Thiamine-Responsive Megaloblastic Anemia Syndrome

MONDO:0009575 Pathograph 22 Show in embeddings browser

Thiamine-responsive megaloblastic anemia syndrome (TRMA, Rogers syndrome) is an autosomal recessive disorder caused by biallelic variants in SLC19A2, which encodes THTR-1, the high-affinity thiamine transporter. Losing it does not abolish thiamine uptake - the low-affinity transporter THTR-2 and passive diffusion remain - so the disease is a defect of transport capacity rather than of the vitamin itself. That distinction is the whole of its pathophysiology and its treatment: raising extracellular thiamine to pharmacologic concentrations drives enough through the residual routes to restore intracellular thiamine pyrophosphate. The clinical triad is megaloblastic anemia, non-type-1 diabetes mellitus and progressive sensorineural hearing loss, corresponding to the three cell populations least able to tolerate the shortfall. The three arms respond to thiamine differently, and the hearing loss does not recover.

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1
Inheritance
9
Pathophys.
2
Histopath.
9
Phenotypes
2
Gaps
22
Pathograph
1
Genes
5
Medical Actions
1
Models
7
References
1
Deep Research
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Inheritance

1
Autosomal recessive HP:0000007
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"TRMA is inherited in an autosomal recessive manner."
The GeneReviews Genetic Counseling statement of inheritance.
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Discussions and Knowledge Gaps

2
Why does thiamine rescue the anemia and the diabetes but not the hearing loss?
INTERPRETATION trma_why_hearing_does_not_respond
Attached to
pathophysiology#Selective Inner Hair Cell Loss treatments#Pharmacologic Oral Thiamine
The three arms differ in whether the affected cells persist. Erythroid precursors are continuously replaced, so restoring the cofactor restores production. Beta cell dysfunction is at least partly functional, and the mouse diabetes resolved on repletion. Inner hair cells, by contrast, are lost - the mouse shows selective death of those cells under thiamine restriction - and mammalian cochlear hair cells do not regenerate. On that reading the deafness is irreversible not because the arm is thiamine-independent but because its endpoint is cell death rather than cell dysfunction, which predicts that treatment started before hair cell loss would preserve hearing while treatment started after would not. Whether that prediction holds in patients is the practical question, and the case-series emphasis on early diagnosis is consistent with it without establishing it.
What determines the thiamine concentration at which residual transport becomes sufficient, and does it differ between the affected tissues?
KNOWLEDGE GAP trma_residual_transport_threshold
Attached to
pathophysiology#Loss of High-Affinity Thiamine Transport
Pharmacologic thiamine works by driving flux through low-affinity routes, so each tissue's threshold depends on its residual transporter expression and its cofactor demand. The mouse becomes normal on a high-thiamine diet and sick on a thiamine-free one, which brackets the threshold in that model but not in patients. If the thresholds differ between marrow, islet and cochlea, that would explain the differing arm responses as a dosing problem rather than an intrinsic one - and would imply the standard 50-100 mg/day is adequate for some tissues and not others. No tissue-level threshold data were found in the sources used here.
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Pathophysiology

9
Biallelic SLC19A2 Loss of Function
Homozygous or compound heterozygous SLC19A2 variants. Characterized variants disrupt trafficking of THTR-1 to the plasma membrane rather than only its catalytic behaviour, so the transporter is absent from the site where it would act.
Downstream
Loss of High-Affinity Thiamine Transport Absent functional THTR-1 removes the high-affinity uptake route.
Show evidence (1 reference)
PMID:33649974 SUPPORT In Vitro
"Three previously uncharacterized SLC19A2 variants identified in TRMA patients exhibited disrupted localization to the plasma membrane along with near-complete loss-of-function."
Establishes mislocalization as the molecular consequence of patient variants, measured directly rather than predicted.
Loss of High-Affinity Thiamine Transport
The high-affinity component of thiamine uptake is lost. Crucially, uptake is not abolished: the low-affinity transporter and passive diffusion remain, which is why the defect is one of capacity at physiological thiamine concentrations rather than an absolute block.
thiamine transmembrane transport GO:0071934 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased thiamine transmembrane transport (GO:0071934). GO:0071934 is a biological process from the Gene Ontology. ↓ DECREASED
thiamine transmembrane transporter activity GO:0015234 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased thiamine transmembrane transporter activity (GO:0015234). GO:0015234 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Intracellular Thiamine Pyrophosphate Deficiency At physiological extracellular thiamine, residual uptake is insufficient to maintain the intracellular cofactor pool.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"Erythrocytes from Slc19a2(-/-) mice lacked the high-affinity component of thiamin transport."
Demonstrates that specifically the high-affinity component is lost, which is the basis for the residual-capacity model.
Intracellular Thiamine Pyrophosphate Deficiency
Thiamine pyrophosphate, the active cofactor for transketolase, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, falls below requirement in the cells that depend most on high-affinity uptake. This node is the branch point for the whole disease, and it branches wider than the triad. The three classic arms - erythroid, beta cell, inner hair cell - are the tissues whose demand exceeds what low-affinity transport can supply. But THTR-1 is expressed elsewhere too, which is the entry's stated mechanistic reason for the cardiac, neurologic and ocular manifestations, so those hang off this node as well. For the cardiac, neurologic and ocular arms the cofactor requirement is established while the route from it to any particular organ failure is not.
Downstream
Impaired Nucleotide Synthesis in Erythroid Precursors Transketolase supplies ribose-5-phosphate for nucleotide synthesis; rapidly dividing erythroid precursors are the first to decompensate.
Pancreatic Beta Cell Dysfunction Insulin secretion falls. The intermediate steps between cofactor shortfall and secretory failure are not established.
Selective Inner Hair Cell Loss Cochlear inner hair cells are lost preferentially, by a route that has not been resolved beyond the cofactor requirement.
Cardiac Rhythm Disturbance THTR-1 is expressed in cardiac tissue, so the cofactor shortfall is not confined to the three classic target organs. The route from a thiamine pyrophosphate deficit to a conduction disturbance is not established, and the manifestation is less frequent than the triad.
Seizures The neurologic arm of the same expression argument. GeneReviews names neurologic manifestations as a managed domain of the disease; the intermediate steps between cofactor shortfall and seizure are not established.
Stroke Reported alongside seizures in the wider literature, as a distinct cerebrovascular consequence rather than a variant of the seizure arm.
Optic Atrophy The ocular arm. This edge carries a treatment-timing consequence the others do not: early thiamine appears to prevent it, so the link is between a cofactor shortfall and a preventable structural loss rather than a fixed one.
Retinal Dystrophy Curated separately from optic atrophy because the source series separates them - one patient had both, another peripheral pigmentary retinal alterations only.
Show evidence (1 reference)
PMID:33649974 SUPPORT Human Clinical
"Data from electronic health records revealed reduced levels of thiamine pyrophosphate (TPP) in patients prescribed erythromycin, consistent with inhibition of SLC19A2-mediated thiamine transport."
Graded PARTIAL: this demonstrates that reducing SLC19A2 function lowers TPP in humans, but does so via pharmacological inhibition rather than in TRMA patients, so it supports the mechanism by analogy rather than directly.
Impaired Nucleotide Synthesis in Erythroid Precursors
Ineffective DNA synthesis in dividing haematopoietic precursors, producing the megaloblastic morphology. In the mouse the defect extends beyond the erythroid line.
erythroid progenitor cell CL:0000038 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves erythroid progenitor cell (CL:0000038). CL:0000038 is a cell type from the Cell Ontology.
transketolase activity GO:0004802 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased transketolase activity (GO:0004802). GO:0004802 is a molecular function from the Gene Ontology. ↓ DECREASED
Animal models
Slc19a2-null mouse on thiamine-restricted diet Mouse recapitulates Reproduces the marrow lesion, and extends it: the megaloblastosis in the mouse is not confined to the erythroid line but affects the myeloid and megakaryocyte lines as well. That is the observation behind this node's own statement that the defect is broader in the mouse than the node's erythroid scope implies, and it fits the proposed mechanism - a transketolase-dependent shortfall of ribose-5-phosphate would be expected to constrain any rapidly dividing precursor, not erythroid ones specifically.
Downstream
Persistent Macrocytosis The erythroid lesion outlives the anaemia it causes: red cells stay macrocytic on thiamine even after the haemoglobin corrects, so correcting the blood count is not the same as correcting the defect behind it.
Megaloblastic Anemia Ineffective erythropoiesis produces the anemia.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines."
Shows the marrow lesion and, notably, that it is not confined to the erythroid line even though anemia is what presents clinically.
Pancreatic Beta Cell Dysfunction
Reduced insulin secretion, without the autoimmune features of type 1 diabetes.
type B pancreatic cell CL:0000169 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves type B pancreatic cell (CL:0000169). CL:0000169 is a cell type from the Cell Ontology.
Animal models
Slc19a2-null mouse on thiamine-restricted diet Mouse recapitulates Develops diabetes with reduced insulin secretion on a thiamine-free diet, and the diabetes resolves on repletion.
Downstream
Diabetes Mellitus Insufficient insulin secretion produces hyperglycaemia.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"On a thiamin-free diet, Slc19a2(-/-) mice developed diabetes mellitus with reduced insulin secretion and an enhanced response to insulin."
Localizes the defect to secretion rather than to insulin resistance, matching the non-type-1 character of the human diabetes.
Selective Inner Hair Cell Loss
Cochlear inner hair cells are lost while outer hair cells are relatively spared - an unusual pattern for sensorineural hearing loss, and the reason the deficit behaves as an auditory neuropathy with a discrepancy between brainstem-response and otoacoustic-emission thresholds.
cochlear inner hair cell CL:0000589 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves cochlear inner hair cell (CL:0000589). CL:0000589 is a cell type from the Cell Ontology.
Animal models
Slc19a2-null mouse on thiamine-restricted diet Mouse recapitulates Reproduces the hearing loss and localizes it to selective inner hair cell loss, which explains the auditory-neuropathy pattern seen clinically.
Downstream
Progressive Sensorineural Hearing Loss Loss of the primary sensory receptor cells produces the hearing deficit; because the cells do not regenerate, the deficit does not recover.
Show evidence (1 reference)
PMID:16642288 SUPPORT Model Organism
"Cochlear histological analysis showed a pattern uncommon for sensorineural hearing loss: selective loss of inner hair cells after 1-2 weeks on low thiamine and significantly greater inner than outer hair cell loss after longer low-thiamine challenges."
Establishes the specific cellular lesion and its selectivity, which is what distinguishes this deafness mechanistically.
Megaloblastic Anemia
Onset between infancy and adolescence, with normal vitamin B12 and folate - the combination that distinguishes it from the common megaloblastic anemias.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"megaloblastic anemia with normal vitamin B12 / folic acid levels, with or without diabetes or hearing loss, in whom there is a response to oral thiamine"
The GeneReviews diagnostic criterion, which states both the finding and what excludes the common alternatives.
Diabetes Mellitus
Non-type-1 diabetes with onset from infancy to adolescence.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"The diabetes mellitus is non-type I in nature, with age of onset from infancy to adolescence."
Characterizes the diabetes and its timing.
Progressive Sensorineural Hearing Loss
Often detectable in toddlers, progressive, and irreversible. This is the arm that thiamine does not rescue.
Show evidence (2 references)
PMID:20301459 SUPPORT Human Clinical
"Progressive sensorineural hearing loss often occurs early and can be detected in toddlers; hearing loss is irreversible and may not be prevented by thiamine treatment."
States both the natural history and the crucial negative: treatment does not reliably prevent it.
PMID:38037112 SUPPORT Human Clinical
"In all Cases, thiamine therapy did not resolve the clinical manifestation of deafness."
A four-patient series in which every treated patient's deafness persisted, converting the GeneReviews hedge into a direct observation.
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Histopathology

2
Dysplastic Erythropoiesis with Megaloblastic Changes FREQUENT
The marrow finding, and the reason this entry needs one: it looks like myelodysplastic neoplasm. Dysplastic erythropoiesis with megaloblastic change, against normal serum folate and B12, is the picture that gets a TRMA patient diagnosed with MDS - one reported patient carried that diagnosis from age 26. What separates them is not the smear but what surrounds it: cytogenetics and molecular testing are normal, and the morphology reverts on thiamine. Marked not diagnostic for that reason: a finding that misdirects the diagnosis cannot be pathognomonic for the disease it disguises.
Show evidence (3 references)
PMID:39467528 SUPPORT Human Clinical
"The bone marrow smear showed dysplastic erythropoiesis with megaloblastic changes, and normal findings in cytogenetic and molecular genetic examinations"
The finding itself, together with the normal cytogenetics that is half of what distinguishes it from a myelodysplastic neoplasm.
PMID:39467528 SUPPORT Human Clinical
"Folic acid and vitamin B12 in serum are normal with dysplastic erythropoiesis in the bone marrow often mimicking myelodysplastic neoplasms (MDS) as a potential differential diagnosis"
Generalizes the mimicry beyond the single case, and names the two normal laboratory values that make the marrow picture surprising in the first place.
PMID:39467528 SUPPORT Human Clinical
"Treatment with oral thiamine 100 mg daily was initiated, and 12 weeks later hemoglobin levels and bone marrow morphology had normalized"
The other half of the discrimination, and the one that matters mechanistically: the morphology is a cofactor-supply state rather than a clonal lesion, so it reverts.
Ring Sideroblasts FREQUENT
Iron-laden mitochondria ringing the erythroblast nucleus, reported as a frequent finding on TRMA marrow smears. This is the second half of the resemblance to myelodysplastic neoplasm and arguably the more misleading half, because ring sideroblasts are a defining feature of one MDS subtype rather than a generic dysplastic change. Like the megaloblastic change above, it is not diagnostic of TRMA - it is what makes the wrong diagnosis plausible. Mechanistically it fits: thiamine pyrophosphate is a cofactor for the transketolase step this disease loses, and the mitochondrial iron accumulation reported here is the same lesion seen in the thiamine-responsive sideroblastic anaemias more broadly.
Show evidence (1 reference)
PMID:39467528 SUPPORT Human Clinical
"bone marrow smears frequently show ring sideroblasts"
Reports the finding as frequent, in the sentence that names it as the specific reason distinguishing TRMA from MDS is difficult.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Thiamine-Responsive Megaloblastic Anemia Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

9
Blood 1
Megaloblastic Anemia VERY_FREQUENT HP:0001889 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Megaloblastic anemia (HP:0001889). HP:0001889 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Thiamine-responsive megaloblastic anemia syndrome (TRMA) is characterized by megaloblastic anemia, progressive sensorineural hearing loss, and diabetes mellitus."
Names megaloblastic anemia as a defining feature of the syndrome.
Cardiovascular 2
Cardiac Rhythm Disturbance OCCASIONAL Arrhythmia HP:0011675 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Arrhythmia (HP:0011675). HP:0011675 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:38037112 SUPPORT Human Clinical
"In our report, patient 2 presented at the age of 6 years and 6 months with a sporadic junctional heart rhythm with normal heart rate without compromising cardiac function but probably requiring close cardiological follow-up."
This series' own cardiac observation - a junctional rhythm without functional compromise - which is why it is graded as the series' finding rather than a literature summary.
PMID:38037112 SUPPORT Other
"such as congenital heart defects and arrhythmias"
The wider literature's cardiac manifestations, quoted directly. Graded OTHER because the clause summarizes prior reports rather than this series' observation.
Stroke OCCASIONAL HP:0001297 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Stroke (HP:0001297). HP:0001297 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:20301459 SUPPORT Human Clinical
"Standard treatment for sensorineural hearing loss, diabetes mellitus, and ophthalmologic, cardiovascular, and neurologic manifestations."
GeneReviews names neurologic manifestations as a managed domain of this disease - the authoritative statement that they occur beyond the triad. Graded PARTIAL because the sentence names the domain rather than this specific manifestation.
PMID:38037112 SUPPORT Other
"However, this transporter is expressed in other tissues, and its deficiency may cause other less frequent clinical manifestations"
The mechanistic reason manifestations extend beyond the triad - THTR-1 expression in other tissues. Graded OTHER because the sentence summarizes prior reports rather than this series' own observations.
Ear 1
Sensorineural Hearing Loss VERY_FREQUENT Sensorineural hearing impairment HP:0000407 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorineural hearing impairment (HP:0000407), qualified as course progressive. HP:0000407 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Progressive sensorineural hearing loss often occurs early and can be detected in toddlers; hearing loss is irreversible and may not be prevented by thiamine treatment."
Establishes the course and irreversibility.
Endocrine 1
Diabetes Mellitus VERY_FREQUENT HP:0000819 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Diabetes mellitus (HP:0000819). HP:0000819 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Thiamine-responsive megaloblastic anemia syndrome (TRMA) is characterized by megaloblastic anemia, progressive sensorineural hearing loss, and diabetes mellitus."
Names diabetes as a defining feature of the syndrome.
Eye 2
Optic Atrophy OCCASIONAL HP:0000648 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Optic atrophy (HP:0000648). HP:0000648 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38037112 SUPPORT Human Clinical
"Early institution of high-dose thiamine supplementation seems to prevent the development of retinal changes and optic atrophy in TRMA patients."
Reports the ocular manifestations and links their prevention to early treatment; the series' one late-treated patient was the one who went blind.
Retinal Dystrophy OCCASIONAL HP:0000556 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinal dystrophy (HP:0000556). HP:0000556 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38037112 SUPPORT Human Clinical
"Early institution of high-dose thiamine supplementation seems to prevent the development of retinal changes and optic atrophy in TRMA patients."
Names retinal changes alongside optic atrophy as the ocular manifestations, and ties their prevention to early treatment.
Nervous System 1
Seizures OCCASIONAL HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:20301459 SUPPORT Human Clinical
"Standard treatment for sensorineural hearing loss, diabetes mellitus, and ophthalmologic, cardiovascular, and neurologic manifestations."
GeneReviews names neurologic manifestations as a managed domain of this disease - the authoritative statement that they occur beyond the triad. Graded PARTIAL because the sentence names the domain rather than this specific manifestation.
PMID:38037112 SUPPORT Other
"However, this transporter is expressed in other tissues, and its deficiency may cause other less frequent clinical manifestations"
The mechanistic reason manifestations extend beyond the triad - THTR-1 expression in other tissues. Graded OTHER because the sentence summarizes prior reports rather than this series' own observations.
Other 1
Persistent Macrocytosis FREQUENT Increased mean corpuscular volume HP:0005518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased mean corpuscular volume (HP:0005518). HP:0005518 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"The anemia is corrected with thiamine treatment, but the red cells remain macrocytic and anemia can recur if treatment is withdrawn."
Distinguishes correction of the anemia from correction of the underlying erythroid abnormality, and records treatment dependence.
🧬

Genetic Associations

1
SLC19A2
Gene: SLC19A2 hgnc:10938 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SLC19A2 (hgnc:10938). hgnc:10938 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:10391221 SUPPORT Human Clinical
"Mutations in a new gene, SLC19A2, encoding a putative transmembrane protein homologous to the reduced folate carrier proteins, were found in all affected individuals in six TRMA families"
The original gene identification across six families.
PMID:33649974 SUPPORT Other
"Approximately half of the 60 SLC19A2 mutations associated with TRMA are missense variants (Supplemental Table 1) (5, 25), yet few have been functionally characterized."
Gives the variant-class distribution and, importantly, how little of it has been functionally tested. Graded OTHER because the sentence is a Discussion-section summary of prior reports rather than a result of this study - the same construct this entry already grades OTHER elsewhere.
💊

Medical Actions

5
Pharmacologic Oral Thiamine
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: thiamine CHEBI:26948 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses thiamine, annotated with vitamin B1 (CHEBI:26948). CHEBI:26948 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Lifelong oral thiamine at 50-100 mg/day. It does not replace the missing transporter; it raises extracellular thiamine far enough that the residual low-affinity routes carry sufficient flux. The three disease arms respond differently, and the response is maintained only while treatment continues.
Mechanism Target:
RESTORES Intracellular Thiamine Pyrophosphate Deficiency — Mass action through the residual uptake routes restores the intracellular cofactor pool. This is the step the treatment actually acts on.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"The diabetes mellitus resolved after 6 weeks of thiamin repletion."
Repletion reverses an established arm of the phenotype in the model, which is the clearest demonstration that raising substrate is sufficient.
RESTORES Megaloblastic Anemia — The anemia corrects, though macrocytosis persists and the anemia recurs if treatment stops.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"The anemia is corrected with thiamine treatment, but the red cells remain macrocytic and anemia can recur if treatment is withdrawn."
States both the response and its limits.
MODULATES Diabetes Mellitus — Partial: insulin requirement may fall and onset may be delayed, but not in everyone.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Thiamine treatment may reduce insulin requirement and delay onset of diabetes in some individuals."
Graded PARTIAL because the source itself hedges both the effect and the proportion of patients showing it.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Lifelong use of pharmacologic doses (50-100 mg/day) of oral thiamine (vitamin B1) in affected individuals regardless of age."
The GeneReviews Management recommendation, including dose and duration.
Cochlear Implantation
Action: cochlear device implantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is cochlear device implantation, annotated with Surgical Procedure (NCIT:C15329). NCIT:C15329 is a clinical intervention from the NCI Thesaurus. Ontology label: Surgical Procedure NCIT:C15329
Platform: Device
The intervention that actually addresses the hearing arm. Thiamine does not rescue it, but that does not mean nothing can be done: implantation bypasses the lost inner hair cells rather than treating the metabolic lesion, and it is what is done in practice.
Mechanism Target:
BYPASSES Progressive Sensorineural Hearing Loss — Stimulates the auditory nerve directly, bypassing the inner hair cells whose loss causes the deficit.
Show evidence (1 reference)
PMID:38037112 SUPPORT Human Clinical
"At 13 months, the patient underwent cochlear implantation due to sensorineural hearing loss."
Documents implantation as the management of the hearing arm in a reported patient.
Red Blood Cell Transfusion
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
For severe anemia, ahead of or alongside thiamine.
Mechanism Target:
MODULATES Megaloblastic Anemia — Replaces circulating red cells; does not address the transport defect.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Red blood cell transfusion for severe anemia."
The GeneReviews Management recommendation for the acute anaemia.
Periconceptional and Pregnancy Glycaemic Control
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Other
Good diabetic control before and during pregnancy. This carries more weight here than the generic advice suggests: thiamine only MODULATES the diabetes arm, so this is the one place where the incompletely-treated arm has a defined management consequence.
Mechanism Target:
MODULATES Diabetes Mellitus — Manages the glycaemic consequences of the beta-cell arm during pregnancy; it does not address the transport defect.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"Pregnancy management: Good diabetic control prior to and during pregnancy is recommended."
The GeneReviews Management recommendation for pregnancy.
Audiological and Metabolic Surveillance
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Other
Annual monitoring of the efficacy of thiamine therapy and of progression across all three arms, since the hearing loss progresses independently of the treated arms.
Mechanism Target:
MODULATES Progressive Sensorineural Hearing Loss — Surveillance and standard hearing-loss management address the arm that treatment does not correct.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"At least annual monitoring of the efficacy of the oral thiamine therapy and of disease progression"
The GeneReviews surveillance recommendation.
🌍

Environmental Factors

1
Erythromycin exposure
Erythromycin inhibits SLC19A2-mediated thiamine transport at clinically relevant unbound plasma concentrations, and prescribed patients show reduced thiamine pyrophosphate. In a patient who already has only residual low-affinity uptake, a drug acting on the same transporter is a plausible additional insult, which makes this worth recording even though it was identified in the general population rather than in TRMA.
Show evidence (1 reference)
PMID:33649974 SUPPORT Human Clinical
"Data from electronic health records revealed reduced levels of thiamine pyrophosphate (TPP) in patients prescribed erythromycin, consistent with inhibition of SLC19A2-mediated thiamine transport."
Confirms the inhibition has a measurable consequence for cofactor levels in people.
Mechanism Target:
EXACERBATES Loss of High-Affinity Thiamine Transport — Pharmacological inhibition of the same transporter compounds the genetic loss of its function.
Show evidence (1 reference)
PMID:33649974 SUPPORT In Vitro
"Ten of 63 drugs inhibited SLC19A2-mediated thiamine transport ≥ 50% at screening concentrations; however, with the exception of erythromycin, none was predicted to inhibit SLC19A2 at clinically relevant unbound plasma concentrations."
Identifies erythromycin as the one screened drug expected to inhibit the transporter at achievable concentrations. Graded IN_VITRO because both halves of the sentence are non-clinical: the screen is an isotopic thiamine-uptake assay in HEK293 cells, and "predicted ... at clinically relevant unbound plasma concentrations" is an FDA (fu*Cmax)/IC50 calculation over literature pharmacokinetics, not a human observation. The word "clinically" qualifies the concentration threshold, not the study design. The human half of this paper is cited separately, from its electronic-health-record result.
🔬

Diagnosis

1
Thiamine-responsive megaloblastic anemia with normal B12 and folate
The diagnosis turns on a negative as much as a positive: megaloblastic anemia with normal vitamin B12 and folate excludes the two common causes and points at a transport defect, and the response to oral thiamine is itself diagnostic. Biallelic SLC19A2 variants confirm it.
Show evidence (1 reference)
PMID:20301459 SUPPORT Human Clinical
"megaloblastic anemia with normal vitamin B12 / folic acid levels, with or without diabetes or hearing loss, in whom there is a response to oral thiamine; and/or biallelic pathogenic variants in SLC19A2 identified by molecular genetic testing"
The GeneReviews Diagnosis/Testing criterion, giving both the biochemical-response route and the molecular one.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
Recorded as a case count rather than a rate because no rate exists. The most recent review that says anything quantitative says two things: 183 patients in as many families worldwide, and that the prevalence and incidence remain unknown. Those are not in tension - the count is an ascertainment floor, not an estimate, and the same source notes that next-generation sequencing has been increasing it. One case in the same literature was carried as myelodysplastic neoplasm for years before the molecular diagnosis, which is a concrete reason to read the count as a floor.
Show evidence (2 references)
PMID:38037112 SUPPORT Human Clinical
"A recent literature review conducted by Zhang et al. showed 183 patients with TRMA belonging to as many families from around the world"
The case count behind this record, and the one-family-per-patient detail that makes it a count of independent families rather than of related cases.
PMID:38037112 SUPPORT Human Clinical
"TRMA is an extremely rare syndrome, and to date, its prevalence and incidence are still unknown"
States directly that no rate is available, which is why this record carries a qualitative class and a case count rather than rate_per_100000.
🐁

Animal Models

1
Slc19a2-null mouse on thiamine-restricted diet
Reproduces all three arms of the human triad, but only when dietary thiamine is withdrawn. That conditionality is the model's most informative feature: it shows the phenotype is a function of transport capacity relative to substrate supply, not of the genotype alone.
Species
Mouse
Genotype
Slc19a2 -/-
Publication
PMID:12393806
Pathograph links
Pancreatic Beta Cell Dysfunction recapitulates fidelity: high Develops diabetes with reduced insulin secretion on a thiamine-free diet, and the diabetes resolves on repletion.
Limitations: Requires dietary thiamine restriction to manifest, whereas human patients become symptomatic on a normal diet; the mouse therefore models the mechanism faithfully but not the human threshold.
Readouts
Insulin secretion
Direction: DECREASED
Interpretation: Secretory failure is the proximate cause of the hyperglycaemia.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"On a thiamin-free diet, Slc19a2(-/-) mice developed diabetes mellitus with reduced insulin secretion and an enhanced response to insulin."
Measures the secretory defect and distinguishes it from resistance.
Glycaemic status after thiamine repletion
Direction: RESTORED
Interpretation: Reversibility on repletion establishes that the defect is a substrate-supply problem rather than fixed damage.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"The diabetes mellitus resolved after 6 weeks of thiamin repletion."
The rescue arm of the experiment.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"Thus, Slc19a2(-/-) mice have provided new insights into the TRMA disease pathogenesis and will provide a tool for studying the role of thiamin homeostasis in diabetes mellitus more broadly."
The authors' own statement of the model's relevance to the disease.
Impaired Nucleotide Synthesis in Erythroid Precursors recapitulates fidelity: high Reproduces the marrow lesion, and extends it: the megaloblastosis in the mouse is not confined to the erythroid line but affects the myeloid and megakaryocyte lines as well. That is the observation behind this node's own statement that the defect is broader in the mouse than the node's erythroid scope implies, and it fits the proposed mechanism - a transketolase-dependent shortfall of ribose-5-phosphate would be expected to constrain any rapidly dividing precursor, not erythroid ones specifically.
Limitations: Manifests only under dietary thiamine restriction, as with the other two arms. The trilineage extent is a mouse finding under an imposed deficiency; whether human TRMA marrow shows the same breadth is not established by this source, so the human node stays erythroid-scoped.
Readouts
Bone marrow morphology
Direction: ALTERED
Interpretation: Megaloblastic change across three lineages is the morphological readout of impaired DNA synthesis in dividing precursors.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines."
The measurement itself, including the lineage breadth that makes it more than a confirmation of the human phenotype.
Show evidence (1 reference)
PMID:12393806 SUPPORT Model Organism
"Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines."
Establishes that the model is informative for the haematopoietic arm, which was the one arm of the triad it was not linked to.
Selective Inner Hair Cell Loss recapitulates fidelity: high Reproduces the hearing loss and localizes it to selective inner hair cell loss, which explains the auditory-neuropathy pattern seen clinically.
Limitations: As with the diabetes, manifests only under dietary thiamine restriction; and the histology was obtained after defined low-thiamine challenges rather than across a lifetime of partial deficiency.
Readouts
Auditory brainstem response versus otoacoustic emission thresholds
Direction: INCREASED
Interpretation: The discrepancy between the two measures is the functional signature of a lesion at the inner hair cell rather than the outer.
Show evidence (1 reference)
PMID:16642288 SUPPORT Model Organism
"Slc19a2-null mice showed 40-60 dB threshold elevations by auditory brainstem response (ABR), but only 10-20 dB elevation by otoacoustic emission (OAE) measures."
Quantifies the discrepancy that identifies the site of the lesion.
Show evidence (1 reference)
PMID:16642288 SUPPORT Model Organism
"Cochlear function is normal in these mutants when maintained on a high-thiamine diet."
The control condition that makes the model interpretable: genotype alone is not sufficient.
{ }

Source YAML

click to show 
name: Thiamine-Responsive Megaloblastic Anemia Syndrome
description: >-
  Thiamine-responsive megaloblastic anemia syndrome (TRMA, Rogers syndrome) is an
  autosomal recessive disorder caused by biallelic variants in SLC19A2, which encodes
  THTR-1, the high-affinity thiamine transporter. Losing it does not abolish thiamine
  uptake - the low-affinity transporter THTR-2 and passive diffusion remain - so the
  disease is a defect of transport capacity rather than of the vitamin itself. That
  distinction is the whole of its pathophysiology and its treatment: raising
  extracellular thiamine to pharmacologic concentrations drives enough through the
  residual routes to restore intracellular thiamine pyrophosphate. The clinical triad
  is megaloblastic anemia, non-type-1 diabetes mellitus and progressive sensorineural
  hearing loss, corresponding to the three cell populations least able to tolerate the
  shortfall. The three arms respond to thiamine differently, and the hearing loss does
  not recover.
disease_term:
  preferred_term: thiamine-responsive megaloblastic anemia syndrome
  term:
    id: MONDO:0009575
    label: thiamine-responsive megaloblastic anemia syndrome
creation_date: "2026-08-27T18:45:00Z"

references:
- reference: PMID:20301459
  title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
  tags:
  - GeneReviews
- reference: PMID:10391221
  title: >-
    Mutations in SLC19A2 cause thiamine-responsive megaloblastic anaemia associated
    with diabetes mellitus and deafness.
- reference: PMID:12393806
  title: >-
    Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin
    transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and
    megaloblastosis in mice.
- reference: PMID:16642288
  title: >-
    Deletion of SLC19A2, the high affinity thiamine transporter, causes selective inner
    hair cell loss and an auditory neuropathy phenotype.
- reference: PMID:33649974
  title: >-
    The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine
    Transporter, SLC19A2.
- reference: PMID:38037112
  title: "An Italian case series' description of thiamine responsive megaloblastic anemia\
    \ syndrome: importance of early diagnosis and treatment."
- reference: PMID:39467528
  title: >-
    Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic
    Neoplasm.

pathophysiology:
- name: Biallelic SLC19A2 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Homozygous or compound heterozygous SLC19A2 variants. Characterized variants
    disrupt trafficking of THTR-1 to the plasma membrane rather than only its catalytic
    behaviour, so the transporter is absent from the site where it would act.
  evidence:
  - reference: PMID:33649974
    reference_title: "The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Three previously uncharacterized SLC19A2 variants identified in TRMA patients
      exhibited disrupted localization to the plasma membrane along with
      near-complete loss-of-function.
    explanation: >-
      Establishes mislocalization as the molecular consequence of patient variants,
      measured directly rather than predicted.
  downstream:
  - target: Loss of High-Affinity Thiamine Transport
    causal_link_type: DIRECT
    description: Absent functional THTR-1 removes the high-affinity uptake route.

- name: Loss of High-Affinity Thiamine Transport
  biological_scale: CELLULAR
  description: >-
    The high-affinity component of thiamine uptake is lost. Crucially, uptake is not
    abolished: the low-affinity transporter and passive diffusion remain, which is why
    the defect is one of capacity at physiological thiamine concentrations rather than
    an absolute block.
  molecular_functions:
  - preferred_term: thiamine transmembrane transporter activity
    modifier: DECREASED
    term:
      id: GO:0015234
      label: thiamine transmembrane transporter activity
  biological_processes:
  - preferred_term: thiamine transmembrane transport
    modifier: DECREASED
    term:
      id: GO:0071934
      label: thiamine transmembrane transport
  evidence:
  - reference: PMID:12393806
    reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Erythrocytes from Slc19a2(-/-) mice lacked the high-affinity component of thiamin
      transport.
    explanation: >-
      Demonstrates that specifically the high-affinity component is lost, which is the
      basis for the residual-capacity model.
  downstream:
  - target: Intracellular Thiamine Pyrophosphate Deficiency
    causal_link_type: DIRECT
    description: >-
      At physiological extracellular thiamine, residual uptake is insufficient to
      maintain the intracellular cofactor pool.

- name: Intracellular Thiamine Pyrophosphate Deficiency
  biological_scale: MOLECULAR
  description: >-
    Thiamine pyrophosphate, the active cofactor for transketolase, pyruvate
    dehydrogenase and alpha-ketoglutarate dehydrogenase, falls below requirement in the
    cells that depend most on high-affinity uptake.

    This node is the branch point for the whole disease, and it branches wider than the
    triad. The three classic arms - erythroid, beta cell, inner hair cell - are the
    tissues whose demand exceeds what low-affinity transport can supply. But THTR-1 is
    expressed elsewhere too, which is the entry's stated mechanistic reason for the
    cardiac, neurologic and ocular manifestations, so those hang off this node as well.
    For the cardiac, neurologic and ocular arms the cofactor requirement is
    established while the route from it to any particular organ failure is not.
  evidence:
  - reference: PMID:33649974
    reference_title: "The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Data from electronic health records revealed reduced levels of thiamine
      pyrophosphate (TPP) in patients prescribed erythromycin, consistent with
      inhibition of SLC19A2-mediated thiamine transport.
    explanation: >-
      Graded PARTIAL: this demonstrates that reducing SLC19A2 function lowers TPP in
      humans, but does so via pharmacological inhibition rather than in TRMA patients,
      so it supports the mechanism by analogy rather than directly.
  downstream:
  - target: Impaired Nucleotide Synthesis in Erythroid Precursors
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Transketolase supplies ribose-5-phosphate for nucleotide synthesis; rapidly
      dividing erythroid precursors are the first to decompensate.
  - target: Pancreatic Beta Cell Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Insulin secretion falls. The intermediate steps between cofactor shortfall and
      secretory failure are not established.
  - target: Selective Inner Hair Cell Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cochlear inner hair cells are lost preferentially, by a route that has not been
      resolved beyond the cofactor requirement.
  - target: Cardiac Rhythm Disturbance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      THTR-1 is expressed in cardiac tissue, so the cofactor shortfall is not confined
      to the three classic target organs. The route from a thiamine pyrophosphate
      deficit to a conduction disturbance is not established, and the manifestation is
      less frequent than the triad.
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The neurologic arm of the same expression argument. GeneReviews names neurologic
      manifestations as a managed domain of the disease; the intermediate steps between
      cofactor shortfall and seizure are not established.
  - target: Stroke
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reported alongside seizures in the wider literature, as a distinct cerebrovascular
      consequence rather than a variant of the seizure arm.
  - target: Optic Atrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The ocular arm. This edge carries a treatment-timing consequence the others do
      not: early thiamine appears to prevent it, so the link is between a cofactor
      shortfall and a preventable structural loss rather than a fixed one.
  - target: Retinal Dystrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Curated separately from optic atrophy because the source series separates them -
      one patient had both, another peripheral pigmentary retinal alterations only.

- name: Impaired Nucleotide Synthesis in Erythroid Precursors
  biological_scale: CELLULAR
  description: >-
    Ineffective DNA synthesis in dividing haematopoietic precursors, producing the
    megaloblastic morphology. In the mouse the defect extends beyond the erythroid line.
  cell_types:
  - preferred_term: erythroid progenitor cell
    term:
      id: CL:0000038
      label: erythroid progenitor cell
  molecular_functions:
  - preferred_term: transketolase activity
    modifier: DECREASED
    term:
      id: GO:0004802
      label: transketolase activity
  evidence:
  - reference: PMID:12393806
    reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a
      megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines.
    explanation: >-
      Shows the marrow lesion and, notably, that it is not confined to the erythroid
      line even though anemia is what presents clinically.
  downstream:
  - target: Persistent Macrocytosis
    causal_link_type: DIRECT
    description: >-
      The erythroid lesion outlives the anaemia it causes: red cells stay macrocytic on
      thiamine even after the haemoglobin corrects, so correcting the blood count is not
      the same as correcting the defect behind it.
  - target: Megaloblastic Anemia
    causal_link_type: DIRECT
    description: Ineffective erythropoiesis produces the anemia.

- name: Pancreatic Beta Cell Dysfunction
  biological_scale: CELLULAR
  description: Reduced insulin secretion, without the autoimmune features of type 1 diabetes.
  cell_types:
  - preferred_term: type B pancreatic cell
    term:
      id: CL:0000169
      label: type B pancreatic cell
  evidence:
  - reference: PMID:12393806
    reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      On a thiamin-free diet, Slc19a2(-/-) mice developed diabetes mellitus with
      reduced insulin secretion and an enhanced response to insulin.
    explanation: >-
      Localizes the defect to secretion rather than to insulin resistance, matching the
      non-type-1 character of the human diabetes.
  downstream:
  - target: Diabetes Mellitus
    causal_link_type: DIRECT
    description: Insufficient insulin secretion produces hyperglycaemia.

- name: Selective Inner Hair Cell Loss
  biological_scale: TISSUE
  description: >-
    Cochlear inner hair cells are lost while outer hair cells are relatively spared -
    an unusual pattern for sensorineural hearing loss, and the reason the deficit
    behaves as an auditory neuropathy with a discrepancy between brainstem-response and
    otoacoustic-emission thresholds.
  cell_types:
  - preferred_term: cochlear inner hair cell
    term:
      id: CL:0000589
      label: cochlear inner hair cell
  evidence:
  - reference: PMID:16642288
    reference_title: "Deletion of SLC19A2, the high affinity thiamine transporter, causes selective inner hair cell loss and an auditory neuropathy phenotype."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Cochlear histological analysis showed a pattern uncommon for sensorineural
      hearing loss: selective loss of inner hair cells after 1-2 weeks on low thiamine
      and significantly greater inner than outer hair cell loss after longer
      low-thiamine challenges.
    explanation: >-
      Establishes the specific cellular lesion and its selectivity, which is what
      distinguishes this deafness mechanistically.
  downstream:
  - target: Progressive Sensorineural Hearing Loss
    causal_link_type: DIRECT
    description: >-
      Loss of the primary sensory receptor cells produces the hearing deficit; because
      the cells do not regenerate, the deficit does not recover.

- name: Megaloblastic Anemia
  biological_scale: ORGANISM
  description: >-
    Onset between infancy and adolescence, with normal vitamin B12 and folate - the
    combination that distinguishes it from the common megaloblastic anemias.
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      megaloblastic anemia with normal vitamin B12 / folic acid levels, with or without
      diabetes or hearing loss, in whom there is a response to oral thiamine
    explanation: >-
      The GeneReviews diagnostic criterion, which states both the finding and what
      excludes the common alternatives.

- name: Diabetes Mellitus
  biological_scale: ORGANISM
  description: Non-type-1 diabetes with onset from infancy to adolescence.
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diabetes mellitus is non-type I in nature, with age of onset from infancy to
      adolescence.
    explanation: Characterizes the diabetes and its timing.

- name: Progressive Sensorineural Hearing Loss
  biological_scale: ORGANISM
  description: >-
    Often detectable in toddlers, progressive, and irreversible. This is the arm that
    thiamine does not rescue.
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Progressive sensorineural hearing loss often occurs early and can be detected in
      toddlers; hearing loss is irreversible and may not be prevented by thiamine
      treatment.
    explanation: >-
      States both the natural history and the crucial negative: treatment does not
      reliably prevent it.
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In all Cases, thiamine therapy did not resolve the clinical manifestation of
      deafness.
    explanation: >-
      A four-patient series in which every treated patient's deafness persisted,
      converting the GeneReviews hedge into a direct observation.

phenotypes:
- category: Hematologic
  name: Megaloblastic Anemia
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Megaloblastic anemia
    term:
      id: HP:0001889
      label: Megaloblastic anemia
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thiamine-responsive megaloblastic anemia syndrome (TRMA) is characterized by
      megaloblastic anemia, progressive sensorineural hearing loss, and diabetes
      mellitus.
    explanation: Names megaloblastic anemia as a defining feature of the syndrome.

- category: Endocrine
  name: Diabetes Mellitus
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Diabetes mellitus
    term:
      id: HP:0000819
      label: Diabetes mellitus
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thiamine-responsive megaloblastic anemia syndrome (TRMA) is characterized by
      megaloblastic anemia, progressive sensorineural hearing loss, and diabetes
      mellitus.
    explanation: Names diabetes as a defining feature of the syndrome.

- category: Sensory
  name: Sensorineural Hearing Loss
  frequency: VERY_FREQUENT
  description: >-
    Early-onset, progressive and irreversible; behaves as an auditory neuropathy
    because the lesion is at the inner hair cell.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Progressive sensorineural hearing loss often occurs early and can be detected in
      toddlers; hearing loss is irreversible and may not be prevented by thiamine
      treatment.
    explanation: Establishes the course and irreversibility.

- category: Hematologic
  name: Persistent Macrocytosis
  frequency: FREQUENT
  description: >-
    Red cells remain macrocytic on treatment even after the anemia corrects, so
    normalization of the blood count is not the same as reversal of the cellular defect.
    Bound to the raised-MCV term rather than to Macrocytic anemia, because the whole
    point of this phenotype is that it persists once the anemia has gone.
  phenotype_term:
    preferred_term: Increased mean corpuscular volume
    term:
      id: HP:0005518
      label: Increased mean corpuscular volume
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The anemia is corrected with thiamine treatment, but the red cells remain
      macrocytic and anemia can recur if treatment is withdrawn.
    explanation: >-
      Distinguishes correction of the anemia from correction of the underlying
      erythroid abnormality, and records treatment dependence.

- category: Ophthalmologic
  name: Optic Atrophy
  frequency: OCCASIONAL
  description: >-
    An arm beyond the classic triad, and the one where the timing of treatment appears
    to matter most.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Early institution of high-dose thiamine supplementation seems to prevent the
      development of retinal changes and optic atrophy in TRMA patients.
    explanation: >-
      Reports the ocular manifestations and links their prevention to early treatment;
      the series' one late-treated patient was the one who went blind.

- category: Ophthalmologic
  name: Retinal Dystrophy
  frequency: OCCASIONAL
  description: >-
    Distinguished from optic atrophy because the reported series separates them - one
    patient had both, another peripheral pigmentary retinal alterations only.
  phenotype_term:
    preferred_term: Retinal dystrophy
    term:
      id: HP:0000556
      label: Retinal dystrophy
  evidence:
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Early institution of high-dose thiamine supplementation seems to prevent the
      development of retinal changes and optic atrophy in TRMA patients.
    explanation: >-
      Names retinal changes alongside optic atrophy as the ocular manifestations, and
      ties their prevention to early treatment.

- category: Cardiovascular
  name: Cardiac Rhythm Disturbance
  frequency: OCCASIONAL
  description: >-
    A manifestation beyond the classic triad, reflecting THTR-1 expression in cardiac
    tissue. Reported here as a sporadic junctional rhythm without functional compromise;
    the wider literature also records congenital heart defects and arrhythmias.
  phenotype_term:
    preferred_term: Arrhythmia
    term:
      id: HP:0011675
      label: Arrhythmia
  evidence:
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In our report, patient 2 presented at the age of 6 years and 6 months with a
      sporadic junctional heart rhythm with normal heart rate without compromising
      cardiac function but probably requiring close cardiological follow-up.
    explanation: >-
      This series' own cardiac observation - a junctional rhythm without functional
      compromise - which is why it is graded as the series' finding rather than a
      literature summary.
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: such as congenital heart defects and arrhythmias
    explanation: >-
      The wider literature's cardiac manifestations, quoted directly. Graded OTHER
      because the clause summarizes prior reports rather than this series' observation.

- category: Neurologic
  name: Seizures
  frequency: OCCASIONAL
  description: >-
    A manifestation beyond the classic triad, reflecting THTR-1 expression in neural
    tissue.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:20301459
    reference_title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Standard treatment for sensorineural hearing loss, diabetes mellitus, and
      ophthalmologic, cardiovascular, and neurologic manifestations.
    explanation: >-
      GeneReviews names neurologic manifestations as a managed domain of this disease -
      the authoritative statement that they occur beyond the triad. Graded PARTIAL
      because the sentence names the domain rather than this specific manifestation.
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, this transporter is expressed in other tissues, and its deficiency may
      cause other less frequent clinical manifestations
    explanation: >-
      The mechanistic reason manifestations extend beyond the triad - THTR-1 expression
      in other tissues. Graded OTHER because the sentence summarizes prior reports
      rather than this series' own observations.

- category: Neurologic
  name: Stroke
  frequency: OCCASIONAL
  description: >-
    Reported in the wider literature alongside seizures as a neurologic consequence of
    THTR-1 deficiency outside the classic triad.
  phenotype_term:
    preferred_term: Stroke
    term:
      id: HP:0001297
      label: Stroke
  evidence:
  - reference: PMID:20301459
    reference_title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Standard treatment for sensorineural hearing loss, diabetes mellitus, and
      ophthalmologic, cardiovascular, and neurologic manifestations.
    explanation: >-
      GeneReviews names neurologic manifestations as a managed domain of this disease -
      the authoritative statement that they occur beyond the triad. Graded PARTIAL
      because the sentence names the domain rather than this specific manifestation.
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, this transporter is expressed in other tissues, and its deficiency may
      cause other less frequent clinical manifestations
    explanation: >-
      The mechanistic reason manifestations extend beyond the triad - THTR-1 expression
      in other tissues. Graded OTHER because the sentence summarizes prior reports
      rather than this series' own observations.

diagnosis:
- name: Thiamine-responsive megaloblastic anemia with normal B12 and folate
  description: >-
    The diagnosis turns on a negative as much as a positive: megaloblastic anemia with
    normal vitamin B12 and folate excludes the two common causes and points at a
    transport defect, and the response to oral thiamine is itself diagnostic. Biallelic
    SLC19A2 variants confirm it.
  evidence:
  - reference: PMID:20301459
    reference_title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      megaloblastic anemia with normal vitamin B12 / folic acid levels, with or without
      diabetes or hearing loss, in whom there is a response to oral thiamine; and/or
      biallelic pathogenic variants in SLC19A2 identified by molecular genetic testing
    explanation: >-
      The GeneReviews Diagnosis/Testing criterion, giving both the biochemical-response
      route and the molecular one.

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Recorded as a case count rather than a rate because no rate exists. The most recent
    review that says anything quantitative says two things: 183 patients in as many
    families worldwide, and that the prevalence and incidence remain unknown. Those are
    not in tension - the count is an ascertainment floor, not an estimate, and the same
    source notes that next-generation sequencing has been increasing it. One case in
    the same literature was carried as myelodysplastic neoplasm for years before the
    molecular diagnosis, which is a concrete reason to read the count as a floor.
  evidence:
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A recent literature review conducted by Zhang et al. showed 183 patients with TRMA
      belonging to as many families from around the world
    explanation: >-
      The case count behind this record, and the one-family-per-patient detail that
      makes it a count of independent families rather than of related cases.
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      TRMA is an extremely rare syndrome, and to date, its prevalence and incidence are
      still unknown
    explanation: >-
      States directly that no rate is available, which is why this record carries a
      qualitative class and a case count rather than rate_per_100000.

histopathology:
- name: Dysplastic Erythropoiesis with Megaloblastic Changes
  finding_term:
    preferred_term: dysplastic erythropoiesis with megaloblastic changes
    term:
      id: NCIT:C35825
      label: Megaloblastic Erythroid Hyperplasia
  frequency: FREQUENT
  diagnostic: false
  description: >-
    The marrow finding, and the reason this entry needs one: it looks like
    myelodysplastic neoplasm. Dysplastic erythropoiesis with megaloblastic change,
    against normal serum folate and B12, is the picture that gets a TRMA patient
    diagnosed with MDS - one reported patient carried that diagnosis from age 26. What
    separates them is not the smear but what surrounds it: cytogenetics and molecular
    testing are normal, and the morphology reverts on thiamine. Marked not diagnostic
    for that reason: a finding that misdirects the diagnosis cannot be pathognomonic
    for the disease it disguises.
  context: >-
    The NCIT term is the closest available fit rather than an exact one. NCIT:C206357
    (Dyserythropoiesis) is the better label for the dysplastic component but is not
    reachable from any HistopathologyFindingTerm source node, so it cannot be bound
    here; NCIT:C82929 (Megaloblastoid Changes Present) is reachable but "megaloblastoid"
    is conventionally the hedged form of the word and the source says megaloblastic. The
    preferred_term therefore carries the finding as reported.
  evidence:
  - reference: PMID:39467528
    reference_title: >-
      Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic
      Neoplasm.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The bone marrow smear showed dysplastic erythropoiesis with megaloblastic changes,
      and normal findings in cytogenetic and molecular genetic examinations
    explanation: >-
      The finding itself, together with the normal cytogenetics that is half of what
      distinguishes it from a myelodysplastic neoplasm.
  - reference: PMID:39467528
    reference_title: >-
      Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic
      Neoplasm.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Folic acid and vitamin B12 in serum are normal with dysplastic erythropoiesis in
      the bone marrow often mimicking myelodysplastic neoplasms (MDS) as a potential
      differential diagnosis
    explanation: >-
      Generalizes the mimicry beyond the single case, and names the two normal
      laboratory values that make the marrow picture surprising in the first place.
  - reference: PMID:39467528
    reference_title: >-
      Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic
      Neoplasm.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment with oral thiamine 100 mg daily was initiated, and 12 weeks later
      hemoglobin levels and bone marrow morphology had normalized
    explanation: >-
      The other half of the discrimination, and the one that matters mechanistically:
      the morphology is a cofactor-supply state rather than a clonal lesion, so it
      reverts.

- name: Ring Sideroblasts
  finding_term:
    preferred_term: ring sideroblasts present
    term:
      id: NCIT:C35995
      label: Ring Sideroblasts Present
  frequency: FREQUENT
  diagnostic: false
  description: >-
    Iron-laden mitochondria ringing the erythroblast nucleus, reported as a frequent
    finding on TRMA marrow smears. This is the second half of the resemblance to
    myelodysplastic neoplasm and arguably the more misleading half, because ring
    sideroblasts are a defining feature of one MDS subtype rather than a generic
    dysplastic change. Like the megaloblastic change above, it is not diagnostic of
    TRMA - it is what makes the wrong diagnosis plausible.

    Mechanistically it fits: thiamine pyrophosphate is a cofactor for the
    transketolase step this disease loses, and the mitochondrial iron accumulation
    reported here is the same lesion seen in the thiamine-responsive sideroblastic
    anaemias more broadly.
  evidence:
  - reference: PMID:39467528
    reference_title: >-
      Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic
      Neoplasm.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      bone marrow smears frequently show ring sideroblasts
    explanation: >-
      Reports the finding as frequent, in the sentence that names it as the specific
      reason distinguishing TRMA from MDS is difficult.

genetic:
- name: SLC19A2
  gene_term:
    preferred_term: SLC19A2
    term:
      id: hgnc:10938
      label: SLC19A2
  relationship_type: CAUSATIVE
  notes: >-
    Biallelic variants. The gene was identified by positional cloning in six TRMA
    families and encodes THTR-1, a transmembrane protein homologous to the reduced
    folate carriers. Characterized patient variants act by disrupting plasma-membrane
    localization. Roughly half of the approximately sixty reported SLC19A2 variants are
    missense and few have been functionally characterized, so the mislocalization
    mechanism established for three of them is load-bearing rather than representative.
  evidence:
  - reference: PMID:10391221
    reference_title: "Mutations in SLC19A2 cause thiamine-responsive megaloblastic anaemia associated with diabetes mellitus and deafness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations in a new gene, SLC19A2, encoding a putative transmembrane protein
      homologous to the reduced folate carrier proteins, were found in all affected
      individuals in six TRMA families
    explanation: The original gene identification across six families.
  - reference: PMID:33649974
    reference_title: >-
      The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine
      Transporter, SLC19A2.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Approximately half of the 60 SLC19A2 mutations associated with TRMA are missense
      variants (Supplemental Table 1) (5, 25), yet few have been functionally
      characterized.
    explanation: >-
      Gives the variant-class distribution and, importantly, how little of it has been
      functionally tested. Graded OTHER because the sentence is a Discussion-section
      summary of prior reports rather than a result of this study - the same construct
      this entry already grades OTHER elsewhere.

inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: TRMA is inherited in an autosomal recessive manner.
    explanation: The GeneReviews Genetic Counseling statement of inheritance.

environmental:
- name: Erythromycin exposure
  description: >-
    Erythromycin inhibits SLC19A2-mediated thiamine transport at clinically relevant
    unbound plasma concentrations, and prescribed patients show reduced thiamine
    pyrophosphate. In a patient who already has only residual low-affinity uptake, a
    drug acting on the same transporter is a plausible additional insult, which makes
    this worth recording even though it was identified in the general population rather
    than in TRMA.
  influences_mechanisms:
  - target: Loss of High-Affinity Thiamine Transport
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: >-
      Pharmacological inhibition of the same transporter compounds the genetic loss of
      its function.
    evidence:
    - reference: PMID:33649974
      reference_title: "The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Ten of 63 drugs inhibited SLC19A2-mediated thiamine transport ≥ 50% at
        screening concentrations; however, with the exception of erythromycin, none was
        predicted to inhibit SLC19A2 at clinically relevant unbound plasma
        concentrations.
      explanation: >-
        Identifies erythromycin as the one screened drug expected to inhibit the
        transporter at achievable concentrations. Graded IN_VITRO because both halves of
        the sentence are non-clinical: the screen is an isotopic thiamine-uptake assay in
        HEK293 cells, and "predicted ... at clinically relevant unbound plasma
        concentrations" is an FDA (fu*Cmax)/IC50 calculation over literature
        pharmacokinetics, not a human observation. The word "clinically" qualifies the
        concentration threshold, not the study design. The human half of this paper is
        cited separately, from its electronic-health-record result.
  evidence:
  - reference: PMID:33649974
    reference_title: "The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Data from electronic health records revealed reduced levels of thiamine
      pyrophosphate (TPP) in patients prescribed erythromycin, consistent with
      inhibition of SLC19A2-mediated thiamine transport.
    explanation: >-
      Confirms the inhibition has a measurable consequence for cofactor levels in
      people.

treatments:
- name: Pharmacologic Oral Thiamine
  description: >-
    Lifelong oral thiamine at 50-100 mg/day. It does not replace the missing
    transporter; it raises extracellular thiamine far enough that the residual
    low-affinity routes carry sufficient flux. The three disease arms respond
    differently, and the response is maintained only while treatment continues.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: thiamine
      term:
        id: CHEBI:26948
        label: vitamin B1
  target_mechanisms:
  - target: Intracellular Thiamine Pyrophosphate Deficiency
    treatment_effect: RESTORES
    description: >-
      Mass action through the residual uptake routes restores the intracellular
      cofactor pool. This is the step the treatment actually acts on.
    evidence:
    - reference: PMID:12393806
      reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The diabetes mellitus resolved after 6 weeks of thiamin repletion.
      explanation: >-
        Repletion reverses an established arm of the phenotype in the model, which is
        the clearest demonstration that raising substrate is sufficient.
  - target: Megaloblastic Anemia
    treatment_effect: RESTORES
    description: >-
      The anemia corrects, though macrocytosis persists and the anemia recurs if
      treatment stops.
    evidence:
    - reference: PMID:20301459
      reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The anemia is corrected with thiamine treatment, but the red cells remain
        macrocytic and anemia can recur if treatment is withdrawn.
      explanation: States both the response and its limits.
  - target: Diabetes Mellitus
    treatment_effect: MODULATES
    description: >-
      Partial: insulin requirement may fall and onset may be delayed, but not in
      everyone.
    evidence:
    - reference: PMID:20301459
      reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Thiamine treatment may reduce insulin requirement and delay onset of diabetes
        in some individuals.
      explanation: >-
        Graded PARTIAL because the source itself hedges both the effect and the
        proportion of patients showing it.
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lifelong use of pharmacologic doses (50-100 mg/day) of oral thiamine (vitamin B1)
      in affected individuals regardless of age.
    explanation: The GeneReviews Management recommendation, including dose and duration.

- name: Cochlear Implantation
  description: >-
    The intervention that actually addresses the hearing arm. Thiamine does not rescue
    it, but that does not mean nothing can be done: implantation bypasses the lost inner
    hair cells rather than treating the metabolic lesion, and it is what is done in
    practice.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: cochlear device implantation
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Progressive Sensorineural Hearing Loss
    treatment_effect: BYPASSES
    description: >-
      Stimulates the auditory nerve directly, bypassing the inner hair cells whose loss
      causes the deficit.
  evidence:
  - reference: PMID:38037112
    reference_title: "An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At 13 months, the patient underwent cochlear implantation due to sensorineural
      hearing loss.
    explanation: Documents implantation as the management of the hearing arm in a reported patient.

- name: Red Blood Cell Transfusion
  description: >-
    For severe anemia, ahead of or alongside thiamine.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Megaloblastic Anemia
    treatment_effect: MODULATES
    description: >-
      Replaces circulating red cells; does not address the transport defect.
  evidence:
  - reference: PMID:20301459
    reference_title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Red blood cell transfusion for severe anemia.
    explanation: The GeneReviews Management recommendation for the acute anaemia.

- name: Periconceptional and Pregnancy Glycaemic Control
  description: >-
    Good diabetic control before and during pregnancy. This carries more weight here
    than the generic advice suggests: thiamine only MODULATES the diabetes arm, so this
    is the one place where the incompletely-treated arm has a defined management
    consequence.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Diabetes Mellitus
    treatment_effect: MODULATES
    description: >-
      Manages the glycaemic consequences of the beta-cell arm during pregnancy; it does
      not address the transport defect.
  evidence:
  - reference: PMID:20301459
    reference_title: Thiamine-Responsive Megaloblastic Anemia Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pregnancy management: Good diabetic control prior to and during pregnancy is
      recommended.
    explanation: The GeneReviews Management recommendation for pregnancy.

- name: Audiological and Metabolic Surveillance
  description: >-
    Annual monitoring of the efficacy of thiamine therapy and of progression across all
    three arms, since the hearing loss progresses independently of the treated arms.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Progressive Sensorineural Hearing Loss
    treatment_effect: MODULATES
    description: >-
      Surveillance and standard hearing-loss management address the arm that treatment
      does not correct.
  evidence:
  - reference: PMID:20301459
    reference_title: "Thiamine-Responsive Megaloblastic Anemia Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At least annual monitoring of the efficacy of the oral thiamine therapy and of
      disease progression
    explanation: The GeneReviews surveillance recommendation.

animal_models:
- name: Slc19a2-null mouse on thiamine-restricted diet
  species: Mouse
  genotype: Slc19a2 -/-
  publication: PMID:12393806
  description: >-
    Reproduces all three arms of the human triad, but only when dietary thiamine is
    withdrawn. That conditionality is the model's most informative feature: it shows
    the phenotype is a function of transport capacity relative to substrate supply, not
    of the genotype alone.
  modeled_mechanisms:
  - target: Pancreatic Beta Cell Dysfunction
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Develops diabetes with reduced insulin secretion on a thiamine-free diet, and the
      diabetes resolves on repletion.
    limitations: >-
      Requires dietary thiamine restriction to manifest, whereas human patients become
      symptomatic on a normal diet; the mouse therefore models the mechanism faithfully
      but not the human threshold.
    readouts:
    - name: Insulin secretion
      target: Pancreatic Beta Cell Dysfunction
      direction: DECREASED
      interpretation: Secretory failure is the proximate cause of the hyperglycaemia.
      evidence:
      - reference: PMID:12393806
        reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          On a thiamin-free diet, Slc19a2(-/-) mice developed diabetes mellitus with
          reduced insulin secretion and an enhanced response to insulin.
        explanation: Measures the secretory defect and distinguishes it from resistance.
    - name: Glycaemic status after thiamine repletion
      target: Pancreatic Beta Cell Dysfunction
      direction: RESTORED
      interpretation: >-
        Reversibility on repletion establishes that the defect is a substrate-supply
        problem rather than fixed damage.
      evidence:
      - reference: PMID:12393806
        reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: The diabetes mellitus resolved after 6 weeks of thiamin repletion.
        explanation: The rescue arm of the experiment.
    evidence:
    - reference: PMID:12393806
      reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Thus, Slc19a2(-/-) mice have provided new insights into the TRMA disease
        pathogenesis and will provide a tool for studying the role of thiamin
        homeostasis in diabetes mellitus more broadly.
      explanation: The authors' own statement of the model's relevance to the disease.
  - target: Impaired Nucleotide Synthesis in Erythroid Precursors
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the marrow lesion, and extends it: the megaloblastosis in the mouse is
      not confined to the erythroid line but affects the myeloid and megakaryocyte lines
      as well. That is the observation behind this node's own statement that the defect
      is broader in the mouse than the node's erythroid scope implies, and it fits the
      proposed mechanism - a transketolase-dependent shortfall of ribose-5-phosphate
      would be expected to constrain any rapidly dividing precursor, not erythroid ones
      specifically.
    limitations: >-
      Manifests only under dietary thiamine restriction, as with the other two arms.
      The trilineage extent is a mouse finding under an imposed deficiency; whether
      human TRMA marrow shows the same breadth is not established by this source, so
      the human node stays erythroid-scoped.
    readouts:
    - name: Bone marrow morphology
      target: Impaired Nucleotide Synthesis in Erythroid Precursors
      direction: ALTERED
      interpretation: >-
        Megaloblastic change across three lineages is the morphological readout of
        impaired DNA synthesis in dividing precursors.
      evidence:
      - reference: PMID:12393806
        reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a
          megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines.
        explanation: >-
          The measurement itself, including the lineage breadth that makes it more than
          a confirmation of the human phenotype.
    evidence:
    - reference: PMID:12393806
      reference_title: "Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a
        megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines.
      explanation: >-
        Establishes that the model is informative for the haematopoietic arm, which was
        the one arm of the triad it was not linked to.

  - target: Selective Inner Hair Cell Loss
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the hearing loss and localizes it to selective inner hair cell loss,
      which explains the auditory-neuropathy pattern seen clinically.
    limitations: >-
      As with the diabetes, manifests only under dietary thiamine restriction; and the
      histology was obtained after defined low-thiamine challenges rather than across a
      lifetime of partial deficiency.
    readouts:
    - name: Auditory brainstem response versus otoacoustic emission thresholds
      target: Selective Inner Hair Cell Loss
      direction: INCREASED
      interpretation: >-
        The discrepancy between the two measures is the functional signature of a
        lesion at the inner hair cell rather than the outer.
      evidence:
      - reference: PMID:16642288
        reference_title: "Deletion of SLC19A2, the high affinity thiamine transporter, causes selective inner hair cell loss and an auditory neuropathy phenotype."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Slc19a2-null mice showed 40-60 dB threshold elevations by auditory brainstem
          response (ABR), but only 10-20 dB elevation by otoacoustic emission (OAE)
          measures.
        explanation: Quantifies the discrepancy that identifies the site of the lesion.
    evidence:
    - reference: PMID:16642288
      reference_title: "Deletion of SLC19A2, the high affinity thiamine transporter, causes selective inner hair cell loss and an auditory neuropathy phenotype."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Cochlear function is normal in these mutants when maintained on a high-thiamine
        diet.
      explanation: >-
        The control condition that makes the model interpretable: genotype alone is not
        sufficient.

discussions:
- discussion_id: trma_why_hearing_does_not_respond
  kind: INTERPRETATION
  prompt: >-
    Why does thiamine rescue the anemia and the diabetes but not the hearing loss?
  attaches_to:
  - pathophysiology#Selective Inner Hair Cell Loss
  - treatments#Pharmacologic Oral Thiamine
  rationale: >-
    The three arms differ in whether the affected cells persist. Erythroid precursors
    are continuously replaced, so restoring the cofactor restores production. Beta cell
    dysfunction is at least partly functional, and the mouse diabetes resolved on
    repletion. Inner hair cells, by contrast, are lost - the mouse shows selective
    death of those cells under thiamine restriction - and mammalian cochlear hair cells
    do not regenerate. On that reading the deafness is irreversible not because the arm
    is thiamine-independent but because its endpoint is cell death rather than cell
    dysfunction, which predicts that treatment started before hair cell loss would
    preserve hearing while treatment started after would not. Whether that prediction
    holds in patients is the practical question, and the case-series emphasis on early
    diagnosis is consistent with it without establishing it.

- discussion_id: trma_residual_transport_threshold
  kind: KNOWLEDGE_GAP
  prompt: >-
    What determines the thiamine concentration at which residual transport becomes
    sufficient, and does it differ between the affected tissues?
  attaches_to:
  - pathophysiology#Loss of High-Affinity Thiamine Transport
  rationale: >-
    Pharmacologic thiamine works by driving flux through low-affinity routes, so each
    tissue's threshold depends on its residual transporter expression and its cofactor
    demand. The mouse becomes normal on a high-thiamine diet and sick on a thiamine-free
    one, which brackets the threshold in that model but not in patients. If the
    thresholds differ between marrow, islet and cochlea, that would explain the
    differing arm responses as a dosing problem rather than an intrinsic one - and
    would imply the standard 50-100 mg/day is adequate for some tissues and not others.
    No tissue-level threshold data were found in the sources used here.

notes: >-
  Relationship to the SLC19A3 disease. kb/disorders/Biotin_Thiamine_Responsive_Basal_Ganglia_Disease.yaml
  covers the disease of THTR-2, the low-affinity transporter encoded by SLC19A3. The two
  are transporter paralogues with non-overlapping phenotypes, and the relationship is
  mechanistically informative: the residual uptake that makes TRMA treatable is carried
  substantially by the very transporter whose own loss causes the other disease.

  Named Entity Confusion. The preflight returned WARN on a rival gene "HP" at 26% of
  SLC19A2 mentions. That is a false positive of the gene-symbol matcher: the report
  contains 26 HP:NNNNNNN HPO CURIEs and no mention of haptoglobin. Checked rather than
  assumed before proceeding.

  Treatment modelling. The thiamine treatment carries three separate target_mechanisms
  with different effects rather than one link to the disease, because the arms genuinely
  differ: RESTORES on the cofactor deficiency and on the anemia, MODULATES on the
  diabetes. There is deliberately no link from thiamine to the hearing-loss node; the
  source says the deafness is irreversible and may not be prevented, and a link there
  would assert a benefit the evidence denies. The surveillance treatment carries that
  arm instead.

  Erythromycin. Recorded as an environmental exposure acting on the transport node. The
  evidence comes from the general population rather than from TRMA patients, and the
  entry says so; it is included because a drug that inhibits the same transporter is a
  mechanistically specific hazard for someone already dependent on residual transport.
📚

References & Deep Research

References

7
PMID:20301459
Thiamine-Responsive Megaloblastic Anemia Syndrome.
No top-level findings curated for this source.
PMID:10391221
Mutations in SLC19A2 cause thiamine-responsive megaloblastic anaemia associated with diabetes mellitus and deafness.
No top-level findings curated for this source.
PMID:12393806
Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice.
No top-level findings curated for this source.
PMID:16642288
Deletion of SLC19A2, the high affinity thiamine transporter, causes selective inner hair cell loss and an auditory neuropathy phenotype.
No top-level findings curated for this source.
PMID:33649974
The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2.
No top-level findings curated for this source.
PMID:38037112
An Italian case series' description of thiamine responsive megaloblastic anemia syndrome: importance of early diagnosis and treatment.
No top-level findings curated for this source.
PMID:39467528
Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic Neoplasm.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
Thiamine-Responsive Megaloblastic Anemia Syndrome (TRMA / Rogers Syndrome): Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 26 citations 2026-08-27T18:57:04.345884

Thiamine-Responsive Megaloblastic Anemia Syndrome (TRMA / Rogers Syndrome): Comprehensive Research Report

1. Disease Information

Overview. Thiamine-responsive megaloblastic anemia syndrome (TRMA), also known as Rogers syndrome, is a rare autosomal recessive metabolic disorder caused by biallelic loss-of-function variants in SLC19A2, which encodes the high-affinity thiamine (vitamin B1) transporter THTR-1. The disease is defined by a classic clinical triad — megaloblastic anemia, non-type 1 (non-autoimmune) diabetes mellitus, and progressive sensorineural hearing loss — with onset typically between infancy and adolescence. It is distinguished from other congenital anemias by its dramatic, though incomplete, responsiveness to pharmacologic (supraphysiologic) doses of oral thiamine (GeneReviews, NBK1282).

Key identifiers: - OMIM: #249270 (Thiamine-Responsive Megaloblastic Anemia Syndrome; also called Thiamine Metabolism Dysfunction Syndrome 1, THMD1) (OMIM:249270) - Orphanet: ORPHA:49827 (Orphanet) - MONDO: MONDO:0009575 - ICD-10-CM: D53.1 (Other megaloblastic anemias, not elsewhere classified) — TRMA has no dedicated ICD-10 code and is billed under this broader category - MedGen concept: C0342287 — "Megaloblastic anemia, thiamine-responsive, with diabetes mellitus and sensorineural deafness" (NCBI MedGen) - Gene: SLC19A2 (HGNC:11021), chromosome 1q24.2 (also cited as 1q23.3 in older sources)

Synonyms: Rogers syndrome; TRMA syndrome; Thiamine-responsive anemia with diabetes mellitus and sensorineural deafness; Roger syndrome.

Data provenance. Nearly all published knowledge on TRMA derives from aggregated case reports and small case series (individual-patient/family-level data) rather than large disease-level registries, reflecting the disorder's extreme rarity — GeneReviews estimates "more than 183 individuals from approximately 138 families" reported worldwide (GeneReviews, NBK1282), and MedlinePlus similarly cites "approximately 200 cases documented in medical literature" (MedlinePlus Genetics). A newly reported founder-mutation cluster in the Ingush population (see §9) is the first population/cohort-level epidemiologic dataset for the disease (PMID:42511616).

2. Etiology

Disease causal factor: monogenic, autosomal recessive. TRMA is caused exclusively by biallelic (homozygous or compound heterozygous) pathogenic variants in SLC19A2. There is no known environmental, infectious, or purely mechanistic (non-genetic) cause; dietary thiamine deficiency produces classical beriberi/Wernicke pathology, not TRMA, because TRMA arises from a cellular transport defect rather than systemic vitamin insufficiency.

Genetic risk factors: - Biallelic SLC19A2 pathogenic variants — the sole causal factor. - Consanguinity is a major risk factor for expression of this rare recessive disease; GeneReviews notes it is "exceedingly rare outside of consanguineous families or isolated populations," with reported kindreds from Israeli Arab, Lebanese, Alaskan Native/Russian, Brazilian, Japanese, Omani, Tunisian, Italian, Iranian, Indian, Pakistani, Kashmiri, Kurdish, northern European, and African American populations (GeneReviews, NBK1282). - Founder effects / isolated populations: A newly characterized SLC19A2 c.1223+1G>A canonical splice-site founder variant is endemic in the Ingush population of the North Caucasus, with a heterozygous carrier frequency of 2.7% (≈1/36) in a reference cohort of 328 unrelated adults, sharing a 2.3 Mb ATP1B1–FMO2 founder haplotype on chromosome 1 (PMID:42511616). - No modifier genes have been identified; GeneReviews explicitly states no genotype–phenotype correlation exists — clinical severity and which triad features manifest vary unpredictably even within families carrying the same variant (GeneReviews, NBK1282).

Environmental/risk-modifying factors: None established as independent disease-causing factors. However, dietary thiamine status modulates phenotype severity in model systems — in Slc19a2-null mice, diabetes and cochlear pathology are diet-dependent, emerging specifically on a thiamine-free diet and resolving/normalizing on thiamine repletion or a thiamine-replete diet (PMID:12393806; PMID:16642288), suggesting maternal/dietary thiamine intake could plausibly modulate age of clinical onset in humans, though this is not directly demonstrated in patients.

Protective factors: Pharmacologic-dose thiamine supplementation is the only known modifier that ameliorates (though does not cure) the phenotype — it is protective against progression of anemia, thrombocytopenia, and (partially) diabetes onset, but does not prevent or reverse hearing loss (see §12). No protective genetic variants have been described; a residual second thiamine transporter, THTR-2 (encoded by the paralog SLC19A3), provides partial intestinal compensation but has minimal expression in the tissues driving TRMA pathology (bone marrow, pancreatic β-cells, cochlea), so it does not meaningfully rescue phenotype (GeneReviews, NBK1282).

Gene-environment interaction: The core gene-environment interaction is the treatment mechanism itself: loss of the high-affinity, saturable THTR-1 transport pathway is functionally bypassed by supraphysiologic extracellular thiamine concentrations that drive passive/low-affinity diffusion into cells, restoring intracellular thiamine pyrophosphate (TPP) levels sufficient for thiamine-dependent enzymes (MedlinePlus Genetics).

3. Phenotypes

TRMA phenotypes span hematologic, endocrine, otologic, ophthalmologic, cardiovascular, and neurologic domains. Frequencies below are as reported in GeneReviews' pooled case-series data (GeneReviews, NBK1282).

Phenotype Category Frequency Onset Course HPO suggestion
Megaloblastic anemia Laboratory/hematologic 60–70% with full megaloblastic features (nearly universal macrocytic anemia) Infancy–adolescence Chronic, thiamine-responsive but recurs on withdrawal HP:0001889 (Megaloblastic anemia)
Macrocytosis (elevated MCV) Laboratory Very common Infancy–adolescence Often persists despite treatment HP:0001972 (Macrocytic anemia)
Ringed sideroblasts / dysplastic marrow Laboratory/histopathology Common At diagnosis — HP:0004828 (Ring sideroblasts)
Thrombocytopenia Laboratory/hematologic 10–30% Variable Thiamine-responsive HP:0001873 (Thrombocytopenia)
Neutropenia Laboratory/hematologic Reported, less common Variable Thiamine-responsive HP:0001875 (Neutropenia)
Sensorineural hearing loss Sign, sensory >90% Often detected in toddlers; may be congenital/prelingual Progressive, irreversible; not prevented by thiamine HP:0000407 (Sensorineural hearing impairment)
Non-type 1 diabetes mellitus Sign, endocrine >90% Infancy–adolescence Progressive; often insulin-dependent over time HP:0000857 (Diabetes mellitus, non-insulin dependent context varies)
Diabetic ketoacidosis Complication ~15% — Episodic HP:0004904 (Diabetic ketoacidosis)
Optic atrophy Ophthalmologic Within 20–30% ophthalmologic group Variable Progressive HP:0000648 (Optic atrophy)
Retinal dystrophy / cone-rod dystrophy Ophthalmologic Within 20–30% ophthalmologic group Variable Progressive HP:0000548 (Cone/cone-rod dystrophy)
Congenital heart defects (ASD/VSD) Cardiovascular Within 20–30% cardiovascular group Congenital Static or complicated HP:0001631 (ASD), HP:0001629 (VSD)
Arrhythmia / atrial standstill Cardiovascular Within 20–30% cardiovascular group Variable Can be life-threatening HP:0011675 (Arrhythmia)
High-output heart failure Cardiovascular Within 20–30% cardiovascular group Variable — HP:0001635 (Congestive heart failure)
Sudden death Cardiovascular Reported — — —
Stroke Neurologic/vascular Within 20–40% neurologic group Variable — HP:0001297 (Stroke)
Epilepsy/seizures Neurologic Within 20–40% neurologic group Variable — HP:0001250 (Seizure)
Developmental delay/intellectual disability Neurologic Within 20–40% neurologic group Childhood — HP:0001263 (Global developmental delay)
Mood disorders/behavioral changes Neuropsychiatric Reported Variable — HP:0000708 (Behavioral abnormality)

Quality-of-life impact: No disease-specific EQ-5D/SF-36 data were located. Qualitatively, the irreversible progressive sensorineural hearing loss is the most functionally durable burden (unlike anemia, unresponsive to thiamine), often requiring hearing aids or cochlear implantation for rehabilitation — one case report specifically documents "successful hearing rehabilitation by cochlear implantation" in a TRMA patient (ScienceDirect case report). Insulin-dependent diabetes and its complications, plus the cardiovascular/neurologic complication burden in ~20–40% of patients, are the other major chronic quality-of-life determinants (GeneReviews, NBK1282).

Diagnostic mimicry note: Because bone marrow shows dysplastic hematopoiesis with megaloblasts and ringed sideroblasts, TRMA is noted to be easily mistaken for acquired myelodysplastic syndrome (MDS) — a recent case report is explicitly titled "Thiamine-Responsive Megaloblastic Anemia Syndrome Mimicking Myelodysplastic Neoplasm" (Karger, Acta Haematologica), underscoring the importance of distinguishing the two given their divergent prognosis and management.

4. Genetic/Molecular Information

Causal gene: SLC19A2 (Solute Carrier Family 19 Member 2), HGNC:11021, located on chromosome 1q24.2, spanning 6 exons. It encodes Thiamine Transporter 1 (THTR-1/ThTr1), a 497-amino-acid protein with 12 predicted transmembrane domains, structurally homologous to the reduced folate carrier family (GeneCards SLC19A2; PMID:33649974). THTR-1 is the sole thiamine transporter expressed in bone marrow, cochlear tissue, and pancreatic β-cells, which accounts for the tissue-specificity of the clinical triad — a second, paralogous transporter (THTR-2, encoded by SLC19A3) is more broadly/intestinally expressed but does not substitute in these tissues (PMID:33649974).

Discovery: SLC19A2 was identified by positional cloning in 1999 as the gene mutated in TRMA-segregating families, initially reported by two independent groups; Labay et al. (Nature Genetics, 1999) reported "Mutations in SLC19A2 cause thiamine-responsive megaloblastic anaemia associated with diabetes mellitus and deafness" (PMID:10391221; Nature Genetics ng0799_300).

Pathogenic variant spectrum: A systematic analysis of reported variants found frameshift variants (31%), nonsense variants (24%), and large deletions (3%) — together accounting for 55% of all reported pathogenic alleles and predicted to cause premature termination and protein truncation. Truncating variants localize predominantly to transmembrane domains (46.3%), cytoplasmic domains (34.1%), and extracellular domains (19.5%); missense variants localize to transmembrane domains (59.3%), extracellular domains (29.6%), and cytoplasmic domains (11.1%) (PMID:33649974). Whole-gene deletions/duplications are rare (reported in only 2 families) (GeneReviews, NBK1282). A recently reported complex example combines a heterozygous missense variant (c.1001G>A, p.Gly334Asp) with a 3.4 Mb structural inversion of exons 2–6 on the second allele, producing a functionally null allele — illustrating that structural variant analysis may be needed when standard sequencing finds only one pathogenic allele.

Variant classification/interpretation: Sequence analysis (Sanger or NGS-based) detects >99% of pathogenic variants (missense, nonsense, splice-site, small indels); gene-targeted deletion/duplication analysis (e.g., MLPA, CMA) is recommended as a reflex test when only one or no variant is found by sequencing (GeneReviews, NBK1282). ACMG/AMP-based ClinVar classifications exist for the reported alleles but a curated aggregate summary was not directly retrievable in this search; GeneCards/ClinVar and locus-specific databases should be consulted for the current pathogenic/likely-pathogenic variant list.

Population/allele frequency: SLC19A2 pathogenic alleles are rare in gnomAD generally — most pathogenic alleles are absent or present at frequencies below 0.00001 — but show strong founder enrichment in specific populations. The missense variant p.(Gly334Asp) has one of the higher reported gnomAD allele frequencies (~0.00002). The Ingush founder splice variant c.1223+1G>A reaches a striking 2.7% heterozygous carrier frequency (≈1/36) in that population due to a shared 2.3 Mb founder haplotype (PMID:42511616).

Zygosity/origin: All reported pathogenic variants are germline; TRMA has no described somatic form. Both homozygous and compound heterozygous genotypes are reported. A case report specifically documents maternal uniparental isodisomy as a mechanism producing homozygosity for a single maternally inherited SLC19A2 pathogenic variant, despite only one parent being a carrier — an important non-classical mechanism to consider in apparent "homozygosity" without biparental transmission (PMC8017196).

Functional consequences: Loss-of-function is the uniform mechanism — pathogenic missense variants in transmembrane domains cause aberrant protein folding/mislocalization (disrupted trafficking to the plasma membrane) with near-complete loss of transport function, while nonsense/frameshift variants produce truncated, non-functional or absent protein (PMID:33649974; GeneReviews, NBK1282). There is no described gain-of-function, dominant-negative, or hypermorphic mechanism.

Modifier genes: None established; disease expression is unpredictable across genotypically similar/identical patients (no genotype–phenotype correlation) (GeneReviews, NBK1282).

Epigenetic information / chromosomal abnormalities: No epigenetic mechanism or recurrent chromosomal aneuploidy/translocation has been described for TRMA; disease is driven by point/small-indel/structural loss-of-function variants confined to the SLC19A2 locus.

5. Environmental Information

TRMA is a purely monogenic disorder with no established infectious, toxic, or occupational-exposure etiology. The principal "environmental" lever is dietary/therapeutic thiamine, which is not a disease cause but the disease's specific pharmacologic countermeasure (see §2, §12). No lifestyle risk factor (smoking, alcohol, exercise) has been linked to TRMA onset or severity in the literature reviewed. No infectious trigger is reported. Consanguinity, discussed above, functions as a population-genetic risk factor rather than a true environmental exposure.

6. Mechanism / Pathophysiology

Causal chain overview: Biallelic SLC19A2 loss-of-function → absence of the high-affinity, saturable thiamine transport component at the plasma membrane of bone marrow precursors, pancreatic β-cells, and cochlear cells → low intracellular free thiamine and thiamine pyrophosphate (TPP) concentration in these tissues (despite normal serum thiamine) → impaired function of TPP-dependent enzymes, most notably transketolase in the non-oxidative branch of the pentose phosphate pathway → defective ribose synthesis for nucleic acid (RNA/DNA) production → impaired DNA synthesis and cell-cycle progression in rapidly dividing hematopoietic precursors, producing megaloblastic dysplastic hematopoiesis; and cellular stress/apoptosis in pancreatic β-cells and cochlear hair cells → clinical triad of megaloblastic anemia, diabetes mellitus, and sensorineural deafness (GeneReviews, NBK1282; Blood, PMID search "Defective RNA ribose synthesis").

Molecular pathway / biochemical abnormality: Thiamine pyrophosphate (TPP), the active cofactor form of thiamine, is required by transketolase (pentose phosphate pathway, non-oxidative branch), pyruvate dehydrogenase, and α-ketoglutarate dehydrogenase (TCA cycle). In TRMA fibroblasts, the fractional synthetic rate of ribose is reduced, and the balance of ribose synthesis shifts away from the preferred transketolase/transaldolase-dependent non-oxidative branch toward the oxidative pentose pathway branch, which cannot fully compensate — this reduced nucleic-acid ribose production is proposed as the proximate biochemical lesion driving cell-cycle arrest/apoptosis in bone marrow cells ("Defective RNA ribose synthesis in fibroblasts from patients with thiamine-responsive megaloblastic anemia (TRMA)," Blood — bloodjournal.org). An earlier syndrome overlapping TRMA's triad was also linked to deficient α-ketoglutarate dehydrogenase activity, a second TPP-dependent enzyme (PMID:4045602), consistent with broad TPP-cofactor insufficiency as the shared downstream lesion.

Cell type/tissue involvement: - Hematopoietic precursors (bone marrow): dysplastic megaloblastic erythropoiesis with numerous megaloblasts and iron-laden mitochondria (ringed sideroblasts); thrombocytopenia and neutropenia in a subset, likely reflecting shared TPP-dependence across marrow lineages. - Pancreatic β-cells: THTR-1 is "the only transporter of thiamine into pancreatic β-cells," and its deficiency "leads to cell apoptosis and organ failure" (i.e., β-cell loss driving non-autoimmune, non-type-1 diabetes) — search summary from thiamine/diabetes mechanistic review (PMC8505293, "Thiamine and diabetes: back to the future?"). - Cochlear hair cells: In the Slc19a2-null mouse model on a low-thiamine diet, histology shows selective inner hair cell loss occurring within 1–2 weeks of thiamine restriction, with progressively greater inner-than-outer hair cell loss on longer challenge, producing an auditory neuropathy-like phenotype; auditory brainstem response (ABR) thresholds are markedly elevated on a thiamine-free diet but normal on a thiamine-replete diet (PMID:16642288). This maps the human "unclear basis" hearing loss to selective inner hair cell vulnerability.

Molecular profiling / advanced technologies: No transcriptomic, proteomic, metabolomic, or single-cell/spatial datasets specific to human TRMA tissue were identified in this search; mechanistic insight instead derives from patient fibroblast biochemistry (ribose synthesis assays) and the Slc19a2-knockout mouse model.

GO/CL term suggestions: - Molecular function: GO:0034219 (carbohydrate transmembrane transport) / more specifically thiamine transmembrane transporter activity - Biological process: GO:0006772 (thiamine metabolic process); pentose-phosphate shunt, non-oxidative branch (GO:0009052) - Cell types: CL:0000542 (lymphocyte) not relevant; relevant CL terms include CL:0000038 (erythroid progendaughter/erythroid progenitor cell), CL:0000169 (type B pancreatic cell), CL:0000598 (cochlear inner hair cell)

7. Anatomical Structures Affected

Organ level: - Primary: Bone marrow (hematopoietic system), pancreas (endocrine, islets of Langerhans), inner ear/cochlea (auditory system). - Secondary: Eye (optic nerve, retina), heart (conduction system, septa), central and peripheral nervous system, vasculature (stroke risk). - Body systems involved: Hematologic, endocrine, auditory/vestibular, ophthalmologic, cardiovascular, neurologic.

Tissue and cell level: - Bone marrow erythroid, myeloid, and megakaryocytic precursors (dysplastic, megaloblastic change; ringed sideroblasts on iron stain). - Pancreatic islet β-cells (CL:0000169). - Cochlear inner hair cells (CL:0000598), with relative sparing of outer hair cells in the mouse model, suggesting a similar pattern may occur in humans (PMID:16642288). - Retina/optic nerve (cone-rod dystrophy, optic atrophy). - Cardiac conduction tissue and myocardium (atrial standstill, arrhythmia, high-output failure).

Subcellular level: Mitochondria are directly implicated — the megaloblastic marrow shows iron-filled mitochondria (ringed sideroblasts), and TPP-dependent mitochondrial enzymes (pyruvate dehydrogenase, α-ketoglutarate dehydrogenase) are plausible downstream targets of thiamine deficiency alongside the cytosolic pentose phosphate pathway enzyme transketolase. GO Cellular Component terms of interest: GO:0005739 (mitochondrion), GO:0005829 (cytosol, site of transketolase activity), GO:0005886 (plasma membrane, site of THTR-1 localization).

Localization / laterality: Sensorineural hearing loss and cochlear involvement are typically bilateral; cardiac and ophthalmologic findings are systemic/bilateral in nature rather than lateralized.

UBERON term suggestions: UBERON:0002371 (bone marrow), UBERON:0001264 (pancreas), UBERON:0001846 (cochlea), UBERON:0000970 (eye), UBERON:0000948 (heart).

8. Temporal Development

Onset: TRMA onset spans infancy through adolescence, with the earliest anemia findings in the first year of life and latest reported presentations in the teenage years. All three triad features are frequently not present simultaneously at initial presentation — patients often present with one or two features first, with the remaining feature(s) emerging over subsequent years (GeneReviews, NBK1282). Hearing loss is often detected early, in toddlers, and may be congenital/prelingual in some patients.

Progression: - Megaloblastic anemia: corrects with pharmacologic thiamine but red cells remain macrocytic; anemia recurs promptly if thiamine is withdrawn — i.e., a chronic, treatment-dependent (not curative) course. - Sensorineural hearing loss: progressive and irreversible; thiamine treatment does not halt or reverse it, distinguishing its course sharply from the hematologic component. - Diabetes mellitus: progressive; while thiamine may reduce insulin requirement and delay onset in some individuals, most patients eventually require insulin therapy; diabetic ketoacidosis occurs in ~15%. - Cardiovascular/neurologic/ophthalmologic complications: variable, sometimes severe (sudden death, stroke, atrial standstill), and thiamine's efficacy against these is not established.

Disease course pattern: Chronic and lifelong; not self-limited. No spontaneous remission is described. The disease requires indefinite pharmacologic thiamine dosing — GeneReviews states anemia recurs "if treatment is withdrawn," underscoring that TRMA is managed, not cured.

Critical periods: Early diagnosis and thiamine initiation is repeatedly emphasized as critical — an Italian case series is explicitly titled around "the importance of early diagnosis and treatment" (PMC10691017), consistent with the concept that early thiamine repletion may forestall or blunt onset of diabetes and preserve residual hearing, even though it cannot reverse established sensorineural damage.

9. Inheritance and Population

Epidemiology: TRMA is exceedingly rare, with formal prevalence/incidence statistics unknown; the literature has historically reported "less than 80 cases worldwide" in earlier summaries and up to ~200 cases / 138 families in more recent GeneReviews/MedlinePlus tallies (both figures reflect case-series accumulation rather than population-based ascertainment) (GeneReviews, NBK1282; MedlinePlus Genetics).

Inheritance pattern: Autosomal recessive. At conception, each sibling of an affected individual has a 25% chance of being affected, 50% chance of being an asymptomatic carrier, and 25% chance of being unaffected/non-carrier (GeneReviews, NBK1282). Heterozygous carriers are clinically asymptomatic.

Penetrance/expressivity: Effectively complete penetrance for biallelic pathogenic genotypes (disease manifests), but markedly variable expressivity — which triad components appear, their severity, and age of onset differ unpredictably between and even within families, with no genotype–phenotype correlation established (GeneReviews, NBK1282).

Genetic anticipation: Not described; TRMA is not a repeat-expansion disorder.

Germline mosaicism / uniparental disomy: A documented mechanism of apparent "homozygosity" without both parents being carriers is maternal uniparental isodisomy of chromosome 1, producing two identical maternal copies of a single pathogenic SLC19A2 allele (PMC8017196) — an important consideration for genetic counseling when only one parent tests as a carrier.

Founder effects / consanguinity: TRMA is strongly enriched in consanguineous unions and in geographically/ethnically isolated populations. The best-documented founder effect is the Ingush population of the North Caucasus (Russia), where the canonical splice variant SLC19A2 c.1223+1G>A reaches a heterozygous carrier frequency of 2.7% (≈1/36) in a reference cohort of 328 unrelated adults, tracing to a shared 2.3 Mb ATP1B1–FMO2 founder haplotype; this study newly identifies Ingushetia as a TRMA-endemic region and recommends targeted screening and early thiamine therapy for macrocytic anemia/diabetes of unclear origin in that population — notably, all identified patients became transfusion-independent on high-dose thiamine therapy (PMID:42511616). Other reported founder/cluster populations include Israeli Arab, Lebanese, Alaskan Native/ethnic Russian, Brazilian, Japanese, Omani, Tunisian, Italian, Iranian, Indian, Pakistani, Kashmiri (in Great Britain), and Kurdish kindreds (GeneReviews, NBK1282).

Carrier frequency: Population-wide carrier frequency is presumably very low outside founder populations (consistent with gnomAD data showing most pathogenic SLC19A2 alleles at allele frequency <0.00001), but reaches 2.7% in the Ingush founder population specifically (PMID:42511616).

Sex ratio / geographic distribution: No sex predilection is reported (consistent with autosomal inheritance). Geographic distribution is scattered/sporadic worldwide, reflecting the disorder's dependence on consanguinity/founder effects rather than a specific endemic geography, with the Ingush cluster as a notable exception.

10. Diagnostics

Clinical/biochemical diagnostic criteria: Per GeneReviews, the diagnosis of TRMA is established in a proband with megaloblastic anemia with normal vitamin B12/folic acid levels, with or without diabetes or hearing loss, who shows a response to oral thiamine (GeneReviews, NBK1282). This clinical/biochemical criterion is typically confirmed molecularly.

Laboratory tests: - CBC with elevated MCV (macrocytosis), low hemoglobin. - Reticulocyte count (monitored for treatment response). - Bone marrow aspirate/biopsy: megaloblastic, dysplastic hematopoiesis with ringed sideroblasts (iron stain). - Normal serum vitamin B12 and folate (key distinguishing feature from nutritional megaloblastic anemias). - Fasting glucose, oral glucose tolerance test, urinalysis for glucose intolerance/diabetes screening.

Genetic testing: - First-line: Sequence analysis of SLC19A2 (Sanger or targeted NGS), which detects >99% of pathogenic variants including small indels, missense, nonsense, and splice-site variants. - Reflex testing: Gene-targeted deletion/duplication analysis (e.g., MLPA, chromosomal microarray) when only one or no variant is identified by sequencing — relevant given rare reported whole-gene deletions/duplications and structural variants (e.g., the exon 2–6 inversion case). - Broader testing: Multigene panels for congenital sideroblastic/megaloblastic anemia or syndromic deafness-diabetes, or comprehensive genomic testing (exome/genome sequencing), particularly useful when the clinical presentation is atypical or incomplete (GeneReviews, NBK1282). - Uniparental disomy testing may be informative in cases of apparent unexplained homozygosity (PMC8017196).

Imaging/other: No disease-specific imaging modality; echocardiography is indicated given the 20–30% cardiovascular involvement rate (structural defects, arrhythmia, atrial standstill); audiometry/ABR for hearing assessment; ophthalmologic exam (fundoscopy, possibly electroretinography) for retinal/optic nerve involvement.

Differential diagnosis (from GeneReviews):

Disorder Distinguishing feature vs. TRMA
Wolfram syndrome (WFS1, DIDMOAD) Lacks megaloblastic anemia and thiamine responsiveness
Wolfram syndrome type 2 (CISD2) Lacks megaloblastic anemia; high-frequency-only hearing loss; may feature GI ulcers
Primary mitochondrial disorders Share diabetes + deafness but lack the characteristic thiamine-responsive macrocytic anemia
Acquired myelodysplastic syndrome (MDS) Marrow morphology (megaloblasts, ringed sideroblasts) can closely mimic TRMA; distinguished by young age, family history, biallelic SLC19A2 variants, and thiamine responsiveness — misdiagnosis as MDS is explicitly documented in the literature (Karger Acta Haematologica case report)

Screening: No population newborn-screening program exists for TRMA given its extreme rarity, though the Ingush founder-population study explicitly recommends targeted carrier/diagnostic screening for SLC19A2 c.1223+1G>A in that specific population given macrocytic anemia or diabetes of unclear origin (PMID:42511616).

11. Outcome/Prognosis

Survival/mortality: No systematic survival statistics (5-year/10-year survival, life expectancy) were located in the literature searched; sudden cardiac death is reported as a rare but real complication, and the disease's cardiovascular (20–30%) and neurologic (20–40%, including stroke) complication burden implies meaningful excess morbidity/mortality risk relative to the general population, though quantified rates were not found.

Morbidity/function: The dominant chronic morbidity driver is irreversible progressive sensorineural hearing loss, which persists regardless of thiamine treatment and is managed with hearing aids or cochlear implantation. Insulin-dependent diabetes contributes long-term micro/macrovascular risk typical of any chronic diabetes. The 20–40% rate of neurologic complications (developmental delay, intellectual disability, epilepsy, stroke) and 20–30% rate of cardiovascular complications (arrhythmia, congenital heart defects, high-output failure) represent additional major sources of long-term disability.

Recovery potential / treatment impact: With thiamine treatment, hematologic parameters (anemia, thrombocytopenia, neutropenia) reliably improve, and some patients — as in the Ingush cohort — become fully transfusion-independent on high-dose thiamine therapy (PMID:42511616). Diabetes may be delayed in onset or require reduced insulin dosing with thiamine, but is not reliably reversed. Hearing loss, once established, does not recover with thiamine.

Prognostic factors: Early diagnosis and early initiation of thiamine therapy is repeatedly emphasized in the literature as the single most actionable prognostic factor, given its role in mitigating hematologic disease and potentially delaying diabetes onset, even though it cannot rescue hearing (PMC10691017). No molecular biomarker for prognosis (beyond genotype, which does not correlate with severity) has been established.

12. Treatment

Primary pharmacotherapy: Lifelong oral thiamine (vitamin B1) at pharmacologic doses of 50–100 mg/day (occasionally reported up to 25–100 mg/day in at-risk relatives pending genetic confirmation), regardless of patient age, is the cornerstone of TRMA management. GeneReviews notes no additional clinical benefit is observed above 150 mg/day. Thiamine "invariably improves hematologic findings" but must be continued indefinitely, as anemia recurs upon discontinuation (GeneReviews, NBK1282). - NCIT suggestion: NCIT:C15986 (Pharmacotherapy), with therapeutic_agent bound to thiamine (CHEBI, if available) — vitamin/nutrient supplementation therapy.

Manifestation-specific treatment:

Manifestation Treatment NCIT suggestion
Megaloblastic anemia Oral thiamine 50–100 mg/day; red cell transfusion for severe/acute cases NCIT:C15986 (Pharmacotherapy); NCIT:C15170 (Blood Transfusion)
Sensorineural hearing loss Hearing aids, cochlear implantation, audiologic follow-up (thiamine ineffective) NCIT:C50399 (Hearing Aid), cochlear implantation procedure term
Diabetes mellitus Standard diabetes care (oral hypoglycemics initially, insulin as needed) plus thiamine NCIT:C15986 (Pharmacotherapy)
Thrombocytopenia Oral thiamine (responsive) NCIT:C15986
Cardiac, neurologic, ophthalmologic complications Standard specialist (cardiology, neurology, ophthalmology) supportive care; thiamine efficacy not established for these domains Varies by intervention

Advanced therapeutics: No gene therapy, cell therapy, RNA-based therapy, or targeted molecular therapy has been developed or trialed for TRMA specifically — the disease is managed entirely through cofactor-bypass pharmacotherapy (high-dose thiamine) and manifestation-directed supportive/specialist care. No disease-specific registered clinical trials (ClinicalTrials.gov, NCT identifiers) were identified for TRMA in this search, consistent with its ultra-rare status; management guidance derives from case-series experience rather than randomized trials.

Treatment response/outcomes: Response to thiamine is the diagnostic hallmark itself (see §10) — reticulocytosis and hemoglobin normalization are expected within weeks of thiamine initiation. Diabetes response is more variable: thiamine "may reduce insulin requirement and delay onset of diabetes in some individuals" but is not curative. No systematic adverse-event data for high-dose thiamine in TRMA were found; oral thiamine is generally very well tolerated even at pharmacologic doses.

Pregnancy management: GeneReviews specifically recommends good diabetic control prior to and during pregnancy in affected women.

Genetic counseling / at-risk relative management: GeneReviews recommends empiric thiamine supplementation (25–100 mg/day, compared with the US RDA of ~1.5 mg/day) for at-risk siblings as early as possible, pending determination of their genetic/carrier status, given the low harm profile of thiamine and the benefit of early treatment if affected (GeneReviews, NBK1282).

13. Prevention

Primary prevention: Because TRMA is a fully penetrant monogenic recessive disorder, primary prevention is achieved through genetic counseling and carrier screening in at-risk families/populations (particularly consanguineous families and founder populations such as the Ingush cluster), plus prenatal and preimplantation genetic testing once the family's pathogenic variant(s) are identified (GeneReviews, NBK1282; PMID:42511616). There is no vaccine or environmental-exposure-avoidance strategy relevant to this genetic disease.

Secondary prevention (early detection): Because thiamine treatment cannot reverse established hearing loss but can prevent/attenuate anemia and delay diabetes, early diagnosis via clinical suspicion (megaloblastic anemia with normal B12/folate, especially with diabetes or deafness) followed by prompt genetic confirmation and thiamine initiation functions as the operative secondary-prevention strategy — repeatedly emphasized across case reports as the modifiable determinant of outcome (PMC10691017; PMID:42511616). Empiric thiamine supplementation of at-risk siblings pending genetic testing is a specific, actionable secondary-prevention measure per GeneReviews.

Tertiary prevention: Lifelong surveillance (see below) and manifestation-specific specialist management (audiology, endocrinology, cardiology, ophthalmology, neurology) aim to detect and manage complications before they become severe.

Surveillance schedule (GeneReviews): At least annual evaluation is recommended, including: - Hematologic tests (CBC, reticulocyte count) to monitor thiamine treatment efficacy. - Glucose intolerance assessment (fasting glucose, OGTT, urinalysis). - Hearing, ophthalmologic, cardiac, and neurologic evaluations. - Assessment for manifestations of poor glycemic control (GeneReviews, NBK1282).

Genetic counseling: Standard autosomal recessive counseling applies (25% recurrence risk per pregnancy for carrier parents); population-specific counseling and targeted variant screening is now specifically recommended for the Ingush population given the newly characterized founder mutation (PMID:42511616).

14. Other Species / Natural Disease

No naturally occurring veterinary or wildlife disease analogous to TRMA (i.e., spontaneous SLC19A2-deficiency disease in companion animals or livestock) was identified in this search — this appears to be an area with no OMIA (Online Mendelian Inheritance in Animals) entry located, and no veterinary case series were found. The disease as studied in other species is confined to engineered/induced laboratory models (§15) rather than naturally occurring animal disease.

Orthology: SLC19A2 shows conserved orthology across human, mouse, rat, and zebrafish, indicating cross-species conservation of thiamine transporter biology, though this has not translated into documented spontaneous natural disease reports in non-human species in the literature surveyed.

15. Model Organisms

Mouse (Mus musculus) — the principal TRMA model: - Model: Slc19a2-null (targeted knockout) mouse, generated via homologous recombination/gene-trap disruption in embryonic stem cells (MGI:1928761) (PMID:12393806; MGI Slc19a2). - Phenotype recapitulation: - Erythrocytes from Slc19a2⁻/⁻ mice lack the high-affinity component of thiamine transport, mirroring the human cellular defect. - On a thiamin-free diet, Slc19a2⁻/⁻ mice develop diabetes mellitus with reduced insulin secretion and enhanced peripheral insulin sensitivity; this diabetes resolves after ~6 weeks of thiamin repletion, directly modeling the human treatment-responsiveness (PMID:12393806). - Auditory brainstem response (ABR) thresholds are markedly elevated in Slc19a2⁻/⁻ mice on a thiamin-free diet but remain normal in wild-type mice on the same diet and in thiamin-fed knockouts — demonstrating diet-dependence of the hearing phenotype. - Cochlear histology reveals selective inner hair cell loss after 1–2 weeks of low-thiamine challenge, with progressively greater inner-versus-outer hair cell loss over longer challenge periods, producing an auditory neuropathy phenotype; cochlear function is normal in mutants maintained on a high-thiamine diet (PMID:16642288). - Bone marrow analysis in this model shows evidence for defective deoxyribose and heme synthesis, mechanistically linking the transporter defect to impaired hematopoiesis (ASH Blood abstract, "Role of Defective High-Affinity Thiamine Transporter slc19a2 in Marrow..."). - Model limitations: The mouse phenotype is strongly diet-dependent (requiring a thiamin-free diet to unmask diabetes/deafness), whereas human patients develop disease despite normal dietary thiamine intake — reflecting a difference in baseline thiamine reserve/requirement or transporter redundancy between species that should be considered when extrapolating findings. This is a case where the model requires an added environmental manipulation (dietary thiamine restriction) to recapitulate a phenotype that arises spontaneously from genotype alone in humans — i.e., a PARTIALLY_RECAPITULATES relationship, gated by diet, rather than full spontaneous recapitulation. - Research applications: This model has been the primary tool for establishing the diet-thiamine-dependence of the diabetes and cochlear phenotypes and for identifying selective inner hair cell vulnerability as the auditory pathology substrate.

Human patient-derived cellular models: - Patient dermal fibroblasts and erythrocytes have been used directly (not as engineered lines) to demonstrate loss of high-affinity thiamine uptake and to quantify defective RNA ribose synthesis via the transketolase-dependent non-oxidative pentose phosphate pathway branch, providing the primary human cellular mechanistic evidence base (Blood, "Defective RNA ribose synthesis in fibroblasts from patients with TRMA"; JCI PDF, "Defective high-affinity thiamine transporter leads to cell...").

iPSC / zebrafish / Drosophila models: No TRMA-specific induced pluripotent stem cell line, zebrafish model, or Drosophila model was identified in this search, despite conserved SLC19A2 orthology in zebrafish making such a model theoretically feasible. (For comparison/contrast, iPSC models exist for the related paralog disease, SLC19A3-associated Biotin-Thiamine-Responsive Basal Ganglia Disease — e.g., KAIMRCi004-A/B lines — but these model a genetically and phenotypically distinct disorder, not TRMA itself.) This represents an apparent gap in available model-system resources for TRMA specifically.

Resources: MGI:1928761 (mouse Slc19a2 gene page, with knockout allele information) is the primary curated animal-model database entry identified (MGI).

Summary Table of Key Ontology Term Suggestions

Domain Suggested term
Disease (MONDO) MONDO:0009575
Disease (OMIM) 249270
Disease (Orphanet) ORPHA:49827
Causal gene (HGNC) hgnc:11021 (SLC19A2)
Megaloblastic anemia (HP) HP:0001889
Sensorineural hearing loss (HP) HP:0000407
Diabetes mellitus (HP) HP:0000819 / HP:0000857
Ring sideroblasts (HP) HP:0004828
Thrombocytopenia (HP) HP:0001873
Optic atrophy (HP) HP:0000648
Atrial septal defect (HP) HP:0001631
Thiamine metabolic process (GO) GO:0006772
Pentose-phosphate shunt, non-oxidative branch (GO) GO:0009052
Pancreatic β-cell (CL) CL:0000169
Cochlear inner hair cell (CL) CL:0000598
Bone marrow (UBERON) UBERON:0002371
Cochlea (UBERON) UBERON:0001846
Pancreas (UBERON) UBERON:0001264
Thiamine (CHEBI) CHEBI:18385 (thiamine(1+)) / thiamine
Treatment: Pharmacotherapy (NCIT) NCIT:C15986

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 12
Resolved 12
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 8
Quoted claims found in source 7
Quoted claims not found in source 1
References weighed for topical relevance 12
On topic 10
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMC:PMC10691017 (abstract only): "the importance of early diagnosis and treatment"
  • closest text in source: "In Cases 2 and 3, follow-up showed no blindness, unlike Case 4, in which treatment was started for megaloblastic anemia at age 7 but was increased to high doses only at age 25, when the genetic diagnosis of TRMA was performed"