← Research index  ·  Disorder page  ·  Source YAML

Cross-provider research synthesis

3-Methylcrotonyl-CoA Carboxylase Deficiency

MONDO:0018950 Curated 2026-07-04T00:00:00Z 9 harmonized findings
falcon · 53 citations openscientist · 24 citations
Concordant asserts the finding Partial supports a weaker/qualified form Contradictory conflicts with it Silent does not address it

Harmonized findings

3-Methylcrotonyl-CoA carboxylase deficiency is an autosomal recessive inborn error of leucine catabolism caused by biallelic pathogenic variants in MCCC1 (alpha subunit) or MCCC2 (beta subunit), producing deficiency of the mitochondrial biotin-dependent enzyme 3-methylcrotonyl-CoA carboxylase.

UNANIMOUS INTEGRATED
pathophysiologygenetic_factor
ProviderStanceScoreEvidence
falcon CONCORDANT 95% is an autosomal recessive defect of leucine metabolism caused by deficiency of mitochondrial
Falcon states the autosomal recessive, leucine-metabolism, mitochondrial MCC-deficiency mechanism, attributing it to variants in MCCC1 or MCCC2.
DOI:10.1186/1750-1172-7-31
openscientist CONCORDANT 97% is an autosomal recessive inborn error of leucine catabolism caused by biallelic mutations in either the
OpenScientist gives the same definition and specifies the alpha (MCCC1) and beta (MCCC2) subunit assignment of the heteromeric enzyme.

The clinical phenotype is remarkably variable, spanning from severe/fatal neonatal metabolic disease to entirely asymptomatic adults, with the majority of newborn-screening-identified individuals remaining asymptomatic.

UNANIMOUS INTEGRATED
phenotypeprognosis
ProviderStanceScoreEvidence
falcon CONCORDANT 90% ranging from acute neonatal onset with fatal outcome to asymptomatic adults
Falcon quotes the Grunert cohort framing of the phenotype spectrum and reports that >90% of NBS-identified individuals appear asymptomatic.
DOI:10.1186/1750-1172-7-31
openscientist CONCORDANT 92% an autosomal recessive disorder with a variable phenotype ranging from severe neonatal to asymptomatic adult forms
OpenScientist gives the same variable-phenotype framing and estimates ~85% of NBS-detected cases remain asymptomatic.
PMID:15868465

3-MCCD is the most frequently detected organic aciduria in tandem mass-spectrometry newborn screening, with reported incidence roughly on the order of 1:33,000-1:83,000 across populations.

MAJORITY INTEGRATED
epidemiology
ProviderStanceScoreEvidence
openscientist CONCORDANT 95% It is the most frequently detected organic aciduria in tandem mass spectrometry (MS/MS)-based newborn screening programs worldwide, with incidence estimates ranging from approximately 1:33,000 to 1:83,000 depending on the population studied.
OpenScientist directly states the most-frequent-organic-aciduria claim and the 1:33,000-1:83,000 incidence band.
falcon PARTIAL 55% summarizes literature prevalence ranging from **1:2,400 to 1:68,000** depending on population/screening context
Falcon reports program-specific incidences (e.g., Quanzhou 1/37,859) and a much wider literature prevalence band (1:2,400-1:68,000), overlapping but broader than OpenScientist's range and without the explicit "most-frequent organic aciduria" framing.

There is no reliable genotype-phenotype correlation, and newborn-screening C5OH levels do not predict which individuals will develop clinical symptoms.

UNANIMOUS INTEGRATED
genetic_factorprognosis
ProviderStanceScoreEvidence
falcon CONCORDANT 90% NBS C5OH level did not correlate with outcomes
Falcon reports that genotype/biochemical phenotype are not useful in predicting clinical course and that NBS C5OH did not correlate with outcomes.
DOI:10.1016/j.ymgme.2016.02.002
openscientist CONCORDANT 93% There was no correlation between newborn screening (NBS) C5OH level and presence of metabolic, newborn, later-life or developmental abnormalities in these cases
OpenScientist quotes the IBEM-IS registry finding of no C5OH-outcome correlation, matching the no-genotype-phenotype-correlation claim.
PMID:27033733

Confirmatory diagnosis uses urine organic acids (elevated 3-methylcrotonylglycine and 3-hydroxyisovaleric acid), which are increased in most but not all cases (~76.5%), so definitive diagnosis requires MCCC1/MCCC2 genetic testing.

UNANIMOUS INTEGRATED
diagnosis
ProviderStanceScoreEvidence
falcon CONCORDANT 90% while ~23.5% had normal urine organic acids despite diagnosis, underscoring the need for genetic confirmation
Falcon reports the same Quanzhou cohort figure (76.5% urine-OA positive, 23.5% normal despite diagnosis) and emphasizes genetic confirmation.
DOI:10.1016/j.ymgmr.2024.101127
openscientist CONCORDANT 90% Most patients [76.5%(13/17)] had increased urinary 3-methylcrotonylglycine (3-MCG) and 3-hydroxyisovaleric acid (3-HIVA) levels
OpenScientist quotes the same 76.5% urinary-metabolite figure and treats molecular testing as the definitive diagnostic tier.
PMID:39188588

There is no specific pharmacotherapy; management is supportive and preventive, centering on L-carnitine supplementation for secondary carnitine deficiency and avoidance of prolonged fasting with emergency protocols during catabolic stress.

UNANIMOUS INTEGRATED
treatment
ProviderStanceScoreEvidence
falcon CONCORDANT 88% supplementation with oral L-carnitine and a diet modestly restricted in leucine
Falcon describes real-world management as oral L-carnitine plus modest leucine restriction and notes the evidence base remains limited/unproven.
DOI:10.1186/1750-1172-7-31
openscientist CONCORDANT 90% Management is primarily supportive and preventive
OpenScientist states there is no specific pharmacological treatment and that management is supportive/preventive (carnitine, fasting avoidance, emergency protocols).

Secondary carnitine deficiency is a common, clinically actionable consequence, affecting roughly half of neonates (~47%).

MAJORITY INTEGRATED
pathophysiologydiagnosis
ProviderStanceScoreEvidence
openscientist CONCORDANT 90% approximately 47% of neonates showing secondary carnitine deficiency
OpenScientist quantifies secondary carnitine deficiency at ~47% of neonates as a secondary metabolic effect of acylcarnitine conjugation/excretion.
PMID:39188588
falcon PARTIAL 55% multiple cohorts report low C0/free carnitine in a subset and/or need for supplementation
Falcon confirms frequent secondary carnitine deficiency but reports it as raw counts (8 neonates and all adults in the Quanzhou cohort) rather than the ~47% figure, so it is a partial/qualitative match on the exact rate.

Developmental disability is recorded in roughly 15% of cases with developmental data, but is not clearly attributable to 3-MCCD; nonspecific neurodevelopmental phenotypes in consanguineous families may instead reflect other recessive disorders.

UNANIMOUS LEAD
phenotypeprognosis
ProviderStanceScoreEvidence
openscientist CONCORDANT 80% 15% of those with available developmental information had recorded developmental disabilities not clearly attributable to other causes
OpenScientist reports the IBEM-IS 15% developmental-disability figure with the explicit "not clearly attributable to other causes" caveat.
PMID:27033733
falcon CONCORDANT 75% nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes
Falcon strengthens the attribution caveat with the Shepard exome study, arguing nonspecific phenotypes in consanguineous cases are likely due to other recessive genes, not MCC deficiency. Concordant in direction, with added mechanistic emphasis on the confound.
DOI:10.1038/gim.2014.157
Attribution is genuinely unresolved; the providers agree the association is reported but caution against causal attribution to MCC. Kept as a lead pending disease-specific evidence rather than promoted as a curated phenotype.

Recent (2024) high-resolution cryo-EM structures of human MCC reveal a ligand-dependent relocation of biotin from an exo-site to an endo-site upon acyl-CoA binding, providing a framework for interpreting variant dysfunction.

SINGLE LEAD
gene_functionpathophysiology
ProviderStanceScoreEvidence
falcon CONCORDANT 85% biotin is relocated from an exo-site to an endo-site upon acetyl-CoA binding
Falcon reports the 2024 cryo-EM MCC structures and the exo-to-endo biotin relocation coupled to acyl-CoA binding as a new mechanistic framework.
DOI:10.1101/2024.04.30.591959
openscientist SILENT —
OpenScientist describes the alpha6-beta6 dodecameric holoenzyme and the biotin prosthetic group but does not report the 2024 cryo-EM structures or the exo-to-endo biotin relocation dynamic.
Falcon-only structural insight from a preprint; retained as a mechanistic lead rather than promoted, pending peer review.

Narrative

Overview

Both providers frame 3-MCCD as an autosomal recessive inborn error of leucine catabolism caused by biallelic MCCC1/MCCC2 variants, in which an enzymatic block at the fourth step of leucine degradation diverts 3-methylcrotonyl-CoA to 3-HIVA, 3-MCG, and C5OH. Both emphasize that the condition is the most frequently detected organic aciduria on tandem-MS newborn screening yet has a strikingly variable, predominantly benign phenotype, driving an unresolved debate about screening utility.

Agreement

The reports converge on the core biology (leucine-catabolic block, biallelic MCCC1/MCCC2, mitochondrial biotin-dependent MCC), the highly variable phenotype from severe neonatal disease to asymptomatic adulthood, the absence of a reliable genotype-phenotype correlation and non-predictive NBS C5OH levels, the confirmatory biomarker profile (urine 3-MCG/3-HIVA elevated in ~76.5% of cases, molecular testing definitive), frequent secondary carnitine deficiency, and supportive-only management (L-carnitine, fasting avoidance, emergency protocols). They also both flag the ~15% developmental-disability figure while cautioning that it is not clearly attributable to MCC deficiency.

Divergence

OpenScientist is broader and more registry/database-oriented: it supplies the explicit "most-frequent organic aciduria" claim, a 1:33,000-1:83,000 incidence band, the MCCA-R385S dominant-negative allele, circadian regulation of MCC biotinylation, and structured OMIM/Orphanet/MONDO identifiers. Falcon is more literature-cohort-oriented: it foregrounds program-level newborn-screening performance (very low PPV ~0.69%, a wider 1:2,400-1:68,000 prevalence band), the Morscher single-allele screen-positive caveat, the Shepard consanguinity/other-recessive-gene attribution problem, and a 2024 cryo-EM structural insight (exo-to-endo biotin relocation) that OpenScientist does not cover. The apparent numeric differences (asymptomatic fraction, prevalence framing) are coverage/denominator differences, not contradictions.

Integration

The concordant findings — AR biallelic MCCC1/MCCC2 etiology, the leucine-catabolic block and metabolite diversion, the variable/benign phenotype, absent genotype-phenotype correlation, the confirmatory biomarker hierarchy, secondary carnitine deficiency, and supportive management — are suitable for integration into the disorder entry with verified primary-literature evidence.

Not integrated (leads)

The ~15% developmental-disability association is retained as a lead because both providers caution it may reflect other recessive disorders rather than MCC deficiency, and the 2024 cryo-EM exo-to-endo biotin-relocation insight is retained as a mechanistic lead pending peer review. Provider-specific items (dominant-negative R385S, circadian biotinylation, NBS PPV and single-allele screen-positive caveats) remain leads for targeted curation.

Cross-provider synthesis comparing falcon (Edison Scientific Literature, cohort/structure-focused) and openscientist (autonomous, comprehensive 15-domain) reports. No direct contradictions were found; divergence is coverage, framing, and recency (falcon adds a 2024 cryo-EM structural insight and NBS-performance/attribution caveats; openscientist adds the most-frequent-organic-aciduria framing, incidence band, and dominant-negative allele). All best_matching_text values are verbatim excerpts from the cited report files; literature evidence snippets were intentionally left to the main curation pipeline pending fetch-reference verification.