A de novoSOX10 mutation causing severe type 4 Waardenburg syndrome without Hirschsprung disease

Current phenotypic and genetic spectrum of syndromic deafness in Tunisia: paving the way for precision auditory health

Hearing impairment (HI) is a prevalent neurosensory condition globally, impacting 5% of the population, with over 50% of congenital cases attributed to genetic etiologies. In Tunisia, HI underdiagnosis prevails, primarily due to limited access to comprehensive clinical tools, particularly for syndromic deafness (SD), characterized by clinical and genetic heterogeneity. This study aimed to uncover the SD spectrum through a 14-year investigation of a Tunisian cohort encompassing over 700 patients from four referral centers (2007-2021). Employing Sanger sequencing, Targeted Panel Gene Sequencing, and Whole Exome Sequencing, genetic analysis in 30 SD patients identified diagnoses such as Usher syndrome, Waardenburg syndrome, cranio-facial-hand-deafness syndrome, and H syndrome. This latter is a rare genodermatosis characterized by HI, hyperpigmentation, hypertrichosis, and systemic manifestations. A meta-analysis integrating our findings with existing data revealed that nearly 50% of Tunisian SD cases corresponded to rare inherited metabolic disorders. Distinguishing between non-syndromic and syndromic HI poses a challenge, where the age of onset and progression of features significantly impact accurate diagnoses. Despite advancements in local genetic characterization capabilities, certain ultra-rare forms of SD remain underdiagnosed. This research contributes critical insights to inform molecular diagnosis approaches for SD in Tunisia and the broader North-African region, thereby facilitating informed decision-making in clinical practice.

Inner Ear Malformations in Congenital Deafness Are Not Associated with Increased Risk of Breech Presentation

BackgroundThere is speculation that an immature vestibular system may be associated with breech presentation at delivery. Our aim was to determine whether syndromes with congenital inner ear malformations were accompanied by a higher frequency of breech presentation/malpresentations than in the general population (2%-3%). Methods: A review was conducted for published literature using PubMed/MEDLINE (1936-2016), to determine frequency of breech presentation and transverse lie in cases with congenital deafness (Michel aplasia, Wildervanck syndrome, Mondini-Alexander dysplasia, Waardenburg syndrome, CHARGE syndrome, Large vestibular aqueductal syndrome, Pendred syndrome, Oculo-aurico-vertebral spectrum, Jervel and Lange-Nielsen syndrome, Usher syndrome, and Scheibe dysplasia) and vestibular nerve aplasia. Results: Identified were total of 122 cases. The frequency of breech presentation was 1.64%, and of transverse lie 1.64%, giving a total of 3.28% malpresentations. Conclusion: The results of the study suggest that congenital malformations of the vestibular apparatus are not associated with the increased risk of breech presentation at delivery.

Development and evolution of the vestibular apparatuses of the inner ear

The vertebrate inner ear is a labyrinthine sensory organ responsible for perceiving sound and body motion. While a great deal of research has been invested in understanding the auditory system, a growing body of work has begun to delineate the complex developmental program behind the apparatuses of the inner ear involved with vestibular function. These animal studies have helped identify genes involved in inner ear development and model syndromes known to include vestibular dysfunction, paving the way for generating treatments for people suffering from these disorders. This review will provide an overview of known inner ear anatomy and function and summarize the exciting discoveries behind inner ear development and the evolution of its vestibular apparatuses.

Understanding the Pathophysiology of Congenital Vestibular Disorders: Current Challenges and Future Directions

In congenital vestibular disorders (CVDs), children develop an abnormal inner ear before birth and face postnatal challenges to maintain posture, balance, walking, eye-hand coordination, eye tracking, or reading. Only limited information on inner ear pathology is acquired from clinical imaging of the temporal bone or studying histological slides of the temporal bone. A more comprehensive and precise assessment and determination of the underlying mechanisms necessitate analyses of the disorders at the cellular level, which can be achieved using animal models. Two main criteria for a suitable animal model are first, a pathology that mirrors the human disorder, and second, a reproducible experimental outcome leading to statistical power. With over 40 genes that affect inner ear development, the phenotypic abnormalities resulting from congenital vestibular disorders (CVDs) are highly variable. Nonetheless, there is a large subset of CVDs that form a common phenotype of a sac-like inner ear with the semicircular canals missing or dysplastic, and discrete abnormalities in the vestibular sensory organs. We have focused the review on this subset, but to advance research on CVDs we have added other CVDs not forming a sac-like inner ear. We have included examples of animal models used to study these CVDs. Presently, little is known about the central pathology resulting from CVDs at the cellular level in the central vestibular neural network, except for preliminary studies on a chick model that show significant loss of second-order, vestibular reflex projection neurons.

Corpus callosotomy for drug-resistant epilepsy in a pediatric patient with Waardenburg syndrome Type I

Background:

Waardenburg syndrome (WS) is caused by autosomal dominant mutations. Since the coexistence of epilepsy and WS type I is rare, the detailed clinical features and treatment of epilepsy, including surgery, have not been fully reported for these patients. We report the first case of an individual with WS type I, who underwent corpus callosotomy (CC) for drug-resistant epilepsy and obtained good seizure outcomes.

Case Description:

A boy was diagnosed as having WS type I and developmental delay based on characteristic symptoms and a family history of hearing loss. He underwent cochlear implantation at 18 months of age. At 4 years of age, he developed epileptic seizures with a semiology of drop attack. Electroencephalography (EEG) showed bilateral synchronous high-amplitude spikes and wave bursts, dominant in the right hemisphere. Based on the multimodality examinations, we considered that ictal discharges propagated from the entire right hemisphere to the left, resulting in synchronous discharge and a clinical drop attack; therefore, CC was indicated. At 9 years of age, he underwent a front 2/3^rd CC. At 1 year, the patient became seizure free, and interictal EEG showed less frequent and lower amplitude spike and wave bursts than before.

Conclusion:

When patients with WS Type I and cognitive impairment show drug-resistant epilepsy, clinicians should consider a presurgical evaluation.

Targeted Next-Generation Sequencing Identifies Separate Causes of Hearing Loss in One Deaf Family and Variable Clinical Manifestations for the p.R161C Mutation in SOX10

Hearing loss is the most common sensory deficit in humans. Identifying the genetic cause and genotype-phenotype correlation of hearing loss is sometimes challenging due to extensive clinical and genetic heterogeneity. In this study, we applied targeted next-generation sequencing (NGS) to resolve the genetic etiology of hearing loss in a Chinese Han family with multiple affected family members. Targeted sequencing of 415 deafness-related genes identified the heterozygous c.481C>T (p.R161C) mutation in SOX10 and the homozygous c.235delC (p.L79Cfs∗3) mutation in GJB2 as separate pathogenic mutations in distinct affected family members. The SOX10 c.481C>T (p.R161C) mutation has been previously reported in a Caucasian patient with Kallmann syndrome that features congenital hypogonadotropic hypogonadism with anosmia. In contrast, family members carrying the same p.R161C mutation in this study had variable Waardenburg syndrome-associated phenotypes (hearing loss and/or hair hypopigmentation) without olfactory or reproductive anomalies. Our results highlight the importance of applying comprehensive diagnostic approaches such as NGS in molecular diagnosis of hearing loss and show that the p.R161C mutation in SOX10 may be associated with a wide range of variable clinical manifestations.

A novel frameshift mutation in SOX10 causes Waardenburg syndrome with peripheral demyelinating neuropathy, visual impairment and the absence of Hirschsprung disease

Waardenburg syndrome (WS) is a group of genetic disorders associated with varying components of sensorineural hearing loss and abnormal pigmentation of the hair, skin, and eyes. There exist four different WS subtypes, each defined by the absence or presence of additional features. One of the genes associated with WS is SOX10, a key transcription factor for the development of neural crest-derived lineages. Here we report a 12-year-old boy with a novel de novo SOX10 frameshift mutation and unique combination of clinical features including primary peripheral demyelinating neuropathy, hearing loss and visual impairment but absence of Hirschsprung disease and the typical pigmentary changes of hair or skin. This expands the spectrum of currently recognized phenotypes associated with WS and illustrates the phenotypic heterogeneity of SOX10-associated WS.

Developmental abnormalities of the otic capsule and inner ear following application of prolyl-hydroxylase inhibitors in chick embryos

BACKGROUND

Naturally hypoxic conditions in amniote embryos play important roles in normal development. We previously showed that a hypoxic condition is required to produce a sufficient amount of neural crest cells (NCCs) during embryogenesis and that promoting a hypoxic response by prolyl-hydroxylase (PHD) inhibitors increases NCCs. Given that PHD inhibitors are considered as a potential treatment for anemia and ischemic diseases, we investigated the phenotypic effect of PHD inhibitors on embryonic development.

METHODS

Chick embryos were administered with PHD inhibitors prior to the induction of NCCs on day 1.5. Three main events relating to hypoxia, NCCs induction, vasculogenesis and chondrogenesis, were examined.

RESULTS

PHD inhibitors caused an increase of Sox10-positive NCCs in vivo. Vasculogenesis was promoted temporarily, although rapid vasculogenesis diminished the effect by day 5 in cephalic and pharyngeal regions. Studies on chondrogenesis at day 7 showed advanced development of the otic capsule, a cartilaginous structure encapsulating the inner ear. Analysis by X-ray micro-computed-tomography (μCT) revealed smaller otic capsule, suggesting premature differentiation. This in turn, deformed the developing semicircular canals within it. Other skeletal structures such as the palate and jaw were unaffected. The localized effect on the otic capsule was considered a result of the multiple effects from the hypoxic responses, increased NCCs and promoted chondrogenesis.

CONCLUSION

Given the wide range of clinical applications being considered for PHD inhibitors, this study provides crucial information to caution and guide use of PHD inhibitors when treating women of childbearing age.

A case report of reversible generalized seizures in a patient with Waardenburg syndrome associated with a novel nonsense mutation in the penultimate exon of SOX10

Background

Waardenburg syndrome type 1 (WS1) can be distinguished from Waardenburg syndrome type 2 (WS2) by the presence of dystopia canthorum. About 96% of WS1 are due to PAX3 mutations, and SOX10 mutations have been reported in 15% of WS2.

Case presentation

This report describes a patient with WS1 who harbored a novel SOX10 nonsense mutation (c.652G > T, p.G218*) in exon 3 which is the penultimate exon. The patient had mild prodromal neurological symptoms that were followed by severe attacks of generalized seizures associated with delayed myelination of the brain. The immature myelination recovered later and the neurological symptoms could be improved. This is the first truncating mutation in exon 3 of SOX10 that is associated with neurological symptoms in Waardenburg syndrome. Previous studies reported that the neurological symptoms that associate with WS are congenital and irreversible. These findings suggest that the reversible neurological phenotype may be associated with the nonsense mutation in exon 3 of SOX10.

Conclusions

When patients of WS show mild prodromal neurological symptoms, the clinician should be aware of the possibility that severe attacks of generalized seizures may follow, which may be associated with the truncating mutation in exon 3 of SOX10.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1139-2) contains supplementary material, which is available to authorized users.

Waardenburg syndrome: a rare cause of inherited neuropathy due to SOX10 mutation

Waardenburg syndrome (WS) is a rare disorder comprising sensorineural deafness and pigmentation abnormalities. Four distinct subtypes are defined based on the presence or absence of additional symptoms. Mutations in six genes have been described in WS. SOX10 mutations are usually associated with a more severe phenotype of WS with peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, and Hirschsprung disease. Here we report a 32-year-old man with a novel heterozygous missense variant in SOX10 gene, who presented with congenital deafness, Hirschsprung disease, iris heterochromia, foot deformity, and intermediate conduction velocity length-dependent sensorimotor neuropathy. This case highlights that the presence of other non-neuropathic features in a patient with presumed hereditary neuropathy should alert the clinician to possible atypical rare causes.

Heterozygous deletion at the SOX10 gene locus in two patients from a Chinese family with Waardenburg syndrome type II

OBJECTIVES

Waardenburg syndrome (WS) is a rare disease characterized by sensorineural deafness and pigment disturbance. To date, almost 100 mutations have been reported, but few reports on cases with SOX10 gene deletion. The inheritance pattern of SOX10 gene deletion is still unclear. Our objective was to identify the genetic causes of Waardenburg syndrome type II in a two-generation Chinese family.

METHODS

Clinical evaluations were conducted in both of the patients. Microarray analysis and multiplex ligation-dependent probe amplification (MLPA) were performed to identify disease-related copy number variants (CNVs). DNA sequencing of the SOX10, MITF and SNAI2 genes was performed to identify the pathogenic mutation responsible for WS2.

RESULTS

A 280kb heterozygous deletion at the 22q13.1 chromosome region (including SOX10) was detected in both of the patients. No mutation was found in the patients, unaffected family members and 30 unrelated healthy controls.

CONCLUSIONS

This report is the first to describe SOX10 heterozygous deletions in Chinese WS2 patients. Our result conform the thesis that heterozygous deletions at SOX10 is an important pathogenicity for WS, and present as autosomal dominant inheritance. Nevertheless, heterozygous deletion of the SOX10 gene would be worth investigating to understand their functions and contributions to neurologic phenotypes.

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.

Interpretation of mRNA splicing mutations in genetic disease: review of the literature and guidelines for information-theoretical analysis

The interpretation of genomic variants has become one of the paramount challenges in the post-genome sequencing era. In this review we summarize nearly 20 years of research on the applications of information theory (IT) to interpret coding and non-coding mutations that alter mRNA splicing in rare and common diseases. We compile and summarize the spectrum of published variants analyzed by IT, to provide a broad perspective of the distribution of deleterious natural and cryptic splice site variants detected, as well as those affecting splicing regulatory sequences. Results for natural splice site mutations can be interrogated dynamically with Splicing Mutation Calculator, a companion software program that computes changes in information content for any splice site substitution, linked to corresponding publications containing these mutations. The accuracy of IT-based analysis was assessed in the context of experimentally validated mutations. Because splice site information quantifies binding affinity, IT-based analyses can discern the differences between variants that account for the observed reduced (leaky) versus abolished mRNA splicing. We extend this principle by comparing predicted mutations in natural, cryptic, and regulatory splice sites with observed deleterious phenotypic and benign effects. Our analysis of 1727 variants revealed a number of general principles useful for ensuring portability of these analyses and accurate input and interpretation of mutations. We offer guidelines for optimal use of IT software for interpretation of mRNA splicing mutations.

Interpretation of mRNA splicing mutations in genetic disease: review of the literature and guidelines for information-theoretical analysis

The interpretation of genomic variants has become one of the paramount challenges in the post-genome sequencing era. In this review we summarize nearly 20 years of research on the applications of information theory (IT) to interpret coding and non-coding mutations that alter mRNA splicing in rare and common diseases. We compile and summarize the spectrum of published variants analyzed by IT, to provide a broad perspective of the distribution of deleterious natural and cryptic splice site variants detected, as well as those affecting splicing regulatory sequences. Results for natural splice site mutations can be interrogated dynamically with Splicing Mutation Calculator, a companion software program that computes changes in information content for any splice site substitution, linked to corresponding publications containing these mutations. The accuracy of IT-based analysis was assessed in the context of experimentally validated mutations. Because splice site information quantifies binding affinity, IT-based analyses can discern the differences between variants that account for the observed reduced (leaky) versus abolished mRNA splicing. We extend this principle by comparing predicted mutations in natural, cryptic, and regulatory splice sites with observed deleterious phenotypic and benign effects. Our analysis of 1727 variants revealed a number of general principles useful for ensuring portability of these analyses and accurate input and interpretation of mutations. We offer guidelines for optimal use of IT software for interpretation of mRNA splicing mutations.

Iron upregulates melanogenesis in cultured retinal pigment epithelial cells

The purpose of our studies was to examine the relationship between iron and melanogenesis in retinal pigment epithelial cells, as prior observations had suggested that iron may promote melanogenesis. This relationship has potential clinical importance, as both iron overload and hyperpigmentation are associated with age-related macular degeneration (AMD). Human fetal retinal pigment epithelial cells and ARPE-19 cells were treated with iron in the form of ferric ammonium citrate, after which quantitative RT-PCR and electron microscopy were performed. Melanogenesis genes tyrosinase, tyrosinase-related protein 1, Hermansky-Pudlak Syndrome 3, premelanosome protein and dopachrome tautomerase were upregulated, as was the melanogenesis-controlling transcription factor, microphthalmia-associated transcription factor (MITF). Iron-treated cells had increased pigmentation and melanosome number. Multiple transcription factors upstream of MITF were upregulated by iron.

Notch signaling regulates neural crest differentiation from human pluripotent stem cells

Neural crest (NC) cells are specified at the border of neural plate and epiderm. They are capable of differentiating into various somatic cell types, including craniofacial and peripheral nerve tissues. Notch signaling plays significant roles during neurogenesis; however, its function during human NC development is poorly understood. Here, we generated self-renewing premigratory NC-like cells (pNCCs) from human pluripotent stem cells and investigated the roles of Notch signaling during the NC differentiation. pNCCs expressed various NC specifier genes, including SLUG, SOX10 and TWIST1, and were able to differentiate into most NC derivatives. Blocking Notch signaling during the pNCC differentiation suppressed the expression of NC specifier genes. In contrast, ectopic expression of activated Notch1 intracellular domain (NICD1) augmented the expression of NC specifier genes, and NICD1 was found to bind at their promoter regions. Notch activity was also required for the maintenance of premigratory NC state, and suppression of Notch led to generation of NC-derived neurons. Taken together, we provide a protocol for the generation of pNCCs, and show that Notch signaling regulates the formation, migration and differentiation of NC from hPSCs.

Loss-of-function mutations in SOX10 cause Kallmann syndrome with deafness

Transcription factor SOX10 plays a role in the maintenance of progenitor cell multipotency, lineage specification, and cell differentiation and is a major actor in the development of the neural crest. It has been implicated in Waardenburg syndrome (WS), a rare disorder characterized by the association between pigmentation abnormalities and deafness, but SOX10 mutations cause a variable phenotype that spreads over the initial limits of the syndrome definition. On the basis of recent findings of olfactory-bulb agenesis in WS individuals, we suspected SOX10 was also involved in Kallmann syndrome (KS). KS is defined by the association between anosmia and hypogonadotropic hypogonadism due to incomplete migration of neuroendocrine gonadotropin-releasing hormone (GnRH) cells along the olfactory, vomeronasal, and terminal nerves. Mutations in any of the nine genes identified to date account for only 30% of the KS cases. KS can be either isolated or associated with a variety of other symptoms, including deafness. This study reports SOX10 loss-of-function mutations in approximately one-third of KS individuals with deafness, indicating a substantial involvement in this clinical condition. Study of SOX10-null mutant mice revealed a developmental role of SOX10 in a subpopulation of glial cells called olfactory ensheathing cells. These mice indeed showed an almost complete absence of these cells along the olfactory nerve pathway, as well as defasciculation and misrouting of the nerve fibers, impaired migration of GnRH cells, and disorganization of the olfactory nerve layer of the olfactory bulbs.

Spectrum of temporal bone abnormalities in patients with Waardenburg syndrome and SOX10 mutations

BACKGROUND AND PURPOSE

Waardenburg syndrome, characterized by deafness and pigmentation abnormalities, is clinically and genetically heterogeneous, consisting of 4 distinct subtypes and involving several genes. SOX10 mutations have been found both in types 2 and 4 Waardenburg syndrome and neurologic variants. The purpose of this study was to evaluate both the full spectrum and relative frequencies of inner ear malformations in these patients.

MATERIALS AND METHODS

Fifteen patients with Waardenburg syndrome and different SOX10 mutations were studied retrospectively. Imaging was performed between February 2000 and March 2010 for cochlear implant work-up, diagnosis of hearing loss, and/or evaluation of neurologic impairment. Eleven patients had both CT and MR imaging examinations, 3 had MR imaging only, and 1 had CT only.

RESULTS

Temporal bone abnormalities were bilateral. The most frequent pattern associated agenesis or hypoplasia of ≥1 semicircular canal, an enlarged vestibule, and a cochlea with a reduced size and occasionally an abnormal shape, but with normal partition in the 13/15 cases that could be analyzed. Three patients lacked a cochlear nerve, bilaterally in 2 patients. In addition, associated abnormalities were found when adequate MR imaging sequences were available: agenesis of the olfactory bulbs (7/8), hypoplastic or absent lacrimal glands (11/14), hypoplastic parotid glands (12/14), and white matter signal anomalies (7/13).

CONCLUSIONS

In the appropriate clinical context, bilateral agenesis or hypoplasia of the semicircular canals or both, associated with an enlarged vestibule and a cochlear deformity, strongly suggests a diagnosis of Waardenburg syndrome linked to a SOX10 mutation.

Chromosomal and related Mendelian syndromes associated with Hirschsprung's disease

Hirschsprung's disease (HSCR) is a fairly frequent cause of intestinal obstruction in children. It is characterized as a sex-linked heterogonous disorder with variable severity and incomplete penetrance giving rise to a variable pattern of inheritance. Although Hirschsprung's disease occurs as an isolated phenotype in at least 70% of cases, it is not infrequently associated with a number of congenital abnormalities and associated syndromes, demonstrating a spectrum of congenital anomalies. Certain of these syndromic phenotypes have been linked to distinct genetic sites, indicating underlying genetic associations of the disease and probable gene-gene interaction, in its pathogenesis. These associations with HSCR include Down's syndrome and other chromosomal anomalies, Waardenburg syndrome and other Dominant sensorineural deafness, the Congenital Central Hypoventilation and Mowat-Wilson and other brain-related syndromes, as well as the MEN2 and other tumour associations. A number of other autosomal recessive syndromes include the Shah-Waardenburg, the Bardet-Biedl and Cartilage-hair hypoplasia, Goldberg-Shprintzen syndromes and other syndromes related to cholesterol and fat metabolism among others. The genetics of Hirschsprung's disease are highly complex with the majority of known genetic sites relating to the main susceptibility pathways (RET an EDNRB). Non-syndromic non-familial, short-segment HSCR appears to represent a non-Mendelian condition with variable expression and sex-dependent penetrance. Syndromic and familial forms, on the other hand, have complex patterns of inheritance and being reported as autosomal dominant, recessive and polygenic patterns of inheritance. The phenotypic variability and incomplete penetrance observed in Hirschsprung's disease could also be explained by the involvement of modifier genes, especially in its syndromic forms. In this review, we look at the chromosomal and Mendelian associations and their underlying signalling pathways, to obtain a better understanding of the pathogenetic mechanisms involved in developing aganglionosis of the distal bowel.

Novel mutations in the SOX10 gene in the first two Chinese cases of type IV Waardenburg syndrome

OBJECTIVE

We analyzed the clinical features and family-related gene mutations for the first two Chinese cases of type IV Waardenburg syndrome (WS4).

METHODS

Two families were analyzed in this study. The analysis included a medical history, clinical analysis, a hearing test and a physical examination. In addition, the EDNRB, EDN3 and SOX10 genes were sequenced in order to identify the pathogenic mutation responsible for the WS4 observed in these patients.

RESULTS

The two WS4 cases presented with high phenotypic variability. Two novel heterozygous mutations (c.254G>A and c.698-2A>T) in the SOX10 gene were detected. The mutations identified in the patients were not found in unaffected family members or in 200 unrelated control subjects.

CONCLUSIONS

This is the first report of WS4 in Chinese patients. In addition, two novel mutations in SOX10 gene have been identified.

Hirschsprung's disease and the brain

A link between factors governing brain development and the development of the ENS is not surprising as both processes are largely controlled by the same or similar neural growth factors which are expressed at more or less in the same spatio-temporal time frame. Hirschsprung's disease (HSCR) occurs as an isolated phenotype in 70% of cases but is associated with other congenital abnormalities and syndromic phenotypes in the remainder, with CNS anomalies making up 6.78%. These associations may be underestimated and are possibly pathogenetically linked to genetic associations and probable gene-gene interaction. In this review we explore known syndromes and other ENS associations of HSCR, looking at possible pathogenetic associations. We point out that borderline cognitive abilities, attention-deficit disorders and possible epileptic seizures in Hirschsprung's patients should be fully investigated. We recognise that this group of patients remain a challenge from a clinical and functional management point of view, and suggest possible management guidelines.

Sox proteins in melanocyte development and melanoma

Over 10 years have passed since the first Sox gene was implicated in melanocyte development. Since then, we have discovered that SOX5, SOX9, SOX10 and SOX18 all participate as transcription factors that affect key melanocytic genes in both regulatory and modulatory fashions. Both SOX9 and SOX10 play major roles in the establishment and normal function of the melanocyte; SOX10 has been shown to heavily influence melanocyte development and SOX9 has been implicated in melanogenesis in the adult. Despite these advances, the precise cellular and molecular details of how these SOX proteins are regulated and interact during all stages of the melanocyte life cycle remain unknown. Improper regulation of SOX9 or SOX10 is also associated with cancerous transformation, and thus understanding the normal function of SOX proteins in the melanocyte will be key to revealing how these proteins contribute to melanoma.

Involvement of SOX10 in the pathogenesis of Hirschsprung disease: report of a truncating mutation in an isolated patient

SOX10 protein is a key transcription factor during neural crest development. Mutations in SOX10 are associated with several neurocristopathies such as Waardenburg syndrome type IV (WS4), a congenital disorder characterized by the association of hearing loss, pigmentary abnormalities, and absence of ganglion cells in the myenteric and submucosal plexus of the gastrointestinal tract, also known as aganglionic megacolon or Hirschsprung disease (HSCR). Several mutations at this locus are known to cause a high percentage of WS4 cases, but no SOX10 mutations had been ever reported associated to isolated HSCR patient. Therefore, nonsyndromic HSCR was initially thought not to be associated to mutations at this particular locus. In the present study, we describe the evaluation of the SOX10 gene in a series of 196 isolated HSCR cases, the largest patient series evaluated so far, and report a truncating c.153-155del mutation. This is the first time that a SOX10 mutation is detected in an isolated HSCR patient, which completely changes the scenario for the implications of SOX10 mutations in human disease, giving us a new tool for genetic counseling.

Aplasia of cochlear nerves and olfactory bulbs in association with SOX10 mutation

A 17-month-old boy was referred with profound sensorineural hearing loss (SNHL), severe visual impairment and developmental delay. Neuroimaging identified hypomyelination and cochlear nerve aplasia. He was noted to have fair skin and hair and multiple areas of cutaneous hyperpigmentation. Previous investigations including karyotype, array comparative genomic hybridization (aCGH) and a full metabolic screen were normal. A novel missense mutation of the highly conserved high mobility group (HMG) domain of SOX10 was identified (Q174P:c.521A>C). This case represents the first description of aplasia of the cochlear nerve due to a SOX10 mutation.

A zebrafish model for Waardenburg syndrome type IV reveals diverse roles for Sox10 in the otic vesicle

In humans, mutations in the SOX10 gene are a cause of the auditory-pigmentary disorder Waardenburg syndrome type IV (WS4) and related variants. SOX10 encodes an Sry-related HMG box protein essential for the development of the neural crest; deafness in WS4 and other Waardenburg syndromes is usually attributed to loss of neural-crest-derived melanocytes in the stria vascularis of the cochlea. However, SOX10 is strongly expressed in the developing otic vesicle and so direct roles for SOX10 in the otic epithelium might also be important. Here, we examine the otic phenotype of zebrafish sox10 mutants, a model for WS4. As a cochlea is not present in the fish ear, the severe otic phenotype in these mutants cannot be attributed to effects on this tissue. In zebrafish sox10 mutants, we see abnormalities in all otic placodal derivatives. Gene expression studies indicate deregulated expression of several otic genes, including fgf8, in sox10 mutants. Using a combination of mutant and morphant data, we show that the three sox genes belonging to group E (sox9a, sox9b and sox10) provide a link between otic induction pathways and subsequent otic patterning: they act redundantly to maintain sox10 expression throughout otic tissue and to restrict fgf8 expression to anterior macula regions. Single-cell labelling experiments indicate a small and transient neural crest contribution to the zebrafish ear during normal development, but this is unlikely to account for the strong defects seen in the sox10 mutant. We discuss the implication that the deafness in WS4 patients with SOX10 mutations might reflect a haploinsufficiency for SOX10 in the otic epithelium, resulting in patterning and functional abnormalities in the inner ear.