Genetic deafness

The Inheritance of Hearing Loss and Deafness: A Historical Perspective

If the term "genetics" is a relatively recent proposition, introduced in 1905 by English biologist William Bateson, who rediscovered and spread in the scientific community Mendel's principles of inheritance, since the dawn of human civilization the influence of heredity has been recognized, especially in agricultural crops and animal breeding. And, later, in familial dynasties. In this concise review, we outline the evolution of the idea of hereditary hearing loss, up to the current knowledge of molecular genetics and epigenetics.

A Rare Mutation in the MARVELD2 Gene Can Cause Nonsyndromic Hearing Loss

The MARVELD2 gene which is located on the 5q13.2 may cause nonsyndromic hearing loss (NSHL) with autosomal recessive inherited pattern. So far c.1331+1G>A (IVS4+1G>A); NM_001038603.3, variant in deafness, has only reported previously in one Pakistani family in 2008 and it is reported for the first time in Iran and second time in the world. The case is a 21-year-old Iranian woman who has NSHL referred for genetic consultation, and her parents had a consanguineous marriage. To study the responsible genes for the mentioned disorder, whole exome sequencing (WES) was performed for the case. The result of WES analysis revealed a transition at the splice donor variant site of the MARVELD2 gene. The NGS result was confirmed by Sanger sequencing.

Prevalence of selected congenital anomalies in Saudi children: a community-based study

BACKGROUND AND OBJECTIVES

Limited data are available on the prevalence of congenital anomalies based on a community survey in Middle East countries. The prevalence of congenital anomalies is expected to be high in these countries because of the high consanguinity rate and high maternal age. The aim of this cross-sectional study was to establish the prevalence of congenital anomalies in Saudi Arab children.

DESIGN AND SETTINGS

This is a prospective, cross-sectional, community-based study conducted over 2 years among the Saudi population.

SUBJECTS AND METHODS

The study sample was determined by a multi-stage probability random sampling of household representatives of the Saudi Arab population. The health status of children was obtained during household visits by primary care physicians who performed a history and physical examination of all children and adolescents younger than 19 years. All cases of congenital anomalies were recorded.

RESULTS

During the 2-year study period (2004-2005), a total of 45 682 children were screened. The commonest congenital anomalies found in this survey were Down syndrome, congenital deafness, and congenital blindness with prevalence rates of 6.6 per 10 000, 4.8 per 10000, and 1.3 per 10000 children, respectively. The prevalence of cleft lip with or without cleft palate was 0.9 per 10000 children, achondroplasia was 0.7 per 10000, and Dandy-Walker syndrome was 0.4 per 10000. Crouzon syndrome, Treacher-Collins syndrome, Angelman syndrome, and Turner syndrome had equal prevalence of 0.2 per 10000 children.

CONCLUSION

The data suggest a significant decline in the prevalence of Down syndrome; however, the prevalence of other anomalies like congenital deafness is still high.

Analysis of the presence of the GJB6 mutations in patients heterozygous for GJB2 mutation in Brazil

Mutations in the GJB2 gene, mainly 35delG, are responsible for most autosomal recessive inherited genetic hearing loss. The audiometric standard of these hearing losses remains inconsistent and other genes, such as GJB6, have been involved in association with GJB2. The objective of the study was to identify the deletions del(GJB6-D13S1830) and del(GJB6-D13S1854) in patients heterozygous for 35delG/GJB2 and analyze the phenotype they present. 101 patients with mild to profound degree of sensorineural hypoacusis were evaluated. The allele-specific PCR technique was used to identify 35delG. The del(GJB6-D13S1830) and del(GJB6-D13S1854) were identified through the PCR multiplex technique. 90% of the subjects presented a normal genotype for the analyzed mutations; 6.93% were shown to be heterozygous for 35delG/GJB2 and 1% presented compound heterozygosis GJB2/GJB6). The data found reinforced the hypothesis of an interaction of more than one gene as the cause of autosomal recessive genetic hearing loss and emphasized the importance of an early diagnosis for appropriate intervention.

[Pendred's syndrome: a cause of goiter associated with deafness]

Pendred's syndrome is an autosomal recessive disorder leading to congenital sensorineural hearing loss and a variable degree of goiter due to reduced iodine organification. The cause of this disease is dysfunction of an anion transporter protein located on the apical membrane of thyrocytes, called pendrin, which is also found in the kidney and cochlea. Molecular analysis of the gene is useful to identify other affected family members and provide proper genetic advice and early diagnosis in descendants. We present the cases of two siblings with sensorineural deafness who were diagnosed with Pendred's syndrome as adults because one of them consulted for goiter.

Identification of SLC26A4 gene mutations in Iranian families with hereditary hearing impairment

Mutations in the SLC26A4 gene at the DFNB4 locus are responsible for Pendred syndrome and non-syndromic hereditary hearing loss (DFNB4). This study included 80 nuclear families with two or more siblings segregating presumed autosomal recessive hearing loss. All deaf persons tested negative for mutations in GJB2 at the DFNB1 locus and were, therefore, screened for autozygosity by descent (ABD) using short tandem repeat polymorphisms (STRPs) that flanked SLC26A4. In 12 families, homozygosity for STRPs suggested possible ABD in this genomic region. Affected individuals in five families had a positive perchlorate discharge test. Sequence analysis of SLC26A4 identified ten mutations in eight families (T420I, 1197delT, G334V, R409H, T721M, R79X, S448L, L597S, 965insA and L445W), of which, four are novel (T420I, G334V, 965insA and R79X). These results imply that Pendred syndrome is the most prevalent form of syndromic hereditary hearing loss in Iran.

Pendred syndrome among patients with congenital hypothyroidism detected by neonatal screening: identification of two novel PDS/SLC26A4 mutations

Pendred syndrome is an autosomal recessive disorder characterised by sensorineural hearing loss and thyroid dyshormonogenesis. It is caused by mutations in the PDS/SLC26A4 gene (OMIM 605646) encoding for pendrin. Hypothyroidism in Pendred syndrome can be--although rarely--present from birth and therefore diagnosed by neonatal screening. The aim of our study was to identify patients with Pendred syndrome among a historical cohort of patients with congenital hypothyroidism (CH) identified by neonatal screening, and to find their mutations in the PDS/SLC26A4 gene. We investigated 197 Czech Caucasian children with CH detected by the neonatal screening between the years 1985 and 2005. The clinical diagnosis of Pendred syndrome was based on the laboratory and sonographic signs of thyroid dyshormonogenesis in association with sensorineural hearing loss. In subjects clinically diagnosed with Pendred syndrome, we sequenced all exons and exon-intron boundaries of the PDS/SLC26A4 gene. Hearing loss was present in 10/197 children with screening-detected CH. Of these, three fulfilled the diagnostic criteria of Pendred syndrome. Two patients were compound heterozygotes for PDS/SLC26A4 mutations: patient 1 carried c.2089+1G>A / c.3G>C and patient 2 carried p.Tyr530His / p.Val422Asp. Two of the four identified mutations were novel (c.3G>C in patient 1 and p.Val422Asp in patient 2). The third patient was free of mutations in the PDS/SLC26A4 gene, representing a phenocopy. In conclusion, our results indicate the rarity of Pendred syndrome as a cause of CH. The identification of two novel mutations expands the spectrum of mutations in the PDS/SLC26A4 gene and emphasizes their marked allelic heterogeneity.

Chudley McCullough syndrome

BACKGROUND

Chudley McCullough syndrome is characterized by partial agenesis of the corpus callosum, interhemispheric cyst, cerebral and cerebellar cortical dysplasias, and hydrocephalus. This syndromic form of sensorineural hearing loss is rare. Our literature search has located 13 siblings in 6 families with this syndrome. We report a case of Chudley McCullough syndrome and discuss the relevant literature. It is amply clear from the review of literature that treatment of ventricular dilatation or drainage of arachnoid cysts in these cases will not improve the sensorineural hearing loss.

CASE ILLUSTRATION

A 14-month-old female child presented with bilateral profound sensorineural hearing loss. Neuroimaging revealed partial agenesis of the corpus callosum, colpocephaly, and an interhemispheric arachnoid cyst. These associations suggested a diagnosis of Chudley McCullough syndrome.

Cochlear implantation in deafness-dystonia-optic neuronopathy (DDON) syndrome

To report the results of the first known cochlear implantation in a patient with deafness-dystonia-optic neuronopathy (DDON) syndrome (Mohr-Tranebaerg syndrome, DFN-1). DDON syndrome is an X-linked condition characterized by postlingual sensorineural hearing loss in early childhood followed by dystonia, psychosis, and optic atrophy in adolescence and adulthood. The gene responsible for the condition maps to Xq22 adjacent to the gene causally related to X-linked agammaglobulinemia. The audiometric characteristics of DDON syndrome are typical of auditory neuropathy, with spiral ganglion cells being the suspected site of pathology. Performance following cochlear implantation in auditory neuropathy patients is variable and has yet to be reported in any patients with DDON syndrome. The reported case describes a male initially diagnosed with X-linked agammaglobulinemia due to recurrent infections. Speech, language and hearing were typical of a child in the first year of life; however profound hearing loss developed and cochlear implantation was performed at age 4. Following implantation, further genetic workup determined that the patient carries a deletion that includes BTK and DDP1/TIMM8a, consistent with the diagnosis of X-linked agammaglobulinemia and DDON syndrome. The patient's performance with the cochlear implant was marginal even after 2 years of use, with continued poor scores in standardized speech, language and audiometric tests. Additionally, his most-comfortable-level implant setting requires higher-than-normal current applied to the electrode array. This case report supports other studies showing that DDON syndrome results in an auditory neuropathy. Further investigation is required to determine the efficacy of cochlear implantation in this patient population. DDON syndrome should be considered in patients with X-linked agammaglobulinemia and hearing loss.

Cognition in children with sensorineural hearing loss: etiologic considerations

OBJECTIVES

A considerable amount of literature has documented the impact of hearing impairment on spoken language skills in deaf children referred for cochlear implantation. Critical areas of neurocognitive development in the acquisition of visual (manual) language also appear to be impacted, although the evidence is less robust. The present study focused on the development of visual and fine motor skills in a sample of preschool-age children diagnosed with sensorineural hearing loss with no known neurologic conditions (n=36).

STUDY DESIGN

Analysis of data collected as part of a standardized screening process for cochlear implantation at an academic medical center.

METHOD

Children underwent a standardized neuropsychological assessment battery. Children were classified into three groups based on the etiology of their deafness (Connexin=15, Structural Malformation=11, and Unknown=10).

RESULTS/CONCLUSIONS

Correlational analyses replicated previous research on the reduction in visual reception and fine motor skills as deaf children age. Children with genetic (Connexin) etiology exhibited a significant reduction in fine motor skills with age, whereas those with an etiology of Structural Abnormality exhibited a significant reduction in visual reception skills with age. Results of planned comparisons conducted as part of a multivariate analysis of variance (Skill x Group) indicated that the Connexin group was significantly better than the Unknown group with regard to fine motor skills. Implications for these findings and future studies are discussed.

Estudo seccional descritivo de crianças com deficiência auditiva atendidas no Instituto Nacional de Educação de Surdos, Rio de Janeiro, Brasil

O estudo das deficiências múltiplas em geral e da surdez em especial é escasso em nosso país. Os pesquisadores iniciaram estudo pioneiro desde 1992, avaliando alunos da educação especial das redes governamentais de ensino do Estado, estando atualmente focados na surdez. Avaliamos 232 alunos com idade variando de 1 a 39 anos, com média de 10,9 anos. O sexo masculino prevaleceu na amostra. A consangüinidade ocorreu 7,6% e a história familiar de surdez em 19% dos casos. Observamos 33% de intercorrências gestacionais. O parto normal foi utilizado em 59% de nossos casos, sendo a termo em 75%. As intercorrências neonatais estiveram presentes em 35% das vezes. As causas ambientais foram responsáveis por 58,5% da amostra, as causas genéticas por 20,7% dos casos. Sendo o restante considerado idiopático. Nossos achados corroboram os dados da literatura. Acreditamos que este estudo possa servir como o início de uma preocupação maior com esta população, e que através do melhor conhecimento de suas características seja possível implementar estratégias de intervenção facilitando a sua interação produtiva na sociedade.

Auditory function and cochlear morphology in the German waltzing guinea pig

The German waltzing guinea pig is a new strain of animals with a recessively inherited inner ear defect resulting in deafness and severe vestibular dysfunction. Measurements of auditory brainstem responses (ABRs) demonstrated that the homozygotes (gw/gw) are deaf while the heterozygotes (gw/+) have normal hearing. In the gw/gw cochlea, a collapse of Reissner's membrane leads to the absence of scala media. Melanin pigment accumulation was clearly observed in the gw/gw stria vascularis, and both the height and width of stria vascularis were significantly reduced. Ultrastructural observations further detailed the disorganization of stria vascularis in the gw/gw animals: marginal cells lacked basolateral infoldings; intermediate cells (melanocytes) were scarce and degenerated; and basal cells were difficult to identify. The level of degeneration of the organ of Corti varied between individual gw/gw animals. The density of spiral ganglion neurons was significantly decreased in old (1-2 years of age) gw/gw animals. In contrast, no pathological changes were observed in the cochleae of gw/+ animals. Our data suggest that the degeneration originates in the stria vascularis (most likely in the melanocytes), and that this is the primary cause for inner ear defects in the German waltzing guinea pig. Here, we describe the auditory function and cochlear morphology in this spontaneously mutated guinea pig strain.

Sensorineural deafness, hydrocephalus and structural brain abnormalities in two sisters: the Chudley-McCullough syndrome

We describe an Italian family in which two sisters have macrocephaly due to hydrocephalus, and sensorineural hearing loss in addition to other brain abnormalities demonstrated by Magnetic resonance imaging (MRI). The girls, born to healthy non-consanguineous parents, have borderline psychomotor development delay (probably due to hearing defect) and minor dysmorphisms. The clinical picture fits the Chudley-McCullough syndrome, an autosomal recessive condition, to date described in only five families. Our data, in particular the neuroradiological findings, include all brain anomalies variably reported in previous works (hydrocephalus, corpus callosum partial agenesis, interhemispheric cyst, cerebral and cerebellar cortex dysplasia), thus illustrating the full phenotype of the syndrome.

The prevalence and causes of hearing impairment in Oman: a community-based cross-sectional study

A community-based nationwide survey for hearing loss was conducted in Oman in 1996-97. Audiometric tests and ear examinations were conducted for 12,400 persons in phase I. For children aged less than 4 years, subjective screening tests were used. In phase II, otologists examined the hearing-impaired subjects to determine the cause. The prevalence of bilateral hearing impairment was 55/1000 (95% CI 51.08-59.47). Gender difference was not significant. The rates were 325/1000 and 17/1000, respectively, in the > or = 60-year and < 10-year age groups. Presbyacusis and middle ear diseases, respectively, were the causes of 33% and 20% of bilateral hearing impairment. In 30% of the bilateral hearing-impaired subjects, the cause could not be determined. The prevalence of bilateral disabling hearing loss was 21/1000 (95% CI 18.07-23.29). Noise-induced trauma was responsible for only 1.4% of cases of disabling hearing loss. Establishing primary ear care, introducing hearing screening for neonates and schoolchildren, promoting safe preventive practices for ear care, strengthening secondary-level ear care services and introducing comprehensive rehabilitative initiatives for the hearing-disabled are recommended to reduce the hearing loss rates.

Causes of severe to profound deafness in Omani paediatric population

The study includes a retrospective analysis of causes of deafness in 1400 Omani children who were detected to be suffering from severe to profound levels of hearing impairment. A standard form was used to collect various details from the otolaryngologists all over the country. The time period included is from 1986 to 2000. The rate of consanguineous marriage in the parents of the affected children was 70%, and 67.8% of these children had a sibling suffering from hearing impairment. There has been a rapid evolution of the antenatal, perinatal and neonatal care delivery in Oman during last couple of decades. The Omani paediatric population has been well covered (>90%) under the vaccination protocols including rubella. It has helped in reducing the share of infectious diseases towards the hearing impairment. The study is an attempt to identify various causes of the identifiable causes of severe to profound hearing impairment in Omani paediatric population which is the first attempt of this kind in this country. Relevant literature has been reviewed.

First report of prenatal diagnosis of genetic congenital deafness in a routine prenatal genetic test

OBJECTIVE

We aimed to screen for connexin26 gene (GJB2) mutations associated with autosomal recessive non-syndromic neurosensory deafness (NSRD) in a general risk population.

METHODS

Screening for the most common connexin26 gene mutations was offered to all women undergoing a second-trimester amniocentesis for fetal karyotype analysis in our Center. After rapid DNA extraction from amniotic fluid, PCR amplification was performed and products analysed to detect mutations of GJB2 gene by a sequencing technique. In particular, we searched for the 20 most frequently reported mutations (out of the approximately 90 so far described) and for which there are commercially available tests.

RESULTS

From a total of 4819 consecutive amniotic fluids examined, the following five different heterozygous mutations were detected: 35delG in 80 cases, 167delT in 3 cases and 1 occurrence of each of the following mutations: M34T, 35insG and W77R. From these data, a prevalence of 1 : 56 (1.78%) for the heterozygous condition can be estimated in the Mediterranean general risk population. The striking predominance of 35delG mutation is confirmed. In addition, we detected a homozygous 35delG mutation condition in a foetus of no risk parents. In this case, the early diagnosis permitted prompt application of an acoustic prosthesis allowing for cochlear implantation in due time, with significant improvement of the prognosis.

CONCLUSIONS

In a general risk population, a carrier status for congenital deafness can be observed in 1 : 56 (1.78%) amniotic fluids; this is mostly due to the presence of a 35delG mutation of the connexin26 gene. Occasional identification of homozygous states, although rare, allows the best therapeutic approach.

The Iranian Human Mutation Gene Bank: a data and sample resource for worldwide collaborative genetics research

As Human Genome Project exploration continues, the necessity of having a broader spectrum of genomic DNA material from different nationalities to study various aspects of hereditary disease becomes more obvious. The existence of high genetic polymorphism within and between different communities in the world makes it necessary for the gene hunters to investigate many different populations. Iran, a large country with close to 66 million people, is a land of different nationalities, tribes, and religions that offers a highly heterogeneous gene pool to the genetics researcher. The purity of many different races in this country has been highly conserved by geographical borders and by an ancient culture that has always encouraged intrafamilial marriages. All these have created a population that is remarkably heterogeneous yet high in consanguinity rate. During the last five years of investigation we have established a DNA bank, the Iranian Human Mutation Gene Bank (www.IHMGB.com), which contains all genetic diseases studied in Iran that have the Mendelian mode of inheritance. Some of the samples are assigned to common or novel mutations and others belong to patients with clinical profiles associated with particular genetic diseases but undefined mutation. This bank stores samples of DNA from the patient and his/her first-degree relatives together with a comprehensive pedigree and clinical profile for each sample. To facilitate collaboration with other scientists around the world with the same interests, we decided to present our experimental projects online. This DNA bank provides opportunities for us to collaborate with scientists outside Iran. It offers a sample resource to research scientists around the world, at no charge, for the purpose of investigating the various aspects of genetic disorders from prenatal diagnosis to gene structure and function. It is strongly stressed that no commercial benefit is involved in the establishment of this DNA bank and the DNA samples are free of charge. However, to meet our goals and to respect ethical values, DNA samples can only be used under certain conditions stated in the User Consent Form.

Nonsyndromic hereditary hearing loss

Like many areas of medicine, the rapid advances in genetics and molecular biology are revolutionizing our understanding of hearing and balance disorders. Dramatic progress has been made in identifying deafness genes in the past few years. These genes encode proteins of diverse function, including transcription factors, cytoskeletal and extracellular matrix components, and ion channels. The diversity of the genes so far identified is testimony to the complexities of auditory development and function and the power of genetic approaches. In what is about to become the postgenomic era, the study of the proteins encoded by these genes will advance our understanding of auditory development and function and lead to innovative approaches toward the treatment of patients with hearing disorders.

Population-based genetic study of childhood hearing impairment in the Trent Region of the United Kingdom

The objective of the study was to investigate childhood hearing impairment in a population-based sample from a genetic perspective. Participants included 82 families with hearing-impaired children (aged 4-13) previously ascertained in the Trent Health Region. A questionnaire was mailed to all families, followed by a home visit and Connexin-26 35delG mutation screen. The Connexin-26 35delG mutation was identified in seven families (approximately 10 per cent of non-syndromal hearing impairment). Children of these families were significantly more likely than children with other modes of inheritance to have a profound hearing loss with a flat audiogram profile. The families of children with a significant admission to a neonatal intensive care unit were significantly less likely to have had genetic counselling. Eight families visited were found to have features suggestive of a genetic syndrome that had not been previously assigned a specific diagnosis. The study concluded that hearing-impaired children should be investigated systematically according to an agreed-upon protocol, which should include Connexin-26 35delG mutation analysis at least for those with severe-to-profound hearing loss.

A novel conserved cochlear gene, OTOR: identification, expression analysis, and chromosomal mapping

We have identified a novel cochlear gene, designated OTOR, from a comparative sequence analysis of over 4000 clones from a human fetal cochlear cDNA library. Northern blot analysis of human and chicken organs shows strong OTOR expression only in the cochlea; very low levels are detected in the chicken eye and spinal cord. Otor and Col2A1 are coexpressed in the cartilaginous plates of the neural and abneural limbs of the chicken cochlea, structures analogous to the mammalian spiral limbus, osseous spiral lamina, and spiral ligament, and not in any other tissues in head and body sections. The human OTOR gene localizes to chromosome 20 in bands p11.23-p12.1 and more precisely to STS marker WI-16380. We have isolated cDNAs orthologous to human OTOR in the mouse, chicken, and bullfrog. The encoded protein, designated otoraplin, has a predicted secretion signal peptide sequence and shows a high degree of cross-species conservation. Otoraplin is homologous to the protein encoded by CDRAP/MIA (cartilage-derived retinoic acid sensitive protein/melanoma inhibitory activity), which is expressed predominantly by chondrocytes, functions in cartilage development and maintenance, and has growth-inhibitory activity in melanoma cell lines.

Dilated cardiomyopathy and sensorineural hearing loss: a heritable syndrome that maps to 6q23-24

BACKGROUND

Dilated cardiomyopathy (DCM) and sensorineural hearing loss (SNHL) are prevalent disorders that occur alone or as components of complex multisystem syndromes. Multiple genetic loci have been identified that, when mutated, cause DCM or SNHL. However, the isolated coinheritance of these phenotypes has not been previously recognized.

METHODS AND RESULTS

Clinical evaluations of 2 kindreds demonstrated autosomal-dominant transmission and age-related penetrance of both SNHL and DCM in the absence of other disorders. Moderate-to-severe hearing loss was evident by late adolescence, whereas ventricular dysfunction produced progressive congestive heart failure after the fourth decade. DNA samples from the larger kindred (29 individuals) were used to perform a genome-wide linkage study. Polymorphic loci on chromosome 6q23 to 24 were coinherited with the disease (maximum logarithm of odds score, 4.88 at locus D6S2411). The disease locus must lie within a 2.8 cM interval between loci D6S975 and D6S292, a location that overlaps an SNHL disease locus (DFNA10). However, DFNA10 does not cause cardiomyopathy. The epicardin gene, which encodes a transcription factor expressed in the myocardium and cochlea, was assessed as a candidate gene by nucleotide sequence analysis; no mutations were identified.

CONCLUSIONS

A syndrome of juvenile-onset SNHL and adult-onset DCM is caused by a mutation at 6q23 to 24 (locus designated CMD1J). Recognition of this cardioauditory disorder allows for the identification of young adults at risk for serious heart disease, thereby enabling early intervention. Definition of the molecular cause of this syndrome may provide new information about important cell physiology common to both the ear and heart.

Refining the DFNB7-DFNB11 deafness locus using intragenic polymorphisms in a novel gene, TMEM2

The combined DFNB7-DFNB11 deafness locus maps to chromosome 9q13-q21 between markers D9S1806 and D9S769. We have determined the cDNA sequence and genomic structure of a novel gene, TMEM2, that maps to this interval and is expressed in the cochlea. The mouse orthologue of this gene (Tmem2) maps to the murine dn (deafness) locus on mouse chromosome 19. Screens for transmembrane helices reveal the presence of at least one putative transmembrane domain in the TMEM2 protein. To determine whether mutations in TMEM2 cause hearing loss at the DFNB7-DFNB11 locus, we screened the coding region of this gene in DFNB7-DFNB11 affected families by direct sequencing. All DNA variants that segregated with the deafness and changed the predicted amino acid sequence of TMEM2 were common polymorphisms, as demonstrated by allele-specific amplification of pooled control DNA. Northern blot analysis showed no difference in transcript size or expression level of Tmem2 in dn/dn and control mice. The intragenic polymorphisms in TMEM2 represent a novel centromeric boundary for the DFNB7-DFNB11 interval.

Histopathological findings suggest the diagnosis in an atypical case of Pendred syndrome

Radiological malformation of the labyrinth, specifically dilatation of the vestibular aqueduct, has been clearly established as a feature in the majority of patients with Pendred syndrome. Mutations of the Pendred syndrome (PDN) gene have been identified in this autosomal recessive form of deafness. There is no direct correlation between the nature of the underlying mutation and the clinical features of deafness, thyroid dysfunction and cochlear malformation. We report a family, the proband of which was thought to deafness secondary to congenital hypothyroidism. At autopsy, histopathological examination of this patient revealed a dilated vestibular aqueduct. Subsequent work on the family has confirmed the diagnosis of Pendred syndrome in the proband and her affected sister.

Clinical otosclerosis, prevalence estimates and spontaneous progress

This retrospective study was performed in order to estimate the prevalence of clinical otosclerosis as a function of age and gender, characterize the hearing level in otosclerosis and describe the spontaneous progress of the disease as a function of age. Clinically based samples were obtained from an audiological department, including 556 subjects: n = 166 (30%) males and n = 390 (70%) females with a median age of 75 years (range 22-95 years) at the time of examination. A subdivision of the sample into 3 age-bands, 20-39 years (n = 39), 40-59 years (n = 78) and > or = 60 years (n = 439), was performed. The overall prevalence estimate of clinical otosclerosis in the area in question was 1.41/1,000 [95% confidence interval (CI) = 1.3-1.5/1,000] with an estimate of 0.9/1,000 (95% CI = 0.8-1.0/1,000) in males and 1.85/1,000 (95% CI = 1.7-2.1/1,000) in females, with an increase in the prevalence as a function of age from 0.22/1,000 (95% CI = 0.15-0.29/1,000) to 3.53/1,000 (95% CI = 3.2-3.86/1,000) in the elderly. The estimates should be considered underestimates, as not all clinical otosclerosis in the area was included. No significant differences in the better and worse ear hearing levels averaged across 0.5-4 kHz (BEHL/WEHL 0.5-4 kHz) were found as a function of gender, and in general the impairment in the BEHL 0.5-4 kHz was fairly moderate until the age of 60 years. In ears previously subjected to surgery a significantly better hearing level of median 63 dB (range 24-119 dB) was found than in the no-surgery ears, with a median hearing level of 71 dB (range 5-120 dB). An estimate of the progress showed an increment in the hearing level in the elderly > or = 60 years of 30 dB over 30 years in non-operated ears, fairly similar to the 40 dB progress in operated ears. It was concluded that a significantly higher prevalence of clinical otosclerosis is present in females than in males, that the overall hearing level in otosclerosis is fairly moderate until the age of 60 years, and that previously operated ears have significantly better hearing than non-operated ears.

Prevalence, age of onset, and natural history of thyroid disease in Pendred syndrome

BACKGROUND

We have sought to establish the prevalence of goitre within a Pendred syndrome (PS) cohort and to document the course of thyroid disease in this patient group. As part of a genetic study of PS we have assessed 57 subjects by perchlorate discharge test and in 52 (M 21, F 31, age range 9-54 years) a discharge of radioiodide of >10% was observed.

RESULTS

Goitre was present in 43 (83%) of the cohort (28 F, 15 M), generally developing after the age of 10 years, 56% remained euthyroid (age range 9-37 years), and 19 patients (44%) had objective evidence of hypothyroidism, all of whom had goitre.

CONCLUSIONS

In summary, thyroid dysfunction in PS is variable and inclusion of goitre as a diagnostic requirement will maintain significant underascertainment. The recent identification of the genetic defect underlying PS is likely to provide an important diagnostic aid in the identification of this disorder and this communication should assist clinicians in identifying deaf patients who ought to be considered for this investigation.

Computed tomography evaluation of the inner ear as a diagnostic, counselling and management strategy in patients with congenital sensorineural hearing impairment

The value of computed tomography (CT) of the petrous bone in the investigation of congenital sensorineural hearing impairment has been questioned. We have conducted a study to establish the usefulness of CT of the temporal bone in the evaluation and management of a consecutive series of unselected adolescent patients with congenital sensorineural hearing impairment of greater than 50 dB HL. Seventy-one patients (142 ears) were identified and images reviewed to establish the incidence of inner ear malformations. Fifteen ears were found to be abnormal in eight patients (seven bilateral and one unilateral abnormality). Three patients had Mondini abnormalities and one of these also had dilatation of the lateral semicircular canals. There were five patients with dilatation of the vestibular aqueduct. One patient had a unilateral dysplasia of the middle and external ear. A variety of incidental intracranial abnormalities were also discovered. We conclude that CT does have a valuable role in the management of SNHI.

Prevalence of hereditary hearing impairment in adults

This contribution, part of an EU-Concerted Action on the genetics of hearing impairment (H.E.A.R.), describes the preliminary estimated prevalence of hereditary hearing impairment based on retrospective data from a clinical series. Of 27,692 subjects examined in the period 1987-91, we sampled 1265 suffering from unilateral or bilateral hereditary hearing impairment, which is roughly 5% of those examined (n = 384 (31%) male; n = 881 (69%) female). Median age of the subjects is 70 years (range 22-98). Subdividing them into 10-year birth cohorts and applying the local annual population statistics, the prevalence of an overall age-related hereditary hearing impairment was roughly estimated to be 3.2/1000, reflecting prevalences as a function of age from 0.8 to 9.4/1000--prevalence in females being significantly more than in males (4.1/1000 and 2.1/1000, respectively). Overall, a moderate hearing impairment of median 51 dB in the better hearing ear was found, averaged across 0.5-4 kHz, this being fairly constant up to the age of 60, when a significant reduction in hearing sensitivity developed. No significant differences are present as a function of gender, except for the birth cohorts 1910-19 and 1920-29. The most frequent type of hereditary hearing impairment in this sample is otosclerosis, comprising 2% of the total clinical series with a rough population prevalence estimate of 1.4/1000. It is concluded that the established database may be of importance in the aggregation of very rare diseases, and for providing the inspiration for future prospective population studies, resulting in knowledge on the epidemiology of hereditary hearing impairment in adults.

Familial carotid body paragangliomas and sensorineural hearing-loss: a new syndrome

BACKGROUND

Carotid body paragangliomas are rare tumors that are sometimes familial, the transmission of which is thought to be by genomic imprinting. We have treated a family who exhibited co-inheritance of carotid body paraganglioma and sensorineural hearing-loss, a relationship that has not been previously reported.

METHODS

We studied a large Australian family who exhibited familial carotid body paragangliomas, many of whose members also suffered tinnitus or hearing-loss. This relationship was examined by reviewing the medical records of family members with confirmed tumors, carrying out neck ultrasonic scanning or computed tomography on their relatives to look for previously unrecognized tumors, and arranging audiometric testing. This information was used to characterize the type of hearing-loss present in this family and to construct a pedigree for the two traits.

RESULTS

The hearing-loss observed in this family was sensorineural in character. Of 15 family members studied over four generations, eight were confirmed positive for both carotid body paraganglioma and sensorineural hearing-loss, two for the tumor only (one of whom did not have his hearing assessed) and one for hearing-loss alone. Four family members were negative for both traits.

CONCLUSIONS

The pedigree provides evidence of a previously undescribed association between familial carotid body paraganglioma and sensorineural hearing-loss, a combination that appears to be co-inherited in this family.

Mutations in the gene encoding gap junction protein beta-3 associated with autosomal dominant hearing impairment

Hearing impairment is the most commonly occurring condition that affects the ability of humans to communicate. More than 50% of the cases of profound early-onset deafness are caused by genetic factors. Over 40 loci for non-syndromic deafness have been genetically mapped, and mutations in several genes have been shown to cause hearing loss. Mutations in the gene encoding connexin 26 (GJB2) cause both autosomal recessive and dominant forms of hearing impairment. To study the possible involvement of other members of the connexin family in hereditary hearing impairment, we cloned the gene (GJB3) encoding human gap junction protein beta-3 using homologous EST searching and nested PCR. GJB3 was mapped to human chromosome 1p33-p35. Mutation analysis revealed that a missense mutation and a nonsense mutation of GJB3 were associated with high-frequency hearing loss in two families. Moreover, expression of Gjb3 was identified in rat inner ear tissue by RT-PCR. These findings suggest that mutations in GJB3 may be responsible for bilateral high-frequency hearing impairment.

Medical genetic evaluation for the etiology of hearing loss in children

The purpose of the medical genetic evaluation is to identify the etiology of the hearing loss. To do so requires a multidisciplinary team that includes the otolaryngologist, audiologist, medical geneticist, and radiologist. A number of tests and procedures are now available to assist in the search for the cause of hearing losses. The importance of sensitivity when providing genetic counseling is emphasized. Molecular genetics offers potential for continued progress in understanding the etiologies of hearing loss. Recent advances in this area are discussed.

[Hereditary deafness in Turkey. Initial results]

The authors describe a study in progress to identify Turkish families with hereditary hearing loss and isolate possible responsible disease genes. Due to extreme genetic heterogeneity and limited audiological differentiation of hereditary hearing loss, it is necessary to identify large or small families from genetic isolates to locate loci responsible for hearing loss on a chromosome. To accomplish this goal, the medical records of 3800 children were examined at the ENT Clinic of Ege University between 1975 and 1994. All were suspected of having various hearing impairments. Additionally, students from two schools for the hearing impaired in Izmir and Eskisehir, Turkey were examined. To date, 16 families with syndromal deafness and 55 families with non-syndromal hereditary hearing loss involving two or more affected individuals have been identified and categorized according to the mode of inheritance. The majority (66%) of the non-syndromal families showed an autosomal recessive pattern, 29% an autosomal dominant inheritance and 5% an X-linked mode of inheritance. In the study presented there has been a predominance of affected males versus females and the consanguinity rate was 22%.

A gene for recessive nonsyndromic sensorineural deafness (DFNB18) maps to the chromosomal region 11p14-p15.1 containing the Usher syndrome type 1C gene

Autosomal recessive nonsyndromic sensorineural deafness segregating in a large consanguineous Indian family was mapped to chromosome 11p14-p15.1 defining a new locus, DFNB18. A maximum lod score of 4.4 at theta = 0 was obtained for the polymorphic micro-satellite marker D11S1888. Haplotype analysis localizes this gene between markers D11S1307 and D11S2368, which is approximately 1.6 cM and encompasses the region of Usher syndrome type 1C (USH1C). We postulate that DFNB18 and USH1C are allelic variants of the same gene.

The Bjornstad syndrome (sensorineural hearing loss and pili torti) disease gene maps to chromosome 2q34-36

We report that the Bjornstad syndrome gene maps to chromosome 2q34-36. The clinical association of sensorineural hearing loss with pili torti (broken, twisted hairs) was described >30 years ago by Bjornstad; subsequently, several small families have been studied. We evaluated a large kindred with Bjornstad syndrome in which eight members inherited pili torti and prelingual sensorineural hearing loss as autosomal recessive traits. A genomewide search using polymorphic loci demonstrated linkage between the disease gene segregating in this kindred and D2S434 (maximum two-point LOD score = 4.98 at theta = 0). Haplotype analysis of recombination events located the disease gene in a 3-cM region between loci D2S1371 and D2S163. We speculate that intermediate filament and intermediate filament-associated proteins are good candidate genes for causing Bjornstad syndrome.

Nonsyndromic autosomal dominant progressive sensorineural hearing loss: audiologic analysis of a pedigree linked to DFNA2

An analysis was performed of the regression of the individual hearing threshold on age in the affected persons in a six-generation Dutch family with nonsyndromic autosomal dominant sensorineural hearing loss, which showed linkage to the DFNA2(1p34) region, similar to at least four previously reported nonrelated families. The offset threshold was significantly higher at the high frequencies (around 30 dB at 2 to 8 kHz) than at the lower ones (approximately 0 dB at 0.25 to 1 kHz). Hearing impairment at the higher frequencies may therefore have been present already at birth or in early childhood. The regression coefficient, or the 'annual threshold increase,' expressed in dB/y, was about 1 dB/y on average, but the higher frequencies (1 to 8 kHz) showed significantly more rapid progression than the lower frequencies (0.25 to 0.5 kHz).

Construction of P1-derived artificial chromosome and yeast artificial chromosome contigs encompassing the DFNB7 and DFNB11 region of chromosome 9q13-21

DFNB7 and DFNB11, two loci for autosomal recessive nonsyndromic hearing loss (ARNSHL), have been mapped to chromosome 9q13-21 in separate consanguineous families. Using a radiation hybrid map, we have determined the correct marker order in the DFNB7/11 region and have demonstrated that the DFNB11 locus resides within a redefined DFNB7 interval. The gene(s) responsible for ARNSHL at these loci resides within an approximately 1 cM interval bounded by markers D9S1806 (centromeric) and D9S769 (telomeric). A recently discovered Indian family confirms the new telomeric boundary. To assist in the identification and cloning of candidate genes, YAC and PAC contigs were constructed. A total of 19 YAC and 23 PAC clones were utilized to span the affected region and ensure double coverage throughout. Twenty-two previously published STSs and 21 new STSs were used to determine marker order and confirm the integrity of the contig. Using a positional cloning strategy we have identified three cochlear expressed genes that map to the DFNB7/11 interval.

Oto-facio-osseous-gonadal syndrome: a new form of syndromic deafness?

In this study, we report on two brothers, born to consanguineous parents, with a syndrome of sensorineural deafness, short stature, cryptorchidism, inguinal hernia, brachycephaly, prominent forehead, flat face, downslanting palpebral fissures, low nasal root, hypoplastic alae and round tip to the nose, low-set prominent ears, narrow thorax, genu valgum, wormian bones, fusion of carpal bones, delayed bone age and congenital clubfeet. This combination of anomalies appears to be a previously undescribed syndrome, with probable autosomal recessive inheritance.

Bilateral sensorineural deafness and hydrocephalus due to foramen of Monro obstruction in sibs: a newly described autosomal recessive disorder

We identified a Canadian-Mennonite family in which a brother and sister have hydrocephalus due to obstruction at the foramen of Monro and profound bilateral sensorineural deafness. This appears to be a unique combination of anomalies and, to our knowledge, has not been reported previously. Both parents and a brother are phenotypically normal. The parents are second cousins. Thus, on the basis of consanguinity, affected sibs of both sexes, and in the absence of evidence for intrauterine infections or other adverse perinatal events, this syndrome is likely inherited in an autosomal recessive fashion.

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.

Linkage of congenital recessive deafness (gene DFNB10) to chromosome 21q22.3

Deafness is a heterogeneous trait affecting approximately 1/1,000 newborns. Genetic linkage studies have already implicated more than a dozen distinct loci causing deafness. We conducted a genome search for linkage in a large Palestinian family segregating an autosomal recessive form of nonsyndromic deafness. Our results indicate that in this family the defective gene, DFNB10, is located in a 12-cM region near the telomere of chromosome 21. This genetic distance corresponds to <2.4 Mbp. Five marker loci typed from this region gave maximum LOD scores > or = to 3. Homozygosity of marker alleles was evident for only the most telomeric marker, D21S1259, suggesting that DFNB10 is closest to this locus. To our knowledge, this is the first evidence, at this location, for a gene that is involved in the development or maintenance of hearing. As candidate genes at these and other deafness loci are isolated and characterized, their roles in hearing will be revealed and may lead to development of mechanisms to prevent deafness.

Database for sensorineural hearing loss

We are creating a bank of EBV immortalized lymphoblast cells and extracted DNA taken from the blood of deaf children and their relatives, in order to study the molecular basis of hereditary deafness. We have established a corresponding database for sensorineural hearing loss that records clinical data for each entered specimen. The purpose of this paper is to present the content and design of the computerized relational database. The data model is designed first to identify known etiologies of deafness, either acquired or syndromic, and then to characterize the clinical features of the deaf individual, and both their affected and non-affected family members. The application operates in a graphical environment of visual prompts and message panels. The database is organized by sections which record demographic data, presenting complaints, otologic history, birth and perinatal history, developmental history, symptoms of chronic airway obstruction, family history, neurologic history, congenital infections, hospitalizations and surgical history, medication history, vestibular findings, audiometry, radiology, medical conditions and syndromes and physical examination. The database was developed on a commercially available software product. Our database is presented as a model for use by other clinicians and investigators.

Pendred syndrome (goitre and sensorineural hearing loss) maps to chromosome 7 in the region containing the nonsyndromic deafness gene DFNB4

Inherited causes account for about 50% of individuals presenting with childhood (prelingual) hearing loss, of which 70% are due to mutation in numerous single genes which impair auditory function alone (non-syndromic). The remainder are associated with other developmental anomalies termed syndromic deafness. Genes responsible for syndromic forms of hearing loss include the COL4A5 gene in Alport syndrome and the PAX3 and MITF genes in Waardenburg syndrome. Pendred syndrome is an autosomal recessive disorder associated with developmental abnormalities of the cochlea, sensorineural hearing loss and diffuse thyroid enlargement (goitre). Pendred syndrome is the most common syndromal form of deafness, yet the primary defect remains unknown. We have established a panel of 12 families with two or more affected individuals and used them to search for the location of the Pendred gene by linkage analysis. We excluded localization to four previously mapped nonsyndromic deafness loci but obtained conclusive evidence for linkage of the Pendred syndrome gene to microsatellite markers on chromosome 7q31 (D7S495 Zmax 7.32, Qmax = 0). This region contains a gene, DFNBL, for autosomal recessive non-syndromic sensorineural hearing loss. Multipoint analysis indicates that DFNB4 and Pendred syndrome co-localize to the same 5.5 centiMorgan (cM) interval flanked by D7S501 and D7S523. These data raise the possibility that Pendred syndrome is either allelic with DFNB4 or may represent an inherited contiguous gene disorder, not clinically manifest in the heterozygote.

A new X linked recessive deafness syndrome with blindness, dystonia, fractures, and mental deficiency is linked to Xq22

X linked recessive deafness accounts for only 1.7% of all childhood deafness. Only a few of the at least 28 different X linked syndromes associated with hearing impairment have been characterised at the molecular level. In 1960, a large Norwegian family was reported with early onset progressive sensorineural deafness, which was indexed in McKusick as DFN-1, McKusick 304700. No associated symptoms were described at that time. This family has been restudied clinically. Extensive neurological, neurophysiological, neuroradiological, and biochemical, as well as molecular techniques, have been applied to characterise the X linked recessive syndrome. The family history and extensive characterisation of 16 affected males in five generations confirmed the X linked recessive inheritance and the postlingual progressive nature of the sensorineural deafness. Some obligate carrier females showed signs of minor neuropathy and mild hearing impairment. Restudy of the original DFN-1 family showed that the deafness is part of a progressive X linked recessive syndrome, which includes visual disability leading to cortical blindness, dystonia, fractures, and mental deficiency. Linkage analysis indicated that the gene was linked to locus DXS101 in Xq22 with a lod score of 5.37 (zero recombination). Based on lod-1 support interval of the multipoint analysis, the gene is located in a region spanning from 5 cM proximal to 3 cM distal to this locus. As the proteolipid protein gene (PLP) is within this region and mutations have been shown to be associated with non-classical PMD (Pelizaeus-Merzbacher disease), such as complex X linked hereditary spastic paraplegia, PLP may represent a candidate gene for this disorder. This family represents a new syndrome (Mohr-Tranebjaerg syndrome, MTS) and provides significant new information about a new X linked recessive sydromic type of deafness which was previously thought to be isolated deafness.

Linkage of autosomal dominant hearing loss to the short arm of chromosome 1 in two families

BACKGROUND

At least half of the cases of profound deafness of early onset are caused by genetic factors, but few of the genetic defects have been identified. This is particularly true of the most common hereditary forms of deafness, which occur in the absence of any associated syndrome.

METHODS

We studied a large Indonesian family in which hearing loss was inherited in an autosomal dominant pattern. The hearing loss first affects the high frequencies during the teens or 20s and becomes profound within 10 years. To locate the responsible gene, we performed genetic-linkage analysis, using microsatellite markers distributed over the entire genome. We then performed linkage analyses in an American family and a Dutch family with similar patterns of hereditary hearing loss.

RESULTS

In the extended Indonesian family, a gene linked to deafness mapped to chromosome 1p, with a multipoint lod score of more than 7. In the American family, deafness was linked to the same locus on chromosome 1p, with a multipoint lod score of more than 5. In the Dutch family, however, this locus was ruled out. The flanking markers D1S255 and D1S211 defined a region of 6 cM on chromosome 1p that is likely to contain the gene associated with deafness in the first two families.

CONCLUSIONS

In some families with early-onset autosomal dominant hearing loss, the responsible gene is on chromosome 1p.

A non-syndrome form of neurosensory, recessive deafness maps to the pericentromeric region of chromosome 13q

Non-syndromic, recessively inherited deafness is the most predominant form of severe inherited childhood deafness. Until now, no gene responsible for this type of deafness has been localized, due to extreme genetic heterogeneity and limited clinical differentiation. Linkage analyses using highly polymorphic microsatellite markers were performed on two consanguineous families from Tunisia affected by this form of deafness. The deafness was profound, fully penetrant and prelingual. A maximum two-point lod score of 9.88 (theta = 0.001) was found with a marker detecting a 13q locus (D13S175). Linkage was also observed to the pericentromeric 13q12 loci D13S115 and D13S143. These data map this neurosensory deafness gene to the same region of chromosome 13q as the gene for severe, childhood autosomal recessive muscular dystrophy.