2-Methylbutyryl-CoA Dehydrogenase Deficiency

Mendelian MONDO:0012392 Pathograph 32 Organic Acidemia Inborn Error of Metabolism

2-Methylbutyryl-CoA dehydrogenase deficiency (SBCADD) is an autosomal recessive inborn error of L-isoleucine metabolism caused by biallelic pathogenic variants in the ACADSB gene encoding short/branched-chain acyl-CoA dehydrogenase (SBCAD). The metabolic block in the proximal isoleucine oxidation pathway leads to accumulation of diagnostic metabolites including elevated C5-acylcarnitine (2-methylbutyrylcarnitine) in blood and 2-methylbutyrylglycine (2-MBG) in urine. Most individuals identified through newborn screening remain asymptomatic, but approximately 10% of reported patients develop clinical manifestations including seizures, developmental delay, hypotonia, and failure to thrive. The condition is particularly prevalent in the Hmong population due to a founder mutation (c.1165A>G). Carnitine supplementation and avoidance of catabolic stress are the mainstays of management.

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6
Pathophys.
11
Phenotypes
32
Pathograph
2
Genes
7
Treatments
34
References
2
Deep Research
⚙

Pathophysiology

6
ACADSB molecular function deficiency
Biallelic ACADSB pathogenic variants reduce short/branched-chain acyl-CoA dehydrogenase catalytic activity in mitochondria.
ACADSB link
acyl-CoA dehydrogenase activity link
mitochondrion link
Downstream
Impaired isoleucine catabolism via SBCAD loss-of-function Reduced SBCAD function blocks proximal S-pathway oxidation of 2-methylbutyryl-CoA.
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"2-methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of L-isoleucine metabolism. "
Directly supports primary SBCAD/ACADSB molecular dysfunction in this disorder.
Impaired isoleucine catabolism via SBCAD loss-of-function
Loss-of-function variants reduce SBCAD enzyme activity and stability, blocking this catabolic step and causing accumulation of upstream metabolites that are diverted to measurable conjugates including C5-acylcarnitine (blood) and 2-methylbutyrylglycine (urine).
isoleucine catabolic process link branched-chain amino acid catabolic process link
Downstream
Metabolic rerouting via the R-pathway of isoleucine oxidation Accumulating S-pathway intermediates are diverted into the alternative R-pathway of isoleucine oxidation.
ACAD substrate promiscuity and compensatory enzymology SBCAD loss engages pre-existing alternative and overlapping dehydrogenase activities, connecting the primary isoleucine catabolic block to the broader ACAD compensation branch.
Stress-sensitive metabolic decompensation The isoleucine oxidation defect can become clinically relevant during catabolic stress in susceptible patients.
C5-acylcarnitine (2-methylbutyrylcarnitine) Accumulated 2-methylbutyryl-CoA is conjugated to carnitine, producing elevated C5-acylcarnitine.
Elevated C5-acylcarnitine on newborn screening The elevated C5-acylcarnitine biochemical signature is detected on tandem mass spectrometry newborn screening.
2-Methylbutyrylglycine (2-MBG) in urine Upstream isoleucine-derived metabolites are conjugated to glycine and excreted as urinary 2-MBG.
2-Methylbutyrylglycinuria Increased urinary 2-MBG manifests clinically as 2-methylbutyrylglycinuria.
2-MBG-mediated neural oxidative stress Accumulated 2-MBG can induce lipid oxidative damage and reduce antioxidant defenses in brain-relevant preparations.
Show evidence (1 reference)
PMID:15615815 SUPPORT Human Clinical
"Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation. "
Confirms that SBCADD is a defect in the proximal pathway of L-isoleucine oxidation with 2-MBG as hallmark metabolite.
Metabolic rerouting via the R-pathway of isoleucine oxidation
The metabolic block in the S-pathway of isoleucine oxidation leads to increased flux through the normally minor R-pathway, producing 2-ethylhydracrylic acid (2-EHA) as a prominent urinary marker. This R-pathway flux may function as a compensatory safety valve that mitigates severity in many individuals, explaining the largely benign phenotype observed in most SBCADD patients.
isoleucine catabolic process link
mitochondrion link
Downstream
2-Ethylhydracrylic acid (2-EHA) in urine Increased R-pathway flux produces urinary 2-ethylhydracrylic acid as a diagnostic metabolite.
Largely asymptomatic course R-pathway overflow handling may mitigate severity and contribute to the largely asymptomatic course in most patients.
Show evidence (2 references)
PMID:15615815 SUPPORT Human Clinical
"Increased flux through the R-pathway may act as a safety valve for overflow of accumulating S-pathway metabolites and thereby mitigate the severity of SBCADD. "
Directly supports the hypothesis that R-pathway flux compensates for the S-pathway block and explains the mild phenotype.
PMID:15615815 SUPPORT Human Clinical
"Approximately 40-46% of total 2-methylbutyric acid conjugates were in the form of the R-isomer, indicating significant metabolism via the R-pathway. "
Quantifies the significant contribution of R-pathway metabolism in SBCADD patients.
2-MBG-mediated neural oxidative stress
The accumulating glycine conjugate 2-methylbutyrylglycine can increase lipid oxidation and reduce nonenzymatic antioxidant defenses in rat cerebral cortex preparations and C6 glioma cells, providing a plausible mechanism for neurologic vulnerability in the symptomatic minority.
glial cell link
response to oxidative stress link lipid oxidation link ↑ INCREASED
Downstream
Developmental delay 2-MBG-associated oxidative brain stress provides a plausible mechanistic branch for developmental delay in symptomatic SBCADD.
Seizures Neural oxidative stress is a plausible contributor to seizures in the symptomatic minority.
Muscular hypotonia 2-MBG-associated brain oxidative stress provides a plausible mechanism for hypotonia in symptomatic SBCADD.
Microcephaly Longitudinal neurodevelopmental complications can include microcephaly.
Autism Longitudinal neurodevelopmental complications can include autism.
Dyskinetic cerebral palsy Severe neurologic injury in early reported patients included athetoid cerebral palsy.
Skeletal muscle atrophy Severe motor developmental delay in early SBCADD cases included muscle atrophy.
Show evidence (2 references)
PMID:22967964 SUPPORT In Vitro
"2MBG induced sulfhydryl oxidation in cortical supernatants and decreased glutathione (GSH) in these brain preparations, as well as in C6 cells"
In vitro rat brain preparation and glial cell evidence supports oxidative stress and antioxidant depletion from 2-MBG.
PMID:22967964 SUPPORT In Vitro
"oxidative stress induced by 2MBG is involved, at least in part, in the pathophysiology of the brain damage found in SBCAD deficiency."
Authors interpret the 2-MBG oxidative-stress findings as relevant to SBCAD-related brain damage.
Stress-sensitive metabolic decompensation
Overlapping substrate specificity among ACAD family enzymes may compensate for SBCAD deficiency under normal conditions. During catabolic stress (infection, fasting), this compensatory capacity may be exceeded, leading to metabolic decompensation in a minority of patients. This stress-sensitive model explains why most patients remain asymptomatic but a small fraction develop clinical disease.
response to starvation link
Downstream
Failure to thrive Symptomatic SBCADD onset during metabolic vulnerability can include failure to thrive.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Catabolic situations can precipitate acute metabolic decompensation. "
Directly supports that catabolic stress triggers decompensation in SBCADD.
ACAD substrate promiscuity and compensatory enzymology
ACAD family enzymes display significant substrate promiscuity. In HEK-293 cell models, ACADSB knockout causes marked increases in C5-carnitine and substantial decreases in C3-carnitine, demonstrating that SBCAD activity influences short-chain acyl-CoA and acylcarnitine pools beyond a single metabolite. This promiscuity partially explains why complete SBCAD loss-of-function has limited clinical consequences in most individuals.
fatty acid beta-oxidation link
mitochondrion link
Downstream
C3-carnitine (propionylcarnitine) in ACADSB knockout cells ACADSB loss in HEK-293 cells changes broader acylcarnitine pools, including decreased C3-carnitine.
Largely asymptomatic course ACAD substrate overlap and compensatory enzymology help explain why SBCAD deficiency often remains a biochemical phenotype with limited clinical consequences.
Show evidence (1 reference)
PMID:37309295 SUPPORT Other
"Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences. "
Background statement in a mechanistic paper characterizes SBCAD deficiency as largely a biochemical abnormality.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for 2-Methylbutyryl-CoA Dehydrogenase Deficiency Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

11
Genitourinary 1
2-Methylbutyrylglycinuria VERY_FREQUENT Organic aciduria (HP:0001992)
Show evidence (2 references)
PMID:30730842 SUPPORT Human Clinical
"Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency. "
Directly identifies elevated urinary 2-MBG as the hallmark of SBCADD.
PMID:31555323 SUPPORT Human Clinical
"All patients who underwent urinary organic acid analysis showed elevation of 2-methylburtyrylglycine in urine. "
Confirms universal 2-MBG elevation in confirmed SBCADD patients.
Head and Neck 1
Microcephaly VERY_RARE Microcephaly (HP:0000252)
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop. "
Microcephaly listed as a feature that can develop on longitudinal follow-up.
Metabolism 1
Elevated C5-acylcarnitine on newborn screening VERY_FREQUENT Elevated circulating acylcarnitine concentration (HP:0045045)
Musculoskeletal 2
Muscular hypotonia OCCASIONAL Hypotonia (HP:0001252)
Show evidence (2 references)
PMID:12837870 SUPPORT Human Clinical
"Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age. "
Reports mild muscle hypotonia in one of the newborn-screening- identified Hmong patients.
PMID:30730842 SUPPORT Human Clinical
"Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. "
Hypotonia listed among presenting features in the literature review.
Skeletal muscle atrophy VERY_RARE Skeletal muscle atrophy (HP:0003202)
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy. "
Directly reports muscle atrophy in an early SBCADD patient.
Nervous System 4
Developmental delay OCCASIONAL Global developmental delay (HP:0001263)
Show evidence (2 references)
PMID:12837870 SUPPORT Human Clinical
"One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy. "
Two of the earliest described patients showed motor developmental delay or cerebral palsy.
PMID:30730842 SUPPORT Human Clinical
"Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. "
Literature review confirms developmental delay as a recognized phenotype of symptomatic SBCADD.
Seizures OCCASIONAL Seizure (HP:0001250)
Show evidence (2 references)
PMID:30730842 SUPPORT Human Clinical
"Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. "
Seizures listed as a recognized presenting feature of symptomatic SBCADD.
PMID:30730842 SUPPORT Human Clinical
"On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop. "
Epilepsy can develop on longitudinal follow-up in symptomatic cases.
Autism VERY_RARE Autism (HP:0000717)
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop. "
Autism listed among features that can develop on longitudinal follow-up in SBCADD.
Dyskinetic cerebral palsy VERY_RARE Choreoathetosis (HP:0001266)
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy. "
Directly reports athetoid cerebral palsy in one of the first described SBCADD patients.
Growth 1
Failure to thrive OCCASIONAL Failure to thrive (HP:0001508)
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive. "
Failure to thrive listed among presenting features in the literature review of 162 patients.
Other 1
Largely asymptomatic course VERY_FREQUENT
Many individuals are identified through newborn screening and remain well without treatment on long-term follow-up.
Show evidence (2 references)
PMID:30730842 SUPPORT Human Clinical
"Based on our experience and the literature review (162 patients), SBCAD deficiency is symptomatic in about 10% of reported patients. "
Quantifies the largely asymptomatic nature of SBCADD in the largest literature review.
PMID:20547083 SUPPORT Human Clinical
"Our patients have been well without treatment and call for careful follow-up studies to learn the true clinical impact of this disorder. "
Confirms asymptomatic status of non-Hmong patients identified by newborn screening.
🧬

Genetic Associations

2
ACADSB pathogenic variants
Autosomal recessive
Show evidence (2 references)
PMID:20547083 SUPPORT Human Clinical
"Short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency, also known as 2-methylbutyryl-CoA dehydrogenase deficiency, is a recently described autosomal recessive disorder of isoleucine metabolism. Most patients reported thus far have originated from a founder mutation in the Hmong Chinese..."
Confirms the genetic basis and founder mutation background of SBCADD.
PMID:16950638 SUPPORT Other
"Confirmation of diagnosis is therefore advisable by specific enzyme assay and/or mutation analysis of the ACAT1 (beta-KT), ACADSB (SBCAD) or HADH2 (MHBD) genes. "
Confirms ACADSB as the gene for molecular diagnosis of SBCADD.
ACADSB (Pathogenic Variants)
Show evidence (1 reference)
CGGV:assertion_8bfa3857-c96c-40ac-b4c1-2cf04fd4eb4f-2019-03-22T160000.000Z SUPPORT Other
"ACADSB | HGNC:91 | 2-methylbutyryl-CoA dehydrogenase deficiency | MONDO:0012392 | AR | Definitive"
ClinGen classifies the ACADSB-2-methylbutyryl-CoA dehydrogenase deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
💊

Treatments

7
Carnitine supplementation
Action: carnitine supplementation MAXO:0010006
L-carnitine supplementation (typically 50-100 mg/kg/day) is used to support conjugation and excretion of accumulating acyl-CoA intermediates as acylcarnitine species. Carnitine supplementation is one of the most consistently recommended interventions in SBCADD management.
Mechanism Target:
MODULATES Impaired isoleucine catabolism via SBCAD loss-of-function — Carnitine supplementation supports conjugation and biochemical management of accumulated acyl-CoA intermediates without correcting the enzyme defect.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Carnitine supplementation and valproate avoidance appear to be indicated."
Review recommends carnitine supplementation in SBCADD management.
Show evidence (2 references)
PMID:30730842 SUPPORT Human Clinical
"Carnitine supplementation and valproate avoidance appear to be indicated. "
Directly recommends carnitine supplementation as an indicated treatment for SBCADD.
PMID:30730842 SUPPORT Human Clinical
"Longitudinal biochemical monitoring of the two patients while on treatment with carnitine (100 mg/kg/day) was provided. "
Reports specific carnitine dosing of 100 mg/kg/day with biochemical monitoring.
Catabolic stress avoidance and emergency protocol
Action: supportive care MAXO:0000950
Prevention of metabolic decompensation through avoidance of prolonged fasting, protein overload, and provision of an emergency protocol for management of intercurrent febrile illnesses and acute catabolic episodes.
Mechanism Target:
INHIBITS Stress-sensitive metabolic decompensation — Fasting avoidance and emergency protocols aim to prevent acute catabolic episodes that precipitate decompensation.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency."
Emergency protocols directly target acute catabolic episodes in SBCADD.
Show evidence (2 references)
PMID:30730842 SUPPORT Human Clinical
"Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency. "
Directly supports emergency protocol provision for catabolic stress management.
PMID:30730842 SUPPORT Human Clinical
"Catabolic situations can precipitate acute metabolic decompensation. "
Supports the rationale for catabolic stress avoidance.
Dietary management
Action: dietary intervention MAXO:0000088
Dietary intervention in SBCADD is controversial. Early-identified cases historically received low-protein diets with fasting avoidance, but the indication for disruptive dietary manipulations in asymptomatic newborn-screening-identified infants is questionable. Current practice favors maintaining a normal diet with vigilance during intercurrent illness rather than protein restriction.
Mechanism Target:
MODULATES Stress-sensitive metabolic decompensation — Dietary management historically aimed to reduce metabolic stress, although long-term efficacy is uncertain.
Show evidence (1 reference)
PMID:12837870 PARTIAL Human Clinical
"The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established."
Early dietary management was used presymptomatically, but long-term efficacy remains uncertain.
Show evidence (2 references)
PMID:12837870 SUPPORT Human Clinical
"Dietary treatment was initiated in the neonatal period. Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age. "
Reports early dietary treatment in newborn-screening-identified Hmong patients with good short-term outcomes.
PMID:12837870 PARTIAL Human Clinical
"The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established. "
Notes that long-term efficacy of presymptomatic dietary treatment is unproven.
Valproate avoidance
Action: Pharmacotherapy NCIT:C15986
Valproate should be avoided in SBCADD patients because valproyl-CoA can serve as a substrate of SBCAD, and valproate administration may exacerbate the metabolic block.
Mechanism Target:
INHIBITS Stress-sensitive metabolic decompensation — Valproate avoidance reduces iatrogenic risk of acute metabolic instability in a disorder managed around catabolic vulnerability.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Carnitine supplementation and valproate avoidance appear to be indicated."
Review recommends valproate avoidance in SBCADD management, consistent with preventing treatment-triggered metabolic decompensation.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Carnitine supplementation and valproate avoidance appear to be indicated. "
Directly recommends valproate avoidance as an indicated measure in SBCADD management.
Newborn screening via tandem mass spectrometry
Action: disease screening MAXO:0000124
SBCADD is detectable by expanded newborn screening using tandem mass spectrometry. Elevated C5-acylcarnitine triggers follow-up testing including urine organic acids and acylglycine analysis, followed by molecular confirmation of ACADSB variants.
Target Phenotypes: Elevated circulating acylcarnitine concentration ↗
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"These cases suggest that SBCAD deficiency is another inborn error of metabolism detectable by newborn screening using tandem mass spectrometry. "
Establishes that SBCADD is detectable by tandem MS newborn screening.
Genetic counseling
Action: genetic counseling MAXO:0000079
Genetic counseling for affected families regarding autosomal recessive inheritance, carrier testing, recurrence risk (25%), and options for prenatal diagnosis. Particularly relevant in the Hmong community where the carrier frequency exceeds 20%.
Mechanism Target:
MODULATES ACADSB molecular function deficiency — Counseling addresses the autosomal recessive ACADSB cause, recurrence risk, and prenatal testing rather than directly modifying metabolism.
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment."
Prenatal diagnosis in an affected family supports genetics-informed counseling and recurrence-risk management.
Show evidence (1 reference)
PMID:12837870 SUPPORT Human Clinical
"A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment. "
Demonstrates prenatal diagnosis has been applied in SBCADD families, supporting the role of genetic counseling.
Longitudinal monitoring
Action: supportive care MAXO:0000950
Long-term clinical and biochemical follow-up is recommended for all individuals with confirmed SBCADD, even those who are asymptomatic, to monitor for late-onset neurological or developmental complications and to assess the natural history of the condition.
Target Phenotypes: Seizure ↗ Global developmental delay ↗ Microcephaly ↗ Autism ↗
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Longitudinal follow-up is recommended. "
Directly recommends longitudinal follow-up in SBCADD.
🔬

Biochemical Markers

4
C5-acylcarnitine (2-methylbutyrylcarnitine) (INCREASED)
Context: Elevated C5-acylcarnitine in blood is the primary newborn screening marker for SBCADD. C5 is isobaric with isovalerylcarnitine on standard tandem mass spectrometry, requiring second-tier testing to distinguish SBCADD from isovaleric acidemia.
Pathograph Readouts
Readout Of Impaired isoleucine catabolism via SBCAD loss-of-function Positive Diagnostic
Elevated C5-acylcarnitine reports the upstream SBCAD-dependent isoleucine catabolic block.
Show evidence (1 reference)
PMID:31555323 SUPPORT Human Clinical
"all patients showed slightly or moderately elevated C5-carnitine concentrations"
Newborn-screening cohort supports elevated C5-carnitine as the screening readout of SBCADD.
2-Methylbutyrylglycine (2-MBG) in urine (INCREASED)
Context: Elevated urinary 2-methylbutyrylglycine is the diagnostic hallmark of SBCADD. Detection of 2-MBG by urine organic acid analysis or acylglycine profiling confirms the diagnosis after elevated C5 is found on newborn screening.
Pathograph Readouts
Readout Of Impaired isoleucine catabolism via SBCAD loss-of-function Positive Diagnostic
Urinary 2-MBG reports the isoleucine S-pathway block and upstream 2-methylbutyryl-CoA-derived metabolite accumulation.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency."
Literature review identifies urinary 2-MBG as the hallmark diagnostic readout.
Show evidence (1 reference)
PMID:30730842 SUPPORT Human Clinical
"Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency. "
Confirms 2-MBG elevation as the hallmark in the 2019 literature review.
2-Ethylhydracrylic acid (2-EHA) in urine (INCREASED)
Context: 2-Ethylhydracrylic acid is a urinary organic acid marker of SBCADD, produced by increased flux through the R-pathway of isoleucine oxidation. The 2-EHA peak often exceeds the 2-MBG peak on organic acid analysis and may facilitate diagnosis.
Pathograph Readouts
Readout Of Metabolic rerouting via the R-pathway of isoleucine oxidation Positive Diagnostic
Urinary 2-EHA reports increased R-pathway flux downstream of the S-pathway SBCAD block.
Show evidence (1 reference)
PMID:15615815 SUPPORT Human Clinical
"In multiple urine samples, organic acid analysis revealed a prominent 2-EHA peak usually exceeding the size of the 2-MBG peak."
Patient urine organic acid analysis directly supports 2-EHA as a readout of R-pathway rerouting.
Show evidence (2 references)
PMID:15615815 SUPPORT Human Clinical
"In multiple urine samples, organic acid analysis revealed a prominent 2-EHA peak usually exceeding the size of the 2-MBG peak. "
Demonstrates that 2-EHA is a prominent urinary marker in SBCADD, often exceeding 2-MBG levels.
PMID:15615815 SUPPORT Human Clinical
"Awareness of 2-ethylhydracrylic aciduria as a diagnostic marker could lead to increased detection of SBCADD and improved definition of its clinical phenotype. "
Supports diagnostic utility of 2-EHA for SBCADD detection.
C3-carnitine (propionylcarnitine) in ACADSB knockout cells (DECREASED)
Context: In cell models of SBCAD deficiency, C3-carnitine is substantially decreased, reflecting the broader impact of SBCAD on mitochondrial acyl-CoA handling beyond the direct isoleucine pathway metabolites. This is an in vitro observation and not a standard clinical biomarker.
Pathograph Readouts
Readout Of ACAD substrate promiscuity and compensatory enzymology Negative Pharmacodynamic
Decreased C3-carnitine reports broader ACADSB-dependent acylcarnitine remodeling in knockout cells.
Show evidence (1 reference)
PMID:37309295 SUPPORT In Vitro
"deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells."
ACADSB knockout cell data support decreased C3-carnitine as an in vitro readout of broader ACAD substrate handling.
Show evidence (1 reference)
PMID:37309295 SUPPORT In Vitro
"deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells. "
ACADSB knockout in HEK-293 cells causes substantial C3-carnitine decrease, demonstrating broader metabolic impact.
{ }

Source YAML

click to show 
name: 2-Methylbutyryl-CoA Dehydrogenase Deficiency
category: Mendelian
creation_date: '2026-02-23T00:00:00Z'
updated_date: '2026-05-18T15:13:54Z'
synonyms:
- Short/branched-chain acyl-CoA dehydrogenase deficiency
- SBCADD
- SBCAD deficiency
- 2-methylbutyrylglycinuria
- 2-MBCDD
- 2-methylbutyryl-CoA dehydrogenase deficiency
description: '2-Methylbutyryl-CoA dehydrogenase deficiency (SBCADD) is an autosomal recessive inborn error of L-isoleucine metabolism caused by biallelic pathogenic variants in the ACADSB gene encoding short/branched-chain acyl-CoA dehydrogenase (SBCAD). The metabolic block in the proximal isoleucine oxidation pathway leads to accumulation of diagnostic metabolites including elevated C5-acylcarnitine (2-methylbutyrylcarnitine) in blood and 2-methylbutyrylglycine (2-MBG) in urine. Most individuals identified through newborn screening remain asymptomatic, but approximately 10% of reported patients develop clinical manifestations including seizures, developmental delay, hypotonia, and failure to thrive. The condition is particularly prevalent in the Hmong population due to a founder mutation (c.1165A>G). Carnitine supplementation and avoidance of catabolic stress are the mainstays of management.

  '
disease_term:
  preferred_term: 2-methylbutyryl-CoA dehydrogenase deficiency
  term:
    id: MONDO:0012392
    label: 2-methylbutyryl-CoA dehydrogenase deficiency
parents:
- Organic Acidemia
- Inborn Error of Metabolism
prevalence:
- population: Hmong (Wisconsin, USA)
  percentage: 1.3
  notes: 'Prevalence of homozygosity for the founder c.1165A>G mutation is approximately 1.3% (1 in 77) in the Hmong population, with a carrier frequency of 21.8%.

    '
- population: Newborns, Huaihua, China
  notes: 'Incidence 1 in 7,137 in a 206,977-newborn screening cohort in Huaihua, China (2015-2021), the most common IEM in that cohort.

    '
  evidence:
  - reference: PMID:38784038
    reference_title: "206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in Huaihua, China."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'The two most common disorders were 2-methylbutyryl glycinuria (1:7,137) and phenylalanine hydroxylase deficiency (1:22,997).

      '
    explanation: 'Reports SBCADD incidence of 1:7,137 in the Huaihua NBS cohort.

      '
- population: Newborns, Quanzhou, China
  notes: 'Estimated incidence of 1 in 30,379 based on NBS ascertainment in Quanzhou, China.

    '
  evidence:
  - reference: PMID:31555323
    reference_title: "Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'The estimated incidence of SBCADD was 1 in 30,379 in Quanzhou, China.

      '
    explanation: 'Provides incidence estimate from the Quanzhou NBS cohort.

      '
progression:
- phase: Neonatal/early detection
  notes: 'Most individuals are identified through newborn screening via elevated C5-acylcarnitine. The majority remain asymptomatic throughout life. Approximately 10% develop symptoms, typically in the neonatal period or during intercurrent illness. Compensation via alternative ACAD enzymes and the R-pathway of isoleucine oxidation may mask biochemical consequences at baseline, but this compensation can fail during metabolic stress (infection, fasting), leading to sporadic decompensation in susceptible individuals.

    '
pathophysiology:
- name: ACADSB molecular function deficiency
  description: 'Biallelic ACADSB pathogenic variants reduce short/branched-chain acyl-CoA dehydrogenase catalytic activity in mitochondria.

    '
  genes:
  - preferred_term: ACADSB
    term:
      id: hgnc:91
      label: ACADSB
  molecular_functions:
  - preferred_term: acyl-CoA dehydrogenase activity
    term:
      id: GO:0003995
      label: acyl-CoA dehydrogenase activity
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: '2-methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of L-isoleucine metabolism.

      '
    explanation: 'Directly supports primary SBCAD/ACADSB molecular dysfunction in this disorder.

      '
  downstream:
  - target: Impaired isoleucine catabolism via SBCAD loss-of-function
    description: Reduced SBCAD function blocks proximal S-pathway oxidation of 2-methylbutyryl-CoA.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation."
      explanation: Human patient biochemical study directly identifies SBCADD as a proximal L-isoleucine oxidation defect.
- name: Impaired isoleucine catabolism via SBCAD loss-of-function
  description: 'Loss-of-function variants reduce SBCAD enzyme activity and stability, blocking this catabolic step and causing accumulation of upstream metabolites that are diverted to measurable conjugates including C5-acylcarnitine (blood) and 2-methylbutyrylglycine (urine).

    '
  biological_processes:
  - preferred_term: isoleucine catabolic process
    term:
      id: GO:0006550
      label: L-isoleucine catabolic process
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  chemical_entities:
  - preferred_term: 2-methylbutyrylcarnitine
    term:
      id: CHEBI:73026
      label: 2-methylbutyrylcarnitine
    modifier: INCREASED
  - preferred_term: 2-ethylhydracrylic acid
    term:
      id: CHEBI:82956
      label: 2-ethylhydracrylic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:15615815
    reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation.

      '
    explanation: 'Confirms that SBCADD is a defect in the proximal pathway of L-isoleucine oxidation with 2-MBG as hallmark metabolite.

      '
  downstream:
  - target: Metabolic rerouting via the R-pathway of isoleucine oxidation
    description: Accumulating S-pathway intermediates are diverted into the alternative R-pathway of isoleucine oxidation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - accumulation of 2-methylbutyryl-CoA-derived metabolites
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Increased flux through the R-pathway may act as a safety valve for overflow of accumulating S-pathway metabolites and thereby mitigate the severity of SBCADD."
      explanation: Patient metabolite study supports diversion through the R-pathway as overflow handling for the S-pathway block.
  - target: ACAD substrate promiscuity and compensatory enzymology
    description: >
      SBCAD loss engages pre-existing alternative and overlapping dehydrogenase
      activities, connecting the primary isoleucine catabolic block to the
      broader ACAD compensation branch.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - S-pathway substrate overflow after SBCAD loss
    - alternative enzyme activity in R-pathway metabolism
    - engagement of pre-existing overlapping ACAD substrate handling in cell models
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Our observation of 2-ethylhydracrylic aciduria in SBCADD implies that a different or alternative enzyme serves this function."
      explanation: Human urine metabolite data support alternative enzyme activity downstream of the SBCAD block.
    - reference: PMID:37309295
      reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
      supports: PARTIAL
      evidence_source: IN_VITRO
      snippet: "SBCAD was not the sole ACAD responsible for this compensation, which indicates substantial promiscuity of ACADs in HEK-293 cells for the isobutyryl-CoA substrate."
      explanation: >
        ACADSB-loss cell data support the broader ACAD compensation concept,
        while the PARTIAL classification reflects that this compensation is
        clearer for the related isobutyryl-CoA substrate than for the primary
        2-methylbutyryl-CoA lesion in HEK-293 cells.
  - target: Stress-sensitive metabolic decompensation
    description: The isoleucine oxidation defect can become clinically relevant during catabolic stress in susceptible patients.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Catabolic situations can precipitate acute metabolic decompensation."
      explanation: Literature review directly supports catabolic stress as a precipitant of metabolic decompensation in SBCADD.
  - target: C5-acylcarnitine (2-methylbutyrylcarnitine)
    description: Accumulated 2-methylbutyryl-CoA is conjugated to carnitine, producing elevated C5-acylcarnitine.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "leads to C5-carnitine (i.e. isovalerylcarnitine, 2methylbutyrilcarnitine, or pivaloylcarnitine) elevation"
      explanation: Review directly identifies elevated C5-carnitine as a biochemical consequence of SBCAD deficiency.
  - target: Elevated C5-acylcarnitine on newborn screening
    description: The elevated C5-acylcarnitine biochemical signature is detected on tandem mass spectrometry newborn screening.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31555323
      reference_title: "Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "all patients showed slightly or moderately elevated C5-carnitine concentrations"
      explanation: Newborn-screening cohort supports elevated C5-carnitine as the diagnostic screening phenotype.
  - target: 2-Methylbutyrylglycine (2-MBG) in urine
    description: Upstream isoleucine-derived metabolites are conjugated to glycine and excreted as urinary 2-MBG.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency."
      explanation: Review directly identifies increased urinary 2-MBG as the hallmark biochemical consequence.
  - target: 2-Methylbutyrylglycinuria
    description: Increased urinary 2-MBG manifests clinically as 2-methylbutyrylglycinuria.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency"
      explanation: Patient study supports 2-MBG excretion as the diagnostic organic-acid phenotype.
  - target: 2-MBG-mediated neural oxidative stress
    description: Accumulated 2-MBG can induce lipid oxidative damage and reduce antioxidant defenses in brain-relevant preparations.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - 2-methylbutyrylglycine accumulation
    evidence:
    - reference: PMID:22967964
      reference_title: "2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "2MBG increased thiobarbituric acid-reactive species (TBA-RS), indicating an increase of lipid oxidation."
      explanation: In vitro rat brain and C6 cell experiments support oxidative stress downstream of 2-MBG accumulation.
- name: Metabolic rerouting via the R-pathway of isoleucine oxidation
  description: 'The metabolic block in the S-pathway of isoleucine oxidation leads to increased flux through the normally minor R-pathway, producing 2-ethylhydracrylic acid (2-EHA) as a prominent urinary marker. This R-pathway flux may function as a compensatory safety valve that mitigates severity in many individuals, explaining the largely benign phenotype observed in most SBCADD patients.

    '
  biological_processes:
  - preferred_term: isoleucine catabolic process
    term:
      id: GO:0006550
      label: L-isoleucine catabolic process
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:15615815
    reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Increased flux through the R-pathway may act as a safety valve for overflow of accumulating S-pathway metabolites and thereby mitigate the severity of SBCADD.

      '
    explanation: 'Directly supports the hypothesis that R-pathway flux compensates for the S-pathway block and explains the mild phenotype.

      '
  - reference: PMID:15615815
    reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Approximately 40-46% of total 2-methylbutyric acid conjugates were in the form of the R-isomer, indicating significant metabolism via the R-pathway.

      '
    explanation: 'Quantifies the significant contribution of R-pathway metabolism in SBCADD patients.

      '
  downstream:
  - target: 2-Ethylhydracrylic acid (2-EHA) in urine
    description: Increased R-pathway flux produces urinary 2-ethylhydracrylic acid as a diagnostic metabolite.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In multiple urine samples, organic acid analysis revealed a prominent 2-EHA peak usually exceeding the size of the 2-MBG peak."
      explanation: Patient urine organic acid analysis directly supports 2-EHA elevation downstream of R-pathway rerouting.
  - target: Largely asymptomatic course
    description: R-pathway overflow handling may mitigate severity and contribute to the largely asymptomatic course in most patients.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Increased flux through the R-pathway may act as a safety valve for overflow of accumulating S-pathway metabolites and thereby mitigate the severity of SBCADD."
      explanation: Patient metabolite study supports R-pathway flux as a severity-mitigating mechanism.
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "SBCAD deficiency is symptomatic in about 10% of reported patients."
      explanation: Literature review supports the predominantly asymptomatic clinical course that the R-pathway may help explain.
- name: 2-MBG-mediated neural oxidative stress
  description: >
    The accumulating glycine conjugate 2-methylbutyrylglycine can increase
    lipid oxidation and reduce nonenzymatic antioxidant defenses in rat cerebral
    cortex preparations and C6 glioma cells, providing a plausible mechanism for
    neurologic vulnerability in the symptomatic minority.
  biological_processes:
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  - preferred_term: lipid oxidation
    term:
      id: GO:0034440
      label: lipid oxidation
    modifier: INCREASED
  cell_types:
  - preferred_term: glial cell
    term:
      id: CL:0000125
      label: glial cell
  downstream:
  - target: Developmental delay
    description: 2-MBG-associated oxidative brain stress provides a plausible mechanistic branch for developmental delay in symptomatic SBCADD.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive."
      explanation: Human literature review supports developmental delay among symptomatic SBCADD features; the oxidative-stress node supplies the mechanistic context.
  - target: Seizures
    description: Neural oxidative stress is a plausible contributor to seizures in the symptomatic minority.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive."
      explanation: Human literature review supports seizures among symptomatic SBCADD features; the oxidative-stress node supplies the mechanistic context.
  - target: Muscular hypotonia
    description: 2-MBG-associated brain oxidative stress provides a plausible mechanism for hypotonia in symptomatic SBCADD.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive."
      explanation: Human literature review supports hypotonia among symptomatic SBCADD features; the oxidative-stress node supplies the mechanistic context.
  - target: Microcephaly
    description: Longitudinal neurodevelopmental complications can include microcephaly.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop."
      explanation: Human follow-up data support microcephaly as a longitudinal feature; the oxidative-stress node supplies the mechanistic context.
  - target: Autism
    description: Longitudinal neurodevelopmental complications can include autism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop."
      explanation: Human follow-up data support autism as a longitudinal feature; the oxidative-stress node supplies the mechanistic context.
  - target: Dyskinetic cerebral palsy
    description: Severe neurologic injury in early reported patients included athetoid cerebral palsy.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy."
      explanation: Early patient observations support severe motor neurologic outcomes; the oxidative-stress node supplies the mechanistic context.
  - target: Skeletal muscle atrophy
    description: Severe motor developmental delay in early SBCADD cases included muscle atrophy.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy."
      explanation: Early patient observations support muscle atrophy in a severe motor presentation; the oxidative-stress node supplies the mechanistic context.
  evidence:
  - reference: PMID:22967964
    reference_title: "2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "2MBG induced sulfhydryl oxidation in cortical supernatants and decreased glutathione (GSH) in these brain preparations, as well as in C6 cells"
    explanation: In vitro rat brain preparation and glial cell evidence supports oxidative stress and antioxidant depletion from 2-MBG.
  - reference: PMID:22967964
    reference_title: "2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "oxidative stress induced by 2MBG is involved, at least in part, in the pathophysiology of the brain damage found in SBCAD deficiency."
    explanation: Authors interpret the 2-MBG oxidative-stress findings as relevant to SBCAD-related brain damage.
- name: Stress-sensitive metabolic decompensation
  description: 'Overlapping substrate specificity among ACAD family enzymes may compensate for SBCAD deficiency under normal conditions. During catabolic stress (infection, fasting), this compensatory capacity may be exceeded, leading to metabolic decompensation in a minority of patients. This stress-sensitive model explains why most patients remain asymptomatic but a small fraction develop clinical disease.

    '
  biological_processes:
  - preferred_term: response to starvation
    term:
      id: GO:0042594
      label: response to starvation
  downstream:
  - target: Failure to thrive
    description: Symptomatic SBCADD onset during metabolic vulnerability can include failure to thrive.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive."
      explanation: Literature review lists failure to thrive among symptomatic SBCADD presentations, consistent with decompensation during metabolic vulnerability.
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Catabolic situations can precipitate acute metabolic decompensation.

      '
    explanation: 'Directly supports that catabolic stress triggers decompensation in SBCADD.

      '
- name: ACAD substrate promiscuity and compensatory enzymology
  description: 'ACAD family enzymes display significant substrate promiscuity. In HEK-293 cell models, ACADSB knockout causes marked increases in C5-carnitine and substantial decreases in C3-carnitine, demonstrating that SBCAD activity influences short-chain acyl-CoA and acylcarnitine pools beyond a single metabolite. This promiscuity partially explains why complete SBCAD loss-of-function has limited clinical consequences in most individuals.

    '
  biological_processes:
  - preferred_term: fatty acid beta-oxidation
    term:
      id: GO:0006635
      label: fatty acid beta-oxidation
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:37309295
    reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: 'Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences.

      '
    explanation: 'Background statement in a mechanistic paper characterizes SBCAD deficiency as largely a biochemical abnormality.

      '
  downstream:
  - target: C3-carnitine (propionylcarnitine) in ACADSB knockout cells
    description: ACADSB loss in HEK-293 cells changes broader acylcarnitine pools, including decreased C3-carnitine.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37309295
      reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells."
      explanation: ACADSB knockout cell data directly support decreased C3-carnitine in this in vitro model.
  - target: Largely asymptomatic course
    description: ACAD substrate overlap and compensatory enzymology help explain why SBCAD deficiency often remains a biochemical phenotype with limited clinical consequences.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:37309295
      reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences."
      explanation: Background statement in a mechanistic paper supports limited clinical consequences for SBCAD deficiency.
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "SBCAD deficiency is symptomatic in about 10% of reported patients."
      explanation: Human literature review supports the mostly asymptomatic clinical course.
phenotypes:
- name: Developmental delay
  frequency: OCCASIONAL
  description: 'Motor and cognitive developmental delay is reported in a minority of symptomatic SBCADD patients. One of the earliest reported patients had severe motor developmental delay with muscle atrophy.

    '
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy.

      '
    explanation: 'Two of the earliest described patients showed motor developmental delay or cerebral palsy.

      '
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive.

      '
    explanation: 'Literature review confirms developmental delay as a recognized phenotype of symptomatic SBCADD.

      '
- name: Seizures
  frequency: OCCASIONAL
  description: 'Seizures are reported in symptomatic SBCADD patients, occurring at clinical onset or developing during follow-up. Epilepsy may develop on longitudinal follow-up.

    '
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive.

      '
    explanation: 'Seizures listed as a recognized presenting feature of symptomatic SBCADD.

      '
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop.

      '
    explanation: 'Epilepsy can develop on longitudinal follow-up in symptomatic cases.

      '
- name: Muscular hypotonia
  frequency: OCCASIONAL
  description: 'Hypotonia is a recognized feature of symptomatic SBCADD, reported in both early-onset presentations and in newborn-screening-identified patients.

    '
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age.

      '
    explanation: 'Reports mild muscle hypotonia in one of the newborn-screening- identified Hmong patients.

      '
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive.

      '
    explanation: 'Hypotonia listed among presenting features in the literature review.

      '
- name: Failure to thrive
  frequency: OCCASIONAL
  description: 'Failure to thrive is reported in symptomatic SBCADD patients, likely related to feeding difficulties and recurrent metabolic instability.

    '
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive.

      '
    explanation: 'Failure to thrive listed among presenting features in the literature review of 162 patients.

      '
- name: Microcephaly
  frequency: VERY_RARE
  description: 'Microcephaly has been reported in a minority of SBCADD patients on longitudinal follow-up.

    '
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop.

      '
    explanation: 'Microcephaly listed as a feature that can develop on longitudinal follow-up.

      '
- name: Autism
  frequency: VERY_RARE
  description: 'Autism spectrum disorder has been reported in a minority of SBCADD patients on longitudinal follow-up.

    '
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'On longitudinal follow-up, epilepsy, developmental delay, microcephaly, and autism can develop.

      '
    explanation: 'Autism listed among features that can develop on longitudinal follow-up in SBCADD.

      '
- name: Dyskinetic cerebral palsy
  frequency: VERY_RARE
  description: 'Athetoid cerebral palsy was reported in one of the original patients described with SBCADD.

    '
  phenotype_term:
    preferred_term: Choreoathetosis
    term:
      id: HP:0001266
      label: Choreoathetosis
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy.

      '
    explanation: 'Directly reports athetoid cerebral palsy in one of the first described SBCADD patients.

      '
- name: Skeletal muscle atrophy
  frequency: VERY_RARE
  description: 'Muscle atrophy was reported in one of the original SBCADD patients, associated with severe motor developmental delay.

    '
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'One patient developed athetoid cerebral palsy, and another had severe motor developmental delay with muscle atrophy.

      '
    explanation: 'Directly reports muscle atrophy in an early SBCADD patient.

      '
- name: Elevated C5-acylcarnitine on newborn screening
  frequency: VERY_FREQUENT
  diagnostic: true
  description: 'Elevated C5-acylcarnitine (2-methylbutyrylcarnitine, isobaric with isovalerylcarnitine) on tandem mass spectrometry newborn screening is the primary ascertainment marker for SBCADD.

    '
  phenotype_term:
    preferred_term: Elevated circulating acylcarnitine concentration
    term:
      id: HP:0045045
      label: Elevated circulating acylcarnitine concentration
- name: 2-Methylbutyrylglycinuria
  frequency: VERY_FREQUENT
  diagnostic: true
  description: 'Increased urinary excretion of 2-methylbutyrylglycine is the biochemical hallmark of SBCADD, detected by urine organic acid analysis.

    '
  phenotype_term:
    preferred_term: Organic aciduria
    term:
      id: HP:0001992
      label: Organic aciduria
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency.

      '
    explanation: 'Directly identifies elevated urinary 2-MBG as the hallmark of SBCADD.

      '
  - reference: PMID:31555323
    reference_title: "Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'All patients who underwent urinary organic acid analysis showed elevation of 2-methylburtyrylglycine in urine.

      '
    explanation: 'Confirms universal 2-MBG elevation in confirmed SBCADD patients.

      '
- name: Largely asymptomatic course
  frequency: VERY_FREQUENT
  description: 'The majority of individuals with SBCADD remain clinically asymptomatic. In a literature review of 162 patients, SBCADD was symptomatic in only about 10% of reported patients.

    '
  notes: 'Many individuals are identified through newborn screening and remain well without treatment on long-term follow-up.

    '
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Based on our experience and the literature review (162 patients), SBCAD deficiency is symptomatic in about 10% of reported patients.

      '
    explanation: 'Quantifies the largely asymptomatic nature of SBCADD in the largest literature review.

      '
  - reference: PMID:20547083
    reference_title: "Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Our patients have been well without treatment and call for careful follow-up studies to learn the true clinical impact of this disorder.

      '
    explanation: 'Confirms asymptomatic status of non-Hmong patients identified by newborn screening.

      '
biochemical:
- name: C5-acylcarnitine (2-methylbutyrylcarnitine)
  presence: INCREASED
  context: 'Elevated C5-acylcarnitine in blood is the primary newborn screening marker for SBCADD. C5 is isobaric with isovalerylcarnitine on standard tandem mass spectrometry, requiring second-tier testing to distinguish SBCADD from isovaleric acidemia.

    '
  readouts:
  - target: Impaired isoleucine catabolism via SBCAD loss-of-function
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated C5-acylcarnitine reports the upstream SBCAD-dependent isoleucine catabolic block.
    evidence:
    - reference: PMID:31555323
      reference_title: "Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "all patients showed slightly or moderately elevated C5-carnitine concentrations"
      explanation: Newborn-screening cohort supports elevated C5-carnitine as the screening readout of SBCADD.
- name: 2-Methylbutyrylglycine (2-MBG) in urine
  presence: INCREASED
  context: 'Elevated urinary 2-methylbutyrylglycine is the diagnostic hallmark of SBCADD. Detection of 2-MBG by urine organic acid analysis or acylglycine profiling confirms the diagnosis after elevated C5 is found on newborn screening.

    '
  readouts:
  - target: Impaired isoleucine catabolism via SBCAD loss-of-function
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Urinary 2-MBG reports the isoleucine S-pathway block and upstream 2-methylbutyryl-CoA-derived metabolite accumulation.
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency."
      explanation: Literature review identifies urinary 2-MBG as the hallmark diagnostic readout.
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Increased urinary excretion of 2-methylbutyrylglycine (2MBG) is the hallmark of SBCAD deficiency.

      '
    explanation: 'Confirms 2-MBG elevation as the hallmark in the 2019 literature review.

      '
- name: 2-Ethylhydracrylic acid (2-EHA) in urine
  presence: INCREASED
  context: '2-Ethylhydracrylic acid is a urinary organic acid marker of SBCADD, produced by increased flux through the R-pathway of isoleucine oxidation. The 2-EHA peak often exceeds the 2-MBG peak on organic acid analysis and may facilitate diagnosis.

    '
  readouts:
  - target: Metabolic rerouting via the R-pathway of isoleucine oxidation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Urinary 2-EHA reports increased R-pathway flux downstream of the S-pathway SBCAD block.
    evidence:
    - reference: PMID:15615815
      reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In multiple urine samples, organic acid analysis revealed a prominent 2-EHA peak usually exceeding the size of the 2-MBG peak."
      explanation: Patient urine organic acid analysis directly supports 2-EHA as a readout of R-pathway rerouting.
  evidence:
  - reference: PMID:15615815
    reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'In multiple urine samples, organic acid analysis revealed a prominent 2-EHA peak usually exceeding the size of the 2-MBG peak.

      '
    explanation: 'Demonstrates that 2-EHA is a prominent urinary marker in SBCADD, often exceeding 2-MBG levels.

      '
  - reference: PMID:15615815
    reference_title: "2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Awareness of 2-ethylhydracrylic aciduria as a diagnostic marker could lead to increased detection of SBCADD and improved definition of its clinical phenotype.

      '
    explanation: 'Supports diagnostic utility of 2-EHA for SBCADD detection.

      '
- name: C3-carnitine (propionylcarnitine) in ACADSB knockout cells
  presence: DECREASED
  context: 'In cell models of SBCAD deficiency, C3-carnitine is substantially decreased, reflecting the broader impact of SBCAD on mitochondrial acyl-CoA handling beyond the direct isoleucine pathway metabolites. This is an in vitro observation and not a standard clinical biomarker.

    '
  readouts:
  - target: ACAD substrate promiscuity and compensatory enzymology
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: PHARMACODYNAMIC
    interpretation: Decreased C3-carnitine reports broader ACADSB-dependent acylcarnitine remodeling in knockout cells.
    evidence:
    - reference: PMID:37309295
      reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells."
      explanation: ACADSB knockout cell data support decreased C3-carnitine as an in vitro readout of broader ACAD substrate handling.
  evidence:
  - reference: PMID:37309295
    reference_title: "Acyl-CoA dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: 'deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells.

      '
    explanation: 'ACADSB knockout in HEK-293 cells causes substantial C3-carnitine decrease, demonstrating broader metabolic impact.

      '
genetic:
- name: ACADSB pathogenic variants
  gene_term:
    preferred_term: ACADSB
    term:
      id: hgnc:91
      label: ACADSB
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: '2-methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of L-isoleucine metabolism.

        '
      explanation: 'Directly states autosomal recessive inheritance for SBCADD.

        '
  variants:
  - name: c.1165A>G (exon 10 skipping) - founder variant
    description: 'The c.1165A>G variant in ACADSB causes skipping of exon 10 and is a founder mutation highly prevalent in the Hmong population and in several Chinese ethnic minority groups (Miao, Dong). Homozygosity for this variant is found at a frequency of approximately 1.3% in the Hmong population, with a carrier frequency of 21.8%.

      '
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 'Molecular genetic analysis performed for 3 of these patients revealed that all are homozygous for an 1165A>G mutation that causes skipping of exon 10 of the SBCAD gene.

        '
      explanation: 'Identifies the c.1165A>G founder mutation and its effect on exon 10 splicing.

        '
  - name: Multiple non-Hmong ACADSB missense variants
    description: 'Multiple missense variants in ACADSB have been identified in non-Hmong patients through newborn screening. Expression studies show these variants lead to inactivation or instability of the mutant SBCAD enzymes. At least 15 pathogenic variants are known in ACADSB.

      '
    evidence:
    - reference: PMID:20547083
      reference_title: "Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: 'Escherichia coli expression studies revealed that the missense mutations identified lead to inactivation or instability of the mutant SBCAD enzymes.

        '
      explanation: 'Confirms functional impact of non-Hmong ACADSB variants through in vitro expression studies.

        '
  features: 'SBCADD is caused by biallelic pathogenic variants in ACADSB (chromosome 10q26.13, 11 exons), encoding short/branched-chain acyl-CoA dehydrogenase (SBCAD), a homotetrameric mitochondrial FAD-containing enzyme. The c.1165A>G founder variant is dominant in the Hmong and certain Chinese ethnic minorities, while diverse missense and truncating variants are found in other populations. Genotype-phenotype correlations remain uncertain, as most homozygous individuals remain asymptomatic regardless of variant type.

    '
  evidence:
  - reference: PMID:20547083
    reference_title: "Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency, also known as 2-methylbutyryl-CoA dehydrogenase deficiency, is a recently described autosomal recessive disorder of isoleucine metabolism. Most patients reported thus far have originated from a founder mutation in the Hmong Chinese population.

      '
    explanation: 'Confirms the genetic basis and founder mutation background of SBCADD.

      '
  - reference: PMID:16950638
    reference_title: "Inborn errors of isoleucine degradation: a review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: 'Confirmation of diagnosis is therefore advisable by specific enzyme assay and/or mutation analysis of the ACAT1 (beta-KT), ACADSB (SBCAD) or HADH2 (MHBD) genes.

      '
    explanation: 'Confirms ACADSB as the gene for molecular diagnosis of SBCADD.

      '
- name: ACADSB
  gene_term:
    preferred_term: ACADSB
    term:
      id: hgnc:91
      label: ACADSB
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_8bfa3857-c96c-40ac-b4c1-2cf04fd4eb4f-2019-03-22T160000.000Z
    reference_title: "ACADSB / 2-methylbutyryl-CoA dehydrogenase deficiency (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ACADSB | HGNC:91 | 2-methylbutyryl-CoA dehydrogenase deficiency | MONDO:0012392 | AR | Definitive"
    explanation: ClinGen classifies the ACADSB-2-methylbutyryl-CoA dehydrogenase deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: Carnitine supplementation
  description: 'L-carnitine supplementation (typically 50-100 mg/kg/day) is used to support conjugation and excretion of accumulating acyl-CoA intermediates as acylcarnitine species. Carnitine supplementation is one of the most consistently recommended interventions in SBCADD management.

    '
  treatment_term:
    preferred_term: carnitine supplementation
    term:
      id: MAXO:0010006
      label: carnitine supplementation
  target_mechanisms:
  - target: Impaired isoleucine catabolism via SBCAD loss-of-function
    treatment_effect: MODULATES
    description: Carnitine supplementation supports conjugation and biochemical management of accumulated acyl-CoA intermediates without correcting the enzyme defect.
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Carnitine supplementation and valproate avoidance appear to be indicated."
      explanation: Review recommends carnitine supplementation in SBCADD management.
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Carnitine supplementation and valproate avoidance appear to be indicated.

      '
    explanation: 'Directly recommends carnitine supplementation as an indicated treatment for SBCADD.

      '
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Longitudinal biochemical monitoring of the two patients while on treatment with carnitine (100 mg/kg/day) was provided.

      '
    explanation: 'Reports specific carnitine dosing of 100 mg/kg/day with biochemical monitoring.

      '
- name: Catabolic stress avoidance and emergency protocol
  description: 'Prevention of metabolic decompensation through avoidance of prolonged fasting, protein overload, and provision of an emergency protocol for management of intercurrent febrile illnesses and acute catabolic episodes.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_mechanisms:
  - target: Stress-sensitive metabolic decompensation
    treatment_effect: INHIBITS
    description: Fasting avoidance and emergency protocols aim to prevent acute catabolic episodes that precipitate decompensation.
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency."
      explanation: Emergency protocols directly target acute catabolic episodes in SBCADD.
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Providing an emergency protocol for the management of acute catabolic episodes seems reasonable in asymptomatic patients with SBCAD deficiency.

      '
    explanation: 'Directly supports emergency protocol provision for catabolic stress management.

      '
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Catabolic situations can precipitate acute metabolic decompensation.

      '
    explanation: 'Supports the rationale for catabolic stress avoidance.

      '
- name: Dietary management
  description: 'Dietary intervention in SBCADD is controversial. Early-identified cases historically received low-protein diets with fasting avoidance, but the indication for disruptive dietary manipulations in asymptomatic newborn-screening-identified infants is questionable. Current practice favors maintaining a normal diet with vigilance during intercurrent illness rather than protein restriction.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_mechanisms:
  - target: Stress-sensitive metabolic decompensation
    treatment_effect: MODULATES
    description: Dietary management historically aimed to reduce metabolic stress, although long-term efficacy is uncertain.
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established."
      explanation: Early dietary management was used presymptomatically, but long-term efficacy remains uncertain.
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Dietary treatment was initiated in the neonatal period. Except for 1 patient who developed mild muscle hypotonia, all patients remain asymptomatic at ages ranging from 3 to 14 months of age.

      '
    explanation: 'Reports early dietary treatment in newborn-screening-identified Hmong patients with good short-term outcomes.

      '
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: 'The continued efficacy of long-term dietary therapy instituted presymptomatically remains to be established.

      '
    explanation: 'Notes that long-term efficacy of presymptomatic dietary treatment is unproven.

      '
- name: Valproate avoidance
  description: 'Valproate should be avoided in SBCADD patients because valproyl-CoA can serve as a substrate of SBCAD, and valproate administration may exacerbate the metabolic block.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Stress-sensitive metabolic decompensation
    treatment_effect: INHIBITS
    description: Valproate avoidance reduces iatrogenic risk of acute metabolic instability in a disorder managed around catabolic vulnerability.
    evidence:
    - reference: PMID:30730842
      reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Carnitine supplementation and valproate avoidance appear to be indicated."
      explanation: Review recommends valproate avoidance in SBCADD management, consistent with preventing treatment-triggered metabolic decompensation.
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Carnitine supplementation and valproate avoidance appear to be indicated.

      '
    explanation: 'Directly recommends valproate avoidance as an indicated measure in SBCADD management.

      '
- name: Newborn screening via tandem mass spectrometry
  description: 'SBCADD is detectable by expanded newborn screening using tandem mass spectrometry. Elevated C5-acylcarnitine triggers follow-up testing including urine organic acids and acylglycine analysis, followed by molecular confirmation of ACADSB variants.

    '
  treatment_term:
    preferred_term: disease screening
    term:
      id: MAXO:0000124
      label: disease screening
  target_phenotypes:
  - preferred_term: Elevated circulating acylcarnitine concentration
    term:
      id: HP:0045045
      label: Elevated circulating acylcarnitine concentration
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'These cases suggest that SBCAD deficiency is another inborn error of metabolism detectable by newborn screening using tandem mass spectrometry.

      '
    explanation: 'Establishes that SBCADD is detectable by tandem MS newborn screening.

      '
- name: Genetic counseling
  description: 'Genetic counseling for affected families regarding autosomal recessive inheritance, carrier testing, recurrence risk (25%), and options for prenatal diagnosis. Particularly relevant in the Hmong community where the carrier frequency exceeds 20%.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  target_mechanisms:
  - target: ACADSB molecular function deficiency
    treatment_effect: MODULATES
    description: Counseling addresses the autosomal recessive ACADSB cause, recurrence risk, and prenatal testing rather than directly modifying metabolism.
    evidence:
    - reference: PMID:12837870
      reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment."
      explanation: Prenatal diagnosis in an affected family supports genetics-informed counseling and recurrence-risk management.
  evidence:
  - reference: PMID:12837870
    reference_title: "Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'A sibling of the first patient is asymptomatic after prenatal diagnosis and early treatment.

      '
    explanation: 'Demonstrates prenatal diagnosis has been applied in SBCADD families, supporting the role of genetic counseling.

      '
- name: Longitudinal monitoring
  description: 'Long-term clinical and biochemical follow-up is recommended for all individuals with confirmed SBCADD, even those who are asymptomatic, to monitor for late-onset neurological or developmental complications and to assess the natural history of the condition.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  - preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  - preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:30730842
    reference_title: "Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Longitudinal follow-up is recommended.

      '
    explanation: 'Directly recommends longitudinal follow-up in SBCADD.

      '
notes: 'SBCADD is a condition of uncertain clinical significance for most affected individuals. Expert consensus from 2023 characterizes SBCAD deficiency as a biochemical abnormality with limited or no clinical consequences in most cases. However, the 2019 literature review cautions that considering SBCADD a non-disease in non-Hmong subjects appears unsafe, as catabolic stress can precipitate acute decompensation. The condition is particularly common in the Hmong population (carrier frequency ~22%) and in certain Chinese ethnic minorities (Miao, Dong) due to the founder c.1165A>G variant. The role of treatment in SBCADD remains unclear pending further delineation of its clinical phenotype and pathogenicity.

  '
references:
- reference: DOI:10.1002/jimd.12642
  title: '<scp>Acyl‐CoA</scp> dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: '<scp>Acyl‐CoA</scp> dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism'
    supporting_text: Toxicity of accumulating substrates is a significant problem in several disorders of valine and isoleucine degradation notably short‐chain enoyl‐CoA hydratase (ECHS1 or crotonase) deficiency, 3‐hydroxyisobutyryl‐CoA hydrolase (HIBCH) deficiency, propionic acidemia (PA), and methylmalonic aciduria (MMA).
- reference: DOI:10.1016/j.ymgme.2013.03.021
  title: Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin
    supporting_text: Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin
- reference: DOI:10.1186/s13023-025-04163-8
  title: Identification of a novel ACADSB variant for the presymptomatic diagnosis of 2-Methylbutyryl-CoA dehydrogenase deficiency through newborn screening in Iran
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: 2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
    supporting_text: 2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
- reference: PMID:17883863
  title: '2-methylbutyryl-CoA dehydrogenase deficiency associated with autism and mental retardation: a case report.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: 2-methylbutyryl-CoA dehydrogenase deficiency or short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is caused by a defect in the degradation pathway of the amino acid L-isoleucine.
    supporting_text: 2-methylbutyryl-CoA dehydrogenase deficiency or short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is caused by a defect in the degradation pathway of the amino acid L-isoleucine.
- reference: PMID:17945527
  title: '2-Methylbutyryl-coenzyme A dehydrogenase deficiency: functional and molecular studies on a defect in isoleucine catabolism.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2008 Jan;93(1):30-5. doi: 10.1016/j.ymgme.2007.09.002.'
    supporting_text: '2008 Jan;93(1):30-5. doi: 10.1016/j.ymgme.2007.09.002.'
- reference: PMID:21290185
  title: Advances and challenges in the treatment of branched-chain amino/keto acid metabolic defects.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2012 Jan;35(1):29-40. doi: 10.1007/s10545-010-9269-1.'
    supporting_text: '2012 Jan;35(1):29-40. doi: 10.1007/s10545-010-9269-1.'
- reference: PMID:21430231
  title: 'Role of isovaleryl-CoA dehydrogenase and short branched-chain acyl-CoA dehydrogenase in the metabolism of valproic acid: implications for the branched-chain amino acid oxidation pathway.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2011 Jul;39(7):1155-60. doi: 10.1124/dmd.110.037606.'
    supporting_text: '2011 Jul;39(7):1155-60. doi: 10.1124/dmd.110.037606.'
- reference: PMID:22967964
  title: 2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2012 Oct 10;1478:74-82. doi: 10.1016/j.brainres.2012.08.039.'
    supporting_text: '2012 Oct 10;1478:74-82. doi: 10.1016/j.brainres.2012.08.039.'
- reference: PMID:23499962
  title: UPLC-MS/MS analysis of C5-acylcarnitines in dried blood spots.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: Metabolic screening including newborn screening requires further differentiation of C5-acylcarnitines in order to separate different metabolic disorders and to detect interferents like pivalic acid originating from antibiotics.
    supporting_text: Metabolic screening including newborn screening requires further differentiation of C5-acylcarnitines in order to separate different metabolic disorders and to detect interferents like pivalic acid originating from antibiotics.
- reference: PMID:27727436
  title: Acylglycine Analysis by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS).
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2016 Oct 11;91:17.25.1-17.25.12. doi: 10.1002/cphg.19.'
    supporting_text: '2016 Oct 11;91:17.25.1-17.25.12. doi: 10.1002/cphg.19.'
- reference: PMID:29185933
  title: Severe riboflavin deficiency induces alterations in the hepatic proteome of starter Pekin ducks.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2017 Nov;118(9):641-650. doi: 10.1017/S0007114517002641.'
    supporting_text: '2017 Nov;118(9):641-650. doi: 10.1017/S0007114517002641.'
- reference: PMID:32451238
  title: Biochemical and anaplerotic applications of in vitro models of propionic acidemia and methylmalonic acidemia using patient-derived primary hepatocytes.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2020 Jul;130(3):183-196. doi: 10.1016/j.ymgme.2020.05.003.'
    supporting_text: '2020 Jul;130(3):183-196. doi: 10.1016/j.ymgme.2020.05.003.'
- reference: PMID:34287228
  title: Development of Second-Tier Liquid Chromatography-Tandem Mass Spectrometry Analysis for Expanded Newborn Screening in Japan.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2021 Jul 14;7(3):44. doi: 10.3390/ijns7030044.'
    supporting_text: '2021 Jul 14;7(3):44. doi: 10.3390/ijns7030044.'
- reference: PMID:34556413
  title: Development and characterization of a mouse model for Acad9 deficiency.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2021 Sep-Oct;134(1-2):156-163. doi: 10.1016/j.ymgme.2021.09.002.'
    supporting_text: '2021 Sep-Oct;134(1-2):156-163. doi: 10.1016/j.ymgme.2021.09.002.'
- reference: PMID:36147814
  title: 'Long-term monitoring for short/branched-chain acyl-CoA dehydrogenase deficiency: A single-center 4-year experience and open issues.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2022 Sep 6;10:895921. doi: 10.3389/fped.2022.895921. eCollection 2022.'
    supporting_text: '2022 Sep 6;10:895921. doi: 10.3389/fped.2022.895921. eCollection 2022.'
- reference: PMID:36604934
  title: 'Inborn Errors of Metabolism Associated With Autism Among Children: A Multicenter Study from Iran.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: 'Inborn Errors of Metabolism Associated With Autism Among Children: A Multicenter Study from Iran'
    supporting_text: Moravej H(1), Inaloo S(2), Nahid S(3), Mazloumi S(4), Nemati H(5), Moosavian T(6), Nasiri J(7), Ghasemi F(8), Alaei MR(9), Dalili S(10), Aminzadeh M(11), Katibeh P(12), Amirhakimi A(4), Yazdani N(13), Ilkhanipoor H(4), Afshar Z(4), Hadipour F(14), Hadipour Z(14).
- reference: PMID:36709932
  title: '[Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening].'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '[Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening]'
    supporting_text: '2023 Feb 10;40(2):155-160. doi: 10.3760/cma.j.cn511376-20220318-00179. [Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening]. [Article in Chinese] Zhao H(1), Zhou D, Miao H, Chen C, Yang J, Yang R, Huang X.'
- reference: PMID:40835664
  title: 'Large-scale newborn screening for organic acidemias in Quanzhou, China: a 10-year retrospective observational study.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2025 Aug 20;15(1):30592. doi: 10.1038/s41598-025-15625-1.'
    supporting_text: '2025 Aug 20;15(1):30592. doi: 10.1038/s41598-025-15625-1.'
- reference: PMID:41440809
  title: 'Incidence of Organic Acid Disorders in 13 Million Chinese Newborns: A Systematic Review and Meta-Analysis.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2025 Dec 13;11(4):113. doi: 10.3390/ijns11040113.'
    supporting_text: '2025 Dec 13;11(4):113. doi: 10.3390/ijns11040113.'
- reference: PMID:7698750
  title: Isolation and expression of a cDNA encoding the precursor for a novel member (ACADSB) of the acyl-CoA dehydrogenase gene family.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '1994 Nov 15;24(2):280-7. doi: 10.1006/geno.1994.1617.'
    supporting_text: '1994 Nov 15;24(2):280-7. doi: 10.1006/geno.1994.1617.'
- reference: PMID:7993663
  title: 'Anabolic effect of human growth hormone: management of inherited disorders of catabolic pathways.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '1994 Aug;52(2):145-54. doi: 10.1006/bmmb.1994.1047.'
    supporting_text: '1994 Aug;52(2):145-54. doi: 10.1006/bmmb.1994.1047.'
- reference: DOI:10.1016/j.ymgme.2006.07.010
  title: 'Inborn errors of isoleucine degradation: A review'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: 'Inborn errors of isoleucine degradation: A review'
    supporting_text: 'Inborn errors of isoleucine degradation: A review'
- reference: DOI:10.1016/j.ymgme.2010.04.014
  title: Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening
    supporting_text: Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening
- reference: DOI:10.1373/clinchem.2004.043265
  title: '2-Ethylhydracrylic Aciduria in Short/Branched-Chain Acyl-CoA Dehydrogenase Deficiency: Application to Diagnosis and Implications for the R-Pathway of Isoleucine Oxidation'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of l-isoleucine oxidation.
    supporting_text: Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of l-isoleucine oxidation.
- reference: DOI:10.1515/jpem-2018-0311
  title: 'Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance.
    supporting_text: Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance.
- reference: DOI:10.1542/peds.112.1.74
  title: Prospective Diagnosis of 2-Methylbutyryl-CoA Dehydrogenase Deficiency in the Hmong Population by Newborn Screening Using Tandem Mass Spectrometry
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: 2-Methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of l-isoleucine metabolism.
    supporting_text: 2-Methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of l-isoleucine metabolism.
- reference: DOI:10.3389/fgene.2019.00802
  title: Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening
    supporting_text: Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening
- reference: DOI:10.3389/fgene.2024.1387423
  title: 206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in Huaihua, China
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-falcon.md
  findings:
  - statement: Inborn errors of metabolism (IEMs) are rare diseases caused by inherited defects in various biochemical pathways that strongly correlate with early neonatal mortality and stunting.
    supporting_text: Inborn errors of metabolism (IEMs) are rare diseases caused by inherited defects in various biochemical pathways that strongly correlate with early neonatal mortality and stunting.
- reference: PMID:23712021
  title: Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2013 Sep-Oct;110(1-2):111-5. doi: 10.1016/j.ymgme.2013.03.021.'
    supporting_text: '2013 Sep-Oct;110(1-2):111-5. doi: 10.1016/j.ymgme.2013.03.021.'
- reference: PMID:41527137
  title: Identification of a novel ACADSB variant for the presymptomatic diagnosis of 2-Methylbutyryl-CoA dehydrogenase deficiency through newborn screening in Iran.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: 2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
    supporting_text: 2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
- reference: PMID:12837870
  title: Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2003 Jul;112(1 Pt 1):74-8. doi: 10.1542/peds.112.1.74.'
    supporting_text: '2003 Jul;112(1 Pt 1):74-8. doi: 10.1542/peds.112.1.74.'
- reference: PMID:15615815
  title: '2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation.
    supporting_text: Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation.
- reference: PMID:20547083
  title: Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening.
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2010 Aug;100(4):333-8. doi: 10.1016/j.ymgme.2010.04.014.'
    supporting_text: '2010 Aug;100(4):333-8. doi: 10.1016/j.ymgme.2010.04.014.'
- reference: PMID:30730842
  title: 'Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature.'
  found_in:
  - 2-Methylbutyryl-CoA_Dehydrogenase_Deficiency-deep-research-openscientist.md
  findings:
  - statement: '2019 Feb 25;32(2):101-108. doi: 10.1515/jpem-2018-0311.'
    supporting_text: '2019 Feb 25;32(2):101-108. doi: 10.1515/jpem-2018-0311.'
📚

References & Deep Research

References

34
DOI:10.1002/jimd.12642
<scp>Acyl‐CoA</scp> dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism
1 finding
<scp>Acyl‐CoA</scp> dehydrogenase substrate promiscuity: Challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism
"Toxicity of accumulating substrates is a significant problem in several disorders of valine and isoleucine degradation notably short‐chain enoyl‐CoA hydratase (ECHS1 or crotonase) deficiency, 3‐hydroxyisobutyryl‐CoA hydrolase (HIBCH) deficiency, propionic acidemia (PA), and methylmalonic aciduria (MMA)."
DOI:10.1016/j.ymgme.2013.03.021
Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin
1 finding
Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin
"Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin"
DOI:10.1186/s13023-025-04163-8
Identification of a novel ACADSB variant for the presymptomatic diagnosis of 2-Methylbutyryl-CoA dehydrogenase deficiency through newborn screening in Iran
1 finding
2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
"2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia."
PMID:17883863
2-methylbutyryl-CoA dehydrogenase deficiency associated with autism and mental retardation: a case report.
1 finding
2-methylbutyryl-CoA dehydrogenase deficiency or short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is caused by a defect in the degradation pathway of the amino acid L-isoleucine.
"2-methylbutyryl-CoA dehydrogenase deficiency or short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) is caused by a defect in the degradation pathway of the amino acid L-isoleucine."
PMID:17945527
2-Methylbutyryl-coenzyme A dehydrogenase deficiency: functional and molecular studies on a defect in isoleucine catabolism.
1 finding
2008 Jan;93(1):30-5. doi: 10.1016/j.ymgme.2007.09.002.
"2008 Jan;93(1):30-5. doi: 10.1016/j.ymgme.2007.09.002."
PMID:21290185
Advances and challenges in the treatment of branched-chain amino/keto acid metabolic defects.
1 finding
2012 Jan;35(1):29-40. doi: 10.1007/s10545-010-9269-1.
"2012 Jan;35(1):29-40. doi: 10.1007/s10545-010-9269-1."
PMID:21430231
Role of isovaleryl-CoA dehydrogenase and short branched-chain acyl-CoA dehydrogenase in the metabolism of valproic acid: implications for the branched-chain amino acid oxidation pathway.
1 finding
2011 Jul;39(7):1155-60. doi: 10.1124/dmd.110.037606.
"2011 Jul;39(7):1155-60. doi: 10.1124/dmd.110.037606."
PMID:22967964
2-Methylbutyrylglycine induces lipid oxidative damage and decreases the antioxidant defenses in rat brain.
1 finding
2012 Oct 10;1478:74-82. doi: 10.1016/j.brainres.2012.08.039.
"2012 Oct 10;1478:74-82. doi: 10.1016/j.brainres.2012.08.039."
PMID:23499962
UPLC-MS/MS analysis of C5-acylcarnitines in dried blood spots.
1 finding
Metabolic screening including newborn screening requires further differentiation of C5-acylcarnitines in order to separate different metabolic disorders and to detect interferents like pivalic acid originating from antibiotics.
"Metabolic screening including newborn screening requires further differentiation of C5-acylcarnitines in order to separate different metabolic disorders and to detect interferents like pivalic acid originating from antibiotics."
PMID:27727436
Acylglycine Analysis by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS).
1 finding
2016 Oct 11;91:17.25.1-17.25.12. doi: 10.1002/cphg.19.
"2016 Oct 11;91:17.25.1-17.25.12. doi: 10.1002/cphg.19."
PMID:29185933
Severe riboflavin deficiency induces alterations in the hepatic proteome of starter Pekin ducks.
1 finding
2017 Nov;118(9):641-650. doi: 10.1017/S0007114517002641.
"2017 Nov;118(9):641-650. doi: 10.1017/S0007114517002641."
PMID:32451238
Biochemical and anaplerotic applications of in vitro models of propionic acidemia and methylmalonic acidemia using patient-derived primary hepatocytes.
1 finding
2020 Jul;130(3):183-196. doi: 10.1016/j.ymgme.2020.05.003.
"2020 Jul;130(3):183-196. doi: 10.1016/j.ymgme.2020.05.003."
PMID:34287228
Development of Second-Tier Liquid Chromatography-Tandem Mass Spectrometry Analysis for Expanded Newborn Screening in Japan.
1 finding
2021 Jul 14;7(3):44. doi: 10.3390/ijns7030044.
"2021 Jul 14;7(3):44. doi: 10.3390/ijns7030044."
PMID:34556413
Development and characterization of a mouse model for Acad9 deficiency.
1 finding
2021 Sep-Oct;134(1-2):156-163. doi: 10.1016/j.ymgme.2021.09.002.
"2021 Sep-Oct;134(1-2):156-163. doi: 10.1016/j.ymgme.2021.09.002."
PMID:36147814
Long-term monitoring for short/branched-chain acyl-CoA dehydrogenase deficiency: A single-center 4-year experience and open issues.
1 finding
2022 Sep 6;10:895921. doi: 10.3389/fped.2022.895921. eCollection 2022.
"2022 Sep 6;10:895921. doi: 10.3389/fped.2022.895921. eCollection 2022."
PMID:36604934
Inborn Errors of Metabolism Associated With Autism Among Children: A Multicenter Study from Iran.
1 finding
Inborn Errors of Metabolism Associated With Autism Among Children: A Multicenter Study from Iran
"Moravej H(1), Inaloo S(2), Nahid S(3), Mazloumi S(4), Nemati H(5), Moosavian T(6), Nasiri J(7), Ghasemi F(8), Alaei MR(9), Dalili S(10), Aminzadeh M(11), Katibeh P(12), Amirhakimi A(4), Yazdani N(13), Ilkhanipoor H(4), Afshar Z(4), Hadipour F(14), Hadipour Z(14)."
PMID:36709932
[Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening].
1 finding
[Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening]
"2023 Feb 10;40(2):155-160. doi: 10.3760/cma.j.cn511376-20220318-00179. [Analysis of clinical features, biochemical indices and genetic variants among children with Short/branched-chain acyl-CoA dehydrogenase deficiency detected by neonatal screening]. [Article in Chinese] Zhao H(1), Zhou D, Miao..."
PMID:40835664
Large-scale newborn screening for organic acidemias in Quanzhou, China: a 10-year retrospective observational study.
1 finding
2025 Aug 20;15(1):30592. doi: 10.1038/s41598-025-15625-1.
"2025 Aug 20;15(1):30592. doi: 10.1038/s41598-025-15625-1."
PMID:41440809
Incidence of Organic Acid Disorders in 13 Million Chinese Newborns: A Systematic Review and Meta-Analysis.
1 finding
2025 Dec 13;11(4):113. doi: 10.3390/ijns11040113.
"2025 Dec 13;11(4):113. doi: 10.3390/ijns11040113."
PMID:7698750
Isolation and expression of a cDNA encoding the precursor for a novel member (ACADSB) of the acyl-CoA dehydrogenase gene family.
1 finding
1994 Nov 15;24(2):280-7. doi: 10.1006/geno.1994.1617.
"1994 Nov 15;24(2):280-7. doi: 10.1006/geno.1994.1617."
PMID:7993663
Anabolic effect of human growth hormone: management of inherited disorders of catabolic pathways.
1 finding
1994 Aug;52(2):145-54. doi: 10.1006/bmmb.1994.1047.
"1994 Aug;52(2):145-54. doi: 10.1006/bmmb.1994.1047."
DOI:10.1016/j.ymgme.2006.07.010
Inborn errors of isoleucine degradation: A review
1 finding
Inborn errors of isoleucine degradation: A review
"Inborn errors of isoleucine degradation: A review"
DOI:10.1016/j.ymgme.2010.04.014
Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening
1 finding
Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening
"Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening"
DOI:10.1373/clinchem.2004.043265
2-Ethylhydracrylic Aciduria in Short/Branched-Chain Acyl-CoA Dehydrogenase Deficiency: Application to Diagnosis and Implications for the R-Pathway of Isoleucine Oxidation
1 finding
Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of l-isoleucine oxidation.
"Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of l-isoleucine oxidation."
DOI:10.1515/jpem-2018-0311
Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature
1 finding
Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance.
"Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency is a rare inborn error of metabolism with uncertain clinical significance."
DOI:10.1542/peds.112.1.74
Prospective Diagnosis of 2-Methylbutyryl-CoA Dehydrogenase Deficiency in the Hmong Population by Newborn Screening Using Tandem Mass Spectrometry
1 finding
2-Methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of l-isoleucine metabolism.
"2-Methylbutyryl-CoA dehydrogenase deficiency, also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a recently described autosomal recessive disorder of l-isoleucine metabolism."
DOI:10.3389/fgene.2019.00802
Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening
1 finding
Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening
"Biochemical, Clinical, and Genetic Characteristics of Short/Branched Chain Acyl-CoA Dehydrogenase Deficiency in Chinese Patients by Newborn Screening"
DOI:10.3389/fgene.2024.1387423
206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in Huaihua, China
1 finding
Inborn errors of metabolism (IEMs) are rare diseases caused by inherited defects in various biochemical pathways that strongly correlate with early neonatal mortality and stunting.
"Inborn errors of metabolism (IEMs) are rare diseases caused by inherited defects in various biochemical pathways that strongly correlate with early neonatal mortality and stunting."
PMID:23712021
Prevalence and mutation analysis of short/branched chain acyl-CoA dehydrogenase deficiency (SBCADD) detected on newborn screening in Wisconsin.
1 finding
2013 Sep-Oct;110(1-2):111-5. doi: 10.1016/j.ymgme.2013.03.021.
"2013 Sep-Oct;110(1-2):111-5. doi: 10.1016/j.ymgme.2013.03.021."
PMID:41527137
Identification of a novel ACADSB variant for the presymptomatic diagnosis of 2-Methylbutyryl-CoA dehydrogenase deficiency through newborn screening in Iran.
1 finding
2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia.
"2-Methylbutyryl-CoA dehydrogenase deficiency (2-MBDD), also known as short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency, is a rare inborn error of metabolism classified as an organic acidemia."
PMID:12837870
Prospective diagnosis of 2-methylbutyryl-CoA dehydrogenase deficiency in the Hmong population by newborn screening using tandem mass spectrometry.
1 finding
2003 Jul;112(1 Pt 1):74-8. doi: 10.1542/peds.112.1.74.
"2003 Jul;112(1 Pt 1):74-8. doi: 10.1542/peds.112.1.74."
PMID:15615815
2-ethylhydracrylic aciduria in short/branched-chain acyl-CoA dehydrogenase deficiency: application to diagnosis and implications for the R-pathway of isoleucine oxidation.
1 finding
Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation.
"Isolated excretion of 2-methylbutyrylglycine (2-MBG) is the hallmark of short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD), a recently identified defect in the proximal pathway of L-isoleucine oxidation."
PMID:20547083
Characterization of new ACADSB gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening.
1 finding
2010 Aug;100(4):333-8. doi: 10.1016/j.ymgme.2010.04.014.
"2010 Aug;100(4):333-8. doi: 10.1016/j.ymgme.2010.04.014."
PMID:30730842
Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature.
1 finding
2019 Feb 25;32(2):101-108. doi: 10.1515/jpem-2018-0311.
"2019 Feb 25;32(2):101-108. doi: 10.1515/jpem-2018-0311."

Deep Research

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Disease Pathophysiology Research Template
Edison Scientific Literature 34 citations 2026-02-23T23:38:51.539350

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Pathophysiology Research Template

Target Disease

  • Disease Name: 2-Methylbutyryl-CoA Dehydrogenase Deficiency
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of 2-Methylbutyryl-CoA Dehydrogenase Deficiency. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

  • What are the primary pathophysiological mechanisms?
  • What molecular pathways are dysregulated?
  • What cellular processes are affected?

2. Key Molecular Players

  • Genes/Proteins: Which genes are causally involved or implicated?
  • Chemical Entities: What metabolites, drugs, or small molecules are relevant?
  • Cell Types: Which cell types are primarily affected?
  • Anatomical Locations: Which tissues/organs are involved?

3. Biological Processes (for GO annotation)

  • What biological processes (GO terms) are disrupted?
  • Consider: signaling pathways, metabolic processes, cellular responses, transport, etc.

4. Cellular Components

  • Where in the cell do key processes occur?
  • Consider: organelles, membrane compartments, extracellular space, etc.

5. Disease Progression

  • What is the sequence of events from initial trigger to clinical manifestation?
  • Are there distinct stages or phases?

6. Phenotypic Manifestations

  • What are the key clinical phenotypes?
  • How do they relate to the underlying mechanisms?

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes where possible to support key statements

Output Format

Structure your response as a narrative that could be used to populate a disease knowledge base entry with: - Pathophysiology description - Gene/protein annotations with ontology terms (HGNC, GO) - Phenotype associations (HP terms) - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Evidence items with PMIDs

Comprehensive Research Report: 2‑Methylbutyryl‑CoA Dehydrogenase Deficiency (SBCAD deficiency; “2‑methylbutyrylglycinuria”)

Publication scope and evidence base This report synthesizes mechanistic and clinical pathophysiology evidence from primary literature and authoritative reviews, emphasizing the most recent available disease-specific sources retrieved (notably a 2024 population newborn-screening study and a 2023 mechanistic cell-model paper), plus key foundational work defining biomarkers and pathways. (houten2023acyl‐coadehydrogenasesubstrate pages 6-8, xiao2024206977newbornscreening pages 1-2)

  1. Key concepts and definitions (current understanding)

Disease definition and identifiers • Disease entity: 2‑methylbutyryl‑CoA dehydrogenase deficiency (also called short/branched-chain acyl‑CoA dehydrogenase deficiency; SBCADD/SBCAD deficiency). (porta2019clinicalbiochemicaland pages 1-2) • MONDO: MONDO_0012392 (2‑methylbutyryl‑CoA dehydrogenase deficiency) (derived from Open Targets disease record for this entity; evidence snippets were not returned, but the MONDO identifier itself was returned by the tool call). (calcar2013prevalenceandmutation pages 1-3) • OMIM: sources variably cite OMIM 600301 and/or 610006 for SBCAD deficiency; some texts also use OMIM 600301 for the gene entry and OMIM 610006 for the disease phenotype entry. (lin2019biochemicalclinicaland pages 1-2, porta2019clinicalbiochemicaland pages 1-2)

Core biochemical concept SBCAD deficiency is an inborn error of branched-chain amino acid metabolism in which the mitochondrial acyl‑CoA dehydrogenase SBCAD (encoded by ACADSB) has impaired activity in the proximal pathway of L‑isoleucine oxidation. A defining biochemical hallmark is increased urinary 2‑methylbutyrylglycine (2‑MBG), and patients are often detected by elevated C5 acylcarnitine on MS/MS newborn screening (recognizing that “C5” is isobaric with isovalerylcarnitine). (jaffar2010characterizationofnew pages 5-7)

  1. Core pathophysiology (molecular/cellular mechanisms)

2.1 Primary pathophysiological mechanisms Primary lesion: mitochondrial SBCAD (ACADSB) loss-of-function SBCAD is a mitochondrial acyl‑CoA dehydrogenase (ACAD) family enzyme. ACAD enzymes catalyze α,β‑dehydrogenation of acyl‑CoAs and transfer electrons to electron transferring flavoprotein (ETF). (jaffar2010characterizationofnew pages 1-2)

Block in isoleucine oxidation with metabolite accumulation and “overflow” routes • The metabolic block leads to accumulation of upstream metabolites that are diverted to measurable diagnostic conjugates, including C5 (2‑methylbutyrylcarnitine), urinary 2‑MBG (2‑methylbutyrylglycine), and urinary 2‑ethylhydracrylic acid (2‑EHA). (korman20052ethylhydracrylicaciduriain pages 2-3, jaffar2010characterizationofnew pages 5-7) • A central mechanistic hypothesis explaining variable severity is partial compensation via alternative enzymes/pathways and stereochemical “R‑pathway” flux. Korman et al. report that 2‑EHA (a normally minor R‑pathway intermediate) is prominent in SBCADD urine and that this “raises questions regarding the presumed role of SBCAD in the R‑pathway of isoleucine oxidation,” implying compensatory enzymology and rerouting. (korman20052ethylhydracrylicaciduriain pages 2-3) • Pathway schematic evidence: Figure 1 in Korman et al. depicts the S‑ and R‑pathways of L‑isoleucine catabolism and highlights 2‑MBG and 2‑EHA as accumulating/diagnostic metabolites. (korman20052ethylhydracrylicaciduriain media 5fdd71b3)

Stress-sensitive phenotype model A mechanistic interpretation in the review literature is that overlapping substrate specificity (“compensation by other ACAD enzymes”) may mask biochemical consequences at baseline but may fail during metabolic stress (infection/fasting), contributing to sporadic decompensation in a minority of patients. (korman2006inbornerrorsof pages 8-9)

2.2 Dysregulated pathways • Branched-chain amino acid (BCAA) catabolism: L‑isoleucine oxidation (proximal steps; S‑pathway and minor R‑pathway). (korman20052ethylhydracrylicaciduriain pages 1-2, korman20052ethylhydracrylicaciduriain media 5fdd71b3) • Mitochondrial acyl‑CoA dehydrogenation / fatty‑acid-oxidation–adjacent electron-transfer processes via ETF (shared biochemical machinery across ACAD enzymes). (jaffar2010characterizationofnew pages 1-2)

2.3 Cellular processes affected • Mitochondrial substrate processing and redox electron transfer during acyl‑CoA dehydrogenation (via ETF). (jaffar2010characterizationofnew pages 1-2) • Metabolic rerouting and detoxification via conjugation (acylcarnitine formation; glycine conjugation) producing C5‑carnitine and 2‑MBG. (jaffar2010characterizationofnew pages 5-7)

  1. Key molecular players

3.1 Genes / proteins (HGNC) • ACADSB (protein: short/branched-chain acyl‑CoA dehydrogenase; SBCAD). ACADSB is reported on chromosome 10q26.13 and comprises 11 exons. (wanders2015branchedchainamino pages 10-12) • Enzyme features: SBCAD is a homotetrameric mitochondrial ACAD; the crystal structure context supports flavin (FAD) binding and structural sensitivity of pathogenic variants. (jaffar2010characterizationofnew pages 11-14)

Functional evidence for loss-of-function variants • In vitro mutagenesis and heterologous expression studies support that multiple ACADSB missense variants destabilize protein and/or abolish activity. For example, Jaffar et al. describe variants that were “minimally or not detectable” by Western blot and show markedly reduced enzyme activity relative to wild type in recombinant assays. (jaffar2010characterizationofnew pages 11-14, jaffar2010characterizationofnew pages 2-4)

Population founder variant • ACADSB c.1165A>G is repeatedly implicated as a high-frequency/founder allele in specific populations (Hmong in the US; multiple Chinese ethnic groups). (calcar2013prevalenceandmutation pages 4-6, xiao2024206977newbornscreening pages 1-2)

3.2 Chemical entities / metabolites (CHEBI-style) Key diagnostic/biomarker metabolites in this disorder include: • C5 acylcarnitine (2‑methylbutyrylcarnitine; isobaric with isovalerylcarnitine on many MS/MS workflows). (jaffar2010characterizationofnew pages 5-7) • 2‑methylbutyrylglycine (2‑MBG) in urine (hallmark). (jaffar2010characterizationofnew pages 5-7, porta2019clinicalbiochemicaland pages 1-2) • 2‑ethylhydracrylic acid (2‑EHA) in urine (prominent R‑pathway marker; sensitive but not fully specific). (jaffar2010characterizationofnew pages 5-7, korman20052ethylhydracrylicaciduriain pages 2-3)

Drug-relevant small molecules • Valproate: Porta et al. state “valproate avoidance appear to be indicated,” and also note biochemical rationale that valproyl‑CoA can be a substrate of SBCAD, supporting an expert-opinion contraindication/avoidance approach. (porta2019clinicalbiochemicaland pages 1-2, porta2019clinicalbiochemicaland pages 3-5)

3.3 Cell types (CL) and anatomical locations (UBERON) Evidence in the retrieved sources primarily supports a systemic mitochondrial metabolic defect with clinically relevant readouts in: • Blood (dried blood spots for acylcarnitines; plasma acylcarnitines). (matern2003prospectivediagnosisof pages 2-4, jaffar2010characterizationofnew pages 5-7) • Urine (organic acids/acylglycines, including 2‑MBG and 2‑EHA). (porta2019clinicalbiochemicaland pages 1-2, korman20052ethylhydracrylicaciduriain pages 2-3) • Cultured skin fibroblasts are used for confirmatory enzyme and acylcarnitine studies. (matern2003prospectivediagnosisof pages 2-4, wanders2015branchedchainamino pages 10-12) Given the pathway, the most relevant tissues are high-oxidative organs (liver, skeletal muscle, brain) by biological plausibility; however, explicit tissue-level mechanistic localization was not directly stated in the retrieved excerpts and is therefore not asserted here without additional sourced evidence.

  1. Biological processes and cellular components (GO-oriented)

4.1 Disrupted biological processes (candidate GO terms) Based on direct pathway and mechanism descriptions: • Branched-chain amino acid catabolic process / isoleucine catabolic process (block in proximal L‑isoleucine oxidation with S‑ and R‑pathway involvement). (korman20052ethylhydracrylicaciduriain pages 1-2, korman20052ethylhydracrylicaciduriain media 5fdd71b3) • Acyl‑CoA dehydrogenase activity–linked fatty acid β‑oxidation/electron transfer module (ACAD enzymes transfer electrons to ETF). (jaffar2010characterizationofnew pages 1-2) • Acylcarnitine metabolic process and glycine conjugation/detoxification processes (reflected by elevated C5‑carnitine and 2‑MBG). (jaffar2010characterizationofnew pages 5-7)

4.2 Cellular components (candidate GO cellular component terms) • Mitochondrion / mitochondrial matrix: ACAD enzymes including SBCAD are described as mitochondrial enzymes. (jaffar2010characterizationofnew pages 1-2)

  1. Disease progression model (sequence of events)

Trigger → metabolic block → biomarker accumulation → clinical outcomes (variable) 1) Genetic biallelic ACADSB variants reduce SBCAD protein abundance and/or catalytic activity (shown by recombinant assays and Western blot evidence for instability/inactivity). (jaffar2010characterizationofnew pages 11-14, jaffar2010characterizationofnew pages 2-4) 2) The isoleucine oxidation pathway step(s) handled by SBCAD become limiting, leading to increased upstream 2‑methylbutyryl‑CoA–related metabolites. These are shunted to measurable C5‑carnitine (blood) and 2‑MBG/2‑EHA (urine). (jaffar2010characterizationofnew pages 5-7, korman20052ethylhydracrylicaciduriain pages 2-3) 3) Compensation via alternative enzymes and/or increased R‑pathway flux may mitigate metabolite burden; Korman et al. propose increased R‑pathway flux as a “safety valve” based on prominent 2‑EHA excretion. (korman20052ethylhydracrylicaciduriain pages 1-2) 4) Clinical expression is often absent or mild, but catabolic stress (infection/fasting) is proposed as a precipitating factor for overt symptoms in susceptible individuals because compensatory capacity may be exceeded. (korman2006inbornerrorsof pages 8-9)

  1. Phenotypic manifestations (HP-aligned) and mechanistic linkage

Clinical spectrum The phenotype is heterogeneous; many individuals identified through newborn screening remain asymptomatic, while a minority develop neurological/developmental features. • Porta et al. review 162 patients and conclude SBCAD deficiency is symptomatic in ~10% of reported patients; reported symptomatic features include seizures, developmental delay, hypotonia, failure to thrive, and later outcomes including epilepsy, microcephaly, and autism. (porta2019clinicalbiochemicaland pages 1-2) • Newborn screening cohorts in multiple regions show largely benign follow-up in many cases (e.g., the Chinese cohort in Quanzhou followed 12 patients reported “asymptomatic at diagnosis” with normal development during follow-up). (lin2019biochemicalclinicaland pages 1-2)

Mechanistic mapping Neurological features (seizures/developmental delay) are consistent with brain vulnerability to mitochondrial metabolic stress and accumulation of potentially toxic intermediates during catabolic states; however, the retrieved excerpts largely describe this association clinically and infer stress-triggering rather than providing direct neurotoxic mechanism experiments specific to SBCADD. (korman2006inbornerrorsof pages 8-9, porta2019clinicalbiochemicaland pages 1-2)

  1. Recent developments and latest research (prioritizing 2023–2024)

7.1 2024: large newborn-screening cohort with ethnic stratification and ACADSB variant spectrum Xiao et al. (Frontiers in Genetics; published 09 May 2024; screening January 2015–December 2021; n=206,977) report: • Overall IEM incidence 1:3,000, and 2‑methylbutyryl glycinuria (SBCADD) as the most common disorder with incidence 1:7,137 in the screened cohort. (xiao2024206977newbornscreening pages 1-2) • Ethnic differences: minority groups (Miao, Dong, Tujia, Yao) IEM incidence 1:1,852 vs Han 1:4,741. (xiao2024206977newbornscreening pages 1-2) • Variant spectrum: 29 confirmed SBCADD cases; c.1165A>G is the most prevalent variant (reported as 85.96% in the excerpted table/text), and 21/29 cases were homozygous, all for c.1165A>G. (xiao2024206977newbornscreening pages 12-12) These data reinforce that SBCADD can be relatively common in specific ethnic/geographic contexts and that founder alleles can dominate local case series. (xiao2024206977newbornscreening pages 12-12, xiao2024206977newbornscreening pages 1-2)

7.2 2023: mechanistic cell-model work on ACAD substrate promiscuity and implications for therapy development Houten et al. (Journal of Inherited Metabolic Disease; June 2023) provide a contemporary mechanistic perspective relevant to SBCAD biology: • They note that ACAD8 and SBCAD deficiencies are “considered biochemical abnormalities with limited or no clinical consequences,” reflecting current expert consensus in many metabolic clinics and the broader literature. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3) • In HEK‑293 cell models, ACADSB knockout caused a marked increase in C5‑carnitine (~10‑fold, range 4–11‑fold across clones) and a substantial decrease in C3‑carnitine (~4‑fold on average), indicating that SBCAD activity influences short‑chain acyl‑CoA/acylcarnitine pools beyond a single metabolite. (houten2023acyl‐coadehydrogenasesubstrate pages 6-8) • Pharmacologic inhibition using MCPA (which inhibits SBCAD among multiple ACADs) shifted acylcarnitine profiles (large reductions in C3‑carnitine with corresponding increases in C5‑carnitine and other acylcarnitines), highlighting ACAD substrate promiscuity as both a challenge and an opportunity for “substrate reduction therapy” strategies in propionic acidemia/methylmalonic acidemia. (houten2023acyl‐coadehydrogenasesubstrate pages 6-8) Although not a therapy for SBCADD itself, this work is a recent, high-mechanistic-content source clarifying SBCAD’s network role in mitochondrial acyl‑CoA handling and the consequences of reduced SBCAD function/inhibition. (houten2023acyl‐coadehydrogenasesubstrate pages 6-8)

  1. Current applications and real-world implementations

8.1 Newborn screening (NBS) implementation Primary screening marker • Elevated C5 on dried blood spot MS/MS is the main NBS finding, but it is not specific because “isovaleryl- and 2-methylbutyrylcarnitine share the same mass/charge ratio.” (jaffar2010characterizationofnew pages 5-7) Cut-offs and algorithm considerations (example: Wisconsin) • In Wisconsin (2001–2011), infants were flagged with C5 ≥0.44 μmol/L and ratio criteria (C5/C2 ≥0.05 and C5/C3 ≥0.50) in the described program; 97 infants met C5 ≥0.44 μmol/L and 92 were confirmed SBCADD. (calcar2013prevalenceandmutation pages 3-4)

8.2 Confirmatory diagnostics Recommended confirmatory tests after elevated C5 • ACMG ACT-sheet–aligned approach: urine organic acids and urine acylglycine determination are recommended as initial follow-up tests. (jaffar2010characterizationofnew pages 5-7) Biochemical confirmation markers • Increased urinary 2‑MBG is repeatedly emphasized as a diagnostic hallmark. (porta2019clinicalbiochemicaland pages 1-2) • 2‑EHA can be a prominent urinary marker and may facilitate recognition, though it is not fully specific. (korman20052ethylhydracrylicaciduriain pages 2-3, jaffar2010characterizationofnew pages 5-7) Molecular confirmation • ACADSB sequencing (Sanger/NGS/WES depending on context) is used for confirmation and for variant interpretation; this is standard in modern NBS follow-up workflows and is explicitly reported in multiple cohorts/case studies. (nasri2026identificationofa pages 1-2, matern2003prospectivediagnosisof pages 2-4)

8.3 Management practices (expert-opinion guidance reflected in the literature) Because many individuals remain asymptomatic, management recommendations are cautious and emphasize prevention/monitoring rather than aggressive chronic restriction. Commonly described measures • Carnitine supplementation: reported doses include 50–100 mg/kg/day in early NBS-identified cohorts and 100 mg/kg/day in later case series, often with biochemical monitoring of C5. (matern2003prospectivediagnosisof pages 2-4, porta2019clinicalbiochemicaland pages 2-3) • Catabolic stress management: Porta et al. recommend avoiding fasting/protein overload and providing “an emergency protocol for the management of inter-current febrile illnesses” / acute catabolic episodes. (porta2019clinicalbiochemicaland pages 2-3, porta2019clinicalbiochemicaland pages 6-7) Dietary interventions: uncertain indication in asymptomatic NBS cases • Jaffar et al. state that early cases used “a low protein diet, avoidance of fasting, and carnitine supplementation,” but caution that “disruptive dietary manipulations for infants identified by newborn screening are of questionable indication” and suggest maintaining a normal diet with vigilance during intercurrent illnesses. (jaffar2010characterizationofnew pages 5-7) Medication avoidance • Porta et al. state “carnitine supplementation and valproate avoidance appear to be indicated.” (porta2019clinicalbiochemicaland pages 1-2)

  1. Expert opinion and analysis (authoritative interpretations)

Clinical significance remains uncertain for many genotypes Multiple authoritative sources emphasize that the condition is frequently a biochemical phenotype with limited clinical consequences, but not invariably benign. • The 2023 JIMD perspective states ACAD8 and SBCAD deficiencies are “considered biochemical abnormalities with limited or no clinical consequences,” reflecting a current expert synthesis. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3) • The 2019 literature review emphasizes that labeling SBCADD a non-disease may be unsafe in non-Hmong subjects, notes catabolic stressors can precipitate decompensation, and supports longitudinal follow-up. (porta2019clinicalbiochemicaland pages 1-2) • The 2006 review highlights small case numbers, possible compensation by overlapping ACAD activities, and the role of stressors (fever/infection/fasting) in precipitating symptoms, framing the disorder as conditionally expressed. (korman2006inbornerrorsof pages 8-9)

  1. Relevant statistics and data (recent studies prioritized; older landmark datasets included)

10.1 2024 Huaihua, China (Frontiers in Genetics; published 09 May 2024) • Screened: 206,977 newborns (2015–2021). (xiao2024206977newbornscreening pages 1-2) • 2‑methylbutyryl glycinuria incidence: 1:7,137 (one of the most common IEMs in this cohort). (xiao2024206977newbornscreening pages 1-2) • Confirmed SBCADD cases: 29; c.1165A>G most prevalent, with 21/29 homozygous (all c.1165A>G homozygotes). (xiao2024206977newbornscreening pages 12-12)

10.2 2019 Quanzhou, China (Frontiers in Genetics; Aug 2019) • Estimated incidence of SBCADD in Quanzhou: 1 in 30,379 based on NBS ascertainment. (lin2019biochemicalclinicaland pages 1-2)

10.3 2013 Wisconsin, USA (Molecular Genetics and Metabolism; Sep 2013) • Ten years of NBS (2001–2011): 97 infants with C5 ≥0.44 μmol/L; 92 confirmed SBCADD. (calcar2013prevalenceandmutation pages 1-3) • Hmong birth prevalence among screen-positives: 1 in 131 (7.6 per 1000; 95% CI 6.2–9.3 per 1000). (calcar2013prevalenceandmutation pages 4-6) • Genotype frequencies in an anonymous Hmong sample (n=1,139): c.1165A>G homozygotes 1.3% (≈1 in 77; 95% CI 0.8–2.2%); heterozygotes 21.8% (95% CI 19.4–24.3%). (calcar2013prevalenceandmutation pages 4-6)

10.4 2003 Hmong cohort inference (Pediatrics; Jul 2003) • Authors report that “the incidence of SBCAD deficiency among the Hmong could be higher than 1 in 500 live births,” based on clustered ascertainment in the screened Hmong population. (matern2003prospectivediagnosisof pages 5-7)

  1. Knowledge-base–ready ontology-style annotations (evidence-linked)

Gene/protein • HGNC: ACADSB (short/branched-chain acyl‑CoA dehydrogenase; SBCAD). (wanders2015branchedchainamino pages 10-12)

Molecular function / process (GO-like) • Mitochondrial acyl‑CoA dehydrogenase activity coupled to ETF electron transfer (ACAD family property). (jaffar2010characterizationofnew pages 1-2) • Isoleucine catabolic process (S‑ and R‑pathway; accumulation of S-pathway conjugates and R‑pathway metabolite 2‑EHA). (korman20052ethylhydracrylicaciduriain pages 2-3, korman20052ethylhydracrylicaciduriain media 5fdd71b3)

Cellular component • Mitochondrion / mitochondrial matrix (enzyme class described as mitochondrial). (jaffar2010characterizationofnew pages 1-2)

Phenotypes (HP-like; evidence of spectrum) • Seizures, developmental delay, hypotonia, failure to thrive, epilepsy/autism reported in a minority; many asymptomatic. (porta2019clinicalbiochemicaland pages 1-2)

Anatomical locations (UBERON-like; evidence-supported) • Blood (dried blood spots/plasma) and urine are the main sampled compartments for clinical biomarkers. (jaffar2010characterizationofnew pages 5-7, porta2019clinicalbiochemicaland pages 1-2)

Chemical entities (CHEBI-like) • C5 acylcarnitine (2‑methylbutyrylcarnitine / isovalerylcarnitine isobar). (jaffar2010characterizationofnew pages 5-7) • 2‑methylbutyrylglycine (2‑MBG). (porta2019clinicalbiochemicaland pages 1-2) • 2‑ethylhydracrylic acid (2‑EHA). (korman20052ethylhydracrylicaciduriain pages 2-3)

  1. Evidence items with PMIDs (availability note) The tool-retrieved excerpts did not include PMID fields; therefore, this report cites DOI/URL and bibliographic metadata as retrieved. Key sources include: • Xiao et al., Frontiers in Genetics (09 May 2024): https://doi.org/10.3389/fgene.2024.1387423 (xiao2024206977newbornscreening pages 1-2) • Houten et al., J Inherit Metab Dis (Jun 2023): https://doi.org/10.1002/jimd.12642 (houten2023acyl‐coadehydrogenasesubstrate pages 6-8) • Van Calcar et al., Mol Genet Metab (Sep 2013): https://doi.org/10.1016/j.ymgme.2013.03.021 (calcar2013prevalenceandmutation pages 4-6) • Porta et al., J Pediatr Endocrinol Metab (Feb 2019): https://doi.org/10.1515/jpem-2018-0311 (porta2019clinicalbiochemicaland pages 1-2) • Korman et al., Clin Chem (Mar 2005): https://doi.org/10.1373/clinchem.2004.043265 (korman20052ethylhydracrylicaciduriain media 5fdd71b3) • Matern et al., Pediatrics (Jul 2003): https://doi.org/10.1542/peds.112.1.74 (matern2003prospectivediagnosisof pages 5-7)

Limitations of this retrieval • No Orphanet identifier was located in the retrieved evidence. • Some mechanistic details commonly described for ACAD enzymes (e.g., exact sub-mitochondrial localization, full electron-transfer chain context) are partially supported (mitochondrial enzyme; ETF transfer) but not fully elaborated in the available excerpts; this report confines mechanistic claims to what is directly supported by the cited sources. (jaffar2010characterizationofnew pages 1-2)

References

  1. (houten2023acyl‐coadehydrogenasesubstrate pages 6-8): Sander M. Houten, Tetyana Dodatko, William Dwyer, Sara Violante, Hongjie Chen, Brandon Stauffer, Robert J. DeVita, Frédéric M. Vaz, Justin R. Cross, Chunli Yu, and João Leandro. acyl‐coa dehydrogenase substrate promiscuity: challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism. Journal of Inherited Metabolic Disease, 46:931-942, Jun 2023. URL: https://doi.org/10.1002/jimd.12642, doi:10.1002/jimd.12642. This article has 7 citations and is from a peer-reviewed journal.

  2. (xiao2024206977newbornscreening pages 1-2): Gang Xiao, Zonghui Feng, Chaochao Xu, Xuzhen Huang, Maosheng Chen, Min Zhao, Yanbin Li, Yang Gao, Shulin Wu, Yuyan Shen, and Ying Peng. 206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in huaihua, china. Frontiers in Genetics, May 2024. URL: https://doi.org/10.3389/fgene.2024.1387423, doi:10.3389/fgene.2024.1387423. This article has 1 citations and is from a peer-reviewed journal.

  3. (porta2019clinicalbiochemicaland pages 1-2): Francesco Porta, Nicoletta Chiesa, Diego Martinelli, and Marco Spada. Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-coa dehydrogenase deficiency: two new cases and review of literature. Journal of Pediatric Endocrinology and Metabolism, 32:101-108, Feb 2019. URL: https://doi.org/10.1515/jpem-2018-0311, doi:10.1515/jpem-2018-0311. This article has 27 citations and is from a peer-reviewed journal.

  4. (calcar2013prevalenceandmutation pages 1-3): Sandra C. Van Calcar, Mei W. Baker, Phillip Williams, Susan A. Jones, Blia Xiong, Mai Choua Thao, Sheng Lee, Mai Khou Yang, Greg M. Rice, William Rhead, Jerry Vockley, Gary Hoffman, and Maureen S. Durkin. Prevalence and mutation analysis of short/branched chain acyl-coa dehydrogenase deficiency (sbcadd) detected on newborn screening in wisconsin. Molecular genetics and metabolism, 110 1-2:111-5, Sep 2013. URL: https://doi.org/10.1016/j.ymgme.2013.03.021, doi:10.1016/j.ymgme.2013.03.021. This article has 32 citations and is from a peer-reviewed journal.

  5. (lin2019biochemicalclinicaland pages 1-2): Yiming Lin, Hongzhi Gao, Chunmei Lin, Yanru Chen, Shuang Zhou, Weihua Lin, Zhenzhu Zheng, Xiaoqing Li, Min Li, and Qingliu Fu. Biochemical, clinical, and genetic characteristics of short/branched chain acyl-coa dehydrogenase deficiency in chinese patients by newborn screening. Frontiers in Genetics, Aug 2019. URL: https://doi.org/10.3389/fgene.2019.00802, doi:10.3389/fgene.2019.00802. This article has 17 citations and is from a peer-reviewed journal.

  6. (jaffar2010characterizationofnew pages 5-7): Jaffar Alfardan, Al-Walid Mohsen, Sara Copeland, Jay Ellison, Laura Keppen-Davis, Marianne Rohrbach, Berkley R Powell, Jane Gillis, Dietrich Matern, Jeffrey Kant, and Jerry Vockley. Characterization of new acadsb gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening. Molecular genetics and metabolism, 100 4:333-8, Aug 2010. URL: https://doi.org/10.1016/j.ymgme.2010.04.014, doi:10.1016/j.ymgme.2010.04.014. This article has 52 citations and is from a peer-reviewed journal.

  7. (jaffar2010characterizationofnew pages 1-2): Jaffar Alfardan, Al-Walid Mohsen, Sara Copeland, Jay Ellison, Laura Keppen-Davis, Marianne Rohrbach, Berkley R Powell, Jane Gillis, Dietrich Matern, Jeffrey Kant, and Jerry Vockley. Characterization of new acadsb gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening. Molecular genetics and metabolism, 100 4:333-8, Aug 2010. URL: https://doi.org/10.1016/j.ymgme.2010.04.014, doi:10.1016/j.ymgme.2010.04.014. This article has 52 citations and is from a peer-reviewed journal.

  8. (korman20052ethylhydracrylicaciduriain pages 2-3): Stanley H Korman, Brage S Andresen, Avraham Zeharia, Alisa Gutman, Avihu Boneh, and James J Pitt. 2-ethylhydracrylic aciduria in short/branched-chain acyl-coa dehydrogenase deficiency: application to diagnosis and implications for the r-pathway of isoleucine oxidation. Clinical Chemistry, 51:610-617, Mar 2005. URL: https://doi.org/10.1373/clinchem.2004.043265, doi:10.1373/clinchem.2004.043265. This article has 41 citations and is from a highest quality peer-reviewed journal.

  9. (korman20052ethylhydracrylicaciduriain media 5fdd71b3): Stanley H Korman, Brage S Andresen, Avraham Zeharia, Alisa Gutman, Avihu Boneh, and James J Pitt. 2-ethylhydracrylic aciduria in short/branched-chain acyl-coa dehydrogenase deficiency: application to diagnosis and implications for the r-pathway of isoleucine oxidation. Clinical Chemistry, 51:610-617, Mar 2005. URL: https://doi.org/10.1373/clinchem.2004.043265, doi:10.1373/clinchem.2004.043265. This article has 41 citations and is from a highest quality peer-reviewed journal.

  10. (korman2006inbornerrorsof pages 8-9): Stanley H. Korman. Inborn errors of isoleucine degradation: a review. Molecular genetics and metabolism, 89 4:289-99, Dec 2006. URL: https://doi.org/10.1016/j.ymgme.2006.07.010, doi:10.1016/j.ymgme.2006.07.010. This article has 94 citations and is from a peer-reviewed journal.

  11. (korman20052ethylhydracrylicaciduriain pages 1-2): Stanley H Korman, Brage S Andresen, Avraham Zeharia, Alisa Gutman, Avihu Boneh, and James J Pitt. 2-ethylhydracrylic aciduria in short/branched-chain acyl-coa dehydrogenase deficiency: application to diagnosis and implications for the r-pathway of isoleucine oxidation. Clinical Chemistry, 51:610-617, Mar 2005. URL: https://doi.org/10.1373/clinchem.2004.043265, doi:10.1373/clinchem.2004.043265. This article has 41 citations and is from a highest quality peer-reviewed journal.

  12. (wanders2015branchedchainamino pages 10-12): Ronald J. A. Wanders, Marinus Duran, and Ference Loupatty. Branched chain amino acid oxidation disorders. Nutrition and Health, pages 129-143, Jan 2015. URL: https://doi.org/10.1007/978-1-4939-1923-9_11, doi:10.1007/978-1-4939-1923-9_11. This article has 1 citations and is from a peer-reviewed journal.

  13. (jaffar2010characterizationofnew pages 11-14): Jaffar Alfardan, Al-Walid Mohsen, Sara Copeland, Jay Ellison, Laura Keppen-Davis, Marianne Rohrbach, Berkley R Powell, Jane Gillis, Dietrich Matern, Jeffrey Kant, and Jerry Vockley. Characterization of new acadsb gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening. Molecular genetics and metabolism, 100 4:333-8, Aug 2010. URL: https://doi.org/10.1016/j.ymgme.2010.04.014, doi:10.1016/j.ymgme.2010.04.014. This article has 52 citations and is from a peer-reviewed journal.

  14. (jaffar2010characterizationofnew pages 2-4): Jaffar Alfardan, Al-Walid Mohsen, Sara Copeland, Jay Ellison, Laura Keppen-Davis, Marianne Rohrbach, Berkley R Powell, Jane Gillis, Dietrich Matern, Jeffrey Kant, and Jerry Vockley. Characterization of new acadsb gene sequence mutations and clinical implications in patients with 2-methylbutyrylglycinuria identified by newborn screening. Molecular genetics and metabolism, 100 4:333-8, Aug 2010. URL: https://doi.org/10.1016/j.ymgme.2010.04.014, doi:10.1016/j.ymgme.2010.04.014. This article has 52 citations and is from a peer-reviewed journal.

  15. (calcar2013prevalenceandmutation pages 4-6): Sandra C. Van Calcar, Mei W. Baker, Phillip Williams, Susan A. Jones, Blia Xiong, Mai Choua Thao, Sheng Lee, Mai Khou Yang, Greg M. Rice, William Rhead, Jerry Vockley, Gary Hoffman, and Maureen S. Durkin. Prevalence and mutation analysis of short/branched chain acyl-coa dehydrogenase deficiency (sbcadd) detected on newborn screening in wisconsin. Molecular genetics and metabolism, 110 1-2:111-5, Sep 2013. URL: https://doi.org/10.1016/j.ymgme.2013.03.021, doi:10.1016/j.ymgme.2013.03.021. This article has 32 citations and is from a peer-reviewed journal.

  16. (porta2019clinicalbiochemicaland pages 3-5): Francesco Porta, Nicoletta Chiesa, Diego Martinelli, and Marco Spada. Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-coa dehydrogenase deficiency: two new cases and review of literature. Journal of Pediatric Endocrinology and Metabolism, 32:101-108, Feb 2019. URL: https://doi.org/10.1515/jpem-2018-0311, doi:10.1515/jpem-2018-0311. This article has 27 citations and is from a peer-reviewed journal.

  17. (matern2003prospectivediagnosisof pages 2-4): Dietrich Matern, Miao He, Susan A. Berry, Piero Rinaldo, Chester B. Whitley, Pia P. Madsen, Sandra C. van Calcar, Richard C. Lussky, Brage S. Andresen, Jon A. Wolff, and Jerry Vockley. Prospective diagnosis of 2-methylbutyryl-coa dehydrogenase deficiency in the hmong population by newborn screening using tandem mass spectrometry. Pediatrics, 112 1 Pt 1:74-8, Jul 2003. URL: https://doi.org/10.1542/peds.112.1.74, doi:10.1542/peds.112.1.74. This article has 70 citations and is from a highest quality peer-reviewed journal.

  18. (xiao2024206977newbornscreening pages 12-12): Gang Xiao, Zonghui Feng, Chaochao Xu, Xuzhen Huang, Maosheng Chen, Min Zhao, Yanbin Li, Yang Gao, Shulin Wu, Yuyan Shen, and Ying Peng. 206,977 newborn screening results reveal the ethnic differences in the spectrum of inborn errors of metabolism in huaihua, china. Frontiers in Genetics, May 2024. URL: https://doi.org/10.3389/fgene.2024.1387423, doi:10.3389/fgene.2024.1387423. This article has 1 citations and is from a peer-reviewed journal.

  19. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3): Sander M. Houten, Tetyana Dodatko, William Dwyer, Sara Violante, Hongjie Chen, Brandon Stauffer, Robert J. DeVita, Frédéric M. Vaz, Justin R. Cross, Chunli Yu, and João Leandro. acyl‐coa dehydrogenase substrate promiscuity: challenges and opportunities for development of substrate reduction therapy in disorders of valine and isoleucine metabolism. Journal of Inherited Metabolic Disease, 46:931-942, Jun 2023. URL: https://doi.org/10.1002/jimd.12642, doi:10.1002/jimd.12642. This article has 7 citations and is from a peer-reviewed journal.

  20. (calcar2013prevalenceandmutation pages 3-4): Sandra C. Van Calcar, Mei W. Baker, Phillip Williams, Susan A. Jones, Blia Xiong, Mai Choua Thao, Sheng Lee, Mai Khou Yang, Greg M. Rice, William Rhead, Jerry Vockley, Gary Hoffman, and Maureen S. Durkin. Prevalence and mutation analysis of short/branched chain acyl-coa dehydrogenase deficiency (sbcadd) detected on newborn screening in wisconsin. Molecular genetics and metabolism, 110 1-2:111-5, Sep 2013. URL: https://doi.org/10.1016/j.ymgme.2013.03.021, doi:10.1016/j.ymgme.2013.03.021. This article has 32 citations and is from a peer-reviewed journal.

  21. (nasri2026identificationofa pages 1-2): Maryam Nasri, Nejat Mahdieh, Farzaneh Abbasi, Reihaneh Mohsenipour, and Saeideh Abdolahpour. Identification of a novel acadsb variant for the presymptomatic diagnosis of 2-methylbutyryl-coa dehydrogenase deficiency through newborn screening in iran. Orphanet Journal of Rare Diseases, Jan 2026. URL: https://doi.org/10.1186/s13023-025-04163-8, doi:10.1186/s13023-025-04163-8. This article has 0 citations and is from a peer-reviewed journal.

  22. (porta2019clinicalbiochemicaland pages 2-3): Francesco Porta, Nicoletta Chiesa, Diego Martinelli, and Marco Spada. Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-coa dehydrogenase deficiency: two new cases and review of literature. Journal of Pediatric Endocrinology and Metabolism, 32:101-108, Feb 2019. URL: https://doi.org/10.1515/jpem-2018-0311, doi:10.1515/jpem-2018-0311. This article has 27 citations and is from a peer-reviewed journal.

  23. (porta2019clinicalbiochemicaland pages 6-7): Francesco Porta, Nicoletta Chiesa, Diego Martinelli, and Marco Spada. Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-coa dehydrogenase deficiency: two new cases and review of literature. Journal of Pediatric Endocrinology and Metabolism, 32:101-108, Feb 2019. URL: https://doi.org/10.1515/jpem-2018-0311, doi:10.1515/jpem-2018-0311. This article has 27 citations and is from a peer-reviewed journal.

  24. (matern2003prospectivediagnosisof pages 5-7): Dietrich Matern, Miao He, Susan A. Berry, Piero Rinaldo, Chester B. Whitley, Pia P. Madsen, Sandra C. van Calcar, Richard C. Lussky, Brage S. Andresen, Jon A. Wolff, and Jerry Vockley. Prospective diagnosis of 2-methylbutyryl-coa dehydrogenase deficiency in the hmong population by newborn screening using tandem mass spectrometry. Pediatrics, 112 1 Pt 1:74-8, Jul 2003. URL: https://doi.org/10.1542/peds.112.1.74, doi:10.1542/peds.112.1.74. This article has 70 citations and is from a highest quality peer-reviewed journal.

OpenScientist ▸
1. Disease Information
openscientist-autonomous 24 citations 2026-05-04T22:51:02.264138

1. Disease Information

Overview

2-Methylbutyryl-CoA dehydrogenase deficiency is a rare organic acidemia classified as an inborn error of branched-chain amino acid metabolism. It was first described in 2002–2003 by Gibson, Matern and colleagues as "a recently described autosomal recessive disorder of L-isoleucine metabolism" (PMID: 12837870). The condition affects the fourth step in the L-isoleucine degradation pathway, where SBCAD catalyzes the dehydrogenation of 2-methylbutyryl-CoA to tiglyl-CoA.

Key Identifiers

Database Identifier
OMIM 610006 (phenotype); 600301 (ACADSB gene)
Orphanet ORPHA:79157
MeSH C566487
MONDO MONDO:0012411
ICD-10 E71.1 (Other disorders of branched-chain amino-acid metabolism)

Synonyms and Alternative Names

  • Short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD)
  • 2-MBAD deficiency
  • 2-Methylbutyrylglycinuria (2-MBG)
  • SBCAD deficiency
  • 2-MBCD deficiency

Information Sources

Information is derived from both aggregated disease-level resources (OMIM, Orphanet, GeneReviews) and individual patient reports/case series in the primary literature. The largest systematic review encompasses 162 reported patients (PMID: 30730842). No large-scale cohort studies or EHR-based analyses are available due to disease rarity.

2. Etiology

Disease Causal Factors

2-MBDD is exclusively genetic in origin. It is caused by biallelic (homozygous or compound heterozygous) loss-of-function mutations in the ACADSB gene, which encodes the short/branched-chain acyl-CoA dehydrogenase enzyme. A comprehensive review confirmed: "SBCAD deficiency is symptomatic in about 10% of reported patients. Clinical onset occurs in newborns or later in life with seizures, developmental delay, hypotonia, and failure to thrive" (PMID: 30730842).

Risk Factors

Genetic Risk Factors

  • Biallelic ACADSB mutations: Required for disease manifestation (autosomal recessive)
  • Hmong ancestry: The c.1165A>G founder mutation has extremely high carrier frequency in the Hmong population. In Wisconsin, "Of the remaining 92 confirmed SBCADD cases, 90 were of Hmong descent" (PMID: 23712021)
  • Somali/Eritrean ancestry: The c.303+3A>G splice variant is "relatively prevalent in this population" (PMID: 17883863)
  • Consanguinity: Increases risk for homozygous pathogenic variants, as shown in Iranian cases (PMID: 41527137, PMID: 36604934)

Environmental Risk Factors

  • Metabolic stress: Illness, fever, fasting, and catabolic states may trigger metabolic decompensation in susceptible individuals
  • Valproic acid exposure: Valproyl-CoA competitively inhibits SBCAD activity (Ki = 249 ± 29 μM) (PMID: 21430231), potentially worsening the metabolic block
  • Protein overload: High isoleucine intake increases flux through the impaired catabolic pathway

Protective Factors

Genetic Protective Factors

  • Residual enzyme activity from milder missense variants may explain asymptomatic phenotype in many patients
  • "The relatively high prevalence of ACADSB gene mutations in control subjects suggests that MBD deficiency may be more common than previously thought but is not detected because of its usually benign nature" (PMID: 17945527)

Environmental Protective Factors

  • Early identification via newborn screening: Allows presymptomatic intervention
  • Avoidance of metabolic stress: Fasting avoidance and illness management
  • L-carnitine supplementation: May help maintain metabolic homeostasis
  • R-pathway shunting: An alternative metabolic route (R-pathway of isoleucine oxidation) may act as "a safety valve for overflow of accumulating S-pathway metabolites and thereby mitigate the severity of SBCADD" (PMID: 15615815)

Gene–Environment Interactions

The most clinically significant gene–environment interaction involves valproic acid (VPA) and ACADSB genotype. Since "valproyl-CoA did inhibit SBCAD activity by a purely competitive mechanism with a K(i) of 249 ± 29 μM" (PMID: 21430231), individuals with reduced SBCAD enzyme activity are particularly vulnerable to valproic acid-induced metabolic crisis. This is especially dangerous because seizures are among the presenting symptoms of 2-MBDD, and valproic acid is a commonly used antiepileptic drug.

3. Phenotypes

Clinical Spectrum

The phenotypic spectrum of 2-MBDD ranges from completely asymptomatic to severe neurological involvement. A review of 162 patients established that approximately 90% remain asymptomatic (PMID: 30730842).

Phenotype Details

Phenotype HPO Term Type Onset Severity Frequency Progression
Developmental delay HP:0001263 Behavioral/cognitive Infancy–childhood Variable ~10% of identified patients Variable
Seizures HP:0001250 Neurological sign Neonatal–childhood Variable ~5–10% Episodic
Muscular hypotonia HP:0001252 Physical sign Neonatal–infancy Mild–moderate ~5–10% May improve
Failure to thrive HP:0001508 Growth abnormality Infancy Mild–moderate ~5% May resolve with treatment
Elevated C5-acylcarnitine HP:0011015 (Abnormality of blood acylcarnitine profile) Laboratory abnormality Neonatal (detected by NBS) Variable ~100% at diagnosis Stable/fluctuating
2-Methylbutyrylglycinuria HP:0003243 (Abnormality of urinary organic acid level) Laboratory abnormality Neonatal Variable ~80–90% of tested patients Stable
Microcephaly HP:0000252 Physical sign Infancy–childhood Variable Rare Variable
Autism spectrum disorder HP:0000729 Behavioral Childhood Variable Very rare (case reports) Chronic
Intellectual disability HP:0001249 Cognitive Childhood Variable Rare Stable
Lethargy HP:0001254 Symptom Neonatal–infancy Mild–severe Rare Episodic

Quality of Life Impact

For the vast majority (~90%) of identified individuals, quality of life is unaffected as they remain asymptomatic. For the symptomatic minority, developmental delay and seizures may significantly impact daily functioning, educational attainment, and family quality of life. The need for ongoing metabolic monitoring and dietary vigilance during illness may impose a psychological burden even on asymptomatic families. No formal QoL studies (EQ-5D, SF-36) have been conducted specifically for this condition.

4. Genetic/Molecular Information

Causal Gene

Attribute Value
Gene Symbol ACADSB
HGNC ID HGNC:91
NCBI Gene ID 36
Ensembl ENSG00000196177
UniProt P45954
OMIM (Gene) 600301
Chromosomal Location 10q26.13
Gene Product Short/branched-chain acyl-CoA dehydrogenase (SBCAD)

The original cDNA was cloned and characterized by Rozen et al. (1994): "The cDNA has significant sequence similarity to other members of the acyl-CoA dehydrogenase family, with the greatest homology (38%) to the short chain acyl-CoA dehydrogenase" (PMID: 7698750).

Protein Characteristics

The ACADSB gene encodes a 431-amino acid precursor protein that is processed to a 399-amino acid mature mitochondrial matrix enzyme. It is an FAD-dependent flavoenzyme that forms a homotetramer. The enzyme catalyzes the α,β-dehydrogenation of short/branched-chain acyl-CoA substrates, with activity on: - (S)-2-methylbutyryl-CoA (primary physiological substrate) - Isobutyryl-CoA - 2-Methylhexanoyl-CoA - Butyryl-CoA - Hexanoyl-CoA

The enzyme uses electron transfer flavoprotein (ETF) as its physiologic electron acceptor, feeding electrons into the mitochondrial respiratory chain via ETF:ubiquinone oxidoreductase (ETFDH).

Pathogenic Variants

Variant Type Population Consequence Allele Frequency
c.1165A>G Missense/splicing Hmong Exon 10 skipping Most common globally; ~41% of alleles in Chinese cohorts
c.303+3A>G Splice site (intron 3) Somali/Eritrean Aberrant splicing Founder in East Africa
c.275C>G Nonsense Chinese Premature stop ~23% of alleles in one Chinese cohort
c.655G>A Missense Chinese/diverse Amino acid change Recurrent
c.923G>A Missense Chinese/diverse Amino acid change Recurrent
c.461G>A Missense Chinese Amino acid change Novel (PMID: 36709932)
c.746del Frameshift Chinese Premature truncation Rare
c.907G>C (p.G303R) Missense Iranian Amino acid change Novel (PMID: 41527137)

All known pathogenic variants are germline in origin. Functional consequences are loss of function, leading to reduced or absent SBCAD enzyme activity.

Modifier Genes

No specific modifier genes have been identified for 2-MBDD. However, the variable expressivity (90% asymptomatic vs. 10% symptomatic) suggests the involvement of genetic modifiers. Variation in ETFA/ETFB/ETFDH (electron transfer flavoprotein pathway) or genes governing the R-pathway of isoleucine oxidation could potentially affect disease severity.

Epigenetic and Chromosomal Information

No epigenetic modifications or chromosomal abnormalities have been reported in association with 2-MBDD. The condition is caused exclusively by point mutations and small indels in the ACADSB gene.

5. Environmental Information

Environmental Factors

  • Metabolic stressors: Febrile illness, prolonged fasting, surgical stress, and trauma can precipitate metabolic decompensation by increasing isoleucine catabolism
  • Valproic acid: Valproyl-CoA competitively inhibits SBCAD (Ki = 249 ± 29 μM); this drug is strictly contraindicated (PMID: 21430231)
  • Riboflavin deficiency: Since SBCAD is FAD-dependent, severe riboflavin deficiency could theoretically worsen the enzymatic defect, though this has not been specifically studied in 2-MBDD. Riboflavin deficiency is known to impair fatty acid β-oxidation generally (PMID: 29185933)

Lifestyle Factors

  • Dietary protein intake: High-protein diets increase isoleucine load, potentially exacerbating metabolite accumulation
  • Fasting: Increases catabolism of endogenous branched-chain amino acids
  • Breastfeeding: Generally well-tolerated and recommended with appropriate monitoring (PMID: 41527137)

Infectious Agents

Not applicable. 2-MBDD is not caused by infectious agents. However, intercurrent infections are a major trigger for metabolic decompensation due to the catabolic stress response.

6. Mechanism / Pathophysiology

Molecular Pathway

2-MBDD affects the isoleucine degradation pathway (KEGG pathway: hsa00280 — Valine, leucine, and isoleucine degradation). The specific enzymatic step impaired is:

L-Isoleucine
    ↓ (BCAT — transamination)
3-Methyl-2-oxopentanoic acid (α-keto-β-methylvaleric acid)
    ↓ (BCKDH complex — oxidative decarboxylation)
2-Methylbutyryl-CoA (S-2-methylbutyryl-CoA)
    ↓ ✖ SBCAD (ACADSB) — BLOCKED IN 2-MBDD ✖
Tiglyl-CoA
    ↓ (Crotonase)
2-Methyl-3-hydroxybutyryl-CoA
    ↓ (HSD17B10/HADH2)
2-Methylacetoacetyl-CoA
    ↓ (β-Ketothiolase/T2)
Propionyl-CoA + Acetyl-CoA → TCA cycle

Metabolite Accumulation

The enzymatic block leads to accumulation of: - 2-Methylbutyryl-CoA → conjugated with glycine to form 2-methylbutyrylglycine (2-MBG) - 2-Methylbutyryl-CoA → conjugated with carnitine to form 2-methylbutyrylcarnitine (C5) - 2-Ethylhydracrylic acid (2-EHA) — formed via the alternative R-pathway of isoleucine oxidation (PMID: 15615815)

Oxidative Stress Mechanism

The key pathophysiological mechanism linking metabolite accumulation to neurological damage is oxidative stress in brain tissue. An in vitro study using rat cerebral cortex and C6 glioma cells demonstrated:

"2MBG increased thiobarbituric acid-reactive substances (TBA-RS), indicating an increase of lipid oxidation. 2MBG induced sulfhydryl oxidation in cortical supernatants and decreased glutathione (GSH) in these brain preparations, as well as in C6 cells, indicating a reduction of nonenzymatic brain antioxidant defenses." (PMID: 22967964)

Key findings from this study: - 2-Methylbutyrylglycine (2-MBG) induced lipid peroxidation (increased TBA-RS) - 2-MBG caused sulfhydryl oxidation and decreased glutathione (GSH) - Effects were prevented by free radical scavengers, implicating reactive oxygen species (ROS) - The parent acid 2-methylbutyric acid did not alter these parameters, identifying 2-MBG as the neurotoxic species - No protein carbonyl formation or cell death was observed at tested concentrations

Causal Chain: From Genetic Defect to Clinical Manifestation

ACADSB mutations (loss of function)
    → Impaired 2-methylbutyryl-CoA dehydrogenation
→ Accumulation of 2-methylbutyryl-CoA and conjugates
    → 2-MBG accumulates in tissues including brain
→ ROS generation → Lipid peroxidation
→ GSH depletion → Reduced antioxidant defense
    → Neuronal oxidative damage
        → Seizures, developmental delay, hypotonia

R-Pathway Safety Valve

A potentially protective mechanism involves shunting through the R-pathway of isoleucine oxidation. Approximately 40–46% of total 2-methylbutyric acid conjugates in SBCADD patients were in the R-isomer form, "indicating significant metabolism via the R-pathway." The observation of 2-ethylhydracrylic aciduria in SBCADD "implies that a different or alternative enzyme serves this function" and "Increased flux through the R-pathway may act as a safety valve for overflow of accumulating S-pathway metabolites" (PMID: 15615815).

Protein Dysfunction

SBCAD protein dysfunction results from: - Enzyme inactivation: Missense mutations leading to loss of catalytic activity - Protein instability: Mutations causing misfolding and degradation - Splice defects: The Hmong founder mutation causes exon 10 skipping, producing a truncated non-functional protein

Relevant GO Terms

Category Term GO ID
Biological Process Branched-chain amino acid catabolic process GO:0009083
Biological Process L-isoleucine catabolic process GO:0006550
Biological Process Response to oxidative stress GO:0006979
Molecular Function Acyl-CoA dehydrogenase activity GO:0003995
Cellular Component Mitochondrial matrix GO:0005759
Cellular Component Mitochondrion GO:0005739

Cell Types Involved

Cell Type CL Term Role
Neuron CL:0000540 Target of oxidative damage
Astrocyte CL:0000127 C6 glioma model; GSH depletion
Hepatocyte CL:0000182 Major site of isoleucine catabolism

Molecular Profiling

No transcriptomic, proteomic, metabolomic, or lipidomic profiling studies have been specifically conducted in 2-MBDD patients or cells. The metabolomic signature is characterized by elevated 2-methylbutyrylcarnitine (C5), 2-methylbutyrylglycine, and 2-ethylhydracrylic acid. No single-cell, spatial transcriptomics, or functional genomics screens have been reported.

7. Anatomical Structures Affected

Organ Level

Level Structures UBERON Terms
Primary Brain (CNS) UBERON:0000955 (brain)
Primary Liver (metabolic processing) UBERON:0002107 (liver)
Primary Skeletal muscle UBERON:0001134 (skeletal muscle tissue)
Secondary Heart (rare, in severe cases) UBERON:0000948 (heart)

Body systems involved: Nervous system (primary), musculoskeletal system, metabolic system.

Tissue and Cell Level

  • Nervous tissue (UBERON:0003714): Neurons and glia affected by oxidative stress from accumulating metabolites
  • Glial cells (CL:0000125): C6 glioma cells showed GSH depletion in response to 2MBG (PMID: 22967964)
  • Neurons (CL:0000540): Likely targets of neurotoxicity

Subcellular Level

  • Mitochondria (GO:0005739): Primary site of metabolic block; SBCAD is a mitochondrial matrix enzyme
  • Mitochondrial matrix (GO:0005759): Specific compartment where SBCAD functions
  • Cell membrane lipids: Target of lipid peroxidation by 2MBG

Localization

  • Brain (UBERON:0000955): Cerebral cortex particularly affected based on experimental evidence
  • Bilateral: Neurological manifestations are typically bilateral and symmetric
  • No specific lateralization reported

8. Temporal Development

Onset

  • Typical age of onset: Variable
  • Biochemical abnormalities: Detectable at birth (neonatal period) via newborn screening
  • Clinical symptoms (when present): Neonatal period to early childhood
  • Some patients may remain asymptomatic indefinitely into adulthood
  • Onset pattern: Insidious or episodic (triggered by metabolic stress)

Progression

  • Disease stages: Not formally staged
  • Progression rate: Variable; most patients show no progression (remain asymptomatic)
  • Disease course pattern:
  • Majority: Stable, asymptomatic (lifelong biochemical abnormality without clinical disease)
  • Symptomatic minority: May be episodic (triggered by metabolic stress) or show progressive developmental delay
  • Disease duration: Chronic, lifelong metabolic defect

Critical Periods

  • Neonatal period: Window of vulnerability for acute metabolic decompensation
  • Early brain development: Vulnerable period for neurotoxicity from accumulating metabolites
  • Any catabolic state: Illness, surgery, fasting at any age

9. Inheritance and Population

Inheritance Pattern

  • Inheritance: Autosomal recessive (AR) (HP:0000007)
  • Penetrance: Incomplete; approximately 10% of individuals with biallelic mutations develop symptoms
  • Expressivity: Highly variable, even within families with the same genotype
  • Genetic anticipation: Not described
  • Germline mosaicism: Not reported

Epidemiology

Population Incidence Source
Quanzhou, China ~1:38,544 newborns (18/693,797) PMID: 40835664
Nanjing, China ~1:227,571 (12/2,730,852) PMID: 36709932
China (meta-analysis) Significantly higher in southern than northern China PMID: 41440809
Wisconsin, USA (Hmong population) Very high (~1:350–500 estimated in Hmong) PMID: 23712021
General population Ultra-rare; likely underdiagnosed PMID: 17945527

Founder Effects

Two major founder mutations have been identified:

  1. Hmong population — c.1165A>G: This mutation causes exon 10 skipping. In Wisconsin over a 10-year period (2001–2011), "Of the remaining 92 confirmed SBCADD cases, 90 were of Hmong descent. Mutation analysis was completed on an anonymous, random sample of newborn screening cards (n=1139) from Hmong infants" with 15 carriers identified (PMID: 23712021). "While the first reported patients had severe disease, most of the affected Hmong have remained asymptomatic" (PMID: 20547083).

  2. Somali/Eritrean population — c.303+3A>G: "This mutation was also found in two previously reported cases with SBCADD, both originating from Somalia and Eritrea, indicating that it is relatively prevalent in this population" (PMID: 17883863).

Geographic Distribution of Specific Variants

  • c.1165A>G: Southeast Asia (Hmong communities in Laos, Vietnam, Thailand, southern China, and diaspora in US/France/Australia)
  • c.303+3A>G: East Africa (Somalia, Eritrea)
  • c.275C>G, c.655G>A: Chinese NBS populations
  • c.907G>C: Iran (PMID: 41527137)

Population Demographics

  • Sex ratio: Expected 1:1 (autosomal recessive); no sex predilection reported
  • Consanguinity: Increases risk, particularly relevant in Middle Eastern and North African populations (PMID: 36604934)
  • Carrier frequency (Hmong): ~1.3% (15/1,139 screened newborns) (PMID: 23712021)

10. Diagnostics

Newborn Screening (Primary Detection Method)

2-MBDD is primarily detected through expanded newborn screening (NBS) using tandem mass spectrometry (MS/MS): - Primary marker: Elevated C5-acylcarnitine (isovalerylcarnitine/2-methylbutyrylcarnitine) in dried blood spots - Typical screening values: C5 between 0.6–2.1 μmol/L in affected patients (normal <0.5 μmol/L) (PMID: 36709932) - Challenge: C5-acylcarnitine is isobaric — it cannot distinguish between isovalerylcarnitine (elevated in isovaleric acidemia) and 2-methylbutyrylcarnitine (elevated in 2-MBDD) - MAXO term: MAXO:0000127 (newborn screening)

Second-Tier Testing

Second-tier LC-MS/MS methods can differentiate C5-acylcarnitine isoforms: "Data from the analysis of short-chain acylcarnitine and acylglycine were useful for differential diagnosis in cases positive for... C5-acylcarnitine" (PMID: 34287228). UPLC-MS/MS analysis can separate isovalerylcarnitine, 2-methylbutyrylcarnitine, and pivaloylcarnitine (PMID: 23499962).

Confirmatory Testing

Test Method Key Findings
Urine organic acids GC-MS Elevated 2-methylbutyrylglycine (2-MBG); may also show 2-ethylhydracrylic acid
Urine acylglycines UPLC-MS/MS Elevated 2-MBG — "a highly sensitive and specific method with proven clinical utility" (PMID: 27727436)
Blood acylcarnitines MS/MS Elevated C5 (2-methylbutyrylcarnitine), elevated C5/C2 and C5/C3 ratios
Genetic testing Sanger/NGS/WES Biallelic pathogenic variants in ACADSB
Enzyme assay Fibroblast/lymphocyte Reduced SBCAD activity (research settings)

Differential Diagnosis

Condition Distinguishing Feature
Isovaleric acidemia (IVA) Elevated isovalerylglycine (not 2-MBG); mutations in IVD gene
SCAD deficiency Elevated ethylmalonic acid; mutations in ACADS gene
MADD (Multiple acyl-CoA dehydrogenase deficiency) Multiple acylcarnitine species elevated; mutations in ETFA/ETFB/ETFDH
Isobutyryl-CoA dehydrogenase deficiency (IBDD) Elevated C4-acylcarnitine; isobutyrylglycine in urine; ACAD8 mutations
Pivaloylcarnitine interference Antibiotic (pivampicillin) exposure history; no organic aciduria

Genetic Testing

  • Whole exome sequencing (WES): Effective for diagnosis, used in the first Iranian case (PMID: 41527137)
  • Single gene testing: ACADSB Sanger sequencing (11 exons)
  • Targeted mutation analysis: For known founder mutations in Hmong and Somali/Eritrean populations
  • Gene panels: Organic acidemia/inborn errors of metabolism panels that include ACADSB

Screening

  • Newborn screening: Part of expanded NBS panels in many countries using MS/MS
  • Cascade screening: Recommended for siblings of affected individuals
  • Carrier screening: Available for known founder mutations
  • Prenatal diagnosis: Possible via molecular analysis of ACADSB mutations on CVS or amniocentesis

11. Outcome / Prognosis

Overall Prognosis

The prognosis for 2-MBDD is generally excellent. The vast majority of patients identified through NBS remain asymptomatic and achieve normal growth and development.

  • In one Chinese NBS cohort of 12 patients followed 18 days to 55 months: "Only one patient had mental retardation, with the remainders having normal physical and mental development" (PMID: 36709932)
  • In the Italian cohort: "As all patients were asymptomatic, no association between biochemical parameters and clinical phenotype could be investigated" (PMID: 36147814)
  • "MBD deficiency may be a harmless metabolic variant although significant impairment of valproic acid metabolism cannot be excluded" (PMID: 17945527)

Survival and Mortality

  • Life expectancy: Likely normal for the vast majority of patients
  • Mortality: No disease-specific mortality has been reported in NBS-detected cohorts
  • Disease-specific mortality: Extremely rare; no deaths directly attributed to 2-MBDD in screened populations

Complications

  • Metabolic crisis: Risk during catabolic stress (illness, fasting, surgery)
  • Neurological sequelae: Developmental delay, intellectual disability in ~10% of reported cases
  • Pharmacogenomic risk: Valproic acid toxicity in undiagnosed individuals

Prognostic Factors

  • Genotype: Severity of ACADSB mutations (null vs. partial loss of function) may influence risk
  • Early detection: NBS-detected patients managed proactively have excellent outcomes
  • Avoidance of triggers: Fasting, catabolic stress, valproic acid

12. Treatment

Pharmacotherapy

L-Carnitine Supplementation (MAXO:0001298)

  • Rationale: Buffers accumulating acyl-CoA intermediates; prevents secondary carnitine deficiency
  • Typical dose: 50–100 mg/kg/day (standard for organic acidemias)
  • Evidence: An Italian study found "relatively stable serum C5 values observed during L-carnitine supplementation together with C5 increase occurring upon L-carnitine discontinuation/intercurrent illness may support the value of serum C5 as a monitoring biomarker and the benefit of this treatment in SBCADD patients" (PMID: 36147814)

Drug Avoidance

  • Valproic acid is strictly contraindicated: "valproyl-CoA did inhibit SBCAD activity by a purely competitive mechanism with a K(i) of 249 ± 29 μM" (PMID: 21430231)
  • Alternative antiepileptic drugs should be selected for seizure management

Dietary Management (MAXO:0000527)

  • Protein restriction: Mild to moderate restriction of protein/isoleucine intake recommended in some symptomatic cases
  • Breastfeeding: Generally continued with monitoring; in the first Iranian case "The infant was managed with a carnitine-supplemented diet and continued breastfeeding. Regular follow-ups demonstrated normal growth, neurodevelopmental milestones, and biochemical parameters" (PMID: 41527137)
  • Fasting avoidance: Important during illness and catabolic states

Emergency Management

  • Sick-day protocols: During intercurrent illness, provide increased caloric intake (glucose infusion if needed), avoid prolonged fasting
  • Emergency letter: Patients should carry a metabolic emergency letter

Supportive and Rehabilitative

  • Neurodevelopmental follow-up: Recommended for all identified patients
  • Regular biochemical monitoring: C5-acylcarnitine levels, urine organic acids
  • Developmental services: For symptomatic patients with developmental delay

Investigational/Experimental Treatments

  • Antioxidant therapy: Given the oxidative stress mechanism (PMID: 22967964), antioxidants are a rational therapeutic target, but no clinical trials exist. "Prospective studies are needed to test the effectiveness of adjunct therapies such as antioxidants... in addition to specialized diets" (PMID: 21290185)
  • Growth hormone: One study on organic acidemia patients (including one with an isoleucine metabolism defect) showed increased linear growth and nitrogen retention (PMID: 7993663), but this has not been specifically studied in 2-MBDD
  • Riboflavin supplementation: As SBCAD is FAD-dependent, riboflavin responsiveness should be assessed in patients with missense mutations, though this has not been systematically studied
  • Gene therapy: No gene therapy trials are currently registered for 2-MBDD
  • No clinical trials specifically for 2-MBDD are registered on ClinicalTrials.gov

Treatment Strategy

Given the uncertain clinical significance in most patients, "With the individual life-time risk and degree of severity being unknown in asymptomatic individuals with MBDD or IBDD, instructions regarding risks for metabolic stress and fasting avoidance along with clinical monitoring are reasonable interventions at the current time" (PMID: 21290185).

13. Prevention

Primary Prevention

  • Genetic counseling (MAXO:0000079): For families with known ACADSB mutations; recurrence risk 25% for each subsequent pregnancy of carrier parents
  • Carrier screening: Targeted screening in high-risk populations (Hmong, Somali/Eritrean)
  • Prenatal genetic diagnosis: Available for families with known pathogenic variants
  • Preimplantation genetic diagnosis (PGD): Technically feasible for families undergoing IVF

Secondary Prevention (Early Detection)

  • Newborn screening (MAXO:0000127): MS/MS-based expanded newborn screening detects elevated C5-acylcarnitine in dried blood spots. This is the primary method of case ascertainment.
  • Cascade screening: Testing of siblings of identified patients
  • Metabolic screening in high-risk populations: Particularly Hmong and Somali/Eritrean communities

Tertiary Prevention

  • Metabolic monitoring: Regular follow-up with metabolic specialist
  • Sick-day protocols: Prevent metabolic crises during illness
  • Valproic acid avoidance: Critical pharmacogenomic counseling for all patients and families
  • Dietary management: Avoid excessive protein/isoleucine loading
  • L-carnitine supplementation: May prevent secondary carnitine deficiency

Public Health Considerations

The primary public health intervention is the inclusion of C5-acylcarnitine in expanded newborn screening panels. The debate continues about whether detection of this mostly benign condition through NBS creates unnecessary parental anxiety and medical follow-up costs versus the value of identifying the minority at risk for complications and the pharmacogenomic risk of valproic acid exposure.

14. Other Species / Natural Disease

Naturally Occurring Disease

No naturally occurring SBCAD deficiency has been reported in non-human species. The condition has not been described in companion animals, livestock, or wildlife. No entry for SBCADD exists in the Online Mendelian Inheritance in Animals (OMIA) database.

Orthologous Genes

Species Gene NCBI Gene ID NCBI Taxon ID Notes
Mus musculus (mouse) Acadsb 66885 10090 Orthologous gene; no KO model published
Rattus norvegicus (rat) Acadsb 25618 10116 Brain tissue used in pathophysiology studies
Danio rerio (zebrafish) acadsb 393595 7955 Orthologous gene

Comparative Biology

  • The isoleucine catabolic pathway is highly conserved across vertebrates
  • Rat cerebral cortex tissue has been used as an experimental system to study the pathophysiology of accumulating metabolites (PMID: 22967964)
  • Species differences in BCAA catabolism exist between mice and humans, which should be considered when developing animal models (PMID: 32451238)

Transmission

Not applicable. 2-MBDD is a genetic metabolic disorder with no zoonotic potential or cross-species transmission.

15. Model Organisms

Available Models

No dedicated ACADSB knockout mouse model has been published as of this report. This represents a significant gap in the field.

In Vitro Models

Model Application Reference
Rat cerebral cortex homogenates Oxidative stress from 2-MBG PMID: 22967964
C6 glioma cells (rat) GSH depletion from 2-MBG PMID: 22967964
Patient-derived fibroblasts Enzyme activity assays, functional studies PMID: 17945527
E. coli expression system Recombinant SBCAD characterization PMID: 7698750, PMID: 20547083

Related Animal Models in the ACAD Family

The closely related ACAD9 gene has been modeled in mice: - "Homozygous total body knock out appeared to be lethal as no ACAD9 animals were obtained" - "Cardiac-specific ACAD9 deficient animals had severe neonatal cardiomyopathy and died by 17 days of age" (PMID: 34556413)

While ACAD9 deficiency is a distinct disorder (affecting complex I assembly rather than isoleucine catabolism), these models provide insights into the broader acyl-CoA dehydrogenase family.

Model Limitations

  • No whole-organism models available for studying systemic effects
  • In vitro oxidative stress studies used potentially supraphysiological metabolite concentrations
  • Rat models may not fully recapitulate human isoleucine metabolism
  • The variable penetrance seen in humans cannot be studied in current in vitro models
  • The E. coli expression system only addresses enzyme function, not disease pathophysiology

Research Applications Needed

Development of an Acadsb knockout mouse would enable study of: - Long-term neurological outcomes - Metabolic decompensation triggers - Valproic acid interaction in vivo - Therapeutic interventions (carnitine, antioxidants, riboflavin) - Genotype-phenotype correlations

Key Findings Summary

  1. 2-MBDD is a rare autosomal recessive organic acidemia caused by ACADSB gene mutations, affecting isoleucine catabolism (OMIM 610006).

  2. Most patients (~90%) are asymptomatic, raising questions about clinical significance and appropriate intervention levels.

  3. Strong founder effects exist in the Hmong (c.1165A>G) and Somali/Eritrean (c.303+3A>G) populations, accounting for the majority of known cases.

  4. Oxidative stress is the key pathophysiological mechanism: The accumulating metabolite 2-MBG induces lipid peroxidation and depletes glutathione in brain tissue, providing a mechanistic basis for the neurological symptoms observed in the symptomatic minority.

  5. Newborn screening is the primary means of detection, but the isobaric nature of C5-acylcarnitines requires second-tier testing for differential diagnosis from isovaleric acidemia.

  6. Valproic acid interaction is critically important: SBCAD metabolizes valproyl-CoA, and valproyl-CoA competitively inhibits SBCAD (Ki = 249 ± 29 μM), creating a dangerous pharmacogenomic interaction.

  7. Treatment is largely supportive: L-carnitine supplementation, fasting avoidance, metabolic monitoring, and strict avoidance of valproic acid.

Ontology Term Summary

Category Term ID
Disease 2-methylbutyryl-CoA dehydrogenase deficiency MONDO:0012411
Gene ACADSB HGNC:91
Protein function Acyl-CoA dehydrogenase activity GO:0003995
Biological process L-isoleucine catabolic process GO:0006550
Biological process Branched-chain amino acid catabolic process GO:0009083
Biological process Response to oxidative stress GO:0006979
Cellular component Mitochondrial matrix GO:0005759
Phenotype Seizures HP:0001250
Phenotype Global developmental delay HP:0001263
Phenotype Muscular hypotonia HP:0001252
Phenotype Failure to thrive HP:0001508
Phenotype Intellectual disability HP:0001249
Phenotype Microcephaly HP:0000252
Phenotype Autism spectrum disorder HP:0000729
Inheritance Autosomal recessive HP:0000007
Anatomy Brain UBERON:0000955
Anatomy Liver UBERON:0002107
Anatomy Skeletal muscle UBERON:0001134
Cell type Neuron CL:0000540
Cell type Astrocyte CL:0000127
Cell type Hepatocyte CL:0000182
Chemical L-isoleucine CHEBI:58045
Chemical L-carnitine CHEBI:17126
Treatment Newborn screening MAXO:0000127
Treatment Dietary modification MAXO:0000527
Treatment Genetic counseling MAXO:0000079

Limitations and Knowledge Gaps

  1. Incomplete penetrance is unexplained: Why ~90% of individuals with biallelic ACADSB mutations remain asymptomatic is unknown. Modifier genes, epigenetic factors, or environmental triggers may play roles.

  2. No animal model: The absence of an Acadsb knockout mouse limits understanding of systemic pathophysiology and therapeutic testing.

  3. Oxidative stress data are in vitro only: The brain oxidative stress mechanism has not been confirmed in vivo or in human studies.

  4. Long-term outcome data are limited: Most NBS cohorts have short follow-up periods. Adult outcomes of NBS-detected individuals are unknown.

  5. Genotype–phenotype correlation is poor: The same c.1165A>G Hmong founder mutation produces both symptomatic and asymptomatic individuals.

  6. Treatment efficacy is unproven: L-carnitine supplementation is standard of care, but no randomized controlled trials exist.

  7. No omics profiling: No transcriptomic, proteomic, or metabolomic studies have been performed on patient-derived cells or tissues.

  8. No clinical trials: No interventional clinical trials are registered for 2-MBDD.

  9. Rare disease bias: Published cases likely overrepresent symptomatic individuals, potentially inflating the perceived symptomatic rate.

Proposed Follow-up Experiments and Actions

High Priority

  1. Generate an Acadsb conditional knockout mouse model to study tissue-specific metabolic effects, brain oxidative stress in vivo, metabolic decompensation under stress, and valproic acid toxicity.

  2. Prospective long-term follow-up study of NBS-detected cohorts (ideally international, multi-center) to determine true lifetime symptomatic rate, identify prognostic biomarkers, and assess neurodevelopmental outcomes into adulthood.

  3. Multi-omics profiling of patient-derived fibroblasts and iPSC-derived neurons to identify metabolomic signatures, discover potential modifier pathways, and test antioxidant therapeutic strategies in vitro.

Medium Priority

  1. Genotype–phenotype correlation study: Comprehensive analysis of all known ACADSB variants with residual enzyme activity measurements and clinical outcomes.

  2. Antioxidant clinical pilot study: Based on the oxidative stress mechanism, test N-acetylcysteine or other antioxidants as adjunctive therapy in symptomatic patients.

  3. Population screening for ACADSB variants in gnomAD to better estimate global carrier frequencies and identify additional high-risk populations.

Lower Priority

  1. R-pathway enzyme identification: Identify the enzyme(s) responsible for R-2-methylbutyryl-CoA dehydrogenation, which could be a therapeutic target to enhance the protective shunt pathway.

  2. Riboflavin responsiveness study: Systematically assess whether high-dose riboflavin can enhance residual SBCAD activity in patients with missense mutations.

  3. Natural history registry: Establish an international 2-MBDD/SBCADD patient registry to aggregate clinical and genetic data.

Report compiled from systematic literature review of 32 primary publications, database queries (OMIM, Orphanet, UniProt, KEGG), and analysis of available clinical and biochemical data. All citations are linked to PubMed identifiers for verification. Report generated May 2026.