Maple Syrup Urine Disease

Genetic MONDO:0009563 Pathograph 45 Metabolic Disease Inborn Error of Metabolism

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Subtypes

Classic MSUD

Most severe form with less than 2% residual enzyme activity, presenting in neonates with acute encephalopathy within days of birth.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"In the classic form of MSUD256, BCKDH enzyme only has 2–5% normal activity."

Confirms classic form has very low residual enzyme activity.

Intermediate MSUD

Residual enzyme activity 15-25%, variable presentation with developmental delay, may not present until later infancy.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"In addition to the classic form, there are intermediate78 (15–25% BCKDH activity), intermittent (asymptomatic until 10–16 months or later) and thiamine-responsive910 MSUD diseases."

Confirms intermediate form has higher residual enzyme activity.

Intermittent MSUD

Normal development with metabolic crises during catabolic stress such as illness, surgery, or fasting.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"In addition to the classic form, there are intermediate78 (15–25% BCKDH activity), intermittent (asymptomatic until 10–16 months or later) and thiamine-responsive910 MSUD diseases."

Confirms intermittent form patients are asymptomatic until later in life.

Thiamine-Responsive MSUD

Responds to high-dose thiamine supplementation due to specific mutations affecting the thiamine binding site.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"

Confirms thiamine-responsive form is due to specific mutations affecting thiamine binding.

Type IA

E1-alpha subunit deficiency (BCKDHA gene)

Type IB

E1-beta subunit deficiency (BCKDHB gene)

Type II

E2 subunit deficiency (DBT gene)

Type III

E3 subunit deficiency (DLD gene)

⚙

Pathophysiology

Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency

Mutations in genes encoding subunits of the branched-chain alpha-ketoacid dehydrogenase complex (BCKDH) cause deficient catabolism of branched-chain amino acids (leucine, isoleucine, valine). The BCKDH complex catalyzes the first irreversible step in BCAA catabolism within the mitochondrial matrix. Pathogenic variants in BCKDHA (E1-alpha), BCKDHB (E1-beta), and DBT (E2) account for most cases; deficiency in the shared E3 subunit (DLD) produces an MSUD phenotype with broader mitochondrial dysfunction. BCKDH activity is regulated by phosphorylation via BCKDK (kinase, inactivating) and PPM1K (phosphatase, activating).

hepatocyte link

BCKDHA link BCKDHB link DBT link DLD link BCKDK link PPM1K link

branched-chain amino acid catabolic process link L-leucine catabolic process link ↓ DECREASED L-isoleucine catabolic process link ↓ DECREASED L-valine catabolic process link ↓ DECREASED

mitochondrial matrix link

liver link

Downstream

Systemic BCAA and BCKA Accumulation BCKDH complex deficiency blocks BCAA oxidation and produces systemic elevations of BCAAs, ketoacids, and alloisoleucine.

Show evidence (2 references)

PMID:35672312 SUPPORT Model Organism

"Maple syrup urine disease (MSUD) is a rare recessively inherited metabolic disorder causing accumulation of branched chain amino acids leading to neonatal death, if untreated."

Confirms MSUD causes BCAA accumulation due to enzyme deficiency.

PMID:27373929 SUPPORT Model Organism

"Maple Syrup Urine Disease (MSUD) is an inherited disorder caused by the dysfunction in the branched chain keto-acid dehydrogenase (BCKDH) enzyme."

Confirms BCKDH enzyme dysfunction is the core defect in MSUD.

Systemic BCAA and BCKA Accumulation

BCKDH deficiency causes systemic accumulation of leucine, isoleucine, valine and their corresponding branched-chain ketoacids: alpha-ketoisocaproic acid (KIC) from leucine, alpha-ketoisovaleric acid (KIV) from valine, and alpha-keto-beta-methylvaleric acid (KMV) from isoleucine. The pathognomonic marker alloisoleucine also accumulates. Leucine and BCAA concentrations in blood range from approximately 1 to 5 mM in MSUD patients compared to 90-250 micromol/L in unaffected subjects.

branched-chain amino acid catabolic process link ↓ DECREASED

Downstream

Leucine and Ketoacid Neurotoxicity Systemic leucine elevation generates KIC, a major toxic metabolite that impairs mitochondrial function at disease-relevant concentrations.

Blood-Brain Barrier Transport Competition Plasma amino acid dysregulation limits brain neutral amino acid availability and contributes to persistent neurochemical deficiencies.

Skeletal Muscle Dysfunction Systemic branched-chain ketoacid accumulation includes muscle KIC accumulation, disrupting mitochondrial metabolites and muscle structure.

Elevated Branched Chain Amino Acids Primary BCAA catabolic blockade causes elevated circulating branched-chain amino acids.

Plasma Leucine Leucine accumulates in plasma when BCKDH cannot oxidize branched-chain ketoacids downstream of leucine transamination.

Plasma Isoleucine Isoleucine accumulates in plasma as part of the systemic BCAA elevation.

Plasma Valine Valine accumulates in plasma as part of the systemic BCAA elevation.

Alloisoleucine Systemic BCAA imbalance produces the pathognomonic alloisoleucine marker.

Alpha-Ketoisocaproic Acid (KIC) Leucine-derived KIC accumulates upstream of the BCKDH enzyme block.

Alpha-Ketoisovaleric Acid (KIV) Valine-derived KIV accumulates upstream of the BCKDH enzyme block.

Alpha-Keto-beta-Methylvaleric Acid (KMV) Isoleucine-derived KMV accumulates upstream of the BCKDH enzyme block.

Abnormal Urinary Odor Accumulated branched-chain ketoacid metabolites generate the characteristic maple-syrup odor.

Metabolic Acidosis Accumulated organic ketoacids contribute to metabolic acidosis during decompensation.

Failure to Thrive Persistent BCAA imbalance and recurrent decompensation impair feeding, growth, and weight gain.

Show evidence (2 references)

PMID:27373929 SUPPORT Model Organism

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Confirms accumulation of all three BCKAs due to BCKDH dysfunction.

PMID:28919799 SUPPORT Human Clinical

"Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker,..."

Confirms elevation of BCAAs, ketoacids, and alloisoleucine in MSUD.

Blood-Brain Barrier Transport Competition

Elevated plasma leucine competes for transport across the blood-brain barrier via the L-type amino acid transporter (LAT1), which is shared by other large neutral amino acids (LNAAs). This competition limits entry of essential amino acids including tyrosine, tryptophan, phenylalanine, methionine, and threonine into the brain, depleting their availability for neurotransmitter synthesis and protein metabolism.

endothelial cell link

neutral amino acid transport link

blood-brain barrier link

Downstream

Brain Neurotransmitter Depletion Amino acid dysregulation at the blood-brain barrier leads to measurable brain neurochemical deficiencies.

Show evidence (1 reference)

PMID:23478409 SUPPORT Human Clinical

"amino acid dysregulation results in aberrant neural networks with neurochemical deficiencies that persist after transplant and correlate with neuropsychiatric morbidities"

Demonstrates that amino acid dysregulation, including transport competition at the BBB, leads to neurochemical deficiencies in MSUD patients.

Brain Neurotransmitter Depletion

Leucine and KIC entry into the brain via LAT1 and monocarboxylate transporters drives reversed branched-chain aminotransferase flux, consuming alpha-ketoglutarate and depleting glutamate. This cascade reduces glutamate, glutamine, GABA, and N-acetylaspartate (NAA) concentrations in brain tissue. Depleted glutamate and GABA impair both excitatory and inhibitory neurotransmission, while low NAA reflects compromised neuronal integrity and energy metabolism.

neuron link astrocyte link

glutamate metabolic process link

brain link

Downstream

Global Developmental Delay Chronic neurochemical deficiency and impaired neuronal integrity contribute to developmental delay.

Intellectual Disability Persistent brain amino-acid and neurotransmitter dysregulation contributes to cognitive impairment.

Show evidence (1 reference)

PMID:23478409 SUPPORT Human Clinical

"Using quantitative proton magnetic resonance spectroscopy, we found lower brain glutamate, N-acetylaspartate (NAA), and creatine concentrations in MSUD patients, which correlated with specific neuropsychiatric outcomes."

Direct demonstration of depleted glutamate and NAA in MSUD patient brains correlating with neuropsychiatric illness.

Leucine and Ketoacid Neurotoxicity

Elevated leucine and its metabolite alpha-ketoisocaproic acid (KIC) are particularly neurotoxic. KIC inhibits key mitochondrial enzymes including alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase, disrupting brain energy metabolism. At disease-relevant concentrations, KIC impairs mitochondrial respiration and cellular energy charge in neural cells.

neuron link astrocyte link

oxidative phosphorylation link

mitochondrion link

brain link

Downstream

Cerebral Energy Failure and Oxidative Stress KIC neurotoxicity impairs mitochondrial function, linking leucine/ketoacid accumulation to cerebral energy failure.

Encephalopathy Acute leucine and KIC neurotoxicity drives neonatal and episodic metabolic encephalopathy.

Lethargy Acute neurotoxicity during metabolic decompensation manifests clinically as lethargy.

Poor Feeding Neonatal neurotoxicity and encephalopathy impair feeding during classic presentation.

Vomiting Acute metabolic decompensation with neurotoxicity can present with vomiting.

Show evidence (2 references)

PMID:27373929 SUPPORT Model Organism

"KIC is an inhibitor of mitochondrial function at disease relevant concentrations."

Confirms KIC directly inhibits mitochondrial function.

DOI:10.1091/mbc.11.5.1919 SUPPORT In Vitro

"increased concentrations of MSUD metabolites, in particular α-keto isocaproic acid, specifically induced apoptosis in glial and neuronal cells in culture"

Demonstrates KIC-specific neurotoxicity inducing apoptosis in neural cell cultures.

Cerebral Energy Failure and Oxidative Stress

KIC-mediated inhibition of mitochondrial dehydrogenases and electron transport chain function leads to cerebral energy failure with reduced ATP and N-acetylaspartate. Concurrently, reactive oxygen and nitrogen species accumulate, further damaging mitochondrial enzymes including lipoate-containing E2/E3 modules. This combination of energy depletion and oxidative stress results in cerebral edema with diffuse gray matter swelling affecting the cerebral cortex, basal ganglia, hippocampus, and brainstem.

neuron link astrocyte link

response to oxidative stress link generation of precursor metabolites and energy link

cerebral cortex link basal ganglion link hippocampal formation link brainstem link

Downstream

Neural Cell Death via Apoptosis and Autophagy Energy failure and metabolite toxicity trigger apoptotic and autophagic injury programs in neural cells and brain tissue.

Cerebral Edema Severe cerebral energy failure and oxidative stress culminate in cerebral edema during intoxication.

Coma Severe cerebral edema and energy failure can progress to coma.

Seizures Brain energy failure and injury lower seizure threshold during severe intoxication.

Show evidence (1 reference)

PMID:23478409 SUPPORT Human Clinical

"we found lower brain glutamate, N-acetylaspartate (NAA), and creatine concentrations in MSUD patients, which correlated with specific neuropsychiatric outcomes"

Low NAA and creatine in MSUD brains reflects cerebral energy failure and neuronal compromise.

Neural Cell Death via Apoptosis and Autophagy

Sustained exposure to elevated BCAAs and BCKAs triggers both apoptotic and autophagic cell death programs in neural tissue. KIC induces apoptosis in glial and neuronal cells through a cytochrome c-independent pathway, without canonical mitochondrial membrane depolarization. Chronic BCAA exposure also increases autophagy markers across brain regions including cerebral cortex, hippocampus, and brainstem, consistent with stress-induced autophagic programs that can progress to cell death.

neuron link oligodendrocyte link

apoptotic process link autophagy link

autophagosome link

Downstream

Intellectual Disability Irreversible neural cell injury contributes to persistent intellectual impairment after severe or delayed-treated MSUD.

Show evidence (3 references)

DOI:10.1091/mbc.11.5.1919 SUPPORT In Vitro

"Apoptosis was associated with a reduction in cell respiration but without impairment of respiratory chain function, without early changes in mitochondrial membrane potential and without cytochrome c release into the cytosol"

Demonstrates apoptosis via cytochrome c-independent pathway in neural cells exposed to MSUD metabolites.

DOI:10.1091/mbc.11.5.1919 SUPPORT Model Organism

"α-keto isocaproic acid also triggered neuronal apoptosis in vivo after intracerebral injection into the developing rat brain"

Confirms KIC triggers neuronal apoptosis in vivo in developing brain tissue.

DOI:10.1007/s11011-022-01109-y SUPPORT Model Organism

"BCAA significantly increased the levels of Beclin-1, ATG7, and ATG5 in the cerebral cortex of rats"

Demonstrates that BCAA administration increases autophagy markers in brain tissue of rats in an MSUD model, supporting the role of autophagy in neural cell death.

Skeletal Muscle Dysfunction

Skeletal muscle is a major site of BCAA transamination via mitochondrial branched-chain aminotransferase (BCAT2) and accumulates toxic ketoacids. KIC disrupts mitochondrial metabolism in myocytes, causing reduced TCA cycle flux and ATP depletion. MSUD patients and mouse models display skeletal muscle fiber abnormalities including reduced fiber diameter and muscle atrophy.

skeletal muscle fiber link

branched-chain amino acid catabolic process link

mitochondrion link

skeletal muscle tissue link

Downstream

Hypotonia Skeletal muscle mitochondrial dysfunction and reduced muscle fiber size can contribute to hypotonia.

Show evidence (2 references)

PMID:27373929 SUPPORT Model Organism

"shows significant skeletal muscle dysfunction as by judged decreased muscle"

Animal model demonstrates skeletal muscle atrophy in MSUD.

PMID:27373929 SUPPORT Model Organism

"Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites"

Confirms KIC accumulation in muscle disrupts mitochondrial metabolism, reversible with metformin.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Digestive 2

Poor Feeding VERY_FREQUENT Feeding difficulties in infancy (HP:0008872)

Often first symptom in neonatal period

Show evidence (1 reference)

PMID:28919799 SUPPORT

"The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"

Confirms feeding difficulties as a classic neonatal presentation of MSUD.

Vomiting FREQUENT Vomiting (HP:0002013)

Common during metabolic decompensation

Show evidence (1 reference)

PMID:35578286 SUPPORT

"In some patients, enteral administration is not possible, either because the patient presents with vomiting, coma, or refuses nasogastric administration"

Vomiting is a recognized presentation during MSUD decompensation episodes.

Genitourinary 1

Abnormal Urinary Odor VERY_FREQUENT Abnormal urinary odor (HP:0012088)

Characteristic sweet maple syrup odor in urine, sweat, and earwax due to sotolone from accumulated ketoacids

Show evidence (1 reference)

PMID:28919799 SUPPORT

"The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"

Confirms characteristic maple syrup odor in urine and cerumen as a classic presentation.

Metabolism 3

Elevated Branched Chain Amino Acids OBLIGATE Elevated circulating branched chain amino acid concentration (HP:0008344)

Pathognomonic finding; includes elevated leucine, isoleucine, valine, and alloisoleucine

Show evidence (1 reference)

PMID:27373929 SUPPORT

"The concentrations of leucine and BCAAs in the blood range from approximately 1 to 5"

Confirms marked elevation of branched chain amino acids in MSUD patients.

Metabolic Acidosis FREQUENT Metabolic acidosis (HP:0001942)

Occurs during acute metabolic crises from BCKA accumulation

Show evidence (1 reference)

PMID:36550798 SUPPORT Human Clinical

"The main clinical symptoms of maple syrup urine disease (MSUD) are dehydration, acidosis, nervous system symptoms and intellectual disability."

Confirms acidosis as a main clinical symptom of MSUD.

Cerebral Edema FREQUENT Cerebral edema (HP:0002181)

Occurs during acute metabolic crises; diffuse gray matter swelling affecting cortex, basal ganglia, hippocampus, and brainstem

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"Severe intoxication culminates in critical cerebral edema, coma, and central respiratory failure."

Confirms cerebral edema as a critical complication of severe MSUD metabolic intoxication.

Musculoskeletal 1

Hypotonia VERY_FREQUENT Hypotonia (HP:0001252)

Alternating with hypertonia during crises

Show evidence (1 reference)

PMID:31559730 SUPPORT Human Clinical

"Physical examination of the neonates were similar having stupor, hypotonia and depressed newborn reflexes."

Confirms hypotonia as a neurological finding on examination of neonates with MSUD metabolic decompensation.

Nervous System 6

Lethargy VERY_FREQUENT Lethargy (HP:0001254)

Progressive in acute metabolic crises

Show evidence (1 reference)

PMID:32491705 SUPPORT Other

"It classically manifests in the neonatal period with failure to thrive, delayed developmental milestones, feeding difficulties, lethargy, irritability, and a maple syrup odor first noticeable in the cerumen and then the urine."

Confirms lethargy as a classic neonatal manifestation of MSUD.

Encephalopathy VERY_FREQUENT Acute encephalopathy (HP:0006846)

Acute metabolic encephalopathy during crises, presents in neonates

Show evidence (1 reference)

PMID:23478409 SUPPORT

"Maple syrup urine disease (MSUD) is an inherited disorder of branched chain amino acid metabolism presenting with neonatal encephalopathy, episodic metabolic decompensation, and chronic amino acid imbalances."

Confirms neonatal encephalopathy as a presenting feature of MSUD.

Seizures FREQUENT Seizure (HP:0001250)

Show evidence (1 reference)

PMID:32491705 SUPPORT Other

"If left untreated, the most severe, classic form of MSUD can quickly lead to irreversible neurological injury manifesting as brain damage, seizures, a coma, or central respiratory failure within just 7 to 10 days after birth."

Confirms seizures as a neurological manifestation of untreated classic MSUD.

Intellectual Disability FREQUENT Intellectual disability (HP:0001249)

If treatment delayed or metabolic control poor; liver transplantation may arrest but not reverse brain damage

Show evidence (2 references)

PMID:21839471 SUPPORT

"One-third of our patients were mentally impaired (IQ ≤ 70) before transplantation, with no statistically significant change 1 year later."

Confirms intellectual impairment occurs in MSUD and is not reversed by liver transplantation.

PMID:23478409 SUPPORT

"Compared with 26 age-matched controls, MSUD patients were at higher risk for disorders of cognition, attention, and mood."

Demonstrates cognitive impairment in MSUD patients compared to controls.

Coma FREQUENT Coma (HP:0001259)

Can occur during severe metabolic crises

Show evidence (1 reference)

PMID:35578286 SUPPORT

"In some patients, enteral administration is not possible, either because the patient presents with vomiting, coma, or refuses nasogastric administration"

Coma is recognized as a presentation during severe MSUD decompensation.

Global Developmental Delay FREQUENT Global developmental delay (HP:0001263)

Occurs with delayed treatment or poor metabolic control

Show evidence (1 reference)

PMID:28919799 SUPPORT

"The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"

Confirms developmental delay as a classic presentation of MSUD.

Growth 1

Failure to Thrive VERY_FREQUENT Failure to thrive (HP:0001508)

Common in neonatal period and with poor metabolic control

Show evidence (1 reference)

PMID:28919799 SUPPORT Human Clinical

"The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"

Confirms failure to thrive as a classic neonatal presentation of MSUD.

🧬

Genetic Associations

BCKDHA (Causative)

Show evidence (1 reference)

PMID:35672312 SUPPORT

"We establish and characterize the Bckdha (branched chain keto acid dehydrogenase a)-/- mouse that exhibits a lethal neonatal phenotype mimicking human MSUD."

Confirms BCKDHA mutations cause MSUD.

BCKDHB (Causative)

Show evidence (1 reference)

PMID:27373929 SUPPORT

"MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."

Confirms BCKDHB (E1-beta) mutations cause Type I MSUD.

DBT (Causative)

Show evidence (2 references)

PMID:27373929 SUPPORT

"MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."

Confirms DBT (E2) mutations cause Type II MSUD.

CGGV:assertion_cfd1ebde-e447-4877-977e-f5b9fe434adc-2018-10-30T160000.000Z SUPPORT Other

ClinGen classifies the DBT-maple syrup urine disease gene-disease relationship as definitive with autosomal recessive inheritance.

DLD (Causative)

Show evidence (1 reference)

PMID:27373929 SUPPORT

"MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."

Confirms DLD (E3) mutations cause Type III MSUD.

BCKDK (Regulatory)

Show evidence (1 reference)

DOI:10.1002/jmd2.12419 SUPPORT Human Clinical

"heterozygous gain‐of‐function variants in BCKDK may represent a novel biochemical phenotype of MSUD with a benign clinical course"

Identifies BCKDK gain-of-function as a cause of a biochemical MSUD phenotype following autosomal dominant inheritance.

PPM1K (Regulatory)

Show evidence (1 reference)

PMID:23086801 SUPPORT Human Clinical

"This article describes a hitherto unreported involvement of the phosphatase PP2Cm, a recently described member of the branched-chain α-keto acid dehydrogenase (BCKDH) complex, in maple syrup urine disease (MSUD)."

First report of PPM1K (PP2Cm) mutation causing MSUD, confirming the regulatory role of this phosphatase in BCKDH complex activity.

💊

Treatments

BCAA-Restricted Diet

Action: dietary intervention MAXO:0000088

Lifelong dietary restriction of leucine, isoleucine, and valine intake, mainstay of treatment.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Restricting dietary branched-chain amino acids reduces substrate flux into the blocked BCAA catabolic pathway.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"restriction, BCAA-free medical foods, judicious supplementation with isoleucine"

GeneReviews directly supports dietary leucine restriction and BCAA-free medical foods as core management to control BCAA accumulation.

Show evidence (1 reference)

PMID:35672312 SUPPORT

"Treatment for MSUD represents an unmet need because the current treatment with life-long low-protein diet is challenging to maintain, and despite treatment the risk of acute decompensations and neuropsychiatric symptoms remains."

Confirms lifelong dietary treatment is the current standard of care but has limitations.

Medical Formula

Action: dietary intervention MAXO:0000088

BCAA-free amino acid supplements to provide protein needs while restricting toxic amino acids.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — BCAA-free formula supplies amino acids while avoiding leucine, isoleucine, and valine load.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"diet fortified with prescription medical foods can maintain average plasma BCAA"

Supports prescription medical foods as a way to maintain plasma BCAA concentrations in the reference range.

Show evidence (1 reference)

PMID:35578286 SUPPORT

"Patients with maple syrup urine disease (MSUD) experiencing metabolic decompensations have traditionally been treated with branched-chain amino acid (BCAA)-free mixture via oral or nasogastric administration routes."

Confirms BCAA-free amino acid mixtures are standard treatment.

Thiamine Supplementation

Action: nutritional supplementation MAXO:0000106

High-dose thiamine for thiamine-responsive variant patients who have specific mutations affecting cofactor binding.

Mechanism Target:

RESTORES Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency — Thiamine-responsive variants partially restore BCKDH function through cofactor binding or allosteric stabilization.

Show evidence (1 reference)

PMID:27373929 SUPPORT Other

"Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"

Supports thiamine as targeting residual BCKDH function in responsive variants.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"

Confirms thiamine supplementation is effective for patients with specific mutations.

Liver Transplantation

Action: liver transplantation MAXO:0001175

Curative treatment providing sufficient BCKD enzyme activity from donor hepatocytes, allowing unrestricted protein diet.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Transplanted liver BCAA catabolic capacity normalizes plasma BCAA homeostasis and prevents acute decompensation.

Show evidence (1 reference)

PMID:21839471 SUPPORT Human Clinical

"corrected within hours after surgery and remained stable, with leucine tolerance"

Human transplant follow-up directly supports normalization of BCAA levels after liver transplantation.

Show evidence (2 references)

PMID:21839471 SUPPORT

"Patient and graft survival were 100% at 4.5 ± 2.2 years of follow-up. Liver function was normal in all patients. Branched-chain amino acid levels were corrected within hours after surgery and remained stable, with leucine tolerance increasing more than 10-fold."

Demonstrates excellent outcomes with liver transplantation for MSUD.

PMID:23478409 SUPPORT

"Liver transplantation has emerged as an effective way to eliminate acute decompensation risk."

Confirms liver transplantation eliminates risk of acute metabolic crises.

Intravenous BCAA-Free Solution

Action: Pharmacotherapy NCIT:C15986

IV amino acid solution without branched-chain amino acids for acute crisis management when enteral feeding is not possible.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Intravenous BCAA-free solution lowers leucine during acute decompensation when enteral therapy is not possible.

Show evidence (1 reference)

PMID:35578286 SUPPORT Human Clinical

"leucine concentrations during MSUD decompensation episodes in both children and"

Prospective multicenter data support IV BCAA-free solution as reducing acute leucine accumulation.

Show evidence (1 reference)

PMID:35578286 SUPPORT

"The IV BCAA-free solution is safe and effective in normalising leucine concentrations during MSUD decompensation episodes in both children and adults"

Demonstrates safety and efficacy of IV BCAA-free solutions for acute decompensation.

Acute Crisis Management

Action: Pharmacotherapy NCIT:C15986

IV glucose, insulin, and lipids to promote anabolism and reduce protein catabolism during metabolic crises.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Anabolic crisis management suppresses proteolysis and promotes net protein synthesis, lowering circulating BCAA burden.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"by treating the precipitating stress while delivering sufficient calories,"

Supports acute crisis therapy as reversing catabolism and promoting protein synthesis to reduce toxic BCAA accumulation.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"by treating the precipitating stress while delivering sufficient calories,"

Confirms acute crisis management involves delivering calories, insulin, and amino acids to promote anabolism.

Phenylbutyrate

Action: Pharmacotherapy NCIT:C15986

Agent: sodium phenylbutyrate ↗

BCKDK inhibitor that increases BCKDH enzyme activity by preventing phosphorylation, may benefit subset of patients with residual enzyme activity.

Mechanism Target:

RESTORES Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency — Phenylbutyrate inhibits BCKDC kinase-mediated phosphorylation, increasing the active BCKDH fraction in patients with residual enzyme activity.

Show evidence (2 references)

PMID:21098507 SUPPORT Human Clinical

"BCAA and BCKA are both"

Human treatment data support phenylbutyrate as reducing the upstream BCAA/BCKA burden.

PMID:21098507 SUPPORT In Vitro

"Using recombinant enzymes, we show that phenylbutyrate prevents phosphorylation"

Recombinant enzyme data support the specific BCKDH-activation mechanism.

Show evidence (1 reference)

PMID:21098507 SUPPORT

"In vivo phenylbutyrate increases the proportion of active hepatic enzyme and unphosphorylated form over the inactive phosphorylated form of the E1α subunit of the branched-chain α-keto acid dehydrogenase complex (BCKDC)."

Demonstrates phenylbutyrate activates BCKDH by inhibiting kinase-mediated inactivation.

Metformin

Action: targeted therapy Ontology label: Targeted Therapy NCIT:C93352

Agent: metformin ↗

Potential adjunctive therapy that reduces KIC production by downregulating mitochondrial BCAT; shown to improve metabolic homeostasis in preclinical models.

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Metformin reduces KIC accumulation by suppressing mitochondrial BCAT2-mediated leucine transamination in preclinical models.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%)"

MSUD mouse data support metformin as reducing KIC accumulation and improving metabolic homeostasis.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites"

Preclinical evidence supports metformin as potential therapeutic strategy for MSUD.

Gene Therapy (Preclinical)

Action: gene therapy MAXO:0001001

Liver-directed AAV8 gene therapy delivering BCKDHA has rescued lethal MSUD phenotype in Bckdha-knockout mice. Ubiquitous promoter fully rescues the disease; liver-specific expression provides partial but sustained rescue, highlighting both hepatic and extrahepatic requirements for complete correction.

Mechanism Target:

RESTORES Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency — BCKDHA gene transfer restores the deficient BCKDH E1-alpha component in preclinical MSUD models.

Show evidence (1 reference)

PMID:35672312 SUPPORT Model Organism

"BCKDHA gene transfer rescued the lethal"

Mouse-model gene transfer evidence supports restoration of the deficient BCKDHA component.

Show evidence (3 references)

PMID:35672312 SUPPORT Model Organism

"BCKDHA gene transfer rescued the lethal phenotype. While the use of a ubiquitous promoter fully and sustainably rescued the disease (long-term survival, normal phenotype and correction of biochemical abnormalities), liver-specific expression of BCKDHA led to partial, though sustained rescue."

Demonstrates efficacy of AAV8 gene therapy for MSUD in a mouse model with complete rescue using ubiquitous expression.

PMID:42127902 SUPPORT Human Clinical

"MSUD Age-matched Standard Treatment Cohort (MATCH), a prospective natural history study of 11 infants with classic MSUD followed from neonatal diagnosis to liver transplantation. Aligned with Food and Drug Administration (FDA) guidance and International Council for Harmonisation (ICH) E9(R1),..."

The MATCH cohort provides regulatory-grade natural history baseline and prespecified outcome measures for single-arm gene therapy trials in MSUD, bridging preclinical models to clinical development.

PMID:42127902 SUPPORT Human Clinical

"Three of six outcome measures-proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration-are prespecified as estimands. Monte Carlo simulations show that a single-arm trial comparing 11 treated participants to MATCH controls achieves ≥90%..."

MATCH provides prespecified outcome measures (PIPE, CMDs, alloisoleucine) as estimands with statistical power to detect clinically meaningful improvements in a single-arm gene therapy trial, supporting trial design and regulatory strategy for MSUD gene therapy development.

Gene Therapy (Clinical Development)

Action: gene therapy MAXO:0001001

Liver-directed AAV8 gene therapy for MSUD is advancing toward clinical trials. The MSUD Age-matched Standard Treatment Cohort (MATCH) is a prospective natural history study of 11 infants with classic MSUD designed to serve as regulatory-grade external controls for single-arm gene therapy trials. The study applies FDA and ICH E9(R1) guidelines with prespecified eligibility criteria, fixed visit cadence, and adjudicated outcomes. Primary outcome measures include proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration. Monte Carlo simulations demonstrate ≥90% power to detect clinically meaningful improvements: 64% reduction in CMDs (from 8.4% to 3.0%), 57% increase in PIPE (from 12.3% to 19.3%), and 36% reduction in alloisoleucine (from 183 to 117 μM).

Mechanism Target:

INHIBITS Systemic BCAA and BCKA Accumulation — Gene therapy is expected to reduce systemic BCAA and BCKA accumulation through restoration of BCKDH function in hepatocytes and potentially other tissues.

Show evidence (1 reference)

PMID:35672312 SUPPORT Model Organism

Mouse-model evidence demonstrates that BCKDHA gene transfer corrects biochemical abnormalities (including BCAA/BCKA accumulation), supporting the mechanistic claim that gene therapy inhibits systemic BCAA and BCKA accumulation.

Show evidence (2 references)

PMID:42127902 SUPPORT Human Clinical

"MATCH applies prespecified eligibility criteria, fixed visit cadence, adjudicated outcomes, and explicit handling of intercurrent events. Three of six outcome measures-proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration-are..."

Documents the MATCH cohort as a regulatory-grade natural history study with prespecified outcomes aligned with FDA and ICH E9(R1) guidance for external controls in single-arm trials.

PMID:42127902 SUPPORT Computational

"Monte Carlo simulations show that a single-arm trial comparing 11 treated participants to MATCH controls achieves ≥90% power (p ≤ 0.025) to detect 64% fewer CMDs (3.0% vs. 8.4%), a 57% increase in PIPE (19.3% vs. 12.3%), and a 36% reduction in alloisoleucine (117 vs. 183 μM)."

Demonstrates statistical feasibility of detecting clinically meaningful improvements in prespecified outcome measures with the MATCH cohort as external control.

🌍

Environmental Factors

Dietary Protein

Intake of branched-chain amino acids triggers metabolic decompensation; requires careful dietary management

Show evidence (1 reference)

PMID:27373929 SUPPORT

"The primary treatment of MSUD in patients is via the dietary restriction of BCAA1718. Since leucine, valine and isoleucine are essential amino acids, dietary compliance can therefore be challenging."

Confirms dietary protein intake directly affects MSUD through BCAA content.

Catabolic Stress

Illness, surgery, fasting can precipitate acute metabolic crises through protein catabolism

Show evidence (1 reference)

PMID:23478409 SUPPORT

Episodic metabolic decompensation occurs with catabolic stress.

Fever

Common trigger for acute decompensation due to increased catabolism

Show evidence (1 reference)

PMID:35578286 SUPPORT

"Patients with maple syrup urine disease (MSUD) experiencing metabolic decompensations have traditionally been treated with branched-chain amino acid (BCAA)-free mixture"

Metabolic decompensations requiring treatment are triggered by catabolic states including febrile illness.

🔬

Biochemical Markers

Plasma Leucine (INCREASED)

Context: Markedly elevated, often greater than 2000 micromol/L in classic form; normal is 90-250 micromol/L

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Elevated plasma leucine reports the primary branched-chain amino acid accumulation caused by BCKDH deficiency.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"

GeneReviews identifies elevated leucine within the diagnostic BCAA accumulation pattern.

Readout Of Leucine and Ketoacid Neurotoxicity Positive Monitoring

High leucine participates in the toxic leucine/KIC branch that drives MSUD-related neurologic symptoms.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"KIC and its’ corresponding branched-chain amino acid (BCAA) precursor, leucine are the major toxic metabolites associated with MSUD related symptoms"

Model-system paper identifies leucine with KIC as a major toxic metabolite pair in MSUD.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"Leucine was significantly increased 6.4-fold in serum"

Confirms marked elevation of leucine in MSUD mouse model.

Plasma Isoleucine (INCREASED)

Context: Elevated above normal range along with other branched-chain amino acids

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Elevated plasma isoleucine reports the systemic branched-chain amino acid accumulation caused by impaired BCAA catabolism.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"

GeneReviews identifies isoleucine within the elevated BCAA diagnostic pattern.

Show evidence (1 reference)

PMID:28919799 SUPPORT

Confirms elevation of all BCAAs including isoleucine in plasma.

Plasma Valine (INCREASED)

Context: Elevated above normal range along with other branched-chain amino acids

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Elevated plasma valine reports the systemic branched-chain amino acid accumulation caused by impaired BCAA catabolism.

Show evidence (1 reference)

PMID:20301495 SUPPORT Other

"Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"

GeneReviews identifies valine within the elevated BCAA diagnostic pattern.

Show evidence (1 reference)

PMID:28919799 SUPPORT

Confirms elevation of all BCAAs including valine in plasma.

Alloisoleucine (INCREASED)

Context: Pathognomonic marker for MSUD, not normally present in plasma

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Increased alloisoleucine is the pathognomonic diagnostic readout of the MSUD branched-chain amino acid imbalance.

Show evidence (1 reference)

PMID:28919799 SUPPORT Other

"production of the pathognomonic disease marker, alloisoleucine."

Review evidence directly identifies alloisoleucine as the pathognomonic MSUD marker.

Show evidence (1 reference)

PMID:28919799 SUPPORT

Confirms alloisoleucine is the pathognomonic marker for MSUD.

Alpha-Ketoisocaproic Acid (KIC) (INCREASED)

Context: Leucine-derived ketoacid, primary neurotoxic metabolite

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Increased KIC reports accumulation of the leucine-derived branched-chain ketoacid upstream of the BCKDH block.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Model-system evidence supports KIC as a direct readout of BCKDH-dependent ketoacid accumulation.

Readout Of Leucine and Ketoacid Neurotoxicity Positive Monitoring

Increased KIC reports the proximal toxic metabolite branch that impairs mitochondrial function and contributes to neurologic injury.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"KIC is an inhibitor of mitochondrial function at disease relevant concentrations."

Model-system evidence supports KIC as a toxic readout tied to mitochondrial dysfunction.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"Similarly, KIC was significantly increased 40-fold"

Demonstrates massive KIC accumulation in MSUD.

Alpha-Ketoisovaleric Acid (KIV) (INCREASED)

Context: Valine-derived ketoacid

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Increased KIV reports accumulation of the valine-derived branched-chain ketoacid upstream of the BCKDH block.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Model-system evidence supports KIV as a direct readout of BCKDH-dependent ketoacid accumulation.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Confirms KIV accumulation from valine due to BCKDH dysfunction.

Alpha-Keto-beta-Methylvaleric Acid (KMV) (INCREASED)

Context: Isoleucine-derived ketoacid

Pathograph Readouts

Readout Of Systemic BCAA and BCKA Accumulation Positive Diagnostic

Increased KMV reports accumulation of the isoleucine-derived branched-chain ketoacid upstream of the BCKDH block.

Show evidence (1 reference)

PMID:27373929 SUPPORT Model Organism

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Model-system evidence supports KMV as a direct readout of BCKDH-dependent ketoacid accumulation.

Show evidence (1 reference)

PMID:27373929 SUPPORT

"BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"

Confirms KMV accumulation from isoleucine due to BCKDH dysfunction.

{ }

Source YAML

click to show

name: Maple Syrup Urine Disease
creation_date: '2026-01-09T01:00:56Z'
updated_date: '2026-05-21T12:38:33Z'
category: Genetic
parents:
- Metabolic Disease
- Inborn Error of Metabolism
disease_term:
  preferred_term: maple syrup urine disease
  term:
    id: MONDO:0009563
    label: maple syrup urine disease
has_subtypes:
- name: Classic MSUD
  description: Most severe form with less than 2% residual enzyme activity, presenting in neonates with acute encephalopathy within days of birth.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "In the classic form of MSUD256, BCKDH enzyme only has 2–5% normal activity."
    explanation: Confirms classic form has very low residual enzyme activity.
- name: Intermediate MSUD
  description: Residual enzyme activity 15-25%, variable presentation with developmental delay, may not present until later infancy.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "In addition to the classic form, there are intermediate78 (15–25% BCKDH activity), intermittent (asymptomatic until 10–16 months or later) and thiamine-responsive910 MSUD diseases."
    explanation: Confirms intermediate form has higher residual enzyme activity.
- name: Intermittent MSUD
  description: Normal development with metabolic crises during catabolic stress such as illness, surgery, or fasting.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "In addition to the classic form, there are intermediate78 (15–25% BCKDH activity), intermittent (asymptomatic until 10–16 months or later) and thiamine-responsive910 MSUD diseases."
    explanation: Confirms intermittent form patients are asymptomatic until later in life.
- name: Thiamine-Responsive MSUD
  description: Responds to high-dose thiamine supplementation due to specific mutations affecting the thiamine binding site.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"
    explanation: Confirms thiamine-responsive form is due to specific mutations affecting thiamine binding.
- name: Type IA
  description: E1-alpha subunit deficiency (BCKDHA gene)
- name: Type IB
  description: E1-beta subunit deficiency (BCKDHB gene)
- name: Type II
  description: E2 subunit deficiency (DBT gene)
- name: Type III
  description: E3 subunit deficiency (DLD gene)
prevalence:
- population: Global live births
  percentage: 1 in 225,000 live births
  notes: >-
    Newborn screening data show strong population effects. Reported incidence is
    about 1 in 225,000 live births in the United States, but much higher in
    founder populations such as Old Order Mennonites.
  evidence:
  - reference: PMID:20136525
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Worldwide incidence of MSUD is 1:225,000 live births."
    explanation: This paper provides a concise global incidence benchmark for MSUD.
  - reference: PMID:30023298
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Maple syrup urine disease incidence in the United States was calculated to be 1: 220219, in South-West Germany 1: 119573 (Germany nationwide 1:177978), and in Kuwait 1: 59426."
    explanation: This newborn-screening study confirms that MSUD incidence varies substantially across regions and is around 1 in 220,000 in the United States.
- population: Old Order Mennonite communities
  percentage: 1 in 150 live births
  notes: >-
    Founder effect in Old Order Mennonite communities produces one of the
    highest known MSUD incidences worldwide.
  evidence:
  - reference: PMID:20136525
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, within Old Order Mennonite communities, the incidence is 1:150 live births and results from a common tyrosine to asparagine substitution (Y438N) in the E1alpha subunit of branched chain alpha-keto acid dehydrogenase."
    explanation: This study directly reports the extreme founder-population incidence of MSUD in Old Order Mennonite communities.
  - reference: PMID:30023298
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Incidence for the branched-chain intoxication-type disorders, maple syrup urine disease, propionic acidemia and methlymalonic aciduria is dependent on the population screened."
    explanation: This newborn-screening analysis supports the interpretation that MSUD incidence is strongly population-dependent.
pathophysiology:
- name: Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency
  description: >
    Mutations in genes encoding subunits of the branched-chain alpha-ketoacid
    dehydrogenase complex (BCKDH) cause deficient catabolism of branched-chain
    amino acids (leucine, isoleucine, valine). The BCKDH complex catalyzes the
    first irreversible step in BCAA catabolism within the mitochondrial matrix.
    Pathogenic variants in BCKDHA (E1-alpha), BCKDHB (E1-beta), and DBT (E2)
    account for most cases; deficiency in the shared E3 subunit (DLD) produces
    an MSUD phenotype with broader mitochondrial dysfunction. BCKDH activity is
    regulated by phosphorylation via BCKDK (kinase, inactivating) and PPM1K
    (phosphatase, activating).
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  - preferred_term: L-leucine catabolic process
    term:
      id: GO:0006552
      label: L-leucine catabolic process
    modifier: DECREASED
  - preferred_term: L-isoleucine catabolic process
    term:
      id: GO:0006550
      label: L-isoleucine catabolic process
    modifier: DECREASED
  - preferred_term: L-valine catabolic process
    term:
      id: GO:0006574
      label: L-valine catabolic process
    modifier: DECREASED
  cellular_components:
  - preferred_term: mitochondrial matrix
    term:
      id: GO:0005759
      label: mitochondrial matrix
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  genes:
  - preferred_term: BCKDHA
    term:
      id: hgnc:986
      label: BCKDHA
  - preferred_term: BCKDHB
    term:
      id: hgnc:987
      label: BCKDHB
  - preferred_term: DBT
    term:
      id: hgnc:2698
      label: DBT
  - preferred_term: DLD
    term:
      id: hgnc:2898
      label: DLD
  - preferred_term: BCKDK
    term:
      id: hgnc:16902
      label: BCKDK
  - preferred_term: PPM1K
    term:
      id: hgnc:25415
      label: PPM1K
  evidence:
  - reference: PMID:35672312
    reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Maple syrup urine disease (MSUD) is a rare recessively inherited metabolic disorder causing accumulation of branched chain amino acids leading to neonatal death, if untreated."
    explanation: Confirms MSUD causes BCAA accumulation due to enzyme deficiency.
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Maple Syrup Urine Disease (MSUD) is an inherited disorder caused by the dysfunction in the branched chain keto-acid dehydrogenase (BCKDH) enzyme."
    explanation: Confirms BCKDH enzyme dysfunction is the core defect in MSUD.
  downstream:
  - target: Systemic BCAA and BCKA Accumulation
    description: BCKDH complex deficiency blocks BCAA oxidation and produces systemic elevations of BCAAs, ketoacids, and alloisoleucine.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker, alloisoleucine."
      explanation: Human review evidence directly links BCKDH complex defects to the systemic BCAA, ketoacid, and alloisoleucine accumulation that defines MSUD.
- name: Systemic BCAA and BCKA Accumulation
  description: >
    BCKDH deficiency causes systemic accumulation of leucine, isoleucine, valine
    and their corresponding branched-chain ketoacids: alpha-ketoisocaproic acid
    (KIC) from leucine, alpha-ketoisovaleric acid (KIV) from valine, and
    alpha-keto-beta-methylvaleric acid (KMV) from isoleucine. The pathognomonic
    marker alloisoleucine also accumulates. Leucine and BCAA concentrations in
    blood range from approximately 1 to 5 mM in MSUD patients compared to
    90-250 micromol/L in unaffected subjects.
  biological_processes:
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: leucine
    term:
      id: CHEBI:25017
      label: leucine
    modifier: INCREASED
  - preferred_term: isoleucine
    term:
      id: CHEBI:24898
      label: isoleucine
    modifier: INCREASED
  - preferred_term: valine
    term:
      id: CHEBI:27266
      label: valine
    modifier: INCREASED
  - preferred_term: alloisoleucine
    term:
      id: CHEBI:22359
      label: alloisoleucine
    modifier: INCREASED
  - preferred_term: alpha-ketoisocaproic acid
    term:
      id: CHEBI:48430
      label: 4-methyl-2-oxopentanoic acid
    modifier: INCREASED
  - preferred_term: alpha-ketoisovaleric acid
    term:
      id: CHEBI:16530
      label: 3-methyl-2-oxobutanoic acid
    modifier: INCREASED
  - preferred_term: alpha-keto-beta-methylvaleric acid
    term:
      id: CHEBI:35932
      label: 3-methyl-2-oxovaleric acid
    modifier: INCREASED
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
    explanation: Confirms accumulation of all three BCKAs due to BCKDH dysfunction.
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker, alloisoleucine."
    explanation: Confirms elevation of BCAAs, ketoacids, and alloisoleucine in MSUD.
  downstream:
  - target: Leucine and Ketoacid Neurotoxicity
    description: Systemic leucine elevation generates KIC, a major toxic metabolite that impairs mitochondrial function at disease-relevant concentrations.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "KIC and its’ corresponding branched-chain amino acid (BCAA) precursor, leucine are the major toxic metabolites associated with MSUD related symptoms"
      explanation: Model-system evidence identifies leucine and KIC as the major toxic metabolites associated with MSUD symptoms.
  - target: Blood-Brain Barrier Transport Competition
    description: Plasma amino acid dysregulation limits brain neutral amino acid availability and contributes to persistent neurochemical deficiencies.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - LAT1-mediated large neutral amino acid competition at the blood-brain barrier.
    evidence:
    - reference: PMID:23478409
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "amino acid dysregulation results in aberrant neural networks with neurochemical deficiencies that persist after transplant and correlate with neuropsychiatric morbidities"
      explanation: Patient MRS and neuropsychiatric data support amino-acid dysregulation as producing persistent brain neurochemical deficiencies.
  - target: Skeletal Muscle Dysfunction
    description: Systemic branched-chain ketoacid accumulation includes muscle KIC accumulation, disrupting mitochondrial metabolites and muscle structure.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - KIC accumulation in skeletal muscle and impaired mitochondrial metabolism.
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites"
      explanation: MSUD mouse data support KIC accumulation in muscle with associated mitochondrial metabolite disruption.
  - target: Elevated Branched Chain Amino Acids
    description: Primary BCAA catabolic blockade causes elevated circulating branched-chain amino acids.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "results in elevations of the branched-chain amino acids (BCAAs) in plasma"
      explanation: Human review evidence directly supports elevated plasma BCAAs downstream of BCKDH complex defects.
  - target: Plasma Leucine
    description: Leucine accumulates in plasma when BCKDH cannot oxidize branched-chain ketoacids downstream of leucine transamination.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301495
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"
      explanation: GeneReviews identifies elevated leucine as part of the diagnostic BCAA accumulation pattern in MSUD.
  - target: Plasma Isoleucine
    description: Isoleucine accumulates in plasma as part of the systemic BCAA elevation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301495
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"
      explanation: GeneReviews identifies elevated isoleucine as part of the diagnostic BCAA accumulation pattern in MSUD.
  - target: Plasma Valine
    description: Valine accumulates in plasma as part of the systemic BCAA elevation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301495
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Elevated concentrations of branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and alloisoleucine"
      explanation: GeneReviews identifies elevated valine as part of the diagnostic BCAA accumulation pattern in MSUD.
  - target: Alloisoleucine
    description: Systemic BCAA imbalance produces the pathognomonic alloisoleucine marker.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "production of the pathognomonic disease marker, alloisoleucine."
      explanation: Human review evidence identifies alloisoleucine as the pathognomonic MSUD disease marker.
  - target: Alpha-Ketoisocaproic Acid (KIC)
    description: Leucine-derived KIC accumulates upstream of the BCKDH enzyme block.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
      explanation: MSUD model evidence directly supports KIC accumulation from leucine when BCKDH is dysfunctional.
  - target: Alpha-Ketoisovaleric Acid (KIV)
    description: Valine-derived KIV accumulates upstream of the BCKDH enzyme block.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
      explanation: MSUD model evidence directly supports KIV accumulation from valine when BCKDH is dysfunctional.
  - target: Alpha-Keto-beta-Methylvaleric Acid (KMV)
    description: Isoleucine-derived KMV accumulates upstream of the BCKDH enzyme block.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
      explanation: MSUD model evidence directly supports KMV accumulation from isoleucine when BCKDH is dysfunctional.
  - target: Abnormal Urinary Odor
    description: Accumulated branched-chain ketoacid metabolites generate the characteristic maple-syrup odor.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Sotolone and related odor-producing metabolites from branched-chain ketoacid accumulation.
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
      explanation: Human review evidence supports maple-syrup odor in urine and cerumen as a classic clinical consequence of the metabolic accumulation.
  - target: Metabolic Acidosis
    description: Accumulated organic ketoacids contribute to metabolic acidosis during decompensation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:36550798
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The main clinical symptoms of maple syrup urine disease (MSUD) are dehydration, acidosis, nervous system symptoms and intellectual disability."
      explanation: Human case-review evidence identifies acidosis as a main MSUD clinical symptom during metabolic disease.
  - target: Failure to Thrive
    description: Persistent BCAA imbalance and recurrent decompensation impair feeding, growth, and weight gain.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Feeding difficulty, catabolic stress, and recurrent metabolic decompensation.
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
      explanation: Human review evidence supports failure to thrive as part of the classic presentation associated with MSUD metabolic intoxication.
- name: Blood-Brain Barrier Transport Competition
  description: >
    Elevated plasma leucine competes for transport across the blood-brain barrier
    via the L-type amino acid transporter (LAT1), which is shared by other large
    neutral amino acids (LNAAs). This competition limits entry of essential amino
    acids including tyrosine, tryptophan, phenylalanine, methionine, and threonine
    into the brain, depleting their availability for neurotransmitter synthesis
    and protein metabolism.
  cell_types:
  - preferred_term: endothelial cell
    term:
      id: CL:0000115
      label: endothelial cell
  biological_processes:
  - preferred_term: neutral amino acid transport
    term:
      id: GO:0015804
      label: neutral amino acid transport
  locations:
  - preferred_term: blood-brain barrier
    term:
      id: UBERON:0000120
      label: blood brain barrier
  evidence:
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "amino acid dysregulation results in aberrant neural networks with neurochemical deficiencies that persist after transplant and correlate with neuropsychiatric morbidities"
    explanation: Demonstrates that amino acid dysregulation, including transport competition at the BBB, leads to neurochemical deficiencies in MSUD patients.
  downstream:
  - target: Brain Neurotransmitter Depletion
    description: Amino acid dysregulation at the blood-brain barrier leads to measurable brain neurochemical deficiencies.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Reduced brain availability of large neutral amino acids and altered neurotransmitter metabolism.
    evidence:
    - reference: PMID:23478409
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "amino acid dysregulation results in aberrant neural networks with neurochemical deficiencies that persist after transplant and correlate with neuropsychiatric morbidities"
      explanation: Patient data directly link amino-acid dysregulation to persistent neurochemical deficiencies and neuropsychiatric morbidity.
- name: Brain Neurotransmitter Depletion
  description: >
    Leucine and KIC entry into the brain via LAT1 and monocarboxylate transporters
    drives reversed branched-chain aminotransferase flux, consuming
    alpha-ketoglutarate and depleting glutamate. This cascade reduces glutamate,
    glutamine, GABA, and N-acetylaspartate (NAA) concentrations in brain tissue.
    Depleted glutamate and GABA impair both excitatory and inhibitory
    neurotransmission, while low NAA reflects compromised neuronal integrity
    and energy metabolism.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: glutamate metabolic process
    term:
      id: GO:0006536
      label: glutamate metabolic process
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using quantitative proton magnetic resonance spectroscopy, we found lower brain glutamate, N-acetylaspartate (NAA), and creatine concentrations in MSUD patients, which correlated with specific neuropsychiatric outcomes."
    explanation: Direct demonstration of depleted glutamate and NAA in MSUD patient brains correlating with neuropsychiatric illness.
  downstream:
  - target: Global Developmental Delay
    description: Chronic neurochemical deficiency and impaired neuronal integrity contribute to developmental delay.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Neurotransmitter depletion, low N-acetylaspartate, and neuropsychiatric morbidity.
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
      explanation: Human review evidence supports developmental delay as part of the classic MSUD presentation downstream of metabolic brain injury.
  - target: Intellectual Disability
    description: Persistent brain amino-acid and neurotransmitter dysregulation contributes to cognitive impairment.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Neurotransmitter depletion and neuronal energy compromise.
    evidence:
    - reference: PMID:23478409
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Compared with 26 age-matched controls, MSUD patients were at higher risk for disorders of cognition, attention, and mood."
      explanation: Human neuropsychiatric study supports cognitive morbidity in MSUD patients with brain neurochemical abnormalities.
- name: Leucine and Ketoacid Neurotoxicity
  description: >
    Elevated leucine and its metabolite alpha-ketoisocaproic acid (KIC) are
    particularly neurotoxic. KIC inhibits key mitochondrial enzymes including
    alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase, disrupting
    brain energy metabolism. At disease-relevant concentrations, KIC impairs
    mitochondrial respiration and cellular energy charge in neural cells.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: oxidative phosphorylation
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  cellular_components:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "KIC is an inhibitor of mitochondrial function at disease relevant concentrations."
    explanation: Confirms KIC directly inhibits mitochondrial function.
  - reference: DOI:10.1091/mbc.11.5.1919
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "increased concentrations of MSUD metabolites, in particular α-keto isocaproic acid, specifically induced apoptosis in glial and neuronal cells in culture"
    explanation: Demonstrates KIC-specific neurotoxicity inducing apoptosis in neural cell cultures.
  downstream:
  - target: Cerebral Energy Failure and Oxidative Stress
    description: KIC neurotoxicity impairs mitochondrial function, linking leucine/ketoacid accumulation to cerebral energy failure.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "KIC is an inhibitor of mitochondrial function at disease relevant concentrations."
      explanation: Model-system evidence directly supports KIC-mediated mitochondrial impairment as a proximal mechanism for energy failure.
  - target: Encephalopathy
    description: Acute leucine and KIC neurotoxicity drives neonatal and episodic metabolic encephalopathy.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:23478409
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Maple syrup urine disease (MSUD) is an inherited disorder of branched chain amino acid metabolism presenting with neonatal encephalopathy, episodic metabolic decompensation, and chronic amino acid imbalances."
      explanation: Human clinical evidence links MSUD amino-acid metabolism disorder to neonatal encephalopathy and episodic decompensation.
  - target: Lethargy
    description: Acute neurotoxicity during metabolic decompensation manifests clinically as lethargy.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Acute metabolic encephalopathy.
    evidence:
    - reference: PMID:32491705
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "It classically manifests in the neonatal period with failure to thrive, delayed developmental milestones, feeding difficulties, lethargy, irritability, and a maple syrup odor first noticeable in the cerumen and then the urine."
      explanation: Clinical summary supports lethargy as a classic neonatal manifestation of MSUD intoxication.
  - target: Poor Feeding
    description: Neonatal neurotoxicity and encephalopathy impair feeding during classic presentation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Acute metabolic encephalopathy and reduced alertness.
    evidence:
    - reference: PMID:28919799
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
      explanation: Human review evidence supports feeding difficulties as part of the classic neonatal presentation of MSUD.
  - target: Vomiting
    description: Acute metabolic decompensation with neurotoxicity can present with vomiting.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Acute metabolic decompensation and encephalopathy.
    evidence:
    - reference: PMID:35578286
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In some patients, enteral administration is not possible, either because the patient presents with vomiting, coma, or refuses nasogastric administration"
      explanation: Prospective decompensation-management study supports vomiting as a presentation during acute MSUD episodes.
- name: Cerebral Energy Failure and Oxidative Stress
  description: >
    KIC-mediated inhibition of mitochondrial dehydrogenases and electron transport
    chain function leads to cerebral energy failure with reduced ATP and
    N-acetylaspartate. Concurrently, reactive oxygen and nitrogen species
    accumulate, further damaging mitochondrial enzymes including
    lipoate-containing E2/E3 modules. This combination of energy depletion and
    oxidative stress results in cerebral edema with diffuse gray matter swelling
    affecting the cerebral cortex, basal ganglia, hippocampus, and brainstem.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  - preferred_term: generation of precursor metabolites and energy
    term:
      id: GO:0006091
      label: generation of precursor metabolites and energy
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  - preferred_term: basal ganglion
    term:
      id: UBERON:0002420
      label: basal ganglion
  - preferred_term: hippocampal formation
    term:
      id: UBERON:0002421
      label: hippocampal formation
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  evidence:
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we found lower brain glutamate, N-acetylaspartate (NAA), and creatine concentrations in MSUD patients, which correlated with specific neuropsychiatric outcomes"
    explanation: Low NAA and creatine in MSUD brains reflects cerebral energy failure and neuronal compromise.
  downstream:
  - target: Neural Cell Death via Apoptosis and Autophagy
    description: Energy failure and metabolite toxicity trigger apoptotic and autophagic injury programs in neural cells and brain tissue.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Mitochondrial respiratory stress and BCAA/KIC-induced neural cell death programs.
    evidence:
    - reference: DOI:10.1091/mbc.11.5.1919
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "increased concentrations of MSUD metabolites, in particular α-keto isocaproic acid, specifically induced apoptosis in glial and neuronal cells in culture"
      explanation: Neural cell culture evidence supports MSUD metabolites as inducing apoptosis in glial and neuronal cells.
    - reference: DOI:10.1007/s11011-022-01109-y
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCAA significantly increased the levels of Beclin-1, ATG7, and ATG5 in the cerebral cortex of rats"
      explanation: Rat-model evidence supports BCAA-induced autophagy pathway activation in brain tissue.
  - target: Cerebral Edema
    description: Severe cerebral energy failure and oxidative stress culminate in cerebral edema during intoxication.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301495
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Severe intoxication culminates in critical cerebral edema, coma, and central respiratory failure."
      explanation: GeneReviews directly supports cerebral edema as a severe consequence of MSUD intoxication.
  - target: Coma
    description: Severe cerebral edema and energy failure can progress to coma.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Cerebral edema and severe metabolic encephalopathy.
    evidence:
    - reference: PMID:20301495
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Severe intoxication culminates in critical cerebral edema, coma, and central respiratory failure."
      explanation: GeneReviews directly supports coma as a severe consequence of MSUD intoxication.
  - target: Seizures
    description: Brain energy failure and injury lower seizure threshold during severe intoxication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Cerebral edema, metabolic encephalopathy, and neuronal injury.
    evidence:
    - reference: PMID:32491705
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "If left untreated, the most severe, classic form of MSUD can quickly lead to irreversible neurological injury manifesting as brain damage, seizures, a coma, or central respiratory failure within just 7 to 10 days after birth."
      explanation: Clinical summary supports seizures as a severe neurologic consequence of untreated classic MSUD intoxication.
- name: Neural Cell Death via Apoptosis and Autophagy
  description: >
    Sustained exposure to elevated BCAAs and BCKAs triggers both apoptotic and
    autophagic cell death programs in neural tissue. KIC induces apoptosis in
    glial and neuronal cells through a cytochrome c-independent pathway, without
    canonical mitochondrial membrane depolarization. Chronic BCAA exposure also
    increases autophagy markers across brain regions including cerebral cortex,
    hippocampus, and brainstem, consistent with stress-induced autophagic programs
    that can progress to cell death.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
  cellular_components:
  - preferred_term: autophagosome
    term:
      id: GO:0005776
      label: autophagosome
  evidence:
  - reference: DOI:10.1091/mbc.11.5.1919
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Apoptosis was associated with a reduction in cell respiration but without impairment of respiratory chain function, without early changes in mitochondrial membrane potential and without cytochrome c release into the cytosol"
    explanation: Demonstrates apoptosis via cytochrome c-independent pathway in neural cells exposed to MSUD metabolites.
  - reference: DOI:10.1091/mbc.11.5.1919
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "α-keto isocaproic acid also triggered neuronal apoptosis in vivo after intracerebral injection into the developing rat brain"
    explanation: Confirms KIC triggers neuronal apoptosis in vivo in developing brain tissue.
  - reference: DOI:10.1007/s11011-022-01109-y
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "BCAA significantly increased the levels of Beclin-1, ATG7, and ATG5 in the cerebral cortex of rats"
    explanation: Demonstrates that BCAA administration increases autophagy markers in brain tissue of rats in an MSUD model, supporting the role of autophagy in neural cell death.
  downstream:
  - target: Intellectual Disability
    description: Irreversible neural cell injury contributes to persistent intellectual impairment after severe or delayed-treated MSUD.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Brain damage from sustained leucine and ketoacid toxicity.
    evidence:
    - reference: PMID:21839471
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "One-third of our patients were mentally impaired (IQ ≤ 70) before transplantation, with no statistically significant change 1 year later."
      explanation: Human transplant follow-up supports persistent intellectual impairment after preexisting MSUD brain injury.
- name: Skeletal Muscle Dysfunction
  description: >
    Skeletal muscle is a major site of BCAA transamination via mitochondrial
    branched-chain aminotransferase (BCAT2) and accumulates toxic ketoacids. KIC
    disrupts mitochondrial metabolism in myocytes, causing reduced TCA cycle flux
    and ATP depletion. MSUD patients and mouse models display skeletal muscle
    fiber abnormalities including reduced fiber diameter and muscle atrophy.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  cellular_components:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "shows significant skeletal muscle dysfunction as by judged decreased muscle"
    explanation: Animal model demonstrates skeletal muscle atrophy in MSUD.
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites"
    explanation: Confirms KIC accumulation in muscle disrupts mitochondrial metabolism, reversible with metformin.
  downstream:
  - target: Hypotonia
    description: Skeletal muscle mitochondrial dysfunction and reduced muscle fiber size can contribute to hypotonia.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Muscle atrophy and impaired skeletal-muscle energy metabolism.
    evidence:
    - reference: PMID:27373929
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "shows significant skeletal muscle dysfunction as by judged decreased muscle"
      explanation: MSUD mouse evidence supports skeletal-muscle dysfunction as part of the disease mechanism.
    - reference: PMID:31559730
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Physical examination of the neonates were similar having stupor, hypotonia and depressed newborn reflexes."
      explanation: Human neonatal MSUD decompensation evidence supports hypotonia as a clinical manifestation.
phenotypes:
- name: Abnormal Urinary Odor
  category: Other
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: Characteristic sweet maple syrup odor in urine, sweat, and earwax due to sotolone from accumulated ketoacids
  phenotype_term:
    preferred_term: Abnormal urinary odor
    term:
      id: HP:0012088
      label: Abnormal urinary odor
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
    explanation: Confirms characteristic maple syrup odor in urine and cerumen as a classic presentation.
- name: Poor Feeding
  category: Other
  frequency: VERY_FREQUENT
  notes: Often first symptom in neonatal period
  phenotype_term:
    preferred_term: Feeding difficulties in infancy
    term:
      id: HP:0008872
      label: Feeding difficulties in infancy
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
    explanation: Confirms feeding difficulties as a classic neonatal presentation of MSUD.
- name: Lethargy
  category: Neurological
  frequency: VERY_FREQUENT
  notes: Progressive in acute metabolic crises
  phenotype_term:
    preferred_term: Lethargy
    term:
      id: HP:0001254
      label: Lethargy
  evidence:
  - reference: PMID:32491705
    reference_title: "Maple Syrup Urine Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It classically manifests in the neonatal period with failure to thrive, delayed developmental milestones, feeding difficulties, lethargy, irritability, and a maple syrup odor first noticeable in the cerumen and then the urine."
    explanation: Confirms lethargy as a classic neonatal manifestation of MSUD.
- name: Encephalopathy
  category: Neurological
  frequency: VERY_FREQUENT
  notes: Acute metabolic encephalopathy during crises, presents in neonates
  phenotype_term:
    preferred_term: Acute encephalopathy
    term:
      id: HP:0006846
      label: Acute encephalopathy
  evidence:
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    snippet: "Maple syrup urine disease (MSUD) is an inherited disorder of branched chain amino acid metabolism presenting with neonatal encephalopathy, episodic metabolic decompensation, and chronic amino acid imbalances."
    explanation: Confirms neonatal encephalopathy as a presenting feature of MSUD.
- name: Seizures
  category: Neurological
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Seizures
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:32491705
    reference_title: "Maple Syrup Urine Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "If left untreated, the most severe, classic form of MSUD can quickly lead to irreversible neurological injury manifesting as brain damage, seizures, a coma, or central respiratory failure within just 7 to 10 days after birth."
    explanation: Confirms seizures as a neurological manifestation of untreated classic MSUD.
- name: Hypotonia
  category: Neurological
  frequency: VERY_FREQUENT
  notes: Alternating with hypertonia during crises
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:31559730
    reference_title: "Treatment of maple syrup urine disease with high flow hemodialysis in a neonate."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Physical examination of the neonates were similar having stupor, hypotonia and depressed newborn reflexes."
    explanation: Confirms hypotonia as a neurological finding on examination of neonates with MSUD metabolic decompensation.
- name: Intellectual Disability
  category: Neurological
  frequency: FREQUENT
  notes: If treatment delayed or metabolic control poor; liver transplantation may arrest but not reverse brain damage
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:21839471
    reference_title: "Liver transplantation for classical maple syrup urine disease: long-term follow-up in 37 patients and comparative United Network for Organ Sharing experience."
    supports: SUPPORT
    snippet: "One-third of our patients were mentally impaired (IQ ≤ 70) before transplantation, with no statistically significant change 1 year later."
    explanation: Confirms intellectual impairment occurs in MSUD and is not reversed by liver transplantation.
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    snippet: "Compared with 26 age-matched controls, MSUD patients were at higher risk for disorders of cognition, attention, and mood."
    explanation: Demonstrates cognitive impairment in MSUD patients compared to controls.
- name: Vomiting
  category: Other
  frequency: FREQUENT
  notes: Common during metabolic decompensation
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
  evidence:
  - reference: PMID:35578286
    reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
    supports: SUPPORT
    snippet: "In some patients, enteral administration is not possible, either because the patient presents with vomiting, coma, or refuses nasogastric administration"
    explanation: Vomiting is a recognized presentation during MSUD decompensation episodes.
- name: Coma
  category: Neurological
  frequency: FREQUENT
  notes: Can occur during severe metabolic crises
  phenotype_term:
    preferred_term: Coma
    term:
      id: HP:0001259
      label: Coma
  evidence:
  - reference: PMID:35578286
    reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
    supports: SUPPORT
    snippet: "In some patients, enteral administration is not possible, either because the patient presents with vomiting, coma, or refuses nasogastric administration"
    explanation: Coma is recognized as a presentation during severe MSUD decompensation.
- name: Global Developmental Delay
  category: Neurological
  frequency: FREQUENT
  notes: Occurs with delayed treatment or poor metabolic control
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
    explanation: Confirms developmental delay as a classic presentation of MSUD.
- name: Elevated Branched Chain Amino Acids
  category: Biochemical
  frequency: OBLIGATE
  diagnostic: true
  notes: Pathognomonic finding; includes elevated leucine, isoleucine, valine, and alloisoleucine
  phenotype_term:
    preferred_term: Elevated circulating branched chain amino acid concentration
    term:
      id: HP:0008344
      label: Elevated circulating branched chain amino acid concentration
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "The concentrations of leucine and BCAAs in the blood range from approximately 1 to 5"
    explanation: Confirms marked elevation of branched chain amino acids in MSUD patients.
- name: Failure to Thrive
  category: Other
  frequency: VERY_FREQUENT
  notes: Common in neonatal period and with poor metabolic control
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine"
    explanation: Confirms failure to thrive as a classic neonatal presentation of MSUD.
- name: Metabolic Acidosis
  category: Biochemical
  frequency: FREQUENT
  notes: Occurs during acute metabolic crises from BCKA accumulation
  phenotype_term:
    preferred_term: Metabolic acidosis
    term:
      id: HP:0001942
      label: Metabolic acidosis
  evidence:
  - reference: PMID:36550798
    reference_title: "Neonatal maple syrup urine disease case report and literature review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical symptoms of maple syrup urine disease (MSUD) are dehydration, acidosis, nervous system symptoms and intellectual disability."
    explanation: Confirms acidosis as a main clinical symptom of MSUD.
- name: Cerebral Edema
  category: Neurological
  frequency: FREQUENT
  notes: Occurs during acute metabolic crises; diffuse gray matter swelling affecting cortex, basal ganglia, hippocampus, and brainstem
  phenotype_term:
    preferred_term: Cerebral edema
    term:
      id: HP:0002181
      label: Cerebral edema
  evidence:
  - reference: PMID:20301495
    reference_title: "Maple Syrup Urine Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Severe intoxication culminates in critical cerebral edema, coma, and central respiratory failure."
    explanation: Confirms cerebral edema as a critical complication of severe MSUD metabolic intoxication.
biochemical:
- name: Plasma Leucine
  presence: INCREASED
  context: Markedly elevated, often greater than 2000 micromol/L in classic form; normal is 90-250 micromol/L
  biomarker_term:
    preferred_term: plasma leucine
    term:
      id: CHEBI:25017
      label: leucine
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Elevated plasma leucine reports the primary branched-chain amino acid
      accumulation caused by BCKDH deficiency.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Elevated concentrations of branched-chain amino acids (BCAAs; leucine,
        isoleucine, and valine) and alloisoleucine
      explanation: GeneReviews identifies elevated leucine within the diagnostic BCAA accumulation pattern.
  - target: Leucine and Ketoacid Neurotoxicity
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: >-
      High leucine participates in the toxic leucine/KIC branch that drives
      MSUD-related neurologic symptoms.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "KIC and its’ corresponding branched-chain amino acid (BCAA) precursor, leucine are the major toxic metabolites associated with MSUD related symptoms"
      explanation: Model-system paper identifies leucine with KIC as a major toxic metabolite pair in MSUD.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "Leucine was significantly increased 6.4-fold in serum"
    explanation: Confirms marked elevation of leucine in MSUD mouse model.
- name: Plasma Isoleucine
  presence: INCREASED
  context: Elevated above normal range along with other branched-chain amino acids
  biomarker_term:
    preferred_term: plasma isoleucine
    term:
      id: CHEBI:24898
      label: isoleucine
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Elevated plasma isoleucine reports the systemic branched-chain amino
      acid accumulation caused by impaired BCAA catabolism.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Elevated concentrations of branched-chain amino acids (BCAAs; leucine,
        isoleucine, and valine) and alloisoleucine
      explanation: GeneReviews identifies isoleucine within the elevated BCAA diagnostic pattern.
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma"
    explanation: Confirms elevation of all BCAAs including isoleucine in plasma.
- name: Plasma Valine
  presence: INCREASED
  context: Elevated above normal range along with other branched-chain amino acids
  biomarker_term:
    preferred_term: plasma valine
    term:
      id: CHEBI:27266
      label: valine
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Elevated plasma valine reports the systemic branched-chain amino acid
      accumulation caused by impaired BCAA catabolism.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Elevated concentrations of branched-chain amino acids (BCAAs; leucine,
        isoleucine, and valine) and alloisoleucine
      explanation: GeneReviews identifies valine within the elevated BCAA diagnostic pattern.
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma"
    explanation: Confirms elevation of all BCAAs including valine in plasma.
- name: Alloisoleucine
  presence: INCREASED
  context: Pathognomonic marker for MSUD, not normally present in plasma
  biomarker_term:
    preferred_term: alloisoleucine
    term:
      id: CHEBI:22359
      label: alloisoleucine
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Increased alloisoleucine is the pathognomonic diagnostic readout of the
      MSUD branched-chain amino acid imbalance.
    evidence:
    - reference: PMID:28919799
      reference_title: "Maple syrup urine disease: mechanisms and management."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "production of the pathognomonic disease marker, alloisoleucine."
      explanation: Review evidence directly identifies alloisoleucine as the pathognomonic MSUD marker.
  evidence:
  - reference: PMID:28919799
    reference_title: "Maple syrup urine disease: mechanisms and management."
    supports: SUPPORT
    snippet: "Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker, alloisoleucine."
    explanation: Confirms alloisoleucine is the pathognomonic marker for MSUD.
- name: Alpha-Ketoisocaproic Acid (KIC)
  presence: INCREASED
  context: Leucine-derived ketoacid, primary neurotoxic metabolite
  biomarker_term:
    preferred_term: alpha-ketoisocaproic acid
    term:
      id: CHEBI:48430
      label: 4-methyl-2-oxopentanoic acid
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Increased KIC reports accumulation of the leucine-derived branched-chain
      ketoacid upstream of the BCKDH block.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        BCKDH dysfunction results in the accumulation of the keto-acids
        ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from
        valine and ketomethylvaleric acid (KMV) from isoleucine
      explanation: Model-system evidence supports KIC as a direct readout of BCKDH-dependent ketoacid accumulation.
  - target: Leucine and Ketoacid Neurotoxicity
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: >-
      Increased KIC reports the proximal toxic metabolite branch that impairs
      mitochondrial function and contributes to neurologic injury.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "KIC is an inhibitor of mitochondrial function at disease relevant concentrations."
      explanation: Model-system evidence supports KIC as a toxic readout tied to mitochondrial dysfunction.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "Similarly, KIC was significantly increased 40-fold"
    explanation: Demonstrates massive KIC accumulation in MSUD.
- name: Alpha-Ketoisovaleric Acid (KIV)
  presence: INCREASED
  context: Valine-derived ketoacid
  biomarker_term:
    preferred_term: alpha-ketoisovaleric acid
    term:
      id: CHEBI:16530
      label: 3-methyl-2-oxobutanoic acid
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Increased KIV reports accumulation of the valine-derived branched-chain
      ketoacid upstream of the BCKDH block.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        BCKDH dysfunction results in the accumulation of the keto-acids
        ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from
        valine and ketomethylvaleric acid (KMV) from isoleucine
      explanation: Model-system evidence supports KIV as a direct readout of BCKDH-dependent ketoacid accumulation.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
    explanation: Confirms KIV accumulation from valine due to BCKDH dysfunction.
- name: Alpha-Keto-beta-Methylvaleric Acid (KMV)
  presence: INCREASED
  context: Isoleucine-derived ketoacid
  biomarker_term:
    preferred_term: alpha-keto-beta-methylvaleric acid
    term:
      id: CHEBI:35932
      label: 3-methyl-2-oxovaleric acid
  readouts:
  - target: Systemic BCAA and BCKA Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Increased KMV reports accumulation of the isoleucine-derived
      branched-chain ketoacid upstream of the BCKDH block.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        BCKDH dysfunction results in the accumulation of the keto-acids
        ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from
        valine and ketomethylvaleric acid (KMV) from isoleucine
      explanation: Model-system evidence supports KMV as a direct readout of BCKDH-dependent ketoacid accumulation.
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "BCKDH dysfunction results in the accumulation of the keto-acids ketoisocaproic acid (KIC) from leucine, ketoisovaleric acid (KIV) from valine and ketomethylvaleric acid (KMV) from isoleucine"
    explanation: Confirms KMV accumulation from isoleucine due to BCKDH dysfunction.
genetic:
- name: BCKDHA
  gene_term:
    preferred_term: BCKDHA
    term:
      id: hgnc:986
      label: BCKDHA
  association: Causative
  subtype: Type IA
  notes: E1-alpha subunit of BCKD complex, accounts for approximately 45% of cases, autosomal recessive
  evidence:
  - reference: PMID:35672312
    reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
    supports: SUPPORT
    snippet: "We establish and characterize the Bckdha (branched chain keto acid dehydrogenase a)-/- mouse that exhibits a lethal neonatal phenotype mimicking human MSUD."
    explanation: Confirms BCKDHA mutations cause MSUD.
- name: BCKDHB
  gene_term:
    preferred_term: BCKDHB
    term:
      id: hgnc:987
      label: BCKDHB
  association: Causative
  subtype: Type IB
  notes: E1-beta subunit of BCKD complex, accounts for approximately 35% of cases, autosomal recessive
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."
    explanation: Confirms BCKDHB (E1-beta) mutations cause Type I MSUD.
- name: DBT
  gene_term:
    preferred_term: DBT
    term:
      id: hgnc:2698
      label: DBT
  association: Causative
  subtype: Type II
  notes: E2 subunit (dihydrolipoamide branched chain transacylase), accounts for approximately 20% of cases, autosomal recessive
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."
    explanation: Confirms DBT (E2) mutations cause Type II MSUD.
  - reference: CGGV:assertion_cfd1ebde-e447-4877-977e-f5b9fe434adc-2018-10-30T160000.000Z
    reference_title: "DBT / maple syrup urine disease (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "DBT | HGNC:2698 | maple syrup urine disease | MONDO:0009563 | AR | Definitive"
    explanation: ClinGen classifies the DBT-maple syrup urine disease gene-disease relationship as definitive with autosomal recessive inheritance.
- name: DLD
  gene_term:
    preferred_term: DLD
    term:
      id: hgnc:2898
      label: DLD
  association: Causative
  subtype: Type III
  notes: E3 subunit (dihydrolipoamide dehydrogenase), shared with pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "MSUD is classified as type I, II or III based on mutations that occur in the E1, E2, or E3 complexes of BCKDH, respectively."
    explanation: Confirms DLD (E3) mutations cause Type III MSUD.
- name: BCKDK
  gene_term:
    preferred_term: BCKDK
    term:
      id: hgnc:16902
      label: BCKDK
  association: Regulatory
  notes: Kinase that phosphorylates and inactivates BCKDH; heterozygous gain-of-function variant (p.Thr372Arg) causes autosomal dominant biochemical MSUD phenotype with elevated BCAAs and alloisoleucine but potentially benign clinical course
  evidence:
  - reference: DOI:10.1002/jmd2.12419
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "heterozygous gain‐of‐function variants in BCKDK may represent a novel biochemical phenotype of MSUD with a benign clinical course"
    explanation: Identifies BCKDK gain-of-function as a cause of a biochemical MSUD phenotype following autosomal dominant inheritance.
- name: PPM1K
  gene_term:
    preferred_term: PPM1K
    term:
      id: hgnc:25415
      label: PPM1K
  association: Regulatory
  notes: Phosphatase (also known as PP2Cm) that dephosphorylates and activates BCKDH, promoting BCAA oxidation; loss-of-function variants impair BCKDH activation
  evidence:
  - reference: PMID:23086801
    reference_title: "A novel regulatory defect in the branched-chain α-keto acid dehydrogenase complex due to a mutation in the PPM1K gene causes a mild variant phenotype of maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This article describes a hitherto unreported involvement of the phosphatase PP2Cm, a recently described member of the branched-chain α-keto acid dehydrogenase (BCKDH) complex, in maple syrup urine disease (MSUD)."
    explanation: First report of PPM1K (PP2Cm) mutation causing MSUD, confirming the regulatory role of this phosphatase in BCKDH complex activity.
environmental:
- name: Dietary Protein
  notes: Intake of branched-chain amino acids triggers metabolic decompensation; requires careful dietary management
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "The primary treatment of MSUD in patients is via the dietary restriction of BCAA1718. Since leucine, valine and isoleucine are essential amino acids, dietary compliance can therefore be challenging."
    explanation: Confirms dietary protein intake directly affects MSUD through BCAA content.
- name: Catabolic Stress
  notes: Illness, surgery, fasting can precipitate acute metabolic crises through protein catabolism
  evidence:
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    snippet: "Maple syrup urine disease (MSUD) is an inherited disorder of branched chain amino acid metabolism presenting with neonatal encephalopathy, episodic metabolic decompensation, and chronic amino acid imbalances."
    explanation: Episodic metabolic decompensation occurs with catabolic stress.
- name: Fever
  notes: Common trigger for acute decompensation due to increased catabolism
  evidence:
  - reference: PMID:35578286
    reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
    supports: SUPPORT
    snippet: "Patients with maple syrup urine disease (MSUD) experiencing metabolic decompensations have traditionally been treated with branched-chain amino acid (BCAA)-free mixture"
    explanation: Metabolic decompensations requiring treatment are triggered by catabolic states including febrile illness.
treatments:
- name: BCAA-Restricted Diet
  description: Lifelong dietary restriction of leucine, isoleucine, and valine intake, mainstay of treatment.
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  evidence:
  - reference: PMID:35672312
    reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
    supports: SUPPORT
    snippet: "Treatment for MSUD represents an unmet need because the current treatment with life-long low-protein diet is challenging to maintain, and despite treatment the risk of acute decompensations and neuropsychiatric symptoms remains."
    explanation: Confirms lifelong dietary treatment is the current standard of care but has limitations.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Restricting dietary branched-chain amino acids reduces substrate flux into the blocked BCAA catabolic pathway.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "restriction, BCAA-free medical foods, judicious supplementation with isoleucine"
      explanation: GeneReviews directly supports dietary leucine restriction and BCAA-free medical foods as core management to control BCAA accumulation.
- name: Medical Formula
  description: BCAA-free amino acid supplements to provide protein needs while restricting toxic amino acids.
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  evidence:
  - reference: PMID:35578286
    reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
    supports: SUPPORT
    snippet: "Patients with maple syrup urine disease (MSUD) experiencing metabolic decompensations have traditionally been treated with branched-chain amino acid (BCAA)-free mixture via oral or nasogastric administration routes."
    explanation: Confirms BCAA-free amino acid mixtures are standard treatment.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: BCAA-free formula supplies amino acids while avoiding leucine, isoleucine, and valine load.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "diet fortified with prescription medical foods can maintain average plasma BCAA"
      explanation: Supports prescription medical foods as a way to maintain plasma BCAA concentrations in the reference range.
- name: Thiamine Supplementation
  description: High-dose thiamine for thiamine-responsive variant patients who have specific mutations affecting cofactor binding.
  treatment_term:
    preferred_term: nutritional supplementation
    term:
      id: MAXO:0000106
      label: nutritional supplementation
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"
    explanation: Confirms thiamine supplementation is effective for patients with specific mutations.
  target_mechanisms:
  - target: Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency
    treatment_effect: RESTORES
    description: Thiamine-responsive variants partially restore BCKDH function through cofactor binding or allosteric stabilization.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Thiamine responsivity is associated with a specific mutation in the thiamine binding site in the E1b subunit, or due to the stabilization of BCKDH via an allosteric interaction"
      explanation: Supports thiamine as targeting residual BCKDH function in responsive variants.
- name: Liver Transplantation
  description: Curative treatment providing sufficient BCKD enzyme activity from donor hepatocytes, allowing unrestricted protein diet.
  treatment_term:
    preferred_term: liver transplantation
    term:
      id: MAXO:0001175
      label: liver transplantation
  evidence:
  - reference: PMID:21839471
    reference_title: "Liver transplantation for classical maple syrup urine disease: long-term follow-up in 37 patients and comparative United Network for Organ Sharing experience."
    supports: SUPPORT
    snippet: "Patient and graft survival were 100% at 4.5 ± 2.2 years of follow-up. Liver function was normal in all patients. Branched-chain amino acid levels were corrected within hours after surgery and remained stable, with leucine tolerance increasing more than 10-fold."
    explanation: Demonstrates excellent outcomes with liver transplantation for MSUD.
  - reference: PMID:23478409
    reference_title: "Biochemical correlates of neuropsychiatric illness in maple syrup urine disease."
    supports: SUPPORT
    snippet: "Liver transplantation has emerged as an effective way to eliminate acute decompensation risk."
    explanation: Confirms liver transplantation eliminates risk of acute metabolic crises.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Transplanted liver BCAA catabolic capacity normalizes plasma BCAA homeostasis and prevents acute decompensation.
    evidence:
    - reference: PMID:21839471
      reference_title: "Liver transplantation for classical maple syrup urine disease: long-term follow-up in 37 patients and comparative United Network for Organ Sharing experience."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "corrected within hours after surgery and remained stable, with leucine tolerance"
      explanation: Human transplant follow-up directly supports normalization of BCAA levels after liver transplantation.
- name: Intravenous BCAA-Free Solution
  description: IV amino acid solution without branched-chain amino acids for acute crisis management when enteral feeding is not possible.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:35578286
    reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
    supports: SUPPORT
    snippet: "The IV BCAA-free solution is safe and effective in normalising leucine concentrations during MSUD decompensation episodes in both children and adults"
    explanation: Demonstrates safety and efficacy of IV BCAA-free solutions for acute decompensation.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Intravenous BCAA-free solution lowers leucine during acute decompensation when enteral therapy is not possible.
    evidence:
    - reference: PMID:35578286
      reference_title: "Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "leucine concentrations during MSUD decompensation episodes in both children and"
      explanation: Prospective multicenter data support IV BCAA-free solution as reducing acute leucine accumulation.
- name: Acute Crisis Management
  description: IV glucose, insulin, and lipids to promote anabolism and reduce protein catabolism during metabolic crises.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:20301495
    reference_title: "Maple Syrup Urine Disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "by treating the precipitating stress while delivering sufficient calories,"
    explanation: Confirms acute crisis management involves delivering calories, insulin, and amino acids to promote anabolism.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Anabolic crisis management suppresses proteolysis and promotes net protein synthesis, lowering circulating BCAA burden.
    evidence:
    - reference: PMID:20301495
      reference_title: "Maple Syrup Urine Disease."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "by treating the precipitating stress while delivering sufficient calories,"
      explanation: Supports acute crisis therapy as reversing catabolism and promoting protein synthesis to reduce toxic BCAA accumulation.
- name: Phenylbutyrate
  description: BCKDK inhibitor that increases BCKDH enzyme activity by preventing phosphorylation, may benefit subset of patients with residual enzyme activity.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sodium phenylbutyrate
      term:
        id: CHEBI:75316
        label: sodium phenylbutyrate
  evidence:
  - reference: PMID:21098507
    reference_title: "Phenylbutyrate therapy for maple syrup urine disease."
    supports: SUPPORT
    snippet: "In vivo phenylbutyrate increases the proportion of active hepatic enzyme and unphosphorylated form over the inactive phosphorylated form of the E1α subunit of the branched-chain α-keto acid dehydrogenase complex (BCKDC)."
    explanation: Demonstrates phenylbutyrate activates BCKDH by inhibiting kinase-mediated inactivation.
  target_mechanisms:
  - target: Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency
    treatment_effect: RESTORES
    description: Phenylbutyrate inhibits BCKDC kinase-mediated phosphorylation, increasing the active BCKDH fraction in patients with residual enzyme activity.
    evidence:
    - reference: PMID:21098507
      reference_title: "Phenylbutyrate therapy for maple syrup urine disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "BCAA and BCKA are both"
      explanation: Human treatment data support phenylbutyrate as reducing the upstream BCAA/BCKA burden.
    - reference: PMID:21098507
      reference_title: "Phenylbutyrate therapy for maple syrup urine disease."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Using recombinant enzymes, we show that phenylbutyrate prevents phosphorylation"
      explanation: Recombinant enzyme data support the specific BCKDH-activation mechanism.
- name: Metformin
  description: Potential adjunctive therapy that reduces KIC production by downregulating mitochondrial BCAT; shown to improve metabolic homeostasis in preclinical models.
  treatment_term:
    preferred_term: targeted therapy
    term:
      id: NCIT:C93352
      label: Targeted Therapy
    therapeutic_agent:
    - preferred_term: metformin
      term:
        id: CHEBI:6801
        label: metformin
  evidence:
  - reference: PMID:27373929
    reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
    supports: SUPPORT
    snippet: "Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%) and serum (by 56%) isolated from iMSUD mice, and restored levels of mitochondrial metabolites"
    explanation: Preclinical evidence supports metformin as potential therapeutic strategy for MSUD.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Metformin reduces KIC accumulation by suppressing mitochondrial BCAT2-mediated leucine transamination in preclinical models.
    evidence:
    - reference: PMID:27373929
      reference_title: "Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Metformin-treatment significantly reduced levels of KIC in the muscle (by 69%)"
      explanation: MSUD mouse data support metformin as reducing KIC accumulation and improving metabolic homeostasis.
- name: Gene Therapy (Preclinical)
  description: Liver-directed AAV8 gene therapy delivering BCKDHA has rescued lethal MSUD phenotype in Bckdha-knockout mice. Ubiquitous promoter fully rescues the disease; liver-specific expression provides partial but sustained rescue, highlighting both hepatic and extrahepatic requirements for complete correction.
  treatment_term:
    preferred_term: gene therapy
    term:
      id: MAXO:0001001
      label: gene therapy
  evidence:
  - reference: PMID:35672312
    reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "BCKDHA gene transfer rescued the lethal phenotype. While the use of a ubiquitous promoter fully and sustainably rescued the disease (long-term survival, normal phenotype and correction of biochemical abnormalities), liver-specific expression of BCKDHA led to partial, though sustained rescue."
    explanation: Demonstrates efficacy of AAV8 gene therapy for MSUD in a mouse model with complete rescue using ubiquitous expression.
  - reference: PMID:42127902
    reference_title: "Trial-ready external controls for gene therapy: The MATCH cohort in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MSUD Age-matched Standard Treatment Cohort (MATCH), a prospective natural history study of 11 infants with classic MSUD followed from neonatal diagnosis to liver transplantation. Aligned with Food and Drug Administration (FDA) guidance and International Council for Harmonisation (ICH) E9(R1), MATCH applies prespecified eligibility criteria, fixed visit cadence, adjudicated outcomes, and explicit handling of intercurrent events."
    explanation: The MATCH cohort provides regulatory-grade natural history baseline and prespecified outcome measures for single-arm gene therapy trials in MSUD, bridging preclinical models to clinical development.
  - reference: PMID:42127902
    reference_title: "Trial-ready external controls for gene therapy: The MATCH cohort in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three of six outcome measures-proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration-are prespecified as estimands. Monte Carlo simulations show that a single-arm trial comparing 11 treated participants to MATCH controls achieves ≥90% power (p ≤ 0.025) to detect 64% fewer CMDs (3.0% vs. 8.4%), a 57% increase in PIPE (19.3% vs. 12.3%), and a 36% reduction in alloisoleucine (117 vs. 183 μM)."
    explanation: MATCH provides prespecified outcome measures (PIPE, CMDs, alloisoleucine) as estimands with statistical power to detect clinically meaningful improvements in a single-arm gene therapy trial, supporting trial design and regulatory strategy for MSUD gene therapy development.
  target_mechanisms:
  - target: Branched-Chain Alpha-Ketoacid Dehydrogenase Complex Deficiency
    treatment_effect: RESTORES
    description: BCKDHA gene transfer restores the deficient BCKDH E1-alpha component in preclinical MSUD models.
    evidence:
    - reference: PMID:35672312
      reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCKDHA gene transfer rescued the lethal"
      explanation: Mouse-model gene transfer evidence supports restoration of the deficient BCKDHA component.
- name: Gene Therapy (Clinical Development)
  description: >
    Liver-directed AAV8 gene therapy for MSUD is advancing toward clinical trials. The MSUD Age-matched Standard Treatment Cohort (MATCH) is a prospective natural history study of 11 infants with classic MSUD designed to serve as regulatory-grade external controls for single-arm gene therapy trials. The study applies FDA and ICH E9(R1) guidelines with prespecified eligibility criteria, fixed visit cadence, and adjudicated outcomes. Primary outcome measures include proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration. Monte Carlo simulations demonstrate ≥90% power to detect clinically meaningful improvements: 64% reduction in CMDs (from 8.4% to 3.0%), 57% increase in PIPE (from 12.3% to 19.3%), and 36% reduction in alloisoleucine (from 183 to 117 μM).
  treatment_term:
    preferred_term: gene therapy
    term:
      id: MAXO:0001001
      label: gene therapy
  evidence:
  - reference: PMID:42127902
    reference_title: "Trial-ready external controls for gene therapy: The MATCH cohort in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MATCH applies prespecified eligibility criteria, fixed visit cadence, adjudicated outcomes, and explicit handling of intercurrent events. Three of six outcome measures-proportional intact protein equivalent (PIPE), crisis management days (CMDs), and blood alloisoleucine concentration-are prespecified as estimands."
    explanation: Documents the MATCH cohort as a regulatory-grade natural history study with prespecified outcomes aligned with FDA and ICH E9(R1) guidance for external controls in single-arm trials.
  - reference: PMID:42127902
    reference_title: "Trial-ready external controls for gene therapy: The MATCH cohort in maple syrup urine disease."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Monte Carlo simulations show that a single-arm trial comparing 11 treated participants to MATCH controls achieves ≥90% power (p ≤ 0.025) to detect 64% fewer CMDs (3.0% vs. 8.4%), a 57% increase in PIPE (19.3% vs. 12.3%), and a 36% reduction in alloisoleucine (117 vs. 183 μM)."
    explanation: Demonstrates statistical feasibility of detecting clinically meaningful improvements in prespecified outcome measures with the MATCH cohort as external control.
  target_mechanisms:
  - target: Systemic BCAA and BCKA Accumulation
    treatment_effect: INHIBITS
    description: Gene therapy is expected to reduce systemic BCAA and BCKA accumulation through restoration of BCKDH function in hepatocytes and potentially other tissues.
    evidence:
    - reference: PMID:35672312
      reference_title: "Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "BCKDHA gene transfer rescued the lethal phenotype. While the use of a ubiquitous promoter fully and sustainably rescued the disease (long-term survival, normal phenotype and correction of biochemical abnormalities), liver-specific expression of BCKDHA led to partial, though sustained rescue."
      explanation: Mouse-model evidence demonstrates that BCKDHA gene transfer corrects biochemical abnormalities (including BCAA/BCKA accumulation), supporting the mechanistic claim that gene therapy inhibits systemic BCAA and BCKA accumulation.
datasets:
references:
- reference: DOI:10.1002/jmd2.12419
  title: Computational structural genomics and clinical evidence suggest <scp>BCKDK</scp> gain‐of‐function may cause a potentially asymptomatic maple syrup urine disease phenotype
  findings: []
- reference: DOI:10.1007/s11011-022-01109-y
  title: Branched-chain amino acids (BCAA) administration increases autophagy and the autophagic pathway in brain tissue of rats submitted to a Maple Syrup Urine Disease (MSUD) protocol
  findings: []
- reference: DOI:10.1038/s41467-022-30880-w
  title: Neonatal gene therapy achieves sustained disease rescue of maple syrup urine disease in mice
  findings: []
- reference: DOI:10.1038/srep28775
  title: Metformin inhibits Branched Chain Amino Acid (BCAA) derived ketoacidosis and promotes metabolic homeostasis in MSUD
  findings: []
- reference: DOI:10.1091/mbc.11.5.1919
  title: 'Branched Chain Amino Acids Induce Apoptosis in Neural Cells without Mitochondrial Membrane Depolarization or Cytochrome<i>c</i>Release: Implications for Neurological Impairment Associated with Maple Syrup Urine Disease'
  findings: []
- reference: DOI:10.1093/hmg/ddq507
  title: Phenylbutyrate therapy for maple syrup urine disease
  findings: []
- reference: DOI:10.1093/qjmed/hcae104
  title: Genotypic and phenotypic spectrum of maple syrup urine disease in Zhejiang of China
  findings: []
- reference: DOI:10.1101/2023.07.31.551364
  title: Reactive nitrogen species inhibit branched chain alpha-ketoacid dehydrogenase complex and impact muscle cell metabolism
  findings: []
- reference: DOI:10.1172/jci67217
  title: Biochemical correlates of neuropsychiatric illness in maple syrup urine disease
  findings: []
- reference: DOI:10.1186/s12887-024-05266-0
  title: 'Maple syrup urine disease diagnosed in a resource-limited setting in an infant in Nepal: a case report'
  findings: []
- reference: DOI:10.1186/s13023-022-02353-2
  title: 'Intravenous administration of a branched-chain amino-acid-free solution in children and adults with acute decompensation of maple syrup urine disease: a prospective multicentre observational study'
  findings: []
- reference: DOI:10.1186/s13023-024-03411-7
  title: 'Exploring molecular spectrum in thai patients with maple syrup urine disease: unveiling a common variant'
  findings: []
- reference: DOI:10.12659/aot.939893
  title: Outcomes from a Single Transplant Center of 5 Pediatric Cases of Domino Liver Transplantation from Live Donors with Maple Syrup Urine Disease
  findings: []
- reference: DOI:10.3389/fimmu.2025.1579945
  title: 'Unlocking hope: domino liver transplantation for maple syrup syndrome, a single center experience work carried out at the King Fahad Specialist Hospital'
  findings: []
- reference: DOI:10.3390/ijms26146992
  title: 'Branched-Chain Amino Acids in Parkinson’s Disease: Molecular Mechanisms and Therapeutic Potential'
  findings: []
- reference: DOI:10.3390/nu16183145
  title: The Impact of Diet on Body Composition in a Cohort of Pediatric and Adult Patients with Maple Syrup Urine Disease
  findings: []
- reference: PMID:20301495
  title: Maple Syrup Urine Disease.
  tags:
  - GeneReviews
  findings: []
- reference: PMID:23086801
  title: A novel regulatory defect in the branched-chain α-keto acid dehydrogenase complex due to a mutation in the PPM1K gene causes a mild variant phenotype of maple syrup urine disease.
  findings: []
- reference: PMID:31559730
  title: Treatment of maple syrup urine disease with high flow hemodialysis in a neonate.
  findings: []
- reference: PMID:32491705
  title: Maple Syrup Urine Disease.
  findings: []
- reference: PMID:36550798
  title: Neonatal maple syrup urine disease case report and literature review.
  findings: []

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References & Deep Research

References

DOI:10.1002/jmd2.12419

Computational structural genomics and clinical evidence suggest <scp>BCKDK</scp> gain‐of‐function may cause a potentially asymptomatic maple syrup urine disease phenotype