Brown-Vialetto-Van Laere Syndrome

Mendelian MONDO:0008891 Pathograph 17 Show in embeddings browser Motor Neuron Disease

Brown-Vialetto-Van Laere (BVVL) syndrome is a rare, autosomal recessive motor, sensory, and cranial-nerve neuronopathy caused by deficiency of plasma-membrane riboflavin (vitamin B2) transporters — RFVT3 (encoded by SLC52A3, BVVL type 1, MONDO:0024537) and RFVT2 (encoded by SLC52A2, BVVL type 2, MONDO:0013867). Impaired cellular riboflavin uptake depletes the flavocofactors FAD and FMN, producing mitochondrial dysfunction (impaired flavoprotein-dependent electron transport and fatty-acid/amino-acid oxidation) and progressive degeneration of cranial-nerve motor nuclei (pontobulbar palsy), sensory neurons, and spinal motor neurons. The clinical hallmarks are progressive sensorineural deafness, bulbar palsy (dysphagia, dysarthria, facial and tongue weakness), respiratory compromise, limb weakness, sensory ataxia, and optic atrophy; onset ranges from infancy to adulthood. The allelic childhood form presenting as progressive bulbar palsy WITHOUT prominent deafness is Fazio-Londe disease, now regarded as the same disease entity within the riboflavin-transporter-deficiency spectrum. CRITICALLY, BVVL is a TREATABLE neurodegenerative disorder: high-dose oral riboflavin supplementation halts or reverses progression, making early diagnosis (and an empirical riboflavin trial before genetic confirmation) life-saving.

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4
Pathophys.
10
Phenotypes
17
Pathograph
2
Genes
1
Medical Actions
2
Subtypes
3
References
◆

Subtypes

2
SLC52A3-related riboflavin transporter deficiency (BVVL1) MONDO:0024537
The SLC52A3/RFVT3-related subtype, in which impaired intestinal riboflavin uptake commonly lowers plasma riboflavin.
Show evidence (1 reference)
PMID:22864630 SUPPORT Human Clinical
"While mutations in SLC52A3 cause decreased plasma riboflavin levels, concordant with a role of SLC52A3 in riboflavin uptake from food"
Supports the gene-specific intestinal-uptake phenotype of BVVL1.
SLC52A2-related riboflavin transporter deficiency (BVVL2) MONDO:0013867
The SLC52A2/RFVT2-related subtype, in which cellular uptake from blood is impaired and plasma riboflavin may remain normal.
Show evidence (1 reference)
PMID:22864630 SUPPORT Human Clinical
"the SLC52A2-mutant individual had normal plasma riboflavin concentrations, a finding in line with a postulated function of SLC52A2 in riboflavin uptake from blood into target cells."
Supports the gene-specific cellular-uptake phenotype of BVVL2.
⚙

Pathophysiology

4
Riboflavin Transporter Deficiency
Biallelic loss-of-function mutations in the riboflavin transporter genes SLC52A3 (RFVT3; BVVL1) and SLC52A2 (RFVT2; BVVL2) reduce riboflavin transport activity at the plasma membrane, impairing cellular uptake of riboflavin from food (SLC52A3, with decreased plasma riboflavin) and from the blood into target cells (SLC52A2).
motor neuron CL:0000100
SLC52A3 hgnc:16187 SLC52A2 hgnc:30224
riboflavin transport GO:0032218 ↓ DECREASED
Downstream
Flavocofactor (FAD/FMN) Depletion Reduced cellular riboflavin uptake limits the precursor pool for synthesis of the flavin cofactors FMN and FAD.
Show evidence (2 references)
PMID:20206331 SUPPORT Human Clinical
"We identified a candidate gene, C20orf54, by studying a consanguineous family with multiple affected individuals and subsequently demonstrated that mutations in this gene were the cause of disease in other, unrelated families."
Establishes mutations in C20orf54 (SLC52A3, riboflavin transporter RFVT3) as the cause of BVVL syndrome.
PMID:22864630 SUPPORT In Vitro
"Overexpression studies confirmed that the gene products of both mutant alleles have reduced riboflavin transport activities."
Functional confirmation that SLC52A2 (RFVT2) mutant alleles reduce riboflavin transport activity.
Flavocofactor (FAD/FMN) Depletion
Riboflavin is the obligate precursor of the flavin cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Reduced riboflavin availability depletes these flavocofactors, which are essential prosthetic groups for the flavoprotein enzymes of mitochondrial energy metabolism.
motor neuron CL:0000100
FAD biosynthetic process GO:0006747 ↓ DECREASED flavin adenine dinucleotide metabolic process GO:0072387 ↓ DECREASED
Downstream
Mitochondrial Flavoprotein Dysfunction Depletion of FAD/FMN deprives flavoprotein-dependent mitochondrial enzymes (electron transport chain complexes I and II, acyl-CoA dehydrogenases) of their essential cofactors.
Show evidence (2 references)
PMID:29053833 SUPPORT Model Organism
"global knockdown of the single Drosophila melanogaster riboflavin transporter homologue revealed reduced levels of riboflavin, downstream metabolites, and electron transport chain complex I activity."
Riboflavin transporter knockdown reduces riboflavin and its downstream flavin metabolites, depleting the flavocofactor pool.
PMID:22864630 SUPPORT Human Clinical
"providing a rational basis for a high-dose riboflavin treatment."
The flavocofactor-precursor role of riboflavin provides the rationale for high-dose riboflavin supplementation in BVVL.
Mitochondrial Flavoprotein Dysfunction
Loss of FAD/FMN cofactors impairs flavoprotein-dependent mitochondrial bioenergetics: reduced electron transport chain complex I and complex II activity, abnormal mitochondrial membrane potential and morphology, and impaired flavoprotein-dependent fatty-acid beta-oxidation (acyl-CoA dehydrogenation), the latter producing an abnormal acylcarnitine profile in some patients. The brainstem neuropathology resembles that of primary mitochondrial disease.
motor neuron CL:0000100
respiratory electron transport chain GO:0022904 ↓ DECREASED fatty acid beta-oxidation GO:0006635 ↓ DECREASED
Downstream
Cranial, Sensory, and Motor Neuronopathy Energy-demanding cranial-nerve motor nuclei, sensory neurons, and spinal motor neurons are especially vulnerable to flavoprotein-dependent mitochondrial failure, leading to their degeneration.
Show evidence (2 references)
PMID:29053833 SUPPORT In Vitro
"Electron transport chain complex I and complex II activity were decreased in SLC52A2 patient fibroblasts"
Directly demonstrates impaired flavoprotein-dependent electron transport chain activity in patient cells.
PMID:29053833 SUPPORT Human Clinical
"showed classical symmetrical brainstem lesions resembling pathology seen in mitochondrial disease, including severe neuronal loss in the lower cranial nerve nuclei, anterior horns and corresponding nerves"
Neuropathology links mitochondrial-type brainstem lesions to loss of cranial-nerve and anterior-horn (motor) neurons.
Cranial, Sensory, and Motor Neuronopathy
Progressive degeneration of lower cranial-nerve motor nuclei (pontobulbar palsy), sensory neurons (sensory ataxia, sensorineural/auditory neuropathy), spinal anterior-horn motor neurons, and optic and other long tracts. The resulting clinical picture is rapidly progressive axonal sensorimotor neuropathy with sensorineural hearing loss, bulbar palsy, optic atrophy, and respiratory insufficiency; an upper-motor-neuron component reminiscent of amyotrophic lateral sclerosis can also evolve.
cranial nerve motor neuron CL:0015000 sensory neuron CL:0000101 lower motor neuron CL:0008039
motor neuron apoptotic process GO:0097049 ↑ INCREASED
Downstream
Sensorineural hearing loss Auditory-neuron degeneration produces progressive sensorineural hearing loss.
Bulbar palsy Degeneration of lower cranial motor nuclei produces progressive pontobulbar palsy.
Dysphagia Lower cranial motor dysfunction impairs the bulbar swallowing apparatus.
Dysarthria Lower cranial motor dysfunction impairs speech articulation and can progress to anarthria.
Facial weakness Facial motor-nucleus and cranial-nerve involvement produces facial weakness.
Tongue atrophy and fasciculations Hypoglossal lower-motor-neuron loss causes tongue wasting and fasciculations.
Muscle weakness Spinal motor-neuron and peripheral axonal loss produces limb and axial weakness.
Respiratory insufficiency Respiratory motor-neuron and diaphragmatic involvement causes progressive ventilatory insufficiency.
Optic atrophy Optic-neuron degeneration produces optic atrophy and visual impairment.
Sensory ataxia Sensory-neuron and long-tract degeneration impairs proprioceptive coordination.
Show evidence (2 references)
PMID:24253200 SUPPORT Human Clinical
"Affected individuals share a core phenotype of rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia, severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs), hearing loss, optic atrophy and respiratory insufficiency."
Defines the core cranial/sensory/motor neuronopathy phenotype of BVVL.
PMID:20206331 SUPPORT Human Clinical
"The key features are progressive ponto-bulbar palsy and bilateral sensorineural deafness."
Establishes pontobulbar palsy with sensorineural deafness as the cardinal neuronopathy phenotype.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Brown-Vialetto-Van Laere 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.
●

Phenotypes

10
Digestive 1
Dysphagia Dysphagia HP:0002015
Show evidence (1 reference)
PMID:28856173 SUPPORT Human Clinical
"progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
Documents dysphagia (and anarthria/dysarthria, facial weakness) as part of the bulbar phenotype.
Ear 1
Sensorineural hearing loss Sensorineural hearing impairment HP:0000407
Course: PROGRESSIVE
Show evidence (2 references)
PMID:22864630 SUPPORT Human Clinical
"Progressive and severe sensorineural deafness is the most frequently observed presenting symptom."
Sensorineural deafness is the most frequent presenting feature of BVVL.
PMID:26918385 SUPPORT Human Clinical
"Hearing loss in these individuals was due to auditory neuropathy spectrum disorder (ANSD)."
Characterizes the hearing loss as auditory neuropathy spectrum disorder.
Eye 1
Optic atrophy Optic atrophy HP:0000648
Show evidence (1 reference)
PMID:24253200 SUPPORT Human Clinical
"hearing loss, optic atrophy and respiratory insufficiency."
Optic atrophy is part of the core RFVT2-deficient BVVL phenotype.
Head and Neck 1
Facial weakness Facial palsy HP:0010628
Show evidence (1 reference)
PMID:23107375 SUPPORT Human Clinical
"The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise."
Facial weakness is among the most prevalent symptoms in BVVL.
Musculoskeletal 1
Muscle weakness Muscle weakness HP:0001324
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:24253200 SUPPORT Human Clinical
"severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs"
Describes the characteristic upper-limb/axial muscle weakness of RFVT2-deficient BVVL.
Nervous System 1
Dysarthria Dysarthria HP:0001260
Show evidence (1 reference)
PMID:28856173 SUPPORT Human Clinical
"progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
Anarthria (severe dysarthria) is documented as part of the bulbar phenotype.
Respiratory 1
Respiratory insufficiency Respiratory insufficiency HP:0002093
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:24253200 SUPPORT Human Clinical
"characterized by progressive pontobulbar palsy, sensorineural hearing loss and respiratory insufficiency."
Respiratory insufficiency is a cardinal feature of BVVL.
Other 3
Bulbar palsy Bulbar palsy HP:0001283
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:23107375 SUPPORT Human Clinical
"The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise."
Bulbar palsy is among the most prevalent symptoms in BVVL/Fazio-Londe patients.
Tongue atrophy and fasciculations Tongue atrophy HP:0012473
Show evidence (1 reference)
PMID:22864630 SUPPORT Human Clinical
"Neurological examination at the age of 5.5 years showed a right-sided palsy of the facial nerve and tongue wasting with fasciculations."
Documents tongue wasting with fasciculations (and facial nerve palsy) in a BVVL patient.
Sensory ataxia Sensory ataxia HP:0010871
Show evidence (1 reference)
PMID:24253200 SUPPORT Human Clinical
"rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia"
Sensory ataxia is a defining manifestation of the sensorimotor neuropathy in BVVL.
🧬

Genetic Associations

2
SLC52A3
Gene: SLC52A3 hgnc:16187
Autosomal Recessive
Show evidence (2 references)
PMID:20206331 SUPPORT Human Clinical
"Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
Identifies C20orf54 (SLC52A3) as a BVVL gene.
PMID:22864630 SUPPORT Human Clinical
"While mutations in SLC52A3 cause decreased plasma riboflavin levels, concordant with a role of SLC52A3 in riboflavin uptake from food"
SLC52A3 mutations reduce plasma riboflavin, consistent with its role in intestinal riboflavin uptake.
SLC52A2
Gene: SLC52A2 hgnc:30224
Autosomal Recessive
Show evidence (2 references)
PMID:22740598 SUPPORT Human Clinical
"We identified a novel mutation in a second member of the riboflavin transporter gene family (gene symbol: SLC52A2) as the cause of disease in this family."
Identifies SLC52A2 as a second BVVL-causing riboflavin transporter gene.
PMID:22864630 SUPPORT Human Clinical
"the SLC52A2-mutant individual had normal plasma riboflavin concentrations, a finding in line with a postulated function of SLC52A2 in riboflavin uptake from blood into target cells."
SLC52A2 mediates riboflavin uptake into target cells; plasma riboflavin may be normal.
💊

Medical Actions

1
High-dose Riboflavin Supplementation
Action: Pharmacotherapy NCIT:C15986
Agent: riboflavin CHEBI:17015
High-dose oral riboflavin (vitamin B2) replenishes the deficient flavocofactor pool and is a life-saving, disease-modifying therapy. Clinical and biochemical improvement can be rapid (days to weeks) or gradual over months; early initiation, before genetic confirmation, is recommended because outcome depends on prompt treatment. Some deficits (e.g., established sensorineural hearing loss) may not reverse.
Mechanism Target:
RESTORES Flavocofactor (FAD/FMN) Depletion — High-dose riboflavin replenishes the precursor pool for FMN and FAD synthesis, partially bypassing residual transporter deficiency by mass action.
Show evidence (1 reference)
PMID:22864630 PARTIAL Human Clinical
"providing a rational basis for a high-dose riboflavin treatment."
The study supplies the mechanistic rationale for high-dose riboflavin, although the abstract does not directly quantify intracellular FAD/FMN repletion.
Target Phenotypes: Bulbar palsy HP:0001283 Respiratory insufficiency HP:0002093
Show evidence (3 references)
PMID:24253200 SUPPORT Human Clinical
"The clinical and biochemical responses of this SLC52A2-specific cohort suggest that riboflavin supplementation can ameliorate the progression of this neurodegenerative condition, particularly when initiated soon after the onset of symptoms."
Demonstrates that high-dose riboflavin ameliorates progression, especially when started early.
PMID:23107375 SUPPORT Human Clinical
"All 13 patients who were treated with riboflavin survived, with a strong clinical improvement after days to months of treatment in eight patients."
All riboflavin-treated patients survived with clinical improvement, supporting riboflavin responsiveness.
PMID:23107375 SUPPORT Human Clinical
"treatment should be started immediately without first awaiting results of molecular analysis."
Supports immediate empirical riboflavin treatment before genetic confirmation.
{ }

Source YAML

click to show 
name: Brown-Vialetto-Van Laere Syndrome
creation_date: "2026-06-26T00:00:00Z"
category: Mendelian
description: >
  Brown-Vialetto-Van Laere (BVVL) syndrome is a rare, autosomal recessive
  motor, sensory, and cranial-nerve neuronopathy caused by deficiency of
  plasma-membrane riboflavin (vitamin B2) transporters — RFVT3 (encoded by
  SLC52A3, BVVL type 1, MONDO:0024537) and RFVT2 (encoded by SLC52A2, BVVL
  type 2, MONDO:0013867). Impaired cellular riboflavin uptake depletes the
  flavocofactors FAD and FMN, producing mitochondrial dysfunction (impaired
  flavoprotein-dependent electron transport and fatty-acid/amino-acid
  oxidation) and progressive degeneration of cranial-nerve motor nuclei
  (pontobulbar palsy), sensory neurons, and spinal motor neurons. The clinical
  hallmarks are progressive sensorineural deafness, bulbar palsy (dysphagia,
  dysarthria, facial and tongue weakness), respiratory compromise, limb
  weakness, sensory ataxia, and optic atrophy; onset ranges from infancy to
  adulthood. The allelic childhood form presenting as progressive bulbar palsy
  WITHOUT prominent deafness is Fazio-Londe disease, now regarded as the same
  disease entity within the riboflavin-transporter-deficiency spectrum.
  CRITICALLY, BVVL is a TREATABLE neurodegenerative disorder: high-dose oral
  riboflavin supplementation halts or reverses progression, making early
  diagnosis (and an empirical riboflavin trial before genetic confirmation)
  life-saving.
disease_term:
  preferred_term: riboflavin transporter deficiency
  term:
    id: MONDO:0008891
    label: riboflavin transporter deficiency
parents:
- Motor Neuron Disease
has_subtypes:
- name: Brown-Vialetto-van Laere syndrome 1
  display_name: SLC52A3-related riboflavin transporter deficiency (BVVL1)
  subtype_term:
    preferred_term: Brown-Vialetto-van Laere syndrome 1
    term:
      id: MONDO:0024537
      label: Brown-Vialetto-van Laere syndrome 1
  description: >-
    The SLC52A3/RFVT3-related subtype, in which impaired intestinal riboflavin
    uptake commonly lowers plasma riboflavin.
  evidence:
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While mutations in SLC52A3 cause decreased plasma riboflavin levels, concordant with a role of SLC52A3 in riboflavin uptake from food"
    explanation: Supports the gene-specific intestinal-uptake phenotype of BVVL1.
- name: Brown-Vialetto-van Laere syndrome 2
  display_name: SLC52A2-related riboflavin transporter deficiency (BVVL2)
  subtype_term:
    preferred_term: Brown-Vialetto-van Laere syndrome 2
    term:
      id: MONDO:0013867
      label: Brown-Vialetto-van Laere syndrome 2
  description: >-
    The SLC52A2/RFVT2-related subtype, in which cellular uptake from blood is
    impaired and plasma riboflavin may remain normal.
  evidence:
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the SLC52A2-mutant individual had normal plasma riboflavin concentrations, a finding in line with a postulated function of SLC52A2 in riboflavin uptake from blood into target cells."
    explanation: Supports the gene-specific cellular-uptake phenotype of BVVL2.
references:
- reference: PMID:23107375
  title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
- reference: PMID:24253200
  title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
- reference: PMID:29053833
  title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."

pathophysiology:
- name: Riboflavin Transporter Deficiency
  description: >
    Biallelic loss-of-function mutations in the riboflavin transporter genes
    SLC52A3 (RFVT3; BVVL1) and SLC52A2 (RFVT2; BVVL2) reduce riboflavin
    transport activity at the plasma membrane, impairing cellular uptake of
    riboflavin from food (SLC52A3, with decreased plasma riboflavin) and from
    the blood into target cells (SLC52A2).
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: riboflavin transport
    term:
      id: GO:0032218
      label: riboflavin transport
    modifier: DECREASED
  genes:
  - preferred_term: SLC52A3
    term:
      id: hgnc:16187
      label: SLC52A3
  - preferred_term: SLC52A2
    term:
      id: hgnc:30224
      label: SLC52A2
  evidence:
  - reference: PMID:20206331
    reference_title: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified a candidate gene, C20orf54, by studying a consanguineous family with multiple affected individuals and subsequently demonstrated that mutations in this gene were the cause of disease in other, unrelated families."
    explanation: Establishes mutations in C20orf54 (SLC52A3, riboflavin transporter RFVT3) as the cause of BVVL syndrome.
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Overexpression studies confirmed that the gene products of both mutant alleles have reduced riboflavin transport activities."
    explanation: Functional confirmation that SLC52A2 (RFVT2) mutant alleles reduce riboflavin transport activity.
  downstream:
  - target: Flavocofactor (FAD/FMN) Depletion
    description: >
      Reduced cellular riboflavin uptake limits the precursor pool for synthesis
      of the flavin cofactors FMN and FAD.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29053833
      reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "global knockdown of the single Drosophila melanogaster riboflavin transporter homologue revealed reduced levels of riboflavin, downstream metabolites, and electron transport chain complex I activity."
      explanation: >-
        Transporter knockdown directly reduced riboflavin and its downstream
        metabolites, supporting flavocofactor depletion downstream of impaired
        transport.

- name: Flavocofactor (FAD/FMN) Depletion
  description: >
    Riboflavin is the obligate precursor of the flavin cofactors flavin
    mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Reduced
    riboflavin availability depletes these flavocofactors, which are essential
    prosthetic groups for the flavoprotein enzymes of mitochondrial energy
    metabolism.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: FAD biosynthetic process
    term:
      id: GO:0006747
      label: FAD biosynthetic process
    modifier: DECREASED
  - preferred_term: flavin adenine dinucleotide metabolic process
    term:
      id: GO:0072387
      label: flavin adenine dinucleotide metabolic process
    modifier: DECREASED
  evidence:
  - reference: PMID:29053833
    reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "global knockdown of the single Drosophila melanogaster riboflavin transporter homologue revealed reduced levels of riboflavin, downstream metabolites, and electron transport chain complex I activity."
    explanation: Riboflavin transporter knockdown reduces riboflavin and its downstream flavin metabolites, depleting the flavocofactor pool.
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "providing a rational basis for a high-dose riboflavin treatment."
    explanation: The flavocofactor-precursor role of riboflavin provides the rationale for high-dose riboflavin supplementation in BVVL.
  downstream:
  - target: Mitochondrial Flavoprotein Dysfunction
    description: >
      Depletion of FAD/FMN deprives flavoprotein-dependent mitochondrial enzymes
      (electron transport chain complexes I and II, acyl-CoA dehydrogenases) of
      their essential cofactors.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29053833
      reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "global knockdown of the single Drosophila melanogaster riboflavin transporter homologue revealed reduced levels of riboflavin, downstream metabolites, and electron transport chain complex I activity."
      explanation: >-
        The same perturbation links loss of riboflavin metabolites to reduced
        respiratory-chain complex I activity.

- name: Mitochondrial Flavoprotein Dysfunction
  description: >
    Loss of FAD/FMN cofactors impairs flavoprotein-dependent mitochondrial
    bioenergetics: reduced electron transport chain complex I and complex II
    activity, abnormal mitochondrial membrane potential and morphology, and
    impaired flavoprotein-dependent fatty-acid beta-oxidation (acyl-CoA
    dehydrogenation), the latter producing an abnormal acylcarnitine profile in
    some patients. The brainstem neuropathology resembles that of primary
    mitochondrial disease.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: respiratory electron transport chain
    term:
      id: GO:0022904
      label: respiratory electron transport chain
    modifier: DECREASED
  - preferred_term: fatty acid beta-oxidation
    term:
      id: GO:0006635
      label: fatty acid beta-oxidation
    modifier: DECREASED
  evidence:
  - reference: PMID:29053833
    reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Electron transport chain complex I and complex II activity were decreased in SLC52A2 patient fibroblasts"
    explanation: Directly demonstrates impaired flavoprotein-dependent electron transport chain activity in patient cells.
  - reference: PMID:29053833
    reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showed classical symmetrical brainstem lesions resembling pathology seen in mitochondrial disease, including severe neuronal loss in the lower cranial nerve nuclei, anterior horns and corresponding nerves"
    explanation: Neuropathology links mitochondrial-type brainstem lesions to loss of cranial-nerve and anterior-horn (motor) neurons.
  downstream:
  - target: Cranial, Sensory, and Motor Neuronopathy
    description: >
      Energy-demanding cranial-nerve motor nuclei, sensory neurons, and spinal
      motor neurons are especially vulnerable to flavoprotein-dependent
      mitochondrial failure, leading to their degeneration.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29053833
      reference_title: "Clinical, pathological and functional characterization of riboflavin-responsive neuropathy."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "showed classical symmetrical brainstem lesions resembling pathology seen in mitochondrial disease, including severe neuronal loss in the lower cranial nerve nuclei, anterior horns and corresponding nerves"
      explanation: >-
        Patient neuropathology connects the mitochondrial-disease-like lesion
        pattern with cranial-motor-nucleus and anterior-horn neuronal loss,
        although it does not experimentally isolate this causal edge.

- name: Cranial, Sensory, and Motor Neuronopathy
  description: >
    Progressive degeneration of lower cranial-nerve motor nuclei (pontobulbar
    palsy), sensory neurons (sensory ataxia, sensorineural/auditory neuropathy),
    spinal anterior-horn motor neurons, and optic and other long tracts. The
    resulting clinical picture is rapidly progressive axonal sensorimotor
    neuropathy with sensorineural hearing loss, bulbar palsy, optic atrophy, and
    respiratory insufficiency; an upper-motor-neuron component reminiscent of
    amyotrophic lateral sclerosis can also evolve.
  cell_types:
  - preferred_term: cranial nerve motor neuron
    term:
      id: CL:0015000
      label: cranial motor neuron
  - preferred_term: sensory neuron
    term:
      id: CL:0000101
      label: sensory neuron
  - preferred_term: lower motor neuron
    term:
      id: CL:0008039
      label: lower motor neuron
  biological_processes:
  - preferred_term: motor neuron apoptotic process
    term:
      id: GO:0097049
      label: motor neuron apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals share a core phenotype of rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia, severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs), hearing loss, optic atrophy and respiratory insufficiency."
    explanation: Defines the core cranial/sensory/motor neuronopathy phenotype of BVVL.
  - reference: PMID:20206331
    reference_title: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The key features are progressive ponto-bulbar palsy and bilateral sensorineural deafness."
    explanation: Establishes pontobulbar palsy with sensorineural deafness as the cardinal neuronopathy phenotype.
  downstream:
  - target: Sensorineural hearing loss
    description: Auditory-neuron degeneration produces progressive sensorineural hearing loss.
    evidence:
    - reference: PMID:22864630
      reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Progressive and severe sensorineural deafness is the most frequently observed presenting symptom."
      explanation: >-
        The human series identifies progressive severe sensorineural deafness
        as the most frequent presenting manifestation.
  - target: Bulbar palsy
    description: Degeneration of lower cranial motor nuclei produces progressive pontobulbar palsy.
    evidence:
    - reference: PMID:20206331
      reference_title: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The key features are progressive ponto-bulbar palsy and bilateral sensorineural deafness."
      explanation: >-
        The causal human genetic report identifies progressive pontobulbar
        palsy as a cardinal output of the neuronopathy.
  - target: Dysphagia
    description: Lower cranial motor dysfunction impairs the bulbar swallowing apparatus.
    evidence:
    - reference: PMID:28856173
      reference_title: "A Case of Brown-Vialetto-Van Laere Syndrome Due To a Novel Mutation in SLC52A3 Gene: Clinical Course and Response to Riboflavin."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
      explanation: >-
        The case directly links progressive brainstem dysfunction with
        dysphagia.
  - target: Dysarthria
    description: Lower cranial motor dysfunction impairs speech articulation and can progress to anarthria.
    evidence:
    - reference: PMID:28856173
      reference_title: "A Case of Brown-Vialetto-Van Laere Syndrome Due To a Novel Mutation in SLC52A3 Gene: Clinical Course and Response to Riboflavin."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
      explanation: >-
        The case directly links progressive brainstem dysfunction with
        anarthria, the severe end of dysarthria.
  - target: Facial weakness
    description: Facial motor-nucleus and cranial-nerve involvement produces facial weakness.
    evidence:
    - reference: PMID:23107375
      reference_title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise."
      explanation: >-
        The natural-history review identifies facial weakness among the most
        prevalent neuronopathy manifestations.
  - target: Tongue atrophy and fasciculations
    description: Hypoglossal lower-motor-neuron loss causes tongue wasting and fasciculations.
    evidence:
    - reference: PMID:22864630
      reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Neurological examination at the age of 5.5 years showed a right-sided palsy of the facial nerve and tongue wasting with fasciculations."
      explanation: >-
        The patient examination directly documents tongue wasting with
        fasciculations.
  - target: Muscle weakness
    description: Spinal motor-neuron and peripheral axonal loss produces limb and axial weakness.
    evidence:
    - reference: PMID:24253200
      reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs"
      explanation: >-
        The RFVT2-deficient cohort directly documents the characteristic
        upper-limb and axial weakness.
  - target: Respiratory insufficiency
    description: Respiratory motor-neuron and diaphragmatic involvement causes progressive ventilatory insufficiency.
    evidence:
    - reference: PMID:24253200
      reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "characterized by progressive pontobulbar palsy, sensorineural hearing loss and respiratory insufficiency."
      explanation: >-
        The cohort identifies respiratory insufficiency as a cardinal
        manifestation.
  - target: Optic atrophy
    description: Optic-neuron degeneration produces optic atrophy and visual impairment.
    evidence:
    - reference: PMID:24253200
      reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "hearing loss, optic atrophy and respiratory insufficiency."
      explanation: >-
        The cohort documents optic atrophy within the core neuronopathy
        phenotype.
  - target: Sensory ataxia
    description: Sensory-neuron and long-tract degeneration impairs proprioceptive coordination.
    evidence:
    - reference: PMID:24253200
      reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia"
      explanation: >-
        The cohort directly identifies sensory ataxia as a manifestation of the
        progressive sensorimotor neuropathy.

phenotypes:
- category: Neurologic
  name: Sensorineural hearing loss
  description: >
    Progressive bilateral sensorineural deafness, due to auditory neuropathy
    spectrum disorder, is the most frequent presenting symptom and (when
    present) distinguishes BVVL from Fazio-Londe disease.
  phenotype_term:
    preferred_term: Sensorineural hearing loss
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Progressive and severe sensorineural deafness is the most frequently observed presenting symptom."
    explanation: Sensorineural deafness is the most frequent presenting feature of BVVL.
  - reference: PMID:26918385
    reference_title: "Auditory neuropathy in Brown-Vialetto-Van Laere syndrome due to riboflavin transporter RFVT2 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hearing loss in these individuals was due to auditory neuropathy spectrum disorder (ANSD)."
    explanation: Characterizes the hearing loss as auditory neuropathy spectrum disorder.
- category: Neurologic
  name: Bulbar palsy
  description: >
    Pontobulbar (lower cranial nerve) palsy with dysphagia, dysarthria/anarthria,
    and facial and tongue weakness from degeneration of brainstem motor nuclei.
  phenotype_term:
    preferred_term: Bulbar palsy
    term:
      id: HP:0001283
      label: Bulbar palsy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:23107375
    reference_title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise."
    explanation: Bulbar palsy is among the most prevalent symptoms in BVVL/Fazio-Londe patients.
- category: Neurologic
  name: Dysphagia
  description: Difficulty swallowing due to bulbar (lower cranial nerve) motor neuron involvement.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:28856173
    reference_title: "A Case of Brown-Vialetto-Van Laere Syndrome Due To a Novel Mutation in SLC52A3 Gene: Clinical Course and Response to Riboflavin."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
    explanation: Documents dysphagia (and anarthria/dysarthria, facial weakness) as part of the bulbar phenotype.
- category: Neurologic
  name: Dysarthria
  description: Slurred or absent speech (dysarthria/anarthria) from bulbar motor involvement.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:28856173
    reference_title: "A Case of Brown-Vialetto-Van Laere Syndrome Due To a Novel Mutation in SLC52A3 Gene: Clinical Course and Response to Riboflavin."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progressive brain stem dysfunction including ptosis, facial weakness, hearing loss, dysphagia, anarthria with bilateral vocal cord paralysis, and ataxic gait."
    explanation: Anarthria (severe dysarthria) is documented as part of the bulbar phenotype.
- category: Neurologic
  name: Facial weakness
  description: Facial diplegia from facial (cranial nerve VII) motor nucleus involvement.
  phenotype_term:
    preferred_term: Facial weakness
    term:
      id: HP:0010628
      label: Facial palsy
  evidence:
  - reference: PMID:23107375
    reference_title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise."
    explanation: Facial weakness is among the most prevalent symptoms in BVVL.
- category: Neurologic
  name: Tongue atrophy and fasciculations
  description: >
    Tongue wasting with fasciculations reflecting hypoglossal motor nucleus
    degeneration (lower motor neuron involvement of the bulbar muscles).
  phenotype_term:
    preferred_term: Tongue atrophy
    term:
      id: HP:0012473
      label: Tongue atrophy
  evidence:
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological examination at the age of 5.5 years showed a right-sided palsy of the facial nerve and tongue wasting with fasciculations."
    explanation: Documents tongue wasting with fasciculations (and facial nerve palsy) in a BVVL patient.
- category: Neuromuscular
  name: Muscle weakness
  description: >
    Limb and axial muscle weakness from spinal motor neuron involvement; in
    RFVT2 deficiency there is characteristic severe upper-limb and axial weakness
    with relatively preserved lower-limb strength.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe weakness of the upper limbs and axial muscles with distinctly preserved strength of the lower limbs"
    explanation: Describes the characteristic upper-limb/axial muscle weakness of RFVT2-deficient BVVL.
- category: Respiratory
  name: Respiratory insufficiency
  description: >
    Progressive respiratory compromise from diaphragmatic and respiratory motor
    neuron involvement; diaphragmatic paralysis is a major cause of death.
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by progressive pontobulbar palsy, sensorineural hearing loss and respiratory insufficiency."
    explanation: Respiratory insufficiency is a cardinal feature of BVVL.
- category: Ophthalmologic
  name: Optic atrophy
  description: Optic nerve atrophy with impaired visual acuity from optic neuropathy.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hearing loss, optic atrophy and respiratory insufficiency."
    explanation: Optic atrophy is part of the core RFVT2-deficient BVVL phenotype.
- category: Neurologic
  name: Sensory ataxia
  description: >
    Sensory ataxia from degeneration of sensory neurons and the posterior
    column-medial lemniscus / spinocerebellar pathways.
  phenotype_term:
    preferred_term: Sensory ataxia
    term:
      id: HP:0010871
      label: Sensory ataxia
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "rapidly progressive axonal sensorimotor neuropathy (manifesting with sensory ataxia"
    explanation: Sensory ataxia is a defining manifestation of the sensorimotor neuropathy in BVVL.

genetic:
- name: SLC52A3
  gene_term:
    preferred_term: SLC52A3
    term:
      id: hgnc:16187
      label: SLC52A3
  inheritance:
  - name: Autosomal Recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:20206331
      reference_title: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "We identified a candidate gene, C20orf54, by studying a consanguineous family with multiple affected individuals and subsequently demonstrated that mutations in this gene were the cause of disease in other, unrelated families."
      explanation: >-
        The consanguineous multiplex family and replication in unrelated
        families support recessive SLC52A3 disease, although the abstract does
        not state the inheritance label explicitly.
  notes: >
    Biallelic SLC52A3 (formerly C20orf54) mutations cause BVVL type 1
    (MONDO:0024537). SLC52A3 encodes riboflavin transporter RFVT3 (hRFT2),
    which mediates intestinal riboflavin uptake; mutations cause decreased
    plasma riboflavin levels.
  evidence:
  - reference: PMID:20206331
    reference_title: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brown-Vialetto-Van Laere syndrome, a ponto-bulbar palsy with deafness, is caused by mutations in c20orf54."
    explanation: Identifies C20orf54 (SLC52A3) as a BVVL gene.
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While mutations in SLC52A3 cause decreased plasma riboflavin levels, concordant with a role of SLC52A3 in riboflavin uptake from food"
    explanation: SLC52A3 mutations reduce plasma riboflavin, consistent with its role in intestinal riboflavin uptake.
- name: SLC52A2
  gene_term:
    preferred_term: SLC52A2
    term:
      id: hgnc:30224
      label: SLC52A2
  inheritance:
  - name: Autosomal Recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:22864630
      reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Exome sequencing of just one single case revealed that compound heterozygosity for two pathogenic mutations in the SLC52A2 gene coding for riboflavin transporter 3 (hRFT3), another member of the riboflavin transporter family, is also associated with BVVLS."
      explanation: >-
        Two pathogenic SLC52A2 alleles in trans directly support autosomal
        recessive inheritance.
  notes: >
    Biallelic SLC52A2 mutations cause BVVL type 2 (MONDO:0013867). SLC52A2
    encodes riboflavin transporter RFVT2 (hRFT3), which mediates uptake of
    riboflavin from blood into target cells; affected individuals may have
    normal plasma riboflavin concentrations.
  evidence:
  - reference: PMID:22740598
    reference_title: "Exome sequencing reveals riboflavin transporter mutations as a cause of motor neuron disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified a novel mutation in a second member of the riboflavin transporter gene family (gene symbol: SLC52A2) as the cause of disease in this family."
    explanation: Identifies SLC52A2 as a second BVVL-causing riboflavin transporter gene.
  - reference: PMID:22864630
    reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the SLC52A2-mutant individual had normal plasma riboflavin concentrations, a finding in line with a postulated function of SLC52A2 in riboflavin uptake from blood into target cells."
    explanation: SLC52A2 mediates riboflavin uptake into target cells; plasma riboflavin may be normal.

treatments:
- name: High-dose Riboflavin Supplementation
  description: >
    High-dose oral riboflavin (vitamin B2) replenishes the deficient flavocofactor
    pool and is a life-saving, disease-modifying therapy. Clinical and biochemical
    improvement can be rapid (days to weeks) or gradual over months; early
    initiation, before genetic confirmation, is recommended because outcome
    depends on prompt treatment. Some deficits (e.g., established sensorineural
    hearing loss) may not reverse.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: riboflavin
      term:
        id: CHEBI:17015
        label: riboflavin
  target_phenotypes:
  - preferred_term: Bulbar palsy
    term:
      id: HP:0001283
      label: Bulbar palsy
  - preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  target_mechanisms:
  - target: Flavocofactor (FAD/FMN) Depletion
    treatment_effect: RESTORES
    description: >-
      High-dose riboflavin replenishes the precursor pool for FMN and FAD
      synthesis, partially bypassing residual transporter deficiency by mass action.
    evidence:
    - reference: PMID:22864630
      reference_title: "Impaired riboflavin transport due to missense mutations in SLC52A2 causes Brown-Vialetto-Van Laere syndrome."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "providing a rational basis for a high-dose riboflavin treatment."
      explanation: >-
        The study supplies the mechanistic rationale for high-dose riboflavin,
        although the abstract does not directly quantify intracellular FAD/FMN repletion.
  evidence:
  - reference: PMID:24253200
    reference_title: "Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical and biochemical responses of this SLC52A2-specific cohort suggest that riboflavin supplementation can ameliorate the progression of this neurodegenerative condition, particularly when initiated soon after the onset of symptoms."
    explanation: Demonstrates that high-dose riboflavin ameliorates progression, especially when started early.
  - reference: PMID:23107375
    reference_title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All 13 patients who were treated with riboflavin survived, with a strong clinical improvement after days to months of treatment in eight patients."
    explanation: All riboflavin-treated patients survived with clinical improvement, supporting riboflavin responsiveness.
  - reference: PMID:23107375
    reference_title: "The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "treatment should be started immediately without first awaiting results of molecular analysis."
    explanation: Supports immediate empirical riboflavin treatment before genetic confirmation.
📚

References & Deep Research

References

3
PMID:23107375
The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives.
No top-level findings curated for this source.
PMID:24253200
Treatable childhood neuronopathy caused by mutations in riboflavin transporter RFVT2.
No top-level findings curated for this source.
PMID:29053833
Clinical, pathological and functional characterization of riboflavin-responsive neuropathy.
No top-level findings curated for this source.