Calcium mishandling in absence of primary mitochondrial dysfunction drives cellular pathology in Wolfram Syndrome.

Wolfram syndrome (WS) is a recessive multisystem disorder defined by the association of diabetes mellitus and optic atrophy, reminiscent of mitochondrial diseases. The role played by mitochondria remains elusive, with contradictory results on the occurrence of mitochondrial dysfunction. We evaluated 13 recessive WS patients by deep clinical phenotyping, including optical coherence tomography (OCT), serum lactic acid at rest and after standardized exercise, brain Magnetic Resonance Imaging, and brain and muscle Magnetic Resonance Spectroscopy (MRS). Finally, we investigated mitochondrial bioenergetics, network morphology, and calcium handling in patient-derived fibroblasts. Our results do not support a primary mitochondrial dysfunction in WS patients, as suggested by MRS studies, OCT pattern of retinal nerve fiber layer loss, and, in fibroblasts, by mitochondrial bioenergetics and network morphology results. However, we clearly found calcium mishandling between endoplasmic reticulum (ER) and mitochondria, which, under specific metabolic conditions of increased energy requirements and in selected tissue or cell types, may turn into a secondary mitochondrial dysfunction. Critically, we showed that Wolframin (WFS1) protein is enriched at mitochondrial-associated ER membranes and that in patient-derived fibroblasts WFS1 protein is completely absent. These findings support a loss-of-function pathogenic mechanism for missense mutations in WFS1, ultimately leading to defective calcium influx within mitochondria.

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.

Wolfram Syndrome: Diagnosis, Management, and Treatment.

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

False diagnosis of type 1 diabetes mellitus and its complications in Wolfram syndrome--is it the reason for the low number of reported cases of this abnormality?

Wolfram syndrome (WS), also known as DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness), is a rare autosomal recessive syndrome (1/770,000 in the United Kingdom), characterised by juvenile onset of diabetes mellitus, optic nerve atrophy, diabetes insipidus, sensorineural deafness, renal tract and neurological abnormalities, and primary gonadal atrophy. WS is caused mainly by biallelic mutations in the WFS1 gene, which encodes wolframin. Wide tissue distribution of wolframin and many mutations in the wolframin gene resulting in Wolfram syndrome may contribute to different phenotypes and the unusual combinations of clinical features. We describe a female patient with Wolfram syndrome diagnosed at the age of 25, with a previous false diagnosis of type 1 diabetes mellitus and misdiagnosed diabetic complications. The patient was found to be a compound heterozygote for two novel mutations in exon 8 of WFS1 gene: a 2-bp deletion AT at nt 1539 leading to a frameshift (Y513fs) and a single-base substitution 1174C > T resulting in a stop codon (Q392X). A detailed analysis of the patient's medical history and a review of the literature suggest that many cases of Wolfram syndrome may remain undiagnosed due to misdiagnosis as type 1 diabetes mellitus and incorrect interpretation of clinical symptoms of neurodegenerative abnormalities, especially in their early stages.

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 homozygous WFS1 mutations (p.Asp211Asn, p.Gln486*) causing severe Wolfram syndrome and first report of male fertility.

Wolfram syndrome (WFS) is a neurodegenerative genetic condition characterized by juvenile-onset of diabetes mellitus and optic atrophy. We studied clinical features and the molecular basis of severe WFS (neurodegenerative complications) in two consanguineous families from Iran. A clinical and molecular genetic investigation was performed in the affected and healthy members of two families. The clinical diagnosis of WFS was confirmed by the existence of diabetes mellitus and optic atrophy in the affected patients, who in addition had severe neurodegenerative complications. Sequencing of WFS1 was undertaken in one affected member from each family. Targeted mutations were tested in all members of relevant families. Patients had most of the reported features of WFS. Two affected males in the first family had fathered unaffected children. We identified two homozygous mutations previously reported with apparently milder phenotypes: family 1: c.631G>A (p.Asp211Asn) in exon 5, and family 2: c.1456C>T (p.Gln486*) in exon 8. Heterozygous carriers were unaffected. This is the first report of male Wolfram patients who have successfully fathered children. Surprisingly, they also had almost all the complications associated with WFS. Our report has implications for genetic counseling and family planning advice for other affected families.

Stress hypERactivation in the ß-cell.

In pancreatic ß-cells, the endoplasmic reticulum (ER) is the crucial site for insulin biosynthesis, as this is where the protein-folding machinery for secretory proteins is localized. Perturbations to ER function of the ß-cell, such as a high demand for insulin secretion, can lead to an imbalance in protein homeostasis and lead to ER stress. This stress can be mitigated by an adaptive, cellular response, the unfolded protein response (UPR). UPR activation is vital to the survival of ß-cells, as these cells represent one of the most susceptible tissues for ER stress, due to their highly secretory function. However, in some cases, this response is not sufficient to relieve stress, leading to apoptosis and contributing to the pathogenesis of diabetes. Recent evidence shows that ER stress plays a significant role in both type 1 and type 2 diabetes. In this review, we outline the mechanisms of ER stress-mediated ß-cell death and focus on the role of ER stress in various forms of diabetes, particularly a genetic form of diabetes called Wolfram syndrome.

Current developments in Wolfram syndrome.

Wolfram syndrome (WS), an infrequent cause of diabetes mellitus, derives its name from the physician who first reported the combination of juvenile-onset diabetes mellitus and optic atrophy. Also referred to as DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness), it 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 manifestations and gonadal disorders. The condition is very rare with an estimated prevalence of one in 770,000 of the normal population, one out of 150 cases of juvenile-onset insulin-dependent diabetes mellitus, and with a carrier frequency of one in 354. This progressive neurodegenerative disease usually results in death before the age of 50 years and many patients lead a morbid life. The pathogenesis of the disorder although unknown is ascribed to mutation of a gene on chromosome 4p encoding a transmembrane protein of undetermined function called wolframin. This review summarizes the variable presentation of the disorder, its widespread complications, poor quality of life in affected individuals, and the problems in diagnosis and treatment of the syndrome.

WFS1 is a novel component of the unfolded protein response and maintains homeostasis of the endoplasmic reticulum in pancreatic beta-cells.

In Wolfram syndrome, a rare form of juvenile diabetes, pancreatic beta-cell death is not accompanied by an autoimmune response. Although it has been reported that mutations in the WFS1 gene are responsible for the development of this syndrome, the precise molecular mechanisms underlying beta-cell death caused by the WFS1 mutations remain unknown. Here we report that WFS1 is a novel component of the unfolded protein response and has an important function in maintaining homeostasis of the endoplasmic reticulum (ER) in pancreatic beta-cells. WFS1 encodes a transmembrane glyco-protein in the ER. WFS1 mRNA and protein are induced by ER stress. The expression of WFS1 is regulated by inositol requiring 1 and PKR-like ER kinase, central regulators of the unfolded protein response. WFS1 is normally up-regulated during insulin secretion, whereas inactivation of WFS1 in beta-cells causes ER stress and beta-cell dysfunction. These results indicate that the pathogenesis of Wolfram syndrome involves chronic ER stress in pancreatic beta-cells caused by the loss of function of WFS1.

Disruption of the WFS1 gene in mice causes progressive beta-cell loss and impaired stimulus-secretion coupling in insulin secretion.

Wolfram syndrome, an autosomal recessive disorder characterized by juvenile-onset diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene. In order to gain insight into the pathophysiology of this disease, we disrupted the wfs1 gene in mice. The mutant mice developed glucose intolerance or overt diabetes due to insufficient insulin secretion in vivo. Islets isolated from mutant mice exhibited a decrease in insulin secretion in response to glucose. The defective insulin secretion was accompanied by reduced cellular calcium responses to the secretagogue. Immunohistochemical analyses with morphometry and measurement of whole-pancreas insulin content demonstrated progressive beta-cell loss in mutant mice, while the alpha-cell, which barely expresses WFS1 protein, was preserved. Furthermore, isolated islets from mutant mice exhibited increased apoptosis, as assessed by DNA fragment formation, at high concentration of glucose or with exposure to endoplasmic reticulum-stress inducers. These results strongly suggest that WFS1 protein plays an important role in both stimulus-secretion coupling for insulin exocytosis and maintenance of beta-cell mass, deterioration of which leads to impaired glucose homeostasis. These WFS1 mutant mice provide a valuable tool for understanding better the pathophysiology of Wolfram syndrome as well as WFS1 function.

The WFS1 gene, responsible for low frequency sensorineural hearing loss and Wolfram syndrome, is expressed in a variety of inner ear cells.

Heterozygous mutations in the WFS1 gene are responsible for autosomal dominant low frequency hearing loss at the DFNA6/14 locus, while homozygous or compound heterozygous mutations underlie Wolfram syndrome. In this study we examine expression of wolframin, the WFS1-gene product, in mouse inner ear at different developmental stages using immunohistochemistry and in situ hybridization. Both techniques showed compatible results and indicated a clear expression in different cell types of the inner ear. Although there were observable developmental differences, no differences in staining pattern or gradients of expression were observed between the basal and apical parts of the cochlea. Double immunostaining with an endoplasmic reticulum marker confirmed that wolframin localizes to this organelle. A remarkable similarity was observed between cells expressing wolframin and the presence of canalicular reticulum, a specialized form of endoplasmic reticulum. The canalicular reticulum is believed to be involved in the transcellular movements of ions, an important process in the physiology of the inner ear. Although there is nothing currently known about the function of wolframin, our results suggest that it may play a role in inner ear ion homeostasis as maintained by the canalicular reticulum.

Kidney transplantation unraveling Wolfram syndrome: a case report.

BACKGROUND: In Wolfram syndrome insulin-dependent diabetes is associated with a multisystem neurodegenerative disorder. There are no prior reports of kidney transplantation in patients with Wolfram syndrome. METHODS: Kidney transplantation was undertaken in a child with dysplastic kidneys, sensorineural hearing impairment and bilateral optic atrophy-a combination of features insufficient to define Wolfram syndrome. RESULTS: After the procedure diabetes mellitus, diabetes insipidus and urinary bladder dysfunction emerged, thereby revealing Wolfram syndrome. CONCLUSIONS: We discuss the etiology of our patient's postoperative events, and conclude that kidney transplantation may expose dormant manifestations-or aggravate existing manifestations-of Wolfram syndrome.

Diabetes insipidus, diabetes mellitus, optic atrophy and deafness (DIDMOAD syndrome). A clinical study in two Sudanese families.

Four Sudanese children with DIDMOAD syndrome (diabetes insipidus, diabetes mellitus, optic atrophy and deafness) are reported. They were two boys (aged 15 and 16 years) in one family and a boy and a girl (aged 16 and 6 years, respectively) in another family. Diabetes mellitus was first to appear (at 3-8 years) followed by deafness and visual failure; and the disease ended fatally in one patient (aged 20 years). In the other three, diabetes insipidus was confirmed using water deprivation test for 8 hours. The maximum urine osmolality ranged between 131-523 mOsm/kg, whereas the corresponding plasma osmolality ranged between 315-332 mOsm/kg. Slight further improvement in urine concentration was observed in 2 of the patients following the use of desmopressin (DDAVP, 20 micrograms intranasally). Intravenous pyelography, voiding cystourethrography and ultrasound revealed severe bilateral hydronephrosis, dilated ureters and distended bladder without vesicoureteral reflux in the three patients. With the high rate of consanguinity prevalent in North Africa and the Middle East, we recommend examining children who present with diabetes mellitus in this region for features of DIDMOAD syndrome.