In silico investigation on structure-function relationship of members belonging to the human SLC52 transporter family.

Riboflavin is an essential water-soluble vitamin that needs to be provided through the diet because of the conversion into flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), important cofactors in hundreds of flavoenzymes. The adsorption and distribution of riboflavin is mediated by transmembrane transporters of the SLC52 family, namely RFVT1-3, whose mutations are mainly associated with two diseases, MADD and the Brown-Vialetto-Van Laere syndrome. Interest in RFVTs as pharmacological targets has increased in the last few years due to their overexpression in several cancer cells, which can be exploited both by blocking the uptake of riboflavin into the cancerous cells, and by performing cancer targeted delivery of drugs with a high affinity for RFVTs. In this work, we propose three-dimensional structural models for all three human riboflavin transporters obtained by state-of-the-art artificial intelligence-based methods, which were then further refined with molecular dynamics simulations. Furthermore, two of the most notable mutations concerning RFVT2 and RFVT3 (W31S and N21S, respectively) were investigated studying the interactions between the wild-type and mutated transporters with riboflavin.

Genome-Wide Association Study of Obstructive Sleep Apnea and Objective Sleep-related Traits Identifies Novel Risk Loci in Han Chinese Individuals.

Rationale: Previous genetic studies of obstructive sleep apnea (OSA) have limitations in terms of precise case definition, integrated quantitative traits, and interpretation of genetic functions; thus, the heritability of OSA remains poorly explained. Objectives: To identify novel genetic variants associated with OSA and objective sleep-related traits and to explore their functional roles. Methods: A genome-wide association study was performed in 20,590 Han Chinese individuals (5,438 OSA and 15,152 control samples). Human samples and point mutation knockin mice were used for follow-up investigation of gene functions. Measurements and Main Results: Two characteristic study-wide significant loci (P < 2.63 × 10-9) for OSA were identified: the PACRG intronic variant rs6455893 on 6q26 (odds ratio [OR] = 1.62; 95% confidence interval [CI], 1.39-1.89; P = 6.98 × 10-10) and the missense variant rs3746804 (p.Pro267Leu) in the riboflavin transporter SLC52A3 on 20p13 (OR = 0.83; 95% CI, 0.79-0.88; P = 7.57 × 10-10). In addition, 18 genome-wide significant loci associated with quantitative OSA and objective sleep-related traits were identified, 5 of which exceeded the study-wide significance threshold. Rs3746804 was associated with elevated serum riboflavin concentrations, and the corresponding mutation in mice increased riboflavin concentrations, suggesting that this variant may facilitate riboflavin uptake and riboflavin-dependent physiological activity. Conclusions: We identified several novel genome-wide significant loci associated with OSA and objective sleep-related traits. Our findings provide insight into the genetic architecture of OSA and suggest that SLC52A3 might be a therapeutic target, whereas riboflavin might be a therapeutic agent.

Systematic analysis of the role of SLC52A2 in multiple human cancers.

BACKGROUND: In humans, riboflavin must be obtained through intestinal absorption because it cannot be synthesized by the body. SLC52A2 encodes a membrane protein belonging to the riboflavin transporter protein family and is associated with a variety of diseases. Here, we systematically explore its relevance to multiple human tumors. METHODS: We analyzed the association of SLC52A2 with 33 tumors using publicly available databases such as TCGA and GEO. We verified the SLC52A2 expression in hepatocellular carcinoma, gastric cancer, colon cancer, and rectal cancer using immunohistochemistry. RESULTS: We report that SLC52A2 was highly expressed in almost all tumors, and the immunohistochemical results in the hepatocellular, gastric, colon, and rectal cancers were consistent with the above. SLC52A2 expression was linked to patient overall survival, disease-specific survival, progression-free interval, diagnosis, mutations, tumor mutational burden, microsatellite instability, common immune checkpoint genes, and immune cells infiltration. Enrichment analysis showed that SLC52A2 was mainly enriched in oocyte meiosis, eukaryotic ribosome biogenesis, and cell cycle. In hepatocellular carcinoma, the SLC52A2 expression is an independent prognostic factor. The SNHG3 and THUMPD3-AS1/hsa-miR-139-5p-SLC52A2 axis were identified as potential regulatory pathways in hepatocellular carcinoma. CONCLUSION: In conclusion, we have systematically described for the first time that SLC52A2 is closely associated with a variety of tumors, especially hepatocellular carcinoma.

Promotion of rs3746804 (p. L267P) polymorphism to intracellular SLC52A3a trafficking and riboflavin transportation in esophageal cancer cells.

Riboflavin is an essential micronutrient for normal cellular growth and function. Lack of dietary riboflavin is associated with an increased risk for esophageal squamous cell carcinoma (ESCC). Previous studies have identified that the human riboflavin transporter SLC52A3a isoform (encoded by SLC52A3) plays a prominent role in esophageal cancer cell riboflavin transportation. Furthermore, SLC52A3 gene single nucleotide polymorphisms rs3746804 (T>C, L267P) and rs3746803 (C >T, T278M) are associated with ESCC risk. However, whether SLC52A3a (p.L267P) and (p.T278M) act in riboflavin transportation in esophageal cancer cell remains inconclusive. Here, we constructed the full-length SLC52A3a protein fused to green fluorescent protein (GFP-SLC52A3a-WT and mutants L267P, T278M, and L267P/T278M). It was confirmed by immunofluorescence-based confocal microscopy that SLC52A3a-WT, L267P, T278M, and L267P/T278M expressed in cell membrane, as well as in a variety of intracellular punctate structures. The live cell confocal imaging showed that SLC52A3a-L267P and L267P/T278M increased the intracellular trafficking of SLC52A3a in ESCC cells. Fluorescence recovery after photobleaching of GFP-tagged SLC52A3a meant that intracellular trafficking of SLC52A3a-L267P and L267P/T278M was rapid dynamics process, leading to its stronger ability to transport riboflavin. Taken together, the above results indicated that the rs3746804 (p.L267P) polymorphism promoted intracellular trafficking of SLC52A3a and riboflavin transportation in ESCC cells.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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 variation of SLC52A3 rs13042395 predicts survival of Chinese gastric cancer patients.

The solute carrier family 52 member 3 (SLC52A3) gene encodes riboflavin transporter protein which is essential to maintain mitochondrial function in cells. In our research, we found that SLC52A3 rs13042395 C > T variation was significantly associated with poor survival in a 926 Chinese gastric cancer (GCa) patients cohort (CC/CT genotype versus TT genotype, HR = 0.57, 95%CI (0.40-0.82), log-rank P = 0.015). The SLC52A3 rs13042395 C > T change led to its increased mRNA expression according to expression quantitative trait loci analysis (P = 0.0029). In vitro, it was revealed that rs13042395 C allele had higher binding affinity to inhibitory transcription factor Meis homeobox 1 (MEIS1) compared with T allele, knock-down of MEIS1 could up-regulate SLC52A3, and overexpression of SLC52A3 contributed to the increased ability of proliferation, colony formation, migration and invasion in GCa cells. Subsequently, the bioinformatics analysis combined with experiments in vitro suggested that Gap junction protein alpha 1 (GJA1) was the downstream effector of SLC52A3, SLC52A3 may promote the GCa cells aggressiveness by down-regulating the GJA1 expression. Overall, SLC52A3 genetic variant rs13042395 C > T change was associated with poorer survival in Chinese GCa patients and increased SLC52A3 expression by interaction with MEIS1. SLC52A3 promoted the GCa cells aggressiveness by down-regulating the GJA1 expression.

Hematologic presentation and the role of untargeted metabolomics analysis in monitoring treatment for riboflavin transporter deficiency.

Riboflavin transporter deficiency (RTD) (MIM #614707) is a neurogenetic disorder with its most common manifestations including sensorineural hearing loss, peripheral neuropathy, respiratory insufficiency, and bulbar palsy. Here, we present a 2-year-old boy whose initial presentation was severe macrocytic anemia necessitating multiple blood transfusions and intermittent neutropenia; he subsequently developed ataxia and dysarthria. Trio-exome sequencing detected compound heterozygous variants in SLC52A2 that were classified as pathogenic and a variant of uncertain significance. Bone marrow evaluation demonstrated megaloblastic changes. Notably, his anemia and neutropenia resolved after treatment with oral riboflavin, thus expanding the clinical phenotype of this disorder. We reiterate the importance of starting riboflavin supplementation in a young child who presents with macrocytic anemia and neurological features while awaiting biochemical and genetic work up. We detected multiple biochemical abnormalities with the help of untargeted metabolomics analysis associated with abnormal flavin adenine nucleotide function which normalized after treatment, emphasizing the reversible pathomechanisms involved in this disorder. The utility of untargeted metabolomics analysis to monitor the effects of riboflavin supplementation in RTD has not been previously reported.

In Vitro Effects of Paclitaxel and Cremophor EL on Human Riboflavin Transporter SLC52A2.

Paclitaxel, a mitotic inhibitor with anti-cancer effects, is dissolved in Cremophor EL (CrEL). However, peripheral neuropathy is a known side effect. As one of the mechanisms of the neuropathy, mitochondrial dysfunction has been proposed, while peroxidation products are involved in the cause of CrEL-induced neurotoxicity. Riboflavin is an essential nutrient required for ATP production in mitochondria and has an antioxidant role as a coenzyme for glutathione. Therefore, riboflavin transporters might play a key role to mitigate neuropathy. However, it is unclear whether paclitaxel and CrEL affect these transporters. In this study, human riboflavin transporter SLC52A2 was used to analyze the effects of paclitaxel and CrEL. CrEL, but not paclitaxel, inhibited uptake of riboflavin in human embryonic kidney 293 cells transfected with the SLC52A2 expression vector, suggesting that altered riboflavin disposition may be involved in the pathogenesis of paclitaxel/CrEL toxicity.

Development of Novel Experimental Models to Study Flavoproteome Alterations in Human Neuromuscular Diseases: The Effect of Rf Therapy.

Inborn errors of Riboflavin (Rf) transport and metabolism have been recently related to severe human neuromuscular disorders, as resulting in profound alteration of human flavoproteome and, therefore, of cellular bioenergetics. This explains why the interest in studying the "flavin world", a topic which has not been intensively investigated before, has increased much over the last few years. This also prompts basic questions concerning how Rf transporters and FAD (flavin adenine dinucleotide) -forming enzymes work in humans, and how they can create a coordinated network ensuring the maintenance of intracellular flavoproteome. The concept of a coordinated cellular "flavin network", introduced long ago studying humans suffering for Multiple Acyl-CoA Dehydrogenase Deficiency (MADD), has been, later on, addressed in model organisms and more recently in cell models. In the frame of the underlying relevance of a correct supply of Rf in humans and of a better understanding of the molecular rationale of Rf therapy in patients, this review wants to deal with theories and existing experimental models in the aim to potentiate possible therapeutic interventions in Rf-related neuromuscular diseases.

A Chinese pedigree with Brown-Vialetto-Van Laere syndrome due to two novel mutations of SLC52A2 gene: clinical course and response to riboflavin.

BACKGROUND: Brown-Vialetto-Van Laere Syndrome (BVVLS), a rare neurological disorder characterized by motor, sensory, and cranial neuronopathies, is mainly associated with defective riboflavin transporters encoded by SLC52A2 and SLC52A3 genes. Clinical outcomes have been shown to be improved significantly by high-dose riboflavin supplementation. The aim of this study was to identify genetic causes and further evaluate the clinical course and response to riboflavin in a Chinese pedigree with BVVLS. CASE PRESENTATION: We report the novel compound heterozygous variants c.1328G>A p.(Cys443Tyr) and c.1022_1023insC p. (Leu341Profs*103) of SLC52A2 gene in a female proband who presented in our out-patient clinic at the age of one-year-old with progressive mental and motor regression, breath holding, and brain stem dysfunction including facial weakness, hearing loss, dysphagia. Following high-dose riboflavin supplementation, the respiratory insufficiency and mental, motor, and bulbar function improved. However, sensorineural hearing loss was not improved. The missense variant site was highly conserved. Both variants were not found in the population database gnomAD. The two variants were inherited from her mother and father, respectively. Both variants were predicted to be deleterious by Polyphen2, Mutation taster, and SIFT and were classified as likely pathogenic according to the ACMG guideline. CONCLUSIONS: Two novel pathogenic variations of SLC52A2 gene were firstly found from a Chinese pedigree with BVVLS. Clinical outcomes could be improved by early diagnosis and riboflavin supplementation.

An update on the genetics, clinical presentation, and pathomechanisms of human riboflavin transporter deficiency.

Riboflavin transporter deficiency (RTD) is a rare neurological condition that encompasses the Brown-Vialetto-Van Laere and Fazio-Londe syndromes since the discovery of pathogenic mutations in the SLC52A2 and SLC52A3 genes that encode human riboflavin transporters RFVT2 and RFVT3. Patients present with a deteriorating progression of peripheral and cranial neuropathy that causes muscle weakness, vision loss, deafness, sensory ataxia, and respiratory compromise which when left untreated can be fatal. Considerable progress in the clinical and genetic diagnosis of RTDs has been made in recent years and has permitted the successful lifesaving treatment of many patients with high dose riboflavin supplementation. In this review, we first outline the importance of riboflavin and its efficient transmembrane transport in human physiology. Reports on 109 patients with a genetically confirmed diagnosis of RTD are then summarized in order to highlight commonly presenting clinical features and possible differences between patients with pathogenic SLC52A2 (RTD2) or SLC52A3 (RTD3) mutations. Finally, we focus attention on recent work with different models of RTD that have revealed possible pathomechanisms contributing to neurodegeneration in patients.

SLC52A3 expression is activated by NF-κB p65/Rel-B and serves as a prognostic biomarker in esophageal cancer.

The human riboflavin transporter-3 (encoded by SLC52A3) plays a prominent role in riboflavin absorption. Interestingly, abnormal expression patterns of SLC52A3 in multiple types of human cancers have been recently noted. However, the molecular mechanisms underlying its dysregulation remain unclear. In this study, we find that SLC52A3 has two transcript variants that differ in the transcriptional start site, and encode different proteins: SLC52A3a and SLC52A3b. Importantly, aberrant expressions of SLC52A3 are associated with stepwise development of esophageal squamous cell carcinoma (ESCC) as well as the survival rates of ESCC patients. Functionally, SLC52A3a, but not SLC52A3b, strongly promotes the proliferation and colony formation of ESCC cells. Furthermore, SLC52A3 5'-flanking regions contain NF-κB p65/Rel-B-binding sites, which are crucial for mediating SLC52A3 transcriptional activity in ESCC cells. Chromatin immunoprecipitation and electrophoretic mobility shift assay reveal that p65/Rel-B bind to 5'-flanking regions of SLC52A3. Accordingly, NF-κB signaling upregulates SLC52A3 transcription upon TNFα stimulation. Taken together, these results elucidate the mechanisms underlying SLC52A3 overexpression in ESCC. More importantly, our findings identify SLC52A3 as both a predictive and prognostic biomarker for this deadly cancer.

Clinical, pathological and functional characterization of riboflavin-responsive neuropathy.

Brown-Vialetto-Van Laere syndrome represents a phenotypic spectrum of motor, sensory, and cranial nerve neuropathy, often with ataxia, optic atrophy and respiratory problems leading to ventilator-dependence. Loss-of-function mutations in two riboflavin transporter genes, SLC52A2 and SLC52A3, have recently been linked to Brown-Vialetto-Van Laere syndrome. However, the genetic frequency, neuropathology and downstream consequences of riboflavin transporter mutations are unclear. By screening a large cohort of 132 patients with early-onset severe sensory, motor and cranial nerve neuropathy we confirmed the strong genetic link between riboflavin transporter mutations and Brown-Vialetto-Van Laere syndrome, identifying 22 pathogenic mutations in SLC52A2 and SLC52A3, 14 of which were novel. Brain and spinal cord neuropathological examination of two cases with SLC52A3 mutations showed classical symmetrical brainstem lesions resembling pathology seen in mitochondrial disease, including severe neuronal loss in the lower cranial nerve nuclei, anterior horns and corresponding nerves, atrophy of the spinothalamic and spinocerebellar tracts and posterior column-medial lemniscus pathways. Mitochondrial dysfunction has previously been implicated in an array of neurodegenerative disorders. Since riboflavin metabolites are critical components of the mitochondrial electron transport chain, we hypothesized that reduced riboflavin transport would result in impaired mitochondrial activity, and confirmed this using in vitro and in vivo models. Electron transport chain complex I and complex II activity were decreased in SLC52A2 patient fibroblasts, while global knockdown of the single Drosophila melanogaster riboflavin transporter homologue revealed reduced levels of riboflavin, downstream metabolites, and electron transport chain complex I activity. This in turn led to abnormal mitochondrial membrane potential, respiratory chain activity and morphology. Riboflavin transporter knockdown in Drosophila also resulted in severely impaired locomotor activity and reduced lifespan, mirroring patient pathology, and these phenotypes could be partially rescued using a novel esterified derivative of riboflavin. Our findings expand the genetic, clinical and neuropathological features of Brown-Vialetto-Van Laere syndrome, implicate mitochondrial dysfunction as a downstream consequence of riboflavin transporter gene defects, and validate riboflavin esters as a potential therapeutic strategy.

Role of MicroRNA-423-5p in posttranscriptional regulation of the intestinal riboflavin transporter-3.

Riboflavin (RF) is essential for normal cellular functions and health. Humans obtain RF from exogenous sources via intestinal absorption that involves a highly specific carrier-mediated process. We have recently established that the riboflavin transporter-3 (RFVT3) is vital for the normal intestinal RF uptake process and have characterized certain aspects of its transcriptional regulation. Little is known, however, about how this transporter is regulated at the posttranscriptional level. We address this issue by focusing on the role of microRNAs. Using bioinformatics, we identified two potential interacting miRNAs with the human (h) RFVT3-3'-UTR, and showed (using pmirGLO-hRFVT3-3'-UTR) that the hRFVT3-3'-UTR is, indeed, a target for miRNA effect. Of the two putative miRNAs identified, miR-423-5p was found to be highly expressed in intestinal epithelial cells and that its mimic affected luciferase reporter activity of the pmirGLO-hRFVT3-3'-UTR construct, and also led to inhibition in RF uptake by intestinal epithelial Caco-2 and HuTu-80 cells. Furthermore, cells transfected with mutated seed sequences for miR-423-5p showed an abrogation in inhibitory effect of the miR-423-5p mimic on luciferase activity. While miR-423-5p did not affect the level of expression of the hRFVT3 mRNA, it did lead to a significant inhibition in the level of expression of its protein. Similarly, miR-423-5p was found to affect the level of expression of the mouse RFVT3 in cultured intestinal enteroids. These findings demonstrate, for the first time, that the RFVT3 is a target for posttranscriptional regulation by miRNAs in intestinal epithelial cells and that this regulation has functional consequences on intestinal RF uptake.NEW & NOTEWORTHY Our findings show for the first time that RFVT3 is a target for posttranscriptional regulation by miR-423-5p in intestinal epithelial cells, and this regulation has functional consequences on intestinal riboflavin (RF) uptake process.

Single nucleotide polymorphism rs13042395 in the SLC52A3 gene as a biomarker for regional lymph node metastasis and relapse-free survival of esophageal squamous cell carcinoma patients.

BACKGROUND: SLC52A3 was recently identified as a susceptibility gene for esophageal squamous cell carcinoma (ESCC). However, associations between the single nucleotide polymorphisms (SNPs) rs13042395 (C > T) and rs3746803 (G > A) in SLC52A3 and risk, tumor characteristics and survival of ESCC patients remain inconclusive and of unknown prognostic significance. METHODS: Analyses of the association between SNPs in SLC52A3 and ESCC risk were performed on 479 ESCC cases, together with 479 controls, in a case-control study. Blood samples for cases and controls were collected and genotyped by real-time polymerase chain reaction (PCR) using TaqMan assays. Among the 479 ESCC cases, 343 cases with complete clinical data were used to investigate the association between SNPs and ESCC clinical characteristics; 288 cases with complete clinical data and 5-year follow-up data were used to analyze the association between SNPs and prognosis. Dual luciferase reporter assays and electrophoretic mobility shift assays (EMSAs) were used to investigate the biological function of rs13042395. RESULTS: No association was found between SLC52A3 rs3746803 and susceptibility, tumor characteristics or survival of ESCC patients. For rs13042395, TT genotype carriers were likely to have reduced lymph node metastasis (odds ratio (OR) = 0.55, 95 % confidence interval (CI), 0.31-0.98) and longer relapse-free survival time (P = 0.03) . Also, both rs13042395 (hazard ratio (HR) = 0.62, 95 % CI, 0.38-0.99) and regional lymph node metastasis (HR = 2.06, 95 % CI, 1.36-3.13 for N1 vs. N0; HR = 2.88, 95 % CI, 1.70-4.86 for N2 vs. N0; HR = 2.08, 95 % CI, 1.01-4.30 for N3 vs. N0) were independent factors affecting relapse-free survival for ESCC patients who underwent surgery. Dual luciferase reporter assays and EMSAs suggested that the CC genotype of rs13042395 enhanced SLC52A3 expression, probably via binding with specific transcription factors. CONCLUSIONS: The rs13042395 polymorphism in SLC52A3 is associated with regional lymph node metastasis and relapse-free survival in ESCC patients.

Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2.

Childhood onset motor neuron diseases or neuronopathies are a clinically heterogeneous group of disorders. A particularly severe subgroup first described in 1894, and subsequently called Brown-Vialetto-Van Laere syndrome, is characterized by progressive pontobulbar palsy, sensorineural hearing loss and respiratory insufficiency. There has been no treatment for this progressive neurodegenerative disorder, which leads to respiratory failure and usually death during childhood. We recently reported the identification of SLC52A2, encoding riboflavin transporter RFVT2, as a new causative gene for Brown-Vialetto-Van Laere syndrome. We used both exome and Sanger sequencing to identify SLC52A2 mutations in patients presenting with cranial neuropathies and sensorimotor neuropathy with or without respiratory insufficiency. We undertook clinical, neurophysiological and biochemical characterization of patients with mutations in SLC52A2, functionally analysed the most prevalent mutations and initiated a regimen of high-dose oral riboflavin. We identified 18 patients from 13 families with compound heterozygous or homozygous mutations in SLC52A2. Affected individuals share a core phenotype of rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia, severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs), hearing loss, optic atrophy and respiratory insufficiency. We demonstrate that SLC52A2 mutations cause reduced riboflavin uptake and reduced riboflavin transporter protein expression, and we report the response to high-dose oral riboflavin therapy in patients with SLC52A2 mutations, including significant and sustained clinical and biochemical improvements in two patients and preliminary clinical response data in 13 patients with associated biochemical improvements in 10 patients. The clinical and biochemical responses of this SLC52A2-specific cohort suggest that riboflavin supplementation can ameliorate the progression of this neurodegenerative condition, particularly when initiated soon after the onset of symptoms.

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

INTRODUCTION: 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. METHODS: Autozygosity mapping was performed in all affected individuals, followed by whole-exome sequencing (WES) in 2 individuals. RESULTS: 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. CONCLUSIONS: Mutations in SLC52A2 result in a recognizable phenotype distinct from BVVLS. Early recognition of this disorder is critical, given its potential treatability.

Atypical presentations in an RTD patient and report of novel SLC52A3 and SLC52A2 mutations.

INTRODUCTION: Riboflavin Transporter Deficiency (RTD) is a rare neurological disorder characterized by pontobulbar palsy, hearing loss, and motor cranial nerve involvement. SLC52A3 and SLC52A2 mutations are causes of RTD. SLC52A2 mutations are usually found in childhood onset cases. Fifteen Iranian RTD diagnosed patients without SLC52A2 mutations have been previously described. We aimed to identify causative mutations in two childhood cases. METHODS: We recruited patients with diagnosis of BVVL. Comprehensive clinical evaluations were performed on the patients. SLC52A3 and SLC52A2 genes were PCR-amplified and Sanger sequenced. Candidate disease causing variations were screened for segregation with disease status in the respective families and control individuals. RESULTS: A novel homozygous SLC52A3 mutation (p.Met1Val) and a heterozygous SLC52A2 mutation (p.Ala288Val) were both observed in one proband with typical RTD presentations. The aggregate of presentations in the early stages of disease in the second patient that included weakness in the lower extremities, absence of bulbar or hearing defects, prominent sensory polyneuropathy as evidenced in electrodiagnostic studies, and absence of sensory symptoms including sensory ataxia did not prompt immediate RTD diagnosis. Dysarthria and decreased hearing manifested later in the disease course. A novel homozygous SLC52A2 (p.Val314Met) mutation was identified. CONCLUSION: A literature search found recent reports of other atypical RTD presentations. These include MRI findings, speech understanding difficulties accompanied by normal hearing, anemia, and left ventricular non-compaction. Knowledge of unusual presentations lessens the chance of misdiagnosis or delayed RTD diagnosis which, in light of favorable effects of riboflavin supplementation, is of immense importance.

Identification of a mutation in TNRC18 in a patient with clinical features of Fazio-Londe disease.

Fazio-Londe disease and Brown-Vialetto-Van Laere syndrome are rare related neurological disorders. Although SLC52A3 and SLC52A2 that encode riboflavin transporters are their only known causative genes, many patients without mutations in these genes have been reported. Clinical and genetic data of a patient with features suggestive of Fazio-Londe disease are presented. Neurological examination revealed significant involvement of cranial nerves and weakness in the lower extremities. Pontobulbar presentations were prominent. EDX study suggested motor neuronopathy. Hearing was normal. She was diagnosed with FL disease. Response to riboflavin supplementation was not favorable. The patient's pedigree suggested recessive inheritance. SLC52A3 and SLC52A2 were screened and mutations were not observed. Results of exome sequencing and segregation analysis suggested that a mutation in TNRC18 is a candidate cause of disease in the patient. The three dimensional structure of the TNRC18 protein was predicted and it was noted that its two conserved domains (BAH and Tudor) interact and that the valine residue affected by the mutation is positioned close to both domains. A mutation in TNRC18 is cautiously reported as the possible cause of FL disease in the patient. The finding warrants further inquiries on TNRC18 about which little is presently known.

A riboflavin transporter deficiency presenting as pure red cell aplasia: a pediatric case report.

Introduction: Riboflavin transporter deficiency (RTD) is a rare genetic disorder that affects riboflavin transport, leading to impaired red blood cell production and resulting in pure red cell aplasia. Recognizing and understanding its clinical manifestations, diagnosis, and management is important. Case presentation: A 2-year-old patient presented with pure red cell aplasia as the primary symptom of RTD. After confirming the diagnosis, rapid reversal of anemia was achieved after high-dose riboflavin treatment. Conclusion: RTD often has an insidious onset, and neurological symptoms appear gradually as the disease progresses, making it prone to misdiagnosis. Genetic testing and bone marrow biopsy can confirm the diagnosis.