Transcobalamin deficiency - a rare genetic defect in transportation of cobalamin; case report.

BACKGROUND: Vitamin B12 is primarily transported from plasma to cells by Transcobalamin. Deficiency of Transcobalamin is a rare autosomal recessive disorder that results in unavailability of cobalamin in cells and accumulation of homocysteine and methylmalonic acid. CASE REPORT: We report a case of a 2-year-old male child with persistent pancytopenia, recurrent infections, and megaloblastic anemia. Next-generation sequencing identified a novel variant in exon 8 of TCN2 gene. Substantial improvement has been observed following administration of high doses of parenteral methylcobalamin. CONCLUSION: In patients with unresolved pancytopenia and megaloblastic anemia, Transcobalamin deficiency should be investigated and treated promptly to prevent any irreversible and harmful outcome.

Severe megaloblastic anemia in a patient with advanced lung adenocarcinoma during treatment with erlotinib: a case report and literature review.

BACKGROUND: Erlotinib is a first-generation, tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR-TKI) used for the treatment patients with NSCLC. Erlotinib is considered as a safe and effective treatment option, with generally good tolerance. Diarrhea and rash are the most common side effects, and more rare side effects appear in long-term real-world applications. Severe erlotinib related megaloblastic anemia is rare and remains unreported. This is the first case report of severe megaloblastic anemia in a patient with advanced lung adenocarcinoma with an EGFR L858R mutation treated with erlotinib. In this report, the clinical manifestations, diagnosis and treatment of erlotinib related severe megaloblastic anemia are described, and the possible pathogenesis and related treatment options are discussed. CASE DESCRIPTION: Herein, we present a 57- year-old non-smoking female diagnosed with metastatic lung adenocarcinoma harboring an EGFR L858R mutation, who had received erlotinib as the first-line therapy. After 44 weeks of treatment, the patient developed severe anemia. Anemia was manifested as megaloblastic anemia with elevated mean corpuscular volume and mean corpuscular hemoglobin. The total vitamin B12 level was below the detection limit of 50.00 pg /mL. Bone marrow smear suggested megaloblastic anemia. Her hematologic parameters were markedly recovered following the withdrawal of erlotinib and vitamin B12 supplement. As a result, the patient was diagnosed with erlotinib-associated megaloblastic anemia. CONCLUSIONS: This is the first case of severe megaloblastic anemia reported with erlotinib. Few of these hematologic adverse effects have been observed in studies on erlotinib, this case report highlights this possibility for long-term erlotinib administration. Close clinical and blood monitoring is recommended for patients receiving long-term TKI therapy.

The effect of different types of anemia on HbA1c levels in non-diabetics.

BACKGROUND: Diabetes mellitus is one of the most common diseases worldwide with significant morbidity and mortality. HbA1c remains one of the most important methods for diagnosis and monitoring of the disease. Since HbA1c is a reflection of the glucose attached to red blood cells, factors affecting hemoglobin and red blood cells' half-life can influence HbA1c measurements. OBJECTIVE: This study aims to evaluate the effect of different types of anemia including iron deficiency anemia, sickle cell anemia, ß -thalassemia trait, and megaloblastic anemia on HbA1c levels in a tertiary hospital over the past 6 years (2016-2022). METHOD: This is a retrospective chart review study of 324 patients including those with one of the four types of anemia mentioned above and a control group. The control group were healthy adults with normal HbA1c and hemoglobin, who were not known to have diabetes or anemia. Patients with diabetes or prediabetes based on self-reporting or elevated fasting, random blood sugar, or 2 hours post-prandial blood glucose were excluded. RESULTS: The mean HbA1c levels were significantly higher in sickle cell anemia at 5.83% (95% CI = 5.39-6.28) and in iron deficiency anemia at 5.75% (95% CI = 5.68-5.82) when compared to the control group at 5.32% (95% CI = 5.22-5.41). However, the mean HbA1c levels in megaloblastic anemia were 5.38% (95% CI = 5.26-5.5) and 5.45% (95% CI = 5.21-5.69) in beta thalassemia trait, which were not significantly different when compared to the control group. HbA1c significantly decreased from 5.75 to 5.44% after treatment in the iron-deficient group with a p-value of < 0.001. Moreover, lower hemoglobin and higher red cell distribution width correlated with higher HbA1c levels in patients with sickle cell anemia. CONCLUSION: This study found a significant increase in HbA1c levels in iron deficiency anemia and sickle cell disease in patients not known to have diabetes. However, there was no significant effect in those patients with ß-thalassemia trait and megaloblastic anemia. Treatment of iron deficiency anemia significantly decreased the HbA1c level, bringing it back to normal.

Psychiatric symptoms in a female with subacute combined degeneration of the spinal cord (SCD): a case report.

BACKGROUND: Subacute combined degeneration of the spinal cord (SCD) is mainly caused by deficiency of Vitamin B12 and characterized by deep hypoesthesia, sensory ataxia and spasmodic paralysis of lower limbs. SCD often accompanies with megaloblastic anemia. Psychiatric symptoms could be the initial manifestations of SCD by lack of Vitamin B12, but are rarely considered secondary to physical discomfort and psychological factors in SCD. Additionally, treatment experience for psychiatric symptoms in SCD remains little reported. CASE REPORT: We presented a case of a 37-year-old female who complained of being persecuted and controlled for one week and thus was admitted to the psychiatry department. Before that, she had went through persistent paresthesia and numbness of her lower extremities for two-month. Low Vitamin B12 level and hemoglobin concentration, neurologic symptoms and bone marrow smear results supported the clinical diagnosis of SCD and megaloblastic anemia. With supplementation of Vitamin B12 and blood transfusion and short-term prescription of antipsychotics and antidepressants, physical symptoms were improved and psychological symptoms disappeared within 2 weeks. CONCLUSIONS: Psychiatric symptoms of SCD could be generated from lack of Vitamin B12, anemia and neurologic symptoms, where short-term use of antipsychotics and antidepressants may be effective.

Primary Neurologic Symptoms: Have You Considered Pernicious Anemia?

BACKGROUND: Vitamin B12, or cobalamin, is a nutrient that is vital for metabolic function. Absorption of ingested B12 is dependent on intrinsic factor, which is secreted by parietal cells within the stomach. Pernicious anemia is caused by an intrinsic factor deficiency or autoantibodies against intrinsic factor. The presence of parietal cell antibodies can destroy parietal cells, which can also lead to a deficiency in intrinsic factor. Both lead to megaloblastic anemia caused by vitamin B12 deficiency. The typical presentation of pernicious anemia includes fatigue, pale appearance, tingling sensation, depression, alterations to vision and smell, urinary incontinence, psychotic episodes, and weakness. The most effective treatment for pernicious anemia is intramuscular B12. CASE REPORT: A 27-year-old woman with a history of vitiligo presented to the emergency department (ED) with bilateral lower extremity weakness, clumsiness, numbness, and tingling. Physical examination revealed ataxia, no sensation below her umbilicus, decreased strength, and hyperreflexia in both lower extremities. Complete blood count in the ED revealed low hemoglobin and hematocrit and elevated mean corpuscular volume, concerning for pernicious anemia. Further laboratory testing upon inpatient admission revealed a low vitamin B12 level and parietal cell antibodies in the blood. The patient's pernicious anemia was treated with intramuscular vitamin B12 injections, which led to near complete resolution of her symptoms. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Early suspicion and detection of pernicious anemia in the ED can prevent serious and permanent hematologic and neurologic damage and the development of other autoimmune disorders.

Comparison of Serum Holotranscobalamin with Serum Vitamin B12 in Population Prone to Megaloblastic Anemia and their Correlation with Nerve Conduction Study.

Early detection of megaloblastic anemia and associated neurological complications is crucial for management. This study was conducted to compare serum holotranscobalamin level with serum vitamin B12 level as early biomarker in people prone to megaloblastic anemia and to evaluate co-relation between these biomarkers and nerve conduction study in study patients. 83 adult patients (Hb > 12 gm/dl) prone to megaloblastic anemia were studied for basic haematological investigations, random blood sugar, thyroid function test, liver function test, kidney function test, serum vitamin B12, serum holotranscobalamin and serum folic acid levels. 45 patients among them underwent nerve conduction studies. All study patients were classified in 6 groups on the basis of risk factors for megaloblastic anemia. 29 patients (34.9%) were on antiepileptic drugs, 26 (31.3%) were chronic alcoholic, 10 patients (12%) each, had malabsorption and ileal tuberculosis, 6 (7.22%) had chronic pancreatitis and 2 (2.4%) had ileal resection. 30 patients (36.14%) had low serum holotranscobalamin, including 7 patients (8.43%) with low serum vitamin B12 level also, unmasking vitamin B12 deficiency in 23 patients (27.7%). 7 patients (8.43%) had mean corpuscular volume (MCV) > 100fL and 8 patients (9.63%) had vitamin B12 deficiency related changes on peripheral smear. Serum vitamin B12 and holotranscobalamin levels were significantly low in patients with peripheral smear changes, with p value 0.039 and 0.041 respectively, while no such association seen with MCV. Subclinical peripheral neuropathy was detected in 18 (40%) out of 45 patients on nerve conduction study. Serum holotranscobalamin levels were significantly lower (p = 0.031) than serum vitamin B12 levels (p = 0.2) in patients with neuropathic changes. Rest investigations and serum folic acid levels were normal in all patients. Holotranscobalamin levels can be considered early and reliable marker for vitamin B12 deficiency and deficiency associated peripheral neuropathy, even in patients who are prone to megaloblastic anemia, and not yet anemic or symptomatic for neuropathy.

Leber congenital amaurosis as an initial manifestation in a Chinese patient with thiamine-responsive megaloblastic anemia syndrome.

Thiamine-responsive megaloblastic anemia syndrome (TRMA) is an autosomal recessive disorder, inherited by the defective SLC19A2 gene that encodes a high-affinity thiamine transporter (THTR-1). TRMA is characterized by the occurrence of classical triad manifestations including megaloblastic anemia, diabetes mellitus, and sensorineural deafness. In addition to the systemic manifestations, ophthalmic features can be present and include retinitis pigmentosa, optic atrophy, cone-rod dystrophy, maculopathy, and Leber congenital amaurosis. Here we report a 6-year-old boy presenting severe early-onset retinal dystrophy with the initial diagnosis of Leber congenital amaurosis, which followed for 12 years. Diabetes mellitus occurred 3 years after vision problem. Eosinophilic granuloma of the left scapula was confirmed at 13 years old. Whole-exome sequencing was performed to identify two novel compound heterozygous variants c.725dupC (p.Ala243Serfs*3) and c.121G>A (p.Gly41Ser) in SLC19A2 gene (NM_006996.3). Oral thiamine supplementation treatment was initiated at 13 years. This case demonstrates Leber congenital amaurosis can present as the first clinical feature before systemic manifestations. Phenotypic variety should be aware and multidisciplinary teamwork and regular follow-up are important for TRMA patient care.

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

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

Black Cohosh Herbal Extract and Hematologic Alterations in B6C3F1/N Mice.

Black cohosh is a readily available dietary supplement currently marketed as a remedy for dysmenorrhea and menopausal symptoms and is one of the top-selling herbal supplements in the United States. Black cohosh extract (BCE) was nominated to the National Toxicology Program (NTP) by the National Cancer Institute and the National Institute of Environmental Health Sciences due to its widespread use and lack of animal toxicity studies. Results of the NTP BCE subchronic mouse toxicity study revealed a dose-dependent, non-regenerative decrease in the erythron with an increase in the mean corpuscular volume (macrocytosis). Howell-Jolly bodies, or micronuclei, were significantly increased. These particular changes indicated an ineffective erythropoiesis consistent with a condition known as megaloblastic anemia. Megaloblastic anemia is due to disruptions in DNA synthesis during hematopoiesis and can be a result of an inherited or drug-induced disorder or a consequence of folate or cobalamin deficiency. Subsequent mouse studies revealed hematological and biochemical changes that were consistent with a functional cobalamin deficiency. This article will review basic mechanisms and laboratory features of megaloblastic anemia. The results of our studies including morphological abnormalities of the erythron and biomarkers of folate and cobalamin deficiencies, as well as hepatic microarray gene changes, are also discussed.

Overview of Session 3 Mechanisms of Decreased Erythropoiesis and Erythroid Cell Injury.

This session, held during the 41st Annual STP Symposium, focused on mechanisms of decreased erythropoiesis and erythroid cell injury. The speakers provided comprehensive overviews of physiologic and pathologic erythropoiesis, reviewed various mechanisms of erythroid cell injury, and shared innovative investigative research with the audience.

A novel TCN2 mutation with unusual clinical manifestations of hemolytic crisis and unexplained metabolic acidosis: expanding the genotype and phenotype of transcobalamin II deficiency.

BACKGROUND: Transcobalamin deficiency is a rare inborn metabolic disorder, characterized by pancytopenia, megaloblastic anemia, failure to thrive, diarrhea, and psychomotor retardation. CASE PRESENTATION: We describe a patient who first presented at 3 months of age, with pancytopenia, hepatosplenomegaly, recurrent infection, metabolic acidosis, and acute hemolytic crisis. Extensive hematologic and immunologic investigations did not identify inherited bone marrow failure syndrome, acute leukemia or its related disorders. Whole exome sequencing identified a novel homozygous TCN2 mutation, c.428-2A > G and mRNA study confirmed an aberrant transcription of exon 4 skipping. The mutant protein is predicted to have an in-fame 51 amino acids deletion (NP_000346:p.Gly143_Val193del). The patient exhibited marked clinical improvement following hydroxocobalamin treatment. CONCLUSIONS: Transcobalamin deficiency should be investigated in infants with unexplained pancytopenia and acute hemolytic crisis with or without typical evidence of vitamin B12 deficiency.

Enteral Vitamin B12 Supplementation Is Effective for Improving Anemia in Patients Who Underwent Total Gastrectomy.

BACKGROUND: This study aimed to investigate the efficacy of enteral supplementation of vitamin B12 for vitamin B12 deficiency in patients who underwent total gastrectomy for gastric cancer. METHODS: The study enrolled 133 patients who underwent total gastrectomy for gastric cancer at Kochi Medical School. Clinical data were obtained to investigate associations between vitamin B12 supplementation and vitamin B12 levels. Vitamin B12 deficiency was defined as serum vitamin B12 less than 200 pg/mL. Baseline characteristics and changes in hematological variables, including vitamin B12 levels, were examined. RESULTS: Vitamin B12 deficiency was present in 71.4% of the 133 patients. Vitamin B12 levels at 3, 6, and 12 months after enteral supplementation were 306 pg/mL, 294 pg/mL, and 367 pg/mL, respectively, which were all significantly higher than those before supplementation (p < 0.001 for all comparisons). The median red blood cell count at 3, 6, and 12 months after enteral supplementation were 380 × 104/mm3, 394 × 104/mm3, and 395 × 104/mm3, respectively, which were all significantly higher than those before supplementation (p = 0.020, p = 0.001, and p = 0.003, respectively). Vitamin B12 levels at 3, 6, and 12 months after supplementation were significantly higher in patients supplemented enterally than those supplemented parenterally (p < 0.001 for all comparisons). CONCLUSIONS: Vitamin B12 deficiency was found in 71.4% of postoperative patients who underwent total gastrectomy for gastric cancer, and enteral vitamin B12 supplements might be effective to improve anemia in these patients.

Biochemical analysis of patients with mutations in MTHFD1 and a diagnosis of methylenetetrahydrofolate dehydrogenase 1 deficiency.

MTHFD1 is a trifunctional protein containing 10-formyltetrahydrofolate synthetase, 5,10-methenyltetrahydrofolate cyclohydrolase and 5,10-methylenetetrahydrofolate dehydrogenase activities. It is encoded by MTHFD1 and functions in the cytoplasmic folate cycle where it is involved in de novo purine synthesis, synthesis of thymidylate and remethylation of homocysteine to methionine. Since the first reported case of severe combined immunodeficiency resulting from MTHFD1 mutations, seven additional patients ascertained through molecular analysis have been reported with variable phenotypes, including megaloblastic anemia, atypical hemolytic uremic syndrome, hyperhomocysteinemia, microangiopathy, infections and autoimmune diseases. We determined the level of MTHFD1 expression and dehydrogenase specific activity in cell extracts from cultured fibroblasts of three previously reported patients, as well as a patient with megaloblastic anemia and recurrent infections with compound heterozygous MTHFD1 variants that were predicted to be deleterious. MTHFD1 protein expression determined by Western blotting in fibroblast extracts from three of the patients was markedly decreased compared to expression in wild type cells (between 4.8 and 14.3% of mean control values). MTHFD1 expression in the fourth patient was approximately 44% of mean control values. There was no detectable methylenetetrahydrofolate dehydrogenase specific activity in extracts from any of the four patients. This is the first measurement of MTHFD1 function in MTHFD1 deficient patients and confirms the previous molecular diagnoses.

Hereditary intrinsic factor deficiency in China caused by a novel mutation in the intrinsic factor gene-a case report.

BACKGROUND: Hereditary intrinsic factor deficiency is a rare disease characterized by cobalamin deficiency with the lack of gastric intrinsic factor because of gastric intrinsic factor (GIF) mutations. Patients usually present with cobalamin deficiency without gastroscopy abnormality and intrinsic factor antibodies. CASE PRESENTATION: A Chinese patient presented with recurrent severe anemia since age 2 with low cobalamin level and a mild elevation of indirect bilirubin. The hemoglobin level normalized each time after intramuscular vitamin B12 injection. Gene test verified a c.776delA frame shift mutation in exon 6 combined with c.585C > A nonsense early termination mutation in exon 5 of GIF which result in the dysfunction of gastric intrinsic factor protein. The hereditary intrinsic factor deficiency in literature was further reviewed and the ancestry of different mutation sites were discussed. CONCLUSIONS: A novel compound heterozygous mutation of GIF in a Chinese patient of hereditary intrinsic factor deficiency was reported. It was the first identified mutation of GIF in East-Asia and may indicate a new ancestry.

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

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

Macropolycytes: Severe stress time for neutrophils.

Macropolycytes are giant neutrophils found in a variety of benign and neoplastic conditions. Since megaloblastic anaemia is one of the recognised causes of macropolycytes, other blood film features of megaloblastic anaemia should be sought when they harbor hypersegmented nuclei. When they are hypolobulated and hypogranular, the occurrence of a myelodysplastic syndrome must be investigated. Finding macropolycytes in the context of a nonspecific reactive granulopoiesis is more questionable but is often associated with stressed myelopoiesis and/or granulocyte colony-stimulating factor therapy.

[Cancer or vitamin B12 deficiency? Difficult differential diagnosis in elderly]. / Nowotwór czy niedobór witaminy B12? Trudna diagnostyka róznicowa u osób starszych.

Vitamin B12 deficiency anaemia in adults is usually caused by Addison- Biermer's disease. The presence of antibodies against gastric parietal cells and intrinsic factor (IF) in blood is typical for the disease. The gastrointestinal malabsorption or a diet poor in vitamin B12 are rarer causes. The disease manifests in hematological, neurological, psychiatric disorders and trophic changes of the tongue and oral mucosa, which leads to weight loss. A CASE REPORT: The authors describe a case of a 70-year-old woman with severe vitamin B12 deficiency based on chronic inflammatory lesions of the gastric mucosa caused by Helicobacter pylori infection. The patient had haematological (pancytopenia), neurological (problems with memory, concentration, numbness of the limbs, gait instability) and gastrological disorders (loss of appetite, weight loss). The laboratory and imaging diagnostics were performed. The neoplasmatic background was abandoned and pure vitamin B12 deficiency was diagnosed. All symptoms resolved completely after the supplementation and eradication of Helicobacter pylori. CONCLUSIONS: The article demonstrates the problem of many severe, non- specific complications of vitamin B12 deficiency which requires extensive diagnostics and treatment. The similarity of symptoms may suggest a malignant disease especially in elderly patients.

A deep intronic mutation of c.1166-285 T > G in SLC46A1 is shared by four unrelated Japanese patients with hereditary folate malabsorption (HFM).

Hereditary folate malabsorption (HFM) is an autosomal recessive disease caused by mutations in SLC46A1 encoding the proton-coupled folate transporter (PCFT). HFM patients present with various clinical features including megaloblastic anemia, thrombocytopenia, combined immunodeficiency and neurodevelopmental disorders. In this study, we report the same deep intronic mutation of c.1166-285 T > G shared by four unrelated Japanese patients with HFM. This mutation was shown to generate a cryptic splice donor site for a 168-bp insertion of intron 3 sequences, leading to premature termination in the middle of this insertion. This mutation could be a founder mutation in the Japanese population, but also could be a hot-spot and could be present in undiagnosed HFM patients worldwide because of the difficulty to detect this mutation.

Macrocytic anemia in Lesch-Nyhan disease and its variants.

PURPOSE: Lesch-Nyhan disease is an inherited metabolic disorder characterized by overproduction of uric acid and neurobehavioral abnormalities. The purpose of this study was  to describe macrocytic erythrocytes as another common aspect of the phenotype. METHODS: The results of 257 complete blood counts from 65 patients over a 23-year period were collected from 2 reference centers where many patients are seen regularly. RESULTS: Macrocytic erythrocytes occurred in 81-92% of subjects with Lesch-Nyhan disease or its neurological variants. After excluding cases with iron deficiency because it might pseudonormalize erythrocyte volumes, macrocytosis occurred in 97% of subjects. Macrocytic erythrocytes were sometimes accompanied by mild anemia, and rarely by severe anemia. CONCLUSION: These results establish macrocytic erythrocytes as a very common aspect of the clinical phenotype of Lesch-Nyhan disease and its neurological variants. Macrocytosis is so characteristic that its absence should prompt suspicion of a secondary process, such as iron deficiency. Because macrocytosis is uncommon in unaffected children, it can also be used as a clue for early diagnosis in children with neurodevelopmental delay. Better recognition of this characteristic feature of the disorder will also help to prevent unnecessary diagnostic testing and unnecessary attempts to treat it with folate or B12 supplements.

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.