Specificity of Monoclonal Antibodies to Factor VIII: C

Three monoclonal antibodies (42 IgG, 47 IgG, 56 IgG) towards factor-VIII: C (VIII :C) have been produced. In ELISA for VIII:C-antigen (VIII:CAg), 47 IgG showed higher affinity for VIII: CAg than 42 IgG and 56 IgG. In solid phase immunoiso-lation of iodinated VIII :C diluted in EDTA buffer, the three monoclonals, like human VIII: C inhibitors, bound the 77/80 kD-light chain of VIII: C. In the absence of EDTA, 56 IgG bound the heavy chain-light chain complex of VIII: C, while 47 IgG was only able to bind the light chain. When coupled on Sepharose, 56 IgG adsorbed coagulation active VIII :C, while 47 IgG was only able to adsorb coagulation inactive VIII: CAg. In coagulation assay 56 IgG inhibited with 20 BU/mg while 42 IgG and 47 IgG inhibited with 4 BU/mg. A mixture of 42 IgG and 56 IgG showed a synergistic effect and inhibited with 50 BU/mg total IgG. In radioimmunoassay a human VIII: C inhibitor was able to inhibit the VIII: C binding of 42 IgG and 56 IgG but not of 47 IgG. The monoclonals did not inhibit each other. On the contrary, 56 IgG increased the binding of 42 IgG to VIII: C.

Mutation of the nuclear lamin gene LMNB2 in progressive myoclonus epilepsy with early ataxia

We studied a consanguineous Palestinian Arab family segregating an autosomal recessive progressive myoclonus epilepsy (PME) with early ataxia. PME is a rare, often fatal syndrome, initially responsive to antiepileptic drugs which over time becomes refractory and can be associated with cognitive decline. Linkage analysis was performed and the disease locus narrowed to chromosome 19p13.3. Fourteen candidate genes were screened by conventional Sanger sequencing and in one, LMNB2, a novel homozygous missense mutation was identified that segregated with the PME in the family. Whole exome sequencing excluded other likely pathogenic coding variants in the linked interval. The p.His157Tyr mutation is located in an evolutionarily highly conserved region of the alpha-helical rod of the lamin B2 protein. In vitro assembly analysis of mutant lamin B2 protein revealed a distinct defect in the assembly of the highly ordered fibrous arrays typically formed by wild-type lamin B2. Our data suggests that disruption of the organisation of the nuclear lamina in neurons, perhaps through abnormal neuronal migration, causes the epilepsy and early ataxia syndrome and extends the aetiology of PMEs to include dysfunction in nuclear lamin proteins.

PRIMA1 mutation: a new cause of nocturnal frontal lobe epilepsy

Objective

Nocturnal frontal lobe epilepsy (NFLE) can be sporadic or autosomal dominant; some families have nicotinic acetylcholine receptor subunit mutations. We report a novel autosomal recessive phenotype in a single family and identify the causative gene.

Methods

Whole exome sequencing data was used to map the family, thereby narrowing exome search space, and then to identify the mutation.

Results

Linkage analysis using exome sequence data from two affected and two unaffected subjects showed homozygous linkage peaks on chromosomes 7, 8, 13, and 14 with maximum LOD scores between 1.5 and 1.93. Exome variant filtering under these peaks revealed that the affected siblings were homozygous for a novel splice site mutation (c.93+2T>C) in the PRIMA1 gene on chromosome 14. No additional PRIMA1 mutations were found in 300 other NFLE cases. The c.93+2T>C mutation was shown to lead to skipping of the first coding exon of the PRIMA1 mRNA using a minigene system.

Interpretation

PRIMA1 is a transmembrane protein that anchors acetylcholinesterase (AChE), an enzyme hydrolyzing acetycholine, to membrane rafts of neurons. PRiMA knockout mice have reduction of AChE and accumulation of acetylcholine at the synapse; our minigene analysis suggests that the c.93+2T>C mutation leads to knockout of PRIMA1. Mutations with gain of function effects in acetylcholine receptor subunits cause autosomal dominant NFLE. Thus, enhanced cholinergic responses are the likely cause of the severe NFLE and intellectual disability segregating in this family, representing the first recessive case to be reported and the first PRIMA1 mutation implicated in disease.

16p11.2 600 kb Duplications confer risk for typical and atypical Rolandic epilepsy

Rolandic epilepsy (RE) is the most common idiopathic focal childhood epilepsy. Its molecular basis is largely unknown and a complex genetic etiology is assumed in the majority of affected individuals. The present study tested whether six large recurrent copy number variants at 1q21, 15q11.2, 15q13.3, 16p11.2, 16p13.11 and 22q11.2 previously associated with neurodevelopmental disorders also increase risk of RE. Our association analyses revealed a significant excess of the 600 kb genomic duplication at the 16p11.2 locus (chr16: 29.5-30.1 Mb) in 393 unrelated patients with typical (n = 339) and atypical (ARE; n = 54) RE compared with the prevalence in 65,046 European population controls (5/393 cases versus 32/65,046 controls; Fisher's exact test P = 2.83 × 10(-6), odds ratio = 26.2, 95% confidence interval: 7.9-68.2). In contrast, the 16p11.2 duplication was not detected in 1738 European epilepsy patients with either temporal lobe epilepsy (n = 330) and genetic generalized epilepsies (n = 1408), suggesting a selective enrichment of the 16p11.2 duplication in idiopathic focal childhood epilepsies (Fisher's exact test P = 2.1 × 10(-4)). In a subsequent screen among children carrying the 16p11.2 600 kb rearrangement we identified three patients with RE-spectrum epilepsies in 117 duplication carriers (2.6%) but none in 202 carriers of the reciprocal deletion. Our results suggest that the 16p11.2 duplication represents a significant genetic risk factor for typical and atypical RE.

Eeyore: a novel mouse model of hereditary deafness

Animal models that recapitulate human disease are proving to be an invaluable tool in the identification of novel disease-associated genes. These models can improve our understanding of the complex genetic mechanisms involved in disease and provide a basis to guide therapeutic strategies to combat these conditions. We have identified a novel mouse model of non-syndromic sensorineural hearing loss with linkage to a region on chromosome 18. Eeyore mutant mice have early onset progressive hearing impairment and show abnormal structure of the sensory epithelium from as early as 4 weeks of age. Ultrastructural and histological analyses show irregular hair cell structure and degeneration of the sensory hair bundles in the cochlea. The identification of new genes involved in hearing is central to understanding the complex genetic pathways involved in the hearing process and the loci at which these pathways are interrupted in people with a genetic hearing loss. We therefore discuss possible candidate genes within the linkage region identified in eeyore that may underlie the deafness phenotype in these mice. Eeyore provides a new model of hereditary sensorineural deafness and will be an important tool in the search for novel deafness genes.

Epilepsy, hippocampal sclerosis and febrile seizures linked by common genetic variation around SCN1A

Epilepsy comprises several syndromes, amongst the most common being mesial temporal lobe epilepsy with hippocampal sclerosis. Seizures in mesial temporal lobe epilepsy with hippocampal sclerosis are typically drug-resistant, and mesial temporal lobe epilepsy with hippocampal sclerosis is frequently associated with important co-morbidities, mandating the search for better understanding and treatment. The cause of mesial temporal lobe epilepsy with hippocampal sclerosis is unknown, but there is an association with childhood febrile seizures. Several rarer epilepsies featuring febrile seizures are caused by mutations in SCN1A, which encodes a brain-expressed sodium channel subunit targeted by many anti-epileptic drugs. We undertook a genome-wide association study in 1018 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 7552 control subjects, with validation in an independent sample set comprising 959 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 3591 control subjects. To dissect out variants related to a history of febrile seizures, we tested cases with mesial temporal lobe epilepsy with hippocampal sclerosis with (overall n = 757) and without (overall n = 803) a history of febrile seizures. Meta-analysis revealed a genome-wide significant association for mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures at the sodium channel gene cluster on chromosome 2q24.3 [rs7587026, within an intron of the SCN1A gene, P = 3.36 × 10(-9), odds ratio (A) = 1.42, 95% confidence interval: 1.26-1.59]. In a cohort of 172 individuals with febrile seizures, who did not develop epilepsy during prospective follow-up to age 13 years, and 6456 controls, no association was found for rs7587026 and febrile seizures. These findings suggest SCN1A involvement in a common epilepsy syndrome, give new direction to biological understanding of mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures, and open avenues for investigation of prognostic factors and possible prevention of epilepsy in some children with febrile seizures.

Etiology and audiological outcomes at 3 years for 364 children in Australia

Hearing loss is an etiologically heterogeneous trait with differences in the age of onset, severity and site of lesion. It is caused by a combination of genetic and/or environmental factors. A longitudinal study to examine the efficacy of early intervention for improving child outcomes is ongoing in Australia. To determine the cause of hearing loss in these children we undertook molecular testing of perinatal “Guthrie” blood spots of children whose hearing loss was either detected via newborn hearing screening or detected later in infancy. We analyzed the GJB2 and SLC26A4 genes for the presence of mutations, screened for the mitochondrial DNA (mtDNA) A1555G mutation, and screened for congenital CMV infection in DNA isolated from dried newborn blood spots. Results were obtained from 364 children. We established etiology for 60% of children. One or two known GJB2 mutations were present in 82 children. Twenty-four children had one or two known SLC26A4 mutations. GJB2 or SLC26A4 changes with unknown consequences on hearing were found in 32 children. The A1555G mutation was found in one child, and CMV infection was detected in 28 children. Auditory neuropathy spectrum disorder was confirmed in 26 children whose DNA evaluations were negative. A secondary objective was to investigate the relationship between etiology and audiological outcomes over the first 3 years of life. Regression analysis was used to investigate the relationship between hearing levels and etiology. Data analysis does not support the existence of differential effects of etiology on degree of hearing loss or on progressiveness of hearing loss.

Characterization of a novel ENU-generated myosin VI mutant mouse strain with congenital deafness and vestibular dysfunction

Myosin VI (Myo6) is known to play an important role in the mammalian auditory and vestibular systems. We have identified a novel N-ethyl-N-nitrosourea mutagenised mouse strain, charlie, carrying an intronic Myo6 splice site mutation. This mutation (IVS5+5G > A) results in skipping of exon 5, and is predicted to cause a frameshift and premature termination of the protein. We detected essentially no Myo6 transcript in tissue from charlie homozygous mutant mice (Myo6(chl/chl)). Myo6(chl/chl) mice exhibit vestibular dysfunction and profound hearing impairment when first tested at four weeks of age. Analysis of vestibular and cochlear hair cells by scanning electron microscopy and immunohistochemistry revealed highly disorganised hair bundles with irregular orientation and kinocilium position at postnatal stage P2-P3. Within a few weeks, the majority of hair cell stereocilia are missing, or fused and elongated, and degeneration of the sensory epithelium occurs. This novel mouse strain will be an important resource in elucidating the role myosin VI plays in the mammalian auditory system, as well as its non-auditory functions.

Cathepsin F mutations cause Type B Kufs disease, an adult-onset neuronal ceroid lipofuscinosis

Kufs disease, an adult-onset neuronal ceroid lipofuscinosis, is challenging to diagnose and genetically heterogeneous. Mutations in CLN6 were recently identified in recessive Kufs disease presenting as progressive myoclonus epilepsy (Type A), whereas the molecular basis of cases presenting with dementia and motor features (Type B) is unknown. We performed genome-wide linkage mapping of two families with recessive Type B Kufs disease and identified a single region on chromosome 11 to which both families showed linkage. Exome sequencing of five samples from the two families identified homozygous and compound heterozygous missense mutations in CTSF within this linkage region. We subsequently sequenced CTSF in 22 unrelated individuals with suspected recessive Kufs disease, and identified an additional patient with compound heterozygous mutations. CTSF encodes cathepsin F, a lysosomal cysteine protease, dysfunction of which is a highly plausible candidate mechanism for a storage disorder like ceroid lipofuscinosis. In silico modeling suggested the missense mutations would alter protein structure and function. Moreover, re-examination of a previously published mouse knockout of Ctsf shows that it recapitulates the light and electron-microscopic pathological features of Kufs disease. Although CTSF mutations account for a minority of cases of type B Kufs, CTSF screening should be considered in cases with early-onset dementia and may avoid the need for invasive biopsies.

Inner ear morphology is perturbed in two novel mouse models of recessive deafness

Human MYO7A mutations can cause a variety of conditions involving the inner ear. These include dominant and recessive non-syndromic hearing loss and syndromic conditions such as Usher syndrome. Mouse models of deafness allow us to investigate functional pathways involved in normal and abnormal hearing processes. We present two novel mouse models with mutations in the Myo7a gene with distinct phenotypes. The mutation in Myo7a^I487N/I487N ewaso is located within the head motor domain of Myo7a. Mice exhibit a profound hearing loss and manifest behaviour associated with a vestibular defect. A mutation located in the linker region between the coiled-coil and the first MyTH4 domains of the protein is responsible in Myo7a^F947I/F947I dumbo. These mice show a less severe hearing loss than in Myo7a^I487N/I487N ewaso; their hearing loss threshold is elevated at 4 weeks old, and progressively worsens with age. These mice show no obvious signs of vestibular dysfunction, although scanning electron microscopy reveals a mild phenotype in vestibular stereocilia bundles. The Myo7a^F947I/F947I dumbo strain is therefore the first reported Myo7a mouse model without an overt vestibular phenotype; a possible model for human DFNB2 deafness. Understanding the molecular basis of these newly identified mutations will provide knowledge into the complex genetic pathways involved in the maintenance of hearing, and will provide insight into recessively inherited sensorineural hearing loss in humans.

Early onset absence epilepsy: 1 in 10 cases is caused by GLUT1 deficiency

Glucose transporter 1 (GLUT1) deficiency caused by mutations of SLC2A1 is an increasingly recognized cause of genetic generalized epilepsy. We previously reported that >10% (4 of 34) of a cohort with early onset absence epilepsy (EOAE) had GLUT1 deficiency. This study uses a new cohort of 55 patients with EOAE to confirm that finding. Patients with typical absence seizures beginning before 4 years of age were screened for solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) mutations or deletions. All had generalized spike-waves on electroencephalography (EEG). Those with tonic and/or atonic seizures were excluded. Mutations were found in 7 (13%) of 55 cases, including five missense mutations, an in-frame deletion leading to loss of a single amino acid, and a deletion spanning two exons. Over both studies, 11 (12%) of 89 probands with EOAE have GLUT1 deficiency. Given the major treatment and genetic counseling implications, this study confirms that SLC2A1 mutational analysis should be strongly considered in EOAE.

Identification of three novel hearing loss mouse strains with mutations in the Tmc1 gene

We report the identification of three new mouse models, baringo, nice, and stitch, with recessively inherited sensorineural deafness due to novel mutations in the transmembrane channel-like gene 1 (Tmc1). These strains were generated by N-ethyl-N-nitrosourea mutagenesis. DNA sequence analysis revealed changes in c.545A>G, c.1345T>C, and c.1661G>T, causing p.Y182C, p.Y449H, and p.W554L amino acid substitutions in baringo, nice, and stitch mutants, respectively. The mutations affect amino acid residues that are evolutionarily conserved across species. Similar to the previously reported Beethoven Tmc1 mutant, both p.Y182C and p.W554L are located outside a predicted transmembrane domain, whereas the p.Y449H mutation resides in the predicted transmembrane domain 4. Homozygous stitch-mutant mice have severe hearing loss at the age of 4 weeks and are deaf by the age of 8 weeks, whereas both baringo and nice mutants are profoundly deaf at the age of 4 weeks. None of the strains displays signs of vestibular dysfunction. Scanning electron microscopy revealed degeneration of outer hair cells in the basal region of baringo, nice, and stitch mutants. Immunolocalization studies revealed expression of TMC1 protein in the hair cells, spiral ganglion neurons, supporting cells, and stria ligament in the inner ear. Reduced levels of TMC1 protein were observed in the spiral ligament of mutants when compared with wild-type animals. These three allelic mutants provide valuable models for studying nonsyndromic recessive sensorineural hearing loss (DFNB7/11) in humans.

An ENU-induced mutation of Cdh23 causes congenital hearing loss, but no vestibular dysfunction, in mice

Mutations in the human cadherin 23 (CDH23) gene cause deafness, neurosensory, autosomal recessive 12 (DFNB12) nonsyndromic hearing loss or Usher syndrome, type 1D (characterized by hearing impairment, vestibular dysfunction, and visual impairment). Reported waltzer mouse strains each harbor a Cdh23-null mutation and present with hearing loss and vestibular dysfunction. Two additional Cdh23 mouse mutants, salsa and erlong, each carry a homozygous Cdh23 missense mutation and have progressive hearing loss. We report the identification of a novel mouse strain, jera, with inherited hearing loss caused by an N-ethyl-N-nitrosourea-induced c.7079T>A mutation in the Cdh23 gene. The mutation generates a missense change, p.V2360E, in Cdh23. Affected mice have profound sensorineural deafness, with no vestibular dysfunction. The p.V2360E mutation is semidominant because heterozygous mice have milder and more progressive hearing loss in advanced age. The mutation affects a highly conserved Ca(2+)-binding motif in extracellular domain 22, thought to be important for Cdh23 structure and dimerization. Molecular modeling suggests that the Cdh23(V2360E/V2360E) mutation alters the structural conformation of the protein and affects Ca(2+)-binding properties. Similar to salsa mice, but in contrast to waltzer mice, hair bundle development is normal in jera and hearing loss appears to be due to the loss of tip links. Thus, jera is a novel mouse model for DFNB12.

Identification of SLC26A4 mutations in patients with hearing loss and enlarged vestibular aqueduct using high-resolution melting curve analysis

Mutations in the SLC26A4 gene can cause both Pendred syndrome and nonsyndromic enlargement of the vestibular aqueduct, two conditions associated with sensorineural hearing loss. We analyzed the SLC26A4 gene in 44 hearing-impaired patients by nested polymerase chain reaction followed by high-resolution melt analysis. We also used this approach to scan for mutations in KCNJ10 and FOXI1, two genes reported to play a role in the pathogenesis of Pendred syndrome and enlarged vestibular aqueduct. Seven patients with known SLC26A4 mutations were included as controls. All previously identified mutations were detected by high-resolution melt analysis. Of the patients with no known mutations, we detected two SLC26A4 mutations in 5 probands (12%), one mutation in 9 probands (21%), and no mutations in 29 probands (67%). We identified two novel SLC26A4 mutations, p.T485M and p.F718S, and found no evidence of a digenic contribution of KCNJ10 and FOXI1 mutations.

Mutation of C20orf7 disrupts complex I assembly and causes lethal neonatal mitochondrial disease

Complex I (NADH:ubiquinone oxidoreductase) is the first and largest multimeric complex of the mitochondrial respiratory chain. Human complex I comprises seven subunits encoded by mitochondrial DNA and 38 nuclear-encoded subunits that are assembled together in a process that is only partially understood. To date, mutations causing complex I deficiency have been described in all 14 core subunits, five supernumerary subunits, and four assembly factors. We describe complex I deficiency caused by mutation of the putative complex I assembly factor C20orf7. A candidate region for a lethal neonatal form of complex I deficiency was identified by homozygosity mapping of an Egyptian family with one affected child and two affected pregnancies predicted by enzyme-based prenatal diagnosis. The region was confirmed by microcell-mediated chromosome transfer, and 11 candidate genes encoding potential mitochondrial proteins were sequenced. A homozygous missense mutation in C20orf7 segregated with disease in the family. We show that C20orf7 is peripherally associated with the matrix face of the mitochondrial inner membrane and that silencing its expression with RNAi decreases complex I activity. C20orf7 patient fibroblasts showed an almost complete absence of complex I holoenzyme and were defective at an early stage of complex I assembly, but in a manner distinct from the assembly defects caused by mutations in the assembly factor NDUFAF1. Our results indicate that C20orf7 is crucial in the assembly of complex I and that mutations in C20orf7 cause mitochondrial disease.

Keipert syndrome (Nasodigitoacoustic syndrome) is X-linked and maps to Xq22.2-Xq28

Keipert syndrome is a rare condition comprising sensorineural deafness associated with facial and digital abnormalities. To date, Keipert syndrome has been reported in six male patients including two sib pairs; however the genetic basis of Keipert syndrome is yet to be elucidated. We report on the diagnosis of Keipert syndrome in the nephew of the brothers in the first report of Keipert syndrome, with a pedigree consistent with X-linked recessive inheritance. Linkage analysis using microsatellite markers along the X-chromosome suggests that the gene for Keipert syndrome is located in the region Xq22.2-Xq28. We postulate the Keipert syndrome is caused by a novel gene at Xq22.2-Xq28.

A novel splice site mutation inEYA4 causes DFNA10 hearing loss

Nonsyndromic autosomal dominant sensorineural hearing loss (SNHL) at the DFNA10 locus was described in two families in 2001. Causative mutations that affect the EyaHR domain of the 'Eyes absent 4' (EYA4) protein were identified. We report on the clinical and genetic analyses of an Australian family with nonsyndromic SNHL. Screening of the EYA4 gene showed the novel polypyrimidine tract variation ca. 1,282-12T > A that introduces a new 3' splice acceptor site. This is the first report of a point mutation in EYA4 that is hypothesized to lead to aberrant pre-mRNA splicing and human disease. The DFNA10 family described is only the fourth to be identified. One individual presented with apparently the same phenotype as other affected members of the family. However, genotyping illustrated that he did not share the DFNA10 disease haplotype. Detailed clinical investigation showed differences in the onset and severity of his hearing loss and thus he is presumed to represent a phenocopy, perhaps resulting from long-term exposure to loud noise.

Gene expression profiling analysis of the inner ear

Recent developments in molecular genetics, including progress in the human genome project, have allowed identification of genes at an unprecedented rate. To date gene expression profiling studies have focused on identifying transcripts that are specifically or preferentially enriched within the inner ear on the assumption that they are more likely to be important for auditory and vestibular function. It is now apparent that some genes preferentially expressed in the cochleo-vestibular system are not crucial for hearing or balance or their functions are compensated for by other genes. In addition, transcripts expressed at low abundance in the inner ear are generally under-represented in gene profiling studies. In this review, we highlight the limitations of current gene expression profiling strategies as a discovery tool for genes involved in cochleo-vestibular development and function. We argue that expression profiling based on hierarchical clustering of transcripts by gene ontology, combined with tissue enrichment data, is more effective for inner ear gene discovery. This approach also provides a framework to assist and direct the functional characterization of gene products.

Cochlear implants for DFNA17 deafness

BACKGROUND

Nonsyndromic autosomal-dominant, adult-onset sensorineural hearing loss resulting from DFNA17 was described in a single American kindred in 1997, and the causative gene was subsequently identified as MYH9.

OBJECTIVE

The objective of this study was to report clinical and genetic analyses of an Australian family with nonsyndromic adult-onset sensorineural hearing loss.

METHODS

The clinical presentation of the family was detailed and identification of the causative gene was conducted by SNP genotyping and direct sequencing.

RESULTS

Sequence analysis of the MYH9 gene revealed the same missense mutation as in the original DFNA17 family. We are not aware of a link between the two kindreds, making the present one only the second DFNA17 family to be reported.

CONCLUSIONS

One important point of clinical relevance is the excellent outcome with cochlear implants in the Australian family compared with a "poor" response in the American family. Thus, cochlear implants should be strongly considered for clinical management of patients with DFNA17 deafness.

Gene expression changes during step-wise differentiation of embryonic stem cells along the inner ear hair cell pathway

CONCLUSION

Our study outlines an alternative approach for the selection and investigation of genes involved in inner ear function.

OBJECTIVE

To gain understanding of the gene pathways involved in the development of the normal cochlea.

MATERIALS AND METHODS

Microarray technology currently offers the most efficient approach to investigate gene expression and identify pathways involved in cell differentiation. Epidermal growth factor (EGF) induces cultures derived from the organ of Corti to proliferate and produce new hair cells. Since pluripotent embryonic stem (ES) cells have the capacity to generate all tissues, we induced murine ES cells to differentiate towards ectodermal and neuroectodermal cell types and from there investigated their commitment towards the hair cell lineage in the presence of EGF. Cells were collected at three points along the differentiation pathway and their expression profiles were determined using the Soares NMIE mouse inner ear cDNA library printed in microarray format.

RESULTS

Three genes up-regulated after addition of EGF (serine (or cysteine) proteinase inhibitor, clade H, member 1 (Serpinh1), solute carrier family 2 (facilitated glucose transporter), member 10 (Slc2a10) and secreted acidic cysteine-rich glycoprotein (Sparc)) were selected for further analysis and characterization. Of the three genes, Serpinh1 and Slc2a10 have never been implicated in the hearing process.

Detection of mutations in genes associated with hearing loss using a microarray-based approach

Knowing the etiology of hearing loss in a person has implications for counseling and management of the condition. More than 50% of cases of early onset, nonsyndromic sensorineural hearing loss are attributable to genetic factors. However, deafness is a genetically heterogeneous condition and it is therefore currently not economically and practically feasible to screen for mutations in all known deafness genes. We have developed a microarray-based hybridization biochip assay for the detection of known mutations. The current version of the hearing loss biochip detects nine common mutations in the connexin 26 gene, four mutations in the pendrin gene, one mutation in the usherin gene, and one mutation in mitochondrial DNA. The biochip was validated using DNA from 250 people with apparent nonsyndromic, moderate to profound sensorineural hearing loss. The hearing loss biochip detected with 100% accuracy the mutations it was designed for. No false-positives or false-negative results were seen. The biochip can easily be expanded to test for additional mutations in genes associated with hearing impairment or other genetic conditions.

Molecular characterization and expression of maternally expressed gene 3 (Meg3/Gtl2) RNA in the mouse inner ear

The pathways responsible for sound perception in the cochlea involve the coordinated and regulated expression of hundreds of genes. By using microarray analysis, we identified several transcripts enriched in the inner ear, including the maternally expressed gene 3 (Meg3/Gtl2), an imprinted noncoding RNA. Real-time PCR analysis demonstrated that Meg3/Gtl2 was highly expressed in the cochlea, brain, and eye. Molecular studies revealed the presence of several Meg3/Gtl2 RNA splice variants in the mouse cochlea, brain, and eye. In situ hybridizations showed intense Meg3/Gtl2 RNA staining in the nuclei of type I spiral ganglion cells and in cerebellum near the dorsal vestibular region of the cochlea. In embryonic mouse head sections, Meg3/Gtl2 RNA expression was observed in the otocyst, brain, eye, cartilage, connective tissue, and muscle. Meg3/Gtl2 RNA expression increased in the developing otocyst and localized to the spiral ganglion, stria vascularis, Reissner's membrane, and greater epithelial ridge (GER) in the cochlear duct. RT-PCR analysis performed on cell lines derived from the organ of Corti, representing neural, supporting, and hair cells, showed significantly elevated levels of Meg3/Gtl2 expression in differentiated neural cells. We propose that Meg3/Gtl2 RNA functions as a noncoding regulatory RNA in the inner ear and that it plays a role in pattern specification and differentiation of cells during otocyst development, as well as in the maintenance of a number of terminally differentiated cochlear cell types.

Survival of partially differentiated mouse embryonic stem cells in the scala media of the guinea pig cochlea

The low regenerative capacity of the hair cells of the mammalian inner ear is a major obstacle for functional recovery following sensorineural hearing loss. A potential treatment is to replace damaged tissue by transplantation of stem cells. To test this approach, undifferentiated and partially differentiated mouse embryonic stem (ES) cells were delivered into the scala media of the deafened guinea pig cochlea. Transplanted cells survived in the scala media for a postoperative period of at least nine weeks, evidenced by histochemical and direct fluorescent detection of enhanced green fluorescent protein (EGFP). Transplanted cells were discovered near the spiral ligament and stria vascularis in the endolymph fluid of the scala media. In some cases, cells were observed close to the damaged organ of Corti structure. There was no evidence of significant immunological rejection of the implanted ES cells despite the absence of immunosuppression. Our surgical approach allowed efficient delivery of ES cells to the scala media while preserving the delicate structures of the cochlea. This is the first report of the survival of partially differentiated ES cells in the scala media of the mammalian cochlea, and it provides support for the potential of cell-based therapies for sensorineural hearing impairment.

Clinical and molecular features of encephalomyopathy due to the A3302G mutation in the mitochondrial tRNA(Leu(UUR)) gene

BACKGROUND

The mitochondrial DNA mutation A3302G in the tRNA(Leu(UUR)) gene causes respiratory chain complex I deficiency. The main clinical feature appears to be a progressive mitochondrial myopathy with proximal muscle weakness.

OBJECTIVE

To report on clinical and molecular features in 4 novel patients with the A3302G mutation.

DESIGN

Case reports.

PATIENTS

Four patients (3 of whom are from the same family) with a myopathy caused by the A3302G mitochondrial DNA mutation.

MAIN OUTCOME MEASURE

Identification of the A3302G mutation by DNA sequencing.

RESULTS

All 4 patients had an adult-onset progressive mitochondrial myopathy with proximal muscle weakness, resulting in exercise intolerance. In 2 unrelated patients, upper limb reflexes were absent with preservation of at least some lower limb reflexes. Other features including hearing loss, recurrent headaches, ptosis, progressive external ophthalmoplegia, and depression were present.

CONCLUSION

While the dominant clinical features of the A3302G mutation were exercise intolerance and proximal muscle weakness, other features of mitochondrial encephalomyopathies, previously not described for this mutation, were present.

GJB2 mutations and degree of hearing loss: a multicenter study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.

Expression of the carrier protein apolipoprotein D in the mouse inner ear

The cochlear portion of the inner ear converts movements produced by sound waves into electrical impulses. Transcripts enriched in the cochlea are likely to have an important role in hearing. In this paper, we report that microarray analyses of the Soares NMIE inner ear library revealed cochlear enriched expression of apolipoprotein D (apoD), a glycoprotein and member of the lipocalin family that transport small hydrophobic ligands. The cochlear enriched expression of Apod was validated by quantitative real time PCR analysis. To investigate the function of apoD in the inner ear the transcript and protein were localised in the cochlea. Apod messenger RNA (mRNA) expression was localised to the spiral ligament and spiral limbus, particularly in the suprastrial and supralimbral regions. The apoD protein was detected in the spiral ligament, spiral limbus and also in the outer hair cells of the organ of Corti. Investigation of cell lines exhibiting characteristics of hair and supporting cells revealed no Apod mRNA expression in these cells. This suggests transport of the protein within the cochlea, followed by internalisation into outer hair cells. The spiral limbus and ligament contain subpopulations of fibrocytes that are intimately involved in regulation of ion balance in the cochlear fluids and type I, II and III fibrocytes of the spiral ligament were all shown to be positive for apoD protein. On the basis of these results it was hypothesised that apoD could be involved in maintaining cochlear fluid homeostasis. To determine whether the apoD gene product was important for normal auditory function the hearing ability of an apoD knockout mouse was tested. The mouse was found to have a hearing threshold that was not significantly different to the control strain.

NDUFS6 mutations are a novel cause of lethal neonatal mitochondrial complex I deficiency

complex I deficiency, the most common respiratory chain defect, is genetically heterogeneous: mutations in 8 nuclear and 7 mitochondrial DNA genes encoding complex I subunits have been described. However, these genes account for disease in only a minority of complex I-deficient patients. We investigated whether there may be an unknown common gene by performing functional complementation analysis of cell lines from 10 unrelated patients. Two of the patients were found to have mitochondrial DNA mutations. The other 8 represented 7 different (nuclear) complementation groups, all but 1 of which showed abnormalities of complex I assembly. It is thus unlikely that any one unknown gene accounts for a large proportion of complex I cases. The 2 patients sharing a nuclear complementation group had a similar abnormal complex I assembly profile and were studied further by homozygosity mapping, chromosome transfers, and microarray expression analysis. NDUFS6, a complex I subunit gene not previously associated with complex I deficiency, was grossly underexpressed in the 2 patient cell lines. Both patients had homozygous mutations in this gene, one causing a splicing abnormality and the other a large deletion. This integrated approach to gene identification offers promise for identifying other unknown causes of respiratory chain disorders.

Characterisation of DRASIC in the mouse inner ear

Within the cochlea, the hair cells detect sound waves and transduce them into receptor potential. The molecular architecture of the highly specialised cochlea is complex and until recently little was known about the molecular interactions which underlie its function. It is now clear that the coordinated expression and interplay of hundreds of genes and the integrity of cochlear cells regulate this function. It was hypothesised that transcripts expressed highly or specifically in the cochlea are likely to have important roles in normal hearing. Microarray analyses of the Soares NMIE library, consisting of 1536 cDNA clones isolated from the mouse inner ear, suggested that the expression of the mechanoreceptor DRASIC was enriched in the cochlea compared to other tissues. This amiloride-sensitive ion channel is a member of the DEG/ENaC superfamily and a potential candidate for the unidentified mechanoelectrical transduction channel of the sensory hair cells of the cochlea. The cochlear-enriched expression of amiloride-sensitive cation channel 3 (ACCN3) was confirmed by quantitative real-time polymerase chain reaction. Using in situ hybridisation and immunofluorescence, DRASIC expression was localised to the cells and neural fibre region of the spiral ganglion. DRASIC protein was also detected in cells of the organ of Corti. DRASIC may be present in cochlear hair cells as the ACCN3 transcript was shown to be expressed in immortalised cell lines that exhibit characteristics of hair cells. The normal mouse ACCN3 cDNA and an alternatively spliced transcript were elucidated by reverse transcription polymerase chain reaction from mouse inner ear RNA. This transcript may represent a new protein isoform with an as yet unknown function. A DRASIC knockout mouse model was tested for a hearing loss phenotype and was found to have normal hearing at 2 months of age but appeared to develop hearing loss early in life. The human homologue of ACCN3, acid-sensing ion channel 3, maps to the same chromosomal region as the autosomal recessive hearing loss locus DFNB13. However, we did not detect mutations in this gene in a family with DFNB13 hearing loss.

Prevalence and evolutionary origins of the del(GJB6-D13S1830) mutation in the DFNB1 locus in hearing-impaired subjects: a multicenter study

Mutations in GJB2, the gene encoding connexin-26 at the DFNB1 locus on 13q12, are found in as many as 50% of subjects with autosomal recessive, nonsyndromic prelingual hearing impairment. However, genetic diagnosis is complicated by the fact that 10%-50% of affected subjects with GJB2 mutations carry only one mutant allele. Recently, a deletion truncating the GJB6 gene (encoding connexin-30), near GJB2 on 13q12, was shown to be the accompanying mutation in approximately 50% of these deaf GJB2 heterozygotes in a cohort of Spanish patients, thus becoming second only to 35delG at GJB2 as the most frequent mutation causing prelingual hearing impairment in Spain. Here, we present data from a multicenter study in nine countries that shows that the deletion is present in most of the screened populations, with higher frequencies in France, Spain, and Israel, where the percentages of unexplained GJB2 heterozygotes fell to 16.0%-20.9% after screening for the del(GJB6-D13S1830) mutation. Our results also suggest that additional mutations remain to be identified, either in DFNB1 or in other unlinked genes involved in epistatic interactions with GJB2. Analysis of haplotypes associated with the deletion revealed a founder effect in Ashkenazi Jews and also suggested a common founder for countries in Western Europe. These results have important implications for the diagnosis and counseling of families with DFNB1 deafness.

Language and speech perception outcomes in hearing-impaired children with and without connexin 26 mutations

This study addressed the question of whether a hearing loss caused by mutations in the connexin 26 gene had a significant effect on language and speech perception outcomes in children using cochlear implants or hearing aids. The families of children who had participated in two previous studies of language development were invited to participate in this genetic study. From the 52 children whose families agreed to participate, 15 children with connexin 26 mutations in both chromosomes were identified. After taking into account other factors which are known to affect language development and speech perception in children with impaired hearing, no significant differences were found between the 15 children where connexin 26 was known to be the cause of deafness and the other 37 children in the study.

In silico analyses of mouse inner-ear transcripts

The development and function of the inner ear is complex requiring the correct and coordinated expression of many genes. The recent progress in the analyses of the human and other genomes has provided tools for identification of genes involved in hearing. As more and more nucleotide sequence information accumulates, experimental methods of molecular biology are rapidly being supplemented, and partially supplanted, by computational methods. In this study we present comprehensive in silico analyses of a cDNA library representing almost 1600 transcripts isolated from mouse inner ear. By mining the public databases we were able to rapidly and efficiently identify numerous transcripts likely to have a specific role in the auditory or vestibular function of the inner ear. Analyses revealed about 600 known genes and almost 100 inner-ear specific transcripts. Almost 50 of these are candidate genes for hearing impairment based on their chromosomal localization and inner-ear expression pattern. We describe a powerful approach to identify novel genes associated with hearing and vestibular function, further increasing our understanding of the molecular biology of the inner ear.

Clinical and molecular features of adPEO due to mutations in the Twinkle gene

We have analyzed Twinkle, the causative gene for autosomal dominant progressive external ophthalmoplegia (adPEO) on chromosome 10, in 11 Australian autosomal dominant progressive external ophthalmoplegia families of Caucasian origin, and investigated whether there are distinct molecular and clinical features associated with mutations in this gene. We found two new mutations in Twinkle, in 3 of the 11 pedigrees examined. One resides in the linker region of this gene while the other is in the primase domain. Both regions are highly conserved between species. Multiple deletions in the mtDNA from muscle are not always prominent and there are significant variations in the clinical presentation within and between families with mutations in the Twinkle gene. Therefore, genotype/phenotype predictions are difficult. No mutations were found in adenine nucleotide translocator 1 (ANT1), another known adPEO causative gene, in four of the seven remaining families investigated. Thus, Twinkle appears to be the most common gene associated with adPEO in Australian families.

Mutations in the TMPRSS3 gene are a rare cause of childhood nonsyndromic deafness in Caucasian patients

Two loci for nonsyndromic recessive deafness located on chromosome 21q22.3 have previously been reported, DFNB8 and DFNB10. Recently a gene which encodes a transmembrane serine protease, TMPRSS3 or ECHOS1, was found to be responsible for both the DFNB8 and DFNB10 phenotypes. To determine the contribution of TMPRSS3 mutations in the general congenital/childhood nonsyndromic deaf population we performed mutation analysis of the TMPRSS3 gene in 448 unrelated deaf patients from Spain, Italy, Greece, and Australia who did not have the common 35delG GJB2 mutation. From the 896 chromosomes studied we identified two novel pathogenic mutations accounting for four mutant alleles and at least 16 nonpathogenic sequence variants. The pathogenic mutations were a 1-bp deletion resulting in a frameshift and an amino acid substitution in the LDLRA domain of TMPRSS3. From this and another study we estimate the frequency of TMPRSS3 mutations in our sample as 0.45%, and approximately 0.38% in the general Caucasian childhood deaf population. However, TMPRSS3 is still an important contributor to genetic deafness in populations with large consanguineous families.