Genetics of hearing loss: where are we standing now?

The genetic basis and the diagnostic yield of genetic testing related to nonsyndromic hearing loss in Qatar

Hearing loss is the most predominant sensory defect occurring in pediatrics, of which, 66% cases are attributed to genetic factors. The prevalence of hereditary hearing loss increases in consanguineous populations, and the prevalence of hearing loss in Qatar is 5.2%. We aimed to investigate the genetic basis of nonsyndromic hearing loss (NSHL) in Qatar and to evaluate the diagnostic yield of different genetic tests available. A retrospective chart review was conducted for 59 pediatric patients with NSHL referred to the Department of Adult and Pediatric Medical Genetics at Hamad Medical Corporation in Qatar, and who underwent at least one genetic test. Out of the 59 patients, 39 were solved cases due to 19 variants in 11 genes and two copy number variants that explained the NSHL phenotype. Of them 2 cases were initially uncertain and were reclassified using familial segregation. Around 36.8% of the single variants were in GJB2 gene and c.35delG was the most common recurrent variant seen in solved cases. We detected the c.283C > T variant in FGF3 that was seen in a Qatari patient and found to be associated with NSHL for the first time. The overall diagnostic yield was 30.7%, and the diagnostic yield was significantly associated with genetic testing using GJB2 sequencing and using the hearing loss (HL) gene panel. The diagnostic yield for targeted familial testing was 60% (n = 3 patients) and for gene panel was 50% (n = 5). Thus, we recommend using GJB2 gene sequencing as a first-tier genetic test and HL gene panel as a second-tier genetic test for NSHL. Our work provided new insights into the genetic pool of NSHL among Arabs and highlights its unique diversity, this is believed to help further in the diagnostic and management options for NSHL Arab patients.

Postnatal Cytomegalovirus Infection: Is it Important? A 10-Year Retrospective Case-control Study of Characteristics and Outcomes in Very Preterm and Very Low Birth Weight Infants

BACKGROUND

To determine the characteristics and outcomes of postnatal cytomegalovirus (pCMV) infection in preterm infants in a neonatal intensive care unit (NICU).

METHODS

A retrospective, matched case-control study in a tertiary NICU. Infants born between January 2009 and December 2019, <32 weeks' gestational age (GA) and/or birth weight (BW) <1500 g with pCMV infection were matched 1:1 with cytomegalovirus-(CMV)-negative infants by year of admission, gender, GA and BW. Primary outcome was death ≤36 weeks' postmenstrual age or bronchopulmonary dysplasia (BPD). Secondary outcomes were length of ventilation (LOV), length of stay (LOS) and neurodevelopmental impairment (NDI) at corrected age 1 and 2 years.

RESULTS

Forty-eight pCMV-positive infants (median GA 25.3 weeks, BW 695 g, age 58 days) were identified from 1659 infants (incidence 2.9%). The most common symptoms of pCMV infection were abdominal distension (43.8%), sepsis-like syndrome (29.2%), thrombocytopenia (60.5%) and conjugated hyperbilirubinemia (60.9%). Compared with controls, there were no significant differences in the composite outcome of death or BPD (56.3% vs. 37.5%; P = 0.1) or NDI at 1 and 2 years (51.9% vs. 44%; P = 0.8; 71.4% vs. 50%; P = 0.4). pCMV-positive infants had a significantly longer median LOV (23.5 vs. 12 days)* and LOS (140 vs. 110.5 days)*. Eleven (22.9%) infants received antivirals. Ten improved and 1 died. Two untreated infants died (1 from pCMV infection).

CONCLUSIONS

Clinically identifiable pCMV infections are significant and associated with increased respiratory support and prolonged hospital stay in vulnerable infants. pCMV screening and preventive measures against transmission merit consideration.*P < 0.05.

Using the Zebrafish Lateral Line to Understand the Roles of Mitochondria in Sensorineural Hearing Loss

Hair cells are the mechanosensory receptors of the inner ear and can be damaged by noise, aging, and ototoxic drugs. This damage often results in permanent sensorineural hearing loss. Hair cells have high energy demands and rely on mitochondria to produce ATP as well as contribute to intracellular calcium homeostasis. In addition to generating ATP, mitochondria produce reactive oxygen species, which can lead to oxidative stress, and regulate cell death pathways. Zebrafish lateral-line hair cells are structurally and functionally analogous to cochlear hair cells but are optically and pharmacologically accessible within an intact specimen, making the zebrafish a good model in which to study hair-cell mitochondrial activity. Moreover, the ease of genetic manipulation of zebrafish embryos allows for the study of mutations implicated in human deafness, as well as the generation of transgenic models to visualize mitochondrial calcium transients and mitochondrial activity in live organisms. Studies of the zebrafish lateral line have shown that variations in mitochondrial activity can predict hair-cell susceptibility to damage by aminoglycosides or noise exposure. In addition, antioxidants have been shown to protect against noise trauma and ototoxic drug–induced hair-cell death. In this review, we discuss the tools and findings of recent investigations into zebrafish hair-cell mitochondria and their involvement in cellular processes, both under homeostatic conditions and in response to noise or ototoxic drugs. The zebrafish lateral line is a valuable model in which to study the roles of mitochondria in hair-cell pathologies and to develop therapeutic strategies to prevent sensorineural hearing loss in humans.

Novel pathogenic mutations and further evidence for clinical relevance of genes and variants causing hearing impairment in Tunisian population

Introduction

Hearing impairment (HI) is characterized by complex genetic heterogeneity. The evolution of next generation sequencing, including targeted enrichment panels, has revolutionized HI diagnosis.

Objectives

In this study, we investigated genetic causes in 22 individuals with non-GJB2 HI.

Methods

We customized a Haloplex^HS kit to include 30 genes known to be associated with autosomal recessive nonsyndromic HI (ARNSHI) and Usher syndrome in North Africa.

Results

In accordance with the ACMG/AMP guidelines, we report 11 pathogenic variants; as follows; five novel variants including three missense (ESRRB-Tyr295Cys, MYO15A-Phe2089Leu and MYO7A-Tyr560Cys) and two nonsense (USH1C-Gln122Ter and CIB2-Arg104Ter) mutations; two previously reported mutations (OTOF-Glu57Ter and PNPT1-Glu475Gly), but first time identified among Tunisian families; and four other identified mutations namely WHRN-Gly808AspfsX11, SLC22A4-Cys113Tyr and two MYO7A compound heterozygous splice site variants that were previously described in Tunisia. Pathogenic variants in WHRN and CIB2 genes, in patients with convincing phenotype ruling out retinitis pigmentosa, provide strong evidence supporting their association with ARNSHI. Moreover, we shed lights on the pathogenic implication of mutations in PNPT1 gene in auditory function providing new evidence for its association with ARNSHI. Lack of segregation of a previously identified causal mutation OTOA-Val603Phe further supports its classification as variant of unknown significance. Our study reports absence of otoacoustic emission in subjects using bilateral hearing aids for several years indicating the importance of screening genetic alteration in OTOF gene for proper management of those patients.

Conclusion

In conclusion, our findings do not only expand the spectrum of HI mutations in Tunisian patients, but also improve our knowledge about clinical relevance of HI causing genes and variants.

[Analysis of genotypes and hearing phenotypes of mutation infants with deafness]

Objective:The aim of this study is to explore the genotype and hearing phenotype of deaf infants with mutation of GJB2 gene. Method:Subjects were 121 infants with GJB2 gene mutations who were treated in the Children's Hearing Diagnosis Center of Beijing Tongren hospital. All subjects were accepted to undertake the universal newborns hearing screening（UNHS） and series of objective audiometry, including auditory brainstem response, distortion product otoacoustic emission, auditory steady-state response and other audiological tests. All subjects were screened for nine pathogenic variants in four genes or all exons of the GJB2 gene, and then were diagnosed as infants with GJB2 gene mutations. Initially, analyzing their genotypes and hearing phenotypes generally. Then, the subjects were divided into two groups according to the genotypes: T/T group（truncated/truncated mutations, 89 cases） and T/NT group（truncated/non-truncated mutations, 32 cases）. Chi-square test was used to analyze the results of UNHS, hearing degree, audiogram patterns and symmetry/asymmetry of binaural hearing phenotype. Eventually, analyzing the results of UNHS. Result:The most common truncated mutation was c.235delC（64.88%, 157/242） and the most common non-truncated mutation was c.109G>A（11.16%, 27/242）. The homozygous mutation of c.235delC/c.235delC was the dominant in T/T group（38.84%, 47/121）, and the compound heterozygous mutation of c.235delC/c.109G>A was the dominant in T/NT group（18.18%, 22/121）. 81.82%（99/121） of subjects failed in UNHS, including 74.38%（90/121） with bilateral reference, 7.44%（9/121） with a single pass. The refer rate of UNHS of group T/T and T/NT were 86.52%（77/89） and 68.75%, respectively. There was a statistically significant difference between the two groups（P<0.05）. 85.95%（104/121） of subjects were diagnosed as hearing loss and 14.05%（17/121） of subjects were diagnosed as normal hearing. The degree of hearing loss: profound, severe, moderate and mild were 31.40%（38/121）, 19.01%（23/121）, 24.79%（30/121） and 10.74%（13/121）, respectively. There was no subjects with normal hearing in T/T group and individuals with severe and profound hearing loss accounted for the highest proportion（65.17%, 58/89）, while in T/NT group, normal hearing accounted for 53.13%（17/32） and mild and moderate hearing loss accounted for the highest proportion（37.5%, 12/32）. There was statistically significant difference between the two groups（P<0.05）. Of 104 patients（208 ears） with hearing loss, the audiogram patterns: flat, descending, ascending, residual, Valley and other types were 49.03%（102/208）, 12.02%（25/208）, 8.65%（18/208）, 7.69%（16/204）, 3.36%（7/204） and 19.23%（40/204）, respectively. The two most common types in T/T group were flat（47.19%, 84/178） and other types（20.22%, 36/178）, while in T/NT group were flat（60.00%, 18/30） and ascending（20.00%, 6/30）. There was statistically significant difference between the two groups（P<0.05）. There were 50 cases（48.07%） with symmetrical hearing phenotype and 54 cases（51.93%） with asymmetrical hearing phenotype. Asymmetry was predominant in T/T group（53.93%, 48/89）, and symmetry was predominant in T/NT group（60.00%, 9/15）. There was no statistically significant difference between the two groups（P>0.05）. Conclusion:In this study, c.235delC/c.235delC homozygous mutation was dominant in T/T group and c.235delC/c.109G>A heterozygous mutation was dominant in T/NT Group. The hearing phenotypes in T/T group were mostly bilateral asymmetric severe hearing loss, and those in T/NT Group were bilateral symmetric mild to moderate hearing loss, special attention should be paid to the audiological characteristics of different genotypes.

Disparities in discovery of pathogenic variants for autosomal recessive non-syndromic hearing impairment by ancestry

Hearing impairment (HI) is characterized by extensive genetic heterogeneity. To determine the population-specific contribution of known autosomal recessive nonsyndromic (ARNS)HI genes and variants to HI etiology; pathogenic and likely pathogenic (PLP) ARNSHI variants were selected from ClinVar and the Deafness Variation Database and their frequencies were obtained from gnomAD for seven populations. ARNSHI prevalence due to PLP variants varies greatly by population ranging from 96.9 affected per 100,000 individuals for Ashkenazi Jews to 5.2 affected per 100,000 individuals for Africans/African Americans. For Europeans, Finns have the lowest prevalence due to ARNSHI PLP variants with 9.5 affected per 100,000 individuals. For East Asians, Latinos, non-Finish Europeans, and South Asians, ARNSHI prevalence due to PLP variants ranges from 17.1 to 33.7 affected per 100,000 individuals. ARNSHI variants that were previously reported in a single ancestry or family were observed in additional populations, e.g., USH1C p.(Q723*) reported in a Chinese family was the most prevalent pathogenic variant observed in gnomAD for African/African Americans. Variability between populations is due to how extensively ARNSHI has been studied, ARNSHI prevalence and ancestry specific ARNSHI variant architecture which is impacted by population history. Our study demonstrates that additional gene and variant discovery studies are necessary for all populations and particularly for individuals of African ancestry.

Novel recessive PDZD7 biallelic mutations associated with hereditary hearing loss in a Chinese pedigree

BACKGROUND

Autosomal recessive non-syndromic hearing loss (ARNSHL) is a highly heterogeneous genetic disease. PDZD7 is a new ARNSHL associated gene. Until now, nine PDZD7 biallelic mutation families with ARNSHL have been reported. Here we report a case of Chinese patient with ARNSHL linked to novel mutations in PDZD7 genes.

METHOD

The pathogenic mutations were detected by whole exome sequencing for hereditary deafness-related genes of both the proband and his parents. We used kinship detection, mutational hazard prediction, genotype-phenotype correlation analysis and variation screening for potential pathogenic mutations. Re-sequencing was used to confirm the mutations by Sanger sequence. Real time quantitative PCR (RT-qPCR) was used to analyze the PDZD7 gene expression. Population-based screening for variation frequency, evolutionary conservation comparisons, pathogenicity evaluation, and protein structure prediction were conducted to assess the pathogenicity of the novel mutations of PDZD7 gene.

RESULTS

We determined three variants of the PDZD7 gene that contributed to the deafness of the patient (PDZD7 c.192G > A, p. Met64Ile; c.1648C > T p. Gln550* and c.2341_2352delCGCAGCCGCAGCp. Arg781_Ser 784del). Pathogenic analysis in accordance with the ACMG/AMP Standards and Guidelines identified two novel mutations as Likely Pathogenic. The expression level of PDZD7 gene in the patient was decreased compared to the normal control (P < 0.001).

CONCLUSION

Three mutations in PDZD7 gene linked to ARNSHL were identified in a Chinese pedigree. The findings expand not only our knowledge of genetic causes of ARNSHL, but also PDZD7 genes mutation spectrum of the disease. They will aid personalized genetic counseling, molecular diagnostics and clinical management of this condition.

Prevalence of mutations in the GJB2, SLC26A4, GJB3, and MT-RNR1 genes in 103 children with sensorineural hearing loss in Shaoxing, China

Mutations in the GJB2, SLC26A4, GJB3, and MT-RNR1 genes are known to be a common cause of hearing loss. However, the frequency of hot-spot mutations and genotype-phenotype correlations in patients with sensorineural hearing loss (SNHL) has been less frequently reported. We conducted a study of 103 children-56 boys and 47 girls, aged 5 months to 9 years (mean: 4.1 yr)-with SNHL who underwent genetic screening for 20 hot-spot mutations of the GJB2, SLC26A4, GJB3, and MT-RNR1 genes. Mutations were detected by multiple-PCR-based MALDI-TOF MS assay. At least one mutated allele was detected in 48 patients (46.6%), and 30 patients (29.1%) carried pathogenic mutations. Among all the detected mutations, the most common were GJB2 c.235delC and SLC26A4 c.919-2A>G, with allele frequencies of 23.8 and 6.8%, respectively. At least one mutant allele of SLC26A4 was detected in the 13 patients who had an enlarged vestibular aqueduct (EVA). Almost half of the children with SNHL carried a common deafness-related mutation, and nearly one-third carried a pathogenic mutation. The mutations in SLC26A4 were prevalent and correlated strongly with EVA.

Successful preimplantation genetic diagnosis by targeted next-generation sequencing on an ion torrent personal genome machine platform

Hearing loss may place a heavy burden on the patient and patient's family. Given the high incidence of hearing loss among newborns and the huge cost of treatment and care (including cochlear implantation), prenatal diagnosis is strongly recommended. Termination of the fetus may be considered as an extreme outcome to the discovery of a potential deaf fetus, and therefore preimplantation genetic diagnosis has become an important option for avoiding the birth of affected children without facing the risk of abortion following prenatal diagnosis. In one case, a couple had a 7-year-old daughter affected by non-syndromic sensorineural hearing loss. The affected fetus carried a causative compound heterozygous mutation c.919-2 A>G (IVS7-2 A>G) and c.1707+5 G>A (IVS15+5 G>A) of the solute carrier family 26 member 4 gene inherited from maternal and paternal sides, respectively. The present study applied multiple displacement amplification for whole genome amplification of biopsied trophectoderm cells and next-generation sequencing (NGS)-based single nucleotide polymorphism haplotyping on an Ion Torrent Personal Genome Machine. One unaffected embryo was transferred in a frozen-thawed embryo transfer cycle and the patient was impregnated. To conclude, to the best of our knowledge, this may be the first report of NGS-based preimplantation genetic diagnosis (PGD) for non-syndromic hearing loss caused by a compound heterozygous mutation using an Ion Torrent Personal Genome Machine. NGS provides unprecedented high-throughput, highly parallel and base-pair resolution data for genetic analysis. The method meets the requirements of medium-sized diagnostics laboratories. With decreased costs compared with previous techniques (such as Sanger sequencing), this technique may have potential widespread clinical application in PGD of other types of monogenic disease.

Fluvastatin protects cochleae from damage by high-level noise

Exposure to noise and ototoxic drugs are responsible for much of the debilitating hearing loss experienced by about 350 million people worldwide. Beyond hearing aids and cochlear implants, there have been no other FDA approved drug interventions established in the clinic that would either protect or reverse the effects of hearing loss. Using Auditory Brainstem Responses (ABR) in a guinea pig model, we demonstrate that fluvastatin, an inhibitor of HMG-CoA reductase, the rate-limiting enzyme of the mevalonate pathway, protects against loss of cochlear function initiated by high intensity noise. A novel synchrotron radiation based X-ray tomographic method that imaged soft tissues at micrometer resolution in unsectioned cochleae, allowed an efficient, qualitative evaluation of the three-dimensional internal structure of the intact organ. For quantitative measures, plastic embedded cochleae were sectioned followed by hair cell counting. Protection in noise-exposed cochleae is associated with retention of inner and outer hair cells. This study demonstrates the potential of HMG-CoA reductase inhibitors, already vetted in human medicine for other purposes, to protect against noise induced hearing loss.

Genetic frequencies related to severe or profound sensorineural hearing loss in Inner Mongolia Autonomous Region

The aim was to study the frequencies of common deafness-related mutations and their contribution to hearing loss in different regions of Inner Mongolia. A total of 738 deaf children were recruited from five different ethnic groups of Inner Mongolia, including Han Chinese (n=486), Mongolian (n=216), Manchurian (n=24), Hui (n=6) and Daur (n=6). Nine common mutations in four genes (GJB2, SLC26A4, GJB3 and mitochondrial MT-RNR1 gene) were detected by allele-specific PCR and universal array. At least one mutated allele was detected in 282 patients. Pathogenic mutations were detected in 168 patients: 114 were homozygotes and 54 were compound heterozygotes. The 114 patients were carriers of only one mutated allele. The frequency of GJB2 variants in Han Chinese (21.0%) was higher than that in Mongolians (16.7%), but not significantly different. On the other hand, the frequency of SLC26A4 variants in Han Chinese (14.8%) was lower than that in Mongolians (19.4%), but also not significantly different. The frequency of patients with pathogenic mutations was different in Ulanqab (21.4%), Xilingol (40.0%), Chifeng (40.0%), Hulunbeier (30.0%), Hohhot (26.3%), and in Baotou (0%). In conclusion, the frequency of mutated alleles in deafness-related genes did not differ between Han Chinese and Mongolians. However, differences in the distribution of common deafness-related mutations were found among the investigated areas of Inner Mongolia.

Analysis of p.V37I compound heterozygous mutations in the GJB2 gene in Chinese infants and young children

The p.V37I (c.109G>A) mutation in the GJB2 gene is the common frequent cause of congenital deafness; however, its pathogenicity is debated. The present study investigated the prevalence of p.V37I in Chinese infants and young children and associated clinical characteristics. The subjects of the present study were screened for mutations in GJB2 (235delC, 299delAT, 176dell6, 35delG), SLC26A4 (IVS7-2A>G, 2168A>G), GJB3 (538C>T), and in the mitochondrial 12S rRNA gene (1555A>G, 1494C>T). Subjects with p.V37I underwent an audiological evaluation. GJB2 exon sequencing revealed that 20 subjects had p.V37I compound heterozygous mutations, one of whom had a family history; the mutations included c.235delC/p.V37I (n = 12), c.299AT/p.V37I (n = 7), and c.176del16/p.V37I (n = 1). Of the 20 subjects, 12 were referred for Universal Newborn Hearing Screening (UNHS). Nine of the 20 subjects had mild hearing loss in the better ear and 5 had moderate hearing loss in the better ear while 4 had normal hearing. Among subjects with the c.235delC/p.V37I mutation, 5 had mild hearing loss and 2 had moderate hearing loss while 3 had normal hearing. Among subjects with the c.299AT/p.V37I mutation, 3 had mld hearing loss and 3 had moderate hearing loss while 1 had normal hearing. One subject with the c.176del16/p.V37I mutation had mild hearing loss. Few studies have reported on the clinical characteristics of Chinese infants with p.V37I compound heterozygous mutations identified via screening for deafness genes and GJB2 sequencing. The c.235delC/p.V37I mutation was the most prevalent mutation found in subjects. The degree of hearing loss associated with p.V37I compound heterozygous mutations was mainly mild to moderate.

Screening of the SLC17A8 gene as a causative factor for autosomal dominant non-syndromic hearing loss in Koreans

Background

One of the causes of sensorineural hearing loss (SNHL) is degeneration of the inner hair cells in the organ of Corti in the cochlea. The SLC17A8 (solute carrier family 17, member 8) gene encodes vesicular glutamate transporter 3 (VGLUT3), and among its isoforms (VGLUT1-3), only VGLUT3 is expressed selectively in the inner hair cells (IHCs). VGLUT3 transports the neurotransmitter glutamate into the synaptic vesicles of the IHCs. Mutation of the SLC17A8 gene is reported to be associated with DFNA25 (deafness, autosomal dominant 25), an autosomal dominant non-syndromic hearing loss (ADNSHL) in humans.

Methods

In this study, we performed a genetic analysis of 87 unrelated Korean patients with ADNSHL to determine whether the SLC17A8 gene affects hearing ability in the Korean population.

Results

We found a novel heterozygous frameshift mutation, 2 non-synonymous variations, and a synonymous variation. The novel frameshift mutation, p.M206Nfs*4, in which methionine is changed to asparagine at amino acid position 206, resulted in a termination codon at amino acid position 209. This alteration is predicted to encode a truncated protein lacking transmembrane domains 5 to 12. This mutation is located in a highly conserved region in VGLUT3 across multiple amino acid alignments in different vertebrate species, but it was not detected in 100 unrelated controls who had normal hearing ability. The results from our study suggest that the p.M206Nfs*4 mutation in the SLC17A8 gene is likely a pathogenic mutation that causes ADNSHL.

Conclusion

Our findings can facilitate the prediction of the primary cause of ADNSHL in Korean patients.

Is there a relationship between premature hair greying and hearing impairment?

OBJECTIVE

There is evidence for a strong correlation between low bone mineral density and hearing loss. Furthermore, premature hair greying has been associated with low bone mineral density. Hence, this study aimed to investigate, for the first time, the relationship between premature hair greying and hearing impairment.

METHODS

Fifty patients with premature hair greying (20 women and 30 men), aged under 40 years (mean, 30.1 ± 4.9 years), who had onset of hair greying in their twenties, were recruited, along with 45 age- and sex-matched healthy control subjects (17 women and 28 men; mean age, 28.7 ± 5.1 years). Each participant was tested with low frequency audiometry at 0.125 to 2 kHz, high frequency audiometry at 4 to 8 kHz, and extended high frequency audiometry at 9 to 20 kHz.

RESULTS

Hearing thresholds were similar at all frequencies from 0.25 to 4 kHz (p > 0.05); however, significant hearing loss was observed at all frequencies from 8 to 20 kHz in the premature hair greying group compared with the control group (p < 0.05).

CONCLUSION

Patients with premature hair greying had hearing impairment at extended high frequencies. Premature hair greying may be an important risk factor for hearing loss.

Genetics of hearing loss in Africans: use of next generation sequencing is the best way forward

Hearing loss is the most common communication disorder affecting about 1-7/1000 births worldwide. The most affected areas are developing countries due toextensively poor health care systems. Environmental causes contribute to 50-70% of cases, specifically meningitis in sub-Saharan Africa. The other 30-50% is attributed to genetic factors. Nonsyndromic hearing loss is the most common form of hearing loss accounting for up to 70% of cases. The most common mode of inheritance is autosomal recessive. The most prevalent mutations associated with autosomal recessive nonsyndromic hearing loss (ARNSHL) are found within connexin genes such as GJB2, mostly in people of European and Asian origin. For example, the c.35delG mutation ofGJB2 is found in 70% of ARNSHL patients of European descentand is rare in populations of otherethnicities. Other GJB2 mutations have been reported in various populations. The second most common mutations are found in theconnexin gene, GJB6, also with a high prevalencein patients of European descent. To date more than 60 genes have been associated with ARNSHL. We previously showed that mutations in GJB2, GJB6 and GJA1 are not significant causes of ARNSHL inpatients from African descents, i.e. Cameroonians and South AfricansIn order to resolve ARNSHL amongst sub-Saharan African patients, additional genes would need to be explored. Currently at least 60 genes are thought to play a role in ARNSHL thus the current approach using Sanger sequencing would not be appropriate as it would be expensive and time consuming. Next Generation sequencing (NGS) provides the best alternative approach. In this review, we reported on the success of using NGSas observed in various populations and advocate for the use of NGS to resolve cases of ARNSHL in sub-Saharan African populations.

Hearing impairment and language delay in infants: Diagnostics and genetics

This overview study provides information on important phoniatric and audiological aspects of early childhood hearing and language development with the aim of presenting diagnostic and therapeutic approaches. The article first addresses the universal newborn hearing screening that has been implemented in Germany for all infants since January 2009. The process of newborn hearing screening from the maternity ward to confirmation diagnostics is presented in accordance with a decision by the Federal Joint Committee (G-BA). The second topic is pediatric audiology diagnostics. Following confirmation of a permanent early childhood hearing disorder, the search for the cause plays an important role. Hereditary hearing disorders and intrauterine cytomegalovirus (CMV) infection, probably the most common cause of an acquired hearing disorder, are discussed and compared with the most common temporary hearing disorder, otitis media with effusion, which in some cases is severe enough to be relevant for hearing and language development and therefore requires treatment. The third topic covered in this article is speech and language development in the first 3 years of life, which is known today to be crucial for later language development and learning to read and write. There is a short overview and introduction to modern terminology, followed by the abnormalities and diagnostics of early speech and language development. Only some aspects of early hearing and language development are addressed here. Important areas such as the indication for a cochlear implant in the first year of life or because of unilateral deafness are not included due to their complexity.

A1555G homoplasmic mutation from A1555G heteroplasmic mother with Pendred syndrome

Hearing loss (HL) is genetically heterogeneous and can be caused by mutations in multiple gene lesions. Pendred syndrome, caused by mutation of SLC26A4, is one of the common causes of recessive syndromic profound HL. Mitochondrial mutation is another rare cause of genetic HL, resulting in late onset sensorineural HL. Recently, we evaluated a young woman representing bilateral progressive moderate HL with delayed language development, along with her family. Hearing test, temporal bone computed tomography, and genetic evaluation of GJB2, MT-RNR1, SLC26A4 gene mutations were performed on each family member. Her mother was prelingually deaf and displayed enlarged vestibular aqueduct (EVA) along with goiter. Interestingly, subject's mother showed both SLC26A4 mutation and mitochondrial A1555G heteroplasmic mutation at the same time. The sisters did not display EVA or goiter. Although the subject's older sister showed both prelingual deafness and mitochondrial A1555G heteroplasmy, her younger sister showed only A1555G homoplasmy, which suggests A1555G homoplasmy as the genetic cause of hearing loss. This is the first report of HL caused by mitochondrial A1555G homoplasmy from a mother with Pendred syndrome coexistent with A1555G heteroplasmy in the Korean population.

A missense variant of the ATP1A2 gene is associated with a novel phenotype of progressive sensorineural hearing loss associated with migraine

Hereditary sensorineural hearing loss is an extremely clinical and genetic heterogeneous disorder in humans. Especially, syndromic hearing loss is subdivided by combinations of various phenotypes, and each subtype is related to different genes. We present a new form of progressive hearing loss with migraine found to be associated with a variant in the ATP1A2 gene. The ATP1A2 gene has been reported as the major genetic cause of familial migraine by several previous studies. A Korean family presenting progressive hearing loss with migraine was ascertained. The affected members did not show any aura or other neurologic symptoms during migraine attacks, indicating on a novel phenotype of syndromic hearing loss. To identify the causative gene, linkage analysis and whole-exome sequencing were performed. A novel missense variant, c.571G>A (p.(Val191Met)), was identified in the ATP1A2 gene that showed co-segregation with the phenotype in the family. In silico studies suggest that this variant causes a change in hydrophobic interactions and thereby slightly destabilize the A-domain of Na(+)/K(+)-ATPase. However, functional studies failed to show any effect of the p.(Val191Met) substitution on the catalytic rate of this enzyme. We describe a new phenotype of progressive hearing loss with migraine associated with a variant in the ATP1A2 gene. This study suggests that a variant in Na(+)/K(+)-ATPase can be involved in both migraine and hearing loss.

Selective ablation of pillar and deiters' cells severely affects cochlear postnatal development and hearing in mice

Mammalian auditory hair cells (HCs) are inserted into a well structured environment of supporting cells (SCs) and acellular matrices. It has been proposed that when HCs are irreversibly damaged by noise or ototoxic drugs, surrounding SCs seal the epithelial surface and likely extend the survival of auditory neurons. Because SCs are more resistant to damage than HCs, the effects of primary SC loss on HC survival and hearing have received little attention. We used the Cre/loxP system in mice to specifically ablate pillar cells (PCs) and Deiters' cells (DCs). In Prox1CreER(T2)+/-;Rosa26(DTA/+) (Prox1DTA) mice, Cre-estrogen receptor (CreER) expression is driven by the endogenous Prox1 promoter and, in presence of tamoxifen, removes a stop codon in the Rosa26(DTA/+) allele and induces diphtheria toxin fragment A (DTA) expression. DTA produces cell-autonomous apoptosis. Prox1DTA mice injected with tamoxifen at postnatal days 0 (P0) and P1 show significant DC and outer PC loss at P2-P4, that reaches ∼70% by 1 month. Outer HC loss follows at P14 and is almost complete at 1 month, while inner HCs remain intact. Neural innervation to the outer HCs is disrupted in Prox1DTA mice and auditory brainstem response thresholds in adults are 40-50 dB higher than in controls. The hearing deficit correlates with loss of cochlear amplification. Remarkably, in Prox1DTA mice, the auditory epithelium preserves the ability to seal the reticular lamina and spiral ganglion neuron counts are normal, a key requirement for cochlear implant success. In addition, our results show that cochlear SC pools should be appropriately replenished during HC regeneration strategies.