SLC26A4 genotypes and phenotypes associated with enlargement of the vestibular aqueduct

Mutation spectrum of GJB2, SLC26A4 and mtDNA12SrRNA genes in non-syndromic hearing loss patients from Gansu, China

OBJECTIVE

This study examined the mutation spectrum and frequency of three prevalent pathogenic genes in patients with non-syndromic hearing loss (NSHL) from Gansu Province, China.

METHODS

We analyzed 452 NSHL patients from five special education schools across several cities in Gansu Province using SNPscan technology to determine the mutation spectrum of mtDNA 12S rRNA, GJB2, and SLC26A4 genes.

RESULTS

Among the 452 patients evaluated, mutations in the GJB2 gene were observed in 91 cases (20.13 %), mutations in the SLC26A4 gene in 81 cases (17.92 %), and homoplasmic mutations in mtDNA 12S rRNA in 26 cases (5.75 %). Significant differences in GJB2 mutations were observed between Han patients and those of Hui, Tibetan and Mongolian ethnicity (χ2 = 4.554, p = 0.033; χ2 = 3.987, p = 0.046; χ2 = 4.041, p = 0.044), as well as in SLC26A4 gene mutations between Han patients and both Hui and Tu patients (χ2 = 4.247, p = 0.039; p = 0.035, two-sided). MT-RNR1 mutations were exclusively identified in Tibetans, Han, and Hui patients.

CONCLUSION

Our findings demonstrate variations in the mutation spectra of the GJB2, SLC26A4, and mtDNA 12S rRNA genes across different ethnic groups, highlighting ethnic variations in mutation prevalence. This study expands the understanding of the genetic mutation spectrum associated with deafness in Gansu and supports the enhancement of molecular diagnostic accuracy for diverse ethnic populations in the region.

A Three-Year Follow-Up of a Patient With Large Vestibular Aqueduct Syndrome Who Underwent Bilateral Endolymphatic Duct Blockage Surgery

Large vestibular aqueduct syndrome (LVAS) is a congenital malformation characterized by an abnormally large vestibular aqueduct, diagnosed primarily via CT scans. Patients with LVAS often experience progressive hearing loss and recurrent vertigo, with treatment strategies mirroring those for Meniere's disease. Traditional surgical interventions such as endolymphatic sac decompression (ESD) are common; however, the efficacy of endolymphatic duct blockage (EDB) as an alternative still remains under investigation. We present the case of a female in her 20s who was diagnosed with Meniere's disease after presenting with hearing loss and recurrent vertigo since the age of 17. Despite conservative treatments and tympanostomy tube insertion, her symptoms worsened, prompting surgical intervention. CT scans revealed bilaterally enlarged vestibular aqueducts, which suggested LVAS. The patient underwent EDB combined with ESD on both ears, starting with the more affected right ear. The surgical approach involved mastoidectomy, exposure of the enlarged endolymphatic duct, placement of a 4 mm titanium clip followed by drainage of the endolymphatic duct. Over a three-year follow-up, the patient experienced no recurrence of dizziness or tinnitus. However, hearing in the right ear gradually deteriorated, suggesting the necessity of future cochlear implant surgery. The patient has returned to work and maintained stable vertigo control post-bilateral surgery. This case introduces a new surgical method of combining EDB with ESD. Three years post-surgery, the method has resulted in potentially stabilized hearing in the better ear while effectively managing vertigo. It may be a solution to the challenge of vertigo in LVAS. The combined EDB and ESD procedure shows possibility for vertigo management in LVAS patients, along with the potential to preserve hearing when performed before significant deterioration. Despite hearing loss progression in the initially worse ear, the patient's quality of life improved significantly, highlighting the procedure's viability as a treatment option.

Validating the splicing effect of rare variants in the SLC26A4 gene using minigene assay

BACKGROUND

The SLC26A4 gene is the second most common cause of hereditary hearing loss in human. The aim of this study was to utilize the minigene assay in order to identify pathogenic variants of SLC26A4 associated with enlarged vestibular aqueduct (EVA) and hearing loss (HL) in two patients.

METHODS

The patients were subjected to multiplex PCR amplification and next-generation sequencing of common deafness genes (including GJB2, SLC26A4, and MT-RNR1), then bioinformatics analysis was performed on the sequencing data to identify candidate pathogenic variants. Minigene experiments were conducted to determine the potential impact of the variants on splicing.

RESULTS

Genetic testing revealed that the first patient carried compound heterozygous variants c.[1149 + 1G > A]; [919-2 A > G] in the SLC26A4 gene, while the second patient carried compound heterozygous variants c.[2089 + 3 A > T]; [919-2 A > G] in the same gene. Minigene experiments demonstrated that both c.1149 + 1G > A and c.2089 + 3 A > T affected mRNA splicing. According to the ACMG guidelines and the recommendations of the ClinGen Hearing Loss Expert Panel for ACMG variant interpretation, these variants were classified as "likely pathogenic".

CONCLUSIONS

This study identified the molecular etiology of hearing loss in two patients with EVA and elucidated the impact of rare variants on splicing, thus contributing to the mutational spectrum of pathogenic variants in the SLC26A4 gene.

[Advances in vestibular function and rehabilitation of large vestibular aqueduct syndrome]

Large vestibular aqueduct syndrome（LVAS） is a common recessive hereditary hearing loss disease, and some patients may also experience vestibular dysfunction. With the wide application of cochlear implant（CI） and the development of vestibular medicine, the pathophysiological mechanism of LVAS and the influence mechanism of CI on vestibular function are gradually elucidated. Consequently, the evaluation and rehabilitation of vestibular dysfunction function have also become research hotspots. This article reviews studies on vestibular function and related rehabilitation in patients with large vestibular aqueduct syndrome.

The role of SLC26A4 in bony labyrinth development and otoconial mineralization in mouse models

Inner ear malformations are predominantly attributed to developmental arrest during the embryonic stage of membranous labyrinth development. Due to the inherent difficulty in clinically assessing the status of the membranous labyrinth, these malformations are diagnosed with radiographic imaging, based on the morphological characteristics of the bony labyrinth. While extensive research has elucidated the intricacies of membranous labyrinth development in mouse models, comprehensive investigations into the developmental trajectory of the bony labyrinth, especially about its calcification process, have been notably lacking. One of the most prominent types of inner ear malformations is known as incomplete partition (IP), characterized by nearly normal external cochlear appearance but pronounced irregularities in the morphology of the modiolus and inter-scalar septa. IP type II (IP-II), also known as Mondini dysplasia, is generally accompanied by an enlargement of the vestibular aqueduct and is primarily attributed to mutations in the SLC26A4 gene. In the case of IP-II, the modiolus and inter-scalar septa of the cochlear apex are underdeveloped or missing, resulting in the manifestation of a cystic structure on radiographic imaging. In this overview, we not only explore the normal development of the bony labyrinth in mice but also present our observations on otolith mineralization. Furthermore, we investigated the specifics of bony labyrinth and otolith mineralization in Slc26a4-deficient mice, which served as an animal model for IP-II. We ensured that these findings promise to provide valuable insights for the establishment of therapeutic interventions, optimal timing, targeted sites, and preventive measures when considering the management of this condition.

Autosomal recessive non-syndromic hearing loss genes in Pakistan during the previous three decades

Hearing loss is a clinically and genetically heterogeneous disorder, with over 148 genes and 170 loci associated with its pathogenesis. The spectrum and frequency of causal variants vary across different genetic ancestries and are more prevalent in populations that practice consanguineous marriages. Pakistan has a rich history of autosomal recessive gene discovery related to non-syndromic hearing loss. Since the first linkage analysis with a Pakistani family that led to the mapping of the DFNB1 locus on chromosome 13, 51 genes associated with this disorder have been identified in this population. Among these, 13 of the most prevalent genes, namely CDH23, CIB2, CLDN14, GJB2, HGF, MARVELD2, MYO7A, MYO15A, MSRB3, OTOF, SLC26A4, TMC1 and TMPRSS3, account for more than half of all cases of profound hearing loss, while the prevalence of other genes is less than 2% individually. In this review, we discuss the most common autosomal recessive non-syndromic hearing loss genes in Pakistani individuals as well as the genetic mapping and sequencing approaches used to discover them. Furthermore, we identified enriched gene ontology terms and common pathways involved in these 51 autosomal recessive non-syndromic hearing loss genes to gain a better understanding of the underlying mechanisms. Establishing a molecular understanding of the disorder may aid in reducing its future prevalence by enabling timely diagnostics and genetic counselling, leading to more effective clinical management and treatments of hearing loss.

Characteristics of hearing loss-associated gene mutations: A multi-center study of 119,606 neonates in Gannan

BACKGROUND

HL is the second most common congenital disability in China, and its high incidence brings a serious burden of medical and educational sequelae. HL genetic screening enables the identification of individuals with inherited HL and carriers in a large scale.

OBJECTIVE

This study aimed to measure the detection rates of hearing loss (HL)-associated gene mutations in the Gannan population. The molecular etiology and risk factors of hereditary HL were also analyzed.

METHODS

In total, 119,606 newborns from 18 districts of Gannan were enrolled in this multi-center study conducted between April 2019 and April 2021. Otoacoustic Emission (OAE) was used for primary hearing screening 3 days after birth in quiet conditions, and OAE combined with automated auditory brainstem response (AABR) was applied 29-42 days after birth for those who failed or missed the initial screening. Meanwhile, high-throughput sequencing of hotspot HL-associated mutations in GJB2, GJB3, MTRNR1, and SLC26A4 were performed.

RESULTS

Among the 119,606 newborns, 7796 (6.52%) failed the hearing screening. Genetic screening revealed that 5092 neonates (4.26%) carried HL-associated mutations. The detection rate of GJB2, SLC26A4, MTRNR1 and GJB3 mutations were 2.09%, 1.51%, 0.42% and 0.24%, respectively. The most prevalent variant was GJB2 c.235delC (1.74%). The second most prevalent variant was SLC26A4 c.919-2A > G (0.93%). The population who failed the hearing screening had a lower proportion (24.64%) of SLC26A4 gene variants compared to the population who passed (37.46%). Genetic screening identified 4612 (3.86%) carriers who were normal in hearing screenings. The concurrent hearing and genetic screening identified 480 (0.40%) neonates at high risk for hereditary HL.

CONCLUSIONS

The results of this study suggest that the concurrent hearing screening and high-throughput genetic screening would greatly improve the effectiveness of newborn HL programs. This integration also facilitates the management of congenital HL, and aids in the prevention of aminoglycoside antibiotics-induced HL.

Syndromic Hearing Loss in Children

Pattern recognition of specific temporal bone radiological phenotypes, in association with abnormalities in other organ systems, is critical in the diagnosis and management of syndromic causes of hearing loss. Several recent publications have demonstrated the presence of specific radiological appearances, allowing precise genetic and/or syndromic diagnosis, in the right clinical context. This review article aims to provide an extensive but practical guide to the radiologist dealing with syndromic causes of hearing loss.

Quantitative analysis and correlative evaluation of video-oculography, micro-computed tomography, and histopathology in Pendrin-null mice

Patients with SLC26A4 mutations exhibit highly variable hearing loss and vestibular dysfunction. Although Slc26a4 mutant mice similarly exhibit vestibular deficits, including circling behavior, head tilting, and torticollis, the underlying pathogenesis of the vestibular symptoms remains unclear, hindering its effective management for patients with SLC26A4 mutations. In this study, we evaluated the equilibrium function using the inspection equipment, which can record eye movements against rotational, gravitational, and thermal stimulations. Moreover, we correlated the degree of functional impairment with the morphological alterations observed in Slc26a4^Δ/Δ mice. The rotational stimulus and ice water caloric tests revealed considerable impairment of the semicircular canal, while the tilted gravitational stimulus test showed a severe functional decline of the otolithic system in Slc26a4^Δ/Δ mice. Generally, the degree of impairment was more severe in circling Slc26a4^Δ/Δ mice than in non-circling Slc26a4^Δ/Δ mice. In non-circling Slc26a4^Δ/Δ mice, the semicircular canal function was normal. Micro-computed tomography results showed enlargement of the vestibular aqueduct and bony semicircular canals but no correlative relationship between the severity of the caloric response and the size of bony labyrinths. Giant otoconia and a significant decrease in total otolith volume in the saccule and utricle were observed in Slc26a4^Δ/Δ mice. However, the giant otoconia were not overly dislocated in the bony otolithic system and ectopic otoconia were absent in the semicircular canal. The number and morphology of the utricular hair cells in Slc26a4^Δ/Δ mice were not significantly reduced compared to those in Slc26a4^Δ/+ mice. Collectively, we can conclude that vestibular impairments are mainly associated with otoconia formation and morphology rather than hair cell degeneration. In addition, severe disturbances of semicircular canals cause circling behavior in Slc26a4^Δ/Δ mice. Our comprehensive morphological and functional assessments apply to mouse models of other genetic diseases with vestibular impairment.

The Genetic Background of Hearing Loss in Patients with EVA and Cochlear Malformation

The most frequently observed congenital inner ear malformation is enlarged vestibular aqueduct (EVA). It is often accompanied with incomplete partition type 2 (IP2) of the cochlea and a dilated vestibule, which together constitute Mondini malformation. Pathogenic SLC26A4 variants are considered the major cause of inner ear malformation but the genetics still needs clarification. The aim of this study was to identify the cause of EVA in patients with hearing loss (HL). Genomic DNA was isolated from HL patients with radiologically confirmed bilateral EVA (n = 23) and analyzed by next generation sequencing using a custom HL gene panel encompassing 237 HL-related genes or a clinical exome. The presence and segregation of selected variants and the CEVA haplotype (in the 5' region of SLC26A4) was verified by Sanger sequencing. Minigene assay was used to evaluate the impact of novel synonymous variant on splicing. Genetic testing identified the cause of EVA in 17/23 individuals (74%). Two pathogenic variants in the SLC26A4 gene were identified as the cause of EVA in 8 of them (35%), and a CEVA haplotype was regarded as the cause of EVA in 6 of 7 patients (86%) who carried only one SLC26A4 genetic variant. In two individuals with a phenotype matching branchio-oto-renal (BOR) spectrum disorder, cochlear hypoplasia resulted from EYA1 pathogenic variants. In one patient, a novel variant in CHD7 was detected. Our study shows that SLC26A4, together with the CEVA haplotype, accounts for more than half of EVA cases. Syndromic forms of HL should also be considered in patients with EVA. We conclude that to better understand inner ear development and the pathogenesis of its malformations, there is a need to look for pathogenic variants in noncoding regions of known HL genes or to link them with novel candidate HL genes.

Pearls of Temporal Bone Imaging in Children with Hearing Loss

Hearing loss is one of the most common indications for temporal bone imaging in children. Hearing loss may be congenital or acquired, and it may be conductive, sensorineural, or mixed audiologically. Temporal bone imaging plays an important role in the assessment and management of this condition. An understanding of the embryology of ear structures better enables the radiologist to interpret abnormalities on imaging of the temporal bone. Here, we provide a general review of ear development and a description of known genetic defects that contribute to congenital ear anomalies associated with hearing loss. We provide appropriate imaging techniques for the temporal bone depending on the clinical presentation and a systematic approach to imaging for children with hearing loss. Diagnostic imaging for developmental anomalies of the ear and cholesteatoma will be discussed.

Cochlear Pathomorphogenesis of Incomplete Partition Type II in Slc26a4-Null Mice

Incomplete partition type II (IP-II) is frequently identified in ears with SLC26A4 mutations. Cochleae with IP-II are generally observed to have 1½ turns; the basal turns are normally formed, and the apical turn is dilated or cystic. The objective of this study was to characterize the pathomorphogenesis of the IP-II cochlear anomaly in Slc26a4-null mice. Otic capsules were dissected from Slc26a4^Δ/+ and Slc26a4^Δ/Δ mice at 1 and 8 days of age and at 1 and 3 months of age. X-ray micro-computed tomography was used to image samples. We used a multiplanar view and three-dimensional reconstructed models to calculate the cochlear duct length, cochlear turn rotation angle, and modiolus tilt angle. The number of inner hair cells was counted, and the length of the cochlear duct was measured in a whole-mount preparation of the membranous labyrinth. X-ray micro-computed tomography mid-modiolar planar views demonstrated cystic apical turns in Slc26a4^Δ/Δ mice resulting from the loss or deossification of the interscalar septum, which morphologically resembles IP-II in humans. Planes vertical to the modiolus showed a similar mean rotation angle between Slc26a4^Δ/+ and Slc26a4^Δ/Δ mice. In contrast, the mean cochlear duct length and mean number of inner hair cells in Slc26a4^Δ/Δ mice were significantly smaller than in Slc26a4^Δ/+ mice. In addition, there were significant differences in the mean tilt angle and mean width of the modiolus. Our analysis of Slc26a4-null mice suggests that IP-II in humans reflects loss or deossification of the interscalar septum but not a decreased number of cochlear turns.

Incidence of childhood hearing loss after in utero exposure to platinum agents

OBJECTIVE

When treated for childhood cancers, at least 50% of children exposed to platinum agents have permanent hearing loss. We determined the relative risk of childhood hearing loss after in utero exposure to platinum chemotherapy in our registry cohort.

METHOD

After exposure to platinum chemotherapy in utero, all children undergo routine newborn hearing screening. This consists of Otoacoustic Emissions. Children who failed this screen were evaluated by audiologists. For those children with hearing loss by Automated Auditory Brainstem Response, prenatal and postnatal treatment details were compared to platinum exposed children without hearing loss.

RESULTS

Three hundred and seven children were exposed to chemotherapy in utero. Four children were diagnosed with hearing loss, all exposed to platinum agents. Chemotherapy exposures included: Cisplatin/Paclitaxel (2), Etoposide/Cisplatin/Bleomycin (1), Carboplatin/Paclitaxel (1) to treat ovarian (2), or cervical cancer (2). Of the 39 platinum exposed without hearing loss: 11 children were exposed to oxaliplatin, 16 were exposed to cisplatin and 12 to carboplatin in utero. Two hundred and sixty four women received non-platinum based chemotherapy for various cancers during pregnancy. Among these, there were no cases of hearing loss. There was a significant difference in hearing loss based on exposure to platinum agents in utero compared to non-platinum-containing chemotherapy regimens, 4/43 versus 0/264, p = 0.0003. There were no statistical differences in prenatal and postnatal treatment details, including: gestational age at diagnosis, at first chemotherapy treatment, at first platinum treatment, at delivery (<32 weeks, <35 weeks, <37 weeks), gender, birthweight, birthweight percentile, rates of intrauterine growth restriction, neonatal complications or use of postnatal antibiotics between the platinum exposed children with and without hearing loss.

CONCLUSION

The only children in the registry exposed to chemotherapy who were diagnosed with hearing loss had been exposed to cisplatin or carboplatin in utero. No hearing loss occurred in children exposed to oxaliplatin, or non-platinum agents. Due to a concern for cisplatin ototoxicity, carboplatin is the preferred platinum agent for use in pregnancy when equivalent maternal survival can be expected for the particular cancer type. For newborns exposed to platinum agents in utero, newborn screening with an auditory emissions test at birth (OES) may not detect sensorineural hearing loss and auditory brainstem response testing is recommended, regardless of the newborn screening result.

Natural Course of Residual Hearing with Reference to GJB2 and SLC26A4 Genotypes: Clinical Implications for Hearing Rehabilitation

BACKGROUND

Understanding the characteristics of residual hearing at low frequencies and its natural course in relation to molecular genetic etiology may be important in developing rehabilitation strategies. Thus, we aimed to explore the characteristics and natural course of residual hearing at low frequencies associated with the two most frequent deafness genes: GJB2 and SLC26A4.

METHODS

Initially, 53 GJB2 and 65 SLC26A4 subjects were enrolled, respectively. Only those whose audiograms exhibited hearing thresholds ≤70 dB at 250 and 500 Hz, and who had at least 1-year follow-up period between the first and last audiograms, were included. Collectively, the clinical characteristics of 14 ears from eight subjects with GJB2 variants, and 31 ears from 22 subjects with SLC26A4 variants fulfilled the strict criteria. In this study, a dropout rate refers to an incidence of dropping out of the cohort by cochlear implant surgery due to severe hearing deterioration.

RESULTS

Among the ears with complete serial audiogram data set, significant residual hearing at low frequencies at the time of inclusion was observed in 18.8% of those with GJB2 variants (15 out of 80 ears) and 42.6% of those with SLC26A4 variants (46 out of 108 ears), revealing a difference between two deafness genes. Subsequently, ears with SLC26A4 variants (11 of 46 ears, 23.9%) turned out to have a higher dropout rate for cochlear implantation due to hearing deterioration within the first year than those with GJB2 variants (1 of 15, 6.7%), albeit with no statistical significance. Throughout the follow-up period (mean: 37.2 ± 6.8, range: 12 to 80 months), deterioration of residual hearing at low frequencies at 250 Hz (dB HL/y) and 500 Hz (dB HL/y) of those with GJB2 variants exhibited 3.1 ± 1.3 (range: 0 to 15) and 5.2 ± 1.6 (range: 0 to 20), respectively, suggesting the deterioration of residual hearing in GJB2 variants was rather slow and gradual. Specifically, GJB2 p.Leu79Cysfs*3 show less remarkable residual hearing at low frequencies, but then a relatively stable nature. In contrast, SLC26A4 variants demonstrated a significantly higher dropout rate due to severe hearing deterioration requiring cochlear implantation compared with the GJB2 variants. This trend was observed not only in the first-year follow-up period but also in the follow-up periods thereafter. The p.His723Arg;c.919-2A>G genotype of SLC26A4, in particular, was associated with a high propensity for sudden hearing deterioration, as indicated by the dropout rate, which was as high as 46.2% for cochlear implantation due to hearing deterioration during the first year follow-up period. Furthermore, the dropout rate for cochlear implantation was observed in 7.1% of those with GJB2 variants (one out of 14 ears) and 30.3% of those with SLC26A4 variants (10 out of 33 ears) throughout the entire follow-up period.

CONCLUSIONS

Our results suggest that there is a difference with respect to the progressive nature of residual hearing at low frequencies between the two most common genes responsible for hearing loss, which may provide clinical implications of having individualized rehabilitation and timely intervention.

Mechanisms of hearing loss and cell death in the cochlea of connexin mutant mice

Mutations in connexin 30 (Cx30) are known to cause severe congenital hearing impairment; however, the mechanism by which Cx30 mediates homeostasis of endocochlear gap junctions is unclear. We used a gene deletion mouse model to explore the mechanisms of Cx30 in preventing hearing loss. Our results suggest that despite severe loss of the auditory brain-stem response and endocochlear potential at postnatal day 18, Cx30^-/- mice only show sporadic loss of the outer hair cells. This inconsistency in the time course and severity of hearing and hair cell losses in Cx30^-/- mice might be explained, in part, by an increase in reactive oxygen species generation beginning at postnatal day 10. The expression of oxidative stress genes was increased in Cx30^-/- mice in the stria vascularis, spiral ligament, and organ of Corti. Furthermore, Cx30 deficiency caused mitochondrial dysfunction at postnatal day 18, as assessed by decreased ATP levels and decreased expression of mitochondrial complex I proteins, especially in the stria vascularis. Proteomic analysis further identified 444 proteins that were dysregulated in Cx30^-/- mice, including several that are involved in mitochondria electron transport, ATP synthesis, or ion transport. Additionally, proapoptotic proteins, including Bax, Bad, and caspase-3, were upregulated at postnatal day 18, providing a molecular basis to explain the loss of hearing that occurs before hair cell loss. Therefore, our results are consistent with an environment of oxidative stress and mitochondrial damage in the cochlea of Cx30^-/- mice that is coincident with hearing loss but precedes hair cell loss.

Genetics of pediatric hearing loss: A functional perspective

OBJECTIVES

This article reviews the current role of genetics in pediatric hearing loss (HL).

METHODS

A review of the current literature regarding the genetic basis of HL in children was performed.

RESULTS

To date, 119 nonsyndromic genes have been associated with HL. There are also hundreds of syndromic causes that have HL as part of the clinical phenotype.

CONCLUSIONS

Identifying HL genes coupled with clinical characteristics ("genotype-phenotype") yields a more accurate diagnosis and prognosis. Although the complexity of the auditory apparatus presents challenges, gene therapy is emerging and may be a viable management option in the future.

Next-generation sequencing-based mutation analysis of genes associated with enlarged vestibular aqueduct in Chinese families

OBJECTIVES

The identification of gene mutations enables more appropriate genetic counseling and proper medical management for EVA patients. The purpose of this study was to validate the accuracy and sensitivity of our method for comprehensive mutation detection in EVA, and summarize these data to explore a more accurate and convenient genetic diagnosis method.

METHODS

A multiplex PCR sequencing panel was designed to capture the exons of three known EVA-associated genes (SLC26A4, KCNJ10, and FOXI1), and NGS was conducted in 17 Chinese families with EVA.

RESULTS

A total of 16 SLC26A4 variants were found in 21 probands with bilateral EVA, including three novel variants (c.416G>A, c.823G>A and c.1027G>C), which were not reported in the dbSNP, gnomAD database, and ClinVar databases. One patient carried a FOXI1 variant (heterozygous, c.214C>A) and one patient carried a KCNJ10 variant (heterozygous, c.1054C>A), both of which were novel variants. Biallelic potential pathogenic variants were detected in 21/21patient samples, leading to a purported diagnostic rate of 100%. All results were verified by Sanger sequencing.

CONCLUSION

This result supplemented the mutation spectrum of EVA, and supports that combined multiple PCR-targeted enrichment, and NGS is a valuable molecular diagnostic tool for EVA, and is suitable for clinical application.

Prenatal electroporation-mediated gene transfer restores Slc26a4 knock-out mouse hearing and vestibular function

The otocyst, an anlage of the inner ear, presents an attractive target to study treatment strategies for genetic hearing loss and inner ear development. We have previously reported that electroporation-mediated transuterine gene transfer of Connexin30, utilizing a monophasic pulse into Connexin30^−/− mouse otocysts at embryonic day 11.5, is able to prevent putative hearing deterioration. However, it is not clear whether supplementary gene transfer can rescue significant morphological changes, caused by genetic deficits. In addition, with the transuterine gene transfer technique utilized in our previous report, the survival rate of embryos and their mothers after treatment was low, which became a serious obstacle for effective in vivo experiments. Here, we set out to elucidate the feasibility of supplementation therapy in Slc26a4 deficient mice, utilizing biphasic pulses, optimized by modifying pulse conditions. Modification of the biphasic pulse conditions during electroporation increased the survival rate. In addition, supplementation of the target gene cDNA into the otocysts of homozygous Slc24a4 knockout mice significantly prevented enlargement of the endolymphatic space in the inner ear areas; moreover, it rescued hearing and vestibular function of mice in vivo.

Lessons From an Analysis of Newborn Hearing Screening Data for Children With Cochlear Implants

OBJECTIVES

The aims of the study are to identify the limitations of the current newborn hearing screening (NHS) programs and provide recommendations for better protocols.

STUDY DESIGN

Retrospective analysis.

SETTING

Tertiary referral center.

PATIENTS

The study participants were 185 children who received cochlear implants (CIs) at ≤5 years of age.

INTERVENTIONS

Therapeutic and rehabilitative.

MAIN OUTCOME MEASURES

The results of NHS, screening tools used, age, and hearing thresholds at which hearing loss was confirmed, causes of the hearing loss, age of CI insertion, aided pure-tone audiogram findings, and language development level were analyzed.

RESULTS

NHS data was available for 109 children, and 24 patients (22.0%) had passed NHS for both ears. Hearing loss was confirmed considerably later in children who had passed NHS than in children who were referred for further evaluation (p < 0.01). The most common cause for hearing loss in the NHS-pass group was SLC26A4 mutations (41.7%). Patients in the NHS-pass group received CIs considerably later than those in the NHS-referred group (p < 0.01). Among patients with SLC26A4 mutations, the language development level was significantly lower in the NHS-pass group than in the NHS-referred group (p < 0.01).

CONCLUSIONS

Careful counseling regarding NHS results is necessary for parents to understand that the absence of hearing loss at birth does not mean that the child will not develop hearing loss later in life. Genetic testing for SLC26A4 mutations may be necessary in regions with a high incidence of these mutations, such as East Asia.

Next generation sequencing study in a cohort of Italian patients with syndromic hearing loss

Hearing loss (HL), one of the most common congenital disorder, affects about one child in 1000. Among the genetic forms of HL, ∼30% of the cases are associated with other signs or symptoms, leading to Syndromic Hearing Loss (SHL) with about 700 different forms described so far. In this report, we refer the clinical and molecular data of 38 Italian SHL unrelated patients, and their relatives, affected by the most common syndromes associated with HL (i.e., Usher, Pendred, Charge, Waardenburg, Alport, Stickler, Branchiootorenal and Microdeletions syndromes). Patients have been analysed using next-generation sequencing (NGS) and High Density (HD)-SNP array technologies. Data analysis led to the identification of nine novel and 27 known causative mutations in 12 genes and two microdeletions in chromosomes 1 and 10, respectively. In particular, as regards to Usher syndrome, that affects 32% of our patients, we were able to reach a molecular diagnosis in 83% of the cases and to identify in Northern Eastern Italy a very common USH2A gene mutation (39%) (c.11864G > A, p.(Trp3955*) which can be defined "Central-Eastern European allele." As regards to Alport syndrome, we were able to potentially reclassify a pathogenic allele in the COL4A3 gene, previously associated only with benign familial hematuria. In all the other cases, the genomic analysis allowed us to confirm the role of known causative genes and to identify several novel and known alleles. Overall, our results highlight the effectiveness of combining an accurate clinical characterization with the use of genomic technologies (NGS and SNP arrays) for the molecular diagnosis of SHL, with a clear positive impact in the management and treatment of all the patients.

Analysis between phenotypes and genotypes of inner ear malformation

BACKGROUND

The clinical characteristics of LVAS have attracted more and more attention, its audiology and imaging features have also been deeply studied.

OBJECTIVE

To analyze phenotypes, genotypes of EVA, and find out the relationship between them.

METHODS

Sixty EVA patients were tested by audiometry, temporal bone high-resolution CT and inner ear MRI. SNPscan technology were carried out after the patients signed informed consent. SPSS19.0 software was used.

RESULT

1. Three types malformations include EVA, EVA with Mondini and Mondini were found. They accounted for 48.20%, 40.10%, and 11.70%. 2. The SLC26A4 gene mutation frequency was (47/53) 88.68% in EVA patients. The most common genotype was c.919-2A > G/c.919-2A > G, accounting for 28.30%. The most common mutation type was c.9I9-2A > G. 3. GJB2 and SLC26A4 gene mutation frequencies were significantly different (χ2＝65.185, p<.001).

CONCLUSIONS

1. EVA patients with severe sensorineural hearing loss were always diagnosed in childhood and Cochlear implantation was feasible for these patients with the bilateral hearing loss. 2. SLC26A4 gene was closely related to EVA. 3. GJB2 and mtDNA genes were not responsible for EVA.

SIGNIFICANCE

The relationship between genotype and clinical phenotype provides a theoretical basis for future gene diagnosis and prevention and treatment of LVAS.

DNA methylation dynamics during embryonic development and postnatal maturation of the mouse auditory sensory epithelium

The inner ear is a complex structure responsible for hearing and balance, and organ pathology is associated with deafness and balance disorders. To evaluate the role of epigenomic dynamics, we performed whole genome bisulfite sequencing at key time points during the development and maturation of the mouse inner ear sensory epithelium (SE). Our single-nucleotide resolution maps revealed variations in both general characteristics and dynamics of DNA methylation over time. This allowed us to predict the location of non-coding regulatory regions and to identify several novel candidate regulatory factors, such as Bach2, that connect stage-specific regulatory elements to molecular features that drive the development and maturation of the SE. Constructing in silico regulatory networks around sites of differential methylation enabled us to link key inner ear regulators, such as Atoh1 and Stat3, to pathways responsible for cell lineage determination and maturation, such as the Notch pathway. We also discovered that a putative enhancer, defined as a low methylated region (LMR), can upregulate the GJB6 gene and a neighboring non-coding RNA. The study of inner ear SE methylomes revealed novel regulatory regions in the hearing organ, which may improve diagnostic capabilities, and has the potential to guide the development of therapeutics for hearing loss by providing multiple intervention points for manipulation of the auditory system.

Increased expression of pendrin in eosinophilic chronic rhinosinusitis with nasal polyps

Introduction

Chronic rhinosinusitis with nasal polyps is a heterogeneous disease and appropriate diagnostic algorithms in individual cases are necessary for effective medical treatment.

Objective

The purpose of this study was to clarify the relationship between the pendrin expression of nasal polyps and clinical and pathological characteristic features of eosinophilic chronic rhinosinusitis.

Methods

A total of 68 patients were classified into eosinophilic chronic rhinosinusitis or non-eosinophilic chronic rhinosinusitis groups according to the degree of eosinophilic infiltration into the nasal polyps. Clinical, hematological, and immunohistochemical analyses were performed and statistically compared between both groups.

Results

Thirty-eight were classified into eosinophilic chronic rhinosinusitis and 30 into non-eosinophilic chronic rhinosinusitis groups. There were no significant differences in age distribution, sex ratio, prevalence of asthma, or any other complications between the groups. The mean Lund–Mackay score and the number of serum eosinophils was significantly higher in the eosinophilic chronic rhinosinusitis than in the non-eosinophilic chronic rhinosinusitis groups. The pendrin expression was more frequently detected in the epithelial surface layer of nasal polyps in the eosinophilic chronic rhinosinusitis than in the non-eosinophilic chronic rhinosinusitis groups. In addition, mucin 5AC was more widely expressed in the eosinophilic chronic rhinosinusitis than in the non-eosinophilic chronic rhinosinusitis.

Conclusion

Increased expression of pendrin and mucin 5AC in the nasal polyps would be associated with development of eosinophilic chronic rhinosinusitis. This finding could allow the development of a novel therapeutic agent targeted specifically to patients with eosinophilic chronic rhinosinusitis.

A novel mutation in the SLC26A4 gene in a Chinese family with non-syndromic hearing loss and enlarged vestibular aqueduct

OBJECTIVES

To identity the genetic causes of hearing loss in a Han Chinese family with enlarged vestibular aqueduct syndrome.

METHODS

Multiplex PCR technology combined with Ion Torrent™ next-generation sequencing technology was used to search for pathogenic mutations. A group of 1500 ethnically-matched normal hearing subjects screened for mutations in deafness-related genes using the same method in previously studied were included as a control.

RESULTS

The proband and his little sister suffered from typical features of sensorineural hearing loss with enlarged vestibular aqueduct (EVA). Both subjects harbored two compound heterozygous mutations in the SLC26A4 gene. A novel mutation named c.2110 G > C (p.Glu704Gln) in exon 19 and another previously reported mutation c.1673 A > T (p.Asn558Ile) were identified. These mutations were carried in the heterozygous state by the parents and therefore co-segregated with the genetic disease. The c.2110 G > C (p.Glu704Gln) mutation was absent in 1500 healthy newborns. Protein alignment indicated high evolutionary conservation of the p.E704 residue, and this mutation was predicted by online tools to be damaging and deleterious.

CONCLUSION

This study demonstrates that the novel mutation c.2110 G > C (p.Glu704Gln) in compound heterozygosity with c.1673 A > T (p.Asn558Ile) in the SLC26A4 gene corresponds to the EVA in this family. Our study will provide a foundation for elucidating the SLC26A4-related mechanisms of hearing loss.

A common SLC26A4-linked haplotype underlying non-syndromic hearing loss with enlargement of the vestibular aqueduct

BACKGROUND

Enlargement of the vestibular aqueduct (EVA) is the most common radiological abnormality in children with sensorineural hearing loss. Mutations in coding regions and splice sites of the SLC26A4 gene are often detected in Caucasians with EVA. Approximately one-fourth of patients with EVA have two mutant alleles (M2), one-fourth have one mutant allele (M1) and one-half have no mutant alleles (M0). The M2 genotype is correlated with a more severe phenotype.

METHODS

We performed genotype-haplotype analysis and massively parallel sequencing of the SLC26A4 region in patients with M1 EVA and their families.

RESULTS

We identified a shared novel haplotype, termed CEVA (Caucasian EVA), composed of 12 uncommon variants upstream of SLC26A4. The presence of the CEVA haplotype on seven of ten 'mutation-negative' chromosomes in a National Institutes of Health M1 EVA discovery cohort and six of six mutation-negative chromosomes in a Danish M1 EVA replication cohort is higher than the observed prevalence of 28 of 1006 Caucasian control chromosomes (p<0.0001 for each EVA cohort). The corresponding heterozygous carrier rate is 28/503 (5.6%). The prevalence of CEVA (11 of 126) is also increased among M0 EVA chromosomes (p=0.0042).

CONCLUSIONS

The CEVA haplotype causally contributes to most cases of Caucasian M1 EVA and, possibly, some cases of M0 EVA. The CEVA haplotype of SLC26A4 defines the most common allele associated with hereditary hearing loss in Caucasians. The diagnostic yield and prognostic utility of sequence analysis of SLC26A4 exons and splice sites will be markedly increased by addition of testing for the CEVA haplotype.

DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE

Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.

A novel missense mutation in the SLC26A4 gene causes nonsyndromic hearing loss and enlarged vestibular aqueduct

OBJECTIVES

We aimed to investigate the genetic causes of hearing loss in a Chinese proband with nonsyndromic hearing loss and enlarged vestibular aqueduct syndrome.

METHODS

We conducted clinical and genetic evaluations in a deaf proband and his normal-hearing parents. Multiplex PCR technology combined with Ion Torrent™ next-generation sequencing technology was used to detect the pathogenic mutations. As a control, a group of 1500 previously studied healthy newborns from the same ethnic background were subjected to deafness gene screening using the same method as in our previous study.

RESULTS

The proband harbored two mutations in the SLC26A4 gene in the form of compound heterozygosity. He was found to be heterozygous for a novel mutation named c.1742 G > T (p.Arg581Met) in exon 13 and for the known mutation c.589 G > A (p.Gly197Arg). These variants were carried in the heterozygous state by the parents and therefore co-segregated with the genetic disease. The c.1742 G > T (p.Arg581Met) mutation was absent in 1500 healthy newborns. Protein alignment indicated high evolutionary conservation of the p.R581 residue, and this mutation was predicted by PolyPhen-2 and other online tools to be damaging.

CONCLUSION

This study demonstrates that the novel mutation c.1742 G > T (p.Arg581Met) in compound heterozygosity with c.589 G > A in the SLC26A4 gene is the main cause of deafness in a family clinically diagnosed with enlarged vestibular aqueduct (EVA). Our study will provide a basic foundation for further investigations to elucidate the SLC26A4-related mechanisms of hearing loss.

Heterogeneity of Hereditary Hearing Loss in Iran: a Comprehensive Review

A significant contribution to the causes of hereditary hearing impairment comes from genetic factors. More than 120 genes and 160 loci have been identified to be involved in hearing impairment. Given that consanguine populations are more vulnerable to most inherited diseases, such as hereditary hearing loss (HHL), the genetic picture of HHL among the Iranian population, which consists of at least eight ethnic subgroups with a high rate of intermarriage, is expected to be highly heterogeneous. Using an electronic literature review through various databases such as PubMed, MEDLINE, and Scopus, we review the current picture of HHL in Iran. In this review, we present more than 39 deafness genes reported to cause non-syndromic HHL in Iran, of which the most prevalent causative genes include GJB2, SLC26A4, MYO15A, and MYO7A. In addition, we highlight some of the more common genetic causes of syndromic HHL in Iran. These results are of importance for further investigation and elucidation of the molecular basis of HHL in Iran and also for developing a national diagnostic tool tailored to the Iranian context enabling early and efficient diagnosis of hereditary hearing impairment.

A Novel Frameshift Mutation of SLC26A4 in a Korean Family With Nonsyndromic Hearing Loss and Enlarged Vestibular Aqueduct

Objectives

We aimed to identify the causative mutation for siblings in a Korean family with nonsyndromic hearing loss (HL) and enlarged vestibular aqueduct (EVA). The siblings were a 19-year-old female with bilateral profound HL and an 11-year-old male with bilateral moderately severe HL.

Methods

We extracted genomic DNA from blood samples of the siblings with HL, their parents, and 100 controls. We performed mutation analysis for SLC26A4 using direct sequencing.

Results

The two siblings were compound heterozygotes with the novel mutation p.I713LfsX8 and the previously described mutation p.H723R. Their parents had heterozygous mono-allelic mutations. Father had p.I713LfsX8 mutation as heterozygous, and mother had p.H723R mutation as heterozygous. However, novel mutation p.I713LfsX8 was not detected in 100 unrelated controls.

Conclusion

Both mutations identified in this study were located in the sulfate transporter and anti-sigma factor antagonist domain, the core region for membrane targeting of SulP/SLC26 anion transporters, which strongly suggests that failure in membrane trafficking by SLC26A4 is a direct cause of HL in this family. Our study could therefore provide a foundation for further investigations elucidating the SLC26A4-related mechanisms of HL.

Identification of a novel mutation in SLC26A4 gene in a Chinese family with enlarged vestibular aqueduct syndrome

OBJECTIVE

To investigate the genetic causes of hearing loss in a two generation Chinese family with enlarged vestibular aqueduct syndrome (EVAS).

METHODS

Clinical and genetic evaluations were conducted in a deaf proband and her normal-hearing parents. Sanger sequencing analysis of all the 21 exons, the exon-intron boundaries and the promoter in SLC26A4 gene was performed to detect the pathogenic mutations. PCR-restricted fragment length polymorphism (PCR-RFLP) was used to further identify the mutation. Phylogenetic analysis was carried out with multiple sequence alignment using BioEdit software. Three-dimensional (3D) modeling of the human wild-type and mutant SLC26A4 (NP_000432.1) was carried out using I-TASSER (http://zhanglab.ccmb.med.umich.edu/).

RESULTS

Clinical examinations showed that the proband suffered from typical features of sensorineural hearing loss with enlarged vestibular aqueduct. A novel nonsense mutation c.2118C>A (p.C706X) in exon 19 was identified in compound heterozygosity with the splice-site mutation c.919-2A>G in the proband by using Sanger sequencing. The mother was a heterozygous carrier of c.919-2A>G in intron 7, while the father was a heterozygous carrier of c.2118C>A. The mutation c.2118C>A was not found in 200 unrelated controls using Sanger sequencing. PCR-RFLP showed the PCR product of the proband was not digested at 2110 by Fau I because of the c.2118C>A mutation. 3D-structure modeling indicated that the mutation c.2118C>A resulted in a truncate Pendrin protein. Protein alignment indicated high conservation of p.C706 residue in healthy Homo, Nomascus, Pan, Macaca, Canis, Sus, Mus, Rattus, Cricetulus and Xenopus.

CONCLUSIONS

This study revealed a novel heterozygous mutation c.2118C>A (p.C706X) compound with c.919-2A>G in SLC26A4 gene in a patient with EVAS.

Deafness gene mutations in newborns in Beijing

OBJECTIVE

To determine the incidence of congenital hearing loss (HL) in newborns by the rate of deafness-related genetic mutations.

DESIGN

Clinical study of consecutive newborns in Beijing using allele-specific polymerase chain reaction-based universal array.

STUDY SAMPLE

This study tested 37 573 newborns within 3 days after birth, including nine sites in four genes: GJB2 (35 del G, 176 del 16, 235 del C, 299 del AT), SLC26A4 (IVS7-2 A > G, 2168 A > G), MTRNR1 (1555 A > G, 1494 C > T), and GJB3 (538 C > T). The birth condition of infants was also recorded.

RESULTS

Of 37 573 newborns, 1810 carried pathogenic mutations, or 4.817%. The carrier rates of GJB2 (35 del G, 176 del 16, 235 del C, 299 del AT), GJB3 (538 C > T), SLC26A4 (IVS7-2 A > G, 2168 A > G), and MTRNR1 (1555 A > G, 1494 C > T) mutations were 0.005%, 0.104%, 1.924%, 0.551%, 0.295%, 0.253%, 1.387%, 0.024%, and 0.274%, respectively. Logistic regression analysis indicated no statistically significant relationship between mutations and infant sex, premature delivery, twin status, or birth weight.

CONCLUSIONS

The 235delC GJB2 mutation was the most frequent deafness-related mutation in the Chinese population. Genetic screening for the deafness gene will help detect more cases of newborn congenital HL than current screening practices.

[Hereditary hearing loss: Part 2: Syndromic forms of hearing loss]

Syndromic hearing loss is responsible for approximately 30% of cases of inherited hearing loss. The syndromic form can be differentiated from nonsyndromic hearing loss by the presence of associated symptoms in other organ systems. While for many forms of syndromic hearing loss the individual genes responsible have been identified, the etiology of other associated symptoms remains unclear. The role of the ENT physician is to select appropriate clinical and genetic diagnostic tools based on the presentation of the patient and to subsequently initiate and perform the required hearing loss therapy.

Potential treatments for genetic hearing loss in humans: current conundrums

Genetic defects are a major cause of hearing loss in newborns. Consequently, hearing loss has a profound negative impact on human daily living. Numerous causative genes for genetic hearing loss have been identified. However, presently, there are no truly curative treatments for this condition. There have been several recent reports on successful treatments in mice using embryonic gene therapy, neonatal gene therapy and neonatal antisense oligonucleotide therapy. Herein, we describe state-of-the-art research on genetic hearing loss treatment through gene therapy and discuss the obstacles to overcome in curative treatments of genetic hearing loss in humans.

[Enlarged vestibular aqueduct syndrome: etiology, clinical features, diagnostics, and rehabilitation of the patients]

This publication was designed to describe the clinical manifestations of the enlarged vestibular aqueduct syndrome (EVAS), the currently employed methods for its diagnostics, and the strategy for the rehabilitation of the patients presenting with this pathological condition. In addition, the article provides information about the topographic anatomy and X-ray anatomy of the vestibular aqueduct, the specific clinical features of EVAS, the modern algorithm of its diagnostics, and the facilities for hearing rehabilitation in this group of patients.

SLC26A4 p.Thr410Met homozygous mutation in a patient with a cystic cochlea and an enlarged vestibular aqueduct showing characteristic features of incomplete partition type I and II

Mutations of SLC26A4 are associated with incomplete partition type II (IP-II) and isolated enlargement of the vestibular aqueduct (EVA). We experienced a congenitally deaf 6-year-old boy with a rare p.Thr410Met homozygous mutation in SLC26A4 who underwent bilateral cochlear implantation. He had bilateral inner ear malformation, in which the dilated vestibule and EVA were identical to those in IP-II, but the cochlea lacking a bony modiolus resembled that in incomplete partition type I. These results suggest that homozygous mutations in SLC26A4 are always associated with EVA, while the severity of cochlear malformation may vary depending on the type of SLC26A4 mutation.

Hearing impairment in Estonia: an algorithm to investigate genetic causes in pediatric patients

PURPOSE

The present study was initiated to establish the etiological causes of early onset hearing loss (HL) among Estonian children between 2000-2009.

METHODS

The study group consisted of 233 probands who were first tested with an arrayed primer extension assay, which covers 199 mutations in 7 genes (GJB2, GJB6, GJB3, SLC26A4, SLC26A5 genes, and two mitochondrial genes - 12S rRNA, tRNASer(UCN)). From probands whose etiology of HL remained unknown, DNA analysis of congenital cytomegalovirus (CMV) infection and G-banded karyotype and/or chromosomal microarray analysis (CMA) were performed.

RESULTS

In 110 (47%) cases, the etiology of HL was genetic and in 5 (2%) congenital CMV infection was diagnosed. We found mutations with clinical significance in GJB2 (100 children, 43%) and in 2 mitochondrial genes (2 patients, 1%). A single mutation in SLC26A4 gene was detected in 5 probands (2.2%) and was considered diagnostic. In 4 probands a heterozygous IVS2-2A>G change in the SLC26A5 gene was found. We did not find any instances of homozygosity for this splice variant in the probands. CMA identified in 4 probands chromosomal regions with the loss of one allele. In 2 of them we were able to conclude that the found abnormalities are definitely pathogenic (12q13.3-q14.2 and 17q22-23.2 microdeletion), but the pathogenity of 2 other findings (3p26.2 and 1p33 microdeletion) remained unknown.

CONCLUSION

This practical diagnostic algorithm confirmed the etiology of early onset HL for 115 Estonian patients (49%). This algorithm may be generalized to other populations for clinical application.

Ephrin-B2 governs morphogenesis of endolymphatic sac and duct epithelia in the mouse inner ear

Control over ionic composition and volume of the inner ear luminal fluid endolymph is essential for normal hearing and balance. Mice deficient in either the EphB2 receptor tyrosine kinase or the cognate transmembrane ligand ephrin-B2 (Efnb2) exhibit background strain-specific vestibular-behavioral dysfunction and signs of abnormal endolymph homeostasis. Using various loss-of-function mouse models, we found that Efnb2 is required for growth and morphogenesis of the embryonic endolymphatic epithelium, a precursor of the endolymphatic sac (ES) and duct (ED), which mediate endolymph homeostasis. Conditional inactivation of Efnb2 in early-stage embryonic ear tissues disrupted cell proliferation, cell survival, and epithelial folding at the origin of the endolymphatic epithelium. This correlated with apparent absence of an ED, mis-localization of ES ion transport cells relative to inner ear sensory organs, dysplasia of the endolymph fluid space, and abnormally formed otoconia (extracellular calcite-protein composites) at later stages of embryonic development. A comparison of Efnb2 and Notch signaling-deficient mutant phenotypes indicated that these two signaling systems have distinct and non-overlapping roles in ES/ED development. Homozygous deletion of the Efnb2 C-terminus caused abnormalities similar to those found in the conditional Efnb2 null homozygote. Analyses of fetal Efnb2 C-terminus deletion heterozygotes found mis-localized ES ion transport cells only in the genetic background exhibiting vestibular dysfunction. We propose that developmental dysplasias described here are a gene dose-sensitive cause of the vestibular dysfunction observed in EphB-Efnb2 signaling-deficient mice.

Mouse models for pendrin-associated loss of cochlear and vestibular function

The human gene SLC26A4 and the mouse ortholog Slc26a4 code for the protein pendrin, which is an anion exchanger expressed in apical membranes of selected epithelia. In the inner ear, pendrin is expressed in the cochlea, the vestibular labyrinth and the endolymphatic sac. Loss-of-function and hypo-functional mutations cause an enlargement of the vestibular aqueduct (EVA) and sensorineural hearing loss. The relatively high prevalence of SLC26A4 mutations provides a strong imperative to develop rational interventions that delay, ameliorate or prevent pendrin-associated loss of cochlear and vestibular function. This review summarizes recent studies in mouse models that have been developed to delineate the role of pendrin in the physiology of hearing and balance and that have brought forward the concept that a temporally and spatially limited therapy may be sufficient to secure a life-time of normal hearing in children bearing mutations of SLC26A4.

[Hereditary hearing loss: Part 1: diagnostic overview and practical advice]

Hearing loss is the most frequently occurring congenital sensory defect in humans. It is believed that between one and five of every 1000 children born suffers from hearing loss of at least 40 dB. The economic consequences of deafness are staggering and affect not only the individual patient but also society as a whole. A genetic cause is suspected in 50 %-70 % of cases of congenital hearing loss. To date over 130 loci have been associated with genetic hearing loss, with some loci containing more than one gene and others containing as yet unidentified genes. The present article is intended to provide some insight into the complex background issues involved and offer guidance on appropriate decision-making with regard to genetic testing in affected patients. Part 1 is concerned with non-syndromic hearing loss, while part 2 deals with syndromic hearing loss.

Newborn genetic screening for high risk deafness-associated mutations with a new Tetra-primer ARMS PCR kit

OBJECTIVE

Previous epidemiological studies indicate that GJB2, SLC26A4 or mtDNA 12S rRNA mutations were chiefly responsible for the hearing loss in children. A cost-effective method for screening deafness-associated mutations at early age is needed. This study aimed to develop a simple kit for screening of high risk deafness-associated mutations in newborns using tetra-primer amplification refractory mutation system PCR.

METHODS

The screening kit was designed to detect high risk deafness-associated mutations (GJB2 c.235delC, SLC26A4 c.919-2A>G, mtDNA 12S rRNA mt.1555A>G and mt.1494C>T). The kit was able to amplify both wild-type and mutant alleles with a control fragment. The proposed method was conducted to genotype the above four deafness gene mutations in four PCR reactions. Each mutation was genotyped by a set of four primers, two allele-specific inner primers, and two common outer primers. A mismatch at the penultimate or antepenult nucleotide of the 3' terminus was introduced in order to maximize specificity. The 16 primers were used for the amplification of genomic DNA as a template. Amplified fragments were separated by electrophoresis. We designed and validated the kit with wild and mutant type DNA samples that had been previously been confirmed by Sanger sequencing. Then 1181 newborns were enrolled, and those samples with mutations were further validated with sequencing too.

RESULTS

Among 1181 newborns, 29 individuals had one or two mutant alleles, with the carrier rate being 2.46% (29/1181). For GJB2 c.235delC mutation, one case was homozygote and 12 cases were heterozygote carriers. For SLC26A4 c.919-2A>G mutation, 12 cases were heterozygotes carriers, and no homozygotes were found; for mtDNA 12S rRNA mt.1555A>G mutation, one case was identified; three cases of mtDNA 12S rRNA mt.1494C>T mutation were detected. All mutations were detected with high specificity. Mutation samples were confirmed via Sanger sequencing. No false positive was found.

CONCLUSION

A user-friendly screening kit for deafness-associated mutations was successfully developed. It provided rapid, reproducible, and cost-effective detection of deafness gene mutation without special equipment. The kit allowed the detection of the four high risk deafness-associated mutations with only 4 single tube PCR reactions. In the future, the kit could be applied to large population-based epidemiological studies for newborn hearing defects screening.

SLC26A4 targeted to the endolymphatic sac rescues hearing and balance in Slc26a4 mutant mice

Mutations of SLC26A4 are a common cause of human hearing loss associated with enlargement of the vestibular aqueduct. SLC26A4 encodes pendrin, an anion exchanger expressed in a variety of epithelial cells in the cochlea, the vestibular labyrinth and the endolymphatic sac. Slc26a4 (Δ/Δ) mice are devoid of pendrin and develop a severe enlargement of the membranous labyrinth, fail to acquire hearing and balance, and thereby provide a model for the human phenotype. Here, we generated a transgenic mouse line that expresses human SLC26A4 controlled by the promoter of ATP6V1B1. Crossing this transgene into the Slc26a4 (Δ/Δ) line restored protein expression of pendrin in the endolymphatic sac without inducing detectable expression in the cochlea or the vestibular sensory organs. The transgene prevented abnormal enlargement of the membranous labyrinth, restored a normal endocochlear potential, normal pH gradients between endolymph and perilymph in the cochlea, normal otoconia formation in the vestibular labyrinth and normal sensory functions of hearing and balance. Our study demonstrates that restoration of pendrin to the endolymphatic sac is sufficient to restore normal inner ear function. This finding in conjunction with our previous report that pendrin expression is required for embryonic development but not for the maintenance of hearing opens the prospect that a spatially and temporally limited therapy will restore normal hearing in human patients carrying a variety of mutations of SLC26A4.

Limitations of hearing screening in newborns with PDS mutations

OBJECTIVES

SLC26A4 (PDS) mutations are common cause of congenital hearing loss in East Asia. Hearing loss caused by PDS mutations tends to have delayed presentation; thus universal newborn hearing screening (UNHS) can be less effective in these patients. We examined the efficiency of newborn hearing screening test in patients with bi-allelic PDS mutations.

METHODS

Forty-three patients with sensorineural hearing loss were recruited. Patients had an enlarged vestibular aqueduct and biallelic PDS mutations. Among them, newborn hearing screening test had been performed on 14. The remaining 29 patients did not undergo newborn hearing screening test. Another 15 patients without a PDS mutation but who had sensorineural hearing loss were also recruited as a comparison group. We reviewed the hearing loss history of the children using medical records and parent interviews.

RESULTS

Among 14 patients with PDS mutation, four (28.6%) passed newborn hearing screening test in both ears and six (42.9%) passed in one ear. In contrast, only 2 of 15 (13.3%) children without a PDS mutation passed newborn hearing screening test bilaterally. The age at confirmation of bilateral hearing loss in bilateral "pass" patients with PDS mutation was 31.5 ± 17.9 months, which was significantly delayed compared to the age for bilateral "refer" children (1.75 ± 0.96 months) (p<0.05).

CONCLUSION

The UNHS is not an accurate tool for predicting long-term hearing loss in patients with PDS mutations. We recommend that genetic screening be combined with UNHS, particularly in communities with a high prevalence of PDS mutations, to better identify children in need of early habilitation.