Waardenburg syndrome: clinical differentiation between types I and II

Waardenburg Syndrome: The Contribution of Next-Generation Sequencing to the Identification of Novel Causative Variants

Waardenburg syndrome (WS) is characterized by hearing loss and pigmentary abnormalities of the eyes, hair, and skin. The condition is genetically heterogeneous, and is classified into four clinical types differentiated by the presence of dystopia canthorum in type 1 and its absence in type 2. Additionally, limb musculoskeletal abnormalities and Hirschsprung disease differentiate types 3 and 4, respectively. Genes PAX3, MITF, SOX10, KITLG, EDNRB, and EDN3 are already known to be associated with WS. In WS, a certain degree of molecularly undetected patients remains, especially in type 2. This study aims to pinpoint causative variants using different NGS approaches in a cohort of 26 Brazilian probands with possible/probable diagnosis of WS1 (8) or WS2 (18). DNA from the patients was first analyzed by exome sequencing. Seven of these families were submitted to trio analysis. For inconclusive cases, we applied a targeted NGS panel targeting WS/neurocristopathies genes. Causative variants were detected in 20 of the 26 probands analyzed, these being five in PAX3, eight in MITF, two in SOX10, four in EDNRB, and one in ACTG1 (type 2 Baraitser-Winter syndrome, BWS2). In conclusion, in our cohort of patients, the detection rate of the causative variant was 77%, confirming the superior detection power of NGS in genetically heterogeneous diseases.

Identification of a de novo, Novel Pathogenic Variant in the Splice Region of the SOX10 Gene in an Iranian Azeri Turkish Family with Waardenburg Syndrome

Background

Waardenburg syndrome (WS) is an inherited heterogeneous auditory pigmentary syndrome, divided into at least four types and characterized by iris heterochromia, white forelock, prominent nasal root, dystopia canthorum, middle eyebrow hypertrichosis, and deafness. Pathogenic variants in the SOX10 gene have been reported to be involved in WS disease.

Methods

Whole exome sequencing (WES) was conducted on a 24-year-old male, who originated from Iranian Azeri Turkish ethnic group, with symptoms of deafness and blue eyes from brown-eyed parents. Web-based tools including Mutation Taster, VarSome, SIFT, Human Splicing Finder (HSF), and I-TASSER, were used for bioinformatics analysis. To verify the WES findings, DNAs taken from the blood samples of all family members were subjected to PCR-Sanger sequencing.

Results

A novel heterozygous pathogenic variant, NC_000022.11 (NM_006941):c.428+1G>T, located in the second intron of the SOX10 gene and disrupting the splicing site, was identified in the proband. Sanger sequencing was applied on the proband and his parents. The results showed that the variant was a de novo pathogenic variant with an autosomal dominant inheritance pattern.

Conclusions

Identification of a novel de novo pathogenic variant, NC_000022.11 (NM_006941):c.428+1G>T, in the second intron of the SOX10 gene with autosomal dominant inheritance pattern.

Molecular and genetic characterization of a large Brazilian cohort presenting hearing loss

Hearing loss is one of the most common sensory defects, affecting 5.5% of the worldwide population and significantly impacting health and social life. It is mainly attributed to genetic causes, but their relative contribution reflects the geographical region's socio-economic development. Extreme genetic heterogeneity with hundreds of deafness genes involved poses challenges for molecular diagnosis. Here we report the investigation of 542 hearing-impaired subjects from all Brazilian regions to search for genetic causes. Biallelic GJB2/GJB6 causative variants were identified in 12.9% (the lowest frequency was found in the Northern region, 7.7%), 0.4% carried GJB2 dominant variants, and 0.6% had the m.1555A > G variant (one aminoglycoside-related). In addition, other genetic screenings, employed in selected probands according to clinical presentation and presumptive inheritance patterns, identified causative variants in 2.4%. Ear malformations and auditory neuropathy were diagnosed in 10.8% and 3.5% of probands, respectively. In 3.8% of prelingual/perilingual cases, Waardenburg syndrome was clinically diagnosed, and in 71.4%, these diagnoses were confirmed with pathogenic variants revealed; seven out of them were novel, including one CNV. All these genetic screening strategies revealed causative variants in 16.2% of the cases. Based on causative variants in the molecular diagnosis and genealogy analyses, a probable genetic etiology was found in ~ 50% of the cases. The present study highlights the relevance of GJB2/GJB6 as a cause of hearing loss in all Brazilian regions and the importance of screening unselected samples for estimating frequencies. Moreover, when a comprehensive screening is not available, molecular diagnosis can be enhanced by selecting probands for specific screenings.

Analysis of genotype-phenotype relationships in 90 Chinese probands with Waardenburg syndrome

Waardenburg syndrome (WS) is a phenotypically and genetically heterogeneous disorder characterised by hearing loss and pigmentary abnormalities. We clarified the clinical and genetic features in 90 Chinese WS probands. Disease-causing variants were detected in 55 probands, for a molecular diagnosis rate of 61%, including cases related to PAX3 (14.4%), MITF (24.4%), and SOX10 (22.2%). Altogether, 48 variants were identified, including 44 single-nucleotide variants and 4 copy number variants. By parental genotyping, de novo variants were observed in 60% of probands and 15.4% of the de novo variation was associated with mosaicism. Statistical analyses revealed that brown freckles on the skin were more frequently seen in probands with MITF variants; patchy depigmented skin, asymmetric hearing loss, and white forelocks occurred more often in cases with PAX3 variants; and congenital inner ear malformations were more common and cochlear hypoplasia III was exclusively observed in those with SOX10 variants. In addition, we found that ranges of W-index values overlapped between WS probands with different genetic variants, and the use of the W-index as a tool for assessing dystopia canthorum may be problematic in Chinese. Herein, we report the spectrum of a cohort of WS probands and elucidate the relationship between genotype and phenotype.

Novel mutations of SOX10 gene in Chinese patients with type II Waardenburg syndrome

Waardenburg Syndrome (WS) is a condition characterized by sensorineural deafness and pigment disturbances of the skin, hair and iris. By using the latest genomics technology, the WS-related gene mutations and corresponding mechanisms have been widely studied and reported. and the high genetic heterogeneity of the disease has also been explained. However, the SOX10 gene transcription and expression has still be unclear. In this study, we determined the phenotypic gene expression of WS patients in two Chinese WS families. More importantly, we identified two novel SOX10 mutations, c.482-487del (p.R161-M162del)and c.52G > T (p.E18X) in WSII for the first time in the Chinese population.

Asymmetric choroidal hypopigmentation in a Son and mother with Waardenburg syndrome type I

BACKGROUND

Waardenburg syndrome type I (WS-I) is a rare autosomal-dominant auditory-pigmentary disorder with limited reports in the Ophthalmic literature.

MATERIALS AND METHODS

We describe the history, clinical findings and detailed retinal imaging (ultra-widefield fundus images, fundus autofluorescence and optical coherence tomography) from a patient with WS-I.

CASE DESCRIPTION

Our patient had a history of white forelock and congenital hearing loss. Ophthalmic examination demonstrated iris heterochromia and highly asymmetric choroidal hypopigmentation, with generalised fundus hyperautofluorescence. Similarly, the patient's mother demonstrated highly asymmetric fundus hypopigmentation. Genetic testing confirmed a pathogenic PAX3 nonsense variant.

CONCLUSION

Our report demonstrates that highly asymmetric choroidal hypopigmentation is within the clinical spectrum of WS-I.

ABBREVIATIONS

OCT: Optical coherence tomography; WS-I: Waardenburg syndrome type 1.

Triple diagnosis of Wiedemann-Steiner, Waardenburg and DLG3-related intellectual disability association found by WES: A case report

BACKGROUND

The development of whole-exome sequencing (WES) and whole-genome sequencing (WGS) for clinical purposes now allows the identification of multiple pathogenic variants in patients with a rare disease. This occurs even when a single causative gene was initially suspected. We report the case of an 8-year-old patient with global developmental delays and dysmorphic features, with a possibly pathogenic variant in three distinct genes.

METHODS

Trio-based exome sequencing was performed by IntegraGen SA (Evry, France), on an Illumina HiSeq4000 (Illumina, San Diego, CA, USA). Sanger sequencing was performed to confirm the variants that were found.

RESULTS

WES showed the presence of three possibly deleterious variants: KMT2A: c.9068delA;p.Gln3023Argfs*3 de novo, PAX3: c.530C>G;p.Ala177Gly de novo and DLG3: c.127delG;p.Asp43Metfs*22 hemizygous inherited from the mother. KMT2A pathogenic variants are involved in Wiedemann-Steiner syndrome, and PAX3 is the gene responsible for Waardenburg syndrome. DLG3 variants have been described in a non-syndromic X-related intellectual disability.

CONCLUSIONS

Considering the dysmorphic features and intellectual disability presented by this patient, these three variants were imputed as pathogenic and their association was considered responsible for his phenotype. Dual molecular diagnoses have already been found by WES in several cohorts with an average of diagnostic yield of 7%. This case demonstrates and reminds us of the importance of analyzing exomes rigorously and exhaustively because, in some cases (< 10%), it can explain superimposed traits or blended phenotypes.

Identification of six novel variants in Waardenburg syndrome type II by next-generation sequencing

Background

Waardenburg syndrome (WS) is a dominantly inherited, genetically heterogeneous auditory‐pigmentary syndrome characterized by nonprogressive sensorineural hearing loss and iris discoloration. This study aimed to investigate the underlying molecular pathology in Chinese WS families.

Methods

A total of 13 patients with Waardenburg syndrome type II (WS2) from six unrelated Chinese families were enrolled. We investigated the mutation profile of genes related to congenital deafness in these families through a targeted sequencing technology and validated the candidate variants by Sanger sequencing.

Results

We identified six novel variants in microphthalmia‐associated transcription factor (MITF) and SRY‐box 10 (SOX10), which were predicted to be disease causing by in silico analysis. Our results showed that mutations in SOX10 and MITF are two major causes of deafness associated with WS, and de novo mutations were frequently found in probands with SOX10 mutations but not in those with MITF mutations.

Conclusion

Results showed that targeted next‐generation sequencing (NGS) enabled us to detect disease‐causing mutations with high accuracy, stability, speed and throughput. Our study extends the pathogenic mutation spectrum of MITF and SOX10.

Identification of Waardenburg Syndrome and the Management of Hearing Loss and Associated Sequelae: A Review for the Pediatric Nurse Practitioner

Waardenburg syndrome (WS) is a rare genetic disorder that is further divided into four subtypes with distinguishing clinical manifestations, categorized by phenotypic variations based on activation or deactivation of six specific gene types. The criteria for clinical diagnosis are established based on these phenotypic variants. While key clinical features may cause suspicion of WS, genetic testing confirms the diagnosis. Pigmentary defects are one of the hallmark features of WS while some individuals may exhibit sensorineural hearing loss, which can be progressive. Audiological treatment is essential to mitigate hearing loss and to minimize speech and language deficits as well as behavior and socioemotional development. Associated complications include musculoskeletal abnormalities and Hirschsprung disease. This article aims to discuss the role of the pediatric nurse practitioner in the early identification, diagnosis, treatment, and long-term management of affected children in the primary care setting.

New Genotypes and Phenotypes in Patients with 3 Subtypes of Waardenburg Syndrome Identified by Diagnostic Next-Generation Sequencing

Background

Waardenburg syndrome (WS) is one of the most common forms of syndromic deafness with heterogeneity of loci and alleles and variable expressivity of clinical features.

Methods

The technology of single-nucleotide variants (SNV) and copy number variation (CNV) detection was developed to investigate the genotype spectrum of WS in a Chinese population.

Results

Ninety WS patients and 24 additional family members were recruited for the study. Fourteen mutations had not been previously reported, including c.808C>G, c.117C>A, c.152T>G, c.803G>T, c.793-3T >G, and c.801delT on PAX3; c.642_650delAAG on MITF; c.122G>T and c.127C>T on SOX10; c.230C>G and c.365C>T on SNAI2; and c.481A>G, c.1018C>G, and c.1015C>T on EDNRB. Three CNVs were de novo and first reported in our study. Five EDNRB variants were associated with WS type 1 in the heterozygous state for the first time, with a detection rate of 22.2%. Freckles occur only in WS type 2. Yellow hair, amblyopia, congenital ptosis, narrow palpebral fissures, and pigmentation spots are rare and unique symptoms in WS patients from China.

Conclusions

EDNRB should be considered as another prevalent pathogenic gene in WS type 1. Our study expanded the genotype and phenotype spectrum of WS, and diagnostic next-generation sequencing is promising for WS.

Waardenburg syndrome: Novel mutations in a large Brazilian sample

This paper deals with the molecular investigation of Waardenburg syndrome (WS) in a sample of 49 clinically diagnosed probands (most from southeastern Brazil), 24 of them having the type 1 (WS1) variant (10 familial and 14 isolated cases) and 25 being affected by the type 2 (WS2) variant (five familial and 20 isolated cases). Sequential Sanger sequencing of all coding exons of PAX3, MITF, EDN3, EDNRB, SOX10 and SNAI2 genes, followed by CNV detection by MLPA of PAX3, MITF and SOX10 genes in selected cases revealed many novel pathogenic variants. Molecular screening, performed in all patients, revealed 19 causative variants (19/49 = 38.8%), six of them being large whole-exon deletions detected by MLPA, seven (four missense and three nonsense substitutions) resulting from single nucleotide substitutions (SNV), and six representing small indels. A pair of dizygotic affected female twins presented the c.430delC variant in SOX10, but the mutation, imputed to gonadal mosaicism, was not found in their unaffected parents. At least 10 novel causative mutations, described in this paper, were found in this Brazilian sample. Copy-number-variation detected by MLPA identified the causative mutation in 12.2% of our cases, corresponding to 31.6% of all causative mutations. In the majority of cases, the deletions were sporadic, since they were not present in the parents of isolated cases. Our results, as a whole, reinforce the fact that the screening of copy-number-variants by MLPA is a powerful tool to identify the molecular cause in WS patients.

Outcomes of cochlear implantation for the patients with specific genetic etiologies: a systematic literature review

CONCLUSION

Most of the cases with gene mutations of intra-cochlear etiology showed relatively good CI outcomes. To progress toward more solid evidence-based CI intervention, a greater number of reports including CI outcomes for specific gene mutations are desired.

BACKGROUND

Cochlear implantation (CI) is the most important and effective treatment for patients with profound sensorineural hearing loss. However, the outcomes of CI vary among patients. One of the reasons of this heterogeneous outcome for cochlear implantation is thought to be the heterogeneous nature of hearing loss. Indeed, genetic factors, the most common etiology in severe-to-profound hearing loss, might be one of the key determinants of outcomes for CI and electric acoustic stimulation (EAS). Patients with genetic causes involving an 'intra-cochlear' etiology show good CI/EAS outcomes.

REVIEW

This review article aimed to summarize the reports on CI/EAS outcomes in patients with special genetic causes as well as to assist in future clinical decision-making. Most of the cases were suspected of an intra-cochlear etiology, such as those with GJB2, SLC26A4, and OTOF mutations, which showed relatively good CI outcomes. However, there have only been a limited number of reports on patients with other gene mutations.

Whole-exome sequencing analysis of Waardenburg syndrome in a Chinese family

Waardenburg syndrome (WS) is a dominantly inherited, genetically heterogeneous auditory-pigmentary syndrome characterized by non-progressive sensorineural hearing loss and iris discoloration. By whole-exome sequencing (WES), we identified a nonsense mutation (c.598C>T) in PAX3 gene, predicted to be disease causing by in silico analysis. This is the first report of genetically diagnosed case of WS PAX3 c.598C>T nonsense mutation in Chinese ethnic origin by WES and in silico functional prediction methods.

A Novel Pathogenic Variant in the MITF Gene Segregating with a Unique Spectrum of Ocular Findings in an Extended Iranian Waardenburg Syndrome Kindred

Waardenburg syndrome (WS) is a rare genetic disorder characterized by abnormal pigmentation of the hair, skin, and iris as well as sensorineural hearing loss. WS is subdivided into 4 major types (WS1-4), where WS2 is characterized by the absence of dystopia canthorum. This study was launched to investigate clinical and molecular characteristics of WS in an extended Iranian WS2 family. A comprehensive clinical investigation was performed. Peripheral blood samples were collected and genomic DNA was extracted. Affected members of the family were studied for possible mutations within the SOX10, MITF, and SNAI2 genes. Six WS2 individuals affected from a large Iranian WS2 kindred were enrolled. All affected members carried the novel substitution c.877C>T at exon 9 in the MITF gene, which resulted in p.Arg293* at the protein level. None of the healthy members and also of 50 ethnically matched controls had this variant. In addition, a spectrum of unique ocular findings, including nystagmus, chorioretinal degeneration, optic disc hypoplasia, astigmatism, and myopia, was segregated with the mutant allele in the pedigree. Our data provide insight into the genotypic and phenotypic spectrum of WS2 in an Iranian family and could further expand the spectrum of MITF mutations and have implications for genetic counseling on WS in Iran.

Tietz/Waardenburg type 2A syndrome associated with posterior microphthalmos in two unrelated patients with novel MITF gene mutations

Tietz syndrome and Waardenburg syndrome type 2A are allelic conditions caused by MITF mutations. Tietz syndrome is inherited in an autosomal dominant pattern and is characterized by congenital deafness and generalized skin, hair, and eye hypopigmentation, while Waardenburg syndrome type 2A typically includes variable degrees of sensorineural hearing loss and patches of de-pigmented skin, hair, and irides. In this paper, we report two unrelated families with MITF mutations. The first family showed an autosomal dominant pattern and variable expressivity. The second patient was isolated. MITF gene analysis in the first family demonstrated a c.648A>C heterozygous mutation in exon 8 c.648A>C; p. (R216S), while in the isolated patient, an apparently de novo heterozygous c.1183_1184insG truncating mutation was demonstrated in exon 10. All patients except one had bilateral reduced ocular anteroposterior axial length and a high hyperopic refractive error corresponding to posterior microphthalmos, features that have not been described as part of the disease. Our results suggest that posterior microphthalmos might be part of the clinical characteristics of Tietz/Waardenburg syndrome type 2A and expand both the clinical and molecular spectrum of the disease. © 2016 Wiley Periodicals, Inc.

The Hearing Outcomes of Cochlear Implantation in Waardenburg Syndrome

Objectives. This study aimed to determine the feasibility of cochlear implantation for sensorineural hearing loss in patients with Waardenburg syndrome. Method. A retrospective chart review was performed on patients who underwent cochlear implantation at the University of Tokyo Hospital. Clinical classification, genetic mutation, clinical course, preoperative hearing threshold, high-resolution computed tomography of the temporal bone, and postoperative hearing outcome were assessed. Result. Five children with Waardenburg syndrome underwent cochlear implantation. The average age at implantation was 2 years 11 months (ranging from 1 year 9 months to 6 years 3 months). Four patients had congenital profound hearing loss and one patient had progressive hearing loss. Two patients had an inner ear malformation of cochlear incomplete partition type 2. No surgical complication or difficulty was seen in any patient. All patients showed good hearing outcome postoperatively. Conclusion. Cochlear implantation could be a good treatment option for Waardenburg syndrome.

Targeted Exome Sequencing of Deafness Genes After Failure of Auditory Phenotype-Driven Candidate Gene Screening

OBJECTIVE

To demonstrate the efficacy and advantages of targeted exome sequencing (TES) of known deafness genes in cases with failed or misleading auditory phenotype-driven candidate gene screening.

STUDY DESIGN

Prospective cohort survey.

SETTING

Otolaryngology department of a tertiary referral hospital.

PATIENTS

Six hearing-impaired probands with seemingly non-syndromic features from six deaf families were enrolled in this study after failure of genetic diagnosis using auditory phenotype-driven candidate gene screening.

INTERVENTION

TES of known deafness genes was performed in the six probands, and a final causative variant was pursued using subsequent filtering steps.

MAIN OUTCOME MEASURE

Potential causative variants determined using TES were confirmed by previously introduced filtering steps.

RESULTS

We detected causative variants in three (50%) of six families, and these variants were in the COCH, PAX3, and GJB2 genes. Additionally, we also recapitulated the recent finding from other report arguing for the non-pathogenic potential of MYO1A variant.

CONCLUSIONS

TES of a deafness panel provides a comprehensive genetic screening tool that can be implemented without being misled by the audiogram configuration information and can complement incomplete clinical physical examinations. In addition, the secondary incidental finding obtained by TES contributes useful information regarding the deafness field.

A novel mutation in the PAX3 gene causes Waardenburg syndrome type I in an Iranian family

OBJECTIVES

Sensorineural hearing impairment (HI) is one of the most frequent congenital defects, with a prevalence of 1 in 500 among neonates. Although there are over 400 syndromes involving HI, most cases of HI are nonsyndromic (70%), 20% of which follow autosomal dominant mode of inheritance. Waardenburg syndrome (WS) ranks first among autosomal dominant syndromic forms of HI. WS is characterized by sensorineural hearing impairment, pigmentation abnormalities of hair and skin and hypoplastic blue eyes or heterochromia iridis. WS is subdivided into four major types, WS1-WS4. WS1 is diagnosed by the presence of dystopia canthorum and PAX3 is the only gene involved. This study aims to determine the pathogenic mutation in a large Iranian pedigree affected with WS1 in order to further confirm the clinical diagnosis.

METHODS

In the present study, a family segregating HI was ascertained in a genetic counseling center. Upon clinical inspection, white forelock, dystopia canthorum, broad high nasal root and synophrys, characteristic of WS1 were evident. In order to clarify the genetic etiology and confirm the clinical data, primers were designed to amplify exons and exon-intron boundaries of the responsible gene, PAX3 with 10 exons, followed by the Sanger DNA sequencing method.

RESULTS

Genetic analysis of PAX3 revealed a novel mutation in PAX3 (c.1024_1040 del AGCACGATTCCTTCCAA). Our data provide genotype-phenotype correlation for the mutation in PAX3 and WS1 in the studied family, with implications for genetic counseling, which necessitates detailed clinical inspection of HI patients to distinguish syndromic HI from the more common non-syndromic cases.

CONCLUSION

Our results reveal the value of phenotype-directed genetic analysis and could further expand the spectrum of PAX3 mutations.

Identification of a Novel De Novo Variant in the PAX3 Gene in Waardenburg Syndrome by Diagnostic Exome Sequencing: The First Molecular Diagnosis in Korea

Waardenburg syndrome (WS) is a clinically and genetically heterogeneous hereditary auditory pigmentary disorder characterized by congenital sensorineural hearing loss and iris discoloration. Many genes have been linked to WS, including PAX3, MITF, SNAI2, EDNRB, EDN3, and SOX10, and many additional genes have been associated with disorders with phenotypic overlap with WS. To screen all possible genes associated with WS and congenital deafness simultaneously, we performed diagnostic exome sequencing (DES) in a male patient with clinical features consistent with WS. Using DES, we identified a novel missense variant (c.220C>G; p.Arg74Gly) in exon 2 of the PAX3 gene in the patient. Further analysis by Sanger sequencing of the patient and his parents revealed a de novo occurrence of the variant. Our findings show that DES can be a useful tool for the identification of pathogenic gene variants in WS patients and for differentiation between WS and similar disorders. To the best of our knowledge, this is the first report of genetically confirmed WS in Korea.

Genetic analysis of PAX3 for diagnosis of Waardenburg syndrome type I

CONCLUSION

PAX3 genetic analysis increased the diagnostic accuracy for Waardenburg syndrome type I (WS1). Analysis of the three-dimensional (3D) structure of PAX3 helped verify the pathogenicity of a missense mutation, and multiple ligation-dependent probe amplification (MLPA) analysis of PAX3 increased the sensitivity of genetic diagnosis in patients with WS1.

OBJECTIVES

Clinical diagnosis of WS1 is often difficult in individual patients with isolated, mild, or non-specific symptoms. The objective of the present study was to facilitate the accurate diagnosis of WS1 through genetic analysis of PAX3 and to expand the spectrum of known PAX3 mutations.

METHODS

In two Japanese families with WS1, we conducted a clinical evaluation of symptoms and genetic analysis, which involved direct sequencing, MLPA analysis, quantitative PCR of PAX3, and analysis of the predicted 3D structure of PAX3. The normal-hearing control group comprised 92 subjects who had normal hearing according to pure tone audiometry.

RESULTS

In one family, direct sequencing of PAX3 identified a heterozygous mutation, p.I59F. Analysis of PAX3 3D structures indicated that this mutation distorted the DNA-binding site of PAX3. In the other family, MLPA analysis and subsequent quantitative PCR detected a large, heterozygous deletion spanning 1759-2554 kb that eliminated 12-18 genes including a whole PAX3 gene.

Hearing impairments caused by genetic and environmental factors

Impairments of hearing and balance are major problems in the field of occupational and environmental health. Such impairments have previously been reported to be caused by genetic and environmental factors. However, their mechanisms have not been fully clarified. On the other hand, the inner ear contains spiral ganglion neurons (SGNs) in the organ of Corti, which serve as the primary carriers of auditory information from sensory cells to the auditory cortex in the cerebrum. Inner ears also contain a vestibule in the vicinity of the organ of Corti—one of the organs responsible for balance. Thus, inner ears could be a good target to clarify the pathogeneses of sensorineural hearing losses and impaired balance. In our previous studies with c-Ret knock-in mice and Endothelin receptor B (Ednrb) knock-out mice, it was found that syndromic hearing losses involved postnatal neurodegeneration of SGNs caused by impairments of c-Ret and Ednrb, which play important roles in neuronal development and maintenance of the enteric nervous system. The organ of Corti and the vestibule in inner ears also suffer from degeneration caused by environmental stresses including noise and heavy metals, resulting in impairments of hearing and balance. In this review, we introduce impairments of hearing and balance caused by genetic and environmental factors and focus on impairments of SGNs and the vestibule in inner ears as the pathogeneses caused by these factors.

Partial requirement of endothelin receptor B in spiral ganglion neurons for postnatal development of hearing

Impairments of endothelin receptor B (Ednrb/EDNRB) cause the development of Waardenburg-Shah syndrome with congenital hearing loss, hypopigmentation, and megacolon disease in mice and humans. Hearing loss in Waardenburg-Shah syndrome has been thought to be caused by an Ednrb-mediated congenital defect of melanocytes in the stria vascularis (SV) of inner ears. Here we show that Ednrb expressed in spiral ganglion neurons (SGNs) in inner ears is required for postnatal development of hearing in mice. Ednrb protein was expressed in SGNs from WT mice on postnatal day 19 (P19), whereas it was undetectable in SGNs from WT mice on P3. Correspondingly, Ednrb homozygously deleted mice (Ednrb(-/-) mice) with congenital hearing loss showed degeneration of SGNs on P19 but not on P3. The congenital hearing loss involving neurodegeneration of SGNs as well as megacolon disease in Ednrb(-/-) mice were markedly improved by introducing an Ednrb transgene under control of the dopamine β-hydroxylase promoter (Ednrb(-/-);DBH-Ednrb mice) on P19. Neither defects of melanocytes nor hypopigmentation in the SV and skin in Ednrb(-/-) mice was rescued in the Ednrb(-/-);DBH-Ednrb mice. Thus, the results of this study indicate a novel role of Ednrb expressed in SGNs distinct from that in melanocytes in the SV contributing partially to postnatal hearing development.

Novel mutations of PAX3, MITF, and SOX10 genes in Chinese patients with type I or type II Waardenburg syndrome

Waardenburg syndrome (WS) is a rare disorder characterized by distinctive facial features, pigment disturbances, and sensorineural deafness. There are four WS subtypes. WS1 is mostly caused by PAX3 mutations, while MITF, SNAI2, and SOX10 mutations are associated with WS2. More than 100 different disease-causing mutations have been reported in many ethnic groups, but the data from Chinese patients with WS remains poor. Herein we report 18 patients from 15 Chinese WS families, in which five cases were diagnosed as WS1 and the remaining as WS2. Clinical evaluation revealed intense phenotypic variability in Chinese WS patients. Heterochromia iridis and sensorineural hearing loss were the most frequent features (100% and 88.9%, respectively) of the two subtypes. Many brown freckles on normal skin could be a special subtype of cutaneous pigment disturbances in Chinese WS patients. PAX3, MITF, SNAI2, and SOX10 genes mutations were screened for in all the patients. A total of nine mutations in 11 families were identified and seven of them were novel. The SOX10 mutations in WS2 were first discovered in the Chinese population, with an estimated frequency similar to that of MITF mutations, implying SOX10 is an important pathogenic gene in Chinese WS2 cases and should be considered for first-step analysis in WS2, as well as MITF.

What are melanocytes really doing all day long...?

Everyone knows and seems to agree that melanocytes are there to generate melanin - an intriguing, but underestimated multipurpose molecule that is capable of doing far more than providing pigment and UV protection to skin (1). What about the cell that generates melanin, then? Is this dendritic, neural crest-derived cell still serving useful (or even important) functions when no-one looks at the pigmentation of our skin and its appendages and when there is essentially no UV exposure? In other words, what do epidermal and hair follicle melanocytes do in their spare time - at night, under your bedcover? How much of the full portfolio of physiological melanocyte functions in mammalian skin has really been elucidated already? Does the presence or absence of melanocytes matter for normal epidermal and/or hair follicle functions (beyond pigmentation and UV protection), and for skin immune responses? Do melanocytes even deserve as much credit for UV protection as conventional wisdom attributes to them? In which interactions do these promiscuous cells engage with their immediate epithelial environment and who is controlling whom? What lessons might be distilled from looking at lower vertebrate melanophores and at extracutaneous melanocytes in the endeavour to reveal the 'secret identity' of melanocytes? The current Controversies feature explores these far too infrequently posed, biologically and clinically important questions. Complementing a companion viewpoint essay on malignant melanocytes (2), this critical re-examination of melanocyte biology provides a cornucopia of old, but under-appreciated concepts and novel ideas on the slowly emerging complexity of physiological melanocyte functions, and delineates important, thought-provoking questions that remain to be definitively answered by future research.

Screening program for Waardenburg syndrome in Colombia: clinical definition and phenotypic variability

A screening program to detect Waardenburg syndrome (WS) conducted between 2002 and 2005, among 1,763 deaf individuals throughout Columbia identified 95 affected individuals belonging to 95 families, giving a frequency of 5.38% of WS among the institutionalized deaf population. We confirmed the clinical diagnosis of WS in the 95 propositi and, through the family evaluation, we also identified 45 non-institutionalized affected relatives. Audiologic, ophthalmologic, and genetic studies were performed to confirm the diagnosis. Following the classification of the WS consortium, based on the Waardenburg Index (WI), to define the type of WS. We classified 62.1% of the propositi as WS2 and 37.9% as WS1. We present here the results of the study of clinical manifestations, analyzing the presence, severity, and symmetry of clinical findings among this affected population. Overall, among the 95 propositi, in addition to sensorineural deafness in all, the most frequent features were broad nasal root (58.9%), a first degree relative affected (37.9%), heterochromia irides (36.8%), skin hypopigmentation (31.6%), white forelock (28.0%), intense blue iris (27.4%), synophrys (12.6%), premature graying (10.5%), ptosis of the eyelids (9.5%), and hypoplasia alae nasi (1.1%). The majority of individuals had normal psychomotor development (87%), while the remaining 13% had developmental delay. Among the latter, 9.4% corresponded to WS2 and 3.6% to WS1. Our data confirm an interesting inter- and intrafamilial variability in the phenotypic manifestations as well as extremely variable expression.

Clinical characterization of autosomal dominant and recessive variants of Robinow syndrome

Robinow syndrome is a genetically heterogeneous condition characterized by mesomelic limb shortening associated with facial and genital anomalies that can be inherited in an autosomal dominant or recessive mode. We characterized these two variants clinically, with the aim of establishing clinical criteria to enhance the differential diagnosis between them or other similar conditions. The frequencies of clinical signs considered important for the discrimination of the dominant or recessive variants were estimated in a sample consisting of 38 patients personally examined by the authors and of 50 affected subjects from the literature. Using the presence of rib fusions as diagnostic of the recessive variant, and also based on the inheritance pattern in familial cases, we classified 37 patients as having the recessive form and other 51 as having the dominant form. The clinical signs present in more than 75% of patients with either form, and therefore the most important for the characterization of this syndrome were hypertelorism, nasal features (large nasal bridge, short upturned nose, and anteverted nares), midface hypoplasia, mesomelic limb shortening, brachydactyly, clinodactyly, micropenis, and short stature. Hemivertebrae and scoliosis were present in more than 75% of patients with the recessive form, but in less than 25% of patients with the dominant form. Umbilical hernia (32.3%) and supernumerary teeth (10.3%) were found exclusively in patients with the dominant form.

[Genetic deafness]

OBJECTIVES

The aim of this study was to review the different types of genetic deafness.

METHODS

We describe syndromic and isolated sensorineural deafness and transmission deafness.

RESULTS

Genetic sensorineural syndromic deafness represents 30% of cases of genetic deafness. A frequent cause is Pendred syndrome, which associates congenital sensorineural deafness with goitre and malformations of the inner ear which can be identified on computed tomography scan. Isolated deafness which is responsible for 70% of cases of genetic deafness is then outlined. Among the different types of isolated deafness, 80% are autosomal recessive disorders. A frequent form of autosomal recessive deafness is due to mutations in the connexin 26 gene. Lastly, we detail transmission deafness dominated by aplasia. Major aplasia is characterized by a malformation of the external ear associated with malformations of the middle ear whereas, minor aplasia corresponds to a malformation of the middle ear, sometimes associated with minor external ear malformations.

CONCLUSION

For each type of deafness we propose a systematic assessment.

The rare phakomatoses

This article outlines the clinical, central nervous system, and neuropathologic features,pathogenesis, genetics, molecular biology, and neuroimaging characteristics of the rare vascular phakomatoses, melanophakomatoses, and organoid phakomatoses.