Isobutyryl-CoA Dehydrogenase Deficiency

Mendelian MONDO:0012648 Pathograph 36 Organic Acidemia Inborn Error of Metabolism

Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive inborn error of valine catabolism caused by biallelic pathogenic variants in ACAD8. The enzyme isobutyryl-CoA dehydrogenase catalyzes the conversion of isobutyryl-CoA to methacrylyl-CoA within the mitochondrial valine degradation pathway. IBDD is most commonly identified through newborn screening by elevation of C4-acylcarnitine in dried blood spots. The estimated incidence is approximately 1:62,599 based on a Chinese newborn screening cohort. Most affected individuals remain clinically asymptomatic, and the condition is often regarded as a biochemical phenotype with limited clinical penetrance. In a comprehensive 172-case literature synthesis, 146 individuals (85%) were asymptomatic. A minority of patients develop heterogeneous findings including anemia, transient developmental delay, hepatic transaminase elevations, or rarely cardiomyopathy. Enzyme redundancy and substrate promiscuity among acyl-CoA dehydrogenases may partially explain the low clinical penetrance observed in many individuals. Long-term prognosis is generally favorable, with most NBS-identified patients remaining healthy through childhood.

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0
Mappings
0
Definitions
0
Inheritance
5
Pathophysiology
0
Histopathology
13
Phenotypes
36
Pathograph
2
Genes
8
Treatments
2
Subtypes
0
Differentials
0
Datasets
0
Trials
0
Models
1
Deep Research
🏷

Classifications

Harrison's Chapter
hereditary disease
◆

Subtypes

2
Asymptomatic biochemical isobutyryl-CoA dehydrogenase deficiency
Most individuals identified on newborn screening remain clinically asymptomatic and primarily exhibit persistent biochemical abnormalities (elevated C4-acylcarnitine).
Show evidence (1 reference)
PMID:33432785 SUPPORT Human Clinical
"Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis."
Supports a major asymptomatic biochemical-predominant subtype.
Symptomatic clinical isobutyryl-CoA dehydrogenase deficiency
A minority of individuals develop heterogeneous clinical features, including developmental delay, growth issues, hepatic abnormalities, or rare cardiomyopathy.
Show evidence (1 reference)
PMID:30253142 SUPPORT Human Clinical
"Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms."
Supports a less common symptomatic subtype with variable clinical expression.
⚙

Pathophysiology

5
ACAD8 molecular function deficiency
Biallelic ACAD8 pathogenic variants reduce isobutyryl-CoA dehydrogenase catalytic activity in mitochondria.
hepatocyte link
ACAD8 link
L-valine catabolic process link ↓ DECREASED
acyl-CoA dehydrogenase activity link
mitochondrion link
Downstream
Impaired mitochondrial valine catabolism Reduced ACAD8 activity blocks isobutyryl-CoA oxidation in the valine pathway.
Largely asymptomatic course ACAD8-related isobutyryl-CoA dehydrogenase deficiency is most often a low-penetrance biochemical phenotype detected by newborn screening rather than a consistently symptomatic clinical disease.
Anemia Anemia is a rare reported clinical manifestation in symptomatic IBDD.
Dilated cardiomyopathy Cardiomyopathy was reported in the original symptomatic IBDD case.
Motor developmental delay Motor delay is among the nonspecific manifestations reported in a minority of cases.
Growth delay Failure to thrive or growth delay is reported in a small symptomatic subset.
Speech delay Speech delay is reported in isolated symptomatic cases.
Muscular hypotonia Hypotonia is a nonspecific manifestation in a minority of symptomatic patients.
Autism Autism has been reported in a single IBDD case without an alternative genetic diagnosis, but causality remains uncertain.
Vomiting Emesis is reported among nonspecific symptomatic presentations.
Ketotic hypoglycemia Ketotic hypoglycemia has been reported, but the authors considered causality uncertain.
Show evidence (1 reference)
PMID:34544473 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8"
Supports ACAD8 molecular dysfunction as the initiating defect.
Impaired mitochondrial valine catabolism
Loss of ACAD8 function creates a metabolic block in valine degradation, leading to accumulation of isobutyryl-CoA and diversion into alternate conjugation products including isobutyrylcarnitine (C4) and isobutyrylglycine.
valine catabolic process link branched-chain amino acid catabolic process link
Downstream
Metabolite accumulation and biomarker shunting ACAD8 loss blocks valine catabolism and diverts accumulating isobutyryl-CoA into detectable C4 and glycine conjugates.
Show evidence (1 reference)
PMID:21104317 SUPPORT Other
"Valine is one of the three branched-chain amino acids which undergoes oxidation within mitochondria."
Review confirming valine oxidation occurs in mitochondria via the ACAD8-dependent pathway.
Metabolite accumulation and biomarker shunting
Loss of ACAD8 activity leads to accumulation of isobutyryl-CoA, which is conjugated to carnitine (forming C4-acylcarnitine) and glycine (forming isobutyrylglycine). Elevated C4-acylcarnitine with increased C4/C2 and C4/C3 ratios is the hallmark newborn screening marker. Urinary isobutyrylglycine is variably present and may be intermittently normal.
branched-chain amino acid catabolic process link
Downstream
C4-acylcarnitine (isobutyrylcarnitine) Accumulated isobutyryl-CoA is conjugated to carnitine, producing elevated C4-acylcarnitine.
Elevated C4-acylcarnitine The same C4-acylcarnitine accumulation is detected clinically as the newborn-screening phenotype.
Isobutyrylglycine (urinary) Isobutyryl-CoA can also be conjugated to glycine and excreted as urinary isobutyrylglycine, although this marker is variable.
C4-acylcarnitine ratio biomarkers (C4/C0, C4/C6, C4/C8) Persistent C4-acylcarnitine elevation shifts C4-based acylcarnitine ratios used for screening discrimination.
Free carnitine Carnitine conjugation can contribute to secondary carnitine depletion in rare symptomatic cases.
Hepatic involvement and mitochondrial stress Reported liver-test abnormalities and the ACAD8-deficient mouse liver phenotype suggest a possible hepatic consequence, but the intervening mechanism remains unresolved.
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3. Isobutyrylglycine occurred in only 8 patients."
Demonstrates the characteristic biomarker pattern including variable isobutyrylglycine.
PMID:41606743 SUPPORT Human Clinical
"Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker."
Literature synthesis confirms C4-acylcarnitine as universal in reported IBDD and isobutyrylglycinuria as common but variable.
Enzyme redundancy and low clinical penetrance
A plausible mechanistic explanation for the frequently benign phenotype of IBDD is substrate promiscuity among acyl-CoA dehydrogenase family members. In HEK-293 ACAD8-deletion models, other ACADs appear to compensate for isobutyryl-CoA handling, which may help explain the low clinical penetrance observed in human cohorts.
Downstream
Largely asymptomatic course ACAD substrate promiscuity may help explain why most reported ACAD8-deficient individuals remain clinically asymptomatic despite persistent biochemical abnormalities.
Show evidence (2 references)
PMID:37309295 SUPPORT Other
"Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences."
Directly states ACAD8 deficiency is considered a biochemical abnormality with limited clinical significance.
PMID:37309295 SUPPORT In Vitro
"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."
Demonstrates substrate promiscuity among ACADs for isobutyryl-CoA in cell models.
Hepatic involvement and mitochondrial stress
A subset of IBDD individuals shows liver enzyme abnormalities including elevated transaminases and gamma-glutamyl transferase. One reported human case had hepatomegaly with ultrasound findings suggestive of hepatic steatosis, and an ACAD8-deficient mouse model develops hepatic steatosis with abnormal hepatocyte mitochondria.
hepatocyte link
liver link
Downstream
Elevated hepatic transaminases The hepatic involvement signal most often appears as isolated serum transaminase elevation.
Hepatic steatosis One reported human case and the ACAD8-deficient mouse model suggest possible hepatic steatosis, although causality remains uncertain.
Show evidence (3 references)
PMID:41606743 SUPPORT Human Clinical
"altered biochemical markers of liver function were reported in 19 individuals"
Literature synthesis reports liver biochemical abnormalities in human IBDD cases.
PMID:21659959 SUPPORT Model Organism
"The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis."
Mouse model of IBDD showing progressive hepatic steatosis and mitochondrial abnormalities.
PMID:21659959 SUPPORT Model Organism
"Homozygous mutant mice hepatocytes had abnormal mitochondria with crystalline inclusions, suggestive of mitochondriopathy."
Demonstrates mitochondrial pathology in hepatocytes of ACAD8-deficient mice.
⬡

Pathograph

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

13
Blood 1
Anemia OCCASIONAL Anemia (HP:0001903)
Show evidence (1 reference)
PMID:17304052 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency."
The index case presented with anemia alongside cardiomyopathy.
Cardiovascular 1
Dilated cardiomyopathy VERY_RARE Dilated cardiomyopathy (HP:0001644)
Show evidence (2 references)
PMID:17304052 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency."
The index IBDD case had cardiomyopathy as a presenting feature.
PMID:28053874 SUPPORT Human Clinical
"One reported non-screened patient had dilated cardiomyopathy and anaemia at the age of two years."
Confirms dilated cardiomyopathy in the historically reported symptomatic case.
Digestive 2
Vomiting OCCASIONAL Vomiting (HP:0002013)
Show evidence (1 reference)
PMID:33432785 SUPPORT Human Clinical
"Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis."
Emesis listed among reported IBDD symptoms.
Hepatic steatosis VERY_RARE Hepatic steatosis (HP:0001397)
Show evidence (3 references)
PMID:41606743 SUPPORT Human Clinical
"One 11-year-old boy exhibited hepatomegaly and ultrasound findings suggestive of hepatic steatosis, along with markedly elevated transaminase levels."
Literature synthesis reports a human IBDD case with imaging findings suggestive of hepatic steatosis.
PMID:21659959 SUPPORT Model Organism
"The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis."
Progressive hepatic steatosis demonstrated in ACAD8-deficient mouse model.
PMID:21659959 SUPPORT Model Organism
"This mouse model of isobutyryl-CoA dehydrogenase deficiency could provide us a better understanding of the possible role of IBD deficiency in mitochondriopathy and fatty liver."
Authors propose the mouse model supports investigating fatty liver in IBDD.
Metabolism 3
Elevated C4-acylcarnitine VERY_FREQUENT Elevated circulating acylcarnitine concentration (HP:0045045)
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3."
All 40 patients in the cohort showed persistent C4-acylcarnitine elevation.
PMID:17304052 SUPPORT Human Clinical
"We identified 13 isobutyryl-CoA dehydrogenase-deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots."
Confirms C4-acylcarnitine elevation as the screening marker for IBDD.
Elevated hepatic transaminases OCCASIONAL Elevated circulating hepatic transaminase concentration (HP:0002910)
Show evidence (2 references)
PMID:41606743 SUPPORT Human Clinical
"altered biochemical markers of liver function were reported in 19 individuals, including 18 with isolated elevations of serum transaminases"
Literature synthesis directly supports isolated transaminase elevations in a subset of human IBDD cases.
PMID:21659959 SUPPORT Model Organism
"The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis."
Mouse model demonstrates hepatic pathology consistent with reported human transaminase elevations.
Ketotic hypoglycemia VERY_RARE Hypoglycemia (HP:0001943)
The reported case had an appropriate ketotic response with high free fatty acids and 3-hydroxybutyrate, making this a ketotic rather than hypoketotic episode. The association with IBDD is uncertain.
Show evidence (2 references)
PMID:28053874 PARTIAL Human Clinical
"We report a 13 month old girl diagnosed with IBDD after developing hypoglycaemic encephalopathy (blood glucose 1.9 mmol/l) during an episode of rotavirus-induced gastroenteritis."
Single case presenting with hypoglycemia; causality uncertain.
PMID:28053874 PARTIAL Human Clinical
"Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully"
Authors suspect IBDD did not cause the hypoglycemia episode.
Musculoskeletal 1
Muscular hypotonia OCCASIONAL Hypotonia (HP:0001252)
Show evidence (1 reference)
PMID:33432785 SUPPORT Human Clinical
"Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis."
Hypotonia listed among symptoms reported in IBDD patients.
Nervous System 3
Motor developmental delay OCCASIONAL Motor delay (HP:0001270)
Show evidence (1 reference)
PMID:34544473 SUPPORT Human Clinical
"During follow-up, four patients had a transient motor delay, and two patients had growth delay."
Quantifies transient motor delay in 4 of 40 patients.
Speech delay OCCASIONAL Delayed speech and language development (HP:0000750)
Show evidence (2 references)
PMID:30253142 SUPPORT Human Clinical
"Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms."
Speech delay reported in one of seven Chinese IBDD patients.
PMID:33432785 SUPPORT Human Clinical
"Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis."
Speech delay is listed among reported symptoms in IBDD review.
Autism VERY_RARE Autism (HP:0000717)
Show evidence (1 reference)
PMID:33432785 PARTIAL Human Clinical
"trio whole exome sequencing did not establish an alternative secondary genetic diagnosis for autism, and reported long-term follow-up of IBDD patients is limited, it is possible that autism spectrum disorders could be one of the disease-associated features."
Single case report suggesting possible IBDD-autism association but causality uncertain.
Growth 1
Growth delay OCCASIONAL Growth delay (HP:0001510)
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"During follow-up, four patients had a transient motor delay, and two patients had growth delay."
Growth delay reported in 2 of 40 patients in the Chinese cohort.
PMID:33432785 SUPPORT Human Clinical
"Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis."
Failure to thrive listed among reported IBDD symptoms.
Other 1
Largely asymptomatic course VERY_FREQUENT
Low penetrance is most evident among newborn-screening-identified individuals, while a minority of patients have nonspecific clinical findings.
Show evidence (2 references)
PMID:41606743 SUPPORT Human Clinical
"Of these 172 individuals, 146 were asymptomatic at follow-up, whereas 26 presented with diverse, non-specific manifestations"
Literature synthesis quantifies the predominance of asymptomatic reported IBDD cases.
PMID:34544473 SUPPORT Human Clinical
"After 3-108 months of follow-up, most individuals were healthy except the case harboring the KMT2A variant."
Cohort follow-up supports a predominantly benign/asymptomatic course after newborn-screening diagnosis.
🧬

Genetic Associations

2
ACAD8 pathogenic variants
Autosomal recessive
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"Both the genotypes and ACAD8 variants in IBDD are highly heterogeneous, and no significant correlations between genotype and phenotype are present here in patients with IBDD."
Confirms high genetic heterogeneity and absence of genotype-phenotype correlation.
PMID:33432785 SUPPORT Human Clinical
"Statistical analysis of these parameters did not establish significant differences amongst both groups."
No significant genotype-phenotype correlation found when comparing symptomatic and asymptomatic groups.
ACAD8 (Pathogenic Variants)
Show evidence (1 reference)
CGGV:assertion_0d260f0e-df71-420a-9281-92e4bddcddbb-2019-04-26T160000.000Z SUPPORT Other
"ACAD8 | HGNC:87 | isobutyryl-CoA dehydrogenase deficiency | MONDO:0012648 | AR | Definitive"
ClinGen classifies the ACAD8-isobutyryl-CoA dehydrogenase deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
💊

Treatments

8
Conservative monitoring
Action: supportive care MAXO:0000950
Given the uncertain clinical significance of IBDD, most patients identified through newborn screening are managed with conservative monitoring. Regular clinical assessment with attention to growth, development, and metabolic status is recommended. In many cases, no specific intervention is required.
Target Phenotypes: Largely asymptomatic course
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"All patients were regularly monitored once they were diagnosed, and each patient gradually had a normal diet after 6 months of age."
Describes conservative monitoring approach with gradual diet normalization.
PMID:28053874 SUPPORT Human Clinical
"Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully"
Supports careful monitoring due to uncertain clinical significance.
Dietary management
Action: dietary intervention MAXO:0000088
In the initial period after diagnosis, dietary management may include monitoring of protein intake. In the Chinese NBS cohort, patients gradually transitioned to a normal diet after 6 months of age with favorable outcomes.
Target Phenotypes: Largely asymptomatic course
Show evidence (1 reference)
PMID:34544473 SUPPORT Human Clinical
"All patients were regularly monitored once they were diagnosed, and each patient gradually had a normal diet after 6 months of age."
Describes gradual normalization of diet in monitored IBDD patients.
L-carnitine supplementation
Action: carnitine supplementation MAXO:0010006
Carnitine supplementation may be indicated in patients with documented secondary carnitine deficiency. The original symptomatic case with cardiomyopathy improved with oral L-carnitine. However, carnitine supplementation is not universally required when free carnitine levels are normal.
Mechanism Target:
MODULATES Metabolite accumulation and biomarker shunting — Carnitine supplementation is considered when metabolite shunting is accompanied by secondary carnitine depletion.
Show evidence (1 reference)
PMID:17304052 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency."
The index case links the metabolic defect to secondary carnitine deficiency.
Show evidence (2 references)
PMID:17304052 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency."
The index case had secondary carnitine deficiency, supporting supplementation when deficient.
PMID:28053874 PARTIAL Human Clinical
"Free carnitine was normal in all acylcarnitine samples."
Carnitine supplementation was not needed in this case as free carnitine remained normal.
Emergency glucose regimen
Action: supportive care MAXO:0000950
A glucose polymer emergency regimen may be provided as a precautionary measure for managing potential hypoglycemic episodes during intercurrent illness, although its necessity in IBDD remains uncertain.
Target Phenotypes: Ketotic hypoglycemia ↗
Show evidence (1 reference)
PMID:28053874 PARTIAL Human Clinical
"The patient was given, but has not used, a glucose polymer emergency regimen"
Emergency regimen provided as precaution but never required in 10 years of follow-up.
Newborn screening
Action: disease screening MAXO:0000124
IBDD is detectable through expanded newborn screening using tandem mass spectrometry (MS/MS) via elevated C4-acylcarnitine. A diagnostic follow-up algorithm involving plasma and urine acylcarnitine profiling, urinary organic acid analysis, and molecular genetic testing of ACAD8 has been developed for confirmatory diagnosis.
Target Phenotypes: Elevated circulating acylcarnitine concentration ↗
Show evidence (1 reference)
PMID:34544473 SUPPORT Human Clinical
"The concentration of C4-acylcarnitine in NBS plus subsequent genetic testing is necessary for IBDD diagnosis."
Confirms NBS combined with genetic testing as the diagnostic pathway.
Improved screening biomarker ratios
Action: disease screening MAXO:0000124
Novel C4-based acylcarnitine ratios have been proposed to reduce false positive rates in newborn screening and to improve discrimination between IBDD and SCADD. Seven ratios including C4/C0, C4/C5, C4/C6, and C4/C8 showed robust performance in distinguishing true positives from false positives.
Target Phenotypes: Elevated circulating acylcarnitine concentration ↗
Show evidence (1 reference)
PMID:38137468 SUPPORT Human Clinical
"Our results suggest that the new ratios are optimal indicators for identifying true positives, distinguishing between two rare diseases that share the same primary biomarker, improving the predictive positive value (PPV) and reducing the false positive rate"
Novel ratios demonstrated statistical robustness for screening discrimination.
Genetic counseling
Action: genetic counseling MAXO:0000079
Genetic counseling is recommended for families of affected individuals, including discussion of autosomal recessive inheritance, the typically benign prognosis, recurrence risk, and the uncertain clinical significance of the condition.
Target Phenotypes: Largely asymptomatic course
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8"
Autosomal recessive inheritance supports the role of genetic counseling.
PMID:15505379 SUPPORT Human Clinical
"In view of the limited experience worldwide, careful monitoring of the children is recommended."
Uncertainty about clinical significance supports counseling for informed family decision-making.
Second-tier screening with UPLC-MS/MS
Action: disease screening MAXO:0000124
Second-tier testing using ultraperformance liquid chromatography-tandem mass spectrometry to quantify ethylmalonate and isobutyrylglycine in dried blood spots can reduce referrals by over 90% while maintaining sensitivity for IBDD and SCADD differential diagnosis.
Target Phenotypes: Elevated circulating acylcarnitine concentration ↗
Show evidence (1 reference)
PMID:34869113 SUPPORT Human Clinical
"the application of second-tier tests before the release of neonatal screening results reduced referrals by over 91.89% and improved the positive predictive value (PPV) for short-chain acyl-CoA dehydrogenase deficiency/isobutyryl-CoA dehydrogenase deficiency (SCADD/IBDD) screening."
Demonstrates that second-tier testing greatly reduces unnecessary referrals.
🔬

Biochemical Markers

5
C4-acylcarnitine (isobutyrylcarnitine) (INCREASED)
Context: Elevated C4-acylcarnitine in dried blood spots and plasma is the primary newborn screening marker for IBDD. C4 represents both isobutyrylcarnitine and butyrylcarnitine, requiring differentiation from SCADD. Elevated C4/C2 and C4/C3 ratios improve diagnostic specificity.
Pathograph Readouts
Readout Of Metabolite accumulation and biomarker shunting Positive Diagnostic
Elevated C4-acylcarnitine reports isobutyryl-CoA shunting into carnitine conjugates downstream of impaired ACAD8-dependent valine catabolism.
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3."
All 40 patients showed persistent C4-acylcarnitine elevation with elevated ratios.
PMID:17304052 SUPPORT Human Clinical
"We identified 13 isobutyryl-CoA dehydrogenase-deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots."
Confirms C4-acylcarnitine as the primary NBS marker.
Isobutyrylglycine (urinary) (INCREASED)
Context: Urinary isobutyrylglycine is a supportive diagnostic biomarker for IBDD but is variably present and may be intermittently normal. In a 40-patient cohort, isobutyrylglycine was detected in only 8 patients.
Pathograph Readouts
Readout Of Metabolite accumulation and biomarker shunting Present Absent Diagnostic
Urinary isobutyrylglycine reports glycine conjugation of accumulated isobutyryl-CoA, but this marker is intermittently present.
Show evidence (2 references)
PMID:34544473 SUPPORT Human Clinical
"Isobutyrylglycine occurred in only 8 patients."
Isobutyrylglycine present in only 8 of 40 confirmed IBDD patients.
PMID:41606743 SUPPORT Human Clinical
"Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker."
Literature synthesis supports isobutyrylglycinuria as a variable urinary biomarker.
Ethylmalonic acid (urinary) (DECREASED)
Context: Urinary ethylmalonic acid is typically normal or absent in IBDD, which helps differentiate it from short-chain acyl-CoA dehydrogenase deficiency (SCADD) where ethylmalonic acid is elevated.
Pathograph Readouts
Correlates With Metabolite accumulation and biomarker shunting Negative Diagnostic
Normal or absent ethylmalonic acid helps distinguish IBDD-associated C4 elevation from SCADD-associated C4 elevation.
Show evidence (1 reference)
PMID:17304052 SUPPORT Human Clinical
"Quantification of C4-acylcarnitine in plasma and urine as well as ethylmalonic acid in urine allows the differentiation of isobutyryl-CoA dehydrogenase-deficient from short-chain acyl-CoA dehydrogenase-deficient cases."
Ethylmalonic acid measurement used to distinguish IBDD from SCADD.
Free carnitine (DECREASED)
Context: Secondary carnitine deficiency may occur in some IBDD patients due to excessive conjugation with accumulated isobutyryl-CoA. The index symptomatic case had secondary carnitine deficiency. However, many patients maintain normal free carnitine levels.
Pathograph Readouts
Correlates With Metabolite accumulation and biomarker shunting Negative Monitoring
Low free carnitine can accompany excessive acylcarnitine formation in rare symptomatic cases, but normal free carnitine does not exclude IBDD.
Show evidence (2 references)
PMID:17304052 SUPPORT Human Clinical
"Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency."
Index case had secondary carnitine deficiency.
PMID:28053874 PARTIAL Human Clinical
"Free carnitine was normal in all acylcarnitine samples."
In this case free carnitine remained normal, indicating secondary carnitine deficiency is not universal.
C4-acylcarnitine ratio biomarkers (C4/C0, C4/C6, C4/C8) (INCREASED)
Context: Novel C4-based secondary ratios including C4/C0, C4/C5, C4/C6, C4/C8, C4/C14:1, and C4/C16:1 have been proposed to improve the discrimination of IBDD from false positives and from SCADD in newborn screening programs.
Pathograph Readouts
Readout Of Metabolite accumulation and biomarker shunting Positive Diagnostic
C4-based ratios refine interpretation of the elevated C4-acylcarnitine biomarker produced by ACAD8-related metabolite shunting.
Show evidence (1 reference)
PMID:38137468 SUPPORT Human Clinical
"Seven new biomarkers (C4/C0, C4/C5, C4/C5DC\C6OH, C4/C6, C4/C8, C4/C14:1, C4/C16:1) were identified using a non-parametric ANOVA analysis."
Identifies seven novel ratio biomarkers for distinguishing IBDD from false positives and SCADD.
{ }

Source YAML

click to show 
name: Isobutyryl-CoA Dehydrogenase Deficiency
category: Mendelian
creation_date: '2026-02-23T00:00:00Z'
updated_date: '2026-05-18T08:37:33Z'
synonyms:
- IBDD
- IBD deficiency
- ACAD8 deficiency
- Isobutyrylglycinuria
description: 'Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive inborn error of valine catabolism caused by biallelic pathogenic variants in ACAD8. The enzyme isobutyryl-CoA dehydrogenase catalyzes the conversion of isobutyryl-CoA to methacrylyl-CoA within the mitochondrial valine degradation pathway. IBDD is most commonly identified through newborn screening by elevation of C4-acylcarnitine in dried blood spots. The estimated incidence is approximately 1:62,599 based on a Chinese newborn screening cohort. Most affected individuals remain clinically asymptomatic, and the condition is often regarded as a biochemical phenotype with limited clinical penetrance. In a comprehensive 172-case literature synthesis, 146 individuals (85%) were asymptomatic. A minority of patients develop heterogeneous findings including anemia, transient developmental delay, hepatic transaminase elevations, or rarely cardiomyopathy. Enzyme redundancy and substrate promiscuity among acyl-CoA dehydrogenases may partially explain the low clinical penetrance observed in many individuals. Long-term prognosis is generally favorable, with most NBS-identified patients remaining healthy through
  childhood.

  '
disease_term:
  preferred_term: isobutyryl-CoA dehydrogenase deficiency
  term:
    id: MONDO:0012648
    label: isobutyryl-CoA dehydrogenase deficiency
classifications:
  harrisons_chapter:
  - classification_value: hereditary disease
parents:
- Organic Acidemia
- Inborn Error of Metabolism
prevalence:
- population: Zhejiang newborn screening cohort
  percentage: 1 in 62,599
  notes: >-
    Newborn screening data from Zhejiang identified IBDD more often than older
    case-based literature suggested, while the same study emphasized that only
    dozens of cases had been reported previously and most patients remain
    clinically well.
  evidence:
  - reference: PMID:34544473
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The incidence of IBDD here was 1: 62,599."
    explanation: This newborn-screening cohort provides a direct disease-specific incidence estimate for isobutyryl-CoA dehydrogenase deficiency.
  - reference: PMID:34544473
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8, and is poorly understood, as only dozens of cases have been reported previously."
    explanation: The same study contextualizes the incidence estimate against the very small pre-existing literature, supporting the disorder's rarity.
has_subtypes:
- name: Asymptomatic biochemical isobutyryl-CoA dehydrogenase deficiency
  description: 'Most individuals identified on newborn screening remain clinically asymptomatic and primarily exhibit persistent biochemical abnormalities (elevated C4-acylcarnitine).

    '
  evidence:
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
    explanation: Supports a major asymptomatic biochemical-predominant subtype.
- name: Symptomatic clinical isobutyryl-CoA dehydrogenase deficiency
  description: 'A minority of individuals develop heterogeneous clinical features, including developmental delay, growth issues, hepatic abnormalities, or rare cardiomyopathy.

    '
  evidence:
  - reference: PMID:30253142
    reference_title: "Clinical, biochemical and genetic analysis of Chinese patients with isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms.
    explanation: Supports a less common symptomatic subtype with variable clinical expression.
pathophysiology:
- name: ACAD8 molecular function deficiency
  description: 'Biallelic ACAD8 pathogenic variants reduce isobutyryl-CoA dehydrogenase catalytic activity in mitochondria.

    '
  genes:
  - preferred_term: ACAD8
    term:
      id: hgnc:87
      label: ACAD8
  molecular_functions:
  - preferred_term: acyl-CoA dehydrogenase activity
    term:
      id: GO:0003995
      label: acyl-CoA dehydrogenase activity
  biological_processes:
  - preferred_term: L-valine catabolic process
    modifier: DECREASED
    term:
      id: GO:0006574
      label: L-valine catabolic process
  chemical_entities:
  - preferred_term: isobutyryl-CoA
    modifier: INCREASED
    term:
      id: CHEBI:15479
      label: isobutyryl-CoA
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8
    explanation: Supports ACAD8 molecular dysfunction as the initiating defect.
  downstream:
  - target: Impaired mitochondrial valine catabolism
    description: Reduced ACAD8 activity blocks isobutyryl-CoA oxidation in the valine pathway.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:21104317
      reference_title: "Enzymology of the branched-chain amino acid oxidation disorders: the valine pathway."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "human recombinant enzyme had highest activity with isobutyryl-CoA"
      explanation: Review evidence supports ACAD8 as the enzyme directly responsible for the isobutyryl-CoA dehydrogenation step in valine catabolism.
  - target: Largely asymptomatic course
    description: >
      ACAD8-related isobutyryl-CoA dehydrogenase deficiency is most often a
      low-penetrance biochemical phenotype detected by newborn screening rather
      than a consistently symptomatic clinical disease.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >
        Isobutyryl-coenzyme A dehydrogenase deficiency (IBDD) is a rare inborn
        error of valine metabolism caused by variants in the ACAD8 gene.
      explanation: >
        Literature synthesis roots IBDD in ACAD8 variants.
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >
        Of these 172 individuals, 146 were asymptomatic at follow-up, whereas 26
        presented with diverse, non-specific manifestations
      explanation: >
        The same synthesis quantifies the low-penetrance clinical outcome
        downstream of ACAD8-related IBDD without implying that ACAD8 deficiency
        causes enzyme redundancy itself.
  - target: Anemia
    description: Anemia is a rare reported clinical manifestation in symptomatic IBDD.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        whereas 26 presented with diverse, non-specific manifestations,
        including motor delay, failure to thrive, muscular hypotonia, speech
        delay, developmental delay, and anemia-the latter being the most
        frequently reported abnormality.
      explanation: The 172-person synthesis supports anemia in the symptomatic minority.
  - target: Dilated cardiomyopathy
    description: Cardiomyopathy was reported in the original symptomatic IBDD case.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17304052
      reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
      explanation: The original symptomatic case links IBDD to cardiomyopathy.
  - target: Motor developmental delay
    description: Motor delay is among the nonspecific manifestations reported in a minority of cases.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        whereas 26 presented with diverse, non-specific manifestations,
        including motor delay, failure to thrive, muscular hypotonia, speech
        delay, developmental delay, and anemia-the latter being the most
        frequently reported abnormality.
      explanation: Literature synthesis lists motor delay among reported manifestations.
  - target: Growth delay
    description: Failure to thrive or growth delay is reported in a small symptomatic subset.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        whereas 26 presented with diverse, non-specific manifestations,
        including motor delay, failure to thrive, muscular hypotonia, speech
        delay, developmental delay, and anemia-the latter being the most
        frequently reported abnormality.
      explanation: Literature synthesis lists failure to thrive among reported manifestations.
  - target: Speech delay
    description: Speech delay is reported in isolated symptomatic cases.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        whereas 26 presented with diverse, non-specific manifestations,
        including motor delay, failure to thrive, muscular hypotonia, speech
        delay, developmental delay, and anemia-the latter being the most
        frequently reported abnormality.
      explanation: Literature synthesis lists speech delay among reported manifestations.
  - target: Muscular hypotonia
    description: Hypotonia is a nonspecific manifestation in a minority of symptomatic patients.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        whereas 26 presented with diverse, non-specific manifestations,
        including motor delay, failure to thrive, muscular hypotonia, speech
        delay, developmental delay, and anemia-the latter being the most
        frequently reported abnormality.
      explanation: Literature synthesis lists muscular hypotonia among reported manifestations.
  - target: Autism
    description: Autism has been reported in a single IBDD case without an alternative genetic diagnosis, but causality remains uncertain.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33432785
      reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        trio whole exome sequencing did not establish an alternative secondary genetic diagnosis for autism, and reported long-term follow-up of IBDD patients is limited, it is possible that autism spectrum disorders could be one of the disease-associated features.
      explanation: Single-case evidence supports only a tentative downstream association.
  - target: Vomiting
    description: Emesis is reported among nonspecific symptomatic presentations.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33432785
      reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
      explanation: Review text lists emesis among reported IBDD symptoms.
  - target: Ketotic hypoglycemia
    description: Ketotic hypoglycemia has been reported, but the authors considered causality uncertain.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:28053874
      reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully
      explanation: Authors explicitly caution that causality for hypoglycemia is uncertain.
- name: Impaired mitochondrial valine catabolism
  description: 'Loss of ACAD8 function creates a metabolic block in valine degradation, leading to accumulation of isobutyryl-CoA and diversion into alternate conjugation products including isobutyrylcarnitine (C4) and isobutyrylglycine.

    '
  biological_processes:
  - preferred_term: valine catabolic process
    term:
      id: GO:0006574
      label: L-valine 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: L-valine
    modifier: ABNORMAL
    term:
      id: CHEBI:16414
      label: L-valine
  - preferred_term: isobutyryl-CoA
    modifier: INCREASED
    term:
      id: CHEBI:15479
      label: isobutyryl-CoA
  - preferred_term: methacrylyl-CoA
    modifier: DECREASED
    term:
      id: CHEBI:27754
      label: methacrylyl-CoA
  evidence:
  - reference: PMID:21104317
    reference_title: "Enzymology of the branched-chain amino acid oxidation disorders: the valine pathway."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Valine is one of the three branched-chain amino acids which undergoes oxidation within mitochondria.
    explanation: Review confirming valine oxidation occurs in mitochondria via the ACAD8-dependent pathway.
  downstream:
  - target: Metabolite accumulation and biomarker shunting
    description: ACAD8 loss blocks valine catabolism and diverts accumulating isobutyryl-CoA into detectable C4 and glycine conjugates.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34544473
      reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3. Isobutyrylglycine occurred in only 8 patients.
      explanation: Patient cohort data directly connect the ACAD8 valine-catabolism defect to the characteristic C4-acylcarnitine and isobutyrylglycine biomarker pattern.
- name: Metabolite accumulation and biomarker shunting
  description: 'Loss of ACAD8 activity leads to accumulation of isobutyryl-CoA, which is conjugated to carnitine (forming C4-acylcarnitine) and glycine (forming isobutyrylglycine). Elevated C4-acylcarnitine with increased C4/C2 and C4/C3 ratios is the hallmark newborn screening marker. Urinary isobutyrylglycine is variably present and may be intermittently normal.

    '
  biological_processes:
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3. Isobutyrylglycine occurred in only 8 patients.
    explanation: Demonstrates the characteristic biomarker pattern including variable isobutyrylglycine.
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker.
    explanation: Literature synthesis confirms C4-acylcarnitine as universal in reported IBDD and isobutyrylglycinuria as common but variable.
  downstream:
  - target: C4-acylcarnitine (isobutyrylcarnitine)
    description: Accumulated isobutyryl-CoA is conjugated to carnitine, producing elevated C4-acylcarnitine.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34544473
      reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3.
      explanation: Human cohort data directly support C4-acylcarnitine elevation downstream of IBDD.
  - target: Elevated C4-acylcarnitine
    description: The same C4-acylcarnitine accumulation is detected clinically as the newborn-screening phenotype.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17304052
      reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We identified 13 isobutyryl-CoA dehydrogenase-deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots.
      explanation: Newborn-screening cohort links the biochemical marker to the observable screening phenotype.
  - target: Isobutyrylglycine (urinary)
    description: Isobutyryl-CoA can also be conjugated to glycine and excreted as urinary isobutyrylglycine, although this marker is variable.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker.
      explanation: Literature synthesis supports isobutyrylglycinuria as a downstream urinary biomarker that is not present in every patient.
  - target: C4-acylcarnitine ratio biomarkers (C4/C0, C4/C6, C4/C8)
    description: Persistent C4-acylcarnitine elevation shifts C4-based acylcarnitine ratios used for screening discrimination.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38137468
      reference_title: "Butyrylcarnitine Elevation in Newborn Screening: Reducing False Positives and Distinguishing between Two Rare Diseases through the Evaluation of New Ratios."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Seven new biomarkers (C4/C0, C4/C5, C4/C5DC\C6OH, C4/C6, C4/C8, C4/C14:1, C4/C16:1) were identified using a non-parametric ANOVA analysis.
      explanation: Screening study identifies C4-based ratios as downstream diagnostic biomarkers.
  - target: Free carnitine
    description: Carnitine conjugation can contribute to secondary carnitine depletion in rare symptomatic cases.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - isobutyryl-CoA conjugation to carnitine
    evidence:
    - reference: PMID:17304052
      reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
      explanation: The index case supports secondary carnitine deficiency as a rare downstream biochemical consequence.
  - target: Hepatic involvement and mitochondrial stress
    description: Reported liver-test abnormalities and the ACAD8-deficient mouse liver phenotype suggest a possible hepatic consequence, but the intervening mechanism remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: altered biochemical markers of liver function were reported in 19 individuals
      explanation: Human literature synthesis supports liver biochemical abnormalities in a subset of IBDD individuals.
    - reference: PMID:21659959
      reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Homozygous mutant mice hepatocytes had abnormal mitochondria with crystalline inclusions, suggestive of mitochondriopathy.
      explanation: ACAD8-deficient mouse data provide model-organism support for hepatic mitochondrial involvement.
- name: Enzyme redundancy and low clinical penetrance
  description: 'A plausible mechanistic explanation for the frequently benign phenotype of IBDD is substrate promiscuity among acyl-CoA dehydrogenase family members. In HEK-293 ACAD8-deletion models, other ACADs appear to compensate for isobutyryl-CoA handling, which may help explain the low clinical penetrance observed in human cohorts.

    '
  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: Directly states ACAD8 deficiency is considered a biochemical abnormality with limited clinical significance.
  - 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: 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: Demonstrates substrate promiscuity among ACADs for isobutyryl-CoA in cell models.
  downstream:
  - target: Largely asymptomatic course
    description: ACAD substrate promiscuity may help explain why most reported ACAD8-deficient individuals remain clinically asymptomatic despite persistent biochemical abnormalities.
    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: 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: In vitro ACAD substrate promiscuity supports a plausible compensatory mechanism.
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Of these 172 individuals, 146 were asymptomatic at follow-up, whereas 26 presented with diverse, non-specific manifestations
      explanation: Human literature synthesis supports the downstream low-penetrance clinical pattern.
- name: Hepatic involvement and mitochondrial stress
  description: 'A subset of IBDD individuals shows liver enzyme abnormalities including elevated transaminases and gamma-glutamyl transferase. One reported human case had hepatomegaly with ultrasound findings suggestive of hepatic steatosis, and an ACAD8-deficient mouse model develops hepatic steatosis with abnormal hepatocyte mitochondria.

    '
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: altered biochemical markers of liver function were reported in 19 individuals
    explanation: Literature synthesis reports liver biochemical abnormalities in human IBDD cases.
  - reference: PMID:21659959
    reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis.
    explanation: Mouse model of IBDD showing progressive hepatic steatosis and mitochondrial abnormalities.
  - reference: PMID:21659959
    reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Homozygous mutant mice hepatocytes had abnormal mitochondria with crystalline inclusions, suggestive of mitochondriopathy.
    explanation: Demonstrates mitochondrial pathology in hepatocytes of ACAD8-deficient mice.
  downstream:
  - target: Elevated hepatic transaminases
    description: The hepatic involvement signal most often appears as isolated serum transaminase elevation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: altered biochemical markers of liver function were reported in 19 individuals, including 18 with isolated elevations of serum transaminases
      explanation: Human literature synthesis directly supports elevated transaminases as a liver-related manifestation.
  - target: Hepatic steatosis
    description: One reported human case and the ACAD8-deficient mouse model suggest possible hepatic steatosis, although causality remains uncertain.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - hepatocellular mitochondrial stress
    evidence:
    - reference: PMID:41606743
      reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: One 11-year-old boy exhibited hepatomegaly and ultrasound findings suggestive of hepatic steatosis, along with markedly elevated transaminase levels.
      explanation: Literature synthesis reports a human case with imaging findings suggestive of hepatic steatosis.
    - reference: PMID:21659959
      reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis.
      explanation: ACAD8-deficient mouse data support hepatic steatosis as a model-organism finding.
phenotypes:
- name: Largely asymptomatic course
  frequency: VERY_FREQUENT
  description: 'Most reported individuals with IBDD remain clinically asymptomatic after diagnosis, despite persistent biochemical abnormalities.

    '
  notes: 'Low penetrance is most evident among newborn-screening-identified individuals, while a minority of patients have nonspecific clinical findings.

    '
  evidence:
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Of these 172 individuals, 146 were asymptomatic at follow-up, whereas 26 presented with diverse, non-specific manifestations
    explanation: Literature synthesis quantifies the predominance of asymptomatic reported IBDD cases.
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: After 3-108 months of follow-up, most individuals were healthy except the case harboring the KMT2A variant.
    explanation: Cohort follow-up supports a predominantly benign/asymptomatic course after newborn-screening diagnosis.
- name: Elevated C4-acylcarnitine
  frequency: VERY_FREQUENT
  description: 'Persistent elevation of C4-acylcarnitine (isobutyrylcarnitine) in blood is the hallmark biochemical marker, detectable on newborn screening. C4 represents both isobutyryl- and butyrylcarnitine, requiring differentiation from short-chain acyl-CoA dehydrogenase deficiency.

    '
  phenotype_term:
    preferred_term: Elevated circulating acylcarnitine concentration
    term:
      id: HP:0045045
      label: Elevated circulating acylcarnitine concentration
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3.
    explanation: All 40 patients in the cohort showed persistent C4-acylcarnitine elevation.
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We identified 13 isobutyryl-CoA dehydrogenase-deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots.
    explanation: Confirms C4-acylcarnitine elevation as the screening marker for IBDD.
- name: Anemia
  frequency: OCCASIONAL
  description: 'Anemia was reported in the index symptomatic patient who also had cardiomyopathy and secondary carnitine deficiency. It is the most frequently reported abnormality among the symptomatic minority.

    '
  phenotype_term:
    preferred_term: Anemia
    term:
      id: HP:0001903
      label: Anemia
  evidence:
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
    explanation: The index case presented with anemia alongside cardiomyopathy.
- name: Motor developmental delay
  frequency: OCCASIONAL
  description: 'Transient motor delay was observed in a minority of patients. In a 40-patient Chinese cohort, four patients had transient motor delay.

    '
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: During follow-up, four patients had a transient motor delay, and two patients had growth delay.
    explanation: Quantifies transient motor delay in 4 of 40 patients.
- name: Growth delay
  frequency: OCCASIONAL
  description: 'Growth delay or failure to thrive has been reported in a small subset of patients.

    '
  phenotype_term:
    preferred_term: Growth delay
    term:
      id: HP:0001510
      label: Growth delay
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: During follow-up, four patients had a transient motor delay, and two patients had growth delay.
    explanation: Growth delay reported in 2 of 40 patients in the Chinese cohort.
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
    explanation: Failure to thrive listed among reported IBDD symptoms.
- name: Speech delay
  frequency: OCCASIONAL
  description: 'Speech delay has been reported in isolated IBDD cases. One Chinese cohort of seven IBDD patients included one juvenile with speech delay.

    '
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:30253142
    reference_title: "Clinical, biochemical and genetic analysis of Chinese patients with isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Five patients remained asymptomatic during follow-up, whereas one juvenile had speech delay and one newborn exhibited clinical symptoms.
    explanation: Speech delay reported in one of seven Chinese IBDD patients.
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
    explanation: Speech delay is listed among reported symptoms in IBDD review.
- name: Muscular hypotonia
  frequency: OCCASIONAL
  description: 'Hypotonia has been variably reported among symptomatic IBDD patients.

    '
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
    explanation: Hypotonia listed among symptoms reported in IBDD patients.
- name: Elevated hepatic transaminases
  frequency: OCCASIONAL
  description: 'Elevated serum transaminases and gamma-glutamyl transferase have been reported in a subset of IBDD individuals. An ACAD8-deficient mouse model also exhibits progressive hepatic steatosis with mitochondriopathy.

    '
  phenotype_term:
    preferred_term: Elevated hepatic transaminase
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  evidence:
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: altered biochemical markers of liver function were reported in 19 individuals, including 18 with isolated elevations of serum transaminases
    explanation: Literature synthesis directly supports isolated transaminase elevations in a subset of human IBDD cases.
  - reference: PMID:21659959
    reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis.
    explanation: Mouse model demonstrates hepatic pathology consistent with reported human transaminase elevations.
- name: Dilated cardiomyopathy
  frequency: VERY_RARE
  description: 'Cardiomyopathy was reported in the original index case of IBDD, who presented with dilated cardiomyopathy, anemia, and secondary carnitine deficiency at age two years. This remains a rare presentation.

    '
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
    explanation: The index IBDD case had cardiomyopathy as a presenting feature.
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: One reported non-screened patient had dilated cardiomyopathy and anaemia at the age of two years.
    explanation: Confirms dilated cardiomyopathy in the historically reported symptomatic case.
- name: Ketotic hypoglycemia
  frequency: VERY_RARE
  description: 'One case was diagnosed with IBDD after presenting with hypoglycemic encephalopathy during acute gastroenteritis. The causal relationship between IBDD and hypoglycemia is uncertain.

    '
  phenotype_term:
    preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  notes: 'The reported case had an appropriate ketotic response with high free fatty acids and 3-hydroxybutyrate, making this a ketotic rather than hypoketotic episode. The association with IBDD is uncertain.

    '
  evidence:
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: We report a 13 month old girl diagnosed with IBDD after developing hypoglycaemic encephalopathy (blood glucose 1.9 mmol/l) during an episode of rotavirus-induced gastroenteritis.
    explanation: Single case presenting with hypoglycemia; causality uncertain.
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully
    explanation: Authors suspect IBDD did not cause the hypoglycemia episode.
- name: Autism
  frequency: VERY_RARE
  description: 'One case report describes a girl with IBDD presenting with autism as the main clinical feature. Trio whole exome sequencing did not identify an alternative genetic diagnosis. The causal association remains uncertain.

    '
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: trio whole exome sequencing did not establish an alternative secondary genetic diagnosis for autism, and reported long-term follow-up of IBDD patients is limited, it is possible that autism spectrum disorders could be one of the disease-associated features.
    explanation: Single case report suggesting possible IBDD-autism association but causality uncertain.
- name: Vomiting
  frequency: OCCASIONAL
  description: 'Emesis has been reported in some symptomatic IBDD patients, particularly during episodes of metabolic stress.

    '
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
  evidence:
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis.
    explanation: Emesis listed among reported IBDD symptoms.
- name: Hepatic steatosis
  frequency: VERY_RARE
  description: 'Hepatic steatosis has been observed in the ACAD8-deficient mouse model with abnormal mitochondrial ultrastructure; one reported human case had hepatomegaly with ultrasound findings suggestive of steatosis.

    '
  phenotype_term:
    preferred_term: Hepatic steatosis
    term:
      id: HP:0001397
      label: Hepatic steatosis
  evidence:
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: One 11-year-old boy exhibited hepatomegaly and ultrasound findings suggestive of hepatic steatosis, along with markedly elevated transaminase levels.
    explanation: Literature synthesis reports a human IBDD case with imaging findings suggestive of hepatic steatosis.
  - reference: PMID:21659959
    reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The mutant mice grew normally but demonstrated cold intolerance at young age with a progressive hepatic steatosis.
    explanation: Progressive hepatic steatosis demonstrated in ACAD8-deficient mouse model.
  - reference: PMID:21659959
    reference_title: "Alternative splicing in Acad8 resulting a mitochondrial defect and progressive hepatic steatosis in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: This mouse model of isobutyryl-CoA dehydrogenase deficiency could provide us a better understanding of the possible role of IBD deficiency in mitochondriopathy and fatty liver.
    explanation: Authors propose the mouse model supports investigating fatty liver in IBDD.
biochemical:
- name: C4-acylcarnitine (isobutyrylcarnitine)
  presence: INCREASED
  context: 'Elevated C4-acylcarnitine in dried blood spots and plasma is the primary newborn screening marker for IBDD. C4 represents both isobutyrylcarnitine and butyrylcarnitine, requiring differentiation from SCADD. Elevated C4/C2 and C4/C3 ratios improve diagnostic specificity.

    '
  frequency: VERY_FREQUENT
  biomarker_term:
    preferred_term: O-isobutyrylcarnitine
    term:
      id: CHEBI:73017
      label: O-isobutyrylcarnitine
  readouts:
  - target: Metabolite accumulation and biomarker shunting
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Elevated C4-acylcarnitine reports isobutyryl-CoA shunting into carnitine
      conjugates downstream of impaired ACAD8-dependent valine catabolism.
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients presented continuously elevated C4-acylcarnitine levels with higher ratios of C4/C2 and C4/C3.
    explanation: All 40 patients showed persistent C4-acylcarnitine elevation with elevated ratios.
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We identified 13 isobutyryl-CoA dehydrogenase-deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots.
    explanation: Confirms C4-acylcarnitine as the primary NBS marker.
- name: Isobutyrylglycine (urinary)
  presence: INCREASED
  context: 'Urinary isobutyrylglycine is a supportive diagnostic biomarker for IBDD but is variably present and may be intermittently normal. In a 40-patient cohort, isobutyrylglycine was detected in only 8 patients.

    '
  frequency: OCCASIONAL
  notes: 'Isobutyrylglycine excretion is intermittent and absence does not exclude IBDD diagnosis.

    '
  biomarker_term:
    preferred_term: N-isobutyrylglycine
    term:
      id: CHEBI:70979
      label: N-isobutyrylglycine
  readouts:
  - target: Metabolite accumulation and biomarker shunting
    relationship: READOUT_OF
    direction: PRESENT_ABSENT
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Urinary isobutyrylglycine reports glycine conjugation of accumulated
      isobutyryl-CoA, but this marker is intermittently present.
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyrylglycine occurred in only 8 patients.
    explanation: Isobutyrylglycine present in only 8 of 40 confirmed IBDD patients.
  - reference: PMID:41606743
    reference_title: "Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Elevated blood or plasma C4-acylcarnitine was observed universally, and isobutyrylglycinuria was a common but not invariable urinary marker.
    explanation: Literature synthesis supports isobutyrylglycinuria as a variable urinary biomarker.
- name: Ethylmalonic acid (urinary)
  presence: DECREASED
  context: 'Urinary ethylmalonic acid is typically normal or absent in IBDD, which helps differentiate it from short-chain acyl-CoA dehydrogenase deficiency (SCADD) where ethylmalonic acid is elevated.

    '
  biomarker_term:
    preferred_term: ethylmalonic acid
    term:
      id: CHEBI:741548
      label: ethylmalonic acid
  readouts:
  - target: Metabolite accumulation and biomarker shunting
    relationship: CORRELATES_WITH
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Normal or absent ethylmalonic acid helps distinguish IBDD-associated C4
      elevation from SCADD-associated C4 elevation.
  evidence:
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Quantification of C4-acylcarnitine in plasma and urine as well as ethylmalonic acid in urine allows the differentiation of isobutyryl-CoA dehydrogenase-deficient from short-chain acyl-CoA dehydrogenase-deficient cases.
    explanation: Ethylmalonic acid measurement used to distinguish IBDD from SCADD.
- name: Free carnitine
  presence: DECREASED
  context: 'Secondary carnitine deficiency may occur in some IBDD patients due to excessive conjugation with accumulated isobutyryl-CoA. The index symptomatic case had secondary carnitine deficiency. However, many patients maintain normal free carnitine levels.

    '
  frequency: VERY_RARE
  biomarker_term:
    preferred_term: carnitine
    term:
      id: CHEBI:17126
      label: carnitine
  readouts:
  - target: Metabolite accumulation and biomarker shunting
    relationship: CORRELATES_WITH
    direction: NEGATIVE
    endpoint_context: MONITORING
    interpretation: >-
      Low free carnitine can accompany excessive acylcarnitine formation in rare
      symptomatic cases, but normal free carnitine does not exclude IBDD.
  evidence:
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
    explanation: Index case had secondary carnitine deficiency.
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Free carnitine was normal in all acylcarnitine samples.
    explanation: In this case free carnitine remained normal, indicating secondary carnitine deficiency is not universal.
- name: C4-acylcarnitine ratio biomarkers (C4/C0, C4/C6, C4/C8)
  presence: INCREASED
  context: 'Novel C4-based secondary ratios including C4/C0, C4/C5, C4/C6, C4/C8, C4/C14:1, and C4/C16:1 have been proposed to improve the discrimination of IBDD from false positives and from SCADD in newborn screening programs.

    '
  biomarker_term:
    preferred_term: O-isobutyrylcarnitine
    term:
      id: CHEBI:73017
      label: O-isobutyrylcarnitine
  readouts:
  - target: Metabolite accumulation and biomarker shunting
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      C4-based ratios refine interpretation of the elevated C4-acylcarnitine
      biomarker produced by ACAD8-related metabolite shunting.
  evidence:
  - reference: PMID:38137468
    reference_title: "Butyrylcarnitine Elevation in Newborn Screening: Reducing False Positives and Distinguishing between Two Rare Diseases through the Evaluation of New Ratios."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Seven new biomarkers (C4/C0, C4/C5, C4/C5DC\C6OH, C4/C6, C4/C8, C4/C14:1, C4/C16:1) were identified using a non-parametric ANOVA analysis.
    explanation: Identifies seven novel ratio biomarkers for distinguishing IBDD from false positives and SCADD.
genetic:
- name: ACAD8 pathogenic variants
  gene_term:
    preferred_term: ACAD8
    term:
      id: hgnc:87
      label: ACAD8
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:34544473
      reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8
      explanation: Directly states autosomal recessive inheritance.
  variants:
  - name: c.286G>A (p.Gly96Ser)
    description: 'The most common ACAD8 variant, observed at an allelic frequency of 27.2% in a literature review of 81 IBDD patients. This variant has been found solely in the Chinese population to date.

      '
  - name: c.1000C>T (p.R334C)
    description: 'The second most common ACAD8 variant, observed at an allelic frequency of 8.6% across published IBDD cases.

      '
  - name: c.845C>T
    description: 'Homozygous variant identified in a patient who presented with hypoglycemic encephalopathy and was followed for 10 years with benign outcome.

      '
    evidence:
    - reference: PMID:28053874
      reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: IBDD was confirmed by finding a homozygous c.845C > T substitution
      explanation: Reports the homozygous c.845C>T variant in a symptomatic-onset case.
  features: 'IBDD is caused by biallelic pathogenic variants in ACAD8 (OMIM*604773), encoding isobutyryl-CoA dehydrogenase. Over 50 distinct variants have been reported including missense, frameshift, and splice-site mutations. Genotype-phenotype correlation is poor; no significant correlation between specific variants and clinical outcome has been established.

    '
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Both the genotypes and ACAD8 variants in IBDD are highly heterogeneous, and no significant correlations between genotype and phenotype are present here in patients with IBDD.
    explanation: Confirms high genetic heterogeneity and absence of genotype-phenotype correlation.
  - reference: PMID:33432785
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Statistical analysis of these parameters did not establish significant differences amongst both groups.
    explanation: No significant genotype-phenotype correlation found when comparing symptomatic and asymptomatic groups.
- name: ACAD8
  gene_term:
    preferred_term: ACAD8
    term:
      id: hgnc:87
      label: ACAD8
  association: Pathogenic Variants
  evidence:
  - reference: CGGV:assertion_0d260f0e-df71-420a-9281-92e4bddcddbb-2019-04-26T160000.000Z
    reference_title: "ACAD8 / isobutyryl-CoA dehydrogenase deficiency (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ACAD8 | HGNC:87 | isobutyryl-CoA dehydrogenase deficiency | MONDO:0012648 | AR | Definitive"
    explanation: ClinGen classifies the ACAD8-isobutyryl-CoA dehydrogenase deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: Conservative monitoring
  description: 'Given the uncertain clinical significance of IBDD, most patients identified through newborn screening are managed with conservative monitoring. Regular clinical assessment with attention to growth, development, and metabolic status is recommended. In many cases, no specific intervention is required.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Largely asymptomatic course
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients were regularly monitored once they were diagnosed, and each patient gradually had a normal diet after 6 months of age.
    explanation: Describes conservative monitoring approach with gradual diet normalization.
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully
    explanation: Supports careful monitoring due to uncertain clinical significance.
- name: Dietary management
  description: 'In the initial period after diagnosis, dietary management may include monitoring of protein intake. In the Chinese NBS cohort, patients gradually transitioned to a normal diet after 6 months of age with favorable outcomes.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_phenotypes:
  - preferred_term: Largely asymptomatic course
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients were regularly monitored once they were diagnosed, and each patient gradually had a normal diet after 6 months of age.
    explanation: Describes gradual normalization of diet in monitored IBDD patients.
- name: L-carnitine supplementation
  description: 'Carnitine supplementation may be indicated in patients with documented secondary carnitine deficiency. The original symptomatic case with cardiomyopathy improved with oral L-carnitine. However, carnitine supplementation is not universally required when free carnitine levels are normal.

    '
  treatment_term:
    preferred_term: carnitine supplementation
    term:
      id: MAXO:0010006
      label: carnitine supplementation
  target_mechanisms:
  - target: Metabolite accumulation and biomarker shunting
    treatment_effect: MODULATES
    description: >-
      Carnitine supplementation is considered when metabolite shunting is
      accompanied by secondary carnitine depletion.
    evidence:
    - reference: PMID:17304052
      reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
      explanation: The index case links the metabolic defect to secondary carnitine deficiency.
  evidence:
  - reference: PMID:17304052
    reference_title: "Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency.
    explanation: The index case had secondary carnitine deficiency, supporting supplementation when deficient.
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Free carnitine was normal in all acylcarnitine samples.
    explanation: Carnitine supplementation was not needed in this case as free carnitine remained normal.
- name: Emergency glucose regimen
  description: 'A glucose polymer emergency regimen may be provided as a precautionary measure for managing potential hypoglycemic episodes during intercurrent illness, although its necessity in IBDD remains uncertain.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Ketotic hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  evidence:
  - reference: PMID:28053874
    reference_title: "Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: The patient was given, but has not used, a glucose polymer emergency regimen
    explanation: Emergency regimen provided as precaution but never required in 10 years of follow-up.
- name: Newborn screening
  description: 'IBDD is detectable through expanded newborn screening using tandem mass spectrometry (MS/MS) via elevated C4-acylcarnitine. A diagnostic follow-up algorithm involving plasma and urine acylcarnitine profiling, urinary organic acid analysis, and molecular genetic testing of ACAD8 has been developed for confirmatory diagnosis.

    '
  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:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The concentration of C4-acylcarnitine in NBS plus subsequent genetic testing is necessary for IBDD diagnosis.
    explanation: Confirms NBS combined with genetic testing as the diagnostic pathway.
- name: Improved screening biomarker ratios
  description: 'Novel C4-based acylcarnitine ratios have been proposed to reduce false positive rates in newborn screening and to improve discrimination between IBDD and SCADD. Seven ratios including C4/C0, C4/C5, C4/C6, and C4/C8 showed robust performance in distinguishing true positives from false positives.

    '
  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:38137468
    reference_title: "Butyrylcarnitine Elevation in Newborn Screening: Reducing False Positives and Distinguishing between Two Rare Diseases through the Evaluation of New Ratios."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our results suggest that the new ratios are optimal indicators for identifying true positives, distinguishing between two rare diseases that share the same primary biomarker, improving the predictive positive value (PPV) and reducing the false positive rate
    explanation: Novel ratios demonstrated statistical robustness for screening discrimination.
- name: Genetic counseling
  description: 'Genetic counseling is recommended for families of affected individuals, including discussion of autosomal recessive inheritance, the typically benign prognosis, recurrence risk, and the uncertain clinical significance of the condition.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  target_phenotypes:
  - preferred_term: Largely asymptomatic course
  evidence:
  - reference: PMID:34544473
    reference_title: "Phenotype, genotype and long-term prognosis of 40 Chinese patients with isobutyryl-CoA dehydrogenase deficiency and a review of variant spectra in ACAD8."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isobutyryl-CoA dehydrogenase deficiency (IBDD) is a rare autosomal recessive metabolic disorder resulting from variants in ACAD8
    explanation: Autosomal recessive inheritance supports the role of genetic counseling.
  - reference: PMID:15505379
    reference_title: "Isobutyryl-CoA dehydrogenase deficiency: isobutyrylglycinuria and ACAD8 gene mutations in two infants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In view of the limited experience worldwide, careful monitoring of the children is recommended.
    explanation: Uncertainty about clinical significance supports counseling for informed family decision-making.
- name: Second-tier screening with UPLC-MS/MS
  description: 'Second-tier testing using ultraperformance liquid chromatography-tandem mass spectrometry to quantify ethylmalonate and isobutyrylglycine in dried blood spots can reduce referrals by over 90% while maintaining sensitivity for IBDD and SCADD differential diagnosis.

    '
  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:34869113
    reference_title: "Quantification of Differential Metabolites in Dried Blood Spots Using Second-Tier Testing for SCADD/IBDD Disorders Based on Large-Scale Newborn Screening in a Chinese Population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the application of second-tier tests before the release of neonatal screening results reduced referrals by over 91.89% and improved the positive predictive value (PPV) for short-chain acyl-CoA dehydrogenase deficiency/isobutyryl-CoA dehydrogenase deficiency (SCADD/IBDD) screening.
    explanation: Demonstrates that second-tier testing greatly reduces unnecessary referrals.
notes: 'IBDD is frequently considered a biochemical phenotype rather than a true disease. The clinical significance remains debated, as highlighted by the question posed in a 2026 review entitled "Isobutyryl-coenzyme A dehydrogenase deficiency: disease, or non-disease?" The major practical challenge is not detection but rather managing the high false-positive burden from non-specific C4-acylcarnitine elevation shared with SCADD. Combined NGS and MS/MS first-tier screening approaches have been shown to substantially improve positive predictive value. The ACAD8-deficient mouse model, which develops progressive hepatic steatosis and abnormal mitochondria, supports further study of whether long-term hepatic monitoring is useful in selected individuals.

  '
📚

References & Deep Research

Deep Research

1
Falcon ▸
Disease Pathophysiology Research Template
Edison Scientific Literature 38 citations 2026-02-23T23:50:06.475402

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: Isobutyryl-CoA Dehydrogenase Deficiency
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Isobutyryl-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

Title: Pathophysiology Research Report — Isobutyryl‑CoA Dehydrogenase Deficiency (IBDD; ACAD8 deficiency)

Publication window emphasized: 2023–2024 developments are highlighted where available; foundational mechanistic and clinical references are included for completeness.

  1. Disease identifiers, nomenclature, and definitions

1.1 Canonical name and synonyms Isobutyryl‑CoA dehydrogenase deficiency is a rare, autosomal recessive inborn error of valine catabolism caused by biallelic variants in ACAD8. It has historically been discussed under biochemical nomenclature such as “isobutyrylglycinuria,” reflecting its urinary acylglycine marker. (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, sass2004isobutyrylcoadehydrogenasedeficiency pages 1-4)

OMIM identifiers: disease OMIM#611283; gene ACAD8 OMIM*604773. (feng2021phenotypegenotypeand pages 1-2, oglesbee2007developmentofa pages 1-2)

1.2 Current understanding of clinical significance A recurrent theme in contemporary literature is that IBDD is frequently detected through newborn screening (NBS) and often behaves as a “biochemical phenotype” with limited clinical consequences in many individuals, while a minority shows heterogeneous findings. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3, reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2)

  1. Core pathophysiology (molecular and cellular mechanisms)

2.1 Normal biochemical role of ACAD8 in valine oxidation ACAD8 encodes isobutyryl‑CoA dehydrogenase, a mitochondrial enzyme acting in the valine degradation pathway. In a Chinese cohort description, ACAD8 is reported to “catalyse the conversion of isobutyryl‑CoA to methacrylyl‑CoA” in valine catabolism, ultimately connecting to the tricarboxylic acid (TCA) cycle. (feng2021phenotypegenotypeand pages 1-2)

Mechanistic enzymology/flux evidence supports that ACAD8 loss creates a block at the isobutyryl‑CoA dehydrogenation step: patient‑cell experiments showed that incubation with 13C5‑valine produced a “significant increase in 13C4‑isobutyrylcarnitine” without normal downstream incorporation, consistent with pathway interruption at the ACAD8 step. (wanders2012enzymologyofthe pages 2-4)

2.2 Subcellular localization and cellular components affected IBD (ACAD8) is described as a mitochondrial enzyme in multiple clinical/biochemical analyses. (lin2018clinicalbiochemicaland pages 1-2, feng2021phenotypegenotypeand pages 1-2, oglesbee2007developmentofa pages 1-2)

Accordingly, the most directly implicated cellular component is the mitochondrion (mitochondrial matrix–associated soluble enzyme complex). (feng2021phenotypegenotypeand pages 1-2, lin2018clinicalbiochemicaland pages 1-2)

2.3 Dysregulated pathways and biochemical consequences

2.3.1 Valine degradation (branched‑chain amino acid catabolism) dysregulation Loss of ACAD8 activity disrupts mitochondrial valine oxidation, leading to accumulation and shunting of valine‑derived intermediates into measurable surrogate biomarkers.

2.3.2 Biomarker‑level metabolic rerouting: C4 acylcarnitine and isobutyrylglycine Across cohorts and diagnostic algorithms, the most consistent biochemical signature is elevated C4‑acylcarnitine in dried blood spots/plasma, typically accompanied by increased C4/C2 and C4/C3 ratios. (lin2018clinicalbiochemicaland pages 1-2, feng2021phenotypegenotypeand pages 1-2)

Urinary isobutyrylglycine (IBG) supports diagnosis but is not invariant. Early descriptions emphasized intermittency: “isobutyrylglycine may be intermittently normal in patients with confirmed IBD deficiency.” (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5)

A large literature synthesis similarly reports that isobutyrylglycinuria is “common but not invariable.” (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2)

2.4 Why clinical penetrance is often low: compensatory mechanisms and substrate promiscuity (recent mechanistic framing) A mechanistic hypothesis for why ACAD8 deficiency often has limited clinical impact is enzyme redundancy/substrate promiscuity within the acyl‑CoA dehydrogenase family. A 2023 Journal of Inherited Metabolic Disease study (focused on valine/isoleucine pathway ACADs) notes that deficiencies of ACAD8 are “considered biochemical abnormalities with limited or no clinical consequences” and demonstrates that in HEK‑293 models, “substantial promiscuity of ACADs… for the isobutyryl‑CoA substrate” can occur. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3)

This framework supports the idea that alternate ACAD activities may partially compensate for ACAD8 loss in some cellular contexts, reducing metabolite toxicity and clinical expression.

2.5 Proposed/observed organ involvement and tissue vulnerability

2.5.1 Liver (emerging theme) A 2026 synthesis of cases up to Dec 2024 (useful for current clinical interpretation though outside 2023–2024) reports: “altered biochemical markers of liver function were reported in 19 individuals, including 18 with isolated elevations of serum transaminases and γ‑glutamyl transferase.” It further notes: “One 11‑year‑old boy exhibited hepatomegaly and ultrasound findings suggestive of hepatic steatosis,” and that “Hepatic steatosis has also been observed in an IBDD mouse model,” suggesting a potential hepatic link. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2)

Supporting mechanistic animal data is referenced in a clinical biochemical series: “alternative splicing in ACAD8 caused a mitochondrial defect and progressive hepatic steatosis in mice.” (lin2018clinicalbiochemicaland pages 1-2)

Interpretation: a plausible mechanistic connection is mitochondrial metabolic stress in hepatocytes, potentially contributing to steatosis and mild transaminase elevation in a subset of individuals, but causality and prevalence remain incompletely defined. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2)

2.5.2 Heart, muscle, and brain The index symptomatic patient described in early biochemical/clinical work developed anemia and cardiomyopathy; later reports continue to include cardiomyopathy among rare presentations, while most screened individuals remain asymptomatic. (wanders2012enzymologyofthe pages 2-4, oglesbee2007developmentofa pages 1-2)

Neurologic and developmental findings (e.g., hypotonia, developmental delay, speech delay, seizures) are variably reported, but heterogeneity and comorbid genetic diagnoses complicate attribution. (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6, eleftheriadou2021isobutyryl‐coadehydrogenasedeficiency pages 6-7)

  1. Key molecular players and knowledge-base–ready entities

3.1 Genes/proteins (HGNC) • ACAD8 (acyl‑CoA dehydrogenase family member 8; isobutyryl‑CoA dehydrogenase), OMIM*604773; causative for OMIM#611283. (feng2021phenotypegenotypeand pages 1-2, oglesbee2007developmentofa pages 1-2)

3.2 Metabolites and small molecules (CHEBI‑style entities; representative) • Valine (substrate pathway amino acid) (feng2021phenotypegenotypeand pages 1-2, wanders2012enzymologyofthe pages 2-4) • Isobutyryl‑CoA (ACAD8 substrate) (feng2021phenotypegenotypeand pages 1-2, wanders2012enzymologyofthe pages 2-4) • Methacrylyl‑CoA (product of ACAD8 step) (feng2021phenotypegenotypeand pages 1-2) • C4‑acylcarnitine (includes isobutyrylcarnitine and butyrylcarnitine; key NBS marker) (oglesbee2007developmentofa pages 1-2, oglesbee2007developmentofa pages 3-4) • Isobutyrylglycine (urinary acylglycine marker; intermittent) (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5, feng2021phenotypegenotypeand pages 1-2) • Ethylmalonic acid (used to distinguish SCADD; not expected in IBDD) (oglesbee2007developmentofa pages 1-2, oglesbee2007developmentofa pages 3-4) • L‑carnitine (secondary deficiency described in some; supplementation can be used when deficient) (oglesbee2007developmentofa pages 1-2, sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5) • 3‑hydroxybutyrate and lactate (contextual metabolites in hypoglycemia presentation) (santra2017longtermoutcomeof pages 1-2)

3.3 Cell types (CL‑style; inferred from organ findings and mitochondrial metabolic role) • Hepatocyte (liver enzyme abnormalities/steatosis) (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2) • Cardiomyocyte (cardiomyopathy in rare symptomatic presentations) (wanders2012enzymologyofthe pages 2-4, oglesbee2007developmentofa pages 1-2) • Skeletal muscle cell (myalgia/weakness reported in some cases and literature summaries) (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Neuron (developmental delay/seizures reported in some) (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6)

3.4 Anatomical locations (UBERON‑style) • Liver (transaminase elevations, steatosis) (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2) • Heart (cardiomyopathy) (wanders2012enzymologyofthe pages 2-4, oglesbee2007developmentofa pages 1-2) • Brain (developmental delay, seizures) (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Skeletal muscle (hypotonia, myalgia/weakness in some) (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6, feng2021phenotypegenotypeand pages 1-2)

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

4.1 Disrupted biological processes (GO) Evidence supports disruption of: • Valine catabolic process / branched‑chain amino acid catabolic process (block at isobutyryl‑CoA oxidation step) (feng2021phenotypegenotypeand pages 1-2, wanders2012enzymologyofthe pages 2-4) • Mitochondrial acyl‑CoA dehydrogenase–dependent oxidation steps in amino acid metabolism (lin2018clinicalbiochemicaland pages 1-2, wanders2012enzymologyofthe pages 2-4) • Carnitine homeostasis/transport‑linked processes (secondary carnitine deficiency proposed/observed in some cases) (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5, oglesbee2007developmentofa pages 1-2)

4.2 Cellular components (GO) • Mitochondrion / mitochondrial matrix (ACAD8 described as mitochondrial enzyme) (lin2018clinicalbiochemicaland pages 1-2, feng2021phenotypegenotypeand pages 1-2)

  1. Disease progression (sequence of events) — current model

5.1 Trigger and earliest biochemical changes Primary trigger is congenital ACAD8 loss-of-function. In infancy, expanded NBS detects isolated C4‑acylcarnitine elevation in dried blood spots (C4 comprises both isobutyrylcarnitine and butyrylcarnitine), prompting confirmatory testing. (oglesbee2007developmentofa pages 1-2, oglesbee2007developmentofa pages 3-4)

5.2 Intermediate biochemical phenotype Persistent elevation of C4 and sometimes increased urinary isobutyrylglycine are observed; urinary IBG can be absent/intermittent. (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5, feng2021phenotypegenotypeand pages 1-2)

5.3 Clinical manifestations (if any) Most individuals remain clinically well, but a minority develops nonspecific findings (often anemia; occasionally neurodevelopmental delay, hypotonia, failure to thrive, seizures, or rare cardiomyopathy). (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6)

5.4 Potential later organ involvement A subset may show liver enzyme abnormalities and possible hepatic steatosis (human reports and mouse model), supporting consideration of liver monitoring in follow-up. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2)

  1. Phenotypic manifestations (HP‑style) and mechanistic linkage

6.1 Core biochemical phenotypes • Elevated C4‑acylcarnitine (newborn screening hallmark) (oglesbee2007developmentofa pages 1-2, feng2021phenotypegenotypeand pages 1-2) • Increased C4/C2 and C4/C3 ratios (feng2021phenotypegenotypeand pages 1-2, lin2018clinicalbiochemicaland pages 1-2) • Isobutyrylglycinuria / urinary isobutyrylglycine (variable) (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5, feng2021phenotypegenotypeand pages 1-2)

6.2 Clinical phenotypes reported across cohorts A 172‑case synthesis reports 146 asymptomatic and 26 symptomatic, with anemia most frequent. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6)

In a 40‑patient Chinese NBS cohort with 3–108 months follow‑up, four had transient motor delay and two had growth delay; most were otherwise healthy. (feng2021phenotypegenotypeand pages 1-2)

A 10‑year follow‑up case report describes benign long‑term outcome after presentation with ketotic hypoglycaemia and persistent biochemical markers of IBDD; the child had normal psychomotor development and no cardiomyopathy or anemia during follow-up. (santra2017longtermoutcomeof pages 1-2)

6.3 Liver-related phenotypes • Elevated ALT/AST and γ‑glutamyl transferase in a subset; rare hepatomegaly/steatosis reported; steatosis also observed in mouse model. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2)

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

7.1 2023: Improving newborn screening specificity for C4 elevation (reducing false positives) A 2023 Biomedicines study addressed the major NBS problem that elevated C4 is shared by SCADD and IBDD and is associated with high false-positive burden. It proposed seven C4‑based ratios (C4/C0, C4/C5, C4/C5DC\C6OH, C4/C6, C4/C8, C4/C14:1, C4/C16:1) as secondary biomarkers. (messina2023butyrylcarnitineelevationin pages 1-2, messina2023butyrylcarnitineelevationin pages 2-3)

Quantitative example (IBDD vs false positives; nIBDD=4, nFP=91): mean C4 1.25 μM vs 0.979 μM; C4/C0 0.0796 vs 0.0461; C4/C5 9.82 vs 6.14; C4/C6 27.6 vs 13.4; C4/C8 33.3 vs 15.5. The authors state that these markers “robustly distinguished IBDD patients from FPs.” (messina2023butyrylcarnitineelevationin pages 3-5)

Visual evidence: the paper’s Tables 2–3 compile the evaluated ratios and statistical performance for distinguishing IBDD, SCADD, and false positives (see extracted tables). (messina2023butyrylcarnitineelevationin media 9d25c0d0, messina2023butyrylcarnitineelevationin media c375a74a)

7.2 2023: Mechanistic reframing via ACAD “substrate promiscuity” A 2023 Journal of Inherited Metabolic Disease study demonstrated notable ACAD substrate promiscuity in a cell model and notes that ACAD8 deficiency is “considered” to have limited clinical consequences, supporting a mechanistic explanation for low penetrance in many individuals. (houten2023acyl‐coadehydrogenasesubstrate pages 1-3)

7.3 2024: First-tier genetic screening combined with MS/MS (real-world implementation) A 2024 International Journal of Neonatal Screening multicenter study implemented concurrent NGS and MS/MS in 29,601 newborns and diagnosed 23 IEMs (≈1 in 1,287). Two IBD cases attributable to ACAD8 were identified. (tang2024newbornscreeningfor pages 4-5, tang2024newbornscreeningfor pages 2-4)

Screening performance (single-modality): “the positive predictive value (PPV) for MS/MS was 5.29%, and the sensitivity was 91.3%,” whereas “for genetic screening alone, the PPV for NGS was 70.83%, with 73.91% sensitivity.” (tang2024newbornscreeningfor pages 1-2)

Complementarity was explicitly demonstrated: “Six cases would have been missed but with the results of MS/MS screening… These six cases had MSUD, IBD, PCD, SCADD, MADD, and CPTII.” (tang2024newbornscreeningfor pages 4-5)

  1. Current applications and real‑world implementations

8.1 Newborn screening and confirmatory diagnostic workflows

8.1.1 Established follow-up algorithm for elevated C4 (classic implementation) A widely cited 2007 Genetics in Medicine paper developed a follow-up algorithm for abnormal C4-acylcarnitine NBS results. It emphasizes that C4 comprises both isobutyryl- and butyrylcarnitine, so elevation is non-specific and requires differentiation from SCADD. (oglesbee2007developmentofa pages 1-2)

A key differential approach was: “Quantification of C4-acylcarnitine in plasma and urine as well as ethylmalonic acid in urine allows the differentiation” of IBD from SCAD deficiency. (oglesbee2007developmentofa pages 1-2)

The same work reported that urinary isobutyrylglycine can be normal and highlighted urine acylcarnitines as consistently helpful (urinary C4 elevation and C4/C3 ratio). (oglesbee2007developmentofa pages 3-4, oglesbee2007developmentofa pages 5-6)

8.1.2 2023 ratio-based post-analytical improvement The 2023 ratio approach provides a pragmatic, implementable enhancement to MS/MS interpretation aimed at improving PPV and reducing family/health-system burden from false positives. (messina2023butyrylcarnitineelevationin pages 1-2, messina2023butyrylcarnitineelevationin media 9d25c0d0)

8.1.3 2024 combined NGS + MS/MS screening implementation The 2024 combined approach provides an operational model for integrating targeted NGS panels with MS/MS to increase diagnostic precision and capture cases that may be missed by one modality alone. (tang2024newbornscreeningfor pages 2-4, tang2024newbornscreeningfor pages 4-5)

8.2 Management approaches and clinical monitoring Clinical significance is often uncertain, so management is frequently conservative and individualized.

• Carnitine supplementation: In a historically symptomatic case (cardiomyopathy, anemia, carnitine deficiency), oral L‑carnitine improved the condition, with long-term dependence on supplementation reported. (oglesbee2007developmentofa pages 1-2)

• Diet/feeding: In a 40‑patient NBS cohort, patients were monitored and “gradually had a normal diet after 6 months of age,” with favorable prognosis in most. (feng2021phenotypegenotypeand pages 1-2)

• Hypoglycemia preparedness: In a 10‑year follow‑up case report, a “15% glucose polymer emergency regimen” was provided (never required), and “carnitine supplementation has not been deemed necessary” when carnitine remained normal; authors suggest emergency regimens may be indicated for recurrent hypoglycemia. (santra2017longtermoutcomeof pages 1-2, santra2017longtermoutcomeof pages 2-3)

• Expert/authoritative opinion: The clinical uncertainty is explicitly stated as a management challenge: “the clinical significance of IBDD is uncertain and it remains a dilemma for clinicians managing children diagnosed through newborn screening programmes.” (santra2017longtermoutcomeof pages 2-3)

  1. Relevant statistics and data (recent and cohort-based)

9.1 Incidence estimates (selected) • 2021 Chinese NBS cohort (Zhejiang): incidence 1:62,599 (n=40). (feng2021phenotypegenotypeand pages 1-2) • 2024 NGS+MS/MS multicenter study: IBD incidence in this dataset includes an entry corresponding to 2 IBD cases in 29,601 newborns; the paper’s table excerpt notes “IBD ACAD8 2” (and includes sub-incidence values). (tang2024newbornscreeningfor pages 4-5) • 2025 regional NBS cohort: incidence 1:45,517 (5 confirmed IBDD among 227,583 screened). (tao2025novelacad8variants pages 3-4)

9.2 Penetrance and symptomatic fraction A comprehensive literature review up to Dec 2024 identified 172 individuals, with 146 asymptomatic and 26 symptomatic at follow-up; anemia was the most frequently reported abnormality among the symptomatic group. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6)

9.3 2023 biomarker ratio data for reducing false positives Quantitative discrimination between IBDD and false positives is supported by differences in C4 and C4‑based ratios (e.g., C4/C0, C4/C6, C4/C8), in a dataset of 121 newborns with C4 elevation (IBDD n=4). (messina2023butyrylcarnitineelevationin pages 3-5)

  1. Evidence-backed ontology mapping (knowledge-base ready)

10.1 Gene/protein annotations • ACAD8 (OMIM*604773): mitochondrial enzyme in valine degradation; catalyzes isobutyryl‑CoA → methacrylyl‑CoA. (feng2021phenotypegenotypeand pages 1-2)

10.2 GO biological processes (candidate terms; map to evidence) • Branched‑chain amino acid catabolic process / valine catabolic process (block demonstrated by flux accumulation of isobutyrylcarnitine from 13C5‑valine). (wanders2012enzymologyofthe pages 2-4)

10.3 GO cellular components • Mitochondrion / mitochondrial matrix (ACAD8 described as mitochondrial enzyme; mitochondrial defect in mouse splicing model). (lin2018clinicalbiochemicaland pages 1-2)

10.4 HP phenotypes (candidate terms; evidence mapping) • Increased C4 acylcarnitine (feng2021phenotypegenotypeand pages 1-2, oglesbee2007developmentofa pages 1-2) • Isobutyrylglycinuria / increased urinary isobutyrylglycine (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5, feng2021phenotypegenotypeand pages 1-2) • Anemia (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6, wanders2012enzymologyofthe pages 2-4) • Developmental delay / motor delay / speech delay (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Hypotonia (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Failure to thrive / growth delay (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Seizures (feng2021phenotypegenotypeand pages 1-2, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Dilated cardiomyopathy (rare) (wanders2012enzymologyofthe pages 2-4, oglesbee2007developmentofa pages 1-2) • Ketotic hypoglycemia (rare; uncertain causality) (santra2017longtermoutcomeof pages 1-2) • Elevated transaminases / hepatic steatosis (subset) (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2)

10.5 CL cell types and UBERON tissues (candidate terms; evidence mapping) • Hepatocyte / liver (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2, lin2018clinicalbiochemicaland pages 1-2) • Cardiomyocyte / heart (wanders2012enzymologyofthe pages 2-4, oglesbee2007developmentofa pages 1-2) • Neuron / brain (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6) • Skeletal muscle cell / skeletal muscle (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6)

  1. Evidence items (PMID-oriented; limitations)

The retrieved texts in this environment did not reliably expose PMID fields for all articles; therefore, the evidence table below uses DOI and journal metadata from the retrieved sources. Where a PMID is explicitly needed, the DOI can be used to retrieve PMID via PubMed.

Evidence table (selected core sources)

• Messina et al., “Butyrylcarnitine Elevation in Newborn Screening…” Biomedicines. Publication date: Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247 (messina2023butyrylcarnitineelevationin pages 1-2, messina2023butyrylcarnitineelevationin pages 3-5) • Tang et al., “Newborn Screening… by NGS Combined with MS/MS.” International Journal of Neonatal Screening. Publication date: Mar 2024. URL: https://doi.org/10.3390/ijns10020028 (tang2024newbornscreeningfor pages 1-2, tang2024newbornscreeningfor pages 4-5) • Houten et al., “Acyl‑CoA dehydrogenase substrate promiscuity…” Journal of Inherited Metabolic Disease. Publication date: Jun 2023. URL: https://doi.org/10.1002/jimd.12642 (houten2023acyl‐coadehydrogenasesubstrate pages 1-3) • Feng et al., “Phenotype, genotype and long‑term prognosis of 40 Chinese patients…” Orphanet Journal of Rare Diseases. Publication date: Sep 2021. URL: https://doi.org/10.1186/s13023-021-02018-6 (feng2021phenotypegenotypeand pages 1-2) • Oglesbee et al., “Development of a newborn screening follow‑up algorithm…” Genetics in Medicine. Publication date: Feb 2007. URL: https://doi.org/10.1097/gim.0b013e31802f78d6 (oglesbee2007developmentofa pages 3-4, oglesbee2007developmentofa pages 1-2) • Wanders et al., “Enzymology of the branched‑chain amino acid oxidation disorders: the valine pathway.” J Inherit Metab Dis. Publication date: Nov 2012. URL: https://doi.org/10.1007/s10545-010-9236-x (wanders2012enzymologyofthe pages 2-4) • Santra et al., “Long‑term outcome… diagnosed following ketotic hypoglycaemia.” Mol Genet Metab Rep. Publication date: Mar 2017. URL: https://doi.org/10.1016/j.ymgmr.2016.11.005 (santra2017longtermoutcomeof pages 1-2) • Reyes & Sass, “IBDD: disease, or non‑disease?” Orphanet Journal of Rare Diseases. Publication date: Jan 2026. URL: https://doi.org/10.1186/s13023-026-04207-7 (useful synthesis; outside requested 2023–2024) (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2)

  1. Summary and expert interpretation

IBDD (ACAD8 deficiency) is best conceptualized as a mitochondrial valine catabolism defect whose most robust phenotype is biochemical (persistent C4‑acylcarnitine elevation; variable isobutyrylglycinuria), with low and heterogeneous clinical penetrance. The best-supported mechanistic explanation for frequent benignity is metabolic compensation via acyl‑CoA dehydrogenase substrate promiscuity in some cellular contexts (2023 mechanistic work), but a minority of individuals show nonspecific clinical findings (especially anemia) and a possibly underrecognized hepatic involvement signal (transaminase elevations/steatosis in some reports and animal models). (houten2023acyl‐coadehydrogenasesubstrate pages 1-3, reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6, reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2)

From a public health and implementation standpoint, 2023–2024 literature highlights that the major practical challenge is not detection but specificity and follow-up burden for C4 elevations. The field is responding with improved post-analytical interpretation (C4‑ratio panels) and with integrated first-tier molecular screening strategies (NGS+MS/MS) that substantially improve PPV relative to MS/MS alone while maintaining complementary sensitivity. (messina2023butyrylcarnitineelevationin pages 1-2, messina2023butyrylcarnitineelevationin media 9d25c0d0, tang2024newbornscreeningfor pages 1-2, tang2024newbornscreeningfor pages 4-5)

References

  1. (feng2021phenotypegenotypeand pages 1-2): Junqi Feng, Chenxi Yang, Ling Zhu, Yuchen Zhang, Xiaoxu Zhao, Chi Chen, Qi-xing Chen, Qiang Shu, Pingping Jiang, and Fan Tong. Phenotype, genotype and long-term prognosis of 40 chinese patients with isobutyryl-coa dehydrogenase deficiency and a review of variant spectra in acad8. Orphanet Journal of Rare Diseases, Sep 2021. URL: https://doi.org/10.1186/s13023-021-02018-6, doi:10.1186/s13023-021-02018-6. This article has 17 citations and is from a peer-reviewed journal.

  2. (reyes2026isobutyrylcoenzymeadehydrogenase pages 1-2): María Daniela Santacruz Reyes and Jörn Oliver Sass. Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease? Orphanet Journal of Rare Diseases, Jan 2026. URL: https://doi.org/10.1186/s13023-026-04207-7, doi:10.1186/s13023-026-04207-7. This article has 0 citations and is from a peer-reviewed journal.

  3. (sass2004isobutyrylcoadehydrogenasedeficiency pages 1-4): J. O. Sass, S. Sander, and J. Zschocke. Isobutyryl-coa dehydrogenase deficiency: isobutyrylglycinuria and acad8 gene mutations in two infants. Journal of Inherited Metabolic Disease, 27:741-745, Nov 2004. URL: https://doi.org/10.1023/b:boli.0000045798.12425.1b, doi:10.1023/b:boli.0000045798.12425.1b. This article has 41 citations and is from a peer-reviewed journal.

  4. (oglesbee2007developmentofa pages 1-2): Devin Oglesbee, Miao He, Nilanjana Majumder, Jerry Vockley, Ayesha Ahmad, Brad Angle, Barbara Burton, Joel Charrow, Regina Ensenauer, Can H. Ficicioglu, Laura Davis Keppen, Deborah Marsden, Silvia Tortorelli, Si Houn Hahn, and Dietrich Matern. Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-coa dehydrogenase deficiency. Genetics in Medicine, 9:108-116, Feb 2007. URL: https://doi.org/10.1097/gim.0b013e31802f78d6, doi:10.1097/gim.0b013e31802f78d6. This article has 55 citations and is from a highest quality peer-reviewed journal.

  5. (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.

  6. (wanders2012enzymologyofthe pages 2-4): Ronald J. A. Wanders, Marinus Duran, and Ference J. Loupatty. Enzymology of the branched-chain amino acid oxidation disorders: the valine pathway. Journal of Inherited Metabolic Disease, 35:5-12, Nov 2012. URL: https://doi.org/10.1007/s10545-010-9236-x, doi:10.1007/s10545-010-9236-x. This article has 101 citations and is from a peer-reviewed journal.

  7. (lin2018clinicalbiochemicaland pages 1-2): Yiming Lin, Weilin Peng, Mengyi Jiang, Chunmei Lin, Weihua Lin, Zhenzhu Zheng, Min Li, and Qingliu Fu. Clinical, biochemical and genetic analysis of chinese patients with isobutyryl-coa dehydrogenase deficiency. Clinica chimica acta; international journal of clinical chemistry, 487:133-138, Dec 2018. URL: https://doi.org/10.1016/j.cca.2018.09.033, doi:10.1016/j.cca.2018.09.033. This article has 26 citations.

  8. (sass2004isobutyrylcoadehydrogenasedeficiency pages 4-5): J. O. Sass, S. Sander, and J. Zschocke. Isobutyryl-coa dehydrogenase deficiency: isobutyrylglycinuria and acad8 gene mutations in two infants. Journal of Inherited Metabolic Disease, 27:741-745, Nov 2004. URL: https://doi.org/10.1023/b:boli.0000045798.12425.1b, doi:10.1023/b:boli.0000045798.12425.1b. This article has 41 citations and is from a peer-reviewed journal.

  9. (reyes2026isobutyrylcoenzymeadehydrogenase pages 4-6): María Daniela Santacruz Reyes and Jörn Oliver Sass. Isobutyryl-coenzyme a dehydrogenase deficiency: disease, or non-disease? Orphanet Journal of Rare Diseases, Jan 2026. URL: https://doi.org/10.1186/s13023-026-04207-7, doi:10.1186/s13023-026-04207-7. This article has 0 citations and is from a peer-reviewed journal.

  10. (eleftheriadou2021isobutyryl‐coadehydrogenasedeficiency pages 6-7): Maria Eleftheriadou, Evita Medici‐ van den Herik, Kyra Stuurman, Yolande van Bever, Debby M. E. I. Hellebrekers, Marjon van Slegtenhorst, George Ruijter, and Tahsin Stefan Barakat. Isobutyryl‐coa dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: a case report. Molecular Genetics & Genomic Medicine, Jan 2021. URL: https://doi.org/10.1002/mgg3.1595, doi:10.1002/mgg3.1595. This article has 9 citations and is from a peer-reviewed journal.

  11. (oglesbee2007developmentofa pages 3-4): Devin Oglesbee, Miao He, Nilanjana Majumder, Jerry Vockley, Ayesha Ahmad, Brad Angle, Barbara Burton, Joel Charrow, Regina Ensenauer, Can H. Ficicioglu, Laura Davis Keppen, Deborah Marsden, Silvia Tortorelli, Si Houn Hahn, and Dietrich Matern. Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-coa dehydrogenase deficiency. Genetics in Medicine, 9:108-116, Feb 2007. URL: https://doi.org/10.1097/gim.0b013e31802f78d6, doi:10.1097/gim.0b013e31802f78d6. This article has 55 citations and is from a highest quality peer-reviewed journal.

  12. (santra2017longtermoutcomeof pages 1-2): S. Santra, A. Macdonald, M.A. Preece, R.K. Olsen, and B.S. Andresen. Long-term outcome of isobutyryl-coa dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia. Molecular Genetics and Metabolism Reports, 10:28-30, Mar 2017. URL: https://doi.org/10.1016/j.ymgmr.2016.11.005, doi:10.1016/j.ymgmr.2016.11.005. This article has 17 citations.

  13. (messina2023butyrylcarnitineelevationin pages 1-2): MariaAnna Messina, Alessia Arena, Riccardo Iacobacci, Luisa La Spina, Concetta Meli, Federica Raudino, and Martino Ruggieri. Butyrylcarnitine elevation in newborn screening: reducing false positives and distinguishing between two rare diseases through the evaluation of new ratios. Biomedicines, 11:3247, Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247, doi:10.3390/biomedicines11123247. This article has 2 citations.

  14. (messina2023butyrylcarnitineelevationin pages 2-3): MariaAnna Messina, Alessia Arena, Riccardo Iacobacci, Luisa La Spina, Concetta Meli, Federica Raudino, and Martino Ruggieri. Butyrylcarnitine elevation in newborn screening: reducing false positives and distinguishing between two rare diseases through the evaluation of new ratios. Biomedicines, 11:3247, Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247, doi:10.3390/biomedicines11123247. This article has 2 citations.

  15. (messina2023butyrylcarnitineelevationin pages 3-5): MariaAnna Messina, Alessia Arena, Riccardo Iacobacci, Luisa La Spina, Concetta Meli, Federica Raudino, and Martino Ruggieri. Butyrylcarnitine elevation in newborn screening: reducing false positives and distinguishing between two rare diseases through the evaluation of new ratios. Biomedicines, 11:3247, Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247, doi:10.3390/biomedicines11123247. This article has 2 citations.

  16. (messina2023butyrylcarnitineelevationin media 9d25c0d0): MariaAnna Messina, Alessia Arena, Riccardo Iacobacci, Luisa La Spina, Concetta Meli, Federica Raudino, and Martino Ruggieri. Butyrylcarnitine elevation in newborn screening: reducing false positives and distinguishing between two rare diseases through the evaluation of new ratios. Biomedicines, 11:3247, Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247, doi:10.3390/biomedicines11123247. This article has 2 citations.

  17. (messina2023butyrylcarnitineelevationin media c375a74a): MariaAnna Messina, Alessia Arena, Riccardo Iacobacci, Luisa La Spina, Concetta Meli, Federica Raudino, and Martino Ruggieri. Butyrylcarnitine elevation in newborn screening: reducing false positives and distinguishing between two rare diseases through the evaluation of new ratios. Biomedicines, 11:3247, Dec 2023. URL: https://doi.org/10.3390/biomedicines11123247, doi:10.3390/biomedicines11123247. This article has 2 citations.

  18. (tang2024newbornscreeningfor pages 4-5): Chengfang Tang, Lixin Li, Ting Chen, Yulin Li, Bo Zhu, Yinhong Zhang, Yifan Yin, Xiulian Liu, Cidan Huang, Jingkun Miao, Baosheng Zhu, Xiaohua Wang, Hui Zou, Lianshu Han, Jizhen Feng, and Yonglan Huang. Newborn screening for inborn errors of metabolism by next-generation sequencing combined with tandem mass spectrometry. International Journal of Neonatal Screening, 10:28, Mar 2024. URL: https://doi.org/10.3390/ijns10020028, doi:10.3390/ijns10020028. This article has 19 citations.

  19. (tang2024newbornscreeningfor pages 2-4): Chengfang Tang, Lixin Li, Ting Chen, Yulin Li, Bo Zhu, Yinhong Zhang, Yifan Yin, Xiulian Liu, Cidan Huang, Jingkun Miao, Baosheng Zhu, Xiaohua Wang, Hui Zou, Lianshu Han, Jizhen Feng, and Yonglan Huang. Newborn screening for inborn errors of metabolism by next-generation sequencing combined with tandem mass spectrometry. International Journal of Neonatal Screening, 10:28, Mar 2024. URL: https://doi.org/10.3390/ijns10020028, doi:10.3390/ijns10020028. This article has 19 citations.

  20. (tang2024newbornscreeningfor pages 1-2): Chengfang Tang, Lixin Li, Ting Chen, Yulin Li, Bo Zhu, Yinhong Zhang, Yifan Yin, Xiulian Liu, Cidan Huang, Jingkun Miao, Baosheng Zhu, Xiaohua Wang, Hui Zou, Lianshu Han, Jizhen Feng, and Yonglan Huang. Newborn screening for inborn errors of metabolism by next-generation sequencing combined with tandem mass spectrometry. International Journal of Neonatal Screening, 10:28, Mar 2024. URL: https://doi.org/10.3390/ijns10020028, doi:10.3390/ijns10020028. This article has 19 citations.

  21. (oglesbee2007developmentofa pages 5-6): Devin Oglesbee, Miao He, Nilanjana Majumder, Jerry Vockley, Ayesha Ahmad, Brad Angle, Barbara Burton, Joel Charrow, Regina Ensenauer, Can H. Ficicioglu, Laura Davis Keppen, Deborah Marsden, Silvia Tortorelli, Si Houn Hahn, and Dietrich Matern. Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-coa dehydrogenase deficiency. Genetics in Medicine, 9:108-116, Feb 2007. URL: https://doi.org/10.1097/gim.0b013e31802f78d6, doi:10.1097/gim.0b013e31802f78d6. This article has 55 citations and is from a highest quality peer-reviewed journal.

  22. (santra2017longtermoutcomeof pages 2-3): S. Santra, A. Macdonald, M.A. Preece, R.K. Olsen, and B.S. Andresen. Long-term outcome of isobutyryl-coa dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia. Molecular Genetics and Metabolism Reports, 10:28-30, Mar 2017. URL: https://doi.org/10.1016/j.ymgmr.2016.11.005, doi:10.1016/j.ymgmr.2016.11.005. This article has 17 citations.

  23. (tao2025novelacad8variants pages 3-4): Yilun Tao, Dong Han, Jianfang Li, Xiaoyun Li, Luna Hao, Wenxia Song, Lihong Wang, and Xiaoze Li. Novel acad8 variants identified in isobutyryl-coa dehydrogenase deficiency: challenges in phenotypic variability and management. Frontiers in Genetics, Apr 2025. URL: https://doi.org/10.3389/fgene.2025.1532902, doi:10.3389/fgene.2025.1532902. This article has 0 citations and is from a peer-reviewed journal.