SLC19A1 Genetic Variation Leads to Altered Thiamine Diphosphate Transport: Implications for the Risk of Developing Wernicke-Korsakoff's Syndrome.

AIMS: Wernicke-Korsakoff syndrome (WKS) is commonly associated with chronic alcohol misuse, a condition known to have multiple detrimental effects on thiamine metabolism. This study was conducted to identify genetic variants that may contribute to the development of WKS in individuals with alcohol dependence syndrome through alteration of thiamine transport into cells. METHODS: Exome sequencing data from a panel of genes related to alcohol metabolism and thiamine pathways were analysed in a discovery cohort of 29 individuals with WKS to identify possible genetic risk variants associated with its development. Variant frequencies in this discovery cohort were compared with European frequencies in the Genome Aggregation Database browser, and those present at significantly higher frequencies were genotyped in an additional cohort of 87 alcohol-dependent cases with WKS and 197 alcohol-dependent cognitively intact controls. RESULTS: Thirty non-synonymous variants were identified in the discovery cohort and, after filtering, 23 were taken forward and genotyped in the case-control cohort. Of these SLC19A1:rs1051266:G was nominally associated with WKS. SLC19A1 encodes the reduced folate carrier, a major transporter for physiological folate in plasma; rs1051266 is reported to impact folate transport. Thiamine pyrophosphate (TPP) efflux was significantly decreased in HEK293 cells, stably transfected with rs1051266:G, under thiamine deficient conditions when compared with the efflux from cells transfected with rs1051266:A (P = 5.7 × 10-11). CONCLUSION: This study provides evidence for the role of genetic variation in the SLC19A1 gene, which may contribute to the development of WKS in vivo through modulation of TPP transport in cells.

Diabetes Out-of-the-Box: Diabetes Mellitus and Impairment in Hearing and Vision.

PURPOSEOF REVIEW: This review aims to provide an update on the etiologies of diabetes that are due to genetic disorders and that co-occur with impaired hearing or vision and to compare them. The potential mechanisms, including novel treatments, will be detailed. RECENT FINDINGS: Wolfram syndrome, Kearns-Sayre syndrome, thiamine-responsive megaloblastic anemia, and maternally inherited diabetes and deafness are genetic disorders characterized by diabetes, impaired hearing, and vision. They differ in mode of inheritance, age at presentation, and the involvement of other organs; they are often misdiagnosed as type 1 or type 2 diabetes. Suspicion of a genetic diabetes syndrome should be raised when pancreatic autoantibodies are negative, other organs are involved, and family history includes diabetes. Correct diagnosis of the various syndromes is important for tailoring the most advanced treatment, preventing disease progression, and enabling proper genetic counseling.

Identification and functional analysis of novel SLC25A19 variants causing thiamine metabolism dysfunction syndrome 4.

BACKGROUND: Thiamine metabolism dysfunction syndrome 4 (THMD4, OMIM #613710) is an autosomal recessive inherited disease caused by the deficiency of SLC25A19 that encodes the mitochondrial thiamine pyrophosphate (TPP) transporter. This disorder is characterized by bilateral striatal degradation and progressive polyneuropathy with the onset of fever of unknown origin. The limited number of reported cases and lack of functional annotation of related gene variants continue to limit diagnosis. RESULTS: We report three cases of encephalopathy from two unrelated pedigrees with basal ganglia signal changes after fever of unknown origin. To distinguish this from other types of encephalopathy, such as acute necrotizing encephalopathy, exome sequencing was performed, and four novel heterozygous variations, namely, c.169G>A (p.Ala57Thr), c.383C>T (p.Ala128Val), c.76G>A (p.Gly26Arg), and c.745T>A (p.Phe249Ile), were identified in SLC25A19. All variants were confirmed using Sanger sequencing. To determine the pathogenicity of these variants, functional studies were performed. We found that mitochondrial TPP levels were significantly decreased in the presence of SLC25A19 variants, indicating that TPP transport activities of mutated SLC25A19 proteins were impaired. Thus, combining clinical phenotype, genetic analysis, and functional studies, these variants were deemed as likely pathogenic. CONCLUSIONS: Exome sequencing analysis enables molecular diagnosis as well as provides potential etiology. Further studies will enable the elucidation of SLC25A19 protein function. Our investigation supplied key molecular evidence for the precise diagnosis of and clinical decision-making for a rare disease.

The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2.

A rare cause of megaloblastic anemia (MA) is thiamine-responsive megaloblastic anemia (TRMA), a genetic disorder caused by mutations in SLC19A2 (encoding THTR1), a thiamine transporter. The study objectives were to (1) functionally characterize selected TRMA-associated SLC19A2 variants and (2) determine whether current prescription drugs associated with drug-induced MA (DIMA) may act via inhibition of SLC19A2. Functional characterization of selected SLC19A2 variants was performed by confocal microscopy and isotopic uptake studies of [3H]-thiamine in HEK293 cells. Sixty-three drugs associated with DIMA were screened for SLC19A2 inhibition in isotopic uptake studies. Three previously uncharacterized SLC19A2 variants identified in TRMA patients exhibited disrupted localization to the plasma membrane along with near-complete loss-of-function. Ten of 63 drugs inhibited SLC19A2-mediated thiamine transport ≥ 50% at screening concentrations; however, with the exception of erythromycin, none was predicted to inhibit SLC19A2 at clinically relevant unbound plasma concentrations. Data from electronic health records revealed reduced levels of thiamine pyrophosphate (TPP) in patients prescribed erythromycin, consistent with inhibition of SLC19A2-mediated thiamine transport. Here, we confirmed the role of three SLC19A2 variants in TRMA pathology. Additionally, we report that inhibition of SLC19A2 is a potential, but uncommon mechanism for DIMA.

Novel p.P298L SURF1 mutation in thiamine deficient Leigh syndrome patients compromises cytochrome c oxidase activity.

SURF1 is a nuclear gene and encodes for an important assembly factor for cytochrome c oxidase enzyme. A number of mutations in SURF1 gene render cytochrome c oxidase deficiency, a major causative factor for Leigh syndrome. We screened all the 9 exons and exon-intron boundaries of SURF1 gene in 165 Indian Leigh syndrome patients who were thiamine responsive too. Consequently, we identified several novel and reported nucleotide variations in this gene. The nucleotide changes were analysed by using different in-silico tools for predicting their pathogenicity. Based upon the predictions, we further validated the analyzed functional significance of p.N249D and p.P298L mutations in SURF1 protein using COS-7 cells. Though, both the mutations did not affect the localization of SURF1protein into the mitochondria. But, interestingly the novel mutation p.P298L was reported to significantly compromise the COX activity in these cells.

Functional analysis of the third identified SLC25A19 mutation causative for the thiamine metabolism dysfunction syndrome 4.

Thiamine metabolism dysfunction syndrome-4 (THMD4) includes episodic encephalopathy, often associated with a febrile illness, causing transient neurologic dysfunction and a slowly progressive axonal polyneuropathy. Until now only two mutations (G125S and S194P) have been reported in the SLC25A19 gene as causative for this disease and a third mutation (G177A) as related to the Amish lethal microcephaly. In this work, we describe the clinical and molecular features of a patient carrying a novel mutation (c.576G>C; Q192H) on SLC25A19 gene. Functional studies on this mutation were performed explaining the pathogenetic role of c.576G>C in affecting the translational efficiency and/or stability of hMTPPT protein instead of the mRNA expression. These findings support the pathogenetic role of Q192H (c.576G>C) mutation on SLC25A19 gene. Moreover, despite in other patients the thiamine supplementation leaded to a substantial improvement of peripheral neuropathy, our patient did not show a clinical improvement.

TRMA syndrome with a severe phenotype, cerebral infarction, and novel compound heterozygous SLC19A2 mutation: a case report.

BACKGROUND: Thiamine-responsive megaloblastic anemia (TRMA) is a rare autosomal recessive inherited disease characterized by the clinical triad of megaloblastic anemia, sensorineural deafness, and diabetes mellitus. To date, only 100 cases of TRMA have been reported in the world. CASE PRESENTATION: Here, we describe a six-year-old boy with diabetes mellitus, anemia, and deafness. Additionally, he presented with thrombocytopenia, leukopenia, horizontal nystagmus, hepatomegaly, short stature, ventricular premature beat (VPB), and cerebral infarction. DNA sequencing revealed a novel compound heterozygous mutation in the SLC19A2 gene: (1) a duplication c.405dupA, p.Ala136Serfs*3 (heterozygous) and (2) a nucleotide deletion c.903delG p.Trp301Cysfs*13 (heterozygous). The patient was diagnosed with a typical TRMA. CONCLUSION: Novel mutations in the SLC19A2 gene have been identified, expanding the mutation spectrum of the SLC19A2 gene. For the first time, VPB and cerebral infarction have been identified in patients with TRMA syndrome, providing a new understanding of the phenotype.

Genetic heterogeneity of mitochondrial genome in thiamine deficient Leigh syndrome patients.

In our previously published study, we cared for 165 thiamine deficient Leigh syndrome (LS) patients who presented in acute life threatening conditions with severe neurological abnormalities. However the molecular basis for this atypical phenotype was not explored. This study is an effort to undermine the possible molecular defects in mitochondria of those patients and put-forth an explanation towards this clinical presentation. Protein coding genes of mitochondrial (mt) DNA were sequenced in total 165 LS patients and 94 age matched controls. To understand their pathogenic significance, nucleotide variations were also studied using various in-silico tools. Histochemical and electron microscopic analysis was also done in tissue samples obtained from 23 patients. We observed a very high level of genetic heterogeneity across the mt DNA of all these patients. In the concordance of published literature we also observed a large number of variations in ND5 gene (hot spot for LS). We also observed a total 13 nucleotide variations across COX genes, which is otherwise not common in LS. As per in-silico analysis, many of these variations were suggested to be pathogenic. Histochemical and electron microscopic studies also suggested the defects in the mitochondria of these patients. As these patients were thiamine deficient, hence we propose that genetic defects and thiamine deficiency may together severely affect the ATP levelof these patients, leading to acute and life threatening clinical presentation. Present study has opened up many avenues for further research towards understanding the genetic basis and possible role of thiamine deficiency in LS patients.

Whole exome sequencing identifies a new mutation in the SLC19A2 gene leading to thiamine-responsive megaloblastic anemia in an Egyptian family.

BACKGROUND: The Solute Carrier Family 19 Member 2 (SLC19A2, OMIM *603941) encodes the thiamine transporter 1 (THTR-1) that brings thiamine (Vitamin B1) into cells. THTR-1 is the only thiamine transporter expressed in bone marrow, cochlear, and pancreatic beta cells. THTR-1 loss-of-function leads to the rare recessive genetic disease Thiamine-Responsive Megaloblastic Anemia (TRMA, OMIM #249270). METHODS: In vitro stimulated blood lymphocytes were used for cytogenetics and the isolation of genomic DNA used to perform whole exome sequencing (WES). To validate identified mutations, direct Sanger sequencing was performed following PCR amplification. RESULTS: A 6-year-old male born from a consanguineous couple presenting bone marrow failure and microcephaly was referred to our clinic for disease diagnosis. The patient presented a normal karyotype and no chromosomal fragility in response to DNA damage. WES analysis led to the identification of a new pathogenic variant in the SLC19A2 gene (c.596C>G, pSer199Ter) allowing to identify the young boy as a TRMA patient. CONCLUSION: Our analysis extend the number of inactivating mutations in SLC19A2 leading to TRMA that could guide future prenatal diagnosis for the family and follow-up for patients.

Genetic defects of thiamine transport and metabolism: A review of clinical phenotypes, genetics, and functional studies.

Thiamine is a crucial cofactor involved in the maintenance of carbohydrate metabolism and participates in multiple cellular metabolic processes within the cytosol, mitochondria, and peroxisomes. Currently, four genetic defects have been described causing impairment of thiamine transport and metabolism: SLC19A2 dysfunction leads to diabetes mellitus, megaloblastic anemia and sensory-neural hearing loss, whereas SLC19A3, SLC25A19, and TPK1-related disorders result in recurrent encephalopathy, basal ganglia necrosis, generalized dystonia, severe disability, and early death. In order to achieve early diagnosis and treatment, biomarkers play an important role. SLC19A3 patients present a profound decrease of free-thiamine in cerebrospinal fluid (CSF) and fibroblasts. TPK1 patients show decreased concentrations of thiamine pyrophosphate in blood and muscle. Thiamine supplementation has been shown to improve diabetes and anemia control in Rogers' syndrome patients due to SLC19A2 deficiency. In a significant number of patients with SLC19A3, thiamine improves clinical outcome and survival, and prevents further metabolic crisis. In SLC25A19 and TPK1 defects, thiamine has also led to clinical stabilization in single cases. Moreover, thiamine supplementation leads to normal concentrations of free-thiamine in the CSF of SLC19A3 patients. Herein, we present a literature review of the current knowledge of the disease including related clinical phenotypes, treatment approaches, update of pathogenic variants, as well as in vitro and in vivo functional models that provide pathogenic evidence and propose mechanisms for thiamine deficiency in humans.

Identification of two novel TPK1 gene mutations in a Chinese patient with thiamine pyrophosphokinase deficiency undergoing whole exome sequencing.

Background The mutations of thiamine pyrophosphokinase-1 (TPK1) gene have been frequently studied in some patients with thiamine metabolism dysfunction syndrome-5 (THMD5), while TPK1 mutations in Chinese patients have been investigated by only homozygous. A search of the literature on the mutations in the Chinese population currently published revealed that no reports of compound heterozygous mutations were reported. Here, we report a Chinese patient with compound heterozygous TPK1 mutations who underwent magnetic resonance imaging (MRI), whole exome sequencing (WES), molecular diagnosis, bioinformatics analysis, and three-dimensional (3D) protein structure analysis. Case presentation A Chinese boy was born after an uneventful pregnancy to non-consanguineous and healthy parents. On the sixth day after his birth, the lactate level of the patient was between 8.6 mmol/L and 14.59 mmol/L in plasma (the normal level is in the range of 0.5-2.2 mmol/L). Lactate was reduced to the normal level after rehydration, acid correction, expansion, and other treatments. After 4 months, the patient presented with an acute, 3-h-long, non-induced convulsions, and was admitted to our hospital for weakness, decreased oral intake, and lethargy. Results achieved by electroencephalography (EEG), cerebrospinal fluid, and other biochemical findings were normal. A visible hemorrhagic lesion was also observed in the brain. Seizures increased significantly during infection, which was accompanied by higher lactic acid levels. MRI of the brain showed an obvious signal shadow, in which bilateral frontal and temporal parietal subarachnoid cavities were widened, and more abnormal signals were observed; therefore, further consideration of hypoxic-ischemic encephalopathy and genetic metabolic disease was taken into account. Conclusions The results of WES revealed that the patient was associated with compound heterozygous mutations NM_022445.3:c.[263G>A]; [226A>G] of TPK1. His parents were non-consanguineous; while his father was found to be a heterozygous carrier with the mutation c.[263G>A], his mother was identified as a heterozygous carrier with the mutation c.[226A>G]. The results indicated that the patient had a compound heterozygous TPK1 mutation, and this is the first reported case in China.

Telomere shortening in alcohol dependence: Roles of alcohol and acetaldehyde.

Heavy drinking leads to premature aging and precipitates the onset of age-related diseases. Acetaldehyde (AcH), a toxic metabolite of ethanol, has been implicated in various types of cancer. However, whether alcohol accelerates biological aging at a cellular level is controversial and the mechanism involved is unclear. We addressed these questions by measuring telomere length (TL) in peripheral blood leukocytes of Japanese patients with alcohol dependence (AD) and examined the association between TL, genetic variants of alcohol dehydrogenase (ADH)1B and aldehyde dehydrogenase (ALDH)2, and other clinical characteristics. A total of 134 male AD patients and 121 age- and sex-matched healthy controls were evaluated. All patients received endoscopic screening for cancer of the upper aerodigestive tract (UADT). TL was almost 50% shorter in AD patients relative to controls. There were no significant differences in TL between AD patients with and without UADT cancer, and no associations between ADH1B and ALDH2 genotypes and TL. AD patients with thiamine (vitamin B1) deficiency at admission had significantly shorter TL than those with normal thiamine status. Although the exact mechanism underlying the shorter TL in AD patients remain unclear, our findings suggest that alcohol rather than AcH is associated with telomere shortening in AD, which may be accelerated by thiamine deficiency. Future studies should also focus on the association between telomere shortening and TD in the context of oxidative stress.

A novel mutation in the SLC19A2 gene in a Turkish male with thiamine-responsive megaloblastic anemia syndrome.

Odaman-Al I, Gezdirici A, Yildiz M, Ersoy G, Aydogan G, Salcioglu Z, Tahtakesen TN, Önal H, Küçükemre-Aydin B. A novel mutation in the SLC19A2 gene in a Turkish male with thiamine-responsive megaloblastic anemia syndrome. Turk J Pediatr 2019; 61: 257-260. Thiamine-responsive megaloblastic anemia (TRMA) is a very rare syndrome characterized by the triad of early onset megaloblastic anemia, sensorineural deafness and diabetes mellitus. Here we report, a 5-year-old boy who presented with transfusion dependent anemia and diabetes mellitus and was diagnosed with TRMA. Besides reporting a novel mutation of the causative gene SLC19A2, we wanted to emphasize this syndrome in the aspect of coexistence of insulin dependent diabetes, transfusion dependent anemia and thrombocytopenia.

A novel mutation in the SLC19A2 gene in a Turkish male with thiamine-responsive megaloblastic anemia syndrome.

Odaman-Al I, Gezdirici A, Yildiz M, Ersoy G, Aydogan G, Salcioglu Z, Tahtakesen TN, Önal H, Küçükemre-Aydin B. A novel mutation in the SLC19A2 gene in a Turkish male with thiamine-responsive megaloblastic anemia syndrome. Turk J Pediatr 2019; 61: 257-260. Thiamine-responsive megaloblastic anemia (TRMA) is a very rare syndrome characterized by the triad of early onset megaloblastic anemia, sensorineural deafness and diabetes mellitus. Here we report, a 5-year-old boy who presented with transfusion dependent anemia and diabetes mellitus and was diagnosed with TRMA. Besides reporting a novel mutation of the causative gene SLC19A2, we wanted to emphasize this syndrome in the aspect of coexistence of insulin dependent diabetes, transfusion dependent anemia and thrombocytopenia.

A Novel Mutation of SLC19A2 in a Chinese Zhuang Ethnic Family with Thiamine-Responsive Megaloblastic Anemia.

BACKGROUND/AIMS: Thiamine-responsive megaloblastic anemia syndrome is a rare autosomal recessive disorder resulting from mutations in SLC19A2, and is mainly characterized by megaloblastic anemia, diabetes, and progressive sensorineural hearing loss. METHODS: We study a Chinese Zhuang ethnicity family with thiamine-responsive megaloblastic anemia. The proband of the study presented with anemia and diabetes, similar to his late brother, as well as visual impairment. All clinical manifestations were corrected with thiamine (30 mg/d) supplementation for 1-3 months, except for visual impairment, which was irreversible. The presence of mutations in all exons and the flanking sequences of the SLC19A2 gene were analyzed in this family based on the proband's and his brother's clinical data. Computer analysis and prediction of the protein conformation of mutant THTR-1. The relative concentration of thiamine pyrophosphate in the proband's whole blood before and after initiation of thiamine supplement was measured by high performance liquid chromatography (HPLC). RESULTS: Gene sequencing showed a homozygous mutation in exon 6 of the SLC19A2 gene (c.1409insT) in the proband. His parents and sister were diagnosed as heterozygous carriers of the c.1409insT mutation. Computer simulation showed that the mutations caused a change in protein conformation. HPLC results suggested that the relative concentration of thiamine pyrophosphate in the proband's whole blood after thiamine supplement was significantly different (P=0.016) from that at baseline. CONCLUSIONS: This novel homozygous mutation (c.1409insT) caused the onset of thiamine-responsive megaloblastic anemia in the proband.

Pancytopenia in an adult patient with thiamine-responsive megaloblastic anaemia.

Thiamine-responsive megaloblastic anaemia (TRMA) is a syndrome associated with megaloblastic anaemia, diabetes mellitus and sensorineural deafness, due to mutations in the SLC19A2 gene, which codes for a thiamine carrier protein. Oral thiamine supplementation is the main treatment. We report the case of a 25-year-old woman known for TRMA, who presented with pancytopenia (haemoglobin 7.6 g/dL, leucocytes 2.9×109/L, thrombocytes 6×109/L) revealed by dyspnoea. Investigations excluded coagulopathy, a recent viral infection, vitamin and iron deficiencies, and a malignant process. We later found out that thiamine treatment had been discontinued 5 weeks before, due to prescription error. Parenteral thiamine administration resulted in the recovery of haematopoiesis within 3 weeks. Pancytopenia is uncommon in patients with TRMA. Pre-existing medullary impairment caused by the patient's daily antipsychotic medications or the natural course of the syndrome may explain the severity of the laboratory findings in our patient.

Organic cation transporter 1 (OCT1) modulates multiple cardiometabolic traits through effects on hepatic thiamine content.

A constellation of metabolic disorders, including obesity, dysregulated lipids, and elevations in blood glucose levels, has been associated with cardiovascular disease and diabetes. Analysis of data from recently published genome-wide association studies (GWAS) demonstrated that reduced-function polymorphisms in the organic cation transporter, OCT1 (SLC22A1), are significantly associated with higher total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride (TG) levels and an increased risk for type 2 diabetes mellitus, yet the mechanism linking OCT1 to these metabolic traits remains puzzling. Here, we show that OCT1, widely characterized as a drug transporter, plays a key role in modulating hepatic glucose and lipid metabolism, potentially by mediating thiamine (vitamin B1) uptake and hence its levels in the liver. Deletion of Oct1 in mice resulted in reduced activity of thiamine-dependent enzymes, including pyruvate dehydrogenase (PDH), which disrupted the hepatic glucose-fatty acid cycle and shifted the source of energy production from glucose to fatty acids, leading to a reduction in glucose utilization, increased gluconeogenesis, and altered lipid metabolism. In turn, these effects resulted in increased total body adiposity and systemic levels of glucose and lipids. Importantly, wild-type mice on thiamine deficient diets (TDs) exhibited impaired glucose metabolism that phenocopied Oct1 deficient mice. Collectively, our study reveals a critical role of hepatic thiamine deficiency through OCT1 deficiency in promoting the metabolic inflexibility that leads to the pathogenesis of cardiometabolic disease.

Thiamin.

Starting with a brief history of beriberi and the discovery that thiamin deficiency is its cause, the symptoms and signs are reviewed. None are pathognomonic. The disease has a low mortality and a long morbidity. The appearance of the patient can be deceptive, often being mistaken for psychosomatic disease in the early stages. The chemistry of thiamin and the laboratory methodology for depicting its deficiency are outlined. The diseases associated with thiamin deficiency, apart from malnutrition, include a number of genetically determined conditions where mutations, either in the cofactor relationship or a transporter, provide the etiology. It is emphasized that such mutations are often epigenetically responsive to megadoses of thiamin or one of its derivatives. The use of thiamin in clinical practice requires a high index of suspicion on the part of the clinician since it has a part to play in eating disorders, diabetes, neurodegenerative disease, and cancer. A high rate of critical illness and postsurgery thiamin deficiency have been reported, particularly those associated with gastrointestinal bypass. Emphasis is placed on thiamin deficiency as a major cause of asymmetric dysautonomia, because of the high degree of sensitivity to thiamin deficiency in the brainstem, cerebellum, and hypothalamus. The relationship of thiamin with regional pain syndrome, eosinophilic esophagitis, its analgesic capacity, and its preventive use in obstetrics is raised as a potential issue. The role of thiamin in SIDS and autism is outlined. It is emphasized that megadose thiamin is being used as a drug, either in stimulating the damaged cofactor/enzyme combination, or mitochondria.

[Defect of thiamine transport and activation and related disease].

Thiamine, also known as vitamin B1, is an important vitamin for the body. The activated form of thiamine pyrophosphate is involved in cell metabolism as an important co-enzyme. Defects of thiamine transport and activation may cause lack of thiamine and affection of cell metabolism, leading a variety of diseases. This review has summarized defects of thiamine transport and activation and related diseases.