Brown-Vialetto-Van Laere Research Articles

Sudden Onset Auditory Neuropathy Spectrum Disorder: A Rare Case Report of Brown Vialetto Van Laere Syndrome.

Brown Vialetto Van Laere syndrome is a rare disorder characterized by progressive pontobulbar palsy with bilateral sensorineural hearing loss and lower cranial nerve palsies. Fifty-eight cases have been reported in the last hundred years. As the most common presenting complaint of this disorder is hearing loss, audiological evaluation plays a vital role in pointing towards and narrowing its diagnosis. We present a case report of a 12-year male child affected by this disorder.

Audiologic results of child with BVVL syndrome

Brown-Vialetto-Van Laere (BVVL) syndrome is an autosomal-recessive inherited disease, which has mutations in specific genes responsible for the transportation of riboflavin in the intestines. Fifty-eight cases of BVVL have been reported in just over a century. This rare syndrome is generally characterized by motor, sensory, and cranial nerve neuropathy. Although this syndrome manifests with bulbar palsy, sensorineural hearing loss is the second most common consistent manifestation of BVVL syndrome. While auditory neuropathy spectrum disorder (ANSD) often awaits due to the nature of the disease here, we present the results of cochlear hearing loss patient with BVVL syndrome. Timely recognition and proper management of BVVLS are crucial to offer necessary support and interventions for affected individuals because of the progressive nature of hearing loss.

A case report of sudden-onset auditory neuropathy spectrum disorder associated with Brown-Vialetto-Van Laere syndrome (riboflavin transporter deficiency)

Objective The purpose of this paper is to describe a child with auditory neuropathy spectrum disorder (ANSD) associated with Brown-Vialetto-Van Laere (BVVL) syndrome, which is a rare, inherited, neurodegenerative disorder that is caused by defects in riboflavin transporter genes. Design We report the audiological and clinical profile of a child who presented with a complaint of sudden loss of speech understanding associated with an atypical form of ANSD. He was later diagnosed with BVVL. Study Sample An 11-year-old boy with ANSD associated with BVVL. Results The patient’s severe neurological symptoms improved within a year of supplementation with high doses of riboflavin. His fluctuating hearing loss and 0% WDS remained unchanged. The patient was able to use hearing aids without any discomfort after treatment initiation, but he stopped using them again due to a lack of benefit in speech understanding. Although cochlear implantation was recommended, the patient and his family decided not to consider it for another year since they still had hope for complete recovery. Conclusions Sudden-onset ANSD can be the earliest sign of undetected BVVL syndrome. Early detection of BVVL is crucial since all symptoms can be reversible with an early intervention of high doses of riboflavin supplementation.

Brown-Vialetto-Van Laere and Fazio-Londe syndromes: SLC52A3 mutations with puzzling phenotypes and inheritance.

Brown-Vialetto-Van Laere syndrome (BVVLS) and Fazio-Londe disease (FLD) are rare neurological disorders presenting with pontobulbar palsy, muscle weakness and respiratory insufficiency. Mutations in SLC52A2 (hRFVT-2) or SLC52A3 (hRFVT-3) genes can be responsible for these disorders with an autosomal recessive pattern of inheritance. The aim of this study was to screen for mutations in SLC52A2 and SLC52A3 among Indian families diagnosed with BVVLS and FLD. SLC52A2 and SLC52A3 were screened in one FLD and three BVVLS patients by exon-specific amplification using PCR and sequencing. In silico predictions using bioinformatics tools and confocal imaging using HEK-293 cells were performed to determine the functional impact of identified mutations. Genetic analysis of a mother and son with BVVLS was identified with a novel homozygous mutation c.710C>T (p.Ala237Val) in SLC52A3. This variant was found to have an autosomal pseudodominant pattern of inheritance, which was neither listed in the Exome Variant Server or in the 1000 Genomes Project database. In silico analysis and confocal imaging of the p.Ala237Val variant showed higher degree of disorderness in hRFVT-3 that could affect riboflavin transport. Furthermore, a common homozygous mutation c.62A>G (p.Asn21Ser) was identified in other BVVLS and FLD patients. Despite having different clinical phenotypes, both BVVLS and FLD can be attributed to this mutation. A rare and peculiar pattern of autosomal pseudodominant inheritance is observed for the first time in two genetically related BVVLS cases with Indian origin and a common mutation c.62A>G (p.Asn21Ser) in SLC52A3 can be responsible for both BVVLS and FLD with variable phenotypes.

Functional Study of the Human Riboflavin Transporter 2 Using Proteoliposomes System.

Riboflavin is essential for cell viability. The biologically active forms of riboflavin, FMN and FAD, participate in many biochemical redox reactions including the metabolism of carbohydrates, amino acids, and lipids. Differently from bacteria, fungi, and plants which synthesize riboflavin, higher organisms have lost the ability to synthesize the vitamin and must absorb it from food and intestinal microflora production. The riboflavin flux through cell membranes occurs via specific transporters belonging to the SLC52 family. Three members of this family have been identified so far which show poor homology with the riboflavin transporters of Saccharomyces cerevisiae or bacteria. Alterations of RFVTs are causative of severe diseases. Indeed, under pathological stress, humans are susceptible of developing riboflavin deficiency. Such a deficiency in pregnancy induces fetus abnormalities, and has been indicated as a risk factor for anemia, cancer, cardiovascular diseases, and neurodegeneration. Moreover, inherited diseases are also of interest; the most well-described is the Brown-Vialetto-van Laere syndrome, a rare neurological disorder characterized by infancy onset sensorineural deafness and pontobulbar palsy. Numerous polymorphisms of Slc52a2 and Slc52a3 genes associated with this syndrome have been discovered. In spite of their important metabolic role and their relevance to human health, the riboflavin transporters are still poorly characterized. Bacterial overexpression, purification, and protein reconstitution in liposomes represent an up-to-date methodology for obtaining functional data information. The methodology for reconstituting the RFVT2 into proteoliposomes and performing transport assay is described. These methods will be suitable for investigating the functional defects of the variants of RFVTs associated with human pathologies.

Late-onset riboflavin transporter deficiency: a treatable mimic of various motor neuropathy aetiologies

ObjectiveRiboflavin transporter deficiencies (RTDs), involving SLC52A3 and SLC52A2 genes, have recently been related to Brown-Vialetto-Van Laere (BVVL) syndrome, a hereditary paediatric condition associating motor neuropathy (MN) and deafness. BVVL/RTD has...

BVVL/ FL: features caused by SLC52A3 mutations; WDFY4 and TNFSF13B may be novel causative genes

Brown-Vialetto-Van Laere (BVVL) and Fazio-Londe are disorders with amyotrophic lateral sclerosis–like features, usually with recessive inheritance. We aimed to identify causative mutations in 10 probands. Neurological examinations, genetic analysis, audiometry, magnetic resonance imaging, biochemical and immunological testings, and/or muscle histopathology were performed. Mutations in known causative gene SLC52A3 were found in 7 probands. More importantly, only 1 mutated allele was observed in several patients, and variable expressivity and incomplete penetrance were clearly noted. Environmental insults may contribute to variable presentations. Putative causative mutations in other genes were identified in 3 probands. Two of the genes, WDFY4 and TNFSF13B, have immune-related functions. Inflammatory responses were implicated in the patient with the WDFY4 mutation. Malfunction of the immune system and mitochondrial anomalies were shown in the patient with the TNFSF13B mutation. Prevalence of heterozygous SLC52A3 BVVL causative mutations and notable variability in expressivity of homozygous and heterozygous genotypes are being reported for the first time. Identification of WDFY4 and TNFSF13B as candidate causative genes supports conjectures on involvement of the immune system in BVVL and amyotrophic lateral sclerosis.

Brown Vialetto Van Laere syndrome, a fatal disease with a simple solution: a case series

Brown Vialetto Van Laere (BVVL) syndrome is an extremely rare neuro metabolic disorder postulated to be caused by a defect in riboflavin transporter. The disease is characterized by progressive hearing loss with ataxia and difficulty in swallowing and breathing. The diagnosis of the disease requires great deal of suspicion on the part of treating physician. Here authors present 2 cases of BVVL who presented to us with dysphagia and hearing loss and responded to therapy. Brown Vialetto Van Laere (BVVL) syndrome is an extremely rare neuro metabolic disorder postulated to be caused by a defect in Riboflavin transporter. The disease is characterised by progressive hearing loss with ataxia and difficulty in swallowing and breathing. It is a subset in multiple acyl CoA dehydrogenase deficiency (MADD disorder). Age of onset is generally first to third decade of life. Lower cranial nerve involvement with LMN and UMN signs concomitantly is the striking feature. There is no specific treatment for BVVL except supportive care. Response to high dose riboflavin (20mg/kg/day) has produced promising results but the results may take anywhere from 1 week to 12 months to appear.

Cochlear implantation in children with auditory neuropathy: Lessons from Brown–Vialetto–Van Laere syndrome

Objective: Brown–Vialetto–Van Laere syndrome (BVVL) is a rare neurodegenerative disorder associated with auditory neuropathy (AN). The decision process for CI in AN is evolving with increasing evidence of efficacy. We evaluated the benefit of CI in children with BVVL syndrome.Methods: A retrospective study reviewed the pre- and post-operative hearing outcomes of three patients with BVVL who presented for CI. A fourth patient with BVVL who was not suitable for CI is also discussed. The primary outcomes were hearing thresholds and auditory perception. Outcome measurement instruments included visual reinforcement audiometry (VRA) or Play Audiometry (PA), Categories of Auditory Performance (CAP) and Auditory Speech Sound Evaluation (ASSE). Secondary outcomes were parental report (BAPP questionnaire), the perception of our SaLT and compliance.Results: Patient 1 had ASSE levels of 40–45 dB HL 1 year post-operatively, and CAP score had improved from 2 to 5. At 2-year review, aided thresholds were 40 dB at 2–4 kHz. Three months following CI, the CAP score of Patient 2 had improved from 3 to 5. At 6 months, thresholds were 25–30 dB at 2–4 kHz. Single words/phrases are used by both patients and benefit is reported by both families. Patient 3 has recently undergone CI, having been previously rejected at another centre. Three months following CI, his thresholds were 35–40 dB at 2–4 kHz and increased use of sign and vocalization is reported.Conclusion: CI in children with AN complicating BVVL has a variable, but a positive effect. Other manifestations of BVVL make measuring benefit challenging, in the absence of a ‘bespoke’ measurement instrument for children with complex needs. This study provides further evidence for the benefit of CI in children with AN.

Riboflavin Responsive Mitochondrial Dysfunction in Neurodegenerative Diseases

Mitochondria are the repository for various metabolites involved in diverse energy-generating processes, like the TCA cycle, oxidative phosphorylation, and metabolism of amino acids, fatty acids, and nucleotides, which rely significantly on flavoenzymes, such as oxidases, reductases, and dehydrogenases. Flavoenzymes are functionally dependent on biologically active flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN), which are derived from the dietary component riboflavin, a water soluble vitamin. Riboflavin regulates the structure and function of flavoenzymes through its cofactors FMN and FAD and, thus, protects the cells from oxidative stress and apoptosis. Hence, it is not surprising that any disturbance in riboflavin metabolism and absorption of this vitamin may have consequences on cellular FAD and FMN levels, resulting in mitochondrial dysfunction by reduced energy levels, leading to riboflavin associated disorders, like cataracts, neurodegenerative and cardiovascular diseases, etc. Furthermore, mutations in either nuclear or mitochondrial DNA encoding for flavoenzymes and flavin transporters significantly contribute to the development of various neurological disorders. Moreover, recent studies have evidenced that riboflavin supplementation remarkably improved the clinical symptoms, as well as the biochemical abnormalities, in patients with neuronopathies, like Brown-Vialetto-Van-Laere syndrome (BVVLS) and Fazio-Londe disease. This review presents an updated outlook on the cellular and molecular mechanisms of neurodegenerative disorders in which riboflavin deficiency leads to dysfunction in mitochondrial energy metabolism, and also highlights the significance of riboflavin supplementation in aforementioned disease conditions. Thus, the outcome of this critical assessment may exemplify a new avenue to enhance the understanding of possible mechanisms in the progression of neurodegenerative diseases and may provide new rational approaches of disease surveillance and treatment.

Genome-wide RNA-seq of iPSC-derived motor neurons indicates selective cytoskeletal perturbation in Brown\u2013Vialetto disease that is partially rescued by riboflavin

Riboflavin is essential in numerous cellular oxidation/reduction reactions but is not synthesized by mammalian cells. Riboflavin absorption occurs through the human riboflavin transporters RFVT1 and RFVT3 in the intestine and RFVT2 in the brain. Mutations in these genes are causative for the Brown–Vialetto–Van Laere (BVVL), childhood-onset syndrome characterized by a variety of cranial nerve palsies as well as by spinal cord motor neuron (MN) degeneration. Why mutations in RFVTs result in a neural cell–selective disorder is unclear. As a novel tool to gain insights into the pathomechanisms underlying the disease, we generated MNs from induced pluripotent stem cells (iPSCs) derived from BVVL patients as an in vitro disease model. BVVL-MNs explained a reduction in axon elongation, partially improved by riboflavin supplementation. RNA sequencing profiles and protein studies of the cytoskeletal structures showed a perturbation in the neurofilament composition in BVVL-MNs. Furthermore, exploring the autophagy–lysosome pathway, we observed a reduced autophagic/mitophagic flux in patient MNs. These features represent emerging pathogenetic mechanisms in BVVL-associated neurodegeneration, partially rescued by riboflavin supplementation. Our data showed that this therapeutic strategy could have some limits in rescuing all of the disease features, suggesting the need to develop complementary novel therapeutic strategies.

Remarkable motor recovery after riboflavin therapy in adult-onset Brown—Vialetto—Van Laere syndrome

The clinical diagnosis of Brown—Vialetto—Van Laere syndrome in this woman with rapidly progressive pontobulbar palsy led to empirical high-dose oral riboflavin (1200 mg/day) therapy. This resulted in a dramatic improvement...

P.387 - Riboflavin transporter deficiency diagnosed 30 years after onset of symptoms

Mutations in the riboflavin transporter genes SLC52A2 and SLC52A3 cause a neurodegenerative disorder formerly known as Brown–Vialetto–van Laere (BVVL) syndrome, now renamed to riboflavin transporter deficiency. We present a patient who developed hypotonia, respiratory problems and feeding problems at the age of 8 months. His respiratory problems necessitated mechanical ventilation for 8 months. During follow up global developmental delay, bilateral sensorineural deafness and profound sensory ataxia were diagnosed. Extensive additional investigations (MRI, EMG, metabolic workup, CSF analysis and muscle biopsy) in infancy did not reveal any abnormalities apart from raised ethylmalonic acid. As a mitochondrial disorder was suspected he was treated with thiamine, riboflavin, biotin and carnitine. In the ensuing years these supplements were discontinued twice. Each time parents noticed worsening of his clinical condition. A second muscle biopsy performed at the age of 15 years showed central cores. Sequencing of RYR1 gene revealed one missense mutation, which was also present in the asymptomatic mother. Whole exome sequencing performed at the age of 30 years revealed a homozygous mutation in SLC52A3 gene (c.1128C > G(p.(Tyr376*)), which led to the diagnosis of Brown–Vialetto–van Laere syndrome. Riboflavin transporter deficiencies formerly known as Brown–Vialetto–van Laere syndrome present with cranial nerve deficits including hearing loss, weakness, sensory symptoms including sensory ataxia, feeding difficulties and respiratory difficulties which are caused by a progressive axonal sensory and motor peripheral neuropathy and a cranial neuropathy. Diagnosis can only be made through molecular analysis of all genes. Treatment with oral supplementation of riboflavin is lifesaving.

Clinical presentation and outcome of riboflavin transporter deficiency: mini review after five years of experience.

IntroductionRiboflavin (vitamin B2) is absorbed in the small intestine by the human riboflavin transporters RFVT1 and RFVT3. A third riboflavin transporter (RFVT2) is expressed in the brain. In 2010 it was demonstrated that mutations in the riboflavin transporter genes SLC52A2 (coding for RFVT2) and SLC52A3 (coding for RFVT3) cause a neurodegenerative disorder formerly known as Brown-Vialetto-Van Laere (BVVL) syndrome, now renamed to riboflavin transporter deficiency. Five years after the diagnosis of the first patient we performed a review of the literature to study the presentation, treatment and outcome of patients with a molecularly confirmed diagnosis of a riboflavin transporter deficiency.MethodA search was performed in Medline, Pubmed using the search terms ‘Brown-Vialetto-Van Laere syndrome’ and ‘riboflavin transporter’ and articles were screened for case reports of patients with a molecular diagnosis of a riboflavin transporter deficiency.ResultsReports on a total of 70 patients with a molecular diagnosis of a RFVT2 or RTVT3 deficiency were retrieved. The riboflavin transporter deficiencies present with weakness, cranial nerve deficits including hearing loss, sensory symptoms including sensory ataxia, feeding difficulties and respiratory difficulties which are caused by a sensorimotor axonal neuropathy and cranial neuropathy. Biochemical abnormalities may be absent and the diagnosis can only be made or rejected by molecular analysis of all genes. Treatment with oral supplementation of riboflavin is lifesaving. Therefore, if a riboflavin transporter deficiency is suspected, treatment must be started immediately without first awaiting the results of molecular diagnostics.

SLC52A3, A Brown-Vialetto-van Laere syndrome candidate gene is essential for mouse development, but dispensable for motor neuron differentiation.

Riboflavin, also known as vitamin B2, is essential for cellular reduction-oxidation reactions, but is not readily synthesized by mammalian cells. It has been proposed that riboflavin absorption occurs through solute carrier family 52 members (SLC52) A1, A2 and A3. These transporters are also candidate genes for the childhood onset-neural degenerative syndrome Brown-Vialetto-Van Laere (BVVL). Although riboflavin is an essential nutrient, why mutations in its transporters result in a neural cell-specific disorder remains unclear. Here, we provide evidence that Slc52a3 is the mouse ortholog of SLC52A3 and show that Slc52a3 deficiency results in early embryonic lethality. Loss of mutant embryos was associated with both defects in placental formation and increased rates of apoptosis in embryonic cells. In contrast, Slc52a3 -/- embryonic stem cell lines could be readily established and differentiated into motor neurons, suggesting that this transporter is dispensable for neural differentiation and short-term maintenance. Consistent with this finding, examination of Slc52a3 gene products in adult tissues revealed expression in the testis and intestine but little or none in the brain and spinal cord. Our results suggest that BVVL patients with SCL52A3 mutations may be good candidates for riboflavin replacement therapy and suggests that either the mutations these individuals carry are hypomorphic, or that in these cases alternative transporters act during human embryogenesis to allow full-term development.

Motor neuron disease in a young female, Madras pattern or Brown-Vialetto Van Laere syndrome? - A diagnostic dilemma

<p class="abstract">We report a case of a 14 year old female patient with progressive ponto-bulbar palsy, bilateral deafness and distal muscle weakness with wasting. This pattern is seen in Brown-Vialetto-Van Laere which is an extremely rare neurological disorder of unknown etiology with less than 80 cases being reported till date. The syndrome was first described in 1894 by Brown and subsequently by Vialetto in 1936 and Van Laere in 1966. A similar pattern is noted in the Madras form of motor neuron disease which is seen in South India. With the available literature and data it's difficult to differentiate between these entities.</p>

Exome sequencing results in successful riboflavin treatment of a rapidly progressive neurological condition.

Genetically targeted therapies for rare Mendelian conditions are improving patient outcomes. Here, we present the case of a 20-mo-old female suffering from a rapidly progressing neurological disorder. Although diagnosed initially with a possible autoimmune condition, analysis of the child's exome resulted in a diagnosis of Brown–Vialetto–Van Laere syndrome 2 (BVVLS2). This new diagnosis led to a change in the therapy plan from steroids and precautionary chemotherapy to high-dose riboflavin. Improvements were reported quickly, including in motor strength after 1 mo. In this case, the correct diagnosis and appropriate treatment would have been unlikely in the absence of exome sequencing and careful interpretation. This experience adds to a growing list of examples that emphasize the importance of early genome-wide diagnostics.

Sustained therapeutic response to riboflavin in a child with a progressive neurological condition, diagnosed by whole-exome sequencing.

One of the most promising outcomes of whole-exome sequencing (WES) is the alteration of medical management following an accurate diagnosis in patients with previously unresolved disorders. Although case reports of targeted therapies resulting from WES have been published, there are few reports with long-term follow-up that confirm a sustained therapeutic response. Following a diagnosis by WES of Brown–Vialetto–Van Laere Syndrome 2 (BVVLS2), high-dose riboflavin therapy was instituted in a 20-mo-old child. An immediate clinical response with stabilization of signs and symptoms was noted over the first 2–4 wk. Subsequent clinical follow-up over the following 8 mo demonstrates not just stabilization, but continuing and sustained improvements in all manifestations of this usually fatal condition, which generally includes worsening motor weakness, sensory ataxia, hearing, and vision impairments. This case emphasizes that early application of WES can transform patient care, enabling therapy that in addition to being lifesaving can sometimes reverse the disabling disease processes in a progressive condition.

Identification of residues/sequences in the human riboflavin transporter-2 that is important for function and cell biology.

BackgroundRiboflavin (RF) is essential for normal cellular metabolic activities. Human cells obtain RF from their surroundings via a carrier-mediated process that involves RF transporters -1, -2 & -3 (hRFVT -1, -2 & -3; products of SLC52A1, -A2 and -A3 genes, respectively). Little is known about the structural features of these transporters that are important for their function/cell biology. Our aim in this study was to address these issues for the hRFVT-2, a transporter linked to the neurodegenerative disorder Brown-Vialetto-Van Laere Syndrome (BVVLS).MethodsWe used comparative protein-structure modelling to predict residues that interact with two amino acids known to be critical for hRFVT-2 function (the clinical mutants L123 and L339), site-directed mutagenesis, and truncation approach in the human-derived brain U87 cell model.ResultsFirst we showed that the defect in the function of the L123 and L339 hRFVT-2 clinical mutants is related to a reduction in protein stability/translation efficiency and to retention of the protein in the ER. Mutating V120 and L121 (residues predicted to interact with L123) and L342 (a residue predicted to interact with L339) also led to a significant inhibition in hRFVT-2 function (with no change in membrane expression); this inhibition was associated with changes in protein stability/translation efficiency (in the case of V120A and L342A) and an impairment in transport function (in the case of L121). Truncating the N- and C- terminals of hRFVT-2 led to significant inhibition in RF uptake, which was associated with changes in protein stability/translation efficiency (it was also associated with a partial impairment in membrane targeting in the case of the N-terminal truncation).ConclusionThese investigations report on identification of residues/sequences in the hRFVT-2 protein that is important for its physiological function and cell biology.

Mutations in riboflavin transporter present with severe sensory loss and deafness in childhood

We have identified a large consanguineous Lebanese family with 5 individuals with severe childhood-onset recessive sensory loss associated with deafness and variable optic atrophy. Autozygosity mapping was performed in all affected individuals, followed by whole-exome sequencing (WES) in 2 individuals. WES identified a homozygous missense mutation (c.916G>A, p.G306R) in the cerebral riboflavin transporter SLC52A2, recently shown to cause Brown-Vialetto-Van-Laere syndrome (BVVLS), which is considered primarily a motor neuronopathy. Our patients have a phenotype distinct from BVVLS, characterized by severe progressive sensory loss mainly affecting vibration and proprioception that evolves to include sensorineural hearing loss in childhood, variable degrees of optic atrophy, and marked upper extremity weakness and atrophy. Treatment of 3 patients with 400 mg/day riboflavin over 3 months produced definite clinical improvement. Mutations in SLC52A2 result in a recognizable phenotype distinct from BVVLS. Early recognition of this disorder is critical, given its potential treatability.