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.

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.

Retinal disease course in Usher syndrome 1B due to MYO7A mutations.

PURPOSE. To determine the disease course in Usher syndrome type IB (USH1B) caused by myosin 7A (MYO7A) gene mutations. METHODS. USH1B patients (n = 33, ages 2-61) representing 25 different families were studied by ocular examination, kinetic and chromatic static perimetry, dark adaptometry, and optical coherence tomography (OCT). Consequences of the mutant alleles were predicted. RESULTS. All MYO7A patients had severely abnormal ERGs, but kinetic fields revealed regional patterns of visual loss that suggested a disease sequence. Rod-mediated vision could be lost to different degrees in the first decades of life. Cone vision followed a more predictable and slower decline. Central vision ranged from normal to reduced in the first four decades of life and thereafter was severely abnormal. Dark adaptation kinetics was normal. Photoreceptor layer thickness in a wide region of central retina could differ dramatically between patients of comparable ages; and there were examples of severe losses in childhood as well as relative preservation in patients in the third decade of life. Comparisons were made between the mutant alleles in mild versus more severe phenotypes. CONCLUSIONS. A disease sequence in USH1B leads from generally full but impaired visual fields to residual small central islands. At most disease stages, there was preserved temporal peripheral field, a potential target for early phase clinical trials of gene therapy. From data comparing patients' rod disease in this cohort, the authors speculate that null MYO7A alleles could be associated with milder dysfunction and fewer photoreceptor structural losses at ages when other genotypes show more severe phenotypes.

Hearing loss disorders associated with renal disease.

There are several syndromes in which both hearing and renal function are impaired. The two best known are branchio-oto-renal (BOR) syndrome and Alport syndrome. These are reviewed along with several other rarer syndromes. BOR is especially important since it is likely to be first recognized by the otolaryngologist because of the hearing and branchial anomalies. It is important for the practicing otolaryngologist to recognize these disorders and to ensure that renal problems are being treated. In addition, the syndromes discussed here are all hereditary and referral to a clinical geneticist may be helpful to the individual and family.

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.

Phenotypes in defined genotypes including siblings with Usher syndrome.

OBJECTIVE: To characterize visual function in defined genotypes including siblings with Usher syndrome. METHODS: Thirteen patients with phenotypically different subtypes of Usher syndrome, including 3 families with affected siblings, were selected. Genetic analysis and ophthalmological examinations including visual fields, full-field electroretinography (ERG), multifocal electroretinography (mf ERG), and optical coherence tomography (OCT) were assessed. The patients' degree of visual handicap was evaluated by a questionnaire (ADL). RESULTS: Twelve of thirteen patients were genotyped as Usher 1B, 1D, 1F, 2A, 2C or 3A. In 12 of 13 patients examined with ERG the 30 Hz flickering light response revealed remaining cone function. In 3 of the patients with Usher type 1 mf ERG demonstrated a specific pattern, with a sharp distinction between the area with reduced function and the central area with remaining macular function and normal peak time. OCT demonstrated loss of foveal depression with distortion of the foveal architecture in the macula in all patients. The foveal thickness ranged from 159 to 384 µm and was not correlated to retinal function. Three siblings shared the same mutation for Usher 2C but in contrast to previous reports regarding this genotype, 1 of them diverged in phenotype with substantially normal visual fields, almost normal OCT and mf ERG findings, and only moderately reduced rod and cone function according to ERG. CONCLUSIONS: Evaluation of visual function comprising both the severity of the rod cone degeneration and the function in the macular region confirm phenotypical heterogeneity within siblings and between different genotypes of Usher syndrome.

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 the first MyTH4 domain of MYO15A are a common cause of DFNB3 hearing loss.

OBJECTIVES: To use clinical and genetic analyses to determine the mutation causing autosomal recessive nonsyndromic hearing loss (ARNSHL) segregating in two consanguineous Iranian families. STUDY DESIGN: Family study. METHODS: Members of each family received otologic and audiometric examination for the type and extent of hearing loss. Linkage mapping using Affymetrix 50K GeneChips and short tandem repeat (STRP) analysis localized the hearing loss in both families to the DFNB3 locus. Direct sequencing of the MYO15A gene was completed on affected members of both families. RESULTS: Family L-3165 segregated a novel homozygous missense mutation (c.6371G>A) that results in a p.R2124Q amino acid substitution in the myosin XVa protein, while family L-896 segregated a novel homozygous missense (c.6555C>T) mutation resulting in a p.P2073S amino acid change. CONCLUSIONS: These are the first MYO15A mutations reported to cause DFNB3 sensorineural hearing loss in the Iranian population. Like other mutations located in the myosin tail homology 4 (MyTH4) domain, the p.R2124Q and p.P2073S mutations are predicted to disrupt the function of the myosin XVa protein, which is integral to the mechanosensory activity of hair cells in the inner ear.

Disease boundaries in the retina of patients with Usher syndrome caused by MYO7A gene mutations.

PURPOSE: To study retinal microstructure in Usher Syndrome type 1B (USH1B) caused by MYO7A mutations as a prelude to treatment initiatives. METHODS: Patients with MYO7A-USH1B (n=17; ages 5-61) were studied with optical coherence tomography. Retinal laminae across horizontal and vertical meridians were measured. Colocalized visual sensitivity was measured with automated perimetry to enable comparisons of function and structure in the transition zones. RESULTS: Laminar architecture of the central retina in MYO7A-USH1B ranged from normal to severely abnormal. Within the transition zone between normal and abnormal retina, the first detectable abnormality was an increase in prominence of the OLM (outer limiting membrane). Declining ONL thickness was accompanied by increased thickness of the OPL and normal or increased INL. Undetectable ONL and OPL and hyperthick INL were features of severe laminopathy at further eccentricities into the transition zone. Visual sensitivity in the transition zone declined with the decrease in ONL thickness. CONCLUSIONS: Patients with MYO7A-USH1B can have regions of structurally and functionally normal retina with definable transitions to severe laminopathy and visual loss. The earliest detectable structural markers of disease may represent Müller glial cell response to photoreceptor stress and apoptosis. Visual losses were predictably related to a decline in ONL thickness. The prospect of focal treatment of MYO7A-USH1B, such as subretinal gene therapy, prompts the need to identify retinal locations that warrant consideration for treatment in early phase trials. The transition zones are candidate sites for treatment, and laminar architecture and visual sensitivity are possible outcomes to assess safety and efficacy.

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.

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.

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.

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.

Transcription factor SIX5 is mutated in patients with branchio-oto-renal syndrome.

Branchio-oto-renal syndrome (BOR) is an autosomal dominant developmental disorder characterized by the association of branchial arch defects, hearing loss, and renal anomalies. Mutations in EYA1 are known to cause BOR. More recently, mutations in SIX1, which interacts with EYA1, were identified as an additional cause of BOR. A second member of the SIX family of proteins, unc-39 (SIX5), has also been reported to directly interact with eya-1 in Caenorhabditis elegans. We hypothesized that this interaction would be conserved in humans and that interactors of EYA1 represent good candidate genes for BOR. We therefore screened a cohort of 95 patients with BOR for mutations in SIX5. Four different heterozygous missense mutations were identified in five individuals. Functional analyses of these mutations demonstrated that two mutations affect EYA1-SIX5 binding and the ability of SIX5 or the EYA1-SIX5 complex to activate gene transcription. We thereby identified heterozygous mutations in SIX5 as a novel cause of BOR.

Branchio-oto-renal syndrome.

Branchio-oto-renal syndrome, a phenotype consisting of hearing loss, auricular malformations, branchial arch remnants, and renal anomalies is now recognized as one of the more common forms of autosomal dominant syndromic hearing impairment. Three loci known to be associated with the BOR phenotype have been identified and two genes that act in a regulatory network have been cloned, EYA1 and SIX1. EYA1 and SIX1 are homologous to genes involved in Drosophila eye development, eyes absent gene (eya), and sine oculis (so), respectively. EYA1, a transcriptional co-activator has a conserved, 271-amino acid, C-terminal known as the Eya Domain (ED). SIX1 has two highly conserved domains; a homeodomain (HD) and a specific Six-domain (SD) whose products function as transcription factors with specific DNA-binding activity that are crucial for protein-protein interaction. To determine the molecular basis for the organ defects that occur in BOR syndrome, many studies have focused on the effects of mutations to EYA and effects of mutations of the EYA-SIX regulatory system. However, over 60% of BOR syndrome patients do not have known mutations in EYA1 and relatively little is known about mutations to SIX1. Further evaluation of SIX1 and its related target genes may provide a better understanding of the pathophysiology of BOR syndrome and offer greater clues to the disease mechanisms.

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.

Estimation of the frequency of occult mutations for an autosomal recessive disease in the presence of genetic heterogeneity: application to genetic hearing loss disorders.

The routine testing for pathologic mutation(s) in a patient's DNA has become the foundation of modern molecular genetic diagnosis. It is especially valuable when the phenotype shows genetic heterogeneity, and its importance will grow as treatments become genotype specific. However, the technology of mutation detection is imperfect and mutations are often missed. This can be especially troublesome when dealing with a recessive disorder where the combination of genetic heterogeneity and missed mutation creates an imprecision in the genotypic assessment of individuals who do not appear to have the expected complement of two pathologic mutations. This article describes a statistical approach to the estimation of the likelihood of a genetic diagnosis under these conditions. In addition to providing a means of testing for missed mutations, it also provides a method of estimating and testing for the presence of genetic heterogeneity in the absence of linkage data. Gene frequencies as well as estimates of sensitivity and specificity can be obtained as well. The test is applied to GJB2 recessive nonsyndromic deafness, Usher syndrome types Ib and IIa, and Pendred-enlarged vestibular aqueduct syndrome.

Disease expression in Usher syndrome caused by VLGR1 gene mutation (USH2C) and comparison with USH2A phenotype.

PURPOSE: To investigate the retinal disease expression in USH2C, the subtype of Usher syndrome type 2 recently shown to be caused by mutation in the VLGR1 gene, and compare results with those from USH2A, a more common cause of Usher syndrome. METHODS: Three siblings with USH2C and 14 patients with USH2A were studied. Visual function was measured by kinetic perimetry, static chromatic perimetry, and electroretinography (ERG). Central retinal microstructure was studied with optical coherence tomography (OCT). RESULTS: The siblings with VLGR1 mutation showed abnormal photoreceptor-mediated function in all retinal regions, and there was greater rod than cone dysfunction. USH2A had a wider spectrum of disease expression and included patients with normal function in some retinal regions. When abnormalities were detected, there was more rod than cone dysfunction. Retinal microstructure in both USH2C and USH2A shared the abnormality of loss of outer nuclear layer thickness. Central retinal structure in both genotypes was complicated by cystic macular lesions. A coincidental finding in an USH2C patient was that oral intake of antihistamines was associated with temporary resolution of the macular cystic change. CONCLUSIONS: USH2C and USH2A manifest photoreceptor disease with rod- and cone-mediated visual losses and thinning of the outer nuclear layer. An orderly progression through disease stages was estimated from cross-sectional and limited longitudinal data. Intrafamilial and interfamilial variation in retinal severity in USH2A, however, suggests that genetic or nongenetic modifiers may be involved in the disease expression.

Genetic analysis of a four generation Indian family with Usher syndrome: a novel insertion mutation in MYO7A.

PURPOSE: Usher syndrome (USH) is a rare autosomal recessive disorder characterized by deafness and retinitis pigmentosa. The purpose of this study was to determine the genetic cause of USH in a four generation Indian family. METHODS: Peripheral blood samples were collected from individuals for genomic DNA isolation. To determine the linkage of this family to known USH loci, microsatellite markers were selected from the candidate regions of known loci and used to genotype the family. Exon specific intronic primers for the MYO7A gene were used to amplify DNA samples from one affected individual from the family. PCR products were subsequently sequenced to detect mutation. PCR-SSCP analysis was used to determine if the mutation segregated with the disease in the family and was not present in 50 control individuals. RESULTS: All affected individuals had a classic USH type I (USH1) phenotype which included deafness, vestibular dysfunction and retinitis pigmentosa. Pedigree analysis suggested an autosomal recessive mode of inheritance of USH in the family. Haplotype analysis suggested linkage of this family to the USH1B locus on chromosome 11q. DNA sequence analysis of the entire coding region of the MYO7A gene showed a novel insertion mutation c.2663_2664insA in a homozygous state in all affected individuals, resulting in truncation of MYO7A protein. CONCLUSIONS: This is the first study from India which reports a novel MYO7A insertion mutation in a four generation USH family. The mutation is predicted to produce a truncated MYO7A protein. With the novel mutation reported here, the total number of USH causing mutations in the MYO7A gene described to date reaches to 75.