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.

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.

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.

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.

Thiamine deficiency in childhood with attention to genetic causes: Survival and outcome predictors.

Primary and secondary conditions leading to thiamine deficiency have overlapping features in children, presenting with acute episodes of encephalopathy, bilateral symmetric brain lesions, and high excretion of organic acids that are specific of thiamine-dependent mitochondrial enzymes, mainly lactate, alpha-ketoglutarate, and branched chain keto-acids. Undiagnosed and untreated thiamine deficiencies are often fatal or lead to severe sequelae. Herein, we describe the clinical and genetic characterization of 79 patients with inherited thiamine defects causing encephalopathy in childhood, identifying outcome predictors in patients with pathogenic SLC19A3 variants, the most common genetic etiology. We propose diagnostic criteria that will aid clinicians to establish a faster and accurate diagnosis so that early vitamin supplementation is considered. Ann Neurol 2017;82:317-330.

First 2 cases with thiamine-responsive megaloblastic anemia in the Czech Republic, a rare form of monogenic diabetes mellitus: a novel mutation in the thiamine transporter SLC19A2 gene-intron 1 mutation c.204+2T>G.

Thiamine-responsive megaloblastic anemia (TRMA) is a rare autosomal recessive disorder caused by mutations in the SLC19A2 gene. To date at least 43 mutations have been reported for the gene encoding a plasma membrane thiamine transporter protein (THTR-1). TRMA has been reported in less than 80 cases worldwide. Here, we illustrate 2 female patients with TRMA first diagnosed in the Czech Republic and in central Europe being confirmed by sequencing of the THTR-1 gene SLC19A2. Both subjects are compound heterozygotes with 3 different mutations in the SLC19A2 gene. In case 2, the SLC19A2 intron 1 mutation c.204+2T>G has never been reported before. TRMA subjects are at risk of diabetic ketoacidosis during intercurrent disease and arrythmias. Thiamine supplementation has prevented hematological disorders over a few years in both pediatric subjects, and improved glycaemic control of diabetes mellitus. Patient 1 was suffering from hearing loss and rod-cone dystrophy at the time of diagnosis, however, she was unresponsive to thiamine substitution. Our patient 2 developed the hearing loss despite the early thiamine substitution, however no visual disorder had developed. The novel mutation described here extends the list of SLC19A2 mutations causing TRMA.

Spatial cognitive deficits in an animal model of Wernicke-Korsakoff syndrome are related to changes in thalamic VDAC protein concentrations.

Proteomic profiles of the thalamus and the correlation between the rats' performance on a spatial learning task and differential protein expression were assessed in the thiamine deficiency (TD) rat model of Wernicke-Korsakoff syndrome. Two-dimensional gel-electrophoresis detected 320 spots and a significant increase or decrease in seven proteins. Four proteins were correlated to rat behavioral performance in the Morris Water Maze. One of the four proteins was identified by mass spectrometry as Voltage-Dependent Anion Channels (VDACs). The association of VDAC is evident in trials in which the rats' performance was worst, in which the VDAC protein was reduced, as confirmed by Western blot. No difference was observed on the mRNA of Vdac genes, indicating that the decreased VDAC expression may be related to a post-transcriptional process. The results show that TD neurodegeneration involves changes in thalamic proteins and suggest that VDAC protein activity might play an important role in an initial stage of the spatial learning process.

Thiamine responsive megaloblastic anemia syndrome: a novel homozygous SLC19A2 gene mutation identified.

Thiamine responsive megaloblastic anemia syndrome (TRMAS) is a rare autosomal recessive disorder especially in countries where consanguinity is uncommon. Three main features are characteristic of the disease - megaloblastic anemia, early onset deafness, and non-type I diabetes. TRMAS is a Mendelian disorder; a gene SLC19A2 coding high affinity thiamine transporter mediating vitamin B1 uptake through cell membrane has been identified. We present the first patient with TRMAS in Lithuania - a 3-year-old boy born to a non-consanguineous family with a novel homozygous SLC19A2 gene mutation. The patient had insulin dependent diabetes (onset 11 months), respiratory illness (onset 11 months), bilateral profound hearing loss (onset at 7 months, verified at 20 months), refractory anemia (onset 2 years), and decreased vision acuity and photophobia (onset 2.5 years). The psychomotor abilities developed according to age. Phenotypic evaluation did not reveal any dysmorphic features. The clinical diagnosis of TRMAS was suspected and daily supplementation with thiamine 100 mg was started. The condition of the patient markedly improved several days after the initiation of treatment. The results of SLC19A2 gene molecular testing confirmed the clinical diagnosis - novel homozygous c.[205G>T], p.[(Val69Phe)] mutation changing conserved amino acid residue or even interfering the mRNA splicing. Clinical heterogeneity, diverse dynamics, and wide spectrum of symptoms are aggravating factors in the diagnosis. The possibility of treatment demands early recognition of disorder to facilitate the improvement of the patient's condition.

Defects of thiamine transport and metabolism.

Thiamine, in the form of thiamine pyrophosphate, is a cofactor for a number of enzymes which play important roles in energy metabolism. Although dietary thiamine deficiency states have long been recognised, it is only relatively recently that inherited defects in thiamine uptake, activation and the attachment of the active cofactor to target enzymes have been described, and the underlying genetic defects identified. Thiamine is transported into cells by two carriers, THTR1 and THTR2, and deficiency of these results in thiamine-responsive megaloblastic anaemia and biotin-responsive basal ganglia disease respectively. Defective synthesis of thiamine pyrophosphate has been found in a small number of patients with episodic ataxia, delayed development and dystonia, while impaired transport of thiamine pyrophosphate into the mitochondrion is associated with Amish lethal microcephaly in most cases. In addition to defects in thiamine uptake and metabolism, patients with pyruvate dehydrogenase deficiency and maple syrup urine disease have been described who have a significant clinical and/or biochemical response to thiamine supplementation. In these patients, an intrinsic structural defect in the target enzymes reduces binding of the cofactor and this can be overcome at high concentrations. In most cases, the clinical and biochemical abnormalities in these conditions are relatively non-specific, and the range of recognised presentations is increasing rapidly at present as new patients are identified, often by genome sequencing. These conditions highlight the value of a trial of thiamine supplementation in patients whose clinical presentation falls within the spectrum of documented cases.

Analysis of thiamine transporter genes in sporadic beriberi.

OBJECTIVE: Thiamine or vitamin B1 deficiency diminishes thiamine-dependent enzymatic activity, alters mitochondrial function, impairs oxidative metabolism, and causes selective neuronal death. We analyzed for the first time, the role of all known mutations within three specific thiamine carrier genes, SLC19 A2, SLC19 A3, and SLC25 A19, in a patient with atrophic beriberi, a multiorgan nutritional disease caused by thiamine deficiency. METHODS: A 44-year-old male alcoholic patient from Morocco developed massive bilateral leg edema, a subacute sensorimotor neuropathy, and incontinence. Despite normal vitamin B1 serum levels, his clinical picture was rapidly reverted by high-dose intramuscular thiamine treatment, suggesting a possible genetic resistance. We used polymerase chain reaction followed by amplicon sequencing to study all the known thiamine-related gene mutations identified within the Human Gene Mutation Database. RESULTS: Thirty-seven mutations were tested: 29 in SLC19 A2, 6 in SLC19 A3, and 2 in SLC25 A19. Mutational analyses showed a wild-type genotype for all sequences investigated. CONCLUSION: This is the first genetic study in beriberi disease. We did not detect any known mutation in any of the three genes in a sporadic dry beriberi patient. We cannot exclude a role for other known or unknown mutations, in the same genes or in other thiamine-associated genes, in the occurrence of this nutritional neuropathy.

The role of thiamine in cancer: possible genetic and cellular signaling mechanisms.

The relationship between supplemental vitamins and various types of cancer has been the focus of recent investigation, and supplemental vitamins have been reported to modulate cancer rates. A significant association has been demonstrated between cancer and low levels of thiamine in the serum. Genetic studies have helped identify a number of factors that link thiamine to cancer, including the solute carrier transporter (SLC19) gene, transketolase, transcription factor p53, poly(ADP-ribose) polymerase-1 gene, and the reduced form of nicotinamide adenine dinucleotide phosphate. Thiamine supplementation may contribute to a high rate of tumor cell survival, proliferation and chemotherapy resistance. Thiamine has also been implicated in cancer through its effects on matrix metalloproteinases, prostaglandins, cyclooxygenase-2, reactive oxygen species, and nitric oxide synthase. However, some studies have suggested that thiamine may exhibit some antitumor effects. The role of thiamine in cancer is controversial. However, thiamine deficiency may occur in patients with cancer and cause serious disorders, including Wernicke's encephalopathy, that require parenteral thiamine supplementation. A very high dose of thiamine produces a growth-inhibitory effect in cancer. Therefore, further investigations of thiamine in cancer are needed to clarify this relationship.

Reversible lactic acidosis in a newborn with thiamine transporter-2 deficiency.

Thiamine transporter-2 deficiency is a recessive disease caused by mutations in the SLC19A3 gene. Patients manifest acute episodes of encephalopathy; symmetric lesions in the cortex, basal ganglia, thalami or periaqueductal gray matter, and a dramatic response to biotin or thiamine. We report a 30-day-old patient with mutations in the SLC19A3 gene who presented with acute encephalopathy and increased level of lactate in the blood (8.6 mmol/L) and cerebrospinal fluid (7.12 mmol/L), a high excretion of α-ketoglutarate in the urine, and increased concentrations of the branched-chain amino acids leucine and isoleucine in the plasma. MRI detected bilateral and symmetric cortico-subcortical lesions involving the perirolandic area, bilateral putamina, and medial thalami. Some lesions showed low apparent diffusion coefficient values suggesting an acute evolution; others had high values likely to be subacute or chronic, most likely related to the perinatal period. After treatment with thiamine and biotin, irritability and opisthotonus disappeared, and the patient recovered consciousness. Biochemical disturbances also disappeared within 48 hours. After discontinuing biotin, the patient remained stable for 6 months on thiamine supplementation (20 mg/kg/day). The examination revealed subtle signs of neurologic sequelae, and MRI showed necrotic changes and volume loss in some affected areas. Our observations suggest that patients with thiamine transporter 2 deficiency may be vulnerable to metabolic decompensation during the perinatal period, when energy demands are high. Thiamine defects should be excluded in newborns and infants with lactic acidosis because prognosis largely depends on the time from diagnosis to thiamine supplementation.

Thiamine-responsive megaloblastic anaemia syndrome: long-term follow-up and mutation analysis of seven families.

AIM: Thiamine-responsive megaloblastic anaemia syndrome (TRMA) is the association of diabetes mellitus, anaemia and deafness, due to mutations in SLC19A2, encoding a thiamine transporter protein. This is a unique monogenic form of vitamin-dependent diabetes for which there is limited long-term data. We aimed to study genotype-phenotype relationships and long-term follow-up in our cohort. METHODS: We have studied 13 patients from seven families and have follow-up data for a median of 9 y (2-30 y). RESULTS: All patients originated from Kashmir or Punjab, and presented with non-immune, insulin-deficient diabetes mellitus, sensorineural deafness and a variable anaemia in the first 5 y of life, the anaemia progressing to megaloblastic and sideroblastic changes in the bone marrow. The anaemia and diabetes mellitus responded to oral thiamine hydrochloride 25 mg/d, but during puberty thiamine supplements became ineffective, and almost all patients require insulin therapy and regular blood transfusions in adulthood. All patients are homozygous for mutations in the SLC19A2 gene. We have identified a novel missense mutation (T158R) that was excluded in 100 control alleles. CONCLUSION: Diabetes in this syndrome is due to an insulin insufficiency that initially responds to thiamine supplements; however, most patients become fully insulin dependent after puberty. A mutation screening strategy is feasible and likely to identify mutations in almost all cases.

Increased "peripheral-type" benzodiazepine receptor sites and mRNA in thalamus of thiamine-deficient rats.

"Peripheral-type" benzodiazepine receptors (PTBRs) are highly expressed on the outer mitochondrial membrane of several types of glial cells. In order to further elucidate the nature of the early glial cell changes in thiamine deficiency, PTBR sites and PTBR mRNA were measured in thalamus, a brain structure which is particularly vulnerable to thiamine deficiency, of thiamine-deficient rats at presymptomatic and symptomatic stages of deficiency. PTBR sites were measured using an in vitro binding technique and the selective radio ligand [3H]-PK11195. PTBR gene expression was measured by RT-PCR using oligonucleotide primers based upon the published sequence of the cloned rat PTBR. Microglial and astrocytic changes in thalamus due to thiamine deficiency were assessed using immunohistochemistry and antibodies to specific microglial (ED-1) and astrocytic (GFAP) proteins respectively. Significant increases of [3H]-PK11195 binding sites and concomitantly increased PTBR mRNA were observed in thalamus at the symptomatic stage of thiamine deficiency, coincident with severe neuronal cell loss and increased GFAP-immunolabelling (indicative of reactive gliosis). Positron Emission Tomography using 11C-PK11195 could provide a novel approach to the diagnosis and assessment of the extent of thalamic damage due to thiamine deficiency in humans with Wernicke's Encephalopathy.