Constitutional Megaloblastic Anemia With Severe Neurologic Disease

1. Disease Information

• Overview: A recessive inborn error of intracellular folate metabolism combining bone-marrow failure (megaloblastic anemia/pancytopenia) with a severe central-nervous-system phenotype driven by cerebral folate and BH4 deficiency. It is a treatable metabolic encephalopathy when recognized early. [HUMAN clinical; PMID 21310277, 21310276]
• Key identifiers:
• MONDO: MONDO:0013456
• OMIM (phenotype): #613839 "Megaloblastic anemia due to dihydrofolate reductase deficiency"
• OMIM (gene): *126060 (DHFR)
• Orphanet: ORPHA:319651 (Megaloblastic anemia due to dihydrofolate reductase deficiency)
• Gene / HGNC: DHFR (HGNC:2861); NCBI Gene 1719; Ensembl ENSG00000228716; UniProt P00374
• ICD-10: D53.1 (Other megaloblastic anemias, not elsewhere classified); ICD-11: 3A01.0 area / 5C50 (inborn errors of metabolism) — no unique code
• MeSH: Folic Acid Deficiency (D005494); Anemia, Megaloblastic (D000749); Tetrahydrofolate Dehydrogenase (D013894)
• Synonyms / alternative names: DHFR deficiency; Dihydrofolate reductase deficiency; Megaloblastic anemia due to dihydrofolate reductase deficiency; Constitutional megaloblastic anemia with severe neurologic disease; Cerebral folate deficiency due to DHFR deficiency.
• Information source type: Aggregated disease-level (OMIM/Orphanet/MONDO) plus individual-patient case series (EHR-derived clinical descriptions of ~6 patients). Not derived from large population EHR datasets.

2. Etiology

• Primary cause (genetic): Biallelic (homozygous) germline missense mutations in DHFR producing a stable but catalytically deficient enzyme. Cario et al. identified c.458A>T (p.Asp153Val); Banka et al. identified a homozygous DHFR missense mutation resulting in profound enzyme deficiency. [HUMAN clinical; PMID 21310277, 21310276]

  "DHFR sequencing revealed a homozygous DHFR mutation, c.458A>T (p.Asp153Val), in all siblings." (PMID 21310277)

• Genetic risk factors: Homozygous DHFR pathogenic variants are causal (Mendelian, not susceptibility loci). Consanguinity / relatedness is a major risk factor — reported families were consanguineous or distantly related, consistent with a rare recessive founder-type allele.
• Environmental risk factors: None are causal. However, low dietary folate intake would be expected to worsen the phenotype, and exposure to antifolate drugs (methotrexate, trimethoprim, pyrimethamine) that further inhibit residual DHFR could exacerbate disease (mechanistic inference).
• Protective factors: Dietary folate as reduced folates (folinic acid / 5-formyl-THF, 5-MTHF) bypasses the block and is protective/therapeutic. Common population DHFR polymorphisms (e.g., the 19-bp intron-1 deletion, c.594+59del19; p.Leu80Phe) modulate folate handling/antifolate response in the general population but are not causes of this monogenic disease.
• Gene–environment interactions: Folate/antifolate status interacts strongly with residual DHFR activity — the phenotype is a genetic enzyme deficiency whose severity is modifiable by folate form and dose (folinic acid rescue is the clearest example). [HUMAN clinical; PMID 21310277, 21310276]

3. Phenotypes

Frequencies are qualitative given the very small case number (n≈6). Onset is typically neonatal to infancy/early childhood; course is progressive if untreated, largely reversible/stabilizable with folinic acid.

Hematologic (laboratory abnormalities / clinical signs): - Megaloblastic anemia — core feature, most/all patients. HPO: HP:0001889 (Megaloblastic anemia). Onset infancy; severe; treatment-responsive. - Pancytopenia — reported in some patients. HP:0001876 (Pancytopenia); HP:0001873 (Thrombocytopenia), HP:0001882 (Leukopenia). - Macrocytosis / elevated MCV, megaloblastic bone marrow, hypersegmented neutrophils. HP:0001972 (Macrocytic anemia).

"characterized by megaloblastic anemia and/or pancytopenia" (PMID 21310276)

Neurologic (symptoms / signs): - Seizures / epilepsy, characteristically atypical childhood absence epilepsy. HP:0002121 (Absence seizure), HP:0001250 (Seizure). [HUMAN clinical; PMID 21310277]

"megaloblastic anemia and cerebral folate deficiency causing neurologic disease with atypical childhood absence epilepsy." (PMID 21310277) - Global developmental delay / intellectual disability. HP:0001263 (Global developmental delay), HP:0001249 (Intellectual disability). - Microcephaly (reported in cerebral folate deficiency states). HP:0000252. - Cerebral folate deficiency features — variable neurologic findings including hypotonia, movement/motor abnormalities, and, mechanistically expected from BH4/monoamine deficiency, potential extrapyramidal or mood/behavioral changes. HP:0002376 (Developmental regression) variably. - Neuroimaging abnormalities consistent with folate-deficient leukoencephalopathy in some patients. HP:0002352 (Leukoencephalopathy).

Severity / progression / QoL: Severe, potentially life-threatening in the neonatal/infantile period (anemia) with substantial neurodisability risk. Quality-of-life impact is high if untreated (epilepsy + developmental impairment); early folinic acid markedly improves hematologic status and neurologic trajectory, though pre-treatment CNS injury may persist. [HUMAN clinical; PMID 21310277, 21310276]

4. Genetic / Molecular Information

• Causal gene: DHFR (dihydrofolate reductase), 5q14.1; OMIM *126060; HGNC:2861; UniProt P00374 (187 aa cytosolic enzyme). EC 1.5.1.3.
• Pathogenic variants (germline, autosomal recessive):
• c.458A>T; p.Asp153Val (p.D153V) — homozygous; 3 affected siblings (Cario et al.). Missense; classified pathogenic; drastically reduced enzyme activity and reduced methotrexate (FMTX) binding; normal mRNA but reduced protein → destabilizing missense / loss of function. [HUMAN clinical + in vitro; PMID 21310277] > "RT-PCR of DHFR mRNA revealed no differences between wild-type and DHFR mutation-carrying cells, whereas protein expression was reduced in cells with the DHFR mutation." (PMID 21310277)
• Homozygous DHFR missense mutation in 3 individuals from 2 families (Banka et al.) → profound enzyme deficiency (reported as p.Leu80Phe in that cohort). [HUMAN clinical; PMID 21310276]
• Variant type/class: missense (loss-of-function via reduced protein stability/activity). No nonsense/frameshift/structural variants reported as causal to date.
• ACMG/AMP: Pathogenic (functional enzyme assays + segregation + rarity).
• Allele frequency: Causal alleles are private/ultra-rare (essentially absent in gnomAD as homozygotes). Note the common benign DHFR 19-bp intron-1 deletion and p.Leu80Phe polymorphism exist in general populations and affect folate/antifolate pharmacology but are not disease-causing here.
• Somatic vs germline: Germline only.
• Functional consequence: Loss of function (reduced catalytic activity + reduced protein). Heterozygotes show intermediate DHFR activity and FMTX binding but are clinically unaffected (recessive). [in vitro; PMID 21310277]
• Modifier genes: Not formally established; folate-pathway genes (MTHFR, folate transporters SLC46A1/FOLR1, MTHFD1) and dietary folate plausibly modify severity (inference).
• Epigenetic / chromosomal abnormalities: None implicated; no aneuploidy/translocation. Global one-carbon/methylation supply is indirectly reduced (methionine/SAM), a downstream metabolic — not primary epigenetic — effect.

5. Environmental Information

• Environmental factors: No environmental cause. Antifolate drug exposure (methotrexate, trimethoprim–sulfamethoxazole, pyrimethamine) is mechanistically contraindicated/aggravating because it further inhibits DHFR (inference).
• Lifestyle / diet: Folate nutrition is the dominant modifiable factor; adequacy of reduced folate (folinic acid) is protective. Ordinary folic acid supplementation does not rescue the defect. [HUMAN clinical; PMID 21310276]
• Infectious agents: Not applicable (not an infectious disease).

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

1. Biallelic DHFR missense mutation (e.g., p.Asp153Val) → destabilized DHFR protein with severely reduced catalytic activity ([in vitro] reduced enzyme activity + FMTX binding; normal mRNA, low protein). Demonstrated.
2. Reduced DHFR activity → failure to reduce 7,8-dihydrofolate (DHF) to tetrahydrofolate (THF) and failure to reduce dietary folic acid → depletion of the reduced-folate (THF) pool. Demonstrated by patient folate profiling.
3. THF depletion branches into three arms:
4. 3a. Hematologic arm: low THF → impaired thymidylate synthase cycle (dUMP→dTMP) and de novo purine synthesis → uracil misincorporation / imbalanced dNTPs → ineffective DNA synthesis in erythroid precursors → nuclear–cytoplasmic asynchrony → megaloblastic anemia and pancytopenia. Inferred from folate biochemistry; demonstrated hematologic phenotype.
5. 3b. Cerebral folate arm: impaired regeneration/transport of reduced folate → low CSF 5‑methyltetrahydrofolate (cerebral folate deficiency) → impaired CNS one-carbon metabolism, methylation, and neurotransmitter precursor supply → seizures (atypical absence epilepsy), developmental delay. Demonstrated (low CSF folate).
6. 3c. Neurotransmitter/BH4 arm: DHFR also regenerates tetrahydrobiopterin (BH4) from dihydrobiopterin (BH2) (the salvage arm of BH4 metabolism). Loss → cerebral BH4 deficiency → reduced activity of tyrosine/tryptophan/phenylalanine hydroxylases → reduced dopamine, serotonin, norepinephrine → neurologic/neuropsychiatric manifestations. Demonstrated (cerebral BH4 deficiency; PMID 21310276).
7. Convergent CNS effects of 3b + 3c → severe, potentially progressive encephalopathy.
8. Therapeutic branch (reversal): administration of folinic acid (5‑formyl‑THF), a folate already reduced beyond the DHFR block → restores THF pool → corrects anemia, normalizes CSF folate, improves neurologic symptoms. Demonstrated.

Detail by category

• Molecular pathways: Folate one-carbon metabolism (KEGG hsa00670 one-carbon pool by folate; Reactome "Metabolism of folate and pterines"); pterine/BH4 salvage; methionine cycle (SAM methylation).
• Cellular processes: DNA replication in rapidly dividing cells (erythroblasts) → ineffective erythropoiesis/apoptosis of precursors; neuronal signaling via monoamines.
• Protein dysfunction: Destabilizing missense → loss of function with reduced protein abundance (not simply catalytic-site abolition); heterozygous intermediate activity. DHFR is a small (~21 kDa, 187 aa) NADPH-dependent oxidoreductase (Rossmann-like fold) whose catalysis involves hydride transfer from NADPH and protonation of the folate N5 — mechanistic basis for why point mutations near substrate/cofactor contacts abolish activity. [structural; PMID 25453083]. Human DHFR crystal structures (e.g., PDB via Cody et al., PMID 21931219, 26057816) define an active-site pocket with a conserved substrate-anchoring Arg70, and pteridine-binding residues Phe31, Gln35, Val115 (Val115 vs Ile in microbial DHFR underlies antifolate selectivity). The disease missense residues (e.g., Asp153, Leu80) map to this compact fold; substitutions destabilize the protein and/or perturb cofactor/substrate binding, consistent with the observed loss of activity and reduced protein level. UniProt P00374; AlphaFold model AF-P00374.
• Metabolic changes: ↓THF, ↑DHF (relative), ↓5‑MTHF (esp. CSF), ↓BH4, impaired dTMP/purine synthesis, impaired homocysteine remethylation (variable). CHEBI: 7,8-dihydrofolate (CHEBI:20506), tetrahydrofolate (CHEBI:26907), 5‑methyltetrahydrofolate (CHEBI:15641), folinic acid (CHEBI:63606), tetrahydrobiopterin (CHEBI:15372).
• Immune involvement: Not a primary feature (contrast MTHFD1 deficiency, which adds SCID).
• Tissue damage mechanisms: Ineffective hematopoiesis (marrow); neuronal dysfunction from substrate/neurotransmitter insufficiency (largely functional, potentially structural leukoencephalopathy).
• Biochemical abnormality: Enzyme deficiency — dihydrofolate reductase (EC 1.5.1.3).
• Suggested GO terms: GO:0046452 (dihydrofolate metabolic process), GO:0006545 (glycine biosynthetic process), GO:0046655 (folic acid metabolic process), GO:0009394 (2'-deoxyribonucleotide metabolic process), GO:0006760 (folic acid-containing compound metabolic process), GO:0034355 (NAD salvage n/a) ; molecular function GO:0004146 (dihydrofolate reductase activity); GO:0006559 (l-phenylalanine catabolic process, via BH4).
• Suggested CL terms: erythroid progenitor cell (CL:0000038), megakaryocyte-erythroid progenitor, neuron (CL:0000540), dopaminergic neuron (CL:0000700), serotonergic neuron (CL:0000850).

7. Anatomical Structures Affected

• Organ level (primary): Bone marrow / hematopoietic system (UBERON:0002371 bone marrow) and brain / central nervous system (UBERON:0000955 brain).
• Secondary/system involvement: Peripheral blood (all lineages — anemia, leukopenia, thrombocytopenia); potentially cerebrospinal fluid compartment (UBERON:0001359 CSF) showing low 5-MTHF.
• Body systems: Hematologic/immune (blood) and nervous system; digestive absorption of folate is intact (the defect is intracellular reduction, distinguishing it from hereditary folate malabsorption).
• Tissue/cell level: Erythroid and other hematopoietic precursors (megaloblastic marrow); CNS neurons dependent on monoamine neurotransmitters. CL: erythroid progenitor (CL:0000038), neuron (CL:0000540).
• Subcellular level: Cytosol (DHFR is cytosolic; GO:0005829) with folate-dependent one-carbon reactions in cytosol and nucleus; downstream nuclear de novo thymidylate synthesis affected.
• Localization / lateralization: Systemic/bilateral; CNS involvement is diffuse/bilateral (e.g., diffuse white-matter changes), not focal.

8. Temporal Development

• Onset: Congenital enzyme defect; clinical presentation typically neonatal to early infancy/childhood (megaloblastic anemia early; seizures/absence epilepsy in early childhood). [HUMAN clinical; PMID 21310277]
• Onset pattern: Subacute/chronic, insidious neurologic decline with intercurrent anemia.
• Progression: Progressive if untreated; neurologic damage may accrue during the untreated window. With folinic acid, hematologic and biochemical parameters normalize and neurologic symptoms improve/stabilize. [HUMAN clinical; PMID 21310276]
• Course pattern: Chronic, lifelong (requires lifelong folinic acid). Seizures may be episodic.
• Remission: Treatment-induced biochemical/hematologic remission with folinic acid; not spontaneous.
• Critical period: Early infancy/childhood is the critical intervention window — earlier treatment better preserves neurodevelopment (rationale for newborn/early metabolic detection).

9. Inheritance and Population

• Epidemiology: Ultra-rare — only a handful of patients (≈6 from 4 families) reported worldwide; prevalence <1/1,000,000 (Orphanet "unknown/ultra-rare"). Incidence not quantifiable.
• Inheritance: Autosomal recessive. Heterozygous carriers are asymptomatic with intermediate enzyme activity. [in vitro; PMID 21310277]
• Penetrance: Complete in biallelic individuals reported; expressivity variable (neurologic severity varies — "variable neurological findings," PMID 22108709).
• Genetic anticipation: Not applicable (not a repeat-expansion disorder).
• Germline mosaicism: Not reported.
• Founder effects / consanguinity: Reported families were consanguineous or distantly related; private homozygous alleles — consistent with founder/consanguinity mechanism.
• Carrier frequency: Unknown; expected very low given rarity.
• Demographics: No established ethnic predilection given tiny sample; both sexes affected (autosomal). No sex bias expected. Age distribution: pediatric onset.

10. Diagnostics

• Laboratory tests:
• CBC + smear: macrocytic/megaloblastic anemia, possible pancytopenia, hypersegmented neutrophils. LOINC: MCV 30428-7, Hemoglobin 718-7.
• Bone marrow: megaloblastic changes.
• Serum/RBC folate, vitamin B12, homocysteine to position within folate disorders (B12 normal; distinguishes from B12 deficiency).
• CSF 5‑methyltetrahydrofolate (low) — hallmark of cerebral folate deficiency. [HUMAN clinical; PMID 21310277]
• CSF neurotransmitter metabolites / biopterins (low BH4, altered HVA/5-HIAA) reflecting BH4/monoamine deficiency. [HUMAN clinical; PMID 21310276]
• LC-MS/MS folate profiling of RBC, plasma, CSF (as used diagnostically). [PMID 21310277]
• Functional/enzyme assay: DHFR enzyme activity and fluorescein-methotrexate (FMTX) binding in lymphoblastoid cells/fibroblasts — severely reduced in patients, intermediate in carriers. [in vitro; PMID 21310277]
• Imaging: Brain MRI — may show leukoencephalopathy/white-matter changes; used to characterize CNS involvement.
• Electrophysiology: EEG for absence/atypical absence epilepsy characterization.
• Genetic testing: Definitive test = DHFR sequencing (single-gene, or as part of a megaloblastic-anemia / inborn-errors-of-folate / epilepsy-metabolic gene panel; WES/WGS in undiagnosed cases). Homozygosity mapping was pivotal in gene discovery. [PMID 21310277]. GTR panels for "megaloblastic anemia" and "cerebral folate deficiency" include DHFR.
• Clinical criteria / differential diagnosis: Combination of megaloblastic anemia + low CSF folate + folinic-acid responsiveness + biallelic DHFR variants. Differentiate from: vitamin B12 deficiency; folate malabsorption (SLC46A1); FOLR1 cerebral folate deficiency (no anemia); MTHFR deficiency (homocystinuria, no megaloblastic anemia); MTHFD1 deficiency (adds SCID/immunodeficiency; impaired nuclear dTMP synthesis with elevated uracil in DNA, PMID 25548164); thiamine-responsive megaloblastic anemia (SLC19A2); orotic aciduria.
• Screening: No routine newborn screen currently; consider cascade/carrier testing in affected families and prenatal/preimplantation testing where the familial variant is known.

11. Outcome / Prognosis

• Survival/mortality: Untreated severe megaloblastic anemia/pancytopenia is potentially fatal in infancy; prognosis is substantially improved with early folinic acid. No formal survival statistics exist (too few cases).
• Morbidity/function: Neurodevelopmental disability and epilepsy are the main morbidities; degree depends on timing of treatment. Hematologic parameters are fully correctable.
• Recovery potential: Hematologic and biochemical abnormalities are reversible with folinic acid; neurologic recovery is partial — pre-treatment CNS injury may be irreversible, underscoring early diagnosis. [HUMAN clinical; PMID 21310276, 21310277]. The analogous FOLR1 cerebral folate deficiency literature reinforces a critical treatment window: folinic acid begun after >15 years of illness produced no meaningful clinical/neurophysiological improvement in three siblings (PMID 34008900), whereas timely initiation improved outcome (PMID 41132636).
• Prognostic factors: Age at diagnosis/treatment initiation, extent of pre-treatment neurologic damage, adherence to lifelong folinic acid, avoidance of antifolate drugs.

12. Treatment

• First-line pharmacotherapy: Folinic acid (calcium leucovorin / 5‑formyltetrahydrofolate) — a pre-reduced folate that bypasses the DHFR block; corrects anemia/pancytopenia, normalizes CSF folate, improves neurologic symptoms. Lifelong. NCIT: Leucovorin Calcium (C1035) / Folinic Acid. [HUMAN clinical; PMID 21310277, 21310276]

  "Treatment with folinic acid resulted in the resolution of hematological abnormalities, normalization of CSF folate levels, and improvement of neurological symptoms." (PMID 21310277)

• Ineffective/avoid: Folic acid (requires DHFR to become active — does not rescue). Beyond needing DHFR, unmetabolized folic acid actively inhibits 5-MTHF transport across the blood–CSF barrier, worsening cerebral folate deficiency: in two CFD cases high-dose folic acid failed to normalize CSF 5-MTHF, and stopping folic acid normalized it — so folinic acid or 5-MTHF is preferred (PMID 36341171). Avoid antifolate drugs (methotrexate, trimethoprim, pyrimethamine).

  "In the treatment of CFD, supplementation of folinic acid or 5MTHF (in cases of impaired 5MTHF synthesis) is preferred over the use of FA." (PMID 36341171)

• Adjunctive: Dose titration to normalize CSF 5-MTHF; consider that some cerebral folate deficiency benefits from higher folinic acid doses to cross the blood–brain barrier. Antiepileptic therapy for seizures as needed; monitor since folate status interacts with some AEDs.
• Potential neurotransmitter support: Because of BH4/monoamine deficiency, consideration of BH4 (sapropterin) or neurotransmitter precursor supplementation (e.g., L-dopa/carbidopa, 5-hydroxytryptophan) is biologically rational in select patients (inference; not established as standard for DHFR deficiency). Management principles for BH4/monoamine-deficiency disorders are summarized in an international consensus guideline (PMID 32456656).
• Advanced/experimental therapeutics: No gene, cell, or RNA therapy in clinical use; the disorder is largely managed by metabolite replacement. Gene replacement is conceptually feasible but unstudied.
• Supportive care: Transfusion for severe anemia acutely; developmental/rehabilitative therapies for neurodisability.
• Treatment strategy / personalized medicine: Genotype-confirmed diagnosis → lifelong folinic acid + monitoring of CBC, plasma and CSF folate; family cascade testing. NCIT terms: Leucovorin Calcium (C1035); Sapropterin Dihydrochloride (C61815) [experimental rationale].

13. Prevention

• Primary prevention: Not preventable in an affected homozygote (germline). Genetic counseling for at-risk families; carrier/cascade testing; prenatal or preimplantation genetic testing where the familial DHFR variant is known.
• Secondary prevention (early detection): High index of suspicion in infants with megaloblastic anemia + neurologic signs + low CSF folate → early DHFR testing and prompt folinic acid to prevent CNS damage. No population newborn screen exists yet, but the treatable nature makes early metabolic detection valuable.
• Tertiary prevention: Lifelong folinic acid, avoidance of antifolates, seizure control, developmental support to prevent complications and progression.
• Counseling: Autosomal recessive recurrence risk 25% per pregnancy for carrier couples; offer NSGC/ACMG-guided counseling.

14. Other Species / Natural Disease

• Taxonomy: DHFR is universally conserved (essential enzyme) across bacteria, fungi, plants, and animals (NCBI Taxon relevance broad). Human host: Homo sapiens (NCBI:txid9606).
• Orthologous genes: Mouse Dhfr (NCBI Gene 13361); rat Dhfr (NCBI Gene 24312); zebrafish dhfr. High evolutionary conservation of catalytic function.
• Natural disease in animals: No well-characterized spontaneous DHFR-deficiency disease reported in companion animals/wildlife (OMIA — none established). DHFR is a classic antimicrobial/antineoplastic drug target across species.
• Comparative biology: Complete DHFR loss is embryonic-lethal in model organisms (essential gene), which is why human disease arises only from hypomorphic missense alleles retaining partial activity — a key comparative insight.
• Transmission: Not applicable (non-infectious, monogenic).

15. Model Organisms

• Model status: No published dedicated mouse/zebrafish model that recapitulates the human hypomorphic DHFR-deficiency disease was identified in this search; complete Dhfr knockouts are expected to be embryonic-lethal (essential enzyme), a key limitation.
• Cellular/in vitro models (used in the defining studies): Patient-derived EBV-immortalized lymphoblastoid cell lines and fibroblasts demonstrating reduced DHFR activity, reduced FMTX binding, and reduced protein — the primary functional models to date. [in vitro; PMID 21310277]
• Model types feasible: Knock-in of patient missense alleles (e.g., p.Asp153Val, p.Leu80Phe) in mouse/human iPSC or cell lines; conditional/hypomorphic alleles; iPSC-derived neurons/erythroid cultures to model the dual phenotype; humanized DHFR yeast/bacterial complementation assays for variant functional testing.
• Applications: Variant functional classification (enzyme activity, antifolate binding), folate-flux studies, testing folinic acid / BH4 rescue.
• Resources: MGI (Dhfr), Cellosaurus (patient lines), ClinVar (DHFR variants).

Ontology Term Quick-Reference

• Disease: MONDO:0013456; OMIM #613839; ORPHA:319651
• Gene/Protein: DHFR (HGNC:2861; NCBI 1719; UniProt P00374); GO:0004146 (DHFR activity)
• HPO: HP:0001889 (megaloblastic anemia), HP:0001876 (pancytopenia), HP:0002121 (absence seizure), HP:0001250 (seizure), HP:0001263 (global developmental delay), HP:0001249 (intellectual disability), HP:0000252 (microcephaly), HP:0002352 (leukoencephalopathy)
• GO (BP/CC): GO:0046655 (folic acid metabolic process), GO:0046452 (dihydrofolate metabolic process), GO:0006760 (folic acid-containing compound metabolic process), GO:0005829 (cytosol)
• CL: CL:0000038 (erythroid progenitor), CL:0000540 (neuron), CL:0000700 (dopaminergic neuron)
• UBERON: UBERON:0002371 (bone marrow), UBERON:0000955 (brain), UBERON:0001359 (CSF)
• CHEBI: CHEBI:20506 (7,8-dihydrofolate), CHEBI:26907 (tetrahydrofolate), CHEBI:15641 (5-MTHF), CHEBI:63606 (folinic acid), CHEBI:15372 (tetrahydrobiopterin)
• NCIT: Leucovorin Calcium (C1035); Sapropterin (C61815)

Supported vs. Refuted Hypotheses

Supported: - H1 (Supported): Biallelic DHFR missense mutations cause the disease via profound enzyme loss of function. [PMID 21310277, 21310276] - H2 (Supported): The mechanism is THF-pool depletion producing megaloblastic anemia + cerebral folate deficiency + cerebral BH4 deficiency. [PMID 21310276, 21310277] - H3 (Supported): Folinic acid (not folic acid) is corrective because it bypasses the DHFR block. [PMID 21310277, 21310276] - H4 (Supported): The disorder is distinguishable within inborn errors of folate metabolism; MTHFD1 deficiency adds immunodeficiency. [PMID 22108709, 25548164]

Refuted / Not supported: - Environmental or infectious primary etiology — refuted (Mendelian recessive enzyme defect). - Dominant inheritance — refuted (heterozygotes asymptomatic with intermediate activity).

Limitations and Future Directions

• Evidence base is very small (~6 patients from 4 families); frequencies, prognosis, and genotype–phenotype correlations are qualitative. Numbers such as prevalence are order-of-magnitude estimates from Orphanet-class sources.
• The curated literature accessible here is limited; additional post-2012 case reports and any dedicated animal models were not retrievable in this environment and should be sought in OMIM/GeneReviews/HGMD/ClinVar and full PubMed.
• Future directions: systematic natural-history and treatment-timing studies; standardized CSF 5-MTHF/BH4/neurotransmitter panels; functional assays for variant classification; evaluation of BH4/neurotransmitter-precursor adjuncts; and consideration of DHFR in metabolic/epilepsy newborn or early-childhood screening given treatability.

Primary References (PMID)

• 21310277 — Cario H, et al. Dihydrofolate reductase deficiency due to a homozygous DHFR mutation causes megaloblastic anemia and cerebral folate deficiency leading to severe neurologic disease. Am J Hum Genet, 2011. [HUMAN clinical + in vitro]
• 21310276 — Banka S, et al. Identification and characterization of an inborn error of metabolism caused by dihydrofolate reductase deficiency. Am J Hum Genet, 2011. [HUMAN clinical + in vitro]
• 22108709 — Watkins D, Rosenblatt DS. Update and new concepts in vitamin responsive disorders of folate transport and metabolism. J Inherit Metab Dis, 2012. [review]
• 25548164 — Field MS, et al. Human mutations in MTHFD1 impair nuclear de novo thymidylate biosynthesis. (differential) [HUMAN + in vitro]
• 25453083 — Wan Q, et al. Toward resolving the catalytic mechanism of dihydrofolate reductase using neutron and ultrahigh-resolution X-ray crystallography. [structural — DHFR enzymology]
• 36341171 — Akiyama T, et al. Folic acid inhibits 5-methyltetrahydrofolate transport across the blood-cerebrospinal fluid barrier: Clinical biochemical data from two cases. 2022. [HUMAN clinical — treatment rationale; provides pediatric CSF 5-MTHF reference values from 600 cases]
• 34008900 — Brunetti V, et al. Cerebral folate transporter deficiency syndrome in three siblings... 2021. [HUMAN clinical — FOLR1 differential; supports critical treatment window / irreversibility of delayed therapy]
• 41132636 — Ahmadabadi F, et al. A Case of Cerebral Folate Deficiency due to FOLR1 Mutation in a 10-Year-Old Girl. 2025. [HUMAN clinical — FOLR1 differential; timely folinic acid improves outcome]
• 32456656 — Opladen T, et al. Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies. 2020. [guideline — BH4/monoamine management framework]
• 21931219 / 26057816 — Cody V, et al. Structural analyses of human dihydrofolate reductase. 2011/2015. [structural — hDHFR active-site residues Arg70, Phe31, Gln35, Val115]

Artifacts

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Term Validation

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Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0001882 (1 mention) - the report calls it "Leukopenia"; HP calls it Decreased total leukocyte count, and lists "Leukopenia" among its other names
• CHEBI:20506 (2 mentions) - the report calls it "7,8-dihydrofolate"; CHEBI calls it 5,6,7,8-tetrahydrofolic acid, and lists "5,6,7,8-Tetrahydrofolate" among its other names
• CHEBI:26907 (2 mentions) - the report calls it "tetrahydrofolate"; CHEBI calls it tetrahydrofolic acid, and lists "tetrahydrofolate" among its other names
• CHEBI:15641 (2 mentions) - the report calls it "5-MTHF"; CHEBI calls it 5-methyltetrahydrofolic acid, and lists "5-methyl-THF" among its other names
• CHEBI:63606 (2 mentions) - the report calls it "folinic acid"; CHEBI calls it (6S)-5-formyltetrahydrofolic acid, and lists "L-Folinic acid" among its other names
• CHEBI:15372 (2 mentions) - the report calls it "tetrahydrobiopterin"; CHEBI calls it 5,6,7,8-tetrahydrobiopterin, and lists "Tetrahydrobiopterin" among its other names
• GO:0034355 (1 mention) - the report calls it "NAD salvage n/a"; GO calls it NAD+ biosynthetic process via the salvage pathway, and lists "NAD salvage" among its other names
• GO:0004146 (2 mentions) - the report calls it "dihydrofolate reductase activity", "DHFR activity"; GO calls it dihydrofolate reductase activity, and lists "dihydrofolic reductase activity" among its other names
• GO:0006559 (1 mention) - the report calls it "l-phenylalanine catabolic process, via BH4"; GO calls it L-phenylalanine catabolic process
• CL:0000038 (3 mentions) - the report calls it "Suggested CL terms: erythroid progenitor cell", "erythroid progenitor"; CL calls it erythroid progenitor cell**
• UBERON:0001359 (2 mentions) - the report calls it "CSF"; UBERON calls it cerebrospinal fluid, and lists "CSF" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

• HP:0001876 - called "Pancytopenia", "pancytopenia"
• HP:0002121 - called "Absence seizure", "absence seizure"
• HP:0001250 - called "Seizure", "seizure"
• HP:0001263 - called "Global developmental delay", "global developmental delay"
• HP:0001249 - called "Intellectual disability", "intellectual disability"
• HP:0002352 - called "Leukoencephalopathy", "leukoencephalopathy"
• GO:0004146 - called "dihydrofolate reductase activity", "DHFR activity"
• CL:0000038 - called "Suggested CL terms:** erythroid progenitor cell", "erythroid progenitor"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.

34 of 36 terms resolved to a current term; the rest could not be looked up either way.