Hearing loss in Waardenburg syndrome: a systematic review

Waardenburg syndrome (WS) is a rare genetic disorder characterized by hearing loss (HL) and pigment disturbances of hair, skin and iris. Classifications exist based on phenotype and genotype. The auditory phenotype is inconsistently reported among the different Waardenburg types and causal genes, urging the need for an up‐to‐date literature overview on this particular topic. We performed a systematic review in search for articles describing auditory features in WS patients along with the associated genotype. Prevalences of HL were calculated and correlated with the different types and genes of WS. Seventy‐three articles were included, describing 417 individual patients. HL was found in 71.0% and was predominantly bilateral and sensorineural. Prevalence of HL among the different clinical types significantly differed (WS1: 52.3%, WS2: 91.6%, WS3: 57.1%, WS4: 83.5%). Mutations in SOX10 (96.5%), MITF (89.6%) and SNAI2 (100%) are more frequently associated with hearing impairment than other mutations. Of interest, the distinct disease‐causing genes are able to better predict the auditory phenotype compared with different clinical types of WS. Consequently, it is important to confirm the clinical diagnosis of WS with molecular analysis in order to optimally inform patients about the risk of HL.     

A 725 kb deletion at 22q13.1 chromosomal region including SOX10 gene in a boy with a neurologic variant of Waardenburg syndrome type 2

Waardenburg syndrome (WS) is a rare (1/40,000) autosomal dominant disorder resulting from melanocyte defects, with varying combinations of sensorineural hearing loss and abnormal pigmentation of the hair, skin, and inner ear. WS is classified into four clinical subtypes (WS1-S4). Six genes have been identified to be associated with the different subtypes of WS, among which SOX10, which is localized within the region 22q13.1. Lately it has been suggested that whole SOX10 gene deletions can be encountered when testing for WS. In this study we report a case of a 13-year-old boy with a unique de novo 725 kb deletion within the 22q13.1 chromosomal region, including the SOX10 gene and presenting clinical features of a neurologic variant of WS2.     

A homozygous MITF mutation leads to familial Waardenburg syndrome type 4

Waardenburg syndrome (WS) is a genetic disorder characterized by hearing loss and pigmentary abnormalities with variable penetrance. Though heterozygous mutations in MITF are a major cause for Waardenburg syndrome type 2 (WS2), homozygous mutations in this gene and the associated phenotype have been rarely characterized. In this study, we identified a novel p.R223H mutation in MITF in a Chinese Han family with variable WS features. Both parents carried a heterozygous p.R223H mutation. They had normal hearing, and premature greying of the hair is their only pigmentary abnormality. In contrast, their two children both carried a homozygous p.R223H mutation and had classic WS features including profound hearing loss, heterochromia irides and marked pigmentary abnormalities in hair and skin. Interestingly, the two affected children also have persistent chronic constipation since the neonatal period, symptoms suggestive of Waardenburg syndrome type 4 (WS4). Our study revealed a likely association between homozygous mutations in MITF and WS4, which implies a dosage effect for the underlying pathogenesis mechanism.     

SOX10 mutations mimic isolated hearing loss

Ninety genes have been identified to date that are involved in non‐syndromic hearing loss, and more than 300 different forms of syndromic hearing impairment have been described. Mutations in SOX10, one of the genes contributing to syndromic hearing loss, induce a large range of phenotypes, including several subtypes of Waardenburg syndrome and Kallmann syndrome with deafness. In addition, rare mutations have been identified in patients with isolated signs of these diseases. We used the recent characterization of temporal bone imaging aspects in patients with SOX10 mutations to identify possible patients with isolated hearing loss due to SOX10 mutation. We selected 21 patients with isolated deafness and temporal bone morphological defects for mutational screening. We identified two SOX10 mutations and found that both resulted in a non‐functional protein in vitro. Re‐evaluation of the two affected patients showed that both had previously undiagnosed olfactory defects. Diagnosis of anosmia or hyposmia in young children is challenging, and particularly in the absence of magnetic resonance imaging (MRI), SOX10 mutations can mimic non‐syndromic hearing impairment. MRI should complete temporal bones computed tomographic scan in the management of congenital deafness as it can detect brain anomalies, cochlear nerve defects, and olfactory bulb malformation in addition to inner ear malformations.     

EDNRB mutations cause Waardenburg syndrome type II in the heterozygous state

Waardenburg syndrome (WS) is a genetic disorder characterized by sensorineural hearing loss and pigmentation anomalies. The clinical definition of four WS types is based on additional features due to defects in structures mostly arising from the neural crest, with type I and type II being the most frequent. While type I is tightly associated to PAX3 mutations, WS type II (WS2) remains partly enigmatic with mutations in known genes (MITF, SOX10) accounting for only 30% of the cases. We performed exome sequencing in a WS2 index case and identified a heterozygous missense variation in EDNRB. Interestingly, homozygous (and very rare heterozygous) EDNRB mutations are already described in type IV WS (i.e., in association with Hirschsprung disease [HD]) and heterozygous mutations in isolated HD. Screening of a WS2 cohort led to the identification of an overall of six heterozygous EDNRB variations. Clinical phenotypes, pedigrees and molecular segregation investigations unraveled a dominant mode of inheritance with incomplete penetrance. In parallel, cellular and functional studies showed that each of the mutations impairs the subcellular localization of the receptor or induces a defective downstream signaling pathway. Based on our results, we now estimate EDNRB mutations to be responsible for 5%–6% of WS2.     

Two SOX11 variants cause Coffin–Siris syndrome with a new feature of sensorineural hearing loss

Coffin-Siris syndrome (CSS, OMIM#135900) is a rare congenital disorder associated with neurodevelopmental and dysmorphic features. The primary cause of CSS is pathogenic variants in any of 9 BAF chromatin-remodeling complex encoding genes or the genes SOX11 and PHF6. Herein, we performed whole-exome sequencing (WES) and a series of analyses of growth-related, auditory, and radiological findings in two probands with syndromic sensorineural hearing loss and inner ear malformations who exhibited distinctive facial features, intellectual disability, growth retardation, and fifth finger malformation. Two de novo variants in the SOX11 gene (c.148A>C:p.Lys50Asn; c.811_814del:p.Asn271Serfs*10) were detected in these probands and were identified as pathogenic variants as per ACMG guidelines. These probands were diagnosed as having CSS based upon clinical and genetic findings. This is the first report of CSS caused by variants in SOX11 gene in Chinese individuals. Deleterious SOX11 variants can result in sensorineural hearing loss with inner ear malformation, potentially extending the array of phenotypes associated with these pathogenic variants. We suggest that both genetic and clinical findings be considered when diagnosing syndromic hearing loss.     

POLD1 Germline Mutations in Patients Initially Diagnosed with Werner Syndrome

Segmental progeroid syndromes are rare, heterogeneous disorders characterized by signs of premature aging affecting more than one tissue or organ. A prototypic example is the Werner syndrome (WS), caused by biallelic germline mutations in the Werner helicase gene (WRN). While heterozygous lamin A/C (LMNA) mutations are found in a few nonclassical cases of WS, another 10%–15% of patients initially diagnosed with WS do not have mutations in WRN or LMNA. Germline POLD1 mutations were recently reported in five patients with another segmental progeroid disorder: mandibular hypoplasia, deafness, progeroid features syndrome. Here, we describe eight additional patients with heterozygous POLD1 mutations, thereby substantially expanding the characterization of this new example of segmental progeroid disorders. First, we identified POLD1 mutations in patients initially diagnosed with WS. Second, we describe POLD1 mutation carriers without clinically relevant hearing impairment or mandibular underdevelopment, both previously thought to represent obligate diagnostic features. These patients also exhibit a lower incidence of metabolic abnormalities and joint contractures. Third, we document postnatal short stature and premature greying/loss of hair in POLD1 mutation carriers. We conclude that POLD1 germline mutations can result in a variably expressed and probably underdiagnosed segmental progeroid syndrome.     

Novel nonsense mutation of the endothelin-B receptor gene in a family with Waardenburg-Hirschsprung disease

Waardenburg syndrome (WS) comprises sensorineural hearing loss, hypopigmentation of skin and hair, and pigmentary disturbances of the irides. Four types of WS have been classified to date; in WS type IV (WS4), patients additionally have colonic aganglionosis (Hirschsprung disease, HSCR). Mutations in the endothelin-3 (EDN3), endothelin-B receptor (EDNRB), and Sox10 genes have been identified as causative for WS type IV. We screened a family with a combined WS-HSCR phenotype for mutations in the EDNRB locus using standard DNA mutation analysis and sequencing techniques. We have identified a novel nonsense mutation at codon 253 (CGA→TGA, Arg→STOP). This mutation leads to a premature end of the translation of EDNRB at exon 3, and it is predicted to produce a truncated and nonfunctional endothelin-B receptor. All affected relatives were heterozygous for the Arg²⁵³→STOP mutation, whereas it was not observed in over 50 unrelated individuals used as controls. These data confirm the role of EDNRB in the cause of the Waardenburg-Hirschsprung syndrome and demonstrate that in WS-HSCR there is a lack of correlation between phenotype and genotype and a variable expression of disease even within the same family. Am. J. Med. Genet. 87:69–71, 1999. © 1999 Wiley-Liss, Inc.     

A patient with peripheral demyelinating neuropathy,central dysmyelinating leukodystrophy,Waardenburg syndrome,and severe hypoganglionosis associated with a novel SOX10 mutation

In this report, we present the case of a female infant with peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, Waardenburg syndrome, and Hirschsprung disease (PCWH) associated with a novel frameshift mutation (c.842dupT) in exon 5, the last exon of SOX10. She had severe hypoganglionosis in the small intestine and entire colon, and suffered from frequent enterocolitis. The persistence of ganglion cells made both the diagnosis and treatment difficult in the neonatal period. She also showed hypopigmentation of the irises, hair and skin, bilateral sensorineural deafness with hypoplastic inner year, severe demyelinating neuropathy with hypotonia, and diffuse brain hypomyelination. The p.Ser282GlnfsTer12 mutation presumably escapes from nonsense‐mediated decay and may generate a dominant‐negative effect. We suggest that hypoganglionosis can be a variant intestinal manifestation associated with PCWH and that hypoganglionosis and aganglionosis may share the same pathoetiological mechanism mediated by SOX10 mutations.     

Identification and functional analysis of SOX10 missense mutations in different subtypes of Waardenburg syndrome

Waardenburg syndrome (WS) is a rare disorder characterized by pigmentation defects and sensorineural deafness, classified into four clinical subtypes, WS1-S4. Whereas the absence of additional features characterizes WS2, association with Hirschsprung disease defines WS4. WS is genetically heterogeneous, with six genes already identified, including SOX10. About 50 heterozygous SOX10 mutations have been described in patients presenting with WS2 or WS4, with or without myelination defects of the peripheral and central nervous system (PCWH, Peripheral demyelinating neuropathy-Central dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschsprung disease, or PCW, PCWH without HD). The majority are truncating mutations that most often remove the main functional domains of the protein. Only three missense mutations have been thus far reported. In the present study, novel SOX10 missense mutations were found in 11 patients and were examined for effects on SOX10 characteristics and functions. The mutations were associated with various phenotypes, ranging from WS2 to PCWH. All tested mutations were found to be deleterious. Some mutants presented with partial cytoplasmic redistribution, some lost their DNA-binding and/or transactivation capabilities on various tissue-specific target genes. Intriguingly, several mutants were redistributed in nuclear foci. Whether this phenomenon is a cause or a consequence of mutation-associated pathogenicity remains to be determined, but this observation could help to identify new SOX10 modes of action.     

Autosomal Dominant Hearing Loss resulting from p.R75Q Mutation in the GJB2 Gene: Nonsyndromic presentation in a South Indian Family

Mutations in the GJB2 gene encoding the gap junction protein Connexin 26 have been associated with autosomal recessive as well as dominant nonsyndromic hearing loss. Owing to the involvement of connexins in skin homeostasis, GJB2 mutations have also been associated with syndromic forms of hearing loss showing various skin manifestations. We report an assortatively mating hearing impaired family of south Indian origin with three affected members spread over two generations, having p.R75Q mutation in the GJB2 gene in the heterozygous condition. The inheritance pattern was autosomal dominant with mother and son being affected. Dermatological and histopathologic examinations showed absence of palmoplantar keratoderma. To the best of our knowledge, this is the first report from India on p.R75Q mutation in the GJB2 gene with nonsyndromic hearing loss.     

New role of LRP5, associated with nonsyndromic autosomal‐recessive hereditary hearing loss

Human hearing loss is a common neurosensory disorder about which many basic research and clinically relevant questions are unresolved. At least 50% of hearing loss are due to a genetic etiology. Although hundreds of genes have been reported, there are still hundreds of related deafness genes to be found. Clinical, genetic, and functional investigations were performed to identify the causative mutation in a distinctive Chinese family with postlingual nonsyndromic sensorineural hearing loss. Whole‐exome sequencing (WES) identified lipoprotein receptor‐related protein 5 (LRP5), a member of the low‐density lipoprotein receptor family, as the causative gene in this family. In the zebrafish model, lrp5 downregulation using morpholinos led to significant abnormalities in zebrafish inner ear and lateral line neuromasts and contributed, to some extent, to disabilities in hearing and balance. Rescue experiments showed that LRP5 mutation is associated with hearing loss. Knocking down lrp5 in zebrafish results in reduced expression of several genes linked to Wnt signaling pathway and decreased cell proliferation when compared with those in wild‐type zebrafish. In conclusion, the LRP5 mutation influences cell proliferation through the Wnt signaling pathway, thereby reducing the number of supporting cells and hair cells and leading to nonsyndromic hearing loss in this Chinese family.     

Biallelic deletions of the Waardenburg II syndrome gene,SOX10, cause a recognizable arthrogryposis syndrome

Random mating in the general population tends to limit the occurrence of homozygous and compound heterozygous forms of dominant hereditary disorders. Certain phenotypes, the most recognized being skeletal dysplasias associated with short stature, lead to cultural interaction and assortative mating. To this well‐known example, may be added deafness which brings together individuals with a variety of deafness genotypes, some being dominant. Waardenburg syndrome is one such autosomal dominant disorder in which affected individuals may interact culturally because of deafness. Biallelic genetic alterations for two Waardenburg genes, PAX3 and MITF have been previously recognized. Herein, we report biallelic deletions in SOX10, a gene associated with Waardenburg syndromes type II and IV. The affected fetuses have a severe phenotype with a lack of fetal movement resulting in four‐limb arthrogryposis and absence of palmar and plantar creases, white hair, dystopia canthorum, and in one case cleft palate and in the other a cardiac malformation.     

SOX11 is useful in differentiating cyclin D1‐positive diffuse large B‐cell lymphoma from mantle cell lymphoma

Hsiao S‐C, Cortada I R, Colomo L, Ye H, Liu H, Kuo S‐Y, Lin S‐H, Chang S‐T, Kuo T U, Campo E & Chuang S‐S
(2012) Histopathology  61, 685–693 SOX11 is useful in differentiating cyclin D1‐positive diffuse large B‐cell lymphoma from mantle cell lymphoma Aims: To characterize the frequency and clinicopathological features of cyclin D1‐positive diffuse large B‐cell lymphoma (DLBCL) and the usefulness of SOX11 in the differential diagnosis from mantle cell lymphoma (MCL). Methods and results: We retrospectively stained 206 consecutive DLBCLs for cyclin D1, and identified three (1.5%) positive cases, comprising two in the elderly with necrosis, and a third with a starry‐sky pattern. All three cases shared the same non‐germinal centre B‐cell (non‐GCB) phenotype [CD5?/CD10?/bcl‐6+/MUM1+/SOX11?], Epstein–Barr virus (EBV) negativity, and absence of CCND1 aberrations by fluorescence in‐situ hybridization. The third case showed both BCL6 and MYC rearrangements: a double‐hit lymphoma. In the same period there were 22 MCLs, all expressing cyclin D1, with 89% cases expressing SOX11, a frequency that is statistically different from cyclin D1‐positive DLBCL. Notably, we identified a pleomorphic MCL initially misdiagnosed as DLBCL. A separate cohort of 98 DLBCL cases was negative for SOX11, with only one case expressing cyclin D1 with a GCB phenotype (CD10+/bcl‐6+/MUM1?). The two patients with tumour necrosis rapidly died of disease. The other two were in complete remission after immunochemotherapy. Conclusions: Cyclin D1‐positive DLBCLs are rare, and they are negative for SOX11 or CCND1 aberration. SOX11 is useful in differentiating cyclin D1‐positive DLBCL from MCL.     

Ocular albinism with infertility and late‐onset sensorineural hearing loss

Ocular albinism type 1 (OA1) is caused by mutations in the GPR143 gene located at Xp22.2. The manifestations, which are due to hypopigmentation, are confined to the eyes and optic pathway. OA1 associated with late‐onset sensorineural hearing loss was previously reported in a single family and hypothesized to be caused by a contiguous gene deletion syndrome involving GPR143 and the adjacent gene, TBL1X. Here, we report on a family with OA1, infertility, late‐onset sensorineural hearing loss, and a small interstitial Xp microdeletion including the GPR143, TBL1X, and SHROOM2 genes. In addition, we re‐examined a patient previously described with OA1, infertility and a similar Xp deletion with audiologic follow‐up showing a late‐onset sensorineural hearing loss. Our results raise an intriguing question about the possibility for TBL1X (absence) involvement in this type of hearing loss. However, our study cannot claim a causative relationship and more convincing evidence is needed before the hypothesis can be accepted that TBL1X could be involved in late‐onset sensorineural hearing loss and that ocular albinism with late‐onset sensorineural hearing loss can present itself as a contiguous gene deletion/microdeletion syndrome. The finding of infertility in all affected male patients demonstrates that this deletion, including the SHROOM2 gene, may be a potentially causative X‐linked genetic factor of male infertility.