Mutations in the Wolfram syndrome type 1 gene (WFS1) define a clinical entity of dominant low-frequency sensorineural hearing loss

Wfs1E864K knock-in mice illuminate the fundamental role of Wfs1 in endocochlear potential production

Wolfram syndrome (WS) is a rare neurodegenerative disorder encompassing diabetes mellitus, diabetes insipidus, optic atrophy, hearing loss (HL) as well as neurological disorders. None of the animal models of the pathology are presenting with an early onset HL, impeding the understanding of the role of Wolframin (WFS1), the protein responsible for WS, in the auditory pathway. We generated a knock-in mouse, the Wfs1E864K line, presenting a human mutation leading to severe deafness in affected individuals. The homozygous mice showed a profound post-natal HL and vestibular syndrome, a collapse of the endocochlear potential (EP) and a devastating alteration of the stria vascularis and neurosensory epithelium. The mutant protein prevented the localization to the cell surface of the Na+/K+ATPase β1 subunit, a key protein for the maintenance of the EP. Overall, our data support a key role of WFS1 in the maintenance of the EP and the stria vascularis, via its binding partner, the Na+/K+ATPase β1 subunit.

Autosomal Dominant Non-Syndromic Hearing Loss (DFNA): A Comprehensive Narrative Review

Autosomal dominant non-syndromic hearing loss (HL) typically occurs when only one dominant allele within the disease gene is sufficient to express the phenotype. Therefore, most patients diagnosed with autosomal dominant non-syndromic HL have a hearing-impaired parent, although de novo mutations should be considered in all cases of negative family history. To date, more than 50 genes and 80 loci have been identified for autosomal dominant non-syndromic HL. DFNA22 (MYO6 gene), DFNA8/12 (TECTA gene), DFNA20/26 (ACTG1 gene), DFNA6/14/38 (WFS1 gene), DFNA15 (POU4F3 gene), DFNA2A (KCNQ4 gene), and DFNA10 (EYA4 gene) are some of the most common forms of autosomal dominant non-syndromic HL. The characteristics of autosomal dominant non-syndromic HL are heterogenous. However, in most cases, HL tends to be bilateral, post-lingual in onset (childhood to early adulthood), high-frequency (sloping audiometric configuration), progressive, and variable in severity (mild to profound degree). DFNA1 (DIAPH1 gene) and DFNA6/14/38 (WFS1 gene) are the most common forms of autosomal dominant non-syndromic HL affecting low frequencies, while DFNA16 (unknown gene) is characterized by fluctuating HL. A long audiological follow-up is of paramount importance to identify hearing threshold deteriorations early and ensure prompt treatment with hearing aids or cochlear implants.

Monogenic Causes of Low-Frequency Non-Syndromic Hearing Loss

BACKGROUND

Low-frequency non-syndromic hearing loss (LFNSHL) is a rare form of hearing loss (HL). It is defined as HL at low frequencies (≤2,000 Hz) resulting in a characteristic ascending audiogram. LFNSHL is usually diagnosed postlingually and is progressive, leading to HL affecting other frequencies as well. Sometimes it occurs with tinnitus. Around half of the diagnosed prelingual HL cases have a genetic cause and it is usually inherited in an autosomal recessive mode. Postlingual HL caused by genetic changes generally has an autosomal dominant pattern of inheritance and its incidence remains unknown.

SUMMARY

To date, only a handful of genes have been found as causing LFNSHL: well-established WFS1 and, reported in some cases, DIAPH1, MYO7A, TNC, and CCDC50 (respectively, responsible for DFNA6/14/38, DFNA1, DFNA11, DFNA56, and DFNA44). In this review, we set out audiological phenotypes, causative genetic changes, and molecular mechanisms leading to the development of LFNSHL.

KEY MESSAGES

LFNSHL is most commonly caused by pathogenic variants in the WFS1 gene, but it is also important to consider changes in other HL genes, which may result in similar audiological phenotype.

Genotype and Phenotype Analyses of a Novel WFS1 Variant (c.2512C>T p.(Pro838Ser)) Associated with DFNA6/14/38

The aim of this study is to contribute to a better description of the genotypic and phenotypic spectrum of DFNA6/14/38 and aid in counseling future patients identified with this variant. Therefore, we describe the genotype and phenotype in a large Dutch-German family (W21-1472) with autosomal dominant non-syndromic, low-frequency sensorineural hearing loss (LFSNHL). Exome sequencing and targeted analysis of a hearing impairment gene panel were used to genetically screen the proband. Co-segregation of the identified variant with hearing loss was assessed by Sanger sequencing. The phenotypic evaluation consisted of anamnesis, clinical questionnaires, physical examination and examination of audiovestibular function. A novel likely pathogenic WFS1 variant (NM_006005.3:c.2512C>T p.(Pro838Ser)) was identified in the proband and found to co-segregate with LFSNHL, characteristic of DFNA6/14/38, in this family. The self-reported age of onset of hearing loss (HL) ranged from congenital to 50 years of age. In the young subjects, HL was demonstrated in early childhood. At all ages, an LFSNHL (0.25-2 kHz) of about 50-60 decibel hearing level (dB HL) was observed. HL in the higher frequencies showed inter-individual variability. The dizziness handicap inventory (DHI) was completed by eight affected subjects and indicated a moderate handicap in two of them (aged 77 and 70). Vestibular examinations (n = 4) showed abnormalities, particularly in otolith function. In conclusion, we identified a novel WFS1 variant that co-segregates with DFNA6/14/38 in this family. We found indications of mild vestibular dysfunction, although it is uncertain whether this is related to the identified WFS1 variant or is an incidental finding. We would like to emphasize that conventional neonatal hearing screening programs are not sensitive to HL in DFNA6/14/38 patients, because high-frequency hearing thresholds are initially preserved. Therefore, we suggest screening newborns in DFNA6/14/38 families with more frequency-specific methods.

Two Cases of Wolfram Syndrome Who Were Initially Diagnosed With Type 1 Diabetes

Objective

Early diagnosis of syndromic monogenic diabetes allows for proper management and can lead to improved quality of life in the long term. This report aimed to describe 2 genetically confirmed cases of Wolfram syndrome, a rare endoplasmic reticulum disorder characterized by insulin-dependent diabetes mellitus, optic nerve atrophy, and progressive neurodegeneration.

Case Report

A 16-year-old Caucasian male patient and a 25-year-old Caucasian female patient with a history of diabetes mellitus and optic nerve atrophy presented at our medical center. Both patients were initially diagnosed with type 1 diabetes but negative for islet autoantibodies. Their body mass indexes were under 25 at the diagnosis. Their history and presentation were highly suspicious for Wolfram syndrome.

Discussion

The genetic tests revealed a known Wolfram syndrome 1 (WFS1) pathogenic variant (homozygous) in the 16-year-old male patient and 2 known WFS1 pathogenic variants (compound heterozygous) in the 25-year-old female patient with diabetes mellitus and optic nerve atrophy, confirming the diagnosis of Wolfram syndrome. The first patient had a moderate form, and the second patient had a milder form of Wolfram syndrome.

Conclusion

Providers should consider monogenic diabetes genetic testing, including WFS1 gene, for patients with early-onset diabetes who are negative for islet autoantibodies and lean. Two patients described in this article could have been diagnosed with Wolfram syndrome before they developed optic nerve atrophy. Genetic testing is a valuable tool for the early detection of Wolfram syndrome, which leads to proper management and improved quality of life in patients with this rare medical condition.

Early Intervention and Lifelong Treatment with GLP1 Receptor Agonist Liraglutide in a Wolfram Syndrome Rat Model with an Emphasis on Visual Neurodegeneration, Sensorineural Hearing Loss and Diabetic Phenotype

Wolfram syndrome (WS), also known as a DIDMOAD (diabetes insipidus, early-onset diabetes mellitus, optic nerve atrophy and deafness) is a rare autosomal disorder caused by mutations in the Wolframin1 (WFS1) gene. Previous studies have revealed that glucagon-like peptide-1 receptor agonist (GLP1 RA) are effective in delaying and restoring blood glucose control in WS animal models and patients. The GLP1 RA liraglutide has also been shown to have neuroprotective properties in aged WS rats. WS is an early-onset, chronic condition. Therefore, early diagnosis and lifelong pharmacological treatment is the best solution to control disease progression. Hence, the aim of this study was to evaluate the efficacy of the long-term liraglutide treatment on the progression of WS symptoms. For this purpose, 2-month-old WS rats were treated with liraglutide up to the age of 18 months and changes in diabetes markers, visual acuity, and hearing sensitivity were monitored over the course of the treatment period. We found that treatment with liraglutide delayed the onset of diabetes and protected against vision loss in a rat model of WS. Therefore, early diagnosis and prophylactic treatment with the liraglutide may also prove to be a promising treatment option for WS patients by increasing the quality of life.

A novel mutation of WFS1 gene leading to increase ER stress and cell apoptosis is associated an autosomal dominant form of Wolfram syndrome type 1

BACKGROUND

Wolfram syndrome (WS) is a rare autosomal recessive disorder characterized by diabetes insipidus, diabetes mellitus, optic atrophy and deafness. Mutations in Wolfram syndrome 1 (WFS1) gene may cause dysregulated endoplasmic reticulum (ER)-stress and cell apoptosis, contributing to WS symptoms. The aim of this study was to identify the molecular etiology of a case of WS and to explore the functional consequence of the mutant WFS1 gene in vitro.

METHODS

A 27 years-old Chinese man was diagnosed as wolfram syndrome type 1 based on clinical data and laboratory data. DNA sequencing of WFS1 gene and mitochondrial m.3337G > A, m.3243A > G mutations were performed in the patient and his 4 family members. Functional analysis was performed to assessed the in vitro effect of the newly identified mutant. ER stress were evaluated by ER stress response element (ERSE)-luciferase assay. Cell apoptosis were performed by CCK-8, TUNEL staining and flow cytometric analysis.

RESULTS

A novel heterozygous 10-base deletion (c. 2067_2076 del10, p.W690fsX706) was identified in the patient. In vitro studies showed that mutant p.W690fsX706 increased ERSE reporter activity in the presence or absence of thapsigargin instead of wild type WFS1. Knockdown of WFS1 activated the unfolded protein response (UPR) pathway and increased the cell apoptosis, which could not be restored by transfection with WFS1 mutant (p.W690fsX706) comparable to the wild type WFS1.

CONCLUSIONS

A novel heterozygous mutation of WFS1 detected in the patient resulted in loss-of-function of wolframin, thereby inducing dysregulated ER stress signaling and cell apoptosis. These findings increase the spectrum of WFS1 gene mutations and broaden our insights into the roles of mutant WFS1 in the pathogenesis of WS.

Wolfram-like syndrome with bicuspid aortic valve due to a homozygous missense variant in CDK13

Background

Wolfram syndrome (WFS) is characterized by deafness, diabetes mellitus, and diabetes insipidus along with optic atrophy. WFS has an autosomal recessive mode of inheritance and is due to variants in WFS1 and CISD2.

Methods

We evaluated the underlying molecular etiology of three affected members of a consanguineous family with hearing impairment, bicuspid aortic valve, diabetes mellitus and insipidus, clinodactyly, and gastrointestinal tract abnormalities via exome sequencing approach. We correlated clinical and imaging data with the genetic findings and their associated phenotypes.

Results

We identified a homozygous missense variant p.(Asn1097Lys) in CDK13, a gene previously associated with autosomal dominant congenital heart defects, dysmorphic facial features, clinodactyly, gastrointestinal tract abnormalities, intellectual developmental disorder, and seizures with variable phenotypic features.

Conclusion

We report a homozygous variant in CDK13 and suggest that this gene causes an autosomal recessive disorder with hearing impairment, bicuspid aortic valve, diabetes mellitus and insipidus, clinodactyly, and gastrointestinal tract abnormalities.

Identification of Three Novel and One Known Mutation in the WFS1 Gene in Four Unrelated Turkish Families: The Role of Homozygosity Mapping in the Early Diagnosis

OBJECTIVE

Bi-allelic mutations in the wolframin gene (WFS1) cause Wolfram syndrome 1 (WS1 or DIDMOAD) characterized by nonautoimmune diabetes mellitus, optic atrophy, diabetes insipidus, sensorineural deafness, urinary tract abnormalities, and neuropsychiatric disorders. Patients presenting with an incomplete phenotype of WS1 were evaluated using homozygosity mapping and subsequent whole-exome sequencing.

METHODS

Four unrelated consanguineous Turkish families, including seven affected children, and their unaffected parents and siblings were evaluated. Homozygosity mapping was performed, followed by whole-exome sequencing of WFS1. Mutations were classified according to results of “in silico” analyses, protein prediction, and functional consequences.

RESULTS

Homozygosity mapping confirmed shared homozygous regions on chromosome 4 (chr4p16.1) between the affected individuals, that was absent in their unaffected siblings. Exome sequencing identified three novel (c.1215T>A, c.554G>A, c.1525_1540dup) and one known (c.1522_1523delTA) mutations in WFS1. All mutations were predicted to cause stop codon leading to early termination of protein synthesis and complete loss-of-function. All patients were found to be homozygous for the change, with parents and other unaffected siblings being carriers.

CONCLUSION

Our study expands the mutation spectrum of WSF1 mutations with three novel mutations. Homozygosity mapping may provide enrichment for molecular genetic analysis and early diagnosis of WS1 patients with incomplete phenotype, particularly in consanguineous pedigrees.

Monogenic and syndromic diabetes due to endoplasmic reticulum stress

The endoplasmic reticulum (ER) lies at the crossroads of protein folding, calcium storage, lipid metabolism, and the regulation of autophagy and apoptosis. Accordingly, dysregulation of ER homeostasis leads to β-cell dysfunction in type 1 and type 2 diabetes that ultimately culminates in cell death. The ER is therefore an emerging target for understanding the mechanisms of diabetes mellitus that captures the complex etiologies of this multifactorial class of metabolic disorders. Our strategy for developing ER-targeted diagnostics and therapeutics is to focus on monogenic forms of diabetes related to ER dysregulation in an effort to understand the exact contribution of ER stress to β-cell death. In this manner, we can develop personalized genetic medicine for ERstress-related diabetic disorders, such as Wolfram syndrome. In this article, we describe the phenotypes and molecular pathogenesis of ERstress-related monogenic forms of diabetes.

Autosomal-dominant WFS1-related disorder-Report of a novel WFS1 variant and review of the phenotypic spectrum of autosomal recessive and dominant forms

Wolfram syndrome was initially reported as an autosomal recessive (AR), progressive neurodegenerative disorder that leads to diabetes insipidus, childhood onset diabetes mellitus (DM), optic atrophy, and deafness (D) also known as DIDMOAD. However, heterozygous dominant pathogenic variants in Wolfram syndrome type 1 (WFS1) may lead to distinct, allelic conditions, described as isolated sensorineural hearing loss (SNHL), syndromic SNHL, congenital cataracts, or early onset DM. We report a family with a novel dominant, likely pathogenic variant in WFS1 (NM_006005.3) c.2605_2616del12 (p.Ser869_His872del), resulting in cataracts, SNHL, and DM in a female and her mother. A maternal aunt had cataracts, DM, and SNHL but was not tested for the familial WFS1 mutation. Both the mother and maternal aunt had early menopause by age 43 years and infertility which may be a coincidental finding that has not been associated with autosomal dominant AD WFS1-related disorder to the best of our knowledge. Screening at risk individuals in families with the AR Wolfram syndrome, for DM, SNHL, and for cataracts is indicated.

From Biology to Genes and Back Again: Gene Discovery for Monogenic Forms of Beta-Cell Dysfunction in Diabetes

This review focuses on gene discovery strategies used to identify monogenic forms of diabetes caused by reduced pancreatic beta-cell number (due to destruction or defective development) or impaired beta-cell function. Gene discovery efforts in monogenic diabetes have identified 36 genes so far. These genetic causes have been identified using four main approaches: linkage analysis, candidate gene sequencing and most recently, exome and genome sequencing. The advent of next-generation sequencing has allowed researchers to move away from linkage analysis (relying on large pedigrees and/or multiple families with the same genetic condition) and candidate gene (relying on previous knowledge on the gene's role) strategies to use a gene agnostic approach, utilizing genetic evidence (such as variant frequency, predicted variant effect on protein function, and predicted mode of inheritance) to identify the causative mutation. This approach led to the identification of seven novel genetic causes of monogenic diabetes, six by exome sequencing and one by genome sequencing. In many of these cases, the disease-causing gene was not known to be important for beta-cell function prior to the gene discovery study. These novel findings highlight a new role for gene discovery studies in furthering our understanding of beta-cell function and dysfunction in diabetes. While many gene discovery studies in the past were led by knowledge in the field (through the candidate gene strategy), now they often lead the scientific advances in the field by identifying new important biological players to be further characterized by in vitro and in vivo studies.

Current Landscape of Treatments for Wolfram Syndrome

Wolfram syndrome is a rare genetic spectrum disorder characterized by insulin-dependent diabetes mellitus, optic nerve atrophy, and progressive neurodegeneration, and ranges from mild to severe clinical symptoms. There is currently no treatment to delay, halt, or reverse the progression of Wolfram syndrome, raising the urgency for innovative therapeutics for this disease. Here, we summarize our vision for developing novel treatment strategies and achieving a cure for Wolfram-syndrome-spectrum disorder.

Wolfram syndrome, a rare neurodegenerative disease: from pathogenesis to future treatment perspectives

Background

Wolfram syndrome (WS), a rare genetic disorder, is considered the best prototype of endoplasmic reticulum (ER) diseases. Classical WS features are childhood-onset diabetes mellitus, optic atrophy, deafness, diabetes insipidus, neurological signs, and other abnormalities. Two causative genes (WFS1 and WFS2) have been identified. The transmission of the disease takes place in an autosomal recessive mode but autosomal dominant mutations responsible for WS-related disorders have been described. Prognosis is poor, death occurs at the median age of 39 years with a major cause represented by respiratory failure as a consequence of brain stem atrophy and neurodegeneration. The aim of this narrative review is to focus on etiology, pathogenesis and natural history of WS for an adequate patient management and for the discussion of future therapeutic interventions.

Main body

WS requires a multidisciplinary approach in order to be successfully treated. A prompt diagnosis decreases morbidity and mortality through prevention and treatment of complications. Being a monogenic pathology, WS represents a perfect model to study the mechanisms of ER stress and how this condition leads to cell death, in comparison with other prevalent diseases in which multiple factors interact to produce the disease manifestations. WS is also an important disease prototype to identify drugs and molecules associated with ER homeostasis. Evidence indicates that specific metabolic diseases (type 1 and type 2 diabetes), neurodegenerative diseases, atherosclerosis, inflammatory pathologies and also cancer are closely related to ER dysfunction.

Conclusions

Therapeutic strategies in WS are based on drug repurposing (i.e., investigation of approved drugs for novel therapeutic indications) with the aim to stop the progression of the disease by reducing the endoplasmic reticulum stress. An extensive understanding of WS from pathophysiology to therapy is fundamental and more studies are necessary to better manage this devastating disease and guarantee the patients a better quality of life and longer life expectancy.

Diagnosis, Intervention, and Prevention of Genetic Hearing Loss

It is estimated that at least 50% of congenital or childhood hearing loss is attributable to genetic causes. In non-syndromic hearing loss, which accounts for 70% of genetic hearing loss, approximately 80% of cases are autosomal recessive, 15% autosomal dominant, and 1-2% mitochondrial or X-linked. In addition, 30% of genetic hearing loss is syndromic. The genetic causes of hearing loss are highly heterogeneous. So far, more than 140 deafness-related genes have been discovered. Studies on those genes tremendously increased our understanding of the inner ear functions at the molecular level. It also offers important information for the patients and allows personalized and accurate genetic counseling. In many cases, genetic diagnosis of hearing loss can help to avoid unnecessary and costly clinical testing, offer prognostic information, and guide future medical management. On the other hand, a variety of gene therapeutic approaches have been developed aiming to relieve or converse the hearing loss due to genetic causes. Prevention of genetic hearing loss is feasible through prepregnancy and prenatal genetic diagnosis and counseling.

Genetic and clinical aspects of Wolfram syndrome 1, a severe neurodegenerative disease

Wolfram syndrome 1 (WS1) is a rare autosomal recessive neurodegenerative disease characterized by diabetes insipidus, diabetes mellitus, optic atrophy, deafness, and other abnormalities. WS1 usually results in death before the age of 50 years. The pathogenesis of WS1 is ascribed to mutations of human WFS1 gene on chromosome 4p encoding a transmembrane protein called wolframin, which has physiological functions in membrane trafficking, secretion, processing, and/or regulation of ER calcium homeostasis. Different types of WFS1 mutations have been identified, and some of these have been associated with a dominant, severe type of WS. Mutations of CISD2 gene cause autosomal recessive Wolfram syndrome 2 (WS2) characterized by the absence of diabetes insipidus and psychiatric disorders, and by bleeding upper intestinal ulcer and defective platelet aggregation. Other WFS1-related disorders such as DFNA6/14/38 nonsyndromic low-frequency sensorineural hearing loss and Wolfram syndrome-like disease with autosomal dominant transmission have been described. WS1 is a devastating disease for the patients and their families. Thus, early diagnosis is imperative to enable proper prognostication, prevent complications, and reduce the transmission to further progeny. Although there is currently no effective therapy, potential new drugs have been introduced, attempting to improve the progression of this fatal disease.

Wolfram Syndrome: A Case Report and Review of Clinical Manifestations, Genetics Pathophysiology, and Potential Therapies

Background

Classical Wolfram syndrome (WS) is a rare autosomal recessive disorder caused by mutations in WFS1, a gene implicated in endoplasmic reticulum (ER) and mitochondrial function. WS is characterized by insulin-requiring diabetes mellitus and optic atrophy. A constellation of other features contributes to the acronym DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness). This review seeks to raise awareness of this rare form of diabetes so that individuals with WS are identified and provided with appropriate care.

Case

We describe a woman without risk factors for gestational or type 2 diabetes who presented with gestational diabetes (GDM) at the age of 39 years during her first and only pregnancy. Although she had optic atrophy since the age of 10 years, WS was not considered as her diagnosis until she presented with GDM. Biallelic mutations in WFS1 were identified, supporting a diagnosis of classical WS.

Conclusions

The distinct natural history, complications, and differences in management reinforce the importance of distinguishing WS from other forms of diabetes. Recent advances in the genetics and pathophysiology of WS have led to promising new therapeutic considerations that may preserve β-cell function and slow progressive neurological decline. Insight into the pathophysiology of WS may also inform strategies for β-cell preservation for individuals with type 1 and 2 diabetes.

Wolfram syndrome: MAMs' connection?

Wolfram syndrome (WS) is a rare neurodegenerative disease, the main pathological hallmarks of which associate with diabetes, optic atrophy, and deafness. Other symptoms may be identified in some but not all patients. Prognosis is poor, with death occurring around 35 years of age. To date, no treatment is available. WS was first described as a mitochondriopathy. However, the localization of the protein on the endoplasmic reticulum (ER) membrane challenged this hypothesis. ER contacts mitochondria to ensure effective Ca²⁺ transfer, lipids transfer, and apoptosis within stabilized and functionalized microdomains, termed “mitochondria-associated ER membranes” (MAMs). Two types of WS are characterized so far and Wolfram syndrome type 2 is due to mutation in CISD2, a protein mostly expressed in MAMs. The aim of the present review is to collect evidences showing that WS is indeed a mitochondriopathy, with established MAM dysfunction, and thus share commonalities with several neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, as well as metabolic diseases, such as diabetes.

Whole exome sequencing identifies a pathogenic mutation in WFS1 in two large Chinese families with autosomal dominant all-frequency hearing loss and prenatal counseling

OBJECTIVES

To identify the pathogenic mutation and provide prenatal counseling and diagnosis in two large Chinese families with autosomal dominant all-frequency hearing loss.

METHODS

Whole exome sequencing technology was used to identify the pathogenic mutation of the two families. In addition, 298 patients with sporadic hearing loss and 400 normal controls were studied to verify the mutation/polymorphism nature of the identified variant. Prenatal diagnosis was carried out.

RESULTS

A rare missense mutation c.2389G > A (p.D572N) in the Wolframin syndrome 1 (WFS1) gene was identified. It was reported in only one previous Chinese study, and never in other populations/ethnicities. The mutation was also found in one patient with sporadic hearing loss (1/298, 0.3%). A healthy baby was born after prenatal diagnosis.

CONCLUSION

Our findings strongly suggest that the c.2389G > A mutation in WFS1 is associated with all-frequency hearing loss, rather than low- or high-frequency loss. So far, the mutation is only reported in Chinese. Prenatal diagnosis and prenatal counseling is available for these two Chinese families.

A nonsynonymous mutation in the WFS1 gene in a Finnish family with age-related hearing impairment

Wolfram syndrome (WS) is caused by recessive mutations in the Wolfram syndrome 1 (WFS1) gene. Sensorineural hearing impairment (HI) is a frequent feature in WS and, furthermore, certain mutations in WFS1 cause nonsyndromic dominantly inherited low-frequency sensorineural HI. These two phenotypes are clinically distinct indicating that WFS1 is a reasonable candidate for genetic studies in patients with other phenotypes of HI. Here we have investigated, whether the variation in WFS1 has a pathogenic role in age-related hearing impairment (ARHI). WFS1 gene was investigated in a population sample of 518 Finnish adults born in 1938-1949 and representing variable hearing phenotypes. Identified variants were evaluated with respect to pathogenic potential. A rare mutation predicted to be pathogenic was found in a family with many members with impaired hearing. Twenty members were recruited to a segregation study and a detailed clinical examination. Heterozygous p.Tyr528His variant segregated completely with late-onset HI in which hearing deteriorated first at high frequencies and progressed to mid and low frequencies later in life. We report the first mutation in the WFS1 gene causing late-onset HI with audiogram configurations typical for ARHI. Monogenic forms of ARHI are rare and our results add WFS1 to the short list of such genes.

Exome sequencing identifies a novel missense mutation of WFS1 as the cause of non-syndromic low-frequency hearing loss in a Chinese family

OBJECTIVE

Autosomal dominant non-syndromic low-frequency sensorineural hearing loss (LFSNHL) DFNA6/14/38 is an uncommon type of hearing loss that classically affects low frequencies of 2000 Hz and below, demonstrating an ascending configuration. The current study aimed to investigate the cause of LFSNHL in a five-generation Chinese family.

METHODS

The phenotype of the Chinese family was characterized using audiologic testing and pedigree analysis. The combined approach of array screening and whole-exome sequencing was used to identify the disease-causing gene in this family.

RESULTS

This pedigree, in which the affected subjects presented isolated low-frequency sensorineural hearing impairment with childhood onset, was associated with autosomal dominant inheritance of the c.2591A > G mutation in exon 8 of the Wolframin syndrome 1 (WFS1) gene which was not present in 286 unrelated controls with matched ancestry and is highly conserved across species. In addition, several mutations affecting the Glu864 residue have been previously identified in different populations, suggesting that this site is likely to be a mutational hot spot.

CONCLUSIONS

We identified a novel substitution, Glu864Gly, of WFS1 as the causative variant for this pedigree. Our data extend the mutation spectrum of the WFS1 gene in Chinese individuals and may contribute to establishing a better genotype-phenotype correlation for LFSNHL.

Dominant ER Stress-Inducing WFS1 Mutations Underlie a Genetic Syndrome of Neonatal/Infancy-Onset Diabetes, Congenital Sensorineural Deafness, and Congenital Cataracts

Neonatal diabetes is frequently part of a complex syndrome with extrapancreatic features: 18 genes causing syndromic neonatal diabetes have been identified to date. There are still patients with neonatal diabetes who have novel genetic syndromes. We performed exome sequencing in a patient and his unrelated, unaffected parents to identify the genetic etiology of a syndrome characterized by neonatal diabetes, sensorineural deafness, and congenital cataracts. Further testing was performed in 311 patients with diabetes diagnosed before 1 year of age in whom all known genetic causes had been excluded. We identified 5 patients, including the initial case, with three heterozygous missense mutations in WFS1 (4/5 confirmed de novo). They had diabetes diagnosed before 12 months (2 before 6 months) (5/5), sensorineural deafness diagnosed soon after birth (5/5), congenital cataracts (4/5), and hypotonia (4/5). In vitro studies showed that these WFS1 mutations are functionally different from the known recessive Wolfram syndrome-causing mutations, as they tend to aggregate and induce robust endoplasmic reticulum stress. Our results establish specific dominant WFS1 mutations as a cause of a novel syndrome including neonatal/infancy-onset diabetes, congenital cataracts, and sensorineural deafness. This syndrome has a discrete pathophysiology and differs genetically and clinically from recessive Wolfram syndrome.

Molecular diagnostics for hereditary hearing loss in children

INTRODUCTION

Hearing loss (HL) is the most common birth defect in industrialized countries with far-reaching social, psychological and cognitive implications. It is an extremely heterogeneous disease, complicating molecular testing. The introduction of next-generation sequencing (NGS) has resulted in great progress in diagnostics allowing to study all known HL genes in a single assay. The diagnostic yield is currently still limited, but has the potential to increase substantially. Areas covered: In this review the utility of NGS and the problems for comprehensive molecular testing for HL are evaluated and discussed. Expert commentary: Different publications have proven the appropriateness of NGS for molecular testing of heterogeneous diseases such as HL. However, several problems still exist, such as pseudogenic background of some genes and problematic copy number variant analysis on targeted NGS data. Another main challenge for the future will be the establishment of population specific mutation-spectra to achieve accurate personalized comprehensive molecular testing for HL.

WFS1 in Optic Neuropathies: Mutation Findings in Nonsyndromic Optic Atrophy and Assessment of Clinical Severity

PURPOSE

To search for WFS1 mutations in patients with optic atrophy (OA) and assess visual impairment.

DESIGN

Retrospective molecular genetic and clinical study.

PARTICIPANTS

Patients with OA followed at a national referral center specialized in genetic sensory diseases.

METHODS

Mutation screening in WFS1 was performed by Sanger sequencing. WFS1-positive patients were evaluated on visual acuity (VA) and retinal nerve fiber layer (RNFL) thickness using time-domain (TD) or spectral-domain (SD) optical coherence tomography (OCT). Statistical analysis was performed.

MAIN OUTCOME MEASURES

Mutation identification, VA values, and RNFL thickness in sectors.

RESULTS

Biallelic WFS1 mutations were found in 3 of 24 unrelated patients (15%) with autosomal recessive nonsyndromic optic atrophy (arNSOA) and in 8 patients with autosomal recessive Wolfram syndrome (arWS) associated with diabetes mellitus and OA. Heterozygous mutations were found in 4 of 20 unrelated patients (20%) with autosomal dominant OA. The 4 WFS1-mutated patients of this latter group with hearing loss were diagnosed with autosomal dominant Wolfram-like syndrome (adWLS). Most patients had VA decrease, with logarithm of the minimum angle of resolution (logMAR) values lower in arWS than in arNSOA (1.530 vs. 0.440; P = 0.026) or adWLS (0.240; P = 0.006) but not differing between arNSOA and adWLS (P = 0.879). All patients had decreased RNFL thickness that was worse in arWS than in arNSOA (SD OCT, 35.50 vs. 53.80 μm; P = 0.018) or adWLS (TD-OCT, 45.84 vs. 59.33 μm; P = 0.049). The greatest difference was found in the inferior bundle. Visual acuity was negatively correlated with RNFL thickness (r = -0.89; P = 0.003 in SD OCT and r = -0.75; P = 0.01 in TD-OCT).

CONCLUSIONS

WFS1 is a gene causing arNSOA. Patients with this condition had significantly less visual impairment than those with arWS. Thus systematic screening of WFS1 must be performed in isolated, sporadic, or familial optic atrophies.

Wolfram Syndrome: Diagnosis, Management, and Treatment

Wolfram syndrome is a rare genetic disorder characterized by juvenile-onset diabetes mellitus, diabetes insipidus, optic nerve atrophy, hearing loss, and neurodegeneration. Although there are currently no effective treatments that can delay or reverse the progression of Wolfram syndrome, the use of careful clinical monitoring and supportive care can help relieve the suffering of patients and improve their quality of life. The prognosis of this syndrome is currently poor, and many patients die prematurely with severe neurological disabilities, raising the urgency for developing novel treatments for Wolfram syndrome. In this article, we describe natural history and etiology, provide recommendations for diagnosis and clinical management, and introduce new treatments for Wolfram syndrome.

Whole-exome sequencing to decipher the genetic heterogeneity of hearing loss in a Chinese family with deaf by deaf mating

Inherited deafness has been shown to have high genetic heterogeneity. For many decades, linkage analysis and candidate gene approaches have been the main tools to elucidate the genetics of hearing loss. However, this associated study design is costly, time-consuming, and unsuitable for small families. This is mainly due to the inadequate numbers of available affected individuals, locus heterogeneity, and assortative mating. Exome sequencing has now become technically feasible and a cost-effective method for detection of disease variants underlying Mendelian disorders due to the recent advances in next-generation sequencing (NGS) technologies. In the present study, we have combined both the Deafness Gene Mutation Detection Array and exome sequencing to identify deafness causative variants in a large Chinese composite family with deaf by deaf mating. The simultaneous screening of the 9 common deafness mutations using the allele-specific PCR based universal array, resulted in the identification of the 1555A>G in the mitochondrial DNA (mtDNA) 12S rRNA in affected individuals in one branch of the family. We then subjected the mutation-negative cases to exome sequencing and identified novel causative variants in the MYH14 and WFS1 genes. This report confirms the effective use of a NGS technique to detect pathogenic mutations in affected individuals who were not candidates for classical genetic studies.

Comorbidity of GJB2 and WFS1 mutations in one family

It is rarely reported that two distinct genetic mutations affecting hearing have been found in one family. We report on a family exhibiting comorbid mutation of GJB2 and WFS1. A four-generation Japanese family with autosomal dominant sensorineural hearing loss was studied. In 7 of the 24 family members, audiometric evaluations and genetic analysis were performed. We detected A-to-C nucleotide transversion (c.2576G>C) in exon 8 of WFS1 that was predicted to result in an arginine-to-proline substitution at codon 859 (R859P), G-to-A transition (c.109G>A) in exon 2 of GJB2 that was predicted to result in a valine-to-isoleucine substitution at codon 37 (V37I), and C-to-T transition (c.427C>T) in exon 2 of GJB2 that was predicted to result in an arginine-to-tryptophan substitution at codon 143 (R143W). Two individuals who had heterozygosity of GJB2 mutations and heterozygosity of WFS1 mutations showed low-frequency hearing loss. One individual who had homozygosity of GJB2 mutation without WFS1 mutation had moderate, gradual high tone hearing loss. On the other hand, a moderate flat loss configuration was seen in one individual who had compound heterozygosity of GJB2 and heterozygosity of WFS1 mutations. Our results indicate that the individual who has both GJB2 and WFS1 mutations can show GJB2 phenotype.

[Hereditary hearing loss: genetic counselling]

The aim of this review is to provide an updated overview of hereditary hearing loss, with special attention to the etiological diagnosis of sensorineural hearing loss, the genes most frequently mutated in our environment, the techniques available for their analysis and the clinical implications of genetic diagnosis. More than 60% of childhood sensorineural hearing loss is genetic. In adults, the percentage of hereditary hearing loss is unknown. Genetic testing is the highest yielding test for evaluating patients with sensorineural hearing loss. The process of genetic counselling is intended to inform patients and their families of the medical, psychological and familial implications of genetic diseases, as well as the risks, benefits and limitations of genetic testing. The implementation of any genetic analysis must be always preceded by an appropriate genetic counselling process.

In search of the DFNA11 myosin VIIA low- and mid-frequency auditory genetic modifier

OBJECTIVES

To evaluate the auditory, vestibular, and retinal characteristics of a large American DFNA11 pedigree with autosomal dominant progressive sensorineural hearing loss that first impacts the low- and mid-frequency auditory range. The pedigree (referred to as the HL2 family) segregates a myosin VIIA (MYO7A) mutation in exon 17 at DNA residue G2164C (MYO7A) that seems to be influenced by a genetic modifier that either rescues or exacerbates the MYO7A alteration. DNA analysis to examine single-nucleotide polymorphisms in 2 candidate modifier genes (ATP2B2 and Wolfram syndrome 1 [WFS1]) is summarized in this report.

STUDY DESIGN

Family study.

RESULTS

The degree of low- and mid-frequency hearing loss in HL2 family members segregating the MYO7A mutation varies from mild to more severe, with approximately the same number of HL2 family members falling at each end of the severity spectrum. The extent of hearing loss in HL2 individuals can vary between family generations. Differences in the degree of hearing loss in MYO7A HL2 family members may be mirrored by vestibular function in at least 2 of these same individuals. The single-nucleotide polymorphisms examined within ATP2B2 and WFS1 did not segregate with the mild versus more severe auditory phenotype.

CONCLUSION

The severity of the auditory and vestibular phenotypes in MYO7A HL2 family members may run in parallel, suggesting a common modifier gene within the inner ear. The putative MYO7A genetic modifier is likely to represent a common polymorphism that is not linked tightly to the MYO7A mutation on the MYO7A allele.

Forty-six genes causing nonsyndromic hearing impairment: which ones should be analyzed in DNA diagnostics?

Hearing impairment is the most common sensory disorder, present in 1 of every 500 newborns. With 46 genes implicated in nonsyndromic hearing loss, it is also an extremely heterogeneous trait. Here, we categorize for the first time all mutations reported in nonsyndromic deafness genes, both worldwide and more specifically in Caucasians. The most frequent genes implicated in autosomal recessive nonsyndromic hearing loss are GJB2, which is responsible for more than half of cases, followed by SLC26A4, MYO15A, OTOF, CDH23 and TMC1. None of the genes associated with autosomal dominant nonsyndromic hearing loss accounts for a preponderance of cases, although mutations are somewhat more frequently reported in WFS1, KCNQ4, COCH and GJB2. Only a minority of these genes is currently included in genetic diagnostics, the selection criteria typically reflecting: (1) high frequency as a cause of deafness (i.e. GJB2); (2) association with another recognisable feature (i.e. SLC26A4 and enlarged vestibular aqueduct); or (3) a recognisable audioprofile (i.e. WFS1). New and powerful DNA sequencing technologies have been developed over the past few years, but have not yet found their way into DNA diagnostics. Implementing these technologies is likely to happen within the next 5 years, and will cause a breakthrough in terms of power and cost efficiency. It will become possible to analyze most - if not all - deafness genes, as opposed to one or a few genes currently. This ability will greatly improve DNA diagnostics, provide epidemiological data on gene-based mutation frequencies, and reveal novel genotype-phenotype correlations.

A novel WFS1 mutation in a family with dominant low frequency sensorineural hearing loss with normal VEMP and EcochG findings

Background

Low frequency sensorineural hearing loss (LFSNHL) is an uncommon clinical finding. Mutations within three different identified genes (DIAPH1, MYO7A, and WFS1) are known to cause LFSNHL. The majority of hereditary LFSNHL is associated with heterozygous mutations in the WFS1 gene (wolframin protein). The goal of this study was to use genetic analysis to determine if a small American family's hereditary LFSNHL is linked to a mutation in the WFS1 gene and to use VEMP and EcochG testing to further characterize the family's audiovestibular phenotype.

Methods

The clinical phenotype of the American family was characterized by audiologic testing, vestibular evoked myogenic potentials (VEMP), and electrocochleography (EcochG) evaluation. Genetic characterization was performed by microsatellite analysis and direct sequencing of WFS1 for mutation detection.

Results

Sequence analysis of the WFS1 gene revealed a novel heterozygous mutation at c.2054G>C predicting a p.R685P amino acid substitution in wolframin. The c.2054G>C mutation segregates faithfully with hearing loss in the family and is absent in 230 control chromosomes. The p.R685 residue is located within the hydrophilic C-terminus of wolframin and is conserved across species. The VEMP and EcochG findings were normal in individuals segregating the WFS1 c.2054G>C mutation.

Conclusion

We discovered a novel heterozygous missense mutation in exon 8 of WFS1 predicting a p.R685P amino acid substitution that is likely to underlie the LFSNHL phenotype in the American family. For the first time, we describe VEMP and EcochG findings for individuals segregating a heterozygous WFS1 mutation.

Autosomal dominant transmission of diabetes and congenital hearing impairment secondary to a missense mutation in the WFS1 gene

AIMS

Mutations of the WFS1 gene have been implicated in autosomal dominant diseases, such as low-frequency sensorineural hearing impairment (LFSNHI) and/or diabetes mellitus and/or optic atrophy. The aim was to investigate WFS1 gene sequences in a family with diabetes mellitus and hearing impairment.

METHODS

Three members of a family with a maternally inherited combination of diabetes mellitus and hearing impairment, but no specific mutations in its mitochondrial genome, were investigated for mutations in the WFS1 gene.

RESULTS

This pedigree, in which the proband had non-insulin-dependent diabetes mellitus and congenital hearing impairment and his mother a triple combination of diabetes mellitus, hearing impairment and optic atrophy, was found to be associated with autosomal dominant transmission of the E864K mutation of the WFS1 gene.

CONCLUSIONS

In the light of this confirmatory study, we recommend the systematic analysis of WFS1 gene sequences in patients with parentally inherited diabetes mellitus and deafness (+/- optic atrophy), in particular when diabetogenic mtDNA mutations have been excluded.

Mutations in the WFS1 gene are a frequent cause of autosomal dominant nonsyndromic low-frequency hearing loss in Japanese

Mutations in WFS1 are reported to be responsible for two conditions with distinct phenotypes; DFNA6/14/38 and autosomal recessive Wolfram syndrome. They differ in their associated symptoms and inheritance mode, and although their most common clinical symptom is hearing loss, it is of different types. While DNFA6/14/38 is characterized by low frequency sensorineural hearing loss (LFSNHL), in contrast, Wolfram syndrome is associated with various hearing severities ranging from normal to profound hearing loss that is dissimilar to LFSNHL (Pennings et al. 2002). To confirm whether within non-syndromic hearing loss patients WFS1 mutations are found restrictively in patients with LFSNHL and to summarize the mutation spectrum of WFS1 found in Japanese, we screened 206 Japanese autosomal dominant and 64 autosomal recessive (sporadic) non-syndromic hearing loss probands with various severities of hearing loss. We found three independent autosomal dominant families associated with two different WFS1 mutations, A716T and E864K, previously detected in families with European ancestry. Identification of the same mutations in independent families with different racial backgrounds suggests that both sites are likely to be mutational hot spots. All three families with WFS1 mutations in this study showed a similar phenotype, LFSNHL, as in previous reports. In this study, one-third (three out of nine) autosomal dominant LFSNHL families had mutations in the WFS1 gene, indicating that in non-syndromic hearing loss WFS1 is restrictively and commonly found within autosomal dominant LFSNHL families.

A mutation in Wolfram syndrome type 1 gene in a Japanese family with autosomal dominant low-frequency sensorineural hearing loss

CONCLUSION

Our findings suggest that Wolfram syndrome type 1 gene (WFS1) mutation is an important cause of autosomal dominant low-frequency sensorineural hearing loss (LFSNHL) in Japan.

OBJECTIVE

DFNA6/14 is caused by a heterozygous mutation of WFS1 and is a common cause of autosomal dominant LFSNHL among populations in both Europe and the US. The purpose of this study was to investigate WFS1 mutations among Japanese patients whose phenotypes were consistent with those of DFNA6/14.

MATERIAL AND METHODS

Using audiometry and genetic analysis, we searched for WFS1 mutations in three unrelated Japanese patients with LFSNHL and a familial history of autosomal dominant hearing loss.

RESULTS

One patient carried a heterozygous G2700A mutation at codon 844 in exon 8, resulting in substitution of a threonine for an alanine (A844T). Genetic analysis of the available members of the patient's family showed that the A844T mutation segregated with LFSNHL, but was not detected in any of 140 control chromosomes. It thus appears likely that the A844T mutation is causative for hearing loss in this group. Speech audiometry, self-recording audiometry and auditory brainstem responses showed the patient to have cochlear deafness without retrocochlear dysfunction. No mutation was found in the other two patients.

Expressional and functional studies of Wolframin, the gene function deficient in Wolfram syndrome, in mice and patient cells

Wolfram Syndrome is an autosomal recessive degenerative disorder of the neuroendocrine system. Diabetes mellitus is its lead symptom. Patients show mutations in the wolframin (WFS1) gene coding for a hydrophobic transmembrane protein of 890 amino acids. This protein was preliminarily localised in the endoplasmatic reticulum (ER) in cells of mice and rats. Mice lacking the WFS1 gene display degeneration of pancreatic beta-cells following induction of ER stress. We here used antibodies against substructures of the wolframin protein in order to analyse its expression and localisation. Expression was detected in both pancreatic beta-cells and the limbic system of mice. Using the rat insulinoma cell line RIN 5AH and fractionated mouse brain tissue, we confirmed wolframin localisation to the endoplasmic reticulum. Expression profiling on patient's primary fibroblasts revealed down-regulation of the diabetes associated plasma membrane glycoprotein (PC-1) gene, and up-regulation of fibulin-3, a gene connected to senescence. However, cell proliferation was indistinguishable from non-mutated cells. In contrast to data obtained on murine pancreatic islets, we found no increased apoptosis following induction of ER stress but rather by staurosporine treatment in the absence of WFS1 function. This indicates a new role of WFS1 deficiency in programmed cell death.

Two families with nonsyndromic low-frequency hearing loss harbor novel mutations in Wolfram syndrome gene 1

Although hereditary hearing loss is highly heterogeneous, only a few loci have been implicated with low-frequency hearing loss. Mutations in one single gene, Wolfram syndrome 1 (WFS1), have been reported to account for most familial cases with this type of hearing impairment. This study was conducted to determine the cause of nonsyndromic low-frequency hereditary hearing impairment in two large families. Two large families from Switzerland and United States with low-frequency hearing loss were identified. Genomewide linkage analysis was performed followed by mutation screening in the candidate gene WFS1 with direct DNA sequencing and restriction fragment analysis. Both families were linked to DFNA6/14/38 with lod scores>3. Two novel heterozygous missense mutations in WFS1 were identified: c.2311G>C leading to p.D771H in the Swiss family and c.2576G>C leading to p.R859P in the US family. The sequence alteration was absent in 100 control chromosomes. Nonsyndromic low-frequency hereditary hearing impairment seems to be predominantly a monogenic disorder due to WFS1. We confirm that most mutations in WFS1 associated with isolated low-frequency hearing loss are clustered in the C-terminal protein domain coded by exon 8.

A mutation in the gamma actin 1 (ACTG1) gene causes autosomal dominant hearing loss (DFNA20/26)

Linkage analysis in a multigenerational family with autosomal dominant hearing loss yielded a chromosomal localisation of the underlying genetic defect in the DFNA20/26 locus at 17q25-qter. The 6-cM critical region harboured the gamma-1-actin (ACTG1) gene, which was considered an attractive candidate gene because actins are important structural elements of the inner ear hair cells. In this study, a Thr278Ile mutation was identified in helix 9 of the modelled protein structure. The alteration of residue Thr278 is predicted to have a small but significant effect on the gamma 1 actin structure owing to its close proximity to a methionine residue at position 313 in helix 11. Met313 has no space in the structure to move away. Moreover, the Thr278 residue is highly conserved throughout eukaryotic evolution. Using a known actin structure the mutation could be predicted to impair actin polymerisation. These findings strongly suggest that the Thr278Ile mutation in ACTG1 represents the first disease causing germline mutation in a cytoplasmic actin isoform.

Mutational spectrum of the WFS1 gene in Wolfram syndrome, nonsyndromic hearing impairment, diabetes mellitus, and psychiatric disease

WFS1 is a novel gene and encodes an 890 amino-acid glycoprotein (wolframin), predominantly localized in the endoplasmic reticulum. Mutations in WFS1 underlie autosomal recessive Wolfram syndrome and autosomal dominant low frequency sensorineural hearing impairment (LFSNHI) DFNA6/14. In addition, several WFS1 sequence variants have been shown to be significantly associated with diabetes mellitus and this gene has also been implicated in psychiatric diseases. Wolfram syndrome is highly variable in its clinical manifestations, which include diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. Wolfram syndrome mutations are spread over the entire coding region, and are typically inactivating, suggesting that a loss of function causes the disease phenotype. In contrast, only non-inactivating mutations have been found in DFNA6/14 families, and these mutations are mainly located in the C-terminal protein domain. In this paper, we provide an overview of the currently known disease-causing and benign allele variants of WFS1 and propose a potential genotype-phenotype correlation for Wolfram syndrome and LFSNHI.