Splice-altering variant in COL11A1 as a cause of nonsyndromic hearing loss DFNA37.

PURPOSE: The aim of this study was to determine the genetic cause of autosomal dominant nonsyndromic hearing loss segregating in a multigenerational family. METHODS: Clinical examination, genome-wide linkage analysis, and exome sequencing were carried out on the family. RESULTS: Affected individuals presented with early-onset progressive mild hearing impairment with a fairly flat, gently downsloping or U-shaped audiogram configuration. Detailed clinical examination excluded any additional symptoms. Linkage analysis detected an interval on chromosome 1p21 with a logarithm of the odds (LOD) score of 8.29: designated locus DFNA37. Exome sequencing identified a novel canonical acceptor splice-site variant c.652-2A>C in the COL11A1 gene within the DFNA37 locus. Genotyping of all 48 family members confirmed segregation of this variant with the deafness phenotype in the extended family. The c.652-2A>C variant is novel, highly conserved, and confirmed in vitro to alter RNA splicing. CONCLUSION: We have identified COL11A1 as the gene responsible for deafness at the DFNA37 locus. Previously, COL11A1 was solely associated with Marshall and Stickler syndromes. This study expands its phenotypic spectrum to include nonsyndromic deafness. The implications of this discovery are valuable in the clinical diagnosis, prognosis, and treatment of patients with COL11A1 pathogenic variants.

HOMER2, a stereociliary scaffolding protein, is essential for normal hearing in humans and mice.

Hereditary hearing loss is a clinically and genetically heterogeneous disorder. More than 80 genes have been implicated to date, and with the advent of targeted genomic enrichment and massively parallel sequencing (TGE+MPS) the rate of novel deafness-gene identification has accelerated. Here we report a family segregating post-lingual progressive autosomal dominant non-syndromic hearing loss (ADNSHL). After first excluding plausible variants in known deafness-causing genes using TGE+MPS, we completed whole exome sequencing in three hearing-impaired family members. Only a single variant, p.Arg185Pro in HOMER2, segregated with the hearing-loss phenotype in the extended family. This amino acid change alters a highly conserved residue in the coiled-coil domain of HOMER2 that is essential for protein multimerization and the HOMER2-CDC42 interaction. As a scaffolding protein, HOMER2 is involved in intracellular calcium homeostasis and cytoskeletal organization. Consistent with this function, we found robust expression in stereocilia of hair cells in the murine inner ear and observed that over-expression of mutant p.Pro185 HOMER2 mRNA causes anatomical changes of the inner ear and neuromasts in zebrafish embryos. Furthermore, mouse mutants homozygous for the targeted deletion of Homer2 present with early-onset rapidly progressive hearing loss. These data provide compelling evidence that HOMER2 is required for normal hearing and that its sequence alteration in humans leads to ADNSHL through a dominant-negative mode of action.

Loss-of-function mutations of ILDR1 cause autosomal-recessive hearing impairment DFNB42.

By using homozygosity mapping in a consanguineous Pakistani family, we detected linkage of nonsyndromic hearing loss to a 7.6 Mb region on chromosome 3q13.31-q21.1 within the previously reported DFNB42 locus. Subsequent candidate gene sequencing identified a homozygous nonsense mutation (c.1135G>T [p.Glu379X]) in ILDR1 as the cause of hearing impairment. By analyzing additional consanguineous families with homozygosity at this locus, we detected ILDR1 mutations in the affected individuals of 10 more families from Pakistan and Iran. The identified ILDR1 variants include missense, nonsense, frameshift, and splice-site mutations as well as a start codon mutation in the family that originally defined the DFNB42 locus. ILDR1 encodes the evolutionarily conserved immunoglobulin-like domain containing receptor 1, a putative transmembrane receptor of unknown function. In situ hybridization detected expression of Ildr1, the murine ortholog, early in development in the vestibule and in hair cells and supporting cells of the cochlea. Expression in hair cell- and supporting cell-containing neurosensory organs is conserved in the zebrafish, in which the ildr1 ortholog is prominently expressed in the developing ear and neuromasts of the lateral line. These data identify loss-of-function mutations of ILDR1, a gene with a conserved expression pattern pointing to a conserved function in hearing in vertebrates, as underlying nonsyndromic prelingual sensorineural hearing impairment.

Advancing genetic testing for deafness with genomic technology.

BACKGROUND: Non-syndromic hearing loss (NSHL) is the most common sensory impairment in humans. Until recently its extreme genetic heterogeneity precluded comprehensive genetic testing. Using a platform that couples targeted genomic enrichment (TGE) and massively parallel sequencing (MPS) to sequence all exons of all genes implicated in NSHL, we tested 100 persons with presumed genetic NSHL and in so doing established sequencing requirements for maximum sensitivity and defined MPS quality score metrics that obviate Sanger validation of variants. METHODS: We examined DNA from 100 sequentially collected probands with presumed genetic NSHL without exclusions due to inheritance, previous genetic testing, or type of hearing loss. We performed TGE using post-capture multiplexing in variable pool sizes followed by Illumina sequencing. We developed a local Galaxy installation on a high performance computing cluster for bioinformatics analysis. RESULTS: To obtain maximum variant sensitivity with this platform 3.2-6.3 million total mapped sequencing reads per sample were required. Quality score analysis showed that Sanger validation was not required for 95% of variants. Our overall diagnostic rate was 42%, but this varied by clinical features from 0% for persons with asymmetric hearing loss to 56% for persons with bilateral autosomal recessive NSHL. CONCLUSIONS: These findings will direct the use of TGE and MPS strategies for genetic diagnosis for NSHL. Our diagnostic rate highlights the need for further research on genetic deafness focused on novel gene identification and an improved understanding of the role of non-exonic mutations. The unsolved families we have identified provide a valuable resource to address these areas.

Expressivity of hearing loss in cases with Usher syndrome type IIA.

OBJECTIVE: The purpose of this study was to compare the genotype/phenotype relationship between siblings with identical USH2A pathologic mutations and the consequent audiologic phenotypes, in particular degree of hearing loss (HL). Decade audiograms were also compared among two groups of affected subjects with different mutations of USH2A. DESIGN: DNA samples from patients with Usher syndrome type II were analysed. The audiological features of patients and affected siblings with USH2A mutations were also examined to identify genotype-phenotype correlations. STUDY SAMPLE: Genetic and audiometric examinations were performed in 18 subjects from nine families with Usher syndrome type IIA. RESULTS: Three different USH2A mutations were identified in the affected subjects. Both similarities and differences of the auditory phenotype were seen in families with several affected siblings. A variable degree of hearing loss, ranging from mild to profound, was observed among affected subjects. No significant differences in hearing thresholds were found the group of affected subjects with different pathological mutations. CONCLUSIONS: Our results indicate that mutations in the USH2A gene and the resulting phenotype are probably modulated by other variables, such as modifying genes, epigenetics or environmental factors which may be of importance for better understanding the etiology of Usher syndrome.

Mutations in LOXHD1, an evolutionarily conserved stereociliary protein, disrupt hair cell function in mice and cause progressive hearing loss in humans.

Hearing loss is the most common form of sensory impairment in humans and is frequently progressive in nature. Here we link a previously uncharacterized gene to hearing impairment in mice and humans. We show that hearing loss in the ethylnitrosourea (ENU)-induced samba mouse line is caused by a mutation in Loxhd1. LOXHD1 consists entirely of PLAT (polycystin/lipoxygenase/alpha-toxin) domains and is expressed along the membrane of mature hair cell stereocilia. Stereociliary development is unaffected in samba mice, but hair cell function is perturbed and hair cells eventually degenerate. Based on the studies in mice, we screened DNA from human families segregating deafness and identified a mutation in LOXHD1, which causes DFNB77, a progressive form of autosomal-recessive nonsyndromic hearing loss (ARNSHL). LOXHD1, MYO3a, and PJVK are the only human genes to date linked to progressive ARNSHL. These three genes are required for hair cell function, suggesting that age-dependent hair cell failure is a common mechanism for progressive ARNSHL.

Evidence of genetic heterogeneity in Alberta Hutterites with Usher syndrome type I.

PURPOSE: To identify the genetic defect in a Hutterite population from northern Alberta with Usher syndrome type I. METHODS: Complete ophthalmic examinations were conducted on two boys and two girls from two related Hutterite families diagnosed with Usher syndrome type I. DNA from patients and their parents was first evaluated for a mutation in exon 10 of the protocadherin-related 15 (PCDH15) gene (c.1471delG), previously reported in southern Alberta Hutterite patients with Usher syndrome (USH1F). Single nucleotide polymorphic linkage analysis was then used to confirm another locus, and DNA was analyzed with the Usher Chip v4.0 platform. RESULTS: Severe hearing impairment, unintelligible speech, and retinitis pigmentosa with varying degrees of visual acuity and visual field loss established a clinical diagnosis of Usher syndrome type I. The patients did not carry the exon 10 mutation in the PCDH15 gene; however, with microarray analysis, a previously reported mutation (c.52C>T; p.Q18X) in the myosin VIIA (MYO7A) gene was found in the homozygous state in the affected siblings. CONCLUSIONS: The finding of a MYO7A mutation in two related Hutterite families from northern Alberta provides evidence of genetic heterogeneity in Hutterites affected by Usher syndrome type I.

Mutation screening of the PCDH15 gene in Spanish patients with Usher syndrome type I.

PURPOSE: PCDH15 codes for protocadherin-15, a cell-cell adhesion protein essential in the morphogenesis and cohesion of stereocilia bundles and in the function or preservation of photoreceptor cells. Mutations in the PCDH15 gene are responsible for Usher syndrome type I (USH1F) and non-syndromic hearing loss (DFNB23). The purpose of this work was to perform PCDH15 mutation screening to identify the genetic cause of the disease in a cohort of Spanish patients with Usher syndrome type I and establish phenotype-genotype correlation. METHODS: Mutation analysis of PCDH15 included additional exons recently identified and was performed by direct sequencing. The screening was performed in 19 probands with USH already screened for mutations in the most prevalent USH1 genes, myosin VIIA (MYO7A) and cadherin-23 (CDH23), and for copy number variants in PCDH15. RESULTS: Seven different point mutations, five novel, were detected. Including the large PCDH15 rearrangements previously reported in our cohort of patients, a total of seven of 19 patients (36.8%) were carriers of at least one pathogenic allele. Thirteen out of the 38 screened alleles carried pathogenic PCDH15 variants (34.2%). CONCLUSIONS: Five out of the seven point mutations reported in the present study are novel, supporting the idea that most PCDH15 mutations are private. Furthermore, no mutational hotspots have been identified. In most patients, detected mutations led to a truncated protein, reinforcing the hypothesis that severe mutations cause the Usher I phenotype and that missense variants are mainly responsible for non-syndromic hearing impairment.

Usher syndromes due to MYO7A, PCDH15, USH2A or GPR98 mutations share retinal disease mechanism.

Usher syndrome (USH) is a genetically heterogeneous group of autosomal recessive deaf-blinding disorders. Pathophysiology leading to the blinding retinal degeneration in USH is uncertain. There is evidence for involvement of the photoreceptor cilium, photoreceptor synapse, the adjacent retinal pigment epithelium (RPE) cells, and the Crumbs protein complex, the latter implying developmental abnormalities in the retina. Testing hypotheses has been difficult in murine USH models because most do not show a retinal degeneration phenotype. We defined the retinal disease expression in vivo in human USH using optical imaging of the retina and visual function. In MYO7A (USH1B), results from young individuals or those at early stages indicated the photoreceptor was the first detectable site of disease. Later stages showed photoreceptor and RPE cell pathology. Mosaic retinas in Myo7a-deficient shaker1 mice supported the notion that the mutant photoreceptor phenotype was cell autonomous and not secondary to mutant RPE. Humans with PCDH15 (USH1F), USH2A or GPR98 (USH2C) had a similar retinal phenotype to MYO7A (USH1B). There was no evidence of photoreceptor synaptic dysfunction and no dysplastic phenotype as in CRB1 (Crumbs homologue1) retinopathy. The results point to the photoreceptor cell as the therapeutic target for USH treatment trials, such as MYO7A somatic gene replacement therapy.

Frequency of Usher syndrome in two pediatric populations: Implications for genetic screening of deaf and hard of hearing children.

PURPOSE: Usher syndrome is a major cause of genetic deafness and blindness. The hearing loss is usually congenital and the retinitis pigmentosa is progressive and first noticed in early childhood to the middle teenage years. Its frequency may be underestimated. Newly developed molecular technologies can detect the underlying gene mutation of this disorder early in life providing estimation of its prevalence in at risk pediatric populations and laying a foundation for its incorporation as an adjunct to newborn hearing screening programs. METHODS: A total of 133 children from two deaf and hard of hearing pediatric populations were genotyped first for GJB2/6 and, if negative, then for Usher syndrome. Children were scored as positive if the test revealed > or =1 pathogenic mutations in any Usher gene. RESULTS: Fifteen children carried pathogenic mutations in one of the Usher genes; the number of deaf and hard of hearing children carrying Usher syndrome mutations was 15/133 (11.3%). The population prevalence was estimated to be 1/6000. CONCLUSION: Usher syndrome is more prevalent than has been reported before the genome project era. Early diagnosis of Usher syndrome has important positive implications for childhood safety, educational planning, genetic counseling, and treatment. The results demonstrate that DNA testing for Usher syndrome is feasible and may be a useful addition to newborn hearing screening programs.

Mutations in TMC1 are a common cause of DFNB7/11 hearing loss in the Iranian population.

OBJECTIVES: We investigated the cause of autosomal recessive nonsyndromic hearing loss (ARNSHL) that segregated in 2 consanguineous Iranian families. METHODS: Otologic and audiometric examinations were performed on affected members of each family. Genome-wide parametric multipoint linkage mapping using a recessive model was performed with Affymetrix 50K GeneChips or short tandem repeat polymorphisms. Direct sequencing was used to confirm the causative mutation in each family. RESULTS: In 2 Iranian families, L-1651 and L-8600606, with ARNSHL that mapped to the DFNB7/11 locus, homozygosity for a reported splice site mutation (c.776+1G>A), and a novel deletion (c.1589_1590delCT; p.S530*) were identified in the TMC1 gene, respectively. CONCLUSIONS: Consistent with the previously reported phenotype in DFNB7/11 families, the 2 Iranian families had segregated congenital, profound hearing impairment. However, in family L-1651, one affected family member (IV:3) has milder hearing impairment than expected, suggesting a potential genetic modifier effect. These results indicate that DFNB7/11 is a common form of genetic hearing loss in Iran, because this population is the source of 6 of the 29 TMC1 mutations reported worldwide.

SIX1 mutation screening in 247 branchio-oto-renal syndrome families: a recurrent missense mutation associated with BOR.

Branchio-oto-renal syndrome (BOR) is a clinically heterogeneous autosomal dominant form of syndromic hearing loss characterized by variable hearing impairment, malformations of the pinnae, the presence of branchial arch remnants, and various renal abnormalities. Both EYA1 and SIX1 are expressed in developing otic, branchial and renal tissue. Consistent with this expression pattern, mutations in both genes cause BOR syndrome. Mutations in EYA1 are found in approximately 40% of patients with the BOR phenotype, however, the role of SIX1 is much lower. To date only three different SIX1 mutations have been described in BOR patients. The current screen of 247 BOR families detected five novel SIX1 mutations (c.50T>A, c.218A>C, c.317T>G, c.329G>A, c.334C>T) and one previously reported mutation (c.328C>T) seen in 5 unrelated families. All mutations are within the protein-binding Six domain. Phenotypic variability was high in these BOR families. Seven of the eight known SIX1 mutations are missense and the one in frame deletion is predicted to be functionally similar. The wide phenotypic variability precludes making genotype-phenotype correlations at this time.

Branchio-oto-renal syndrome (BOR): novel mutations in the EYA1 gene, and a review of the mutational genetics of BOR.

Branchio-oto-renal syndrome (BOR) is an autosomal dominant disorder characterized by the association of branchial and external ear malformations, hearing loss, and renal anomalies. The phenotype varies from ear pits to profound hearing loss, branchial fistulae, and kidney agenesis. The most common gene mutated in BOR families is EYA1, a transcriptional activator. Over 80 different disease-causing mutations have been published (www.healthcare.uiowa.edu/labs/pendredandbor/, last accessed 20 November 2007). We analyzed the EYA1 coding region (16 exons) from 435 families (345 at the University of Iowa [UI] and 95 at Boys Town National Research Hospital [BTNRH], including five at both) and found 70 different EYA1 mutations in 89 families. Most of the mutations (56/70) were private. EYA1 mutations were found in 31% of families (76/248) fitting established clinical criteria for BOR and 7% of families with questionable BOR phenotype (13/187). Severity of the phenotype did not correlate with type of mutation nor with the domain involved. These results add considerably to the spectrum of EYA1 mutations associated with BOR and indicate that the BOR phenotype is an indication for molecular studies to diagnose EYA1-associated BOR.

Retinal disease in Usher syndrome III caused by mutations in the clarin-1 gene.

PURPOSE: To determine the retinal phenotype of Usher syndrome type III (USH3A) caused by clarin-1 (CLRN1) gene mutations in a non-Finnish population. METHODS: Patients with USH3A (n = 13; age range, 24-69) representing 11 different families were studied and the results compared with those from patients with USH2A (n = 24; age range, 17-66). The patients were evaluated by ocular examination, kinetic and static perimetry, near-infrared autofluorescence, and optical coherence tomography (OCT). RESULTS: Ten of 11 families had Ashkenazi Jewish origins and the N48K CLRN1 mutation. Rod function was lost in the peripheral field in the first two decades of life, but central rod function could be retained for another decade. Peripheral cone function was detectable into the third decade of life. Central cone function had a slower decline that extended for decades. Photoreceptor layer loss and features of retinal remodeling were present in retinal regions with severe visual dysfunction, even at the youngest ages tested. Central retinal structure could be normal in younger patients but structural integrity was lost in older patients. RPE disease generally paralleled photoreceptor degeneration. Comparisons between USH3A and USH2A suggested a common rod and cone phenotype but a more accelerated time course of rod loss in USH3A. CONCLUSIONS: USH3A and USH2A share patterns of rod and cone dysfunction and retinal structural abnormalities. Peripheral function measurements showed USH3A to be more rapidly progressive than USH2A.

Presence of de novo mutations in autosomal dominant polycystic kidney disease patients without family history.

BACKGROUND: At the University of Colorado Health Sciences Center, on detailed questioning, approximately 10% of patients with autosomal dominant polycystic kidney disease (ADPKD) gave no family history of ADPKD. There are several explanations for this observation, including occurrence of a de novo pathogenic sequence variant or extreme phenotypic variability. To confirm de novo sequence variants, we have undertaken clinical and genetic screening of affected offspring and their parents. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: 24 patients with a well-documented ADPKD phenotype and no family history of polycystic kidney disease (PKD) and both parents of each patient. OUTCOME: Presence or absence of PKD1 or PKD2 pathogenic sequence variants in parents of affected offspring. MEASUREMENTS: Abdominal ultrasound of affected offspring and their parents for ADPKD diagnosis. Parentage testing by genotyping. Complete screening of PKD1 and PKD2 genes by using genomic DNA from affected offspring; analysis of genomic DNA from both parents to confirm the absence or presence of all DNA variants found. RESULTS: A positive diagnosis of ADPKD by means of ultrasound or genetic screening was made in 1 parent of 4 patients (17%). No PKD1 or PKD2 pathogenic sequence variants were identified in 10 patients (42%), whereas possible pathological DNA variants were identified in 4 patients (17%) and 1 of their respective parents. Parentage was confirmed in the remaining 6 patients (25%), and de novo sequence variants were documented. LIMITATIONS: Size of patient group. No direct examination of RNA. CONCLUSION: Causes other than de novo pathogenic sequence variants may explain the negative family history of ADPKD in certain families.

Autoimmune disease in a DFNA6/14/38 family carrying a novel missense mutation in WFS1.

Most familial cases of autosomal dominant low frequency sensorineural hearing loss (LFSNHL) are attributable to mutations in the wolframin syndrome 1 (WFS1) gene at the DFNA6/14/38 locus. WFS1 mutations at this locus were first described in 2001 in six families segregating LFSNHL that was non-progressive below 2,000 Hz; the causative mutations all clustered in the C-terminal domain of the wolframin protein. Mutations in WFS1 also cause Wolfram syndrome (WS), an autosomal recessive neurodegenerative disorder defined by diabetes mellitus, optic atrophy and often deafness, while numerous single nucleotide polymorphisms (SNPs) in WFS1 have been associated with increased risk for diabetes mellitus, psychiatric illnesses and Parkinson disease. This study was conducted in an American family segregating autosomal dominant LFSNHL. Two hearing impaired family members also had autoimmune diseases-Graves disease (GD) and Crohn disease (CD). Based on the low frequency audioprofile, mutation screening of WFS1 was completed and a novel missense mutation (c.2576G --> A) that results in an arginine-to-glutamine substitution (p.R859Q) was identified in the C-terminal domain of the wolframin protein where most LFSNHL-causing mutations cluster. The family member with GD also carried polymorphisms in WFS1 that have been associated with other autoimmune diseases.

Development of a genotyping microarray for Usher syndrome.

BACKGROUND: Usher syndrome, a combination of retinitis pigmentosa (RP) and sensorineural hearing loss with or without vestibular dysfunction, displays a high degree of clinical and genetic heterogeneity. Three clinical subtypes can be distinguished, based on the age of onset and severity of the hearing impairment, and the presence or absence of vestibular abnormalities. Thus far, eight genes have been implicated in the syndrome, together comprising 347 protein-coding exons. METHODS: To improve DNA diagnostics for patients with Usher syndrome, we developed a genotyping microarray based on the arrayed primer extension (APEX) method. Allele-specific oligonucleotides corresponding to all 298 Usher syndrome-associated sequence variants known to date, 76 of which are novel, were arrayed. RESULTS: Approximately half of these variants were validated using original patient DNAs, which yielded an accuracy of >98%. The efficiency of the Usher genotyping microarray was tested using DNAs from 370 unrelated European and American patients with Usher syndrome. Sequence variants were identified in 64/140 (46%) patients with Usher syndrome type I, 45/189 (24%) patients with Usher syndrome type II, 6/21 (29%) patients with Usher syndrome type III and 6/20 (30%) patients with atypical Usher syndrome. The chip also identified two novel sequence variants, c.400C>T (p.R134X) in PCDH15 and c.1606T>C (p.C536S) in USH2A. CONCLUSION: The Usher genotyping microarray is a versatile and affordable screening tool for Usher syndrome. Its efficiency will improve with the addition of novel sequence variants with minimal extra costs, making it a very useful first-pass screening tool.

Is hearing loss due to mutations in the Connexin 26 gene progressive?

Serial audiograms were analysed for seven subjects, who were homozygous for the 35delG GJB2 mutation. The criterion for determining progression of hearing loss was at least a 1-dB loss in air conduction pure-tone average-3 (ACPTA-3) or ACPTA-4 per year for 2 to 10 years, with a minimum change of 10 dB ACPTA 3 or 4. Bilateral progression of hearing loss was found in 43% (3/7) of the subjects. A meta-analysis of seven studies with non-overlapping data sets and similar ascertainment criteria indicated that 19% of DFNB1 subjects with GJB2 mutations have progressive hearing loss. These data suggest that it may be incorrect to assume that congenital hearing loss due to this mutation is stable. We recommend rigorous audiologic surveillance for individuals with DFNB1.

Genotype-phenotype correlations for SLC26A4-related deafness.

Pendred syndrome (PS) and non-syndromic enlarged vestibular aqueduct (EVA) are two recessive disorders characterized by the association of sensorineural hearing loss (SNHL) with inner ear malformations that range from isolated EVA to Mondini Dysplasia, a complex malformation that includes a cochlear dysplasia and EVA. Mutations in the SLC26A4 gene, coding for the protein pendrin, have been implicated in the pathophysiology of both disorders. In order to determine whether SLC26A4 genotypes can be correlated to the complexity and severity of the phenotypes, we ascertained 1,506 deaf patients. Inner ear abnormalities were present in 474 patients (32%). Mutation screening of SLC26A4 detected two mutations in 16% of patients, one mutation in 19% of patients and zero mutation in 65% of patients. When the distribution of SLC26A4 genotypes was compared across phenotypes, a statistically significant difference was found between PS patients and non-syndromic EVA-Mondini patients (P = 0.005), as well as between EVA patients and Mondini patients (P = 0.0003). There was a correlation between phenotypic complexity of inner ear malformations and genetic heterogeneity--PS patients have the most severe phenotype and the most homogeneous etiology while EVA patients have the least severe phenotype and the most heterogeneous etiology. For all patients, variability in the degree of hearing loss is seen across genotypes implicating other genetic and/or environmental factors in the pathogenesis of the PS-Mondini-EVA disease spectrum.

The Coxsackievirus and Adenovirus Receptor: a new adhesion protein in cochlear development.

The Coxsackievirus and Adenovirus Receptor (CAR) is an essential regulator of cell growth and adhesion during development. The gene for CAR, CXADR, is located within the genomic locus for Usher syndrome type 1E (USH1E). Based on this and a physical interaction with harmonin, the protein responsible for USH1C, we hypothesized that CAR may be involved in cochlear development and that mutations in CXADR may be responsible for USH1E. The expression of CAR in the cochlea was determined by PCR and immunofluorescence microscopy. We found that CAR expression is highly regulated during development. In neonatal mice, CAR is localized to the junctions of most cochlear cell types but is restricted to the supporting and strial cells in adult cochlea. A screen of two populations consisting of non-syndromic deaf and Usher 1 patients for mutations in CXADR revealed one haploid mutation (P356S). Cell surface expression, viral receptor activity, and localization of the mutant form of CAR were indistinguishable from wild-type CAR. Although we were unable to confirm a role for CAR in autosomal recessive, non-syndromic deafness, or Usher syndrome type 1, based on its regulation, localization, and molecular interactions, CAR remains an attractive candidate for genetic deafness.