Usher Syndrome Type IIa Research Articles

Pathogenesis and Treatment of Usher Syndrome Type IIA.

Usher syndrome (USH) is the most common form of deaf-blindness, with an estimated prevalence of 4.4 to 16.6 per 100,000 people worldwide. The most common form of USH is type IIA (USH2A), which is caused by homozygous or compound heterozygous mutations in the USH2A gene and accounts for around half of all USH cases. USH2A patients show moderate to severe hearing loss from birth, with diagnosis of retinitis pigmentosa in the second decade of life and variable vestibular involvement. Although hearing aids or cochlear implants can provide some mitigation of hearing deficits, there are currently no treatments aimed at preventing or restoring vision loss in USH2A patients. In this review, we first provide an overview of the molecular biology of the USH2A gene and its protein isoforms, which include a transmembrane protein (TM usherin) and an extracellular protein (EC usherin). The role of these proteins in the inner ear and retina and their impact on the pathogenesis of USH2A is discussed. We review animal cell-derived and patient cell-derived models currently used in USH2A research and conclude with an overview of potential treatment strategies currently in preclinical development and clinical trials.

Novel biallelic USH2A variants in a patient with usher syndrome type IIA- a case report

BackgroundUsher Syndrome is the commonest cause of inherited blindness and deafness. The condition is clinically and genetically heterogeneous, with no current treatment. We report a case carrying novel biallelic variants in USH2A causing progressive early adolescent onset visual and hearing impairment consistent with Usher Syndrome Type IIA.Case presentationOur patient presented at age 13 with progressive visual field loss and hearing loss, associated with early onset of cataract in her 40s requiring lens extraction. Now 52 years old, latest best corrected visual acuity (BCVA) stands at Logmar Right Eye (RE) 0.8 and Left Eye (LE) 0.2, with significantly constricted visual fields bilaterally. She was registered partially sighted age 46. Clinical and molecular genetic assessment of the proband was consistent with a diagnosis of Usher Syndrome Type IIA. Genetic testing identified two novel USH2A variants, resulting in the premature termination codon p.Leu30Ter and a missense mutation p.Cys3251Tyr. Segregation analysis confirmed that these variants were biallelic in the affected case. Comprehensive in silico analysis confirmed that these mutations are the probable cause of Usher Syndrome Type IIA in this individual.ConclusionsThe identification of novel mutations in USH2A increases the spectrum of genetic variations that lead to Usher Syndrome, aiding genetic diagnosis, assessment of patient prognosis, and emphasising the importance of genetic testing to identify new mutations in patients with undiagnosed progressive visual loss.

Spectral-Domain Optical Coherence Tomography Analysis in Syndromic and Nonsyndromic Forms of Retinitis Pigmentosa due to USH2A Genetic Variants

Introduction: This study aimed to analyze macular structure by using spectral-domain optical coherence tomography (SD-OCT) in a cohort of patients affected by autosomal recessive retinitis pigmentosa and Usher syndrome, due to genetic variants in USH2A gene, and to correlate optical coherence tomography (OCT) parameters with functional and genetic data. Methods: The subjects of this study were 92 patients, 46 syndromic (Usher syndrome type IIa [Ush2]) and 46 nonsyndromic (autosomal recessive RP [arRP]), with clinical and genetic diagnosis of USH2A-related retinal dystrophy, who underwent a complete ophthalmic examination and spectral-domain OCT analysis. The study focused on evaluating the differences between the 2 groups in the following parameters: best-corrected visual acuity (BCVA), ellipsoid zone (EZ) width, presence of epiretinal membrane (ERM), and cystic macular lesions (CMLs). Variants in USH2A gene were divided into 3 categories, according to the expected impact (low/high) at protein level of the different variants on each allele. Results: BCVA and EZ width were significantly lower in Ush2 than in arRP patients (p < 0.0001 and p = 0.001). ERM was detected in 34.8% (16/46) of arRP patients and in 65.2% (30/46) of Ush2 patients (p = 0.003). CML was detected in 17.4% (8/46) of arRP patients and 30.4% (14/46) of Ush2 patients (p = 0.14). The allelic distribution was statistically different (p = 0.0003) by dividing the 2 diseases: for Ush2 patients it was 45.7% (high/high), 39.1% (low/high) and 15.2% (low/low); for arRP patients it was 8.7% (high/high), 56.5% (low/high), and 34.8% (low/low). The severity class of the variants significantly affected visual acuity and EZ width parameters (p = 0.004 and p = 0.002, respectively). Conclusion: Retinal disease, as evaluated by means of SD-OCT, shows more advanced degeneration signs in the syndromic than the nonsyndromic form of retinal dystrophy related to USH2A gene. Variant types and allelic profiles are determining factors for the onset of syndromic features. However, since the 3 allelic profiles can be found in both Usher and RP patients, other factors must necessarily play a determining role.

This issue of ACTA

This issue of ACTA

Novel compound heterozygous nonsense variants, p.L150* and p.Y3565*, of the USH2A gene in a Chinese pedigree are associated with Usher syndrome typeIIA.

Usher syndrome refers to a group of genetically and clinically heterogeneous autosomal recessive diseases with retinitis pigmentosa (RP) and hearing deficiencies. The association between Usher syndrome-causative genes and resultant Usher syndrome phenotypes in patients are highly variable. In the present study, a Chinese family with Usher syndrome was recruited, and targeted next-generation sequencing, Sanger sequencing and segregation analysis were performed. The expression profiles and functional effects of the pathogenic variants of USH2A identified were analyzed. Novel nonsense compound heterozygous variants, c.T449G (p.L150*) and c.T10695A (p.Y3565*), were identified in the USH2A gene, which showed co-segregation with the disease phenotype causing Usher syndrome type IIA in the recruited Chinese pedigree. The p.L150* variant was predicted to produce a truncated protein which lacked almost all the functional domains of USH2A, whereas the p.Y3565* variant is located in one of the fibronectin type 3 domains, resulting in the loss of several fibronectin type 3 domains at the C-terminus of USH2A by producing the truncated protein. It was shown that Ush2a mRNA expression levels were higher in the retina compared with those in the eye tissues (lens, sclera and cornea), uterus, ovary, breast, testis, spleen, kidney, liver, intestine, brain, skeletal muscle and blood. Additionally, the protein structure was shown to be highly conserved by comparing Homo sapiens USH2A to eight other species. To the best of our knowledge, the present study is the first to identify two novel pathogenic variants, c.T449G (p.L150*) and c.T10695A (p.Y3565*), in the USH2A gene in a patient with Usher syndrome type IIA, thereby expanding the known spectrums of USH2A causative mutations. The present discovery may assist in understanding the molecular pathogenesis underlying the development of RP and Usher syndrome type IIA, and in the development of diagnostic, therapeutic and genetic counseling strategies in patients with Usher syndrome type IIA disease.

USH2A variants in Chinese patients with Usher syndrome type II and non-syndromic retinitis pigmentosa

AimsTo reveal the Usher syndrome type IIA (USH2A) gene variant profile in a large cohort of Chinese patients with non-syndromic retinitis pigmentosa (RP) or Usher syndrome type II (USH2) and...

A case of Usher syndrome type IIA caused by a rare USH2A homozygous frameshift variant with maternal uniparental disomy (UPD) in a Chinese family

Usher syndrome encompasses a group of genetically and clinically heterogeneous autosomal recessive disorders with hearing deficiencies and retinitis pigmentosa. The mechanisms underlying the Usher syndrome are highly variable. In the present study, a Chinese family with Usher syndrome was recruited. Whole exome sequencing (WES), Sanger sequencing, homozygosity mapping, short tandem repeat (STR) analysis and segregation analysis were performed. Functional domains of the pathogenic variant for USH2A were analysed. We identified a homozygous frameshift variant c.99_100insT (p.Arg34Serfs*41) in the USH2A gene in the proband that showed discordant segregation in the father. Further homozygosity mapping and STR analysis identified an unusual homozygous variant of proband that originated from maternal uniparental disomy (UPD). The p.Arg34Serfs*41 variant produced a predicted truncated protein that removes all functional domains of USH2A. The variant was not included in the 1000 Human Genomes Project database, ExAC database, HGMD or gnomAD database, but was included in the ClinVar databases as pathogenic. Although USH2A is an autosomal recessive disease, the effects of UPD should be informed in genetic counselling since the recurrence risk of an affected child is greatly reduced when the disease is due to the UPD mechanism. To test potential patients, WES, combined with STR analysis and homozygosity mapping, provides an accurate and useful strategy for genetic diagnosis. In summary, our discoveries can help further the understanding of the molecular pathogenesis of Usher syndrome type IIA to advance the prevention, diagnosis and therapy for this disorder.

Establishing Genotype-phenotype Correlation in USH2A-related Disorders to Personalize Audiological Surveillance and Rehabilitation.

USH2A-related disorders are characterised by genetic and phenotypic heterogeneity, and are associated with a spectrum of sensory deficits, ranging from deaf blindness to blindness with normal hearing. It has been previously proposed that the presence of specific USH2A alleles can be predictive of unaffected hearing. This study reports the clinical and genetic findings in a group of patients with USH2A-related disease and evaluates the validity of the allelic hierarchy model. USH2A variants from 27 adults with syndromic and nonsyndromic USH2A-related disease were analyzed according to a previously reported model of allelic hierarchy. The analysis was replicated on genotype-phenotype correlation information from 197 individuals previously reported in 2 external datasets. Genotype-phenotype correlations in USH2A-related disease. A valid allelic hierarchy model was observed in 93% of individuals with nonsyndromic USH2A-retinopathy (n = 14/15) and in 100% of patients with classic Usher syndrome type IIa (n = 8/8). Furthermore, when two large external cohorts of cases were combined, the allelic hierarchy model was valid across 85.7% (n = 78/91) of individuals with nonsyndromic USH2A-retinopathy and 95% (n = 123/129) of individuals with classic Usher syndrome type II (p = 0.012, χ test). Notably, analysis of all three patient datasets revealed that USH2A protein truncating variants were reported most frequently in individuals with hearing loss. Genetic testing results in individuals suspected to have an USH2A-related disorder have the potential to facilitate personalized audiological surveillance and rehabilitation pathways.

Cochlear Implantation in Patients With Usher Syndrome Type IIa Increases Performance and Quality of Life.

Usher syndrome type IIa (USH2a) is characterized by congenital moderate to severe hearing impairment and retinitis pigmentosa. Hearing rehabilitation starts in early childhood with the application of hearing aids. In some patients with USH2a, severe progression of hearing impairment leads to insufficient speech intelligibility with hearing aids and issues with adequate communication and safety. Cochlear implantation (CI) is the next step in rehabilitation of such patients. This study evaluates the performance and benefit of CI in patients with USH2a. Retrospective case-control study to evaluate the performance and benefit of CI in 16 postlingually deaf adults (eight patients with USH2a and eight matched controls). Performance and benefit were evaluated by a speech intelligibility test and three quality-of-life questionnaires. Patients with USH2a with a mean age of 59 years at implantation exhibited good performance after CI. The phoneme scores improved significantly from 41 to 87% in patients with USH2a (p = 0.02) and from 30 to 86% in the control group (p = 0.001). The results of the questionnaire survey demonstrated a clear benefit from CI. There were no differences in performance or benefit between patients with USH2a and control patients before and after CI. CI increases speech intelligibility and improves quality of life in patients with USH2a.

Hearing aid fitting for visual and hearing impaired patients with Usher syndrome type IIa.

ObjectivesUsher syndrome is the leading cause of hereditary deaf‐blindness. Most patients with Usher syndrome type IIa start using hearing aids from a young age. A serious complaint refers to interference between sound localisation abilities and adaptive sound processing (compression), as present in today's hearing aids. The aim of this study was to investigate the effect of advanced signal processing on binaural hearing, including sound localisation.Design and participantsIn this prospective study, patients were fitted with hearing aids with a nonlinear (compression) and linear amplification programs. Data logging was used to objectively evaluate the use of either program. Performance was evaluated with a speech‐in‐noise test, a sound localisation test and two questionnaires focussing on self‐reported benefit.ResultsData logging confirmed that the reported use of hearing aids was high. The linear program was used significantly more often (average use: 77%) than the nonlinear program (average use: 17%). The results for speech intelligibility in noise and sound localisation did not show a significant difference between type of amplification. However, the self‐reported outcomes showed higher scores on ‘ease of communication’ and overall benefit, and significant lower scores on disability for the new hearing aids when compared to their previous hearing aids with compression amplification.ConclusionsPatients with Usher syndrome type IIa prefer a linear amplification over nonlinear amplification when fitted with novel hearing aids. Apart from a significantly higher logged use, no difference in speech in noise and sound localisation was observed between linear and nonlinear amplification with the currently used tests. Further research is needed to evaluate the reasons behind the preference for the linear settings.

A combination of two truncating mutations in USH2A causes more severe and progressive hearing impairment in Usher syndrome type IIa

ObjectivesUsher syndrome is an inherited disorder that is characterized by hearing impairment (HI), retinitis pigmentosa, and in some cases vestibular dysfunction. Usher syndrome type IIa is caused by mutations in USH2A. HI in these patients is highly heterogeneous and the present study evaluates the effects of different types of USH2A mutations on the audiometric phenotype. Data from two large centres of expertise on Usher Syndrome in the Netherlands and Sweden were combined in order to create a large combined sample of patients to identify possible genotype-phenotype correlations. DesignA retrospective study on HI in 110 patients (65 Dutch and 45 Swedish) genetically diagnosed with Usher syndrome type IIa. We used methods especially designed for characterizing and testing differences in audiological phenotype between patient subgroups. These methods included Age Related Typical Audiograms (ARTA) and a method to evaluate the difference in the degree of HI developed throughout life between subgroups. ResultsCross-sectional linear regression analysis of last-visit audiograms for the best hearing ear demonstrated a gradual decline of hearing over decades. The congenital level of HI was in the range of 16–33 dB at 0.25–0.5 kHz, and in the range of 51–60 dB at 1–8 kHz. The annual threshold deterioration was in the range of 0.4–0.5 dB/year at 0.25–2 kHz and in the range of 0.7–0.8 dB/year at 4–8 kHz. Patients with two truncating mutations, including homozygotes for the common c.2299delG mutation, developed significantly more severe HI throughout life than patients with one truncating mutation combined with one nontruncating mutation, and patients with two nontruncating mutations. ConclusionsThe results have direct implications for patient counselling in terms of prognosis of hearing and may serve as baseline measures for future (genetic) therapeutic interventions.

Visual Prognosis in USH2A-Associated Retinitis Pigmentosa Is Worse for Patients with Usher Syndrome Type IIa Than for Those with Nonsyndromic Retinitis Pigmentosa

USH2A mutations are an important cause of retinitis pigmentosa (RP) with or without congenital sensorineural hearing impairment. We studied genotype-phenotype correlations and compared visual prognosis in Usher syndrome type IIa and nonsyndromic RP. Clinic-based, longitudinal, multicenter study. Consecutive patients with Usher syndrome type IIa (n= 152) and nonsyndromic RP (n= 73) resulting from USH2A mutations from ophthalmogenetic clinics in the Netherlands and Belgium. Data on clinical characteristics, visual acuity, visual field measurements, retinal imaging, and electrophysiologic features were extracted from medical charts over a mean follow-up of 9 years. Cumulative lifetime risks of low vision and blindness were estimated using Kaplan-Meier survival analysis. Low vision and blindness. Participant groups had similar distributions of gender (48% vs. 45% males in Usher syndrome type IIa vs. nonsydromic RP; P= 0.8), ethnicity (97% vs. 99% European; P= 0.3), and median follow-up time (6.5years vs. 3 years; P=0.3). Usher syndrome type IIa patients demonstrated symptoms at a younger age (median age, 15 years vs. 25 years; P < 0.001), were diagnosed earlier (median age, 26 years vs. 36.5 years; P < 0.001), and became visually impaired 13 years earlier (median age, 41 years vs. 54 years; P < 0.001) based on VF and 18 years earlier based on VA (median age, 54 years vs. 72 years; P < 0.001) than nonsyndromic RP patients. The presence of 2 truncating mutations in USH2A was associated mostly with the syndromic phenotype, whereas other combinations were present in both groups. We found novel variants in Usher syndrome type IIa (25%) and nonsyndromic RP (19%): 29 missense mutations, 10 indels, 14 nonsense mutations, 9 frameshift mutations, and 5 splice-site mutations. Most patients with USH2A-associated RP have severe visual impairment by age 50. However, those with Usher syndrome type IIa have an earlier decline of visual function and a higher cumulative risk of visualimpairment than those without nonsyndromic RP. Complete loss of function of the USH2A protein predisposes toUsher syndrome type IIa, but remnant protein function can lead to RP with or without hearing loss.

Audiometric Characteristics of a Dutch DFNA10 Family With Mid-Frequency Hearing Impairment.

Mutations in EYA4 can cause nonsyndromic autosomal dominant sensorineural hearing impairment (DFNA10) or a syndromic variant with hearing impairment and dilated cardiomyopathy. A mutation in EYA4 was found in a Dutch family, causing DFNA10. This study is focused on characterizing the hearing impairment in this family. Whole exome sequencing was performed in the proband. In addition, peripheral blood samples were collected from 23 family members, and segregation analyses were performed. All participants underwent otorhinolaryngological examinations and pure-tone audiometry, and 12 participants underwent speech audiometry. In addition, an extended set of audiometric measurements was performed in five family members to evaluate the functional status of the cochlea. Vestibular testing was performed in three family members. Two individuals underwent echocardiography to evaluate the nonsyndromic phenotype. The authors present a Dutch family with a truncating mutation in EYA4 causing a mid-frequency hearing impairment. This mutation (c.464del) leads to a frameshift and a premature stop codon (p.Pro155fsX). This mutation is the most N-terminal mutation in EYA4 found to date. In addition, a missense mutation, predicted to be deleterious, was found in EYA4 in two family members. Echocardiography in two family members revealed no signs of dilated cardiomyopathy. Results of caloric and velocity step tests in three family members showed no abnormalities. Hearing impairment was found to be symmetric and progressive, beginning as a mid-frequency hearing impairment in childhood and developing into a high-frequency, moderate hearing impairment later in life. Furthermore, an extended set of audiometric measurements was performed in five family members. The results were comparable to those obtained in patients with other sensory types of hearing impairments, such as patients with Usher syndrome type IIA and presbyacusis, and not to those obtained in patients with (cochlear) conductive types of hearing impairment, such as DFNA8/12 and DFNA13. The mid-frequency hearing impairment in the present family was found to be symmetric and progressive, with a predominantly childhood onset. The results of psychophysical measurements revealed similarities to other conditions involving a sensory type of hearing impairment, such as Usher syndrome type IIA and presbyacusis. The study results suggest that EYA4 is expressed in the sensory cells of the cochlea. This phenotypic description will facilitate counseling for hearing impairment in DFNA10 patients.

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.

Spectrum of USH2A mutations in Scandinavian patients with Usher syndrome type II

Usher syndrome type II (USH2) is an autosomal recessive disorder, characterised by moderate to severe high-frequency hearing impairment, normal balance function and progressive visual impairment due to retinitis pigmentosa. Usher syndrome type IIa, the most common subtype, is defined by mutations in the USH2A gene encoding a short and a recently discovered long usherin isoform comprising 21 and 73 exons, respectively. More than 120 different disease-causing mutations have been reported, however, most of the previous reports concern mutations restricted to exons 1-21 of the USH2A gene. To explore the spectrum of USH2A disease-causing mutations among Scandinavian USH2 cases, patients from 118 unrelated families of which 27 previously had been found to carry mutations in exons 1-21 were subjected to extensive DNA sequence analysis of the full size USH2A gene. Altogether, 122 USH2A DNA sequence alterations were identified of which 57 were predicted to be disease-causing, 7 were considered to be of uncertain pathogenicity and 58 were predicted to be benign variants. Of 36 novel pathogenic USH2A mutations 31 were located in exons 22-73, specific to the long isoform. USH2A mutations were identified in 89/118 (75.4%) families. In 79/89 (88.8%) of these families two pathogenic mutations were identified whereas in 10/89 (11.2%) families the second mutation remained unidentified. In 5/118 (4.2%) families the USH phenotype could be explained by mutations in the USH3A gene. The results presented here provide a comprehensive picture of the genetic aetiology of Usher syndrome type IIA in Scandinavia as it is known to date.

Usherin is required for maintenance of retinal photoreceptors and normal development of cochlear hair cells

Usher syndrome type IIA (USH2A), characterized by progressive photoreceptor degeneration and congenital moderate hearing loss, is the most common subtype of Usher syndrome. In this article, we show that the USH2A protein, also known as usherin, is an exceptionally large ( approximately 600-kDa) matrix protein expressed specifically in retinal photoreceptors and developing cochlear hair cells. In mammalian photoreceptors, usherin is localized to a spatially restricted membrane microdomain at the apical inner segment recess that wraps around the connecting cilia, corresponding to the periciliary ridge complex described for amphibian photoreceptors. In sensory hair cells of the cochlea, it is associated transiently with the hair bundles during postnatal development. Targeted disruption of the Ush2a gene in mice leads to progressive photoreceptor degeneration and a moderate but nonprogressive hearing impairment, mimicking the visual and hearing deficits in USH2A patients. These data suggest that usherin is required for the long-term maintenance of retinal photoreceptors and for the development of cochlear hair cells. We propose a model in which usherin in photoreceptors is tethered via its C terminus to the plasma membrane and its large extracellular domain projecting into the periciliary matrix, where they may interact with the connecting cilium to fulfill important structural or signaling roles.

Usherin, the defective protein in Usher syndrome type IIA, is likely to be a component of interstereocilia ankle links in the inner ear sensory cells

Usher syndrome type IIa (USH2A) combines moderate to severe congenital hearing impairment and retinitis pigmentosa. It is the most common genetic form of USH. USH2A encodes usherin, which was previously defined as a basement membrane protein. A much larger USH2A transcript predicted to encode a transmembrane (TM) isoform was recently reported. Here, we address the role of TM usherin in the inner ear. Analysis of the usherin alternative transcripts in the murine inner ear revealed the existence of several predicted TM usherin isoforms with modular ectodomains of different lengths. In addition, we identified in the usherin cytoplasmic region a predicted 24 amino acid peptide, derived from a newly defined exon that is predominantly expressed in the inner ear but not in the retina. In mouse and rat inner ears, we show that TM usherin is present at the base of the differentiating stereocilia, which make up the mechanosensitive hair bundles receptive to sound. The usherin immunolabeling is transient in the hair bundles of cochlear hair cells (HCs), but persists in mature hair bundles of vestibular HCs. Several lines of evidence support the involvement of TM usherin in the composition of the ankle links, a subset of filamentous lateral links connecting stereocilia at the base. By co-immunoprecipitation and in vitro binding assays, we establish that the usherin cytodomain can bind to whirlin and harmonin, two PDZ domain-containing proteins that are defective in genetic forms of isolated deafness and USH type I, respectively. These PDZ proteins are suitable to provide the anchoring of interstereocilia lateral links to the F-actin core of stereocilia. Our results strongly suggest that congenital deafness in USH type I and type II shares similar pathogenic mechanisms, i.e. the disruption of hair bundle links-mediated adhesion forces that are essential for the proper organization of growing hair bundles.

Evidence for Functional Importance of Usherin/Fibronectin Interactions in Retinal Basement Membranes

Usher syndrome is a genetically heterogeneous disorder characterized by hearing loss with retinitis pigmentosa. Usher syndrome type IIa is the most common of the Usher syndromes, accounting for over half of all cases. The gene encodes a 180 kDa basement membrane glycoprotein called usherin. Here, we demonstrated a specific interaction between usherin and fibronectin in retinal basement membranes. This interaction was confirmed using biochemical, biophysical, and genetic approaches. Surface plasmon resonance assay confirmed that fibronectin binding to usherin is of high affinity and 1:1 stoichiometry. Using a fusion peptide-based co-immunoprecipitation approach, we show that binding to fibronectin occurs at the LE domain of usherin. Recombinant LE domain-specific peptides were engineered that contained single amino acid substitutions corresponding to missense mutations found in humans with Usher syndrome type IIa. Only mutations in loop d of the LE domain abolished the ability of the LE domain to co-immunoprecipitate fibronectin.

Immunohistochemistry and reverse transcriptase-polymerase chain reaction as methods for diagnostic determination of usher syndrome type IIa.

Patients having null mutations in the USH2A gene do not produce usherin and therefore are not positive for immunohistochemical staining of the usherin protein. Thus, immunostaining for usherin can serve as a reliable diagnostic tool for Usher syndrome type IIa. Prospective. Immunohistochemical staining for usherin was carried out in basement membrane of minor salivary gland tissue from subjects with confirmed Usher syndrome type IIa and from archival minor salivary gland tissue from patients without Usher syndrome as control samples. Quantitative usherin messenger RNA analysis was performed using minor salivary gland biopsy tissue. Five subjects with Usher syndrome type IIa had no immunostaining in minor salivary gland tissue, whereas control minor salivary gland tissue did stain with usherin antibody. No usherin RNA was detected in biopsy specimens from patients with confirmed Usher syndrome IIa. The feasibility was confirmed of diagnosing Usher syndrome type IIa using purified usherin antibody in subjects having two null USH2A mutations.

Identification of 51 Novel Exons of the Usher Syndrome Type 2A (USH2A) Gene That Encode Multiple Conserved Functional Domains and That Are Mutated in Patients with Usher Syndrome Type II

The USH2A gene is mutated in patients with Usher syndrome type IIa, which is the most common subtype of Usher syndrome and is characterized by hearing loss and retinitis pigmentosa. Since mutation analysis by DNA sequencing of exons 1-21 revealed only ~63% of the expected USH2A mutations, we searched for so-far-uncharacterized exons of the gene. We identified 51 novel exons at the 3' end of the gene, and we obtained indications for alternative splicing. The putative protein encoded by the longest open reading frame harbors, in addition to the known functional domains, two laminin G and 28 fibronectin type III repeats, as well as a transmembrane region followed by an intracellular domain with a PDZ-binding domain at its C-terminal end. Semiquantitative expression profile analysis suggested a low level of expression for both the long and the short isoform(s) and partial overlap in spatial and temporal expression patterns. Mutation analysis in 12 unrelated patients with Usher syndrome, each with one mutation in exons 1-21, revealed three different truncating mutations in four patients and two missense mutations in one patient. The presence of pathogenic mutations in the novel exons indicates that at least one of the putative long isoforms of the USH2A protein plays a role in both hearing and vision.