Presence of a major WFS1 mutation in Spanish Wolfram syndrome pedigrees

Identification of causative gene variants for patients with known monogenic diabetes using a targeted next-generation sequencing panel in a single-center study

Aims

We aimed to verify the usefulness of targeted next-generation sequencing (NGS) technology for diagnosing monogenic diabetes in a single center.

Methods

We designed an amplicon-based NGS panel targeting 34 genes associated with known monogenic diabetes and performed resequencing in 56 patients with autoantibody-negative diabetes mellitus diagnosed at < 50 years who had not been highly obese. By bioinformatic analysis, we filtered significant variants based on allele frequency (< 0.005 in East Asians) and functional prediction. We estimated the pathogenicity of each variant upon considering the family history.

Results

Overall, 16 candidate causative variants were identified in 16 patients. Among them, two previously known heterozygous nonsynonymous single-nucleotide variants associated with monogenic diabetes were confirmed as causative variants: one each in the GCK and WFS1 genes. The former was found in two independent diabetes-affected families. Two novel putatively deleterious heterozygous variants were also assumed to be causative from the family history: one frameshift and one nonsynonymous single-nucleotide variant in the HNF4A gene. Twelve variants remained as candidates associated with the development of diabetes.

Conclusion

Targeted NGS panel testing was useful to diagnose various forms of monogenic diabetes in combination with familial analysis, but additional ingenuity would be needed for practice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13340-023-00669-3.

WFS1-Associated Optic Neuropathy: Genotype-Phenotype Correlations and Disease Progression

OBJECTIVE

To evaluate the pattern of vision loss and genotype-phenotype correlations in WFS1-associated optic neuropathy (WON).

DESIGN

Multicenter cohort study.

METHODS

The study involved 37 patients with WON carrying pathogenic or candidate pathogenic WFS1 variants. Genetic and clinical data were retrieved from the medical records. Thirteen patients underwent additional comprehensive ophthalmologic assessment. Deep phenotyping involved visual electrophysiology and advanced psychophysical testing with a complementary metabolomic study.

MAIN OUTCOME MEASURES

WFS1 variants, functional and structural optic nerve and retinal parameters, and metabolomic profile.

RESULTS

Twenty-two recessive and 5 dominant WFS1 variants were identified. Four variants were novel. All WFS1 variants caused loss of macular retinal ganglion cells (RGCs) as assessed by optical coherence tomography (OCT) and visual electrophysiology. Advanced psychophysical testing indicated involvement of the major RGC subpopulations. Modeling of vision loss showed an accelerated rate of deterioration with increasing age. Dominant WFS1 variants were associated with abnormal reflectivity of the outer plexiform layer (OPL) on OCT imaging. The dominant variants tended to cause less severe vision loss compared with recessive WFS1 variants, which resulted in more variable phenotypes ranging from isolated WON to severe multisystem disease depending on the WFS1 alleles. The metabolomic profile included markers seen in other neurodegenerative diseases and type 1 diabetes mellitus.

CONCLUSIONS

WFS1 variants result in heterogenous phenotypes influenced by the mode of inheritance and the disease-causing alleles. Biallelic WFS1 variants cause more variable, but generally more severe, vision and RGC loss compared with heterozygous variants. Abnormal cleftlike lamination of the OPL is a distinctive OCT feature that strongly points toward dominant WON.

An Atypical Case of Late-Onset Wolfram Syndrome 1 without Diabetes Insipidus

Wolfram syndrome 1, a rare autosomal recessive neurodegenerative disease, is caused by mutations in the WFS1 gene. It is characterized by diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (DIDMOAD), and other clinical manifestations such as urological and neurological disorders. Here we described the case of a patient with an atypical late-onset Wolfram syndrome 1 without DI. Our WS1 patient was a c.1620_1622delGTG (p.Trp540del)/c.124 C > T (p.Arg42*) heterozygous compound. The p.Arg42* nonsense mutation was also found in heterozygosity in his sister and niece, both suffering from psychiatric disorders. The p.Arg42* nonsense mutation has never been found in WS1 and its pathogenicity is unclear so far. Our study underlined the need to study a greater number of WS1 cases in order to better understand the clinical significance of many WFS1 variants.

Current Drug Repurposing Strategies for Rare Neurodegenerative Disorders

Rare diseases are life-threatening or chronically debilitating low-prevalent disorders caused by pathogenic mutations or particular environmental insults. Due to their high complexity and low frequency, important gaps still exist in their prevention, diagnosis, and treatment. Since new drug discovery is a very costly and time-consuming process, leading pharmaceutical companies show relatively low interest in orphan drug research and development due to the high cost of investments compared to the low market return of the product. Drug repurposing–based approaches appear then as cost- and time-saving strategies for the development of therapeutic opportunities for rare diseases. In this article, we discuss the scientific, regulatory, and economic aspects of the development of repurposed drugs for the treatment of rare neurodegenerative disorders with a particular focus on Huntington’s disease, Friedreich’s ataxia, Wolfram syndrome, and amyotrophic lateral sclerosis. The role of academia, pharmaceutical companies, patient associations, and foundations in the identification of candidate compounds and their preclinical and clinical evaluation will also be discussed.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

Delineation of the genetic and clinical spectrum, including candidate genes, of monogenic diabetes: a multicenter study in South Korea

OBJECTIVES

Monogenic diabetes includes a group of heterogeneous diabetes types. We aimed to identify the frequency, clinical and molecular features of monogenic diabetes in a Korean pediatric cohort.

METHODS

A retrospective cohort and multicenter study of Korean children suspected to have monogenic diabetes, managed by four pediatric endocrine centers in the southeast region of South Korea, from February 2016 to February 2020. We recruited 27 pediatric Korean patients suspected to have monogenic diabetes who had at least two of the following three criteria (age at diagnosis, family history, and clinical presentation). Targeted exome sequencing was conducted in these patients. The functional consequences of the variants were predicted by bioinformatics and protein structure analysis.

RESULTS

Molecular genetic analysis identified 16 patients (59.3%) with monogenic diabetes. We identified a total of eight unique variants, including five novel variants (HNF4A c.1088C>T, CEL c.1627C>T and c.1421C>T, PAX4 c.538+8G>C, INS c.71C>T). We also identified two potential candidate gene variants for monogenic diabetes, namely c.650T>C in the SLC2A2 gene and c.629G>A in the PTF1A gene. Other variants were identified in the WFS1and NPHP3 genes in two rare genetic disorders. Variant-positive individuals had a lower presence of autoantibody positivity at the time of diagnosis and higher glycosylated hemoglobin levels at last follow-up when compared to variant-negative patients (p<0.001 and p=0.029, respectively).

CONCLUSIONS

These results further expand the spectrum of known variants as well as potential candidate gene variants associated with monogenic diabetes in Korea.

Wolfram syndrome 1 in the Italian population: genotype-phenotype correlations

OBJECTIVES

We studied 45 patients with Wolfram syndrome 1 (WS1) to describe their clinical history and to search for possible genotype-phenotype correlations.

METHODS

Clinical criteria contributing to WS1 diagnosis were analyzed. The patients were classified into three genotypic classes according to type of detected mutations.

RESULTS

WS1 prevalence in Italy is 0.74/1,000,000. All four manifestations of DIDMOAD were found in 46.7% of patients. Differently combined WS1 clinical features were detected in 53.3% of patients. We found 35 WFS1 different mutations and a novel missense mutation, c.1523A>G. WS1 patients were homozygotes or compound heterozygotes for WFS1 mutations except for 2 heterozygote patients (4.5%). Each genotypic group exhibited a different age onset of DM, D, and DI but not of OA. Genotypic Group 2 patients manifested a lower number of clinical manifestations compared to Groups 1 and 3. Moreover, genotypic Group 1 patients tended to have a shorter survival time than the other groups. No differences were found regarding type of clinical pictures.

CONCLUSIONS

Our study suggested that molecular WFS1 typing is a useful tool for early assessment of clinical history, follow-up, and prognosis of WS1.

Novel mutations and the ophthalmologic characters in Chinese patients with Wolfram Syndrome

BACKGROUND

Wolfram Syndrome (WFS) is a rare autosomal recessive neurodegenerative disease which has a wide spectrum of manifestations including diabetes insipidus, diabetes mellitus, optic atrophy and deafness. WFS1 and CISD2 are two main causing genes of WFS. The aim of this study was to illustrate the ophthalmologic manifestations and determine the genotype of Chinese WFS patients.

RESULTS

Completed ophthalmic examinations and family investigations were performed on 4 clinically diagnosed WFS patients from 4 unrelated families. Genetic testing was done by the next generation sequencing of candidate genes. One patient carried a homozygous mutation (c.272_273del) in CISD2, two patients carried compound heterozygous mutations (c.1618 T > G + c.2020G > A and c.1048 T > A + c.2020G > A) in WFS1, and one patient carried a heterozygous mutation (c.937C > T) in WFS1. Three of them were novel mutations.

CONCLUSIONS

Our study indicated WFS in Chinese is a neurodegenerative disease with both wide spectrum of clinical features and genetic heterogeneity. We found three novel mutations in WFS patients, and to our best knowledge, this is the first report of Chinese WFS patient with mutation in CISD2.

Identification of a missense variant in the WFS1 gene that causes a mild form of Wolfram syndrome and is associated with risk for type 2 diabetes in Ashkenazi Jewish individuals

AIMS/HYPOTHESIS

Wolfram syndrome is a rare, autosomal recessive syndrome characterised by juvenile-onset diabetes and optic atrophy and is caused by bi-allelic mutations in the WFS1 gene. In a recent sequencing study, an individual with juvenile-onset diabetes was observed to be homozygous for a rare missense variant (c.1672C>T, p.R558C) in the WFS1 gene. The aim of this study was to perform the genetic characterisation of this variant and to determine whether it is causal for young-onset diabetes and Wolfram syndrome.

METHODS

We analysed the allele frequency of the missense variant in multiple variant databases. We genotyped the variant in 475 individuals with type 1 diabetes and 2237 control individuals of Ashkenazi Jewish ancestry and analysed the phenotypes of homozygotes. We also investigated the association of this variant with risk for type 2 diabetes using genotype and sequence data for type 2 diabetes cases and controls.

RESULTS

The missense variant demonstrated an allele frequency of 1.4% in individuals of Ashkenazi Jewish ancestry, 60-fold higher than in other populations. Genotyping of this variant in 475 individuals diagnosed with type 1 diabetes identified eight homozygotes compared with none in 2237 control individuals (genotype relative risk 135.3, p = 3.4 × 10^-15). The age at diagnosis of diabetes for these eight individuals (17.8 ± 8.3 years) was several times greater than for typical Wolfram syndrome (5 ± 4 years). Further, optic atrophy was observed in only one of the eight individuals, while another individual had the Wolfram syndrome-relevant phenotype of neurogenic bladder. Analysis of sequence and genotype data in two case-control cohorts of Ashkenazi ancestry demonstrated that this variant is also associated with an increased risk of type 2 diabetes in heterozygotes (OR 1.81, p = 0.004).

CONCLUSIONS/INTERPRETATION

We have identified a low-frequency coding variant in the WFS1 gene that is enriched in Ashkenazi Jewish individuals and causes a mild form of Wolfram syndrome characterised by young-onset diabetes and reduced penetrance for optic atrophy. This variant should be considered for genetic testing in individuals of Ashkenazi ancestry diagnosed with young-onset non-autoimmune diabetes and should be included in Ashkenazi carrier screening panels.

Endoplasmic reticulum stress and eIF2α phosphorylation: The Achilles heel of pancreatic β cells

BACKGROUND

Pancreatic β cell dysfunction and death are central in the pathogenesis of most if not all forms of diabetes. Understanding the molecular mechanisms underlying β cell failure is important to develop β cell protective approaches.

SCOPE OF REVIEW

Here we review the role of endoplasmic reticulum stress and dysregulated endoplasmic reticulum stress signaling in β cell failure in monogenic and polygenic forms of diabetes. There is substantial evidence for the presence of endoplasmic reticulum stress in β cells in type 1 and type 2 diabetes. Direct evidence for the importance of this stress response is provided by an increasing number of monogenic forms of diabetes. In particular, mutations in the PERK branch of the unfolded protein response provide insight into its importance for human β cell function and survival. The knowledge gained from different rodent models is reviewed. More disease- and patient-relevant models, using human induced pluripotent stem cells differentiated into β cells, will further advance our understanding of pathogenic mechanisms. Finally, we review the therapeutic modulation of endoplasmic reticulum stress and signaling in β cells.

MAJOR CONCLUSIONS

Pancreatic β cells are sensitive to excessive endoplasmic reticulum stress and dysregulated eIF2α phosphorylation, as indicated by transcriptome data, monogenic forms of diabetes and pharmacological studies. This should be taken into consideration when devising new therapeutic approaches for diabetes.

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.

Identification of four novel mutations of the WFS1 gene in Iranian Wolfram syndrome pedigrees

AIMS

Wolfram syndrome is a rare neurodegenerative disorder with an autosomal recessive pattern of inheritance characterized by various clinical manifestations. The related gene, WFS1, encodes a transmembrane glycoprotein, named wolframin. Genetic analyses demonstrated that mutations in this gene are associated with WS type 1. Our aim in this study was to sequence WFS1 coding region in Iranian Wolfram syndrome pedigrees.

METHODS

Genomic DNA was extracted from peripheral blood of 12 WS patients and their healthy parents. Exons 2-8 and the exon-intron junctions of WFS1 were sequenced. DNA sequences were compared to the reference using Sequencher software.

RESULTS

Molecular analysis of WFS1 revealed six different mutations. Four novel and two previously reported mutations were identified. One novel mutation, c.1379_1381del, is predicted to produce an aberrant protein. A second novel mutation, c.1384G > T, encodes a truncated protein. Novel mutation, c.1097-1107dup (11 bp), causes a frameshift which results in a premature stop codon. We screened for the novel missense mutation, c.1010C > T, in 100 control alleles. This mutation was not found in any of the healthy controls.

CONCLUSION

Our study increased the spectrum of WFS1 mutations and supported the role of WFS1 in susceptibility to WS. We hope that these findings open new horizons to future molecular investigations which may help to prevent and treat this devastating disease.

Neuromuscular Manifestations in Mitochondrial Diseases in Children

Mitochondrial diseases exhibit significant clinical and genetic heterogeneity. Mitochondria are highly dynamic organelles that are the major contributor of adenosine triphosphate, through oxidative phosphorylation. These disorders may be developed at any age, with isolated or multiple system involvement, and in any pattern of inheritance. Defects in the mitochondrial respiratory chain impair energy production and almost invariably involve skeletal muscle and peripheral nerves, causing exercise intolerance, cramps, recurrent myoglobinuria, or fixed weakness, which often affects extraocular muscles and results in droopy eyelids (ptosis), progressive external ophthalmoplegia, peripheral ataxia, and peripheral polyneuropathy. This review describes the main neuromuscular symptomatology through different syndromes reported in the literature and from our experience. We want to highlight the importance of searching for the "clue clinical signs" associated with inheritance pattern as key elements to guide the complex diagnosis process and genetic studies in mitochondrial diseases.

Exome Sequencing Discerns Syndromes in Patients from Consanguineous Families with Congenital Anomalies of the Kidneys and Urinary Tract

Congenital anomalies of the kidneys and urinary tract (CAKUT) are the leading cause of CKD in children, featuring a broad variety of malformations. A monogenic cause can be detected in around 12% of patients. However, the morphologic clinical phenotype of CAKUT frequently does not indicate specific genes to be examined. To determine the likelihood of detecting causative recessive mutations by whole-exome sequencing (WES), we analyzed individuals with CAKUT from 33 different consanguineous families. Using homozygosity mapping and WES, we identified the causative mutations in nine of the 33 families studied (27%). We detected recessive mutations in nine known disease-causing genes: ZBTB24, WFS1, HPSE2, ATRX, ASPH, AGXT, AQP2, CTNS, and PKHD1 Notably, when mutated, these genes cause multiorgan syndromes that may include CAKUT as a feature (syndromic CAKUT) or cause renal diseases that may manifest as phenocopies of CAKUT. None of the above monogenic disease-causing genes were suspected on clinical grounds before this study. Follow-up clinical characterization of those patients allowed us to revise and detect relevant new clinical features in a more appropriate pathogenetic context. Thus, applying WES to the diagnostic approach in CAKUT provides opportunities for an accurate and early etiology-based diagnosis and improved clinical management.

Identification of unsuspected Wolfram syndrome cases through clinical assessment and WFS1 gene screening in type 1 diabetes mellitus patients

OBJECTIVE

Wolfram syndrome (WS) is a severe autosomal recessive pleiotropic disease primarily characterized by the association of juvenile-onset diabetes mellitus and optic atrophy. Earlier reports have shown that a proportion of WS cases may remain unrecognized due to misdiagnosis as type 1 diabetes mellitus (T1DM). The objectives of this work were to estimate the prevalence of patients fulfilling clinical criteria for WS in a cohort of subjects diagnosed as T1DM and to identify causal WFS1 gene mutations in those individuals meeting clinical criteria for the disease.

METHODS

A cohort of 131 unrelated Mexican T1DM patients was collected, including 77 females and 54 males. Additional clinical anomalies suggesting WS were identified through review of medical files, detailed physical examination and/or specialized tests. WFS1 gene analysis was performed using exon-by-exon PCR amplification and direct Sanger sequencing on genomic DNA from patients reaching WS clinical criteria.

RESULTS

Clinical criteria for a WS diagnosis were reached in 6 probands, corresponding to a 4.58% frequency of the disease. WFS1 mutations were identified in 4 out of 5 (80%) individuals fulfilling WS clinical criteria, including two homozygous, one compound heterozygous, and one patient with a single allele mutation. No WFS1 mutations were identified in the remaining subject.

CONCLUSIONS

In our cohort, approximately 6% of cases diagnosed as T1DM were in fact patients with Wolfram syndrome. WFS1 mutations were identified in 4 out of 5 individuals (80%) fulfilling clinical criteria for WS. Clinical and genetic analyses of large cohorts of T1DM patients from different ethnic origins would help to better estimate the occurrence of WS and will lead to a better management of such patients.

Mutation update and uncommon phenotypes in a French cohort of 96 patients with WFS1-related disorders

WFS1 mutations are responsible for Wolfram syndrome (WS) characterized by juvenile-onset diabetes mellitus and optic atrophy, and for low-frequency sensorineural hearing loss (LFSNHL). Our aim was to analyze the French cohort of 96 patients with WFS1-related disorders in order (i) to update clinical and molecular data with 37 novel affected individuals, (ii) to describe uncommon phenotypes and, (iii) to precise the frequency of large-scale rearrangements in WFS1. We performed quantitative polymerase chain reaction (PCR) in 13 patients, carrying only one heterozygous variant, to identify large-scale rearrangements in WFS1. Among the 37 novel patients, 15 carried 15 novel deleterious putative mutations, including one large deletion of 17,444 base pairs. The analysis of the cohort revealed unexpected phenotypes including (i) late-onset symptoms in 13.8% of patients with a probable autosomal recessive transmission; (ii) two siblings with recessive optic atrophy without diabetes mellitus and, (iii) six patients from four families with dominantly-inherited deafness and optic atrophy. We highlight the expanding spectrum of WFS1-related disorders and we show that, even if large deletions are rare events, they have to be searched in patients with classical WS carrying only one WFS1 mutation after sequencing.

WFS1 variants in Finnish patients with diabetes mellitus, sensorineural hearing impairment or optic atrophy, and in suicide victims

Mutations in the wolframin gene, WFS1, cause Wolfram syndrome, a rare recessive neurodegenerative disorder. The clinical features include early-onset bilateral optic atrophy (OA), diabetes mellitus (DM), diabetes insipidus, hearing impairment, urinary tract abnormalities and psychiatric illness, and, furthermore, WFS1 variants appear to be associated with non-syndromic DM and hearing impairment. Variation of WFS1 was investigated in Finnish subjects consisting 182 patients with DM, 117 patients with sensorineural hearing impairment (SNHI) and 44 patients with OA, and in 95 suicide victims. Twenty-two variants were found in the coding region of WFS1, including three novel nonsynonymous variants. The frequency of the p.[His456] allele was significantly higher in the patients with SNHI (11.5%; corrected P=0.00008), DM (6.6%; corrected P=0.036) or OA (9.1%; corrected P=0.043) than that in the 285 controls (3.3%). The frequency of the p.[His611] allele was 55.8% in the patients with DM being higher than that in the controls (47%; corrected P=0.039). The frequencies of p.[His456] and p.[His611] were similarly increased in an independent group of patients with DM (N=299). The results support previous findings that genetic variation of WFS1 contributes to the risk of DM and SNHI.

Genotypic classification of patients with Wolfram syndrome: insights into the natural history of the disease and correlation with phenotype

PURPOSE

Wolfram syndrome is a degenerative, recessive rare disease with an onset in childhood. It is caused by mutations in WFS1 or CISD2 genes. More than 200 different variations in WFS1 have been described in patients with Wolfram syndrome, which complicates the establishment of clear genotype-phenotype correlation. The purpose of this study was to elucidate the role of WFS1 mutations and update the natural history of the disease.

METHODS

This study analyzed clinical and genetic data of 412 patients with Wolfram syndrome published in the last 15 years.

RESULTS

(i) 15% of published patients do not fulfill the current -inclusion criterion; (ii) genotypic prevalence differences may exist among countries; (iii) diabetes mellitus and optic atrophy might not be the first two clinical features in some patients; (iv) mutations are nonuniformly distributed in WFS1; (v) age at onset of diabetes mellitus, hearing defects, and diabetes insipidus may depend on the patient's genotypic class; and (vi) disease progression rate might depend on genotypic class.

CONCLUSION

New genotype-phenotype correlations were established, disease progression rate for the general population and for the genotypic classes has been calculated, and new diagnostic criteria have been proposed. The conclusions raised could be important for patient management and counseling as well as for the development of treatments for Wolfram syndrome.

Identification of one novel causative mutation in exon 4 of WFS1 gene in two Italian siblings with classical DIDMOAD syndrome phenotype

The aim of the present paper is to describe a novel missense mutation (G107R) of WFS1 gene that was unexpectedly detected, in two siblings from Southern Italy, outside exon 8; a very unusual finding which has previously been reported only twice in Italian patients with Wolfram syndrome (WS). Although in Spanish pedigrees' WFS1 mutations are frequently located in exon 4, this finding is very infrequent in other pedigrees, particularly in Italian patients.

CONCLUSIONS

a) our report of two siblings with one novel WSF1 mutation (G107R) expands the molecular spectrum of WS; b) this is the 3rd report of Italian patients harbouring one mutation outside exon 8 and the 2nd with one mutation in exon 4; c) on the basis of the present observations, and literature data we can infer that mutation locations outside exon 8 do not seem to be clearly associated with peculiar phenotype expressions of WFS1 gene.

Targeted massive parallel sequencing: the effective detection of novel causative mutations associated with hearing loss in small families

Background

Hereditary hearing loss is one of the most common heterogeneous disorders, and genetic variants that can cause hearing loss have been identified in over sixty genes. Most of these hearing loss genes have been detected using classical genetic methods, typically starting with linkage analysis in large families with hereditary hearing loss. However, these classical strategies are not well suited for mutation analysis in smaller families who have insufficient genetic information.

Methods

Eighty known hearing loss genes were selected and simultaneously sequenced by targeted next-generation sequencing (NGS) in 8 Korean families with autosomal dominant non-syndromic sensorineural hearing loss.

Results

Five mutations in known hearing loss genes, including 1 nonsense and 4 missense mutations, were identified in 5 different genes (ACTG1, MYO1F, DIAPH1, POU4F3 and EYA4), and the genotypes for these mutations were consistent with the autosomal dominant inheritance pattern of hearing loss in each family. No mutational hot-spots were revealed in these Korean families.

Conclusion

Targeted NGS allowed for the detection of pathogenic mutations in affected individuals who were not candidates for classical genetic studies. This report is the first documenting the effective use of an NGS technique to detect pathogenic mutations that underlie hearing loss in an East Asian population. Using this NGS technique to establish a database of common mutations in Korean patients with hearing loss and further data accumulation will contribute to the early diagnosis and fundamental therapies for hereditary hearing loss.

Wolfram syndrome: new mutations, different phenotype

Background

Wolfram Syndrome (WS) is an autosomal recessive neurodegenerative disorder characterized by Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and Deafness identified by the acronym “DIDMOAD”. The WS gene, WFS1, encodes a transmembrane protein called Wolframin, which recent evidence suggests may serve as a novel endoplasmic reticulum calcium channel in pancreatic β-cells and neurons. WS is a rare disease, with an estimated prevalence of 1/550.000 children, with a carrier frequency of 1/354.

The aim of our study was to determine the genotype of WS patients in order to establish a genotype/phenotype correlation.

Methodology/Principal Findings

We clinically evaluated 9 young patients from 9 unrelated families (6 males, 3 females). Basic criteria for WS clinical diagnosis were coexistence of insulin-treated diabetes mellitus and optic atrophy occurring before 15 years of age. Genetic analysis for WFS1 was performed by direct sequencing.

Molecular sequencing revealed 5 heterozygous compound and 3 homozygous mutations. All of them were located in exon 8, except one in exon 4. In one proband only an heterozygous mutation (A684V) was found. Two new variants c.2663 C>A and c.1381 A>C were detected.

Conclusions/Significance

Our study increases the spectrum of WFS1 mutations with two novel variants. The male patient carrying the compound mutation [c.1060_1062delTTC]+[c.2663 C>A] showed the most severe phenotype: diabetes mellitus, optic atrophy (visual acuity 5/10), deafness with deep auditory bilaterally 8000 Hz, diabetes insipidus associated to reduced volume of posterior pituitary and pons. He died in bed at the age of 13 years. The other patient carrying the compound mutation [c.409_424dup16]+[c.1381 A>C] showed a less severe phenotype (DM, OA).

Identification of p.A684V missense mutation in the WFS1 gene as a frequent cause of autosomal dominant optic atrophy and hearing impairment

Optic atrophy (OA) and sensorineural hearing loss (SNHL) are key abnormalities in several syndromes, including the recessively inherited Wolfram syndrome, caused by mutations in WFS1. In contrast, the association of autosomal dominant OA and SNHL without other phenotypic abnormalities is rare, and almost exclusively attributed to mutations in the Optic Atrophy-1 gene (OPA1), most commonly the p.R445H mutation. We present eight probands and their families from the US, Sweden, and UK with OA and SNHL, whom we analyzed for mutations in OPA1 and WFS1. Among these families, we found three heterozygous missense mutations in WFS1 segregating with OA and SNHL: p.A684V (six families), and two novel mutations, p.G780S and p.D797Y, all involving evolutionarily conserved amino acids and absent from 298 control chromosomes. Importantly, none of these families harbored the OPA1 p.R445H mutation. No mitochondrial DNA deletions were detected in muscle from one p.A684V patient analyzed. Finally, wolframin p.A684V mutant ectopically expressed in HEK cells showed reduced protein levels compared to wild-type wolframin, strongly indicating that the mutation is disease-causing. Our data support OA and SNHL as a phenotype caused by dominant mutations in WFS1 in these additional eight families. Importantly, our data provide the first evidence that a single, recurrent mutation in WFS1, p.A684V, may be a common cause of ADOA and SNHL, similar to the role played by the p.R445H mutation in OPA1. Our findings suggest that patients who are heterozygous for WFS1 missense mutations should be carefully clinically examined for OA and other manifestations of Wolfram syndrome.

[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.

Inherited mitochondrial neuropathies

Mitochondrial disorders (MIDs) occasionally manifest as polyneuropathy either as the dominant feature or as one of many other manifestations (inherited mitochondrial neuropathy). MIDs in which polyneuropathy is the dominant feature, include NARP syndrome due to the transition m.8993T>, CMT2A due to MFN2 mutations, CMT2K and CMT4A due to GDAP1 mutations, and axonal/demyelinating neuropathy with external ophthalmoplegia due to POLG1 mutations. MIDs in which polyneuropathy is an inconstant feature among others is the MELAS syndrome, MERRF syndrome, LHON, Mendelian PEO, KSS, Leigh syndrome, MNGIE, SANDO; MIRAS, MEMSA, AHS, MDS (hepato-cerebral form), IOSCA, and ADOA syndrome. In the majority of the cases polyneuropathy presents in a multiplex neuropathy distribution. Nerve conduction studies may reveal either axonal or demyelinated or mixed types of neuropathies. If a hereditary neuropathy is due to mitochondrial dysfunction, the management of these patients is at variance from non-mitochondrial hereditary neuropathies. Patients with mitochondrial hereditary neuropathy need to be carefully investigated for clinical or subclinical involvement of other organs or systems. Supportive treatment with co-factors, antioxidants, alternative energy sources, or lactate lowering agents can be tried. Involvement of other organs may require specific treatment. Mitochondrial neuropathies should be included in the differential diagnosis of hereditary neuropathies.

A single base-pair deletion in the WFS1 gene causes Wolfram syndrome

Wolfram syndrome is a progressive neurodegenerative disorder also known as DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness). The majority of cases are caused by mutations in the WFS1 gene. WFS1 is located at 4p16.1 and encodes wolframin, a transmembrane endoplasmic reticulum (ER) protein involved in the negative regulation of ER stress signalling. To date, over 120 WFS1 mutations have been described. In this study, we report a consanguineous family with three siblings affected by Wolfram syndrome. A homozygous single base pair deletion (c.877delC, L293fsX303) was found in the WFS1 gene in all three affected siblings.

WS1 gene mutation analysis of Wolfram syndrome in a Chinese patient and a systematic review of literatures

Wolfram syndrome is a rare hereditary disease characterized by diabetes mellitus and optic atrophy. The outcome of this disease is always poor. WFS1 gene mutation is the main cause of this disease. A patient with diabetes mellitus, diabetes insipidus, renal tract disorder, psychiatric abnormality, and cataract was diagnosed with Wolfram syndrome. Mutations in open reading frame (ORF) of WFS1 gene was analyzed by sequencing. Mutations in WFS1 gene was also summarized by a systematic review in Pubmed and Chinese biological and medical database. Sequencing of WFS1 gene in this patient showed a new mutation, 1962G>A, and two other non-sense mutations, 2433A>G and 2565G>A. Systematic review included 219 patients in total and identified 172 WFS1 gene mutations, most of which were located in Exon 8. These mutations in WFS1 gene might be useful in prenatal diagnosis of Wolfram syndrome.

Wolfram syndrome and WFS1 gene

Wolfram syndrome (WS) (MIM 222300) is a rare multisystem neurodegenerative disorder of autosomal recessive inheritance, also known as DIDMOAD (diabetes insipidus, insulin-deficient diabetes mellitus, optic atrophy and deafness). A Wolfram gene (WFS1) has been mapped to chromosome 4p16.1 which encodes an endoplasmic reticulum (ER) membrane-embedded protein. ER localization suggests that WFS1 protein has physiological functions in membrane trafficking, secretion, processing and/or regulation of ER calcium omeostasis. Disturbances or overloading of these functions induce ER stress responses, including apoptosis. Most WS patients carry mutations in this gene, but some studies provided evidence for genetic heterogeneity, and the genotype-phenotype relationships are not clear. Here we review the data regarding the mechanisms and the mutations of WFS1 gene that relate to WS.

Identification and characterization of wolframin, the product of the wolfram syndrome gene (WFS1), as a novel calmodulin-binding protein

To search for calmodulin (CaM) targets, we performed affinity chromatography purification of a rat brain extract using CaM fused with GST as the affinity ligand. Proteomic analysis was then carried out to identify CaM-binding proteins. In addition to identifying 36 known CaM-binding proteins, including CaM kinases, calcineurin, nNOS, the IP(3) receptor, and Ca(2+)-ATPase, we identified an ER transmembrane protein, wolframin [the product of the Wolfram syndrome gene (WFS1)] as interacting. A CaM overlay and an immunoprecipitation assay revealed that wolframin is capable of binding the Ca(2+)/CaM complex in vitro and in transfected cells. Surface plasmon resonance analysis and zero-length cross-linking showed that the N-terminal cytoplasmic domain (residues 2-285) of wolframin binds to an equimolar unit of CaM in a Ca(2+)-dependent manner with a K(D) for CaM of 0.15 muM. Various truncation and deletion mutants showed that the Ca(2+)/CaM binding region in wolframin is located from Glu90 to Trp186. Furthermore, we demonstrated that three mutations (Ala127Thr, Ala134Thr, and Arg178Pro) associated with Wolfram syndrome completely abolished CaM binding of wolframin. This observation may indicate that CaM binding is important for wolframin function and that impairment of this interaction by mutation contributes to the pathology seen in Wolfram syndrome.

The novel compound heterozygous mutations, V434del and W666X, in WFS1 gene causing the Wolfram syndrome in a Chinese family

Wolfram syndrome (WFS), also known as DIDMOAD, is an infrequent cause of diabetes mellitus. WFS is an autosomal recessive neurodegenerative disease characterized by various clinical manifestations such as diabetes mellitus, optic atrophy, diabetes insipidus, deafness, neurological symptoms, renal tract abnormalities, psychiatric disorders, and gonadal disorders. The majority of patients with WFS carry the loss of function mutations in the WFS1 gene. The exons 2-8 of the WFS1 gene from one Chinese WFS patient were amplified by the polymerase chain reaction (PCR), subcloning techniques and direct sequence determination was applied to the amplified fragments. The compound heterozygous mutation of a 3-bp (GAC) deletion (V434del) and another compound heterozygous mutation (G-->N)(W666X) in exon 8 of WFS1 gene was identified in the patient. Other seventeen members of her family were investigated. Four cases with heterozygotes had been found through screening for the mutation V434del and five cases for the mutation W666X in the whole family. This is the first report of WFS with the mutation V434del and W666X in the WFS1 gene.

Wolfram syndrome 1 (Wfs1) gene expression in the normal mouse visual system

Wolfram syndrome (OMIM 222300) is a neurodegenerative disorder defined by insulin-dependent diabetes mellitus and progressive optic atrophy. This syndrome has been attributed to mutations in the WFS1 gene, which codes for a putative multi-spanning membrane glycoprotein of the endoplasmic reticulum. The function of WFS1 (wolframin), the distribution of this protein in the mammalian visual system, and the pathogenesis of optic atrophy in Wolfram syndrome are unclear. In this study we made a detailed analysis of the distribution of Wfs1 mRNA and protein in the normal mouse visual system by using in situ hybridization and immunohistochemistry. The mRNA and protein were observed in the retina, optic nerve, and brain. In the retina, Wfs1 expression was strong in amacrine and Müller cells, and moderate in photoreceptors and horizontal cells. In addition, it was detectable in bipolar and retinal ganglion cells. Interestingly, moderate Wfs1 expression was seen in the optic nerve, particularly in astrocytes, while little Wfs1 was expressed in the optic chiasm or optic tract. In the brain, moderate Wfs1 expression was observed in the zonal, superficial gray, and intermediate gray layers of the superior colliculus, in the dorsomedial part of the suprachiasmatic nucleus, and in layer II of the primary and secondary visual cortices. Thus, Wfs1 mRNA and protein were widely distributed in the normal mouse visual system. This evidence may provide clues as to the physiological role of Wfs1 protein in the biology of vision, and help to explain the selective vulnerability of the optic nerve to WFS1 loss-of-function.

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.

Mutation analysis of the WFS1 gene in seven Danish Wolfram syndrome families; four new mutations identified

Wolfram syndrome (WS) is a neuro-degenerative autosomal recessive (AR) disorder (OMIM #222300) caused by mutations in the WFS1 gene on 4p16.1. More than 120 mutations have been identified in WFS1 associated with AR WS, as well as autosomal dominant nonsyndromic low-frequency sensorineural hearing loss (LFSNHL). WFS1 variants were identified in eight subjects from seven families with WS, leading to the identification of four novel mutations, Q194X (nonsense), H313Y (missense), L313fsX360 (duplication frame shift) and F883fsX951 (deletion frame shift), and four previously reported mutations, A133T and L543R (missense), V415del (in frame triple deletion) and F883fsX950 (deletion frame shift). A mutation was found in 11/14 disease chromosomes, two subjects were homozygous for one mutation, one subject was compound heterozygous for two nucleotide substitutions (missense), one subject was compound heterozygous for a duplication and a deletion (frame shift), and in three families only one mutation was detected (Q194X and H313Y). All affected individuals shared clinically early-onset diabetes mellitus and progressive optic atrophy with onset in the first and second decades, respectively. In contrast, diabetes insipidus was present in two subjects only. Various degrees and types of hearing impairment were diagnosed in six individuals and cataract was observed in five subjects.

A homozygous mutation in a novel zinc-finger protein, ERIS, is responsible for Wolfram syndrome 2

A single missense mutation was identified in a novel, highly conserved zinc-finger gene, ZCD2, in three consanguineous families of Jordanian descent with Wolfram syndrome (WFS). It had been shown that these families did not have mutations in the WFS1 gene (WFS1) but were mapped to the WFS2 locus at 4q22-25. A G-->C transversion at nucleotide 109 predicts an amino acid change from glutamic acid to glutamine (E37Q). Although the amino acid is conserved and the mutation is nonsynonymous, the pathogenesis for the disorder is because the mutation also causes aberrant splicing. The mutation was found to disrupt messenger RNA splicing by eliminating exon 2, and it results in the introduction of a premature stop codon. Mutations in WFS1 have also been found to cause low-frequency nonsyndromic hearing loss, progressive hearing loss, and isolated optic atrophy associated with hearing loss. Screening of 377 probands with hearing loss did not identify mutations in the WFS2 gene. The WFS1-encoded protein, Wolframin, is known to localize to the endoplasmic reticulum and plays a role in calcium homeostasis. The ZCD2-encoded protein, ERIS (endoplasmic reticulum intermembrane small protein), is also shown to localize to the endoplasmic reticulum but does not interact directly with Wolframin. Lymphoblastoid cells from affected individuals show a significantly greater rise in intracellular calcium when stimulated with thapsigargin, compared with controls, although no difference was observed in resting concentrations of intracellular calcium.

Identification of novel mutations in WFS1 and genotype-phenotype correlation in Wolfram syndrome

Mutations in the WFS1 gene have been reported in Wolfram syndrome (WS), an autosomal recessive disorder defined by early onset of diabetes mellitus (DM) and progressive optic atrophy. Because of the low prevalence of this syndrome and the recent identification of the WFS1 gene, few data are available concerning the relationships between clinical and molecular aspects of the disease. Here, we describe 12 patients from 11 families with WS. We report on eight novel (A214fsX285, L293fsX303, P346L, I427S, V503fsX517, R558C, S605fsX711, P838L) and seven previously reported mutations. We also looked for genotype-phenotype correlation both in patients included in this study and 19 additional WS patients that were previously reported. Subsequently, we performed a systematic review and meta-analysis of five published clinical and molecular studies of WFS1 for genotype-phenotype correlation, combined with our current French patient group for a total of 96 patients. The presence of two inactivating mutations was shown to predispose to an earlier age of onset of both DM and optic atrophy. Moreover, the clinical expression of WS was more complete and occurred earlier in patients harboring no missense mutation.

Ataxie cérébelleuse révélant un syndrome de Wolfram

INTRODUCTION

Wolfram syndrome is a genetic disease with recessive autosomic transmission, associating early-onset diabetes mellitus and bilateral optical atrophy.

CASE REPORT

We report the case of a 47-year-old patient for whom we diagnosed a Wolfram syndrome in view of a late neurological syndrome in association with ataxia and bilateral horizontal nystagmus. The brain resonance magnetic imaging revealed a major atrophy of the brainstem and cerebellum.

CONCLUSION

Wolfram syndrome is a rare pathology, with fatal consequences before the age of 50. The association of diabetes mellitus and optical atrophy, especially when there are other symptoms (ataxia, deafness, diabetes insipidus, neuropsychiatric manifestations or urinary tract disorders) should lead to this diagnosis and to carry out a genetic confirmation.

The characterisation of the human Wolfram syndrome gene promoter demonstrating regulation by Sp1 and Sp3 transcription factors

Wolfram Syndrome (DIDMOAD) is an autosomal recessive disorder characterised by insulin deficient diabetes mellitus and neurodegeneration. Mutations in a novel gene, WFS1, were found in nearly all patients and segregated with the disease. The WFS1 gene is expressed in all tissue types studied and the 890aa protein product is localised to the endoplasmic reticulum (ER). In this study, we used a combination of reporter assays and in vitro and in vivo transcription factor binding assays to analyse the regulation of expression of the human WFS1 gene in neuronal derived cells. A single transcription start site was mapped and a minimal promoter identified within 25 bp upstream of this site. This minimal promoter contains two DNA binding motifs (GC boxes) for the transcription factors Sp1/3/4 and binding of both Sp1 and Sp3 was demonstrated at both motifs in vitro and in vivo. The presence of intact GC boxes is essential for minimal promoter action. Thus, transcription factors of the Sp family are important regulators of the WFS1 promoter. A further up-regulating control region was identified containing three CCAAT box binding motifs; all demonstrated a reduction in expression after mutation. One CCAAT box represented part of a predicted ER stress response element.

Phenotypic characterization of a DFNA6 family showing progressive low-frequency sensorineural hearing impairment

Only three autosomal dominant hearing loss loci (DFNA1, DFNA6/14/38 and DFNA54) have been reported to be associated with predominantly low-frequency (<2kHz) sensorineural hearing impairment (LFSNHI). The DFNA6 locus was previously mapped to chromosome 4p16.3. It was showed that WFS1 is located in this region. This study presents a six-generation family from Hungary with nonsyndromic, post-lingual, bilateral, symmetric, progressive LFSNHI, that discloses positive linkage to the DFNA6 region. Eleven genetically affected family members have LFSNHI. The HI is started before the age of 25 years. The severity of HI varies from mild to moderate, related to age. Progression was mild but significant at all frequencies causing a flat type audiogram. High-resolution temporal bone CT scan showed normal external, middle and inner ear without any osseus malformations in the temporal bone. Studying genotype-phenotype correlations will enhance our understanding of normal and disturbed hearing process.

Clinical picture, evolution and peculiar molecular findings in a very large pedigree with Wolfram syndrome

OBJECTIVES

a) To describe a very extended inbred pedigree with Wolfram syndrome (WS) (OMIM #222300); b) to report both the clinical picture and evolution in this large family and a peculiar mutation which has been reported hitherto only in Italian patients.

DESIGN

The five-generation pedigree from Sicily was reconstructed through a proband with all the main manifestation of WS, born to a couple of healthy consanguineous parents. DNA examination was performed in both patients and healthy family members.

RESULTS

In all seven patients we found a homozygous 16-bp deletion in exon 8 of the WFS1 gene that introduces a stop codon in position 454.

CONCLUSIONS

This inbred pedigree is the largest with WS described in the literature. Its analysis definitively confirms the view of autosomal recessive inheritance in WS. The 16-bp deletion appears to be a relatively frequent mutation only in Italian patients. Before examining the entire coding region of the WSF1 gene a preliminary screening for the 16-bp deletion in exon 8 might be suggested when a new Italian case of WS is investigated.

Phenotype-genotype correlations in a series of wolfram syndrome families

OBJECTIVE

Wolfram syndrome is an extremely rare autosomal-recessive disorder that predisposes the development of type 1 diabetes in association with progressive optic atrophy. The genetic basis of this disease has been shown to be due to mutations in the WFS1 gene. The WFS1 gene encodes a novel transmembrane protein called wolframin, which recent evidence suggests may serve as a novel endoplasmic reticulum calcium channel in pancreatic beta-cells and neurons. Genotype-phenotype correlations in this syndrome are becoming apparent and may help in explaining some of the variable characteristics observed in this disease.

RESEARCH DESIGN AND METHODS

In this report, we have studied 13 patients with Wolfram syndrome from nine families to further define the relationship between mutation site and type with specific disease characteristics.

RESULTS

A severe phenotype was seen in patients with mutations in exon 4 and with a large deletion encompassing most of exon 8. In total, nine novel mutations were identified as well as three new silent polymorphisms.

CONCLUSIONS

Similar to all other mutation reports, most causative changes identified in the WFS1 gene occurred in exon 8, and only one was identified outside this region in exon 4.

Study of the WFS1 gene and mitochondrial DNA in Spanish Wolfram syndrome families

Wolfram syndrome (WS) is an autosomal recessive neurodegenerative disorder characterized by early onset diabetes mellitus and progressive optic atrophy. Patients with WS frequently develop deafness, diabetes insipidus, renal tract abnormalities, and diverse psychiatric illnesses, among others. A gene responsible for WS was identified on 4p16.1 (WFS1). It encodes a putative 890 amino acid transmembrane protein present in a wide spectrum of tissues. A new locus for WS has been located on 4q22-24, providing evidence for the genetic heterogeneity of this syndrome. Six Spanish families with a total of seven WS patients were screened for mutations in the WFS1-coding region by direct sequencing. We found three previously undescribed mutations c.873C > A, c.1949_50delAT, and c.2206G > C, as well as the duplication c.409_424dup16, formerly published as 425ins16. Several groups had detected deletions in the mitochondrial DNA (mtDNA) of WS patients. For this reason, we also studied the presence of mtDNA rearrangements as well as Leber's hereditary optic neuropathy, mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes, and A1555G point mutations in the WS families. No mtDNA abnormalities were detected.

Diabetes mellitus and optic atrophy: a study of Wolfram syndrome in the Lebanese population

Wolfram syndrome (WFS) is a rare hereditary neurodegenerative disorder also known as DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness). WFS seems to be a heterogeneous disease that has not yet been fully characterized in terms of clinical features and pathophysiological mechanisms because the number of patients in most series was small. In this study we describe 31 Lebanese WFS patients belonging to 17 families; this, to our knowledge, is the largest number of patients reported in one series so far. Criteria for diagnosis of WFS were the presence of insulin-dependent diabetes mellitus and optic atrophy unexplained by any other disease. Central diabetes insipidus was found in 87% of the patients, and sensorineural deafness confirmed by audiograms was present in 64.5%. Other less frequent features included neurological and psychiatric abnormalities, urodynamic abnormalities, limited joint motility, cardiovascular and gastrointestinal autonomic neuropathy, hypergonadotropic hypogonadism in males, and diabetic microvascular disease. New features, not reported in previous descriptions, such as heart malformations and anterior pituitary dysfunction, were recognized in some of the patients and participated in the morbidity and mortality of the disease. Genetic analysis revealed WFS1 gene mutations in three families (23.5%), whereas no abnormalities were detected in mitochondrial DNA. In conclusion, WFS is a devastating disease for the patients and their families. More information about WFS will lead to a better understanding of this disease and hopefully to improvement in means of its prevention and treatment.

Evidence for linkage on chromosome 4p16.1 in Type 1 diabetes Danish families and complete mutation scanning of the WFS1 (Wolframin) gene

AIMS

To investigate whether the WFS1 gene, the gene for Wolfram syndrome, is a susceptibility gene for more common forms of diabetes in the Danish population.

METHODS

One hundred and fifty-two Danish Type 1 diabetes mellitus sib-pair families were genotyped for two microsatellite markers situated within 5 cM of the WFS1 gene and analysed for linkage and association using the sib-TDT. The entire coding region, the 5'UTR and 3'UTR of the WFS1 gene, were screened for mutations by direct sequencing in 29 selected Type 1 diabetes patients. Four of the identified mutations were tested for linkage and association in 255 Danish Type 1 diabetes families (including 103 simplex families).

RESULTS

Evidence for linkage to Type 1 diabetes was found as the second most frequent allele of the marker D4S394 were transmitted 137 times (T = 61%) and not transmitted 88 times to affected offspring (Puc = 0.0011). Twelve mutations were found in the coding region and three mutations in the 3'UTR. No evidence for linkage and association to Type 1 diabetes was found testing four of the identified amino acid substitutions.

CONCLUSIONS

Evidence of linkage to Type 1 diabetes was observed in the Danish family collection. However, no evidence of linkage and association was observed for any of the analysed polymorphisms, suggesting that other variations must be responsible for the observed evidence of linkage in the region.

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.

Wolfram (DIDMOAD) syndrome: a multidisciplinary clinical study in nine Turkish patients and review of the literature

AIM

To study Wolfram syndrome (WFS) with multidisciplinary consultations and compare the results with the literature.

METHODS

Nine patients fulfilled the ascertainment criteria of WFS (insulin-dependent diabetes mellitus and optic atrophy). All patients were evaluated by the departments of paediatrics, ophthalmology, audiology, urology and medical biology.

RESULTS

The earliest manifestation of WFS was insulin-dependent diabetes mellitus (at a median age of 6.9 y), followed by optic atrophy (8.9 y), diabetes insipidus (10.2 y) and deafness (10.5 y). Short stature was found in five cases, delayed puberty in two cases and hypergonadotropic hypogonadism in one case. Audiography disclosed hearing loss at high frequency in all patients (100%), but only five patients had clinical subjective hearing problems. Intravenous pyelography revealed hydroureteronephrosis in eight patients. Urodynamics revealed a normal bladder in only one patient. Three patients had a low-capacity, low-compliance bladder, detrusor external sphincteric dyssynergia and emptying problem, while five had an atonic bladder. Ocular findings were optic atrophy, low visual acuity and colour vision defects. Visual field tests revealed concentric and/or peripheral diminution in five patients. Visual evoked potentials were abnormal (reduced amplitude to both flash and pattern stimulation) in seven patients. Cranial magnetic resonance imaging showed mild or moderate atrophy of the optic nerves, chiasm, cerebellum, basal ganglia and brainstem in six patients; there was a partially empty sella in one case. There was no evidence of mitochondrial tRNA(Leu) (UUR) A to G (nucleotide 3243) mutation.

CONCLUSION

Wolfram syndrome should be evaluated in a multidisciplinary manner. Some specific and dynamic tests are necessary to make a more precise estimate of the prevalence and median age of the components of WFS. Short stature is a common feature in WFS. Hypogonadism may be hypogonadotropic or hypergonadotropic. Bladder dysfunction does not always present as a large atonic bladder in WFS. A low-capacity, high-pressure bladder with sphincteric dyssynergia is also common.

Molecular detection of novel WFS1 mutations in patients with Wolfram syndrome by a DHPLC-based assay

Wolfram syndrome (WS) is a recessively inherited mendelian form of diabetes and neurodegeneration also known by the acronym DIDMOAD from the major clinical features, including diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. Affected individuals may also show renal tract abnormalities as well as multiple neurological and psychiatric symptoms. The causative gene for WS (WFS1) encoding wolframin maps to chromosome 4p16.1 and consists of eight exons, spanning 33.44 Kb of genomic DNA. In this study we report on the mutational analysis of the WFS1 coding region in 19 Italian WS patients and 25 relatives, using a DHPLC-based protocol. A total of 19 different mutations in WFS1 were found in 18 of 19 patients (95%). All these mutations, except one, are novel, preferentially located in WFS1 exon 8, and include deletions, insertions, duplications, and nonsense and missense changes. In particular, a 16 base-pair deletion in WFS1 codon 454 was detected in five different unrelated nuclear families, being the most prevalent alteration in this Italian group. Nine neutral changes and polymorphisms were also identified. Overall, this study represents the molecular characterization of the largest cohort of Italian WS patients and carriers studied so far, and increases the number of identified WFS1 allelic variants worldwide.