Good cochlear implantation outcomes in subjects with mono-allelic WFS1-associated sensorineural hearing loss - a case series.

OBJECTIVE: This study aimed to evaluate long-term cochlear implant (CI) outcomes in individuals with mono-allelic pathogenic variants in WFS1, which is associated with both Wolfram-like syndrome and DFNA6/14/38. DESIGN: Retrospective case series. STUDY SAMPLE: Seven CI recipients, ranging from eight months to 58 years of age, were included in the study, including four with Wolfram-like syndrome and three with DFNA6/14/38. A total of ten cochlear implantations were performed among these subjects. RESULTS: At one-year post-implantation, a mean phoneme score of 90 ± 9% at 65 dB SPL in quiet was found, which remained stable up to ten years post-implantation with a mean phoneme score of 94 ± 6%. Despite these excellent outcomes, one subject achieved no speech recognition with CI and eventually became a non-user. This individual had a prolonged absence of auditory stimulation prior to implantation and encountered multiple challenges during rehabilitation. CONCLUSION: Individuals with Wolfram-like syndrome or DFNA6/14/38 demonstrate consistently good outcomes following implantation, which remain stable over time. These findings affirm cochlear implantation as an effective rehabilitation option for these individuals. Furthermore, the stable and good CI outcomes contradict the suggested link between WFS1-associated sensorineural hearing loss and auditory neuropathy.

Wfs1 loss-of-function disrupts the composition of mouse pancreatic endocrine cells from birth and impairs Glut2 localization to cytomembrane in pancreatic ß cells.

Wfs1 is an endoplasmic reticulum (ER) membrane located protein highly expressed in pancreatic ß cells and brain. Wfs1 deficiency causes adult pancreatic ß cells dysfunction following ß cells apoptosis. Previous studies mainly focus on the Wfs1 function in adult mouse pancreatic ß cells. However, whether Wfs1 loss-of-function impairs mouse pancreatic ß cell from its early development is unknown. In our study, Wfs1 deficiency disrupts the composition of mouse pancreatic endocrine cells from early postnatal day 0 (P0) to 8 weeks old, with decreased percentage of ß cells and increased percentage of α and δ cells. Meanwhile, Wfs1 loss-of-function leads to reduced intracellular insulin content. Notably, Wfs1 deficiency impairs Glut2 localization and causes the accumulation of Glut2 in mouse pancreatic ß cell cytoplasm. In Wfs1-deficient mice, glucose homeostasis is disturbed from early 3 weeks old to 8 weeks old. This work reveals that Wfs1 is significantly required for the composition of pancreatic endocrine cells and is essential for Glut2 localization in mouse pancreatic ß cells.

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.

Wolframin is a novel regulator of tau pathology and neurodegeneration.

Selective neuronal vulnerability to protein aggregation is found in many neurodegenerative diseases including Alzheimer's disease (AD). Understanding the molecular origins of this selective vulnerability is, therefore, of fundamental importance. Tau protein aggregates have been found in Wolframin (WFS1)-expressing excitatory neurons in the entorhinal cortex, one of the earliest affected regions in AD. The role of WFS1 in Tauopathies and its levels in tau pathology-associated neurodegeneration, however, is largely unknown. Here we report that WFS1 deficiency is associated with increased tau pathology and neurodegeneration, whereas overexpression of WFS1 reduces those changes. We also find that WFS1 interacts with tau protein and controls the susceptibility to tau pathology. Furthermore, chronic ER stress and autophagy-lysosome pathway (ALP)-associated genes are enriched in WFS1-high excitatory neurons in human AD at early Braak stages. The protein levels of ER stress and autophagy-lysosome pathway (ALP)-associated proteins are changed in tau transgenic mice with WFS1 deficiency, while overexpression of WFS1 reverses those changes. This work demonstrates a possible role for WFS1 in the regulation of tau pathology and neurodegeneration via chronic ER stress and the downstream ALP. Our findings provide insights into mechanisms that underpin selective neuronal vulnerability, and for developing new therapeutics to protect vulnerable neurons in AD.

The Role of ER Stress in Diabetes: Exploring Pathological Mechanisms Using Wolfram Syndrome.

The endoplasmic reticulum (ER) is a cytosolic organelle that plays an essential role in the folding and processing of new secretory proteins, including insulin. The pathogenesis of diabetes, a group of metabolic disorders caused by dysfunctional insulin secretion (Type 1 diabetes, T1DM) or insulin sensitivity (Type 2 diabetes, T2DM), is known to involve the excess accumulation of "poorly folded proteins", namely, the induction of pathogenic ER stress in pancreatic ß-cells. ER stress is known to contribute to the dysfunction of the insulin-producing pancreatic ß-cells. T1DM and T2DM are multifactorial diseases, especially T2DM; both environmental and genetic factors are involved in their pathogenesis, making it difficult to create experimental disease models. In recent years, however, the development of induced pluripotent stem cells (iPSCs) and other regenerative technologies has greatly expanded research capabilities, leading to the development of new candidate therapies. In this review, we will discuss the mechanism by which dysregulated ER stress responses contribute to T2DM pathogenesis. Moreover, we describe new treatment methods targeting protein folding and ER stress pathways with a particular focus on pivotal studies of Wolfram syndrome, a monogenic form of syndromic diabetes caused by pathogenic variants in the WFS1 gene, which also leads to ER dysfunction.

Diagnosis, treatment and genetic analysis of a case of familial aldosteronism type II with WFS1 gene mutation.

Primary aldosteronism (PA) is a disease characterized by hypertension and hypokalemia due to the excessive aldosterone secretion from the adrenal cortex, which leads to the retention of both water and sodium, and the inhibition of the renin-angiotensin system as well. Familial hyperaldosteronism type II (FH-II) is known as an autosomal dominant hereditary disease, which is a scarce cause of PA. In this report, we cllected the clinical data of a patient with repeated hypertension and hypokalemia of uncertain diagnosis since 2014. Nevertheless, we discovered by genetic sequencing in 2021 that the CLCN2 and WFS1 gene mutation of the patient, whose mother belongs to heterozygote genotype and father belongs to wild-type genotype. Combined with a series of endocrine function tests and imaging studies, the patient was finally certified her suffering from FH-II and WFS1 gene mutation. By summarizing and analyzing the characteristics and genetic test results of this case, we recommended gene sequencing for patients with PA whose etiology is difficult to be determined clinically. This case also provides new clinical data for subsequent genetic studies of the disease.

High-fat diet associated sensitization to metabolic stress in Wfs1 heterozygous mice.

Wolfram syndrome is a rare autosomal recessive disorder caused by mutations in the wolframin ER transmembrane glycoprotein (WFS1) gene and characterized by diabetes mellitus, diabetes insipidus, optic atrophy and deafness. In experimental models the homozygous Wfs1 mutant mice have a full penetrance and clearly expressed phenotype, whereas heterozygous mutants have a less-pronounced phenotype between the wild-type and homozygous mutant mice. Heterozygous WFS1 mutations have been shown to be significant risk factors for diabetes and metabolic disorders in humans. In the present study we analyzed the response of heterozygous Wfs1 mice to high fat diet (HFD) by exploring potential outcomes and molecular changes induced by this challenge. The HFD treatment increased the body weight (BW) similarly both in Wfs1 wild-type (WT) and heterozygous (HZ) mice, and therefore HFD also prevented the impaired BW gain found in Wfs1 mutant mice. In Wfs1HZ mutant mice, HFD impaired the normalized insulin secretion and the expression of ER stress genes in isolated pancreatic islets. These results suggest that Wfs1HZ mice have a decreased insulin response and pronounced cellular stress response due to a higher sensitivity to HFD as hypothesized. In Wfs1HZ mice, HFD increased the expression of Ire1α and Chop in pancreas and decreased that of Ire1α and Atf4 in liver. The present study shows that HFD can disturb insulin function with an increased ER stress in Wfs1HZ mice and only one functional Wfs1 gene copy is not sufficient to compensate this challenge. In conclusion, our study indicates that quantitative Wfs1 gene deficiency is sufficient to predispose the carriers of single functional Wfs1 copy to diabetes and metabolic syndrome and makes them susceptible to the environmental challenges such as HFD.

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.

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.

Unique three-site compound heterozygous mutation in the WFS1 gene in Wolfram syndrome.

BACKGROUND: Wolfram syndrome (WFS) is a rare autosomal recessive genetic disease whose main cause is mutations in the WFS1 and CISD2 genes. Its characteristic clinical manifestations are diabetes insipidus, diabetes mellitus, optic atrophy and deafness. METHODS: In this study, two patients from this particular family underwent complete routine biochemical and ophthalmic tests. Blood, urine, routine stool test, visual acuity (VA) examination, visual field assessment, funduscope, optical coherence tomography and periorbital magnetic resonance imaging (MRI) scans were performed for each patient to evaluate whether the nerve fiber layer around the optic nerve head was atrophied and next-generation sequencing of target genes was performed in two patients. RESULTS: When the patients were diagnosed with Wolfram syndrome, their genetic analyses suggested unique three-site compound heterozygous mutations (c.2314C > T + c.2194C > T + c.2171C > T) in exon 8 of both patients' chromosome 4. One mutation (c.2314C > T) was a novel mutation in the known reports of Wolfram syndrome. As a degenerative genetic disease, the types of gene mutations in the Chinese population are generally homozygous mutations at the unit point or compound heterozygous mutations at two nucleotide change sites. However, the two patients reported in this study are the first known cases of compound heterozygous mutations with three mutation sites coexisting on the WFS1 gene in China or even globally. CONCLUSIONS: This study expands the phenotypic spectrum of Wolfram syndrome and may reveal a novel mutation pattern of pathogenesis of Wolfram syndrome. The implications of this discovery are valuable in the clinical diagnosis, prognosis, and treatment of patients with WFS1.

Expression Quantitative Trait Loci (eQTLs) Associated with Retrotransposons Demonstrate their Modulatory Effect on the Transcriptome.

Transposable elements (TEs) are repetitive elements that belong to a variety of functional classes and have an important role in shaping genome evolution. Around 50% of the human genome contains TEs, and they have been termed the "dark matter" of the genome because relatively little is known about their function. While TEs have been shown to participate in aberrant gene regulation and the pathogenesis of diseases, only a few studies have explored the systemic effect of TEs on gene expression. In the present study, we analysed whole genome sequences and blood whole transcriptome data from 570 individuals within the Parkinson's Progressive Markers Initiative (PPMI) cohort to identify expression quantitative trait loci (eQTL) regulating genome-wide gene expression associated with TEs. We identified 2132 reference TEs that were polymorphic for their presence or absence in our study cohort. The presence or absence of the TE element could change the expression of the gene or gene clusters from zero to tens of thousands of copies of RNA. The main finding is that many TEs possess very strong regulatory effects, and they have the potential to modulate large genetic networks with hundreds of target genes over the genome. We illustrate the plethora of regulatory mechanisms using examples of their action at the HLA gene cluster and data showing different TEs' convergence to modulate WFS1 gene expression. In conclusion, the presence or absence of polymorphisms of TEs has an eminent genome-wide regulatory function with large effect size at the level of the whole transcriptome. The role of TEs in explaining, in part, the missing heritability for complex traits is convincing and should be considered.

Clinical and genetic analysis of two wolfram syndrome families with high occurrence of wolfram syndrome and diabetes type II: a case report.

BACKGROUND: Mutations of the WFS1 gene are responsible for most cases of Wolfram syndrome (WS), a rare, recessively inherited neurodegenerative disorder characterized by juvenile-onset non-autoimmune diabetes mellitus and optic atrophy. Variants of WFS1 are also associated with non-syndromic hearing loss and type-2 diabetes mellitus (T2DM). Our study adds to literature significant associations between WS and T2DM. CASE PRESENTATION: In this study, we analyzed the clinical and genetic data of two families with high prevalence of WS and T2DM. Genetic linkage analysis and DNA sequencing were exploited to identify pathogenic variants. One novel pathogenic variant (c.2243-2244insC) and one known pathogenic (c.1232_1233delCT) (frameshift) variant were identified in exon eight of WFS1 gene. CONCLUSIONS: The mutational and phenotypic spectrum of WS is broadened by our report of novel WFS1 mutation. Our results reveal the value of molecular analysis of WFS1 in the improvement of clinical diagnostics for WS. This study also confirms the role of WFS1 in T2DM.

The molecular effect of a polymorphic microRNA binding site of Wolfram syndrome 1 gene in dogs.

BACKGROUND: Although the molecular function of wolframin remains unclear, the lack of this protein is known to cause stress in the endoplasmic reticulum. Some variants in the Wolfram Syndrome 1 gene (WFS1) were associated with various neuropsychiatric disorders in humans, such as aggressiveness, impulsivity and anxiety. RESULTS: Here we present an in silico study predicting a single nucleotide polymorphism (rs852850348) in the canine WFS1 gene which was verified by direct sequencing and was genotyped by a PCR-based technique. We found that the rs852850348 polymorphism is located in a putative microRNA (cfa-miR-8834a and cfa-miR-1838) binding site. Therefore, the molecular effect of allelic variants was studied in a luciferase reporter system that allowed assessing gene expression. We demonstrated that the variant reduced the activity of the reporter protein expression in an allele-specific manner. Additionally, we performed a behavioral experiment and investigated the association with this locus to different performance in this test. Association was found between food possessivity and the studied WFS1 gene polymorphism in the Border collie breed. CONCLUSIONS: Based on our findings, the rs852850348 locus might contribute to the genetic risk of possessivity behavior of dogs in at least one breed and might influence the regulation of wolframin expression.

Effect of 4-phenylbutyrate and valproate on dominant mutations of WFS1 gene in Wolfram syndrome.

PURPOSE: Wolfram syndrome (WS) is a rare disorder caused by mutations in WFS1 that is characterized by diabetes mellitus, optic atrophy, sensorineural deafness, diabetes insipidus, and neurodegeneration. This disease is usually inherited as an autosomal recessive trait, but an autosomal dominant form has been reported. WFS1 encodes a transmembrane protein, which is a maintenance component of endoplasmic homeostasis. These dominant mutations were thought to increase endoplasmic reticulum (ER) stress. Recent studies suggest that 4-phenylbutyrate (PBA) and valproate (VPA) reduce ER stress. The objective of this study was to analyze the effect of PBA and VPA on dominant WFS1 mutants in vitro. METHODS: We determined whether dominant WFS1 mutants (p.His313Tyr, p.Trp314Arg, p.Asp325_Ile328del, p.Glu809Lys, and p.Glu864Lys) have the dominant negative effect using a luciferase assay of ER stress response element marker as ER stress. Moreover, the rescue of cell apoptosis induced by dominant WFS1 mutants following treatment with PBA or VPA was determined by quantitative real-time PCR of C/EBP homologous protein (CHOP) mRNA expression. RESULTS: These mutants showed the dominant negative effect on the wild-type WFS1. In addition, the levels of ER stress and CHOP mRNA were significantly elevated by all dominant WFS1 mutants. After treatment with PBA or VPA, ER stress and cell apoptosis were reduced in each mutant. CONCLUSIONS: PBA and VPA could reduce the ER stress and cell apoptosis caused by dominant WFS1 mutants.

A homozygous missense mutation of WFS1 gene causes Wolfram's syndrome without hearing loss in an Iranian family (a report of clinical heterogeneity).

BACKGROUND: Wolfram's syndrome (WFS) is a hereditary (autosomal recessive) neurodegenerative disorder. The clinical features are related to diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (DIDMOAD) with other variable clinical manifestations. Pathogenic variants in the WFS1 gene, encoding wolframin, are known to be the main cause of Wolfram's syndrome. In this study, we present the clinical and genetic characteristics of two WFS patients from an Iranian family. METHODS: The mutation screening was performed by polymerase chain reaction (PCR) followed by direct Sanger sequencing of all exons from two affected WFS. RESULTS: The complete Sanger sequencing of the WFS1 gene detected a homozygous missense variant, c.2207G>A (p.Gly736Asp), in the eighth exon of the WFS1 gene. Both cases developed all the major symptoms of the disease, interestingly, except hearing loss. CONCLUSIONS: Because of the rarity and clinical heterogeneity of WFS, the molecular genetic assay is essential to confirm the diagnosis and management of the WFS patients.

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.

Ophthalmologic Manifestations of Wolfram Syndrome: Report of 14 Cases.

PURPOSE: The aim of this study was to describe ophthalmological abnormalities in 14 cases of Wolfram syndrome belonging to 9 different families. METHODS: Patients were submitted to a complete ophthalmological, neurological, otorhinolaryngological, urological, and genetic evaluation. RESULTS: Our sample comprised 14 Caucasian patients belonging to 9 different families. Their ages ranged from 10 to 38 years. The mean duration of known disease was 11.3 ± 8.7 years. Genetic confirmation was obtained in 7 families. There was a parental consanguinity history in 2 families. Five families were homozygous for a mutation of exon 8 of the WFS1 gene (Chr. 4), and 2 patients were heterozygous. Diabetes mellitus was the first manifestation in all except 1 patient. The mean age at diagnosis was 8.7 years (range 3-22). None had diabetic retinopathy. The mean age at diagnosis of optic atrophy was 11.1 years (range 8-35). The best-corrected visual acuity ranged from counting fingers to 20/50. CONCLUSIONS: Association of optic atrophy with insulin-dependent diabetes mellitus should raise the suspicion of Wolfram syndrome.

A novel mutation of WFS1 gene in a Chinese patient with Wolfram syndrome: a case report.

BACKGROUND: Wolfram syndrome (WS), caused by mutations of the Wolfram syndrome 1 (WFS1) gene on chromosome 4p16.1, is an autosomal recessive disorder characterized by diabetes insipidus (DI), neuro-psychiatric disorders, hearing deficit, and urinary tract anomalies. CASE PRESENTATION: Here we report a 11-year-old Chinese boy who presented with visual loss, was suspected with optic neuritis (ON) or neuromyelitis optica (NMO) and referred to our department for further diagnosis. Finally he was diagnosed with WS because of diabetes mellitus (DM) and optic atrophy (OA). Eight exons and flanking introns of WFS1 gene were analyzed by sequencing. A novel mutation c.1760G > A in WFS1 gene of exon 8 was identified. CONCLUSION: This report reviews a case of WS associated with a novel mutation, c.1760G > A in WFS1 gene of exon 8, and emphasizes that WS should be taken into account for juveniles with visual loss and diabetes mellitus.

Whole-exome sequencing identified a missense mutation in WFS1 causing low-frequency hearing loss: a case report.

BACKGROUND: Low-frequency nonsyndromic hearing loss (LF-NSHL) is a rare, inherited disorder. Here, we report a family with LF-NSHL in whom a missense mutation was found in the Wolfram syndrome 1 (WFS1) gene. CASE PRESENTATION: Family members underwent audiological and imaging evaluations, including pure tone audiometry and temporal bone computed tomography. Blood samples were collected from two affected and two unaffected subjects. To determine the genetic background of hearing loss in this family, genetic analysis was performed using whole-exome sequencing. Among 553 missense variants, c.2419A → C (p.Ser807Arg) in WFS1 remained after filtering and inspection of whole-exome sequencing data. This missense mutation segregated with affected status and demonstrated an alteration to an evolutionarily conserved amino acid residue. Audiological evaluation of the affected subjects revealed nonprogressive LF-NSHL, with early onset at 10 years of age, but not to a profound level. CONCLUSION: This is the second report to describe a pathological mutation in WFS1 among Korean patients and the second to describe the mutation in a different ethnic background. Given that the mutation was found in independent families, p.S807R possibly appears to be a "hot spot" in WFS1, which is associated with LF-NSHL.

A novel heterozygous mutation of the WFS1 gene leading to constitutive endoplasmic reticulum stress is the cause of Wolfram syndrome.

BACKGROUND: Wolfram syndrome (WS) is a disorder characterized by the association of insulin-dependent diabetes mellitus (DM), diabetes insipidus, deafness, and optic nerve atrophy. WS is caused by WFS1 mutations encoding WFS1 protein expressed in endoplasmic reticulum (ER). During ER protein synthesis, misfolded and unfolded proteins accumulate, known as "ER stress". This is attenuated by the unfolded protein response (UPR), which recovers and maintains ER functions. Because WFS1 is a UPR component, mutant WFS1 might cause unresolvable ER stress conditions and cell apoptosis, the major causes underlying WS symptoms. We encountered an 11-month-old Japanese female WS patient with insulin-dependent DM, congenital cataract and severe bilateral hearing loss. OBJECTIVE: Analyze the WFS1 and functional consequence of the patient WFS1 in vitro. RESULTS: The patient WFS1 contained a heterozygous 4 amino acid in-frame deletion (p.N325_I328del). Her mutant WFS1 increased GRP78 and ATF6α promoter activities in the absence of thapsigargin, indicating constitutive ER stress and nuclear factor of activated T-cell reporter activity, reflecting elevated cytosolic Ca2+ signals. Mutant transfection into cells reduced mRNA expression levels of sarcoplasmic/endoplasmic reticulum Ca2+ transport ATPase 2b (SERCA2b) compared with wild type. Because SERCA2b is required for ER and cytoplasmic Ca2+ homeostasis, decreased SERCA2b expression might affect ER Ca2+ efflux, causing cell apoptosis. CONCLUSION: A novel heterozygous mutation of WFS1 induced constitutive ER stress through ATF6α activation and ER Ca2+ efflux, resulting in cell apoptosis. These results provide new insights into the roles of WFS1 in UPR and mechanism of monogenic DM.