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

Report of a novel recurrent homozygous variant c.620A>T in three unrelated families with thiamine metabolism dysfunction syndrome 5 and review of literature

INTRODUCTION

Biallelic variants in thiamine pyrophosphokinase 1 ( TPK1 ) are known to cause thiamine metabolism dysfunction syndrome 5 (THMD5). This disorder is characterized by neuroregression, ataxia and dystonia with basal ganglia abnormalities on neuroimaging. To date, 27 families have been reported with THMD5 due to variants in TPK1 .

METHODS

We ascertained three individuals from three unrelated families. Singleton exome sequencing was performed on all three individuals, followed by in silico mutagenesis of the mutant TPK protein. Additionally, we reviewed the genotypic and phenotypic information of 27 previously reported individuals with THMD5.

RESULTS

Singleton exome sequencing revealed a novel homozygous variant c.620A>T p.(Asp207Val) in TPK1 (NM_022445.4) in all three individuals. In silico mutagenesis of the mutant protein revealed a decrease in protein stability and altered interactions with its neighboring residues compared to the wild-type protein. Thus, based on strikingly similar clinical and radiological findings compared to the previously reported individuals and with the support of in silico mutagenesis findings, the above-mentioned variant appears to be the probable cause for the condition observed in the affected individuals in this study.

CONCLUSION

We report a novel homozygous variant in TPK1 , which appears to be recurrent among the Indian population.

SLC25A19 is required for NADH homeostasis and mitochondrial respiration

Mitochondrial transporters facilitate the translocation of metabolites between the cytoplasm and mitochondria and are critical for mitochondrial functional integrity. Although many mitochondrial transporters are associated with metabolic diseases, how they regulate mitochondrial function and their metabolic contributions at the cellular level are largely unknown. Here, we show that mitochondrial thiamine pyrophosphate (TPP) transporter SLC25A19 is required for mitochondrial respiration. SLC25A19 deficiency leads to reduced cell viability, increased integrated stress response (ISR), enhanced glycolysis and elevated cell sensitivity to 2-deoxyglucose (2-DG) treatment. Through a series of biochemical assays, we found that the depletion of mitochondrial NADH is the primary cause of the impaired mitochondrial respiration in SLC25A19 deficient cells. We also showed involvement of SLC25A19 in regulating the enzymatic activities of complexes I and III, the tricarboxylic acid (TCA) cycle, malate-aspartate shuttle and amino acid metabolism. Consistently, addition of idebenone, an analog of coenzyme Q10, restores mitochondrial respiration and cell viability in SLC25A19 deficient cells. Together, our findings provide new insight into the functions of SLC25A19 in mitochondrial and cellular physiology, and suggest that restoring mitochondrial respiration could be a novel strategy for treating SLC25A19-associated disorders.

MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration

Leucine aminoacyl tRNA-synthetase 1 (LARS1)-deficiency (infantile liver failure syndrome type 1 (ILFS1)) has a multisystemic phenotype including fever-associated acute liver failure (ALF), chronic neurologic abnormalities, and encephalopathic episodes. In order to better characterize encephalopathic episodes and MRI changes, 35 cranial MRIs from 13 individuals with LARS1 deficiency were systematically assessed and neurological phenotype was analyzed. All individuals had developmental delay and 10/13 had seizures. Encephalopathic episodes in 8/13 were typically associated with infections, presented with seizures and reduced consciousness, mostly accompanied by hepatic dysfunction, and recovery in 17/19 episodes. Encephalopathy without hepatic dysfunction occurred in one individual after liver transplantation. On MRI, 5/7 individuals with MRI during acute encephalopathy had deep gray matter and brainstem changes. Supratentorial cortex involvement (6/13) and cerebellar watershed injury (4/13) occurred with seizures and/or encephalopathy. Abnormal brainstem contour on sagittal images (8/13), atrophy (8/13), and myelination delay (8/13) were not clearly associated with encephalopathy. The pattern of deep gray matter and brainstem changes are apparently characteristic of encephalopathy in LARS1-deficiency, differing from patterns of hepatic encephalopathy or metabolic stroke in organic acidurias and mitochondrial diseases. While the pathomechanism remains unclear, fever and energy deficit during infections might be causative; thus, sufficient glucose and protein intake along with pro-active fever management is suggested. As severe episodes were observed during influenza infections, we strongly recommend seasonal vaccination.

Celiac disease and depressive disorders as nutritional implications related to common factors - A comprehensive review

Celiac disease (CD) is an immune-mediated disease affecting the small intestine. The only treatment strategy for CD is the gluten-free diet (GFD). One of the more common mental disorders in CD patients is major depressive disorder (MDD). The influence of GFD on the occurrence of MDD symptoms in patients with CD will be evaluated. This diet often reduces nutritional deficiencies in these patients and also helps to reduce depressive symptoms. Both disease entities are often dominated by the same deficiencies of nutrients such as iron, zinc, selenium, iodine, or B and D vitamins. Deficiencies of particular components in CD can favor MDD and vice versa. Gluten can adversely affect the mental state of patients without CD. Also, intestinal microbiota may play an important role in the described process. This work aims to comprehensively assess the common factors involved in the pathomechanisms of MDD and CD, with particular emphasis on nutrient imbalances. Given the complexity of both disease entities, and the many common links, more research related to improving mental health in these patients and the implementation of a GFD would need to be conducted, but it appears to be a viable pathway to improving the quality of life and health of people struggling with CD and MDD. Therefore, probiotics, micronutrients, macronutrients, and vitamin supplements are recommended to reduce the risk of MDD, given that they may alleviate the symptoms of both these disease entities. In turn, in patients with MDD, it is worth considering testing for CD.

Expert Panel Curation of 113 Primary Mitochondrial Disease Genes for the Leigh Syndrome Spectrum

OBJECTIVE

Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene-disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes.

METHODS

The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene-Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS.

RESULTS

The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31 of 114 GDRs curated (27%), moderate for 38 (33%), limited for 43 (38%), and disputed for 2 (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 were autosomal dominant, and 3 were X-linked.

INTERPRETATION

GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multisystem organ surveillance, recurrence risk counseling, reproductive choice, natural history studies, and determination of eligibility for interventional clinical trials. ANN NEUROL 2023;94:696-712.

Thiamine pyrophosphokinase deficiency: report of two Chinese cases and a literature review

Thiamine pyrophosphokinase (TPK) deficiency, is a rare autosomal recessive disorder of congenital metabolic dysfunction caused by variants in the TPK1 gene. TPK1 variants can lead to thiamine metabolic pathway obstacles, and its clinical manifestations are highly variable. We describe two cases of TPK deficiency with completely different phenotypes and different therapeutic effects, and 26 cases of previously reported were retrospectively reviewed to improve our understanding of the clinical and genetic features of the disease. Patients with TPK deficiency present with ataxia, dysarthria, dystonia, disturbance of consciousness, seizures, and other nervous system dysfunction. Different gene variant sites may lead to different clinical features and therapeutic effects. Gene analysis is important for the diagnosis of TPK deficiency caused by TPK1 variants, and thiamine supplementation has been the mainstay of treatment for TPK deficiency to date.

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

Child Neurology: Infantile Biotin Thiamine Responsive Basal Ganglia Disease: Case Report and Brief Review

Biotin thiamine responsive basal ganglia disease (BTRBGD) is an inherited autosomal recessive disorder that results from the inability of thiamine to cross the blood-brain barrier. It is considered a treatable condition if vitamin supplementation, most commonly with thiamine and biotin, is initiated early. BTRBGD can present as an infantile form, classical childhood form, or adult Wernicke-like encephalopathy. The infantile form is often the most severe and portends a worse prognosis with high mortality despite vitamin supplementation. We present a two-month-old who presented with irritability, opisthotonos, and abnormal eye movements who was found to have compound heterozygous variants in the SLC19A3 gene inherited in trans, including one known pathogenic intronic variant and a novel variant presumed to be pathogenic. She was therefore diagnosed with infantile BTRBGD. In this report, we discuss the differential for infantile BTRBGD, the clinical and radiologic features of BTRBGD, and describe a rapid, positive response to early vitamin supplementation in an infant with a likely pathogenic novel variant in SLC19A3.

Case report of two affected siblings in a family with thiamine metabolism dysfunction syndrome 5: a rare, but treatable neurodegenerative disease

Background

Thiamine metabolism dysfunction syndrome 5 (THMD5) is a rare inherited metabolic disorder due to thiamine pyrophosphokinase 1(TPK1) deficiency, caused by mutations in TPK1. The core symptoms of the disease is acute or subacute onset encephalopathy, ataxia, muscle hypotonia, and regression of developmental milestones in early infancy, repeatedly triggered by acute infectious illness. However, we report two brothers of THMD5 with compound heterozygous for the mutations c.614-1G > A,c.224 T > A p.(Ile75Asn), but the prognosis is quite different if thiamine suppled. According to our current knowledge, the missense variant c.224 T > A p.(Ile75Asn) was not published previously.

Case presentation

Here, we describe two affected siblings in a Chinese family, after an uneventful pregnancy to non-consanguineous and healthy parents. The older brother presented with normal development during the first 6 months of life, but developed regression of developmental milestones after, accompanied with muscle hypotonia, and chronic encephalopathy, and died at 1 year and 6 months old. The younger brother presented with acute onset encephalopathy, ataxia, muscle hypotonia, repeatedly triggered by acute infectious illness. He was compound heterozygous for the mutations c.614-1G > A,c.224 T > A p.(Ile75Asn) identified by whole exome sequencing. He was diagnosed of THMD5 when he was 11 month. Oral supplementation of thiamine 100 mg/day, the symptoms gradually disappeared. At the age of 2 years and 4 months, he stoped thiamine, his symptoms returned and were once again relieved by oral supplementation of thiamine 100 mg/day.

Conclusions

THMD5 is a rare, but treatable neurodegenerative disease, the clinical phenotype ranges from mild to severe. Massive-dose of thiamine supplementation may ameliorate the course of TPK1 deficiency. When similar clinical cases appear, gene detection is particularly important, which is conducive to early diagnosis. Treatment with thiamine while awaiting the outcome of diagnostic tests may be a good choice.

Mitochondrial transport and metabolism of the vitamin B-derived cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ , and related diseases: A review

Multiple mitochondrial matrix enzymes playing key roles in metabolism require cofactors for their action. Due to the high impermeability of the mitochondrial inner membrane, these cofactors need to be synthesized within the mitochondria or be imported, themselves or one of their precursors, into the organelles. Transporters belonging to the protein family of mitochondrial carriers have been identified to transport the coenzymes: thiamine pyrophosphate, coenzyme A, FAD and NAD+ , which are all structurally similar to nucleotides and derived from different B-vitamins. These mitochondrial cofactors bind more or less tightly to their enzymes and, after having been involved in a specific reaction step, are regenerated, spontaneously or by other enzymes, to return to their active form, ready for the next catalysis round. Disease-causing mutations in the mitochondrial cofactor carrier genes compromise not only the transport reaction but also the activity of all mitochondrial enzymes using that particular cofactor and the metabolic pathways in which the cofactor-dependent enzymes are involved. The mitochondrial transport, metabolism and diseases of the cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ are the focus of this review.

Clinical and genetic studies of thiamine metabolism dysfunction syndrome-4: case series and review of the literature

Thiamine metabolism dysfunction syndrome-4 (THMD-4) is an autosomal recessive inherited rare disease (OMIM #613710) characterized by febrile illness associated episodic encephalopathy, leading to transient neurological dysfunction and progressive polyneuropathy. We report three patients from two different families with normal development, episodic encephalopathy, gait disorder, progressive chronic polyneuropathy characterized by motor difficulties, distal weakness, and hoarseness (dysphonia). We identified a homozygous missense c.576G>C, p.(Gln192His) variant in the SLC25A19 gene in both families by whole-exome sequencing. Following genetic diagnosis, thiamine replacement therapy was started, and improvement was observed in all affected patients. We highlight the associated phenotypes of an SCL25A19 mutation leading to clinical features of THMD-4.

Genetic diagnosis of basal ganglia disease in childhood

AIM

To correlate clinical, radiological, and biochemical features with genetic findings in children with bilateral basal ganglia lesions of unknown aetiology, and propose a diagnostic algorithm for early recognition.

METHOD

Children with basal ganglia disease were recruited in a 2-year prospective multicentre study for clinical, biomarker, and genetic studies. Radiological pattern recognition was examined by hierarchical clustering analysis.

RESULTS

We identified 22 genetic conditions in 30 out of 62 paediatric patients (37 males, 25 females; mean age at onset 2y, SD 3; range 0-10y; mean age at assessment 11y, range 1-25y) through gene panels (n=11), whole-exome sequencing (n=13), and mitochondrial DNA (mtDNA) sequencing (n=6). Genetic aetiologies included mitochondrial diseases (57%), Aicardi-Goutières syndrome (20%), and monogenic causes of dystonia and/or epilepsy (17%) mimicking Leigh syndrome. Radiological abnormalities included T2-hyperintense lesions (n=26) and lesions caused by calcium or manganese mineralization (n=9). Three clusters were identified: the pallidal, neostriatal, and striatal, plus the last including mtDNA defects in the oxidative phosphorylation system with prominent brain atrophy. Mitochondrial biomarkers showed poor sensitivity and specificity in children with mitochondrial disease, whereas interferon signature was observed in all patients with patients with Aicardi-Goutières syndrome.

INTERPRETATION

Combined whole-exome and mtDNA sequencing allowed the identification of several genetic conditions affecting basal ganglia metabolism. We propose a diagnostic algorithm which prioritizes early use of next-generation sequencing on the basis of three clusters of basal ganglia lesions.

Identification of solute carrier family genes related to the prognosis and tumor-infiltrating immune cells of pancreatic ductal adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) has persisted as one of the worst prognostic tumors with a 5-year survival rate of lower than 6%. Although many studies have investigated PDAC, new biomarkers are required to ensure early diagnosis and predict the prognosis of PDAC.

Methods

In this study, we used bioinformatics methods to evaluate differences in the expression of solute carrier (SLC) family genes in tumors and non-tumors. A Kaplan-Meier analysis, least absolute shrinkage and selection operator (LASSO) analysis, and multivariate Cox proportional hazards regression analysis were used to evaluate the relationship between SLC genes and prognosis using The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets. The prognostic signature was constructed depending on the risk score to assess the impact of multiple genes on the prognosis, receiver operating characteristic (ROC) curves and forest plot was constructed to assess the ability to predict the prognosis and effects of clinical variables in both high- and low-risk groups. Tumor-infiltrating immune cells were evaluated using Cell-type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT) in both high- and low-risk groups.

Results

In 32 SLC genes, 9 were significantly associated with the OS after LASSO analysis. SLC19A3 (P=0.007), SLC25A39 (P=0.027), SLC39A11 (P=0.043) were significantly associated with prognosis and included into the prognostic model. CIBERSORT demonstrated that memory B cells (P=0.004), naive B cells (P=0.007), CD8 T cells (P=0.003), activated memory CD4 T cells (P=0.004), and activated NK cells (P=0.019) were significantly higher in the low-risk group. Gene set enrichment analysis (GSEA) showed that potential molecular mechanisms enriched in MYC and p53 signaling pathways.

Conclusions

SLC19A3, SLC25A35, and SLC39A11 were significantly relative to the prognosis of PDAC and changed the tumor microenvironment, as well as the MYC and p53 signaling pathways. The SLC19A3 gene may represent a new tumor suppressor in PDAC.

A dose- and time-dependent effect of oxythiamine on cell growth inhibition in non-small cell lung cancer

The high mortality rate of non-small-cell lung cancer (NSCLC) is mostly due to the high risk of recurrence. A comprehensive understanding of proliferation mechanisms of NSCLC would remarkably contribute to blocking up the invasion and metastasis of tumor cells. In our previous study, the remarkable decreased activity of Thiamine-dependent enzymes (TDEs), involving in intermediary metabolism responsible for energy production of tumor, was found under conditions of thiamine deficiency in vivo. To explore the effect of Oxythiamine (OT), a TDEs antimetabolite, on cell growth, we co-cultured A549 cells with OT in vitro at various doses (0.1, 1, 10 and 100 μM) and time periods (6, 12, 24 and 48 h) and subsequent cell proliferation and apoptosis assays were performed respectively. Our findings demonstrated that A549 cells proliferation was significantly downregulated by OT treatment in a progressively dose as well as time dependent manner. Inhibition of TDEs resulted in antagonism of lung cancer growth by inducing cells to cease the cycle as well as apoptotic cell death. We concluded a critical role of OT, a TDEs antagonistic compound, indicating the potential target of its practical use.

Early treatment of biotin-thiamine-responsive basal ganglia disease improves the prognosis

Background

Biotin–thiamine–responsive basal ganglia disease (BTBGD) is an autosomal recessive neurometabolic disorder associated with pathogenic variants in SLC19A3 gene. The clinical picture includes symptoms of subacute encephalopathy (e.g. confusion, dysphagia, dysarthria, and seizures), which respond very well to early treatment with thiamine and biotin.

Method

A retrospective review of clinical characteristics, magnetic resonance imaging and molecular findings in 3 patients with BTBGD.

Results

The first symptoms in all patients occurred at 12–24 months of age and they had subacute encephalopathy, ataxia and dystonia. The baseline magnetic resonance imaging demonstrated abnormal signal intensity in the basal ganglia with atrophy and necrosis of the basal ganglia during follow-up in two patients. One patient was diagnosed and the treatment was initiated after a long period from symptoms onset and he is currently severely affected, with dystonia, quadriparesis and seizures. The other two patients were diagnosed early in life and are currently stable on treatment, without the clinical symptoms. Genetic testing demonstrated pathogenic variants in SLC19A3 gene.

Conclusion

To avoid diagnostic errors and delayed or incorrect treatment, BTBGD must be recognized early. Adequate prompt treatment gives the chance of significant clinical improvement. Unexplained encephalopathy and MRI abnormalities including bilateral abnormal signal in the basal ganglia should alert the clinician to consider BTBGD in the differential, and the treatment with biotin and thiamine should be introduced immediately.

CPEB alteration and aberrant transcriptome-polyadenylation lead to a treatable SLC19A3 deficiency in Huntington's disease

[Figure: see text].

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

Background

Thiamine metabolism dysfunction syndrome 4 (THMD4, OMIM #613710) is an autosomal recessive inherited disease caused by the deficiency of SLC25A19 that encodes the mitochondrial thiamine pyrophosphate (TPP) transporter. This disorder is characterized by bilateral striatal degradation and progressive polyneuropathy with the onset of fever of unknown origin. The limited number of reported cases and lack of functional annotation of related gene variants continue to limit diagnosis.

Results

We report three cases of encephalopathy from two unrelated pedigrees with basal ganglia signal changes after fever of unknown origin. To distinguish this from other types of encephalopathy, such as acute necrotizing encephalopathy, exome sequencing was performed, and four novel heterozygous variations, namely, c.169G>A (p.Ala57Thr), c.383C>T (p.Ala128Val), c.76G>A (p.Gly26Arg), and c.745T>A (p.Phe249Ile), were identified in SLC25A19. All variants were confirmed using Sanger sequencing. To determine the pathogenicity of these variants, functional studies were performed. We found that mitochondrial TPP levels were significantly decreased in the presence of SLC25A19 variants, indicating that TPP transport activities of mutated SLC25A19 proteins were impaired. Thus, combining clinical phenotype, genetic analysis, and functional studies, these variants were deemed as likely pathogenic.

Conclusions

Exome sequencing analysis enables molecular diagnosis as well as provides potential etiology. Further studies will enable the elucidation of SLC25A19 protein function. Our investigation supplied key molecular evidence for the precise diagnosis of and clinical decision-making for a rare disease.

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.

Blood thiamine (vitamin B1 ), ascorbic acid (vitamin C), and cortisol concentrations in healthy and ill neonatal foals

Background

Sepsis is common in foals and several treatments are used to facilitate recovery. Evidence in people suggests an association between low blood concentrations of thiamine, ascorbic acid, and cortisol and sepsis, with further evidence suggesting that administration of hydrocortisone, thiamine, and ascorbic acid may improve outcome. No information is available with regard to these treatments in foals.

Hypothesis/Objectives

To compare blood concentrations of thiamine, ascorbic acid, and cortisol in healthy and ill foals.

Animals

Fifteen healthy and 27 ill (septic and sick‐nonseptic [SNS]) foals were evaluated at admission. Fewer healthy and ill foals were available for sampling at 72 and 120 hours.

Methods

Prospective study. Blood was collected from healthy foals at 12 (n = 15), 72 (n = 11), and 120 (n = 9) hours of age and from ill foals <48 hours old at admission (n = 27), 72 (n = 8), and 120 (n = 8) hours after presentation. Thiamine, ascorbic acid, and cortisol concentrations were measured in blood samples and compared between groups of foals.

Results

Blood concentrations of thiamine were significantly lower in septic compared to healthy foals at 72 (median, 1.72 ng/mL; P = .02) and 120 (median, 2.0 ng/mL; P = .04) hours after admission; blood concentrations of ascorbic acid also were significantly lower in septic compared to healthy foals at 72 (median, 4.4 μg/mL; P = .02) and 120 hours (median, 4.8 μg/mL; P = .03). Blood concentrations of ascorbic acid were lower in SNS compared to healthy foals at 72 (median, 6.9 μg/mL; P = .03) and 120 (median, 6.4 μg/mL; P = .04) hours after admission. Serum cortisol concentrations were significantly higher at admission in septic (median, 4.23 μg/dL) compared to SNS (median, 1.8 μg/dL; P = .01) and healthy (median, 2.2 μg/dL; P = .002) foals.

Conclusions and Clinical Importance

A potential association exists between illness in foals and lower blood concentrations of thiamine and ascorbic acid during hospitalization. Additional studies are needed to examine a larger population of foals and determine the clinical impact of low vitamin concentrations, if any, on morbidity and mortality.

Genetic Variations in Thiamin Transferase SLC35F3 and the Risk of Hypertension in Koreans

Hypertension is a major health issues globally. Multiple genetic and environmental factors are involved in hypertension etiology. Solute carrier family 35 member F3 (SLC35F3) is a type of transporter uptakes thiamin across the cellular and mitochondrial membrane. Recent studies suggested that variations in SLC35F3 are associated with the risk of hypertension; however, studies are limited in Koreans. This study examined the association of the genetic variations in SLC35F3 and the risk of hypertension in Koreans using the Korean Genome Epidemiology Study (Ansan/Ansung study). A total of 8,298 Koreans (males 3,983, females 4,315) were analyzed for their general characteristics, dietary intake, and blood pressure. Twenty-four tagging variations in SLC35F3 were selected and investigated for their association with the risk of hypertension using a sex-stratified approach. Findings suggested that, in males, rs12135117 A allele carriers were at the lower risk for hypertension (adjusted odds ratio, 0.859; 95% confidence interval [CI], 0.740–0.998). In females, rs10910387 TC genotype tended to increase the risk 1.172-fold for hypertension (95% CI, 1.002–1.370). Multiple linear regression models exhibited that rs12135117 A allele was negatively associated with blood pressure in males, and rs10910387 TC genotype had a positive association with blood pressure in females. However, statistical significance for these genetically modified effects was in lacked (Bonferroni's corrected p > 0.002). In conclusion, genetic variation in SLC35F3 is not a decisive prediction marker for hypertension risk in Koreans. Given the rarity of data, more studies are required to evaluate the role of SLC35F3 and thiamin in the hypertension etiology.

Treatable inherited metabolic disorders causing intellectual disability: 2021 review and digital app

BACKGROUND

The Treatable ID App was created in 2012 as digital tool to improve early recognition and intervention for treatable inherited metabolic disorders (IMDs) presenting with global developmental delay and intellectual disability (collectively 'treatable IDs'). Our aim is to update the 2012 review on treatable IDs and App to capture the advances made in the identification of new IMDs along with increased pathophysiological insights catalyzing therapeutic development and implementation.

METHODS

Two independent reviewers queried PubMed, OMIM and Orphanet databases to reassess all previously included disorders and therapies and to identify all reports on Treatable IDs published between 2012 and 2021. These were included if listed in the International Classification of IMDs (ICIMD) and presenting with ID as a major feature, and if published evidence for a therapeutic intervention improving ID primary and/or secondary outcomes is available. Data on clinical symptoms, diagnostic testing, treatment strategies, effects on outcomes, and evidence levels were extracted and evaluated by the reviewers and external experts. The generated knowledge was translated into a diagnostic algorithm and updated version of the App with novel features.

RESULTS

Our review identified 116 treatable IDs (139 genes), of which 44 newly identified, belonging to 17 ICIMD categories. The most frequent therapeutic interventions were nutritional, pharmacological and vitamin and trace element supplementation. Evidence level varied from 1 to 3 (trials, cohort studies, case-control studies) for 19% and 4-5 (case-report, expert opinion) for 81% of treatments. Reported effects included improvement of clinical deterioration in 62%, neurological manifestations in 47% and development in 37%.

CONCLUSION

The number of treatable IDs identified by our literature review increased by more than one-third in eight years. Although there has been much attention to gene-based and enzyme replacement therapy, the majority of effective treatments are nutritional, which are relatively affordable, widely available and (often) surprisingly effective. We present a diagnostic algorithm (adjustable to local resources and expertise) and the updated App to facilitate a swift and accurate workup, prioritizing treatable IDs. Our digital tool is freely available as Native and Web App (www.treatable-id.org) with several novel features. Our Treatable ID endeavor contributes to the Treatabolome and International Rare Diseases Research Consortium goals, enabling clinicians to deliver rapid evidence-based interventions to our rare disease patients.

Thiamine Treatment and Favorable Outcome in an Infant with Biallelic TPK1 Variants

Episodic encephalopathy due to mutations in the thiamine pyrophosphokinase 1 (TPK1) gene is a rare autosomal recessive metabolic disorder. Patients reported so far have onset in early childhood of acute encephalopathic episodes, which result in a progressive neurologic dysfunction including ataxia, dystonia, and spasticity. Here, we report the case of an infant with TPK1 deficiency (compound heterozygosity for two previously described pathogenic variants) presenting with two encephalopathic episodes and clinical stabilization under oral thiamine and biotin supplementation. In contrast to other reported cases, our patient showed an almost normal psychomotor development, which might be due to an early diagnosis and subsequent therapy.

Thiamine Pyrophosphokinase Deficiency due to Mutations in the TPK1 Gene: A Rare, Treatable Neurodegenerative Disorder

TPK deficiency due to TPK1 mutations is a rare neurodegenerative disorder, also known as thiamine metabolism dysfunction syndrome 5 (OMIM no.: 614458). Here, we report a new patient with compound heterozygous TPK1 mutations, of which one has not been described so far. The individual reported here suffered from acute onset encephalopathy, ataxia, muscle hypotonia, and regression of developmental milestones in early infancy, repeatedly triggered by febrile infections. Initiation of high-dose thiamine and magnesium supplementation led to a marked and sustained improvement of alertness, ataxia, and muscle tone within days. Contrary to the described natural history of patients with TPK deficiency, the disease course was favorable under thiamine treatment without deterioration or developmental regression during the follow-up period. TPK deficiency is a severe neurodegenerative disease. This case report demonstrates that this condition is potentially treatable. High-dose thiamine treatment should therefore be initiated immediately after diagnosis or even upon suspicion.

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 Therapies for Leigh Syndrome: Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Leigh syndrome (LS) is the most frequent paediatric clinical presentation of mitochondrial disease. The clinical phenotype of LS is highly heterogeneous. Though historically the treatment for LS is largely supportive, new treatments are on the horizon. Due to the rarity of LS, large-scale interventional studies are scarce, limiting dissemination of information of therapeutic options to the wider scientific and clinical community.

OBJECTIVE

We conducted a systematic review of pharmacological therapies of LS following the guidelines for FAIR-compliant datasets.

METHODS

We searched for interventional studies within Clincialtrials.gov and European Clinical trials databases. Randomised controlled trials, observational studies, case reports and case series formed part of a wider MEDLINE search.

RESULTS

Of the 1,193 studies initially identified, 157 met our inclusion criteria, of which 104 were carried over into our final analysis. Treatments for LS included very few interventional trials using EPI-743 and cysteamine bitartrate. Wider literature searches identified case series and reports of treatments repleting glutathione stores, reduction of oxidative stress and restoration of oxidative phosphorylation.

CONCLUSIONS

Though interventional randomised controlled trials have begun for LS, the majority of evidence remains in case reports and case series for a number of treatable genes, encoding cofactors or transporter proteins of the mitochondria. Our findings will form part of the international expert-led Solve-RD efforts to assist clinicians initiating treatments in patients with treatable variants of LS.

Thiamine deficiency disorders: a clinical perspective

Thiamine is an essential water‐soluble vitamin that plays an important role in energy metabolism. Thiamine deficiency presents many challenges to clinicians, in part due to the broad clinical spectrum, referred to as thiamine deficiency disorders (TDDs), affecting the metabolic, neurologic, cardiovascular, respiratory, gastrointestinal, and musculoskeletal systems. Concurrent illnesses and overlapping signs and symptoms with other disorders can further complicate this. As such, TDDs are frequently misdiagnosed and treatment opportunities missed, with fatal consequences or permanent neurologic sequelae. In the absence of specific diagnostic tests, a low threshold of clinical suspicion and early therapeutic thiamine is currently the best approach. Even in severe cases, rapid clinical improvement can occur within hours or days, with neurological involvement possibly requiring higher doses and a longer recovery time. Active research aims to help better identify patients with thiamine‐responsive disorders and future research is needed to determine effective dosing regimens for the various clinical presentations of TDDs. Understanding the clinical diagnosis and global burden of thiamine deficiency will help to implement national surveillance and population‐level prevention programs, with education to sensitize clinicians to TDDs. With concerted effort, the morbidity and mortality related to thiamine deficiency can be reduced.

A Proposed Diagnostic Algorithm for Inborn Errors of Metabolism Presenting With Movements Disorders

Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

Mitochondrial diseases are clinically and genetically heterogeneous. These diseases were initially described a little over three decades ago. Limited diagnostic tools created disease descriptions based on clinical, biochemical analytes, neuroimaging, and muscle biopsy findings. This diagnostic mechanism continued to evolve detection of inherited oxidative phosphorylation disorders and expanded discovery of mitochondrial physiology over the next two decades. Limited genetic testing hampered the definitive diagnostic identification and breadth of diseases. Over the last decade, the development and incorporation of massive parallel sequencing has identified approximately 300 genes involved in mitochondrial disease. Gene testing has enlarged our understanding of how genetic defects lead to cellular dysfunction and disease. These findings have expanded the understanding of how mechanisms of mitochondrial physiology can induce dysfunction and disease, but the complete collection of disease-causing gene variants remains incomplete. This article reviews the developments in disease gene discovery and the incorporation of gene findings with mitochondrial physiology. This understanding is critical to the development of targeted therapies.

The Relevance of Thiamine Evaluation in a Practical Setting

Thiamine is a crucial cofactor involved in the maintenance of carbohydrate metabolism and participates in multiple cellular metabolic processes. Although thiamine can be obtained from various food sources, some common food groups are deficient in thiamine, and it can be denatured by high temperature and pH. Additionally, different drugs can alter thiamine metabolism. In addition, the half-life of thiamine in the body is between 1 and 3 weeks. All these factors could provide an explanation for the relatively short period needed to develop thiamine deficiency and observe the consequent clinical symptoms. Thiamine deficiency could lead to neurological and cardiological problems. These clinical conditions could be severe or even fatal. Marginal deficiency too may promote weaker symptoms that might be overlooked. Patients undergoing upper gastrointestinal or pancreatic surgery could have or develop thiamine deficiency for many different reasons. To achieve the best outcome for these patients, we strongly recommend the execution of both an adequate preoperative nutritional assessment, which includes thiamine evaluation, and a close nutritional follow up to avoid a nutrient deficit in the postoperative period.

Vitamin B1 Intake in Multiple Sclerosis Patients and its Impact on Depression Presence: A Pilot Study

Vitamin B1, or thiamine, is one of the most relevant vitamins in obtaining energy for the nervous system. Thiamine deficiency or lack of activity causes neurological manifestations, especially symptoms of depression, intrinsic to multiple sclerosis (MS) and related to its pathogenesis. On this basis, the aim of this study was to determine the possible relationship between the nutritional habits of patients with MS and the presence of depression. Therefore, a cross-sectional and observational descriptive study was conducted. An analysis of dietary habits and vitamin B1 consumption in a Spanish population of 51 MS patients was performed by recording the frequency of food consumption. Results showed a vitamin B1 intake within the established range, mainly provided by the consumption of ultra-processed products such as cold meats or pastries, and a total carbohydrate consumption lower than recommended, which stands out for its high content of simple carbohydrates deriving from processed foods such as dairy desserts, juice, snacks, pastries, chocolate bars, soft drinks and fermented alcohol. In addition, a significant negative correlation between depression and the intake of thiamine and total carbohydrates was observed. These findings could explain the influence of MS patients' eating habits, and consequently vitamin B1 activity, on depression levels.

Resolved External Ophthalmoplegia and Hearing Loss in Wernicke's Encephalopathy With Thiamine Replacement

BACKGROUND

Wernicke encephalopathy (WE) is classically described by a clinical triad consisting of confusion, ataxia, and ophthalmoplegia, but recent reports emphasize a history of malnutrition along with 2 elements of the WE triad (Caine's criteria) to enhance diagnostic sensitivity. The ophthalmoplegia, vestibular, and auditory expeditious improvement with intravenous thiamine usually confirms the diagnosis; serum levels generally provide additional diagnostic certainty.

METHODS

Here, we discuss the case of a woman with a distant history of gastric sleeve, poor nutrition and protracted vomiting, who developed acute confusion, imbalance, near-total external ophthalmoplegia (EO), and hearing loss. The baseline thiamine level was 28 πmol/L (Normal: 70-180 πmol/L). We performed serial neurological, vestibular, and audiological examination to document over 5 days, the effect of intravenous (IV) thiamine, and again at 3 months with continued oral supplementation. We provide serial documentation with photographs and video recording of oculomotor abnormalities, audiometric testing, and a video of horizontal head impulse testing, and imaging findings.

RESULTS

Over the course of 5 days of IV thiamine supplementation, we demonstrate our patient's resolution of near complete EO. We assessed vestibular paresis with horizontal head impulse testing, after complete resolution of the EO. The initially positive bilateral h-HIT showed decreased gain and overt corrective saccades, it clinically resolved by day 5, but video h-HIT testing demonstrated persistent decreased horizontal vestibulo-ocular reflex (VOR) gain and covert horizontal saccades, which persisted at the 3-month examination. By contrast, the vertical VOR gain was normal without corrective saccades. Bedside audiometry completed during the acute phase demonstrated severely restricted auditory speech comprehension, which normalized 3 months later. Severe truncal ataxia improved as well.

CONCLUSIONS

This case is an example of how awareness of the variations in the clinical presentation of WE can be crucial in achieving an early diagnosis and obtaining better outcomes. A history of the poor nutritional status can be an important clue to aid in this early diagnosis.

Eleven novel mutations and clinical characteristics in seven Chinese patients with thiamine metabolism dysfunction syndrome

Thiamine metabolism dysfunction syndrome (THMD) comprises a group of clinically and genetically heterogeneous encephalopathies with autosomal recessive inheritance. Four genes, SLC19A3, SLC25A19, SLC19A2, and TPK1, are associated with this disorder. This study aimed to explore the clinical, biochemical and molecular characteristics of seven Chinese patients with THMD. Targeted next-generation sequencing of mitochondrial DNA and nuclear DNA was used to identify the causative mutations. The patients presented with subacute encephalopathy between the ages of 1-27 months. Brain magnetic resonance imaging (MRI) revealed abnormalities in the basal ganglia, indicating Leigh syndrome. Urine α-ketoglutarate in five patients was elevated. In four patients, five novel mutations (c.1276_1278delTAC, c.265A > C, c.197T > C, c.850T > C, whole gene deletion) were found in SLC19A3, which is associated with THMD2. In two patients, four novel mutations (c.194C > T, c.454C > A, c.481G > A, and c.550G > C) were identified in SLC25A19, supporting a diagnosis of THMD4. In one patient, two novel mutations (c.395T > C and c.614-1G > A) were detected in TPK1, which is indicative of THMD5. The patients received thiamine, biotin, and symptomatic therapy, upon which six patients demonstrated clinical improvement. Our findings expanded the phenotypic and genotypic spectrum of THMD, with eleven novel mutations identified in seven Chinese patients. Early diagnosis and treatment have a significant impact on prognosis.

The SLC transporter in nutrient and metabolic sensing, regulation, and drug development

The prevalence of metabolic diseases is growing worldwide. Accumulating evidence suggests that solute carrier (SLC) transporters contribute to the etiology of various metabolic diseases. Consistent with metabolic characteristics, the top five organs in which SLC transporters are highly expressed are the kidney, brain, liver, gut, and heart. We aim to understand the molecular mechanisms of important SLC transporter-mediated physiological processes and their potentials as drug targets. SLC transporters serve as ‘metabolic gate’ of cells and mediate the transport of a wide range of essential nutrients and metabolites such as glucose, amino acids, vitamins, neurotransmitters, and inorganic/metal ions. Gene-modified animal models have demonstrated that SLC transporters participate in many important physiological functions including nutrient supply, metabolic transformation, energy homeostasis, tissue development, oxidative stress, host defense, and neurological regulation. Furthermore, the human genomic studies have identified that SLC transporters are susceptible or causative genes in various diseases like cancer, metabolic disease, cardiovascular disease, immunological disorders, and neurological dysfunction. Importantly, a number of SLC transporters have been successfully targeted for drug developments. This review will focus on the current understanding of SLCs in regulating physiology, nutrient sensing and uptake, and risk of diseases.

Whole Exome Sequencing Identifies a Novel Mutation of TPK1 in a Chinese Family with Recurrent Ataxia

TPK deficiency, also known as thiamine metabolism dysfunction syndrome 5, is a rare autosomal recessive disorder of inborn error of metabolism caused by TPK1 gene mutation. Its clinical manifestation is highly variable, ranging from spontaneous remission to fatal metabolic crisis. Here, we describe two affected siblings in a Chinese family presenting with recurrent episodes of acute ataxia. Whole exome sequencing identified a homozygous missense variant c.382C > T (p.Leu128Phe) in the TPK gene, which is located in the thiamine binding domain and affects a highly conserved amino acid. Besides, a review of the 18 previously reported patients provides a better understanding of the clinical and genetic features of this disorder. TPK deficiency may be an under-diagnosed cause of acute encephalopathy and ataxia. Given the potential benefit of early intervention, TPK deficiency should be considered in patients with episodic encephalopathy or ataxia, especially those associated with lactic acidosis and α-ketoglutaric aciduria. Significant decreased TPP in the blood is a strong hint of the disease. WES (whole exome sequencing) can help to further identify the molecular diagnosis.

Diseases Caused by Mutations in Mitochondrial Carrier Genes SLC25: A Review

In the 1980s, after the mitochondrial DNA (mtDNA) had been sequenced, several diseases resulting from mtDNA mutations emerged. Later, numerous disorders caused by mutations in the nuclear genes encoding mitochondrial proteins were found. A group of these diseases are due to defects of mitochondrial carriers, a family of proteins named solute carrier family 25 (SLC25), that transport a variety of solutes such as the reagents of ATP synthase (ATP, ADP, and phosphate), tricarboxylic acid cycle intermediates, cofactors, amino acids, and carnitine esters of fatty acids. The disease-causing mutations disclosed in mitochondrial carriers range from point mutations, which are often localized in the substrate translocation pore of the carrier, to large deletions and insertions. The biochemical consequences of deficient transport are the compartmentalized accumulation of the substrates and dysfunctional mitochondrial and cellular metabolism, which frequently develop into various forms of myopathy, encephalopathy, or neuropathy. Examples of diseases, due to mitochondrial carrier mutations are: combined D-2- and L-2-hydroxyglutaric aciduria, carnitine-acylcarnitine carrier deficiency, hyperornithinemia-hyperammonemia-homocitrillinuria (HHH) syndrome, early infantile epileptic encephalopathy type 3, Amish microcephaly, aspartate/glutamate isoform 1 deficiency, congenital sideroblastic anemia, Fontaine progeroid syndrome, and citrullinemia type II. Here, we review all the mitochondrial carrier-related diseases known until now, focusing on the connections between the molecular basis, altered metabolism, and phenotypes of these inherited disorders.

Biotin–Thiamine Responsive Basal Ganglia Disease: A Treatable Metabolic Encephalopathy—Not to Be Missed!

Biotin–thiamine responsive basal ganglia disease (BTBGD) is an autosomal recessive neurometabolic disorder, characterized by encephalopathy, extrapyramidal signs following mild infection, trauma or surgery and is potentially reversible with treatment. We describe a 15-month-old female child of Indian-Muslim origin with characteristic clinical and radiological features of BTBGD that showed complete resolution with treatment. A comparison with previously reported cases reveals a different mutation (exon 2 vs. exon 5 in middle east cases) in the SLC19A3 gene that could be specific for the Indian subcontinent. We also emphasize the importance of a trial of vitamins in patients with acute metabolic encephalopathy.

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.

Conversion of upbeat to downbeat nystagmus in Wernicke encephalopathy

OBJECTIVE

To explain (1) why an initial upbeat nystagmus (UBN) converts to a permanent downbeat nystagmus (DBN) in Wernicke encephalopathy (WE) and (2) why convergence and certain vestibular provocative maneuvers may transiently switch UBN to DBN.

METHODS

Following a literature review and study of our 2 patients, we develop hypotheses for the unusual patterns of vertical nystagmus in WE.

RESULTS

Our overarching hypothesis is that there is a selective vulnerability and a selective recovery from thiamine deficiency of neurons within brainstem gaze-holding networks. Furthermore, since the circuits affected in WE are commonly paraventricular, especially medially, just under the floor of the fourth ventricle where lie structures important for control of vertical gaze, we suggest the patterns of involvement in WE also reflect a breakdown in vulnerable areas of the blood-brain barrier. Many of the initial deficits of our patients improved over time, but their DBN did not. Irreversible changes in paramedian tract neurons, which project to the cerebellar flocculus, may be the cause. Here we suggest that conversion of UBN to permanent DBN points to thiamine deficiency and may argue for a chronic, nonprogressive DBN/truncal ataxia syndrome. Finally, we posit that the transient switch of UBN to DBN reflects abnormal processing of otolith information about linear acceleration, and often points to a diagnosis of WE.

CONCLUSION

Recognizing the unusual patterns of transient switching and then permanent conversion of UBN to DBN in WE is vital since long-term disability from WE may be prevented by timely, parenteral high-dose thiamine.

Peripheral nerve disease secondary to systemic conditions in children

This review is an overview of systemic conditions that can be associated with peripheral nervous system dysfunction. Children may present with neuropathic symptoms for which, unless considered, a causative systemic condition may not be recognized. Similarly, some systemic conditions may be complicated by comorbid peripheral neuropathies, surveillance for which is indicated. The systemic conditions addressed in this review are critical illness polyneuropathy, chronic renal failure, endocrine disorders such as insulin-dependent diabetes mellitus and multiple endocrine neoplasia type 2b, vitamin deficiency states, malignancies and reticuloses, sickle cell disease, neurofibromatosis, connective tissue disorders, bowel dysmotility and enteropathy, and sarcoidosis. In some disorders presymptomatic screening should be undertaken, while in others there is no benefit from early detection of neuropathy. In children with idiopathic peripheral neuropathies, systemic disorders such as celiac disease should be actively excluded. While management is predominantly focused on symptomatic care through pain control and rehabilitation, some neuropathies improve with effective control of the underlying etiology and in a small proportion a more targeted approach is possible. In conclusion, peripheral neuropathies can be associated with a diverse range of medical conditions and unless actively considered may not be recognized and inadequately managed.

Utility of Whole Blood Thiamine Pyrophosphate Evaluation in TPK1-Related Diseases

TPK1 mutations are a rare, but potentially treatable, cause of thiamine deficiency. Diagnosis is challenging given the phenotypic overlap that exists with other metabolic and neurological disorders. We report a case of TPK1-related disease presenting with Leigh-like syndrome and review the diagnostic utility of thiamine pyrophosphate (TPP) blood measurement. The proband, a 35-year-old male, presented at four months of age with recurrent episodes of post-infectious encephalopathy. He subsequently developed epilepsy, learning difficulties, sensorineural hearing loss, spasticity, and dysphagia. There was a positive family history for Leigh syndrome in an older brother. Plasma lactate was elevated (3.51 mmol/L) and brain MRI showed bilateral basal ganglia hyperintensities, indicative of Leigh syndrome. Histochemical and spectrophotometric analysis of mitochondrial respiratory chain complexes I, II+III, and IV was normal. Genetic analysis of muscle mitochondrial DNA was negative. Whole exome sequencing of the proband confirmed compound heterozygous variants in TPK1: c. 426G>C (p. Leu142Phe) and c. 258+1G>A (p.?). Blood TPP levels were reduced, providing functional evidence for the deleterious effects of the variants. We highlight the clinical and bioinformatics challenges to diagnosing rare genetic disorders and the continued utility of biochemical analyses, despite major advances in DNA sequencing technology, when investigating novel, potentially disease-causing, genetic variants. Blood TPP measurement represents a fast and cost-effective diagnostic tool in TPK1-related diseases.

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.

Mutations in the mitochondrial complex I assembly factor NDUFAF6 cause isolated bilateral striatal necrosis and progressive dystonia in childhood

AIM

To perform a deep phenotype characterisation in a pedigree of 3 siblings with Leigh syndrome and compound heterozygous NDUFAF6 mutations.

METHOD

A multi-gene panel of childhood-onset basal ganglia neurodegeneration inherited conditions was analysed followed by functional studies in fibroblasts.

RESULTS

Three siblings developed gait dystonia in infancy followed by rapid progression to generalised dystonia and psychomotor regression. Brain magnetic resonance showed symmetric and bilateral cytotoxic lesions in the putamen and proliferation of the lenticular-striate arteries, latter spreading to the caudate and progressing to cavitation and volume loss. We identified a frameshift novel change (c.554_558delTTCTT; p.Tyr187AsnfsTer65) and a pathogenic missense change (c.371T>C; p.Ile124Thr) in the NDUFAF6 gene, which segregated with an autosomal recessive inheritance within the family. Patient mutations were associated with the absence of the NDUFAF6 protein and reduced activity and assembly of mature complex I in fibroblasts. By functional complementation assay, the mutant phenotype was rescued by the canonical version of the NDUFAF6. A literature review of 14 NDUFAF6 patients showed a consistent phenotype of an early childhood insidious onset neurological regression with prominent dystonia associated with basal ganglia degeneration and long survival.

INTERPRETATION

NDUFAF6-related Leigh syndrome is a relevant cause of childhood onset dystonia and isolated bilateral striatal necrosis. By genetic complementation, we could demonstrate the pathogenicity of novel genetic variants in NDUFAF6.

SLC13A3 variants cause acute reversible leukoencephalopathy and α-ketoglutarate accumulation

OBJECTIVE

SLC13A3 encodes the plasma membrane Na⁺ /dicarboxylate cotransporter 3, which imports inside the cell 4 to 6 carbon dicarboxylates as well as N-acetylaspartate (NAA). SLC13A3 is mainly expressed in kidney, in astrocytes, and in the choroid plexus. We describe two unrelated patients presenting with acute, reversible (and recurrent in one) neurological deterioration during a febrile illness. Both patients exhibited a reversible leukoencephalopathy and a urinary excretion of α-ketoglutarate (αKG) that was markedly increased and persisted over time. In one patient, increased concentrations of cerebrospinal fluid NAA and dicarboxylates (including αKG) were observed. Extensive workup was unsuccessful, and a genetic cause was suspected.

METHODS

Whole exome sequencing (WES) was performed. Our teams were connected through GeneMatcher.

RESULTS

WES analysis revealed variants in SLC13A3. A homozygous missense mutation (p.Ala254Asp) was found in the first patient. The second patient was heterozygous for another missense mutation (p.Gly548Ser) and an intronic mutation affecting splicing as demonstrated by reverse transcriptase polymerase chain reaction performed in muscle tissue (c.1016 + 3A > G). Mutations and segregation were confirmed by Sanger sequencing. Functional studies performed on HEK293T cells transiently transfected with wild-type and mutant SLC13A3 indicated that the missense mutations caused a marked reduction in the capacity to transport αKG, succinate, and NAA.

INTERPRETATION

SLC13A3 deficiency causes acute and reversible leukoencephalopathy with marked accumulation of αKG. Urine organic acids (especially αKG and NAA) and SLC13A3 mutations should be screened in patients presenting with unexplained reversible leukoencephalopathy, for which SLC13A3 deficiency is a novel differential diagnosis. ANN NEUROL 2019;85:385-395.

Dietary Intake and Food Sources of Niacin, Riboflavin, Thiamin and Vitamin B₆ in a Representative Sample of the Spanish Population. The Anthropometry, Intake, and Energy Balance in Spain (ANIBES) Study †

Thiamin, riboflavin, niacin, and vitamin B₆ are essential micronutrients that are mainly involved in energy metabolism; they may prevent the occurrence of developmental abnormalities and chronic degenerative and neoplastic diseases. The aim was to analyze dietary intake and food sources of those four nutrients in subjects (n = 2009) aged 9⁻75 years old from the Spanish ANIBES (Anthropometry, Intake, and Energy Balance in Spain) study. Dietary data were collected by means of a validated, photo-based three-day dietary food record. Underreporting was analysed according to the European Food and Safety Authority (EFSA, Parma, Italy) protocol. Mean (max⁻min) reported intake for the whole population of thiamin was 1.17 ± 0.02 mg/day, (0.30⁻3.44 mg/day), riboflavin 1.44 ± 0.02 mg/day, (0.37⁻3.54 mg/day), niacin 29.1 ± 0.2 mg/day (6.7⁻109 mg/day), and vitamin B₆ 1.54 ± 0.01 mg/day (0.28⁻9.30 mg/day). The main sources of intake for thiamin, niacin, and vitamin B₆ were meat and meat products, and for riboflavin were milk and dairy products. An elevated percentage of the Spanish ANIBES population meets the EFSA recommended intakes for thiamin (71.2%), riboflavin (72.0%), niacin (99.0%), and vitamin B₆ (77.2%).