combination of two of these three mutations causes prelingual profound hearing impairment. However, in combination with the p.Ala426Thr or p.Ala138Glu mutations, a milder phenotype with postlingual onset of the hearing impairment is seen. Therefore, the latter mutations are likely to be less detrimental for protein function. Further studies are needed to distinguish possible phenotypic differences between different TMPRSS3 mutations. Evaluation of performance of patients with a cochlear implant indicated that this is a good treatment option for patients with TMPRSS3 mutations as satisfactory speech reception was reached after implantation.

[Analysis of positive rate of common genetic mutations in 1448 cases with different hearing phenotype]

OBJECTIVE

To analyze the positive rate of common genetic mutations in Chinese non-syndromic sensorineural hearing loss groups with different hearing phenotype.

METHOD

One thousand four hundred and forty-eight subjects with hearing test results received at least one of three genetic testings including: mutations in coding region of GJB2 and SLC26A4 with sequencing analysis and mitochondrial DNA C1494T/A1555G with microarray detection. Of 1448 subjects, 1333 have bilateral sensorineural hearing loss, 65 have unilateral hearing loss and 50 have normal hearing threshold even though they have high frequency hearing loss or family history. The informed consent of each subject was achieved.

RESULT

Mutation positive rate of GJB2, SLC26A4 and mtDNA C1494T/ A1555G of 1448 subjects were 19.23%, 27.55%, 0.1% and 1.72% respectively. The positive rate of GJB2 and SLC26A4 mutations in bilateral hearing loss group (20.22%, 29.17%) was statistically significantly higher than unilateral group (0, 0) (P < 0.01). In bilateral hearing loss group, the positive rate of GJB2 mutations was highest in the profound group (24.67%), and then severe (22.33%), moderate (14.33%) and mild group (6.58%) (P < 0.01). The positive rate of SLC26A4 mutations was highest in the severe group (48.67%), and then profound (28.42%), moderate (21.16%) and mild (8.93%) (P < 0.01).

CONCLUSION

The positive rate of GJB2 and SLC26A4 mutations is high in the groups with bilateral profound and severe sensorineural hearing loss, whose genetic testing should be put emphasis on. However, the genetic testing should be performed in patients with mild to moderate hearing impairment as well if necessary.

Audiovestibular findings in a branchio-oto syndrome patient with a SIX1 mutation

CONCLUSION

A reported mutation in SIX1 was identified in a patient with familial hearing loss (HL), a left preauricular pit, and bilateral enlarged vestibular aqueducts (EVA). Although the characteristic symptoms of EVA including fluctuating HL and repetitive vertigo were not seen in the patient, further studies are needed to clarify the association between EVA and such symptoms.

OBJECTIVES

To study the audiovestibular functions, and to identify the causative gene in a patient with branchio-oto syndrome.

METHODS

We enrolled a 30-year-old female in whom HL was pointed out at the age of 6 years. She visited our department at the age of 21 years, and had not experienced any progression of her HL, tinnitus, or vertigo. Pure-tone audiograms showed bilateral moderate mixed HL with no apparent progression during a 9-year follow-up period. Audiovestibular examinations included distortion product otoacoustic emissions (DPOAEs), electrocochleography (ECochG), and electronystagmography (ENG). Direct sequencing was utilized to screen for SIX1, EYA1, SLC26A4, GJB2, and mitochondrial DNA MTRNR1 including 1555 position.

RESULTS

The findings of DPOAEs, ECochG, and ENG indicated cochlear HL with no vestibular dysfunction. A previously reported mutation of a heterozygous c.386A > G (p.Y129C) in SIX1 was detected. No mutation was identified in EYA1, SLC26A4, GJB2, or MTRNR1.

[The results of audiological examination of children presenting with sensorineural loss of hearing due to GJB2 gene mutations during the first year of life]

One of the topical problems of modern pediatric audiology is early diagnostics of congenital sensorineural loss of hearing in children and their timely rehabilitation. The objective of the present study was to obtain audiological characteristics of sensorineural hearing impairment associated with GJB2 gene mutations in children during the first year of life. The methods used were registration of short-latency auditory evoked potentials (slAEP) and the otoacoustic emission (OAE) techniques. The study included 66 children at the age of several months presenting with bilateral sensorineural loss of hearing who were available for the examination by an otorhinolaryngologist, tympanometry, slAEP recording, delayed EOAE (dEOAE) and distortion-product frequency OAE (dpOAE) techniques, and genetic counseling. The examination was carried out in duplicate, with an interval of 3 months. The genotype containing GJB2 gene mutations was identified in 47 (71.2%) children. The 35delG mutation was found in 41; in 31 of them it occurred in the homozygous state and in 10 in the heterozygous state. In the latter group, 8 children had the 35delG mutation in the compound heterozygous state together with one more mutation. Six children turned out to carry a pathological genotype with other GJB2 gene mutations. It was shown that OAE fails to be recorded in most patients with hearing impairment due to GJB2 gene mutations during the first months of life. The authors conclude that these mutations usually lead to the development of persistent bilateral symmetric sensorineural loss of hearing.

[Genetic screening for hearing disorders in newborn infants in combination with audiological screening]

Congenital deafness has the heterogeneous nature and can be underlain by both acquired and genetically determined causes. It has been estimated that the prevalence of clinically manifest forms of congenital deafness amounts to 1 case per 700 births. Half of these patients present with the deafness of genetic origin. One of the most common forms of congenital deafness is the hereditary one associated with mutations of the GJB2 gene. The most frequent mutation documented in this country is 35delG leading to congenital and prelingual bilateral deafness in 52% of the cases. The number of carriers of the 35delG mutation among healthy populations in the majority of regions of the Russian Federation is estimated at 2-4%. At present, identification of a child with bilateral loss of hearing in the course of detailed audiological screening dictates the necessity of genetic testing. It is believed that combined audiological and molecular genetic screening may be helpful for the early detection of children with a pathological genotype including those with only slightly manifest hearing loss at birth. Families having such a child should be in due time counseled about the risk of giving life to another child with the above disorder by the same couple or other relatives of the childbearing age.

Lenticonus anterior and Alport's syndrome

Six patients, from five families, five males and one female, suffering from lenticonus anterior are presented. Furthermore, all suffered from chronic nephritis and nerve deafness and must be considered cases of Alport's syndrome. As all cases with lenticonus anterior which have been published within the last 13 years likewise were affected with nerve deafness and/or chronic nephritis, the assumption is submitted that lenticonus anterior exists exclusively as a part of Alport's syndrome. It is pointed out that four patients had a weakened bilateral macula reflex with changes in pigmentation. Attention is drawn to the fact that patients with lenticonus anterior often have a cornea astigmatism of 2-3 D. A complete table of all reported patients with anterior lenticonus is presented.

Causation of permanent unilateral and mild bilateral hearing loss in children

Children with permanent unilateral or mild bilateral hearing loss have been a focus of concern by audiologists, educators, and physicians for at least 2 decades. These children are known to be at risk for psychoeducational difficulties. However, despite this concern, little has been learned about the causative factors of these hearing losses and how those factors might be contributing to child development. This review of known causes of permanent unilateral and mild bilateral hearing loss in children is meant to draw attention to the importance of the search for etiologic factors. That is, the identification of the hearing loss should not signal the end of the diagnostic process but, rather, the beginning of a search for causation. With the combined efforts of audiologists, otolaryngologists, pediatricians, geneticists, and other medical professionals, we may enhance our understanding of the primary causes of unilateral and mild bilateral hearing loss and, perhaps, create links between causative factors and psychosocial and psychoeducational outcomes.

[Usher syndrome]

We present the case report of two brothers, PF-21 years old and PN-19 years old, to whom the fundus examination, perimetry and dark adaptation established the diagnosis of Retinitis Pigmentosa. The otorhinolaryngology exam and the audiogram revealed, in both cases, bilateral sensorineural deafness. The simultaneous presence of these two conditions completes the clinical findings of Usher syndrome. The common ectodermic origin of the retina and the inner ear could explain this pathological association.

Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation in three Han Chinese pedigrees

We report here the clinical, genetic and molecular characterization of three Han Chinese pedigrees with maternally transmitted aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the wide range of severity, age-at-onset and audiometric configuration of hearing impairment in matrilineal relatives in these families. The penetrances of hearing loss in these pedigrees were 28%, 20%, and 15%, with an average of 21%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees were 21%, 13% and 8%, with an average of 14%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA C1494T mutation, in addition to distinct sets of mtDNA polymorphism belonging to Eastern Asian haplogroups F1a1, F1a1 and D5a2, respectively. This suggested that the C1494T mutation occurred sporadically and multiplied through evolution of the mtDNA. The absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in their mtDNA suggests that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the C1494T mutation in those Chinese families. In addition, the lack of significant mutation in the GJB2 gene ruled out the possible involvement of GJB2 in the phenotypic expression of the C1494T mutation in those affected subjects. However, aminoglycosides and other nuclear modifier genes play a modifying role in the phenotypic manifestation of the C1494T mutation in these Chinese families.

A novel hearing-loss-related mutation occurring in the GJB2 basal promoter

Mutations in the GJB2 gene are a major cause of non-syndromic recessive hearing loss in many countries. In a significant fraction of patients, only monoallelic GJB2 mutations known to be either recessive or of unclear pathogenicity are identified. This paper reports a novel GJB2 mutation, -3438C-->T, found in the basal promoter of the gene, in trans with V84M, in a patient with profound hearing impairment. This novel mutation can abolish the basal promoter activity of GJB2. These results highlight the importance of extending the mutational screening to regions outside the coding region of GJB2.

Mitochondrial tRNASer(UCN) gene is the hot spot for mutations associated with aminoglycoside-induced and non-syndromic hearing loss

Mutations in mitochondrial DNA is one of the important causes of hearing loss. Here, we performed a mutational screening of tRNA(Ser(UCN)) gene in 1542 Chinese subjects with hearing loss. One subject and five subjects carried tRNA(Ser(UCN)) A7445C and G7444A mutations, respectively, while two subjects harbored both G7444A and 12S rRNA A1555G mutations. Clinical evaluation revealed the variable phenotype of bilateral hearing impairment including severity and audiometric configuration in these subjects. Six pedigrees carrying only G7444A or A7445C mutation exhibited extremely low penetrance of hearing loss, while two families carrying both G7444A and A1555G mutations displayed high penetrance of hearing loss. Of 94 matrilineal relatives in these families, eight subjects suffered from aminoglycoside-induced hearing loss, while seven hearing-impaired subjects did not have a history of exposure to aminoglycosides. Those suggest that G7444A and A7445C mutations themselves are insufficient to produce a clinical phenotype and aminoglycosides are the major modifier factors for the development of deafness in these Chinese families. The combination of A1555G and G7444A mutations increased deafness expression. These observations provide an additional evidence for the early diction and prevention of deafness at the high risk populations carrying these mitochondrial DNA mutations.

Non-syndromal round window atresia: an autosomal dominant genetic disorder with variable penetrance?

Round window atresia can be seen in association with syndromal anomalies such as mandibulofacial dysostosis, Mondini type anomalies or cretinism, or with extensive otosclerosis. Non-syndromal round window atresia is extremely rare and until today there is no proof whether non-syndromal round window atresia can be inherited. We present two family members with non-syndromal round window atresia. Based on this case and on an extensive literature review, we discuss the possible ways of sound transmission with round window occlusion as well as the possibility of an autosomal dominant inheritance pattern of these two non-syndromal cases. Evaluating the hearing test results, the effect of round window atresia in non-syndromal cases cannot be thoroughly explained by current theories of sound transmission. In general, full occlusion of the round window should result in a complete air-bone-gap and a surgical procedure to open the window, e.g. a cochlear fenestration which creates a new pressure outlet for the inner ear fluids, should result in normalizing the hearing levels. Astonishingly, patients with non-syndromal round window atresia, show hearing tests similar to those in patients with otosclerosis. In contrast to otosclerosis, complete closure of the air-bone-gap by surgery in patients with round window atresia does not seem to be possible according to currently reported cases. Therefore, routine examination of the round window in stapes surgery should be part of every stapes surgery and a high resolution CT scan should be considered in particular prior to revision of unsuccessful stapes surgery. As a genetic inheritance pattern can be assumed, specific emphasis should also be laid on the patient's family history.

Very low penetrance of hearing loss in seven Han Chinese pedigrees carrying the deafness-associated 12S rRNA A1555G mutation

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic and molecular characterizations of seven Han Chinese pedigrees with aminoglycoside-induced and nonsyndromic bilateral hearing loss. Clinical evaluation revealed the variable phenotype of hearing impairment including severity, age-at-onset and audiometric configuration in these subjects. The penetrance of hearing loss in these pedigrees ranged from 3% to 29%, with an average of 13.6%, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrances of hearing loss in these seven pedigrees varied from 0% to 17%, with an average of 5.3%. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the presence of the deafness-associated 12S rRNA A1555G mutation, in addition to distinct sets of mtDNA polymorphism belonging to East Asian haplogroups B4, D4, D5 and F1, respectively. This suggested that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in China. Despite the presence of several evolutionary conservative variants in protein-encoding genes, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these seven Chinese families. These suggest that these mtDNA haplogroup-specific variants may not play an important role in the phenotypic expression of the A1555G mutation in those Chinese families with very low penetrance of hearing loss. However, aminoglycosides appear to be a major modifier factor for the phenotypic manifestation of the A1555G mutation in these Chinese families.

Cleft palate, bilateral external auditory canal atresia, and other midline defects associated with Diamond-Blackfan anemia: case report

Diamond-Blackfan anemia (DBA) is associated with congenital anomalies especially of the midline. When present, facial anomalies are reminiscent of Treacher-Collins syndrome, and both DBA and Treacher-Collins syndrome are disorders of ribosomal biogenesis. Herein, we describe a female infant with multiple midline defects associated with DBA and reaffirm the absence of RPS-19 mutations in DBA patients with facial anomalies.

A Japanese case of oto-palato-digital syndrome type II: an apparent lack of phenotype-genotype correlation

We report the case of a 12 year-old boy with oto-palato-digital syndrome type II (OPD II). He had various anomalies at birth, including bilateral cataracts, bilateral glaucoma, bilateral severe hearing impairment, congenital heart defect, umbilical herniation, bowed extremities and constrictions of various joints. These clinical features and whole body X-ray findings were compatible with OPD II. However, his ocular disorders such as congenital cataract and glaucoma, and congenital heart defect have never been associated with OPD II as far as we know. His chromosomal analysis revealed normal karyotype, 46,XY. Analysis of the filamin A gene using a standard PCR-direct sequencing method determined a C586T (Arg196Trp) missense mutation in exon 3. Interestingly, the same C586T mutation was reported previously in a patient with OPD I (mild form). Thus, phenotype-genotype correlation of OPD is lacking in those patients. Further clinical and genetic studies are needed to clarify the relationship between phenotypes and genotypes, or to identify other factor(s) that influence the clinical features of this syndrome.

3p-- syndrome defines a hearing loss locus in 3p25.3

Deletions affecting the terminal end of chromosome 3p result in a characteristic set of clinical features termed 3p-- syndrome. Bilateral, sensorineural hearing loss (SNHL) has been found in some but not all cases, suggesting the possibility that it is due to loss of a critical gene in band 3p25. To date, no genetic locus in this region has been shown to cause human hearing loss. However, the ATP2B2 gene is located in 3p25.3, and haploinsufficiency of the mouse homolog results in SNHL with similar severity. We compared auditory test results with fine deletion mapping in seven previously unreported 3p-- syndrome patients and identified a 1.38Mb region in 3p25.3 in which deletions were associated with moderate to severe, bilateral SNHL. This novel hearing loss locus contains 18 genes, including ATP2B2. ATP2B2 encodes the plasma membrane calcium pump PMCA2. We used immunohistochemistry in human cochlear sections to show that PMCA2 is located in the stereocilia of hair cells, suggesting its function in the auditory system is conserved between humans and mice. Although other genes in this region remain candidates, we conclude that haploinsufficiency of ATP2B2 is the most likely cause of SNHL in 3p-- syndrome.

Molecular and clinical characterisation of three Spanish families with maternally inherited non-syndromic hearing loss caused by the 1494C->T mutation in the mitochondrial 12S rRNA gene

Mutations in the 12S rRNA gene of the mitochondrial genome are responsible for maternally inherited non-syndromic hearing loss (NSHL), and for increased susceptibility to the ototoxicity of aminoglycoside antibiotics. Among these mutations, 1555A-->G is the most prevalent in all populations tested so far. Recently, the 1494C-->T mutation was reported in two large Chinese pedigrees with maternally inherited NSHL. In this study, sequencing of the 12S rRNA gene in a Spanish family with maternally inherited NSHL showed the presence of the 1494C-->T mutation. An additional screening of 1339 unrelated Spanish patients with NSHL allowed the authors to find two other families with the mutation. Audiological data were obtained from 17 confirmed 1494C-->T carriers, which showed that the hearing loss was sensorineural, bilateral and symmetrical, with a remarkable variability in age of onset and severity. Three carriers were asymptomatic. Three affected carriers had a history of treatment with aminoglycoside antibiotics. The mitochondrial genome of one affected person from each of these three families was entirely sequenced, and it was established that they belong to different mitochondrial haplogroups (H, U5b, U6a). The study results further support the pathogenic role of 1494C-->T on hearing, and show that this mutation can be found in different Caucasian mitochondrial DNA backgrounds.

The contribution of GJB2 mutations to slight or mild hearing loss in Australian elementary school children

BACKGROUND

There is a lack of information on prevalence, cause and consequences of slight/mild bilateral sensorineural hearing loss (SNHL) in children. We report the first systematic genetic analysis of the GJB2 gene in a population-derived sample of children with slight/mild bilateral SNHL.

METHODS

Hearing tests were conducted in 6240 Australian elementary school children in Grades 1 and 5. 55 children (0.88%) were found to have a slight/mild sensorineural hearing loss. 48 children with slight/mild sensorineural hearing loss and a matched group of 90 children with normal hearing participated in a genetic study investigating mutations in the GJB2 gene, coding for connexin 26, and the presence of the del(GJB6-D13S1830) and del(GJB6-D13S1854) deletions in the GJB6 gene, coding for connexin 30.

RESULTS

Four of 48 children with slight/mild sensorineural hearing loss were homozygous for the GJB2 V37I change. The four children with homozygous V37I mutations were all of Asian background and analysis of SNPs in or near the GJB2 gene suggests that the V37I mutation arose from a single mutational event in the Asian population.

DISCUSSION

Based on the prevalence of carriers of this change we conclude that V37I can be a causative mutation that is often associated with slight/mild sensorineural hearing loss. No other children in the slight/mild hearing loss group had a hearing loss related to a GJB2 mutation. One child with normal hearing was homozygous for the R127H change and we conclude that this change does not cause hearing loss. Two children of Asian background were carriers of the V37I mutation. Our data indicate that slight/mild sensorineural hearing loss due to the GJB2 V37I mutation is common in people of Asian background.

A novel mutation in FGFR3 causes camptodactyly, tall stature, and hearing loss (CATSHL) syndrome

Activating mutations of FGFR3, a negative regulator of bone growth, are well known to cause a variety of short-limbed bone dysplasias and craniosynostosis syndromes. We mapped the locus causing a novel disorder characterized by camptodactyly, tall stature, scoliosis, and hearing loss (CATSHL syndrome) to chromosome 4p. Because this syndrome recapitulated the phenotype of the Fgfr3 knockout mouse, we screened FGFR3 and subsequently identified a heterozygous missense mutation that is predicted to cause a p.R621H substitution in the tyrosine kinase domain and partial loss of FGFR3 function. These findings indicate that abnormal FGFR3 signaling can cause human anomalies by promoting as well as inhibiting endochondral bone growth.

Autosomal recessive nonsyndromic deafness locus DFNB63 at chromosome 11q13.2–q13.3

A genome wide linkage analysis of nonsyndromic deafness segregating in a consanguineous Pakistani family (PKDF537) was used to identify DFNB63, a new locus for congenital profound sensorineural hearing loss. A maximum two-point lod score of 6.98 at theta = 0 was obtained for marker D11S1337 (68.55 cM). Genotyping of 550 families revealed three additional families (PKDF295, PKDF702 and PKDF817) segregating hearing loss linked to chromosome 11q13.2-q13.3. Meiotic recombination events in these four families define a critical interval of 4.81 cM bounded by markers D11S4113 (68.01 cM) and D11S4162 (72.82 cM), and SHANK2, FGF-3, TPCN2 and CTTN are among the candidate genes in this interval. Positional identification of this deafness gene should reveal a protein necessary for normal development and/or function of the auditory system.

Mutations in the lipoma HMGIC fusion partner-like 5 (LHFPL5) gene cause autosomal recessive nonsyndromic hearing loss

In two large Turkish consanguineous families, a locus for autosomal recessive nonsyndromic hearing loss (ARNSHL) was mapped to chromosome 6p21.3 by genome-wide linkage analysis in an interval overlapping with the loci DFNB53 (COL11A2), DFNB66, and DFNB67. Fine mapping excluded DFNB53 and subsequently homozygous mutations were identified in the lipoma HMGIC fusion partner-like 5 (LHFPL5) gene, also named tetraspan membrane protein of hair cell stereocilia (TMHS) gene, which was recently shown to be mutated in the "hurry scurry" mouse and in two DFNB67-linked families from Pakistan. In one family, we found a homozygous one-base pair deletion, c.649delG (p.Glu216ArgfsX26) and in the other family we identified a homozygous transition c.494C>T (p.Thr165Met). Further screening of index patients from 96 Turkish ARNSHL families and 90 Dutch ARNSHL patients identified one additional Turkish family carrying the c.649delG mutation. Haplotype analysis revealed that the c.649delG mutation was located on a common haplotype in both families. Mutation screening of the LHFPL5 homologs LHFPL3 and LHFPL4 did not reveal any disease causing mutation. Our findings indicate that LHFPL5 is essential for normal function of the human cochlea.

Genomic analysis of a heterogeneous Mendelian phenotype: multiple novel alleles for inherited hearing loss in the Palestinian population

Recessively inherited phenotypes are frequent in the Palestinian population, as the result of a historical tradition of marriages within extended kindreds, particularly in isolated villages. In order to characterise the genetics of inherited hearing loss in this population, we worked with West Bank schools for the deaf to identify children with prelingual, bilateral, severe to profound hearing loss not attributable to infection, trauma or other known environmental exposure. Of 156 families enrolled, hearing loss in 17 families (11 per cent) was due to mutations in GJB2 (connexin 26), a smaller fraction of GJB2-associated deafness than in other populations. In order to estimate how many different genes might be responsible for hearing loss in this population, we evaluated ten families for linkage to all 36 known human autosomal deafness-related genes, fully sequencing hearing-related genes at any linked sites in informative relatives. Four families harboured four novel alleles of TMPRSS3 (988ΔA = 352stop), otoancorin (1067A >T = D356V) and pendrin (716T > A = V239D and 1001G > T = 346stop). In each family, all affected individuals were homozygous for the critical mutation. Each allele was specific to one or a few families in the cohort; none were widespread. Since epidemiological tests of association of mutations with deafness were not feasible for such rare alleles, we used functional and bioinformatics approaches to evaluate their consequences. In six other families, hearing loss was not linked to any known gene, suggesting that these families harbour novel genes responsible for this phenotype. We conclude that inherited hearing loss is highly heterogeneous in this population, with most extended families acting as genetic isolates in this context. We also conclude that the same genes are responsible for hearing loss in this population as elsewhere, so that gene discovery in these families informs the genetics of hearing loss worldwide.

High prevalence of the IVS 1 + 1 G to A/GJB2 mutation among Czech hearing impaired patients with monoallelic mutation in the coding region of GJB2

Biallelic pathogenic GJB2 gene mutations cause pre-lingual genetic hearing loss in up to 50% of individuals with bilateral sensorineural hearing loss worldwide. Sequencing of the entire GJB2 gene-coding region in Czech patients with pre-lingual bilateral hearing loss revealed that 10.3% of Czech patients carry only one monoallelic pathogenic mutation in the coding region of the GJB2 gene, which is significantly more than the population frequency of 3.4%. The 309-kb GJB6 deletion, frequent in Spain and France, is very rare in the Czech population. In order to evaluate the impact of the IVS1 + 1 G to A splice site mutation in the non-coding part of the GJB2 gene among Czech patients, we tested all available patients with pre-lingual hearing loss with only one monoallelic mutation in the coding part of GJB2. By sequencing of the exon 1 region of the GJB2 gene and HphI restriction analysis in 20 Czech patients we identified nine patients carrying IVS1 + 1 G to A. Testing for this mutation explained deafness in 45% of Czech GJB2 monoallelic patients. This mutation represents now 4% of GJB2 pathogenic mutations in Czech patients and is the third most common GJB2 mutation found in our cohort of 242 unrelated Czech patients with prelingual hearing loss. A similar frequency may also be expected in other Central European or Slavic populations.

Ectodermal dysplasia, ectrodactyly, cleft lip/palate syndrome without ectrodactyly

The ectodermal dysplasia, ectrodactyly, cleft lip/palate syndrome (EEC syndrome) is an autosomal dominant dysplasia syndrome, whose pleiotropic effects involve mainly ectodermal structures. The most common clinical manifestations are ectodermal dysplasia, ectrodactyly , cleft lip/palate, and tear-duct anomalies. Very rarely the ectrodactyly may be absent, and skeletal abnormalities may be subtle. We present a 44-month-old girl who had features of EEC syndrome but without the classic ectrodactyly.

Molecular investigation in children candidates and submitted to cochlear implantation

Aim

recent progresses in molecular biology have been made in the diagnosis of sensorineural hearing loss. The high prevalence of a connexin 26 gene mutation, and its easy identification have made the diagnosis possible. The most frequent gene mutation is called 35delG. The purpose of this study was to evaluate the prevalence of 35delG mutation in children submitted to cochlear implantation who had severe and profound hearing loss previously diagnosed as idiopathic.

Method

The study was done at the Cochlear Implantation Clinic of the Otolaryngology Department and at the Laboratório Genética Humana-CBMEG, UNICAMP-SP. 32 children with severe to profound sensorineural hearing loss were evaluated. The detection of the 35delG mutation was made by a allele - specific PCR, using primers and polymerase chain reaction.

Results

69% had a normal exam, 12% were homozygous for the mutation, 19% of the cases were heterozygous. The 35delG mutation in heterozygousity is not a cause of hearing loss.

Conclusion

The data confirm the high prevalence of the 35delG mutation in nonsyndromic bilateral profound sensorineural hearing loss. It was also possible to diagnose the cause of hearing loss as genetic in a significant percentage of patients. That stresses the importance of the molecular investigation in those cases formerly classified as idiopathic.

Cochlear implantation in a patient with profound hearing loss with the A1555G mitochondrial DNA mutation and no history of aminoglycoside exposure

The A1555G mitochondrial deoxyribonucleic acid (mtDNA) point mutation has classically been associated with sensorineural hearing loss in patients following aminoglycoside exposure. More recently, the mutation has been implicated in sensorineural hearing loss in patients without previous aminoglycoside use. In addition, cochlear implantation has been shown to be effective in the group of patients with prior aminoglycoside exposure but, to date, no case of cochlear implantation in a patient with the A1555G mutation and no prior exposure to aminoglycosides has been explicitly described in the literature. We report the case of an 80-year-old woman with the A1555G mtDNA mutation, a 35-year history of bilateral progressive hearing loss and no history of aminoglycoside exposure who underwent successful implantation of a Nucleus 24 Contour device at our institution. Post-operatively, the patient exhibited marked improvement in tests of auditory performance. We conclude that cochlear implantation can be an effective method to restore some sense of hearing in patients with the A1555G mtDNA mutation and sensorineural hearing loss.

Waardenburg syndrome associated with bilateral renal anomaly

A 1-year-old girl with Waardenburg syndrome type I presented with double collecting system of left kidney accompanied by nonobstructive hydronephrosis of lower pole and by ureteropelvic junction obstruction of right kidney. Renal involvement in Waardenburg syndrome was reported once in a 4-month-old boy with unilateral duplication of the renal collecting system and in a 16-day-old girl who had right multicystic dysplastic kidney and hydronephrosis in the left kidney. The third case of renal involvement in Waardenburg syndrome is presented here, with special emphasis on early diagnosis and management of renal anomaly. The authors conclude that urinary system anomalies should also be considered in the wide spectrum of Waardenburg syndrome clinical features to avoid life-threatening complications.

[Mutations of GJB2 gene in infants with non-syndromic hearing impairment]

OBJECTIVE

To explore the relationship between GJB2 gene mutations and severe-to-profound bilateral non-syndromic hearing impairment (NSHI).

METHODS

Peripheral blood was collected from 20 infants with severe-to-profound bilateral NSHI confirmed by otoacoustic emissions (OAE), auditory brainstem responses (ABR) and clinical physical examination, 11 male and 9 female, aged 3 months to 3 years. PCR and sequencing technique were used to analyze the coding region of GJB2 gene. Fifty persons with normal hearing, 25 males and 25 female, aged 20 approximately 50, all without family history of hearing impairment, were used as controls.

RESULTS

Three infants (15%) were identified as 235delC/235delC homozygotes; one infant was identified as 235delC/299-300delAT compound heterozygote; one was identified as 235delC heterozygote; and one as 235delC/605ins46 compound heterozygote with 605ins46 mutation, a novel mutation reported in Chinese for the first time. GJB2 gene mutations were found in 5 NSHI infants (25%). The allelic frequency of 235delC allele was 22.5% in the NSHI infants and 1% in the control group (P < 0.01). Besides, multiple polymorphisms such as V27I, V37I, E114G, T123N were found in both the patients and controls.

CONCLUSION

GJB2 analysis is an important test for infants with severe-to-profound bilateral NSHI. 235delC is the main pathogenic mutation site in GJB2 gene.

Hereditary Bilateral Conductive Hearing Loss Caused by Total Loss of Ossicles: a Report of Familial Expansile Osteolysis

OBJECTIVE

The objective of this study was to report on three members of a family with familial expansile osteolysis; the important point about these patients was that none of them had middle-ear ossicles.

STUDY DESIGN AND SUBJECTS

A retrospective case review including three cases with familial expansile osteolysis.

SETTING

Department of Otolaryngology in a tertiary referral center.

INTERVENTIONS

Each patient underwent computerized tomography of the temporal bone in the coronal view, audiometric and tympanometric evaluations, biochemical investigation, whole body isotope scans by Tc-99 mMDP and X-ray. Also the patients' pedigree was studied. Two of the patients had exploratory middle-ear surgery as well.

RESULTS

The temporal-bone computed-tomography scan in the coronal view of all three patients and also exploratory middle-ear surgery, which was done on two of the patients, showed no ossicles in the middle ear of either ear in all three cases. This feature hadn't been reported in previous studies. Hearing loss was revealed in the medical histories since childhood. Audiometry indicated mild to moderate conductive and mixed hearing loss and also an AD-type tympanogram pattern along with an absence of acoustic reflexes in both ears of the cases. Both serum alkaline phosphatase and hydroxyproline levels were elevated. There was an increase in uptake and activity at multiple foci of the whole skeleton. No improvement in hearing thresholds was obtained after reconstruction of the middle ear.

CONCLUSION

The total absence of middle-ear ossicles can probably be regarded as a new symptom in some patients with familial expansile osteolysis. Common ossiculoplasty for improving the hearing thresholds in this condition may be unsuccessful; therefore, both surgeons and patients must be completely aware of the contingent undesirable results.

Development of a molecular screening test for hereditary hearing loss and genetic susceptibility to aminoglycoside toxicity for Chinese population

OBJECTIVE

To develop a molecular screening test for genetic defects on hearing loss related genes has significant impacts on early identification of hereditary hearing loss and genetic susceptibility to aminoglycoside ototoxicity. Early identification of pre-lingual hearing loss is very important for patient' s language development, academic achievement, and social skill. Two common mutations, the 235delC in GJB2 gene and the mutation A1555G in mitochondrial DNA, are included in the newly developed screening panel for Chinese population.

METHODS

A molecular genetic assay, based on fluorescent labeled multiplex PCR and automatic DNA fragment analyzing techniques, was developed to detect both mutations simultaneously.

RESULTS

This assay was able to detect both mutations from patient's samples, and pooled DNA tests, as well as suitable to detect mutation from the DNA extracted from dried blood spot and buccal swab.

CONCLUSION

This assay could be a useful tool for newborn screening and carrier screening for the hereditary hearing loss for the Chinese population.

GJB2 gene mutations in newborns with non-syndromic hearing impairment in Northern China

Mutations in GJB2 account for the majority of recessive forms of prelingual hearing loss. However, in most previous studies it was not possible to distinguish between congenital (present at birth) and non-congenital prelingual hearing loss. In the present study, the frequency of GJB2 alleles in 20 newborns with bilateral severe-to-profound non-syndromic hearing impairment (NSHI) who were found at birth through newborn hearing screening and clinical examination is reported. PCR was used to amplify the coding region of GJB2 gene followed by sequencing analyses. Fifty volunteers with normal hearing were included as controls. Results showed that three cases were 235delC/235delC homozygotes; one was 235delC/605ins46 compound heterozygotes, 605ins46 mutation was a novel mutation reported in the Chinese population; another was 235delC/299-300delAT compound heterozygotes. 25% (5/20) of the deafness in newborns studied was caused by GJB2 gene mutations. The frequency of 235delC allele carrier in patients and in control group was 22.5% and 1%, respectively. One case was identified as being a 235delC heterozygote without other mutations detected. Besides, multiple polymorphisms such as V27I, V37I, E114G, T123N were also detected. In conclusion, GJB2 analysis is an important test that identifies a major cause of newborns with bilateral severe-to-profound NSHI screened by universal newborn hearing screening in Northern China. The most common pathologic mutation of GJB2 in studied cases was 235delC. Molecular analysis and genetic counseling will be extremely important for congenital deafness present at birth.

GJB2: the spectrum of deafness-causing allele variants and their phenotype

Genetic testing was completed on 1,294 persons with deafness referred to the Molecular Otolaryngology Research Laboratories to establish a diagnosis of DFNB1. Exon 2 of GJB2 was screened for coding sequence allele variants by denaturing high-performance liquid chromatography (DHPLC) complemented by bidirectional sequencing. If two deafness-causing mutations of GJB2 (encoding Connexin 26) were identified, further screening was not performed. If only a single deafness-causing mutation was identified, we screened for the g.1777179_2085947del (hereafter called del(GJB6-D13S1830); GenBank NT_024524.13) and mutations in the noncoding region of GJB2. Phenotype-genotype correlations were evaluated by categorizing mutations as either protein truncating or nontruncating. A total of 205 persons carried two GJB2 exon 2 mutations and were diagnosed as having DFNB1; 100 persons carried only a single deafness-causing allele variant of exon 2. A total of 37 of these persons were c.35delG carriers, and 51 carried other allele variants of GJB2. Persons diagnosed with DFNB1 segregating two truncating/nonsense mutations had a more severe phenotype than persons carrying two missense mutations, with mean hearing impairments being 88 and 37%, respectively (P < 0.05). The number of deaf c.35delG carriers was greater than expected when compared to the c.35delG carrier frequency in normal-hearing controls (P < 0.05), suggesting the existence of at least one other mutation outside the GJB2 coding region that does not complement GJB2 deafness-causing allele variants.

Bjornstad syndrome

A 9-month-old boy presented with the complaints of loose motion, vomiting and difficulty in breathing. His scalp hairs were thin, brittle, and sparse and were of differing lengths with twisted appearance. Hair shaft microscopy revealed alternate light and dark segments and twisting of the hair shafts by 180 degrees along the axis. Serum copper levels were normal. The audiological testing revealed bilateral sensorineural hearing loss. Child was diagnosed as a case of Bjornstad Syndrome.

Chromosome 10p deletion in a patient with hypoparathyroidism, severe mental retardation, autism and basal ganglia calcifications

Chromosome 10p terminal deletions have been associated with a DiGeorge like phenotype. Haploinsufficiency of the region 10p14-pter, results in hypoparathyroidism, sensorineural deafness, renal anomaly, that is the triad that features the HDR syndrome. Van Esch (2000) identified in a HDR patient, within a 200 kb critical region, the GATA3 gene, a transcription factor involved in the embryonic development of the parathyroids, auditory system and kidneys. We describe a new male patient, 33-year-old, with 10p partial deletion affected by hypocalcemia, basal ganglia calcifications and a severe autistic syndrome associated with mental retardation. Neurologically he presented severe impairment of language, hypotonia, clumsiness and a postural dystonic attitude. A peripheral involvement of auditory pathways was documented by auditory evoked potentials alterations. CT scan documented basal ganglia calcifications. Hyperintensity of the lentiform nuclei was evident at the MRI examination. Renal ultrasound scan was normal. Haploinsufficiency for GATA3 gene was documented with FISH analysis using cosmid clone 1.2. Phenotypic spectrum observed in del (10p) is more severe than the classical DGS spectrum. GATA3 has been found to regulate the development of serotoninergic neurons. A serotoninergic dysfunction may be linked with autism in this patient.

Connexin mutation testing of children with nonsyndromic, autosomal recessive sensorineural hearing loss

OBJECTIVE

The etiology of hearing loss is heterogeneous and falls into the two broad categories of genetic and environmental. In the genetic subgroup, 70% are non syndromic. Fifty percent of nonsyndromic sensorineural deafness is due to a mutation in the connexin 26 gene. This article presents the detection rate of connexin mutations in a multiethnic Canadian population.

METHODS

A study of patients with nonsyndromic hearing loss seen over a period of 2 years who had connexin 26 mutation testing.

RESULTS

Nine of the 18 patients had connexin 26 mutations.

CONCLUSION

The majority of our patients with connexin 26 mutations had moderate to profound hearing loss. Testing for connexin mutations should be standard care because it accounts for a large proportion of individuals with nonsyndromic hearing loss. Reasons for testing include ruling out a syndromic cause, predicting moderate to profound hearing loss, and the need for language intervention, cochlear implants, and genetic counselling.

Progressive auditory neuropathy in patients with Leber's hereditary optic neuropathy

OBJECTIVE

To investigate auditory neural involvement in patients with Leber's hereditary optic neuropathy (LHON).

METHODS

Auditory assessment was undertaken in two patients with LHON. One was a 45 year old woman with Harding disease (multiple-sclerosis-like illness and positive 11778mtDNA mutation) and mild auditory symptoms, whose auditory function was monitored over five years. The other was a 59 year old man with positive 11778mtDNA mutation, who presented with a long standing progressive bilateral hearing loss, moderate on one side and severe to profound on the other. Standard pure tone audiometry, tympanometry, stapedial reflex threshold measurements, stapedial reflex decay, otoacoustic emissions with olivo-cochlear suppression, auditory brain stem responses, and vestibular function tests were undertaken.

RESULTS

Both patients had good cochlear function, as judged by otoacoustic emissions (intact outer hair cells) and normal stapedial reflexes (intact inner hair cells). A brain stem lesion was excluded by negative findings on imaging, recordable stapedial reflex thresholds, and, in one of the patients, olivocochlear suppression of otoacoustic emissions. The deterioration of auditory function implied a progressive course in both cases. Vestibular function was unaffected.

CONCLUSIONS

The findings are consistent with auditory neuropathy-a lesion of the cochlear nerve presenting with abnormal auditory brain stem responses and with normal inner hair cells and the cochlear nucleus (lower brain stem). The association of auditory neuropathy, or any other auditory dysfunction, with LHON has not been recognised previously. Further studies are necessary to establish whether this is a consistent finding.

Auditory neuropathy in siblings with Waardenburg's syndrome

We report two siblings with a family history of Waardenburg's syndrome (WS) for whom the audiological profile corresponds to auditory neuropathy (AN). They have; (1) bilateral severe to profound hearing loss, (2) robust oto-acoustic emissions (OAEs) in both ears, and (3) no auditory evoked responses at 95 dBnHL bilaterally. Electrocochleography (ECochG) and auditory middle and late latency potentials were performed in one of the children. Results showed cochlear and neural activities in both ears. Central auditory responses were not conclusive. These children did not have any history of neonatal illness and one child was diagnosed with AN at the age of 3 weeks and the other at the age of 11 months.

Round window atresia and its effect on sound transmission

OBJECTIVE

To document isolated round window atresia and to discuss its impact on current theories of inner ear function.

PATIENTS AND STUDY DESIGN

Retrospective analysis of isolated round window atresia suggesting an autosomal dominant inheritance pattern and review of current concepts of cochlear macromechanics.

SETTING

Tertiary referral center.

RESULTS

The unexpected finding of isolated round window atresia in two female patients of the same family was confirmed intraoperatively as well as postoperatively using high-resolution computed tomography. The current audiograms and the review of the literature highlight a mixed, but predominantly conductive, hearing impairment with thresholds at 30 to 40 dB. Implying that there is no pressure release mechanism for inner ear fluid displaced by the stapes footplate, a total conductive hearing loss would be expected.

CONCLUSIONS

The rare finding of round window atresia can be overlooked at surgery because of insufficient exposure of the round window niche. High-resolution computed tomography confirms the round window obliteration. It seems that an alternative way of cochlear stimulation takes place besides the concept of fluid bulk shifting. Surgery seems not to guarantee favorable results.

Mutation analysis of Connexin 31 (GJB3) in sporadic non-syndromic hearing impairment

Mutations in GJB3, the gene encoding the gap junction protein Connexin 31 (CX31), have been pathogenically linked to erythrokeratodermia and non-syndromic autosomal dominant (DFNA2) or recessive hereditary hearing impairment (HHI). To determine the contribution of CX31 to sporadic deafness, we assessed 63 individuals with non-syndromic hearing impairment for CX31 mutations. Single coding exon of CX31 was amplified from genomic DNA and then sequenced. Single nucleotide sequence alteration was present in 15 out of 63 patients (24%), all of the positives being heterozygous for the four different single base pair changes that were detected: C94T, C201T, C357T and C798T. Of these, only C94T transition, identified in two patients, results in amino acid change, R32W, while the other three changes are single nucleotide polymorphisms (SNPs). The R32W substitution in CX31 has been previously documented and is speculated to manifest variable penetrance, similar to the polymorphic allele encoding CX26M34T. Over one-third of all samples were also screened with denaturing high-performance liquid chromatography (dHPLC). Seven out of 25 individuals screened were determined to be positive for CX31 sequence variation. Sequence analysis of the 25 individuals screened identified nucleotide alterations in all of the 7 'positives' and in none of the 16 'negatives' yielding a specificity and sensitivity of 100%. Thus, dHPLC represents a highly efficient CX31 screening technique. This study suggests that while sequence alterations are common, pathogenic mutations of CX31 are infrequent in sporadic non-syndromic hearing impairment.