Biotin-responsive basal ganglia disease-linked mutations inhibit thiamine transport via hTHTR2: biotin is not a substrate for hTHTR2

Derivation of two iPSC lines (KAIMRCi004-A, KAIMRCi004-B) from a Saudi patient with Biotin-Thiamine-responsive Basal Ganglia Disease (BTBGD) carrying homozygous pathogenic missense variant in the SCL19A3 gene

The neurometabolic disorder known as biotin-thiamine-responsive basal ganglia disease (BTBGD) is a rare autosomal recessive condition linked to bi-allelic pathogenic mutations in the SLC19A3 gene. BTBGD is characterized by progressive encephalopathy, confusion, seizures, dysarthria, dystonia, and severe disabilities. Diagnosis is difficult due to the disease's rare nature and diverse clinical characteristics. The primary treatment for BTBGD at this time is thiamine and biotin supplementation, while its long-term effectiveness is still being investigated. In this study, we have generated two clones of induced pluripotent stem cells (iPSCs) from a 10-year-old female BTBGD patient carrying a homozygous mutation for the pathogenic variant in exon 5 of the SLC19A3 gene, c.1264A > G (p.Thr422Ala). We have confirmed the pluripotency of the generated iPS lines and successfully differentiated them to neural progenitors. Because our understanding of genotype-phenotype correlations in BTBGD is limited, the establishment of BTBGD-iPSC lines with a homozygous SLC19A3 mutation provides a valuable cellular model to explore the molecular mechanisms underlying SLC19A3-associated cellular dysfunction. This model holds potential for advancing the development of novel therapeutic strategies.

Biotin Homeostasis and Human Disorders: Recent Findings and Perspectives

Biotin (vitamin B7, or vitamin H) is a water-soluble B-vitamin that functions as a cofactor for carboxylases, i.e., enzymes involved in the cellular metabolism of fatty acids and amino acids and in gluconeogenesis; moreover, as reported, biotin may be involved in gene regulation. Biotin is not synthesized by human cells, but it is found in food and is also produced by intestinal bacteria. Biotin status/homeostasis in human individuals depends on several factors, including efficiency/deficiency of the enzymes involved in biotin recycling within the human organism (biotinidase, holocarboxylase synthetase), and/or effectiveness of intestinal uptake, which is mainly accomplished through the sodium-dependent multivitamin transporter. In the last years, administration of biotin at high/"pharmacological" doses has been proposed to treat specific defects/deficiencies and human disorders, exhibiting mainly neurological and/or dermatological symptoms and including biotinidase deficiency, holocarboxylase synthetase deficiency, and biotin-thiamine-responsive basal ganglia disease. On the other hand, according to warnings of the Food and Drug Administration, USA, high biotin levels can affect clinical biotin-(strept)avidin assays and thus lead to false results during quantification of critical biomarkers. In this review article, recent findings/advancements that may offer new insight in the abovementioned research fields concerning biotin will be presented and briefly discussed.

Case report: biotin-thiamine-responsive basal ganglia disease with severe subdural hematoma on magnetic resonance imaging

Background: Biotin-thiamine-responsive basal ganglia disease (BTBGD) is a rare, treatable autosomal recessive neurometabolic disorder. This condition eventually leads to severe disability and death if not treated correctly. The clinical features of BTBGD, especially those with unusual complications, are not widely known by neurologists or pediatricians.Case presentation: A 4-month-old male infant was admitted to the hospital with a history of cough for the past 7 days and convulsions of 6 h duration. Physical examination showed confusion, bilateral pupillary light reflex delays, hypertonia of limbs, and brisk tendon reflexes of the limbs. Brain magnetic resonance imaging (MRI) showed multiple abnormal signals in the bilateral basal ganglia, lobes, corpus callosum, brainstem, and brain atrophy. However, his condition continued to worsen. Computed tomography performed 3 months later showed severe subdural hematoma and effusion. Subsequently, he underwent puncture drainage; however, his condition did not improve postoperatively. Repeated MRIs showed increasing subdural hematoma and effusion, and brain atrophy. The patient was diagnosed with BTBGD following whole-genome sequencing, which identified a novel compound heterozygous mutation of SLC19A3 gene. He was treated with biotin and thiamine, and the symptoms gradually improved. Subsequent MRIs showed a decrease in the subdural hematoma and effusion and partial improvement in brain atrophy.Conclusion: To the best of our knowledge, this is the first reported case of BTBGD, complicated by severe subdural hematoma. These observations extend our understanding of the clinical features, neuroimaging spectrum, and gene mutation spectrum of BTBGD. The phenotypic spectrum and pathophysiology of BTBGD are not completely understood and need to be studied further.

Efficacy of high thiamine dosage in treating patients with biotin thiamine responsive basal ganglia disease: a two case reports

BACKGROUND

Biotin-thiamine-responsive basal ganglia disease (BTBGD) is a rare, autosomal recessive neurometabolic disorder caused by mutations in the SLC19A3 gene and characterized by recurrent sub-acute episodes of encephalopathy. Patients with BTBGD have classical neuroimaging findings and a dramatic response to high doses of thiamine.

OBJECTIVE

To highlight the advantages of administering a higher dose of thiamine for patients with BTBGD who have not shown improvement with the standard recommended dosage.

RESULTS

Herein, we report on two Saudi girls with classical clinical and radiological findings of BTBGD. Hallmark symptoms in these patients included an acute onset of ataxia, tremor, slurred speech, dystonia, and dysphagia. The initial routine laboratory workups were unremarkable. Brain magnetic resonance imaging revealed extensive hyperintense signals in the bilateral basal ganglia, which suggested the diagnosis of a BTBGD. Hence started empirically on biotin 10 mg/kg/day and thiamine 40 mg/kg/day, but there was no noticeable improvement. After increasing the thiamine to 75 mg/kg/day the patients started to improve significantly. Genetic testing was requested and came positive for the mutation of the SLC19A3 gene. After two months of initiating the management, thiamine was reduced to 30 mg/kg/day. Subsequent follow-ups showed complete improvement in their condition with no apparent long-term sequel or relapse.

CONCLUSION

we conclude that administration of thiamine at a dosage of up to 40 mg/kg/day may not be sufficient in treating certain patients with BTBGD. Thus, considering a significantly higher dosage could potentially contribute to achieving remission.

Analysis of cerebrospinal fluid metabolites affected by WenDanTang based on ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry

WenDanTang (WDT) is a Chinese herbal formula used to treat various diseases, including neurodegenerative diseases. However, the neuroprotective metabolic pathways and the components involved in this process are not fully understood. In this study, we examined the neuroprotective metabolic pathways of WDT in rat brains using cerebrospinal fluid metabolomics and ultra-high-performance liquid chromatography-high-resolution mass spectrometry. Twelve rats were randomly divided into a WDT (administrated with WDT solution) and a control group. The ultra-high-performance liquid chromatography technique was used to explore the components of the WDT solution and cerebrospinal fluid, and secondary mass spectra of cerebrospinal fluid were used to identify possible brain-incorporating components after WDT. The results of the differential metabolism analysis showed that eight metabolites were typically altered (all p < 0.05). By comparing the secondary mass spectra of the cerebrospinal fluid of rats and WDT solution, two possible brain-incorporating components of WDT, stachydrine and α-methoxyphenylacetic acid, were identified. The data also suggested that WDT affects nucleotide metabolism, glutathione metabolism, and B-vitamin metabolic pathways, the central differential metabolic pathways. These data suggest that WDT protects neurons through its active components, such as stachydrine, and regulates biochemical metabolism to affect the brain's energy metabolism and antioxidant capacity.

Oxidative stress in Wernicke's encephalopathy

Wernicke's encephalopathy (WE) is a severe life-threatening disease that occurs due to vitamin B1 (thiamine) deficiency (TD). It is characterized by acute mental disorder, ataxia, and ophthalmoplegia. TD occurs because of the following reasons: insufficient intake, increased demand, and long-term drinking due to corresponding organ damage or failure. Recent studies showed that oxidative stress (OS) can damage organs and cause TD in the brain, which further leads to neurodegenerative diseases, such as WE. In this review, we discuss the effects of TD caused by OS on multiple organ systems, including the liver, intestines, and brain in WE. We believe that strengthening the human antioxidant system and reducing TD can effectively treat WE.

A Japanese patient with neonatal biotin-responsive basal ganglia disease

Biotin-responsive basal ganglia disease (BBGD) with SLC19A3 mutation was first reported in 1998, and over 30 mutations have been reported. We report a neonatal BBGD case with sudden-onset feeding difficulty and impaired consciousness. Encephalopathy resolved after the initiation of biotin and thiamine treatment. Genetic testing revealed a novel heterozygous mutation [c.384_387del, p.Tyr128fs];[c.265 A > C, p.Ser89Arg] in SLC19A3. Early treatment for BBGD is essential, especially with onset in the neonatal or early infancy period.

Next generation sequencing of Tunisian Leigh syndrome patients reveals novel variations: impact for diagnosis and treatment

Mitochondrial cytopathies, among which the Leigh syndrome (LS), are caused by variants either in the mitochondrial or the nuclear genome, affecting the oxidative phosphorylation process. The aim of the present study consisted in defining the molecular diagnosis of a group of Tunisian patients with LS.

Six children, belonging to five Tunisian families, with clinical and imaging presentations suggestive of LS were recruited. Whole mitochondrial DNA and targeted next-generation sequencing of a panel of 281 nuclear genes involved in mitochondrial physiology were performed. Bioinformatic analyses were achieved in order to identify deleterious variations.

A single m.10197G>A (p.Ala47Thr) variant was found in the mitochondrial MT-ND3 gene in one patient, while the others were related to autosomal homozygous variants: two c.1412delA (p.Gln471ArgfsTer42) and c.1264A>G (p.Thr422Ala) in SLC19A3, one c.454C>G (p.Pro152Ala) in SLC25A19 and one c.122G>A (p.Gly41Asp) in ETHE1.

Our findings demonstrate the usefulness of genomic investigations to improve LS diagnosis in consanguineous populations and further allow for treating the patients harboring variants in SLC19A3 and SLC25A19 that contribute to thiamine transport, by thiamine and biotin supplementation. Considering the Tunisian genetic background, the newly identified variants could be screened in patients with similar clinical presentation in related populations.

Human adipose tissue gene expression of solute carrier family 19 member 3 (SLC19A3); relation to obesity and weight-loss

OBJECTIVE

Adipose tissue is a specialized endocrine organ that is involved in modulating whole-body energy homeostasis and expresses a specific subset of genes, which may play a role in adipose tissue metabolism. The aim of this study was to search for novel adipose tissue-specific genes using a tissue panel of RNAseq expression profiles.

METHODS

RNAseq expression profiles from 53 human tissues were downloaded from the GTex database. SLC19A3 expression was analyzed by microarray or real-time PCR in two sets of paired subcutaneous and omental adipose tissue samples, in two studies with adipose tissue from persons with high or low body mass index (BMI), in adipose tissue from patients who underwent weight loss with a very-low caloric diet and during preadipocyte-adipocyte differentiation.

RESULTS

The RNAseq-based tissue distribution expression screen identified SLC19A3 (encoding the thiamine transporter 2) as adipose tissue-specific. SLC19A3 expression was higher in subcutaneous compared with omental adipose tissue in both sample sets (p = 0.043 and p < 0.001). Preadipocyte differentiation towards adipocytes resulted in increased SLC19A3 gene expression (p = 0.018 or less at all-time points). Subcutaneous adipose tissue expression of SLC19A3 was lower in persons with high BMI in both cohorts (p = 0.008, and p < 0.001) and increased during a weight-loss intervention (p = 0.006).

CONCLUSION

The specific adipose tissue expression pattern of SLC19A3, together with its regulation in obesity and during weight loss, indicate that it plays a key role in adipocyte metabolism.

Report of the Largest Chinese Cohort With SLC19A3 Gene Defect and Literature Review

Thiamine metabolism dysfunction syndrome 2 (THMD2) is a rare metabolic disorder caused by SLC19A3 mutations, inherited in autosomal recessive pattern. As a treatable disease, early diagnosis and therapy with vitamin supplementation is important to improve the prognosis. So far, the reported cases were mainly from Saudi Arab regions, and presented with relatively simple clinical course because of the hot spot mutation (T422A). Rare Chinese cases were described until now. In this study, we investigated 18 Chinese THMD2 patients with variable phenotypes, and identified 23 novel SLC19A3 mutations, which expanded the genetic and clinical spectrum of the disorder. Meanwhile, we reviewed all 146 reported patients from different countries. Approximately 2/3 of patients presented with classical BTBGD, while 1/3 of patients manifested as much earlier onset and poor prognosis, including infantile Leigh-like syndrome, infantile spasms, neonatal lactic acidosis and infantile BTBGD. Literature review showed that elevated lactate in blood and CSF, as well as abnormal OXPHOS activities of muscle or skin usually correlated with infantile phenotypes, which indicated poor outcome. Brainstem involvement on MRI was more common in deceased cases. Thiamine supplementation is indispensable in the treatment of THMD2, whereas combination of biotin and thiamine is not superior to thiamine alone. But biotin supplementation does work in some patients. Genotypic-phenotypic correlation remains unclear which needs further investigation, and biallelic truncated mutations usually led to more severe phenotype.

Early Infantile Thiamine Transporter-2 Deficiency with Epileptic Spasms—A Phenotypic Spectrum with a Novel Mutation

Epileptic seizures are a frequent feature of thiamine transporter deficiency that may present as a clinical continuum between severe epileptic encephalopathy and mixed focal or generalized seizures. Thiamine metabolism dysfunction syndrome 2 (MIM: 607483) or biotin-thiamine-responsive basal ganglia disease (BTBGD) due to biallelic pathogenic mutation in the SLC19A3 gene is a well-recognized cause of early infantile encephalopathy with a Leigh syndrome-like presentation and a lesser-known phenotype of atypical infantile spasms. We reported a 4-month-old infant who presented with progressive epileptic spasms since 1 month of age, psychomotor retardation, and lactic acidosis. Magnetic resonance imaging (MRI) revealed altered signal intensities in bilateral thalamic and basal ganglia, cerebellum, brainstem, cortical and subcortical white matter. Whole exome sequencing identified a homozygous ENST00000258403.3: c.871G > C (p.Gly291Arg) variant in the SLC19A3 gene. We elucidate the features in the proband, which were an amalgamation of both the above subtypes of the SLC19A3 associated with early infantile encephalopathy. We also highlight the features which were atypical for either “Leigh syndrome-like” or “atypical infantile spasm” phenotypes and suggest that the two separate entities can be merged as a clinical continuum. Treatment outcome with high-dose biotin and thiamine is promising. In addition, we report a novel pathogenic variant in the SLC19A3 gene.

Biotin-Thiamine-Responsive Basal Ganglia Disease in Children: A Treatable Neurometabolic Disorder

Biotin-thiamine-responsive basal ganglia disease is a rare, autosomal recessive, treatable, neurometabolic disorder associated with biallelic pathogenic variations in the SLC19A3 gene. The condition may present as an early-childhood encephalopathy, an early-infantile lethal encephalopathy with lactic acidosis, with or without infantile spasms, or a late-onset Wernicke-like encephalopathy. The key radiological features are bilateral, symmetrical lesions in the caudate, putamen, and medial thalamus, with variable extension into the brain stem, cerebral cortex, and cerebellum. Treatment is life long and includes initiation of high dose biotin and thiamine. Genetic testing confirms the diagnosis. The prognosis depends on the time from diagnosis to the time of vitamin supplementation. The genotype-phenotype correlations are not clear yet, but the early infantile phenotype portends a poorer prognosis. We provide a brief overview of the disorder and emphasize the initiation of high-dose biotin and thiamine in infants and children with unexplained encephalopathy and basal ganglia involvement.

Targeted SLC19A3 gene sequencing of 3000 Saudi newborn: a pilot study toward newborn screening

Background

Biotin–thiamine‐responsive basal ganglia disease (BTBGD) is an autosomal recessive neurometabolic disorder mostly presented in children. The disorder is described as having subacute encephalopathy with confusion, dystonia, and dysarthria triggered by febrile illness that leads to neuroregression and death if untreated. Using biotin and thiamine at an early stage of the disease can lead to significant improvement.

Methods

BTBGD is a treatable disease if diagnosed at an early age and has been frequently reported in Saudi population. Keeping this in mind, the current study screened 3000 Saudi newborns for the SLC19A3 gene mutations using target sequencing, aiming to determine the carrier frequency in Saudi Population and whether BTBGD is a good candidate to be included in the newborn‐screened disorders.

Results

Using targeted gene sequencing, DNA from 3000 newborns Saudi was screened for the SLC19A3 gene mutations using standard methods. Screening of the SLC19A3 gene revealed a previously reported heterozygous missense mutation (c.1264A>G (p.Thr422Ala) in six unrelated newborns. No probands having homozygous pathogenic mutations were found in the studied cohort. The variant has been frequently reported previously in homozygous state in Saudi population, making it a hot spot mutation. The current study showed that the carrier frequency of SLC19A3 gene mutation is 1 of 500 in Saudi newborns.

Conclusion

For the first time in the literature, we determined the carrier frequency of SLC19A3 gene mutation in Saudi population. The estimated prevalence is too rare in Saudi population (at least one in million); therefore, the data are not in favor of including such very rare disorders in newborn screening program at population level. However, a larger cohort is needed for a more accurate estimate.

Biotin in metabolism, gene expression, and human disease

Biotin is a water-soluble vitamin that belongs to the vitamin B complex and which is an essential nutrient of all living organisms from bacteria to man. In eukaryotic cells biotin functions as a prosthetic group of enzymes, collectively known as biotin-dependent carboxylases that catalyze key reactions in gluconeogenesis, fatty acid synthesis, and amino acid catabolism. Enzyme-bound biotin acts as a vector to transfer a carboxyl group between donor and acceptor molecules during carboxylation reactions. In recent years, evidence has mounted that biotin also regulates gene expression through a mechanism beyond its role as a prosthetic group of carboxylases. These activities may offer a mechanistic background to a developing literature on the action of biotin in neurological disorders. This review summarizes the role of biotin in activating carboxylases and proposed mechanisms associated with a role in gene expression and in ameliorating neurological disease.

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.

Biotin-Thiamine Responsive Encephalopathy: Report of an Egyptian Family with a Novel SLC19A3 Mutation and Review of the Literature

Biotin-thiamine responsive basal ganglia disease (BTRBGD) is an autosomal recessive neurometabolic disorder with poor genotype-phenotype correlation, caused by mutations in the SLC19A3 gene on chromosome 2q36.6. The disease is characterized by three stages: stage 1 is a sub-acute encephalopathy often triggered by febrile illness; stage 2 is an acute encephalopathy with seizures, loss of motor function, developmental regression, dystonia, external ophthalmoplegia, dysphagia, and dysarthria; stage 3 is represented by chronic or slowly progressive encephalopathy. Clinical and biochemical findings, as well as the magnetic resonance imaging (MRI) pattern, resemble those of Leigh's syndrome, so that BTRBGD can be misdiagnosed as a mitochondrial encephalopathy.Here we report the clinical and radiological phenotypes of two siblings diagnosed with BTRBGD in which a novel SLC19A3 mutation (NM_025243.3: c.548C > T; p.Ala183Val) was found by whole exome sequencing (WES) of the family members.

Are diagnostic magnetic resonance patterns life-saving in children with biotin-thiamine-responsive basal ganglia disease?

BACKGROUND

Biotin-thiamine responsive basal ganglia disease (BTBGD) is an autosomal recessive disorder caused by mutations in the SLC19A3 gene and characterized by recurrent sub-acute episodes of encephalopathy that typically starts in early childhood. This study describes characteristic clinical and magnetic resonance imaging (MRI) findings of six cases of BTBGD diagnosed with newly identified mutations and genetically confirmed, with very early and different presentations compared to cases in the previous literature.

METHODS

Six patients referred from different centers with similar clinical findings were diagnosed with BTBGD with newly identified mutations in the SLC19A3 gene. Two novel mutations in the SLC19A3 gene were identified in two patients at whole exome sequencing analysis. The clinical characteristics, responses to treatment, and electroencephalography (EEG) and MRI findings of these patients were examined. The other four patients presented with similar clinical and cranial MRI findings. These patients were therefore started on high-dose biotin and thiamine therapy, and mutation analysis concerning the SLC19A3 gene was performed. Responses to treatment, clinical courses, EEG findings and follow-up MRI were recorded for all these patients.

RESULTS

Age at onset of symptoms ranged from 1 to 3 months. The first symptoms were generally persistent crying and restlessness. Seizures occurred in five of the six patients. Cranial magnetic resonance imaging revealed involvement in the basal ganglia, brain stem, and the parietal and frontal regions in general. The first two patients were siblings, and both exhibited a novel mutation of the SLC19A3 gene. The third and fourth patients were also siblings and also exhibited a similar novel mutation of the SLC19A3 gene. The fifth and sixth patients were not related, and a newly identified mutation was detected in both these subjects. Three novel mutations were thus detected in six patients.

CONCLUSION

BTBGD is a progressive disease that can lead to severe disability and death. Early diagnosis of treatable diseases such as BTBGD is important in order to prevent long-term complications and disability.

Gastrointestinal Handling of Water-Soluble Vitamins

Nine compounds are classified as water-soluble vitamins, eight B vitamins and one vitamin C. The vitamins are mandatory for the function of numerous enzymes and lack of one or more of the vitamins may lead to severe medical conditions. All the vitamins are supplied by food in microgram to milligram quantities and in addition some of the vitamins are synthesized by the intestinal microbiota. In the gastrointestinal tract, the vitamins are liberated from binding proteins and for some of the vitamins modified prior to absorption. Due to their solubility in water, they all require specific carriers to be absorbed. Our current knowledge concerning each of the vitamins differs in depth and focus and is influenced by the prevalence of conditions and diseases related to lack of the individual vitamin. Because of that we have chosen to cover slightly different aspects for the individual vitamins. For each of the vitamins, we summarize the physiological role, the steps involved in the absorption, and the factors influencing the absorption. In addition, for some of the vitamins, the molecular base for absorption is described in details, while for others new aspects of relevance for human deficiency are included. © 2018 American Physiological Society. Compr Physiol 8:1291-1311, 2018.

Compound heterozygous SLC19A3 mutations further refine the critical promoter region for biotin-thiamine-responsive basal ganglia disease

Mutations in the gene SLC19A3 result in thiamine metabolism dysfunction syndrome 2, also known as biotin-thiamine-responsive basal ganglia disease (BTBGD). This neurometabolic disease typically presents in early childhood with progressive neurodegeneration, including confusion, seizures, and dysphagia, advancing to coma and death. Treatment is possible via supplement of biotin and/or thiamine, with early treatment resulting in significant lifelong improvements. Here we report two siblings who received a refined diagnosis of BTBGD following whole-genome sequencing. Both children inherited compound heterozygous mutations from unaffected parents; a missense single-nucleotide variant (p.G23V) in the first transmembrane domain of the protein, and a 4808-bp deletion in exon 1 encompassing the 5′ UTR and minimal promoter region. This deletion is the smallest promoter deletion reported to date, further defining the minimal promoter region of SLC19A3. Unfortunately, one of the siblings died prior to diagnosis, but the other is showing significant improvement after commencement of therapy. This case demonstrates the power of whole-genome sequencing for the identification of structural variants and subsequent diagnosis of rare neurodevelopmental disorders.

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.

Biotin: From Nutrition to Therapeutics

Although frank symptomatic biotin deficiency is rare, some evidence suggests that marginal biotin deficiency occurs spontaneously in a substantial proportion of women during normal human pregnancy and might confer an increased risk of birth defects. Herein I review 1) advances in assessing biotin status, including the relation between acylcarnitine excretion and biotin status; 2) recent studies of biotin status in pregnancy; 3) advances in understanding the role of biotin in gene expression and the potential roles of biotinylated proteins that are neither histones nor carboxylases; and 4) novel large-dose biotin supplementation as therapy for multiple sclerosis. The review concludes with a summary of recent studies that have reported potentially dangerous erroneous results in individuals consuming large amounts of biotin for measurements of various plasma hormones for common clinical assays that use streptavidin-biotin technology.

Biotin-thiamine responsive basal ganglia disease: Identification of a pyruvate peak on brain spectroscopy, novel mutation in SLC19A3, and calculation of prevalence based on allele frequencies from aggregated next-generation sequencing data

Biotin-thiamine responsive basal ganglia disease is an inborn error of metabolism caused by mutations in SLC19A3, encoding a transporter of thiamine across the plasma membrane. We report a novel mutation identified in the homozygous state in a patient with typical brain MRI changes. In addition, this patient had markedly elevated CSF pyruvate, a low lactate-to-pyruvate molar ratio, and an abnormal pyruvate peak at 2.4 ppm on brain magnetic resonance spectroscopy. Using aggregated exome sequencing data, we calculate the carrier frequency of mutations in SLC19A3 as 1 in 232 individuals in the general population, for an estimated prevalence of the disease of approximately 1 in 215,000 individuals. The disease is thus more frequent than previously recognized, and the presence of a pyruvate peak on spectroscopy could serve as an important diagnostic clue.

The blood-brain barrier fatty acid transport protein 1 (FATP1/SLC27A1) supplies docosahexaenoic acid to the brain, and insulin facilitates transport

We purposed to clarify the contribution of fatty acid transport protein 1 (FATP1/SLC 27A1) to the supply of docosahexaenoic acid (DHA) to the brain across the blood-brain barrier in this study. Transport experiments showed that the uptake rate of [¹⁴ C]-DHA in human FATP1-expressing HEK293 cells was significantly greater than that in empty vector-transfected (mock) HEK293 cells. The steady-state intracellular DHA concentration was nearly 2-fold smaller in FATP1-expressing than in mock cells, suggesting that FATP1 works as not only an influx, but also an efflux transporter for DHA. [¹⁴ C]-DHA uptake by a human cerebral microvascular endothelial cell line (hCMEC/D3) increased in a time-dependent manner, and was inhibited by unlabeled DHA and a known FATP1 substrate, oleic acid. Knock-down of FATP1 in hCMEC/D3 cells with specific siRNA showed that FATP1-mediated uptake accounts for 59.2-73.0% of total [¹⁴ C]-DHA uptake by the cells. Insulin treatment for 30 min induced translocation of FATP1 protein to the plasma membrane in hCMEC/D3 cells and enhanced [¹⁴ C]-DHA uptake. Immunohistochemical analysis of mouse brain sections showed that FATP1 protein is preferentially localized at the basal membrane of brain microvessel endothelial cells. We found that two neuroprotective substances, taurine and biotin, in addition to DHA, undergo FATP1-mediated efflux. Overall, our results suggest that FATP1 localized at the basal membrane of brain microvessels contributes to the transport of DHA, taurine and biotin into the brain, and insulin rapidly increases DHA supply to the brain by promoting translocation of FATP1 to the membrane. Read the Editorial Comment for this article on page 324.

Selective accumulation of biotin in arterial chemoreceptors: requirement for carotid body exocytotic dopamine secretion

KEY POINTS

Biotin, a vitamin whose main role is as a coenzyme for carboxylases, accumulates at unusually large amounts within cells of the carotid body (CB). In biotin-deficient rats biotin rapidly disappears from the blood; however, it remains at relatively high levels in CB glomus cells. The CB contains high levels of mRNA for SLC5a6, a biotin transporter, and SLC19a3, a thiamine transporter regulated by biotin. Animals with biotin deficiency exhibit pronounced metabolic lactic acidosis. Remarkably, glomus cells from these animals have normal electrical and neurochemical properties. However, they show a marked decrease in the size of quantal dopaminergic secretory events. Inhibitors of the vesicular monoamine transporter 2 (VMAT2) mimic the effect of biotin deficiency. In biotin-deficient animals, VMAT2 protein expression decreases in parallel with biotin depletion in CB cells. These data suggest that dopamine transport and/or storage in small secretory granules in glomus cells depend on biotin.

ABSTRACT

Biotin is a water-soluble vitamin required for the function of carboxylases as well as for the regulation of gene expression. Here, we report that biotin accumulates in unusually large amounts in cells of arterial chemoreceptors, carotid body (CB) and adrenal medulla (AM). We show in a biotin-deficient rat model that the vitamin rapidly disappears from the blood and other tissues (including the AM), while remaining at relatively high levels in the CB. We have also observed that, in comparison with other peripheral neural tissues, CB cells contain high levels of SLC5a6, a biotin transporter, and SLC19a3, a thiamine transporter regulated by biotin. Biotin-deficient rats show a syndrome characterized by marked weight loss, metabolic lactic acidosis, aciduria and accelerated breathing with normal responsiveness to hypoxia. Remarkably, CB cells from biotin-deficient animals have normal electrophysiological and neurochemical (ATP levels and catecholamine synthesis) properties; however, they exhibit a marked decrease in the size of quantal catecholaminergic secretory events, which is not seen in AM cells. A similar differential secretory dysfunction is observed in CB cells treated with tetrabenazine, a selective inhibitor of the vesicular monoamine transporter 2 (VMAT2). VMAT2 is highly expressed in glomus cells (in comparison with VMAT1), and in biotin-deficient animals VMAT2 protein expression decreases in parallel with the decrease of biotin accumulated in CB cells. These data suggest that biotin has an essential role in the homeostasis of dopaminergic transmission modulating the transport and/or storage of transmitters within small secretory granules in glomus cells.

CDKN2B, SLC19A3 and DLEC1 promoter methylation alterations in the bone marrow of patients with acute myeloid leukemia during chemotherapy

Previous studies have demonstrated that promoter hypermethylation of tumor suppressor genes contributes to the occurrence and development of acute myeloid leukemia (AML). However, the association of DNA methylation with chemotherapeutic outcomes remains unknown. In the present study, 15 patients with AML were recruited, and the promoter methylation status of cyclin-dependent kinase inhibitor 2B (CDKN2B), solute carrier family 19 member 3 (SLC19A3) and deleted in lung and esophageal cancer 1 (DLEC1) genes was examined prior to and following various chemotherapeutic regimens in order to identify any alterations. The results suggested that chemotherapy-induced hypermethylation of CDKN2B and DLEC1 may be specific to males and females, respectively, and that there were no alterations in SLC19A3 methylation following chemotherapy. These results may provide an improved understanding of gene methylation to guide the development of an individualized chemotherapy for AML. Due to the complexity of AML and the wide range of treatment types, future studies with a larger sample size are required in order to verify the results of the present investigation.

Biotin and Thiamine Responsive Basal Ganglia Disease--A vital differential diagnosis in infants with severe encephalopathy

We report two siblings of Swedish origin with infantile Biotin and Thiamine Responsive Basal Ganglia Disease (BTRBG).

CASE REPORT

Initial symptoms were in both cases lethargia, with reduced contact and poor feeding from the age of 5 weeks. Magnetic resonance imaging showed altered signal in the basal ganglia, along with grey and white matter abnormalities. The diagnosis BTRBG was not recognized in the first sibling who died at the age of 8 weeks. The second sibling was started on biotin and thiamine immediately upon development of symptoms, leading to clinical improvement and partial reversion of the magnetic resonance imaging findings. Genetic analysis of the SLC19A3 gene identified two mutations, c.74dupT and c.1403delA, carried in compound heterozygous form in both boys, each inherited from one parent.

COMMENTS

The first mutation has previously been described in children with BTRBG, and the second mutation is novel. Although the clinical picture in BTRGB is very severe it is also rather unspecific and the diagnosis may be missed.

CONCLUSION

This report highlights the importance of considering biotin and thiamine treatment also in a European infant born to non-consanguineous parents, who presents with symptoms of acute/subacute encephalopathy.

Pharmacokinetics and pharmacodynamics of MD1003 (high-dose biotin) in the treatment of progressive multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is a chronic, potentially highly disabling neurological disorder. No disease-modifying treatments are approved in the progressive and not active forms of the disease.

AREAS COVERED

High doses of biotin were tested in an open-label pilot study involving 23 patients with progressive MS and reported positive results. A randomized, double-blind, placebo-controlled trial in 154 progressive MS patients confirmed the beneficial effect of MD1003 (high-dose biotin) on reversing or stabilizing disability progression, with a good safety profile. It is proposed that MD1003 in progressive MS 1) increases energy production in demyelinated axons and/or 2) enhances myelin synthesis in oligodendrocytes. Biotin is highly bioavailable; absorption and excretion are rapid. The major route of elimination is urinary excretion.

EXPERT OPINION

A high oral dose of biotin seems generally well tolerated but a few important safety concerns were identified: 1) teratogenicity in one species and 2) interference with some biotin-based laboratory immunoassays. The animal toxicity data are limited at such high doses. Further preclinical studies would be useful to address the mechanism of action of MD1003. Assessment of clinical benefit duration in responders will be also very important to set. Results of randomized, placebo-controlled trial are reassuring and provide hope for the treatment of progressive MS.

Novel SLC19A3 Promoter Deletion and Allelic Silencing in Biotin-Thiamine-Responsive Basal Ganglia Encephalopathy

Background

Biotin-thiamine responsive basal ganglia disease is a severe, but potentially treatable disorder caused by mutations in the SLC19A3 gene. Although the disease is inherited in an autosomal recessive manner, patients with typical phenotypes carrying single heterozygous mutations have been reported. This makes the diagnosis uncertain and may delay treatment.

Methods and Results

In two siblings with early-onset encephalopathy dystonia and epilepsy, whole-exome sequencing revealed a novel single heterozygous SLC19A3 mutation (c.337T>C). Although Sanger-sequencing and copy-number analysis revealed no other aberrations, RNA-sequencing in brain tissue suggested the second allele was silenced. Whole-genome sequencing resolved the genetic defect by revealing a novel 45,049 bp deletion in the 5’-UTR region of the gene abolishing the promoter. High dose thiamine and biotin therapy was started in the surviving sibling who remains stable. In another patient two novel compound heterozygous SLC19A3 mutations were found. He improved substantially on thiamine and biotin therapy.

Conclusions

We show that large genomic deletions occur in the regulatory region of SLC19A3 and should be considered in genetic testing. Moreover, our study highlights the power of whole-genome sequencing as a diagnostic tool for rare genetic disorders across a wide spectrum of mutations including non-coding large genomic rearrangements.

Free-thiamine is a potential biomarker of thiamine transporter-2 deficiency: a treatable cause of Leigh syndrome

Thiamine transporter-2 deficiency is caused by mutations in the SLC19A3 gene. As opposed to other causes of Leigh syndrome, early administration of thiamine and biotin has a dramatic and immediate clinical effect. New biochemical markers are needed to aid in early diagnosis and timely therapeutic intervention. Thiamine derivatives were analysed by high performance liquid chromatography in 106 whole blood and 38 cerebrospinal fluid samples from paediatric controls, 16 cerebrospinal fluid samples from patients with Leigh syndrome, six of whom harboured mutations in the SLC19A3 gene, and 49 patients with other neurological disorders. Free-thiamine was remarkably reduced in the cerebrospinal fluid of five SLC19A3 patients before treatment. In contrast, free-thiamine was slightly decreased in 15.2% of patients with other neurological conditions, and above the reference range in one SLC19A3 patient on thiamine supplementation. We also observed a severe deficiency of free-thiamine and low levels of thiamine diphosphate in fibroblasts from SLC19A3 patients. Surprisingly, pyruvate dehydrogenase activity and mitochondrial substrate oxidation rates were within the control range. Thiamine derivatives normalized after the addition of thiamine to the culture medium. In conclusion, we found a profound deficiency of free-thiamine in the CSF and fibroblasts of patients with thiamine transporter-2 deficiency. Thiamine supplementation led to clinical improvement in patients early treated and restored thiamine values in fibroblasts and cerebrospinal fluid.

Targeting demyelination and virtual hypoxia with high-dose biotin as a treatment for progressive multiple sclerosis

Progressive multiple sclerosis (MS) is a severely disabling neurological condition, and an effective treatment is urgently needed. Recently, high-dose biotin has emerged as a promising therapy for affected individuals. Initial clinical data have shown that daily doses of biotin of up to 300 mg can improve objective measures of MS-related disability. In this article, we review the biology of biotin and explore the properties of this ubiquitous coenzyme that may explain the encouraging responses seen in patients with progressive MS. The gradual worsening of neurological disability in patients with progressive MS is caused by progressive axonal loss or damage. The triggers for axonal loss in MS likely include both inflammatory demyelination of the myelin sheath and primary neurodegeneration caused by a state of virtual hypoxia within the neuron. Accordingly, targeting both these pathological processes could be effective in the treatment of progressive MS. Biotin is an essential co-factor for five carboxylases involved in fatty acid synthesis and energy production. We hypothesize that high-dose biotin is exerting a therapeutic effect in patients with progressive MS through two different and complementary mechanisms: by promoting axonal remyelination by enhancing myelin production and by reducing axonal hypoxia through enhanced energy production. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Treatment of biotin-responsive basal ganglia disease: Open comparative study between the combination of biotin plus thiamine versus thiamine alone

OBJECTIVE

To compare the combination of biotin plus thiamine to thiamine alone in treating patients with biotin-responsive basal ganglia disease in an open-label prospective, comparative study.

METHODS

twenty patients with genetically proven biotin-responsive basal ganglia disease were enrolled, and received for at least 30 months a combination of biotin plus thiamine or thiamine alone. The outcome measures included duration of the crisis, number of recurrence/admissions, the last neurological examination, the severity of dystonia using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS), and the brain MRI findings during the crisis and after 30 months of follow-up.

RESULTS

Ten children with a mean age of 6 years(1/2) were recruited in the biotin plus thiamine group (group 1) and ten children (6 females and 4 males) with a mean age of 6 years and 2 months were recruited in the thiamine group (group 2). After 2 years of follow-up treatment, 6 of 20 children achieved complete remission, 10 had minimal sequelae in the form of mild dystonia and dysarthria (improvement of the BFMDRS, mean: 80%), and 4 had severe neurologic sequelae. All these 4 patients had delayed diagnosis and management. Regarding outcome measures, both groups have a similar outcome regarding the number of recurrences, the neurologic sequelae (mean BFMDS score between the groups, p = 0.84), and the brain MRI findings. The only difference was the duration of the acute crisis: group 1 had faster recovery (2 days), versus 3 days in group 2 (p = 0.005).

CONCLUSION

Our study suggests that over 30 months of treatment, the combination of biotin plus thiamine is not superior to thiamine alone in the treatment of biotin-responsive basal ganglia disease.

Biotin-responsive basal ganglia disease: a case diagnosed by whole exome sequencing

Using whole exome sequencing, we confirmed a diagnosis of biotin-responsive basal ganglia disease (BBGD) accompanied by possible Kawasaki Disease. BBGD is an autosomal-recessive disease arising from a mutation of the SLC19A3 gene encoding the human thiamine transporter 2 protein, and usually manifests as subacute to acute encephalopathy. In this case, compound heterozygous mutations of SLC19A3, including a de novo mutation in one allele, was the cause of disease. Although a large number of genetic neural diseases have no efficient therapy, there are several treatable genetic diseases, including BBGD. However, to achieve better outcome and accurate diagnosis, therapeutic analysis and examination for disease confirmation should be done simultaneously. We encountered a case of possible Kawasaki disease, which had progressed to BBGD caused by an extremely rare genetic condition. Although the prevalence of BBGD is low, early recognition of this disease is important because effective improvement can be achieved by early biotin and thiamine supplementation.

Major involvement of Na(+) -dependent multivitamin transporter (SLC5A6/SMVT) in uptake of biotin and pantothenic acid by human brain capillary endothelial cells

The purpose of this study was to clarify the expression of Na(+) -dependent multivitamin transporter (SLC5A6/SMVT) and its contribution to the supply of biotin and pantothenic acid to the human brain via the blood-brain barrier. DNA microarray and immunohistochemical analyses confirmed that SLC5A6 is expressed in microvessels of human brain. The absolute expression levels of SLC5A6 protein in isolated human and monkey brain microvessels were 1.19 and 0.597 fmol/μg protein, respectively, as determined by a quantitative targeted absolute proteomics technique. Using an antibody-free method established by Kubo et al. (2015), we found that SLC5A6 was preferentially localized at the luminal membrane of brain capillary endothelium. Knock-down analysis using SLC5A6 siRNA showed that SLC5A6 accounts for 88.7% and 98.6% of total [(3) H]biotin and [(3) H]pantothenic acid uptakes, respectively, by human cerebral microvascular endothelial cell line hCMEC/D3. SLC5A6-mediated transport in hCMEC/D3 was markedly inhibited not only by biotin and pantothenic acid, but also by prostaglandin E2, lipoic acid, docosahexaenoic acid, indomethacin, ketoprofen, diclofenac, ibuprofen, phenylbutazone, and flurbiprofen. This study is the first to confirm expression of SLC5A6 in human brain microvessels and to provide evidence that SLC5A6 is a major contributor to luminal uptake of biotin and pantothenic acid at the human blood-brain barrier. In humans, it was unclear (not concluded) about what transport system at the blood-brain barrier (BBB) is responsible for the brain uptakes of two vitamins, biotin and pantothenic acid, which are necessary for brain proper function. This study clarified for the first time that the solute carrier 5A6/Na(+) -dependent multivitamin transporter SLC5A6/SMVT is responsible for the supplies of biotin and pantothenic acid into brain across the BBB in humans. DHA, docosahexaenoic acid; NSAID, non-steroidal anti-inflammatory drug; PGE2, prostaglandin E2.

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.

Association of TM4SF4 with the human thiamine transporter-2 in intestinal epithelial cells

BACKGROUND

The human thiamine transporter-2 (hTHTR-2) is involved in the intestinal absorption of thiamine. Recent studies with membrane transporters of other nutrients/substrates have shown that they have associated proteins that affect different aspects of their physiology and cell biology. Nothing is known about protein(s) that interact with hTHTR-2 in intestinal epithelial cells and influence its physiological function and/or its cell biology.

AIMS

The aim of this study was to identify protein partner(s) that interact with hTHTR-2 in human intestinal cells and determine the physiological/biological consequence of that interaction.

METHODS

The yeast split-ubiquitin two-hybrid approach was used to screen a human intestinal cDNA library. GST-pull-down and cellular co-localization approaches were used to confirm the interaction between hTHTR-2 and the associated protein(s). The effect of such an interaction on hTHTR-2 function was examined by (3)H-thiamine uptake assays.

RESULTS

Our screening results identified the human TransMembrane 4 SuperFamily 4 (TM4SF4) as a potential interactor with hTHTR-2. This interaction was confirmed by an in vitro GST-pull-down assay, and by live-cell confocal imaging of HuTu-80 cells co-expressing hTHTR-2-GFP and mCherry-TM4SF4 (the latter displayed a significant overlap of these two proteins in intracellular vesicles and at the cell membrane). Co-expression of hTHTR-2 with TM4SF4 in HuTu-80 cells led to a significant induction in thiamine uptake. In contrast, silencing TM4SF4 with gene-specific siRNA led to a significant decrease in thiamine uptake.

CONCLUSIONS

These results show for the first time that the accessory protein TM4SF4 interacts with hTHTR-2 and influences the physiological function of the thiamine transporter.

Stress-induced upregulation of SLC19A3 is impaired in biotin-thiamine-responsive basal ganglia disease

Biotin-thiamine-responsive basal ganglia disease (BTBGD) is a potentially treatable disorder caused by mutations in the SLC19A3 gene, encoding the human thiamine transporter 2. Manifestation of BTBGD as acute encephalopathy triggered by a febrile infection has been frequently reported, but the underlying mechanisms are not clear. We investigated a family with two brothers being compound heterozygous for the SLC19A3 mutations p.W94R and p.Q393*fs. Post-mortem analysis of the brain of one brother showed a mixture of acute, subacute and chronic changes with cystic and necrotic lesions and hemorrhage in the putamen, and hemorrhagic lesions in the caudate nucleus and cortical layers. SLC19A3 expression was substantially reduced in the cortex, basal ganglia and cerebellum compared with an age-matched control. Importantly, exposure of fibroblasts to stress factors such as acidosis or hypoxia markedly upregulated SLC19A3 in control cells, but failed to elevate SLC19A3 expression in the patient's fibroblasts. These results demonstrate ubiquitously reduced thiamine transporter function in the cerebral gray matter, and neuropathological alterations similar to Wernicke's disease in BTBGD. They also suggest that episodes of encephalopathy are caused by a substantially reduced capacity of mutant neuronal cells to increase SLC19A3 expression, necessary to adapt to stress conditions.

Biotin-responsive Basal Ganglia disease: a treatable differential diagnosis of leigh syndrome

Biotin-responsive basal ganglia disease (BBGD) is an autosomal recessive disorder, which is caused by mutations in the SLC19A3 gene. BBGD typically causes (sub)acute episodes with encephalopathy and subsequent neurological deterioration. If untreated, the clinical course may be fatal. Our report on a 6-year-old child with BBGD highlights that the disease is a crucial differential diagnosis of Leigh syndrome. Therefore, biotin and thiamine treatment is recommended for any patient with symmetrical basal ganglia lesions and neurological symptoms until BBGD is excluded. In addition, we exemplify that deformation-field-based morphometry of brain magnetic resonance images constitutes a novel quantitative tool, which might be very useful to monitor disease course and therapeutic effects in neurometabolic disorders.

Treatable Leigh-like encephalopathy presenting in adolescence

Wernicke's encephalopathy is a triad of ophthalmoplegia, ataxia and confusion seen in alcoholics with dietary vitamin B1 (thiamine) deficiency. A rare genetic defect of thiamine transporter-2 may lead to similar clinical features, biotin-thiamine responsive basal ganglia disease (BTBGD). A 15-year-old girl developed rapid onset ptosis and ophthalmoplegia evolving into a subacute encephalopathy. Neuroimaging demonstrated symmetrical basal ganglia and mid-brain lesions reminiscent of Leigh's subacute necrotising encephalomyelopathy. Oral biotin and thiamine were started, and symptoms improved dramatically the next day. The therapeutic response suggested SLC19A3, encoding thiamine transporter-2, as a strong candidate gene and Sanger sequencing revealed a novel homozygous c.517A>G;p.Asn173Asp mutation, which segregated with disease within the family. BTBGD is a potentially treatable neurological disorder and should be considered in the differential diagnosis of Leigh syndrome and Wernicke's encephalopathy. Since delayed treatment results in permanent neurological dysfunction or death, prompt diagnosis and early initiation of biotin and thiamine therapy are essential.

Folate and thiamine transporters mediated by facilitative carriers (SLC19A1-3 and SLC46A1) and folate receptors

The reduced folate carrier (RFC, SLC19A1), thiamine transporter-1 (ThTr1, SLC19A2) and thiamine transporter-2 (ThTr2, SLC19A3) evolved from the same family of solute carriers. SLC19A1 transports folates but not thiamine. SLC19A2 and SLC19A3 transport thiamine but not folates. SLC19A1 and SLC19A2 deliver their substrates to systemic tissues; SLC19A3 mediates intestinal thiamine absorption. The proton-coupled folate transporter (PCFT, SLC46A1) is the mechanism by which folates are absorbed across the apical-brush-border membrane of the proximal small intestine. Two folate receptors (FOLR1 and FOLR2) mediate folate transport across epithelia by an endocytic process. Folate transporters are routes of delivery of drugs for the treatment of cancer and inflammatory diseases. There are autosomal recessive disorders associated with mutations in genes encoded for SLC46A1 (hereditary folate malabsorption), FOLR1 (cerebral folate deficiency), SLC19A2 (thiamine-responsive megaloblastic anemia), and SLC19A3 (biotin-responsive basal ganglia disease).

Biotin-responsive basal ganglia disease should be renamed biotin-thiamine-responsive basal ganglia disease: a retrospective review of the clinical, radiological and molecular findings of 18 new cases

BACKGROUND

Biotin-responsive basal ganglia disease (BBGD) is an autosomal recessive neurometabolic disorder. It is characterized by sub acute encephalopathy with confusion, seizure, dysarthria and dystonia following a history of febrile illness. If left untreated with biotin, the disease can progress to severe quadriparesis and even death.

METHOD

A retrospective chart review of 18 patients with BBGD from two tertiary institutions describing their clinical, magnetic resonance imaging and molecular findings was conducted.

RESULT

Eighteen children from 13 families seen over a period of nine years (2003-2012) were included. (Age range: 14month to 23 years, M: F: 1:1). The clinical features included sub acute encephalopathy, ataxia (n= 18), seizures (n= 13) dystonia (n=12) ,dysarthria (n= 9), quadriparesis and hyperreflexia (n=9). Magnetic resonance imaging demonstrated abnormal signal intensity with swelling in the basal ganglia during acute crises (n= 13/13) and atrophy of the basal ganglia and necrosis during follow up (n= 13/13). One-third of the present patients showed the recurrence of acute crises while on biotin therapy alone, but after the addition of thiamine, crises did not recur. All of the patients have a homozygous missense mutation in exon 5 of the SLC19A3 gene. The frequency of acute crises, delay in diagnosis and initiation of treatment significantly influenced the outcome. On follow up, four patients died, two had spastic quadriplegia, six had normal outcome and the rest had speech and motor dysfunctions.

CONCLUSION

Clinicians should suspect BBGD in any child presenting with sub acute encephalopathy, abnormal movement and MRI findings as described above. Both biotin and thiamine are essential for disease management. Since biotin alone could not prevent the recurrence of crises in some patients, a more appropriate term to describe the disease would be biotin-thiamine-responsive basal ganglia disease (BTBGD).

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.

Genome-wide association analysis identifies a mutation in the thiamine transporter 2 (SLC19A3) gene associated with Alaskan Husky encephalopathy

Alaskan Husky Encephalopathy (AHE) has been previously proposed as a mitochondrial encephalopathy based on neuropathological similarities with human Leigh Syndrome (LS). We studied 11 Alaskan Husky dogs with AHE, but found no abnormalities in respiratory chain enzyme activities in muscle and liver, or mutations in mitochondrial or nuclear genes that cause LS in people. A genome wide association study was performed using eight of the affected dogs and 20 related but unaffected control AHs using the Illumina canine HD array. SLC19A3 was identified as a positional candidate gene. This gene controls the uptake of thiamine in the CNS via expression of the thiamine transporter protein THTR2. Dogs have two copies of this gene located within the candidate interval (SLC19A3.2 – 43.36–43.38 Mb and SLC19A3.1 – 43.411–43.419 Mb) on chromosome 25. Expression analysis in a normal dog revealed that one of the paralogs, SLC19A3.1, was expressed in the brain and spinal cord while the other was not. Subsequent exon sequencing of SLC19A3.1 revealed a 4bp insertion and SNP in the second exon that is predicted to result in a functional protein truncation of 279 amino acids (c.624 insTTGC, c.625 C>A). All dogs with AHE were homozygous for this mutation, 15/41 healthy AH control dogs were heterozygous carriers while 26/41 normal healthy AH dogs were wild type. Furthermore, this mutation was not detected in another 187 dogs of different breeds. These results suggest that this mutation in SLC19A3.1, encoding a thiamine transporter protein, plays a critical role in the pathogenesis of AHE.

Biotin: biochemical, physiological and clinical aspects

Significant progress has been made in our understanding of the biochemical, physiological and nutritional aspects of the water-soluble vitamin biotin (vitamin H). It is well know now that biotin plays important roles in a variety of critical metabolic reactions in the cell, and thus, is essential for normal human health, growth and development. This is underscored by the serious clinical abnormalities that occur in conditions of biotin deficiency, which include, among other things, growth retardation, neurological disorders, and dermatological abnormalities (reviewed in 1). Studies in animals have also shown that biotin deficiency during pregnancy leads to embryonic growth retardation, congenital malformation and death (Watanabe 1983; Cooper and Brown 1958; Mock et al. 2003; Zempleni and Mock 2000). The aim of this chapter is to provide coverage of current knowledge of the biochemical, physiological, and clinical aspects of biotin nutrition. Many sections of this chapter have been the subject of excellent recent reviews by others (Wolf 2001; McMahon 2002; Mock 2004; Rodriguez-Melendez and Zempleni 2003; Said 2004; Said et al. 2000; Said and Seetheram 2006), and thus, for more information the reader is advised to consider these additional sources.

Thiamine pyrophosphokinase deficiency in encephalopathic children with defects in the pyruvate oxidation pathway

Thiamine pyrophosphate (TPP) is an essential cofactor of the cytosolic transketolase and of three mitochondrial enzymes involved in the oxidative decarboxylation of either pyruvate, α-ketoglutarate or branched chain amino acids. Thiamine is taken up by specific transporters into the cell and converted to the active TPP by thiamine pyrophosphokinase (TPK) in the cytosol from where it can be transported into mitochondria. Here, we report five individuals from three families presenting with variable degrees of ataxia, psychomotor retardation, progressive dystonia, and lactic acidosis. Investigation of the mitochondrial energy metabolism showed reduced oxidation of pyruvate but normal pyruvate dehydrogenase complex activity in the presence of excess TPP. A reduced concentration of TPP was found in the muscle and blood. Mutation analysis of TPK1 uncovered three missense, one splice-site, and one frameshift mutation resulting in decreased TPK protein levels.

Intestinal absorption of water-soluble vitamins in health and disease

Our knowledge of the mechanisms and regulation of intestinal absorption of water-soluble vitamins under normal physiological conditions, and of the factors/conditions that affect and interfere with theses processes has been significantly expanded in recent years as a result of the availability of a host of valuable molecular/cellular tools. Although structurally and functionally unrelated, the water-soluble vitamins share the feature of being essential for normal cellular functions, growth and development, and that their deficiency leads to a variety of clinical abnormalities that range from anaemia to growth retardation and neurological disorders. Humans cannot synthesize water-soluble vitamins (with the exception of some endogenous synthesis of niacin) and must obtain these micronutrients from exogenous sources. Thus body homoeostasis of these micronutrients depends on their normal absorption in the intestine. Interference with absorption, which occurs in a variety of conditions (e.g. congenital defects in the digestive or absorptive system, intestinal disease/resection, drug interaction and chronic alcohol use), leads to the development of deficiency (and sub-optimal status) and results in clinical abnormalities. It is well established now that intestinal absorption of the water-soluble vitamins ascorbate, biotin, folate, niacin, pantothenic acid, pyridoxine, riboflavin and thiamin is via specific carrier-mediated processes. These processes are regulated by a variety of factors and conditions, and the regulation involves transcriptional and/or post-transcriptional mechanisms. Also well recognized now is the fact that the large intestine possesses specific and efficient uptake systems to absorb a number of water-soluble vitamins that are synthesized by the normal microflora. This source may contribute to total body vitamin nutrition, and especially towards the cellular nutrition and health of the local colonocytes. The present review aims to outline our current understanding of the mechanisms involved in intestinal absorption of water-soluble vitamins, their regulation, the cell biology of the carriers involved and the factors that negatively affect these absorptive events.

Chronic alcohol exposure negatively impacts the physiological and molecular parameters of the renal biotin reabsorption process

Normal body homeostasis of biotin is critically dependent on its renal recovery by kidney proximal tubular epithelial cells, a process that is mediated by the sodium-dependent multivitamin transporter (SMVT; a product of the SLC5A6 gene). Chronic ethanol consumption interferes with the renal reabsorption process of a variety of nutrients, including water-soluble vitamins. To date, however, there is nothing known about the effect of chronic alcohol feeding on physiological and molecular parameters of the renal biotin reabsorption process. We addressed these issues using rats and transgenic mice carrying the human SLC5A6 (P1P2) 5'-regulatory region as an in vivo model systems of alcohol exposure, and cultured human renal proximal tubular epithelial HK-2 cells chronically exposed to alcohol as an in vitro model of alcohol exposure. The [(3)H]biotin uptake results showed that chronic ethanol feeding in rats leads to a significant inhibition in carrier-mediated biotin transport across both renal brush border and basolateral membrane domains. This inhibition was associated with a marked reduction in the level of expression of SMVT protein, mRNA, and heterogenous nuclear RNA (hnRNA). Furthermore, studies with transgenic mice carrying the SLC5A6 5'-regulatory region showed that chronic alcohol feeding leads to a significant decrease in promoter activity. Studies with HK-2 cells chronically exposed to alcohol again showed a marked reduction in carrier-mediated biotin uptake, which was associated with a significant reduction in promoter activity of the human SLC5A6 5'-regulatory region. These findings demonstrate for the first time that chronic ethanol feeding inhibits renal biotin transport and that this effect is, at least in part, being exerted at the transcriptional level.

Non-muscle myosin light chain kinase isoform is a viable molecular target in acute inflammatory lung injury

Acute lung injury (ALI) and mechanical ventilator-induced lung injury (VILI), major causes of acute respiratory failure with elevated morbidity and mortality, are characterized by significant pulmonary inflammation and alveolar/vascular barrier dysfunction. Previous studies highlighted the role of the non-muscle myosin light chain kinase isoform (nmMLCK) as an essential element of the inflammatory response, with variants in the MYLK gene that contribute to ALI susceptibility. To define nmMLCK involvement further in acute inflammatory syndromes, we used two murine models of inflammatory lung injury, induced by either an intratracheal administration of lipopolysaccharide (LPS model) or mechanical ventilation with increased tidal volumes (the VILI model). Intravenous delivery of the membrane-permeant MLC kinase peptide inhibitor, PIK, produced a dose-dependent attenuation of both LPS-induced lung inflammation and VILI (~50% reductions in alveolar/vascular permeability and leukocyte influx). Intravenous injections of nmMLCK silencing RNA, either directly or as cargo within angiotensin-converting enzyme (ACE) antibody-conjugated liposomes (to target the pulmonary vasculature selectively), decreased nmMLCK lung expression (∼70% reduction) and significantly attenuated LPS-induced and VILI-induced lung inflammation (∼40% reduction in bronchoalveolar lavage protein). Compared with wild-type mice, nmMLCK knockout mice were significantly protected from VILI, with significant reductions in VILI-induced gene expression in biological pathways such as nrf2-mediated oxidative stress, coagulation, p53-signaling, leukocyte extravasation, and IL-6-signaling. These studies validate nmMLCK as an attractive target for ameliorating the adverse effects of dysregulated lung inflammation.