D-Bifunctional Protein Deficiency

Metabolic Disorder MONDO:0009855 Pathograph 13 Show in embeddings browser hereditary disease metabolic disorder disorder of peroxisomal beta oxidation

D-bifunctional protein (DBP) deficiency is a severe autosomal recessive peroxisomal fatty-acid beta-oxidation disorder caused by biallelic HSD17B4 variants. DBP catalyzes the second and third steps (2-enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase) of peroxisomal beta-oxidation, immediately downstream of the ACOX1 acyl-CoA oxidase step. Loss of activity blocks oxidation of very-long-chain fatty acids (VLCFAs), branched-chain pristanic acid, and bile-acid intermediates, producing their accumulation and an infantile neurodegenerative leukodystrophy with neonatal hypotonia, intractable seizures, craniofacial dysmorphism, deafness, visual loss, and early death. It is the closest non-biogenesis phenocopy of Zellweger syndrome but, unlike biogenesis disorders, has normal plasmalogen synthesis and phytanic-acid oxidation.

Ask OpenScientist

Ask a research question about D-Bifunctional Protein Deficiency. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

2
Mappings
3
Pathophys.
7
Phenotypes
13
Pathograph
1
Genes
2
Medical Actions
3
Subtypes
2
Differentials
🔗

Mappings

MONDO
MONDO:0009855 d-bifunctional protein deficiency
skos:exactMatch MONDO
Primary MONDO disease identifier for D-bifunctional protein deficiency.
NCIT
NCIT:C119676 D-Bifunctional Protein Deficiency
skos:exactMatch NCIT
NCI Thesaurus term for D-bifunctional protein deficiency.
NCIT
NCIT:C119676 D-Bifunctional Protein Deficiency
skos:exactMatch NCIT
NCI Thesaurus term for D-bifunctional protein deficiency.
◆

Subtypes

3
Type I (complete bifunctional deficiency)
Combined loss of both 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activities; the most severe form.
Type II (hydratase-deficient)
Isolated loss of 2-enoyl-CoA hydratase activity with preserved dehydrogenase activity.
Type III (dehydrogenase-deficient)
Isolated loss of 3-hydroxyacyl-CoA dehydrogenase activity with preserved hydratase activity.
⚙

Pathophysiology

3
HSD17B4 D-Bifunctional Protein Deficiency
Biallelic HSD17B4 pathogenic variants reduce peroxisomal D-bifunctional protein activity, disrupting the 2-enoyl-CoA hydratase and D-3-hydroxyacyl-CoA dehydrogenase steps of peroxisomal beta-oxidation immediately downstream of the ACOX1 acyl-CoA oxidase step.
HSD17B4 hgnc:5213
very long-chain fatty acid beta-oxidation GO:0140493 ↓ DECREASED
enoyl-CoA hydratase activity GO:0004300 ↓ DECREASED very long-chain (3S)-3-hydroxyacyl-CoA dehydrogenase activity GO:0035380 ↓ DECREASED
peroxisome GO:0005777
Downstream
Substrate Accumulation (VLCFA, Pristanic Acid, Bile-Acid Intermediates) Loss of DBP activity blocks peroxisomal oxidation of VLCFAs, pristanic acid, and bile-acid intermediates.
Show evidence (2 references)
PMID:34368026 SUPPORT Human Clinical
"D-Bifunctional protein deficiency (D-BPD) is an autosomal recessive disorder caused by peroxisomal β-oxidation defects."
This identifies the peroxisomal beta-oxidation defect as the causal biochemical lesion.
PMID:33115767 SUPPORT Human Clinical
"HSD17B4 is essential in peroxisomal fatty acid β-oxidation, and mutations in HSD17B4 are associated in multiple autosomal recessive disorders, including D-bifunctional protein deficiency and Perrault syndrome."
This supports HSD17B4 as the causal gene for the peroxisomal beta-oxidation defect.
Substrate Accumulation (VLCFA, Pristanic Acid, Bile-Acid Intermediates)
Impaired peroxisomal beta-oxidation causes accumulation of very-long-chain fatty acids (C26:0 and abnormal ratios), branched-chain pristanic acid, and di-/trihydroxycholestanoic acid bile-acid intermediates.
very long-chain fatty acid beta-oxidation GO:0140493 ↓ DECREASED
peroxisome GO:0005777
Downstream
Infantile Neurodegenerative Leukodystrophy Accumulated VLCFAs and related metabolites are toxic to myelin and developing brain, driving leukodystrophy and progressive neurodegeneration.
Craniofacial Dysmorphism Severe peroxisomal beta-oxidation dysfunction in early development is associated with the Zellweger-like craniofacial dysmorphism seen in DBP deficiency.
Show evidence (2 references)
PMID:34368026 SUPPORT Human Clinical
"Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0)."
This documents the characteristic VLCFA elevations in an affected patient.
PMID:34368026 SUPPORT Human Clinical
"The blood bile acid profile showed increased taurocholic acid, glycocholic acid, and taurochenodeoxycholic acid."
This supports accumulation of bile-acid species in affected patients.
Infantile Neurodegenerative Leukodystrophy
Metabolite toxicity produces white-matter disease and progressive neurodegeneration affecting myelinating oligodendrocytes, with cortical malformation and brain atrophy in severe cases.
oligodendrocyte CL:0000128
Downstream
Leukodystrophy
Neonatal Hypotonia
Seizures
Psychomotor Delay
Sensorineural Hearing Loss
Optic Atrophy
Show evidence (2 references)
PMID:33045774 SUPPORT Human Clinical
"However, progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed and follow-up brain imaging revealed leukodystrophy and brain atrophy."
This documents leukodystrophy and brain atrophy on follow-up imaging.
PMID:34368026 SUPPORT Human Clinical
"Cranial MRI revealed bilateral hemispheric and callosal dysplasia, with schizencephaly in the right hemisphere."
This documents cortical/callosal malformation on neuroimaging in a severe neonatal case.
⬡

Pathograph

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

7
Ear 1
Sensorineural Hearing Loss Sensorineural hearing impairment HP:0000407
Show evidence (1 reference)
PMID:33045774 SUPPORT Human Clinical
"progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed"
This documents progressive hearing defects in an affected patient.
Eye 1
Optic Atrophy Optic atrophy HP:0000648
Show evidence (1 reference)
PMID:33045774 SUPPORT Human Clinical
"progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed"
This documents optic nerve atrophy in an affected patient.
Head and Neck 1
Craniofacial Dysmorphism Abnormal facial shape HP:0001999
Show evidence (1 reference)
PMID:33045774 SUPPORT Human Clinical
"This patient showed craniofacial dysmorphism, club foot, and seizures with cyanosis one day after birth."
This documents craniofacial dysmorphism in an affected neonate.
Musculoskeletal 1
Neonatal Hypotonia Hypotonia HP:0001252
Onset: NEONATAL
Show evidence (1 reference)
PMID:34368026 SUPPORT Human Clinical
"The typical symptoms include hypotonia and seizures."
This directly supports hypotonia as a typical feature.
Nervous System 3
Seizures Seizure HP:0001250
Onset: NEONATAL
Show evidence (1 reference)
PMID:34368026 SUPPORT Human Clinical
"The typical symptoms include hypotonia and seizures."
This directly supports seizures as a typical feature.
Leukodystrophy Leukodystrophy HP:0002415
Show evidence (1 reference)
PMID:33045774 SUPPORT Human Clinical
"follow-up brain imaging revealed leukodystrophy and brain atrophy"
This supports leukodystrophy on neuroimaging.
Psychomotor Delay Global developmental delay HP:0001263
Onset: INFANTILE
Show evidence (1 reference)
PMID:34623748 SUPPORT Human Clinical
"neonatal hypotonia, seizures, craniofacial dysmorphisms, psychomotor delay, deafness, blindness"
This lists psychomotor delay among the typical features.
🧬

Genetic Associations

1
HSD17B4 pathogenic variants (Biallelic HSD17B4 variants cause autosomal recessive DBP deficiency; HSD17B4 is located at chromosome 5q23.1.)
Gene: HSD17B4 hgnc:5213 relationship_type: CAUSATIVE variant_origin: GERMLINE
Autosomal recessive
Show evidence (1 reference)
PMID:33115767 SUPPORT Human Clinical
"Most common features are neonatal hypotonia for D-bifunctional protein deficiency and ovarian dysgenesis in females, sensorineural deafness, and other neurological abnormalities in Perrault syndrome"
This documents the allelic relationship between DBP deficiency and Perrault syndrome at the HSD17B4 locus.
💊

Medical Actions

2
Multidisciplinary Supportive Care
Action: supportive care MAXO:0000950
Management is supportive and symptom-directed, including antiepileptic therapy, feeding and respiratory support, and surveillance for sensory and neurologic decline. No disease-modifying therapy is established.
Show evidence (1 reference)
PMID:34368026 SUPPORT Human Clinical
"Supportive care is the main treatment, aiming at controlling symptoms"
This supports supportive, symptom-directed care as the mainstay of management.
Dietary Supplementation (DHA and Fat-Soluble Vitamins)
Action: dietary intervention MAXO:0000088
Docosahexaenoic acid and fat-soluble vitamin supplementation has been used; early management of fat-soluble vitamin deficiency is advocated to reduce complications.
Show evidence (2 references)
PMID:33045774 SUPPORT Human Clinical
"The patient had type III DBP deficiency; therefore, docosahexaenoic acid and non-soluble vitamins were administered."
This documents DHA and vitamin supplementation in an affected patient.
PMID:34623748 SUPPORT Human Clinical
"advocate for the early management of fat-soluble vitamin deficiencies to reduce complications"
This supports early fat-soluble vitamin management.
🔬

Biochemical Markers

2
Elevated very-long-chain fatty acids (INCREASED)
Context: Plasma/fibroblast VLCFA analysis shows elevated C26:0 and abnormal C24:0/C22:0 and C26:0/C22:0 ratios, the biochemical hallmark of a peroxisomal beta-oxidation defect.
Show evidence (1 reference)
PMID:34368026 SUPPORT Human Clinical
"Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0)."
This documents the diagnostic VLCFA elevation pattern.
Elevated bile-acid intermediates (INCREASED)
Context: Accumulation of di- and trihydroxycholestanoic acids (DHCA/THCA) and abnormal bile-acid species reflects impaired peroxisomal bile-acid synthesis.
Show evidence (1 reference)
PMID:33115767 SUPPORT Human Clinical
"D-bifunctional protein deficiency impairs the catabolism of very long chain fatty acids, DHCA and THCA, and pristanic acid resulting in accumulation of these metabolites."
This supports accumulation of DHCA/THCA bile-acid intermediates and pristanic acid.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from D-Bifunctional Protein Deficiency:

Peroxisomal Acyl-CoA Oxidase Deficiency MONDO:0009919
Overlapping Features ACOX1 deficiency is the immediately upstream peroxisomal beta-oxidation defect (the acyl-CoA oxidase step) and shares the downstream VLCFA accumulation and infantile leukodystrophy phenotype.
Distinguishing Features
  • DBP deficiency affects the HSD17B4 hydratase/dehydrogenase steps and additionally impairs pristanic-acid and bile-acid-intermediate oxidation; ACOX1 deficiency affects the upstream straight-chain acyl-CoA oxidase step.
Show evidence (1 reference)
PMID:33115767 SUPPORT Human Clinical
"HSD17B4 is essential in peroxisomal fatty acid β-oxidation, and mutations in HSD17B4 are associated in multiple autosomal recessive disorders, including D-bifunctional protein deficiency and Perrault syndrome."
This anchors DBP deficiency within the peroxisomal beta-oxidation enzyme series, distinguishing it from the ACOX1 step.
Zellweger Spectrum Disorder MONDO:0019234
Overlapping Features DBP deficiency is the closest non-biogenesis phenocopy of severe Zellweger syndrome, sharing neonatal hypotonia, seizures, craniofacial dysmorphism, and VLCFA elevation.
Distinguishing Features
  • DBP deficiency is an isolated beta-oxidation enzyme defect with normal plasmalogen synthesis and phytanic-acid oxidation, whereas Zellweger spectrum disorders are generalized peroxisome biogenesis defects (PEX genes) with broader peroxisomal dysfunction.
Show evidence (1 reference)
PMID:34623748 SUPPORT Human Clinical
"Patients with DBP deficiency resemble those with a severe Zellweger phenotype, with neonatal hypotonia, seizures, craniofacial dysmorphisms, psychomotor delay, deafness, blindness, and death typically within the first 2 years of life, although patients with residual enzyme function can survive longer."
This directly supports the severe Zellweger-phenotype resemblance.
{ }

Source YAML

click to show 
name: D-Bifunctional Protein Deficiency
creation_date: "2026-06-12T12:00:00Z"
description: >-
  D-bifunctional protein (DBP) deficiency is a severe autosomal recessive
  peroxisomal fatty-acid beta-oxidation disorder caused by biallelic HSD17B4
  variants. DBP catalyzes the second and third steps (2-enoyl-CoA hydratase and
  D-3-hydroxyacyl-CoA dehydrogenase) of peroxisomal beta-oxidation, immediately
  downstream of the ACOX1 acyl-CoA oxidase step. Loss of activity blocks
  oxidation of very-long-chain fatty acids (VLCFAs), branched-chain pristanic
  acid, and bile-acid intermediates, producing their accumulation and an
  infantile neurodegenerative leukodystrophy with neonatal hypotonia, intractable
  seizures, craniofacial dysmorphism, deafness, visual loss, and early death. It
  is the closest non-biogenesis phenocopy of Zellweger syndrome but, unlike
  biogenesis disorders, has normal plasmalogen synthesis and phytanic-acid
  oxidation.
category: Metabolic Disorder
synonyms:
- DBP deficiency
- D-BPD
- HSD17B4 deficiency
- Peroxisomal multifunctional enzyme (MFE-2) deficiency
- Peroxisomal D-bifunctional protein deficiency
- Pseudo-Zellweger syndrome
parents:
- hereditary disease
- metabolic disorder
- disorder of peroxisomal beta oxidation
disease_term:
  preferred_term: d-bifunctional protein deficiency
  term:
    id: MONDO:0009855
    label: d-bifunctional protein deficiency
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0009855
      label: d-bifunctional protein deficiency
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: Primary MONDO disease identifier for D-bifunctional protein deficiency.
  ncit_mappings:
  - term:
      id: NCIT:C119676
      label: D-Bifunctional Protein Deficiency
    mapping_predicate: skos:exactMatch
    mapping_source: NCIT
    mapping_justification: NCI Thesaurus term for D-bifunctional protein deficiency.
epidemiology:
- name: Rare reported-patient disorder
  description: >-
    DBP deficiency is rare and reported largely through individual case
    reports and small series; published cases document its presentation
    across multiple populations.
  notes: >-
    DBP deficiency is generally regarded as the most common isolated
    peroxisomal fatty-acid beta-oxidation disorder, but the published
    literature consists of case reports rather than population prevalence
    estimates. OMIM:261515, ORPHA:300.
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report the first case of D-BPD in a Chinese patient with neonatal onset."
    explanation: >-
      The case-report framing supports the rarity and reported-patient
      nature of the disorder.
progression:
- phase: Neonatal-onset neurologic disease
  age_range: neonatal
  notes: >-
    Most affected neonates present in the first days of life with hypotonia,
    intractable seizures, and craniofacial dysmorphism resembling a severe
    Zellweger phenotype.
  evidence:
  - reference: PMID:34623748
    reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with DBP deficiency resemble those with a severe Zellweger phenotype, with neonatal hypotonia, seizures, craniofacial dysmorphisms, psychomotor delay, deafness, blindness, and death typically within the first 2 years of life, although patients with residual enzyme function can survive longer."
    explanation: >-
      This directly supports the neonatal presentation and the typical
      severe early course.
- phase: Progressive neurodegeneration and early mortality
  age_range: infancy to early childhood
  notes: >-
    Affected infants typically develop progressive leukodystrophy, sensory
    loss, and neurodegeneration, with death usually within the first 2 years
    of life; residual enzyme function can extend survival.
  evidence:
  - reference: PMID:34623748
    reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical severity of the disease depends on the degree of enzyme deficiency."
    explanation: >-
      This supports the genotype-dependent severity and variable survival.
pathophysiology:
- name: HSD17B4 D-Bifunctional Protein Deficiency
  description: >-
    Biallelic HSD17B4 pathogenic variants reduce peroxisomal D-bifunctional
    protein activity, disrupting the 2-enoyl-CoA hydratase and
    D-3-hydroxyacyl-CoA dehydrogenase steps of peroxisomal beta-oxidation
    immediately downstream of the ACOX1 acyl-CoA oxidase step.
  genes:
  - preferred_term: HSD17B4
    term:
      id: hgnc:5213
      label: HSD17B4
  molecular_functions:
  - preferred_term: enoyl-CoA hydratase activity
    term:
      id: GO:0004300
      label: enoyl-CoA hydratase activity
    modifier: DECREASED
  - preferred_term: very long-chain (3S)-3-hydroxyacyl-CoA dehydrogenase activity
    term:
      id: GO:0035380
      label: very long-chain (3S)-3-hydroxyacyl-CoA dehydrogenase activity
    modifier: DECREASED
  cellular_components:
  - preferred_term: peroxisome
    term:
      id: GO:0005777
      label: peroxisome
  biological_processes:
  - preferred_term: very long-chain fatty acid beta-oxidation
    term:
      id: GO:0140493
      label: very long-chain fatty acid beta-oxidation
    modifier: DECREASED
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "D-Bifunctional protein deficiency (D-BPD) is an autosomal recessive disorder caused by peroxisomal β-oxidation defects."
    explanation: >-
      This identifies the peroxisomal beta-oxidation defect as the causal
      biochemical lesion.
  - reference: PMID:33115767
    reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HSD17B4 is essential in peroxisomal fatty acid β-oxidation, and mutations in HSD17B4 are associated in multiple autosomal recessive disorders, including D-bifunctional protein deficiency and Perrault syndrome."
    explanation: >-
      This supports HSD17B4 as the causal gene for the peroxisomal
      beta-oxidation defect.
  downstream:
  - target: Substrate Accumulation (VLCFA, Pristanic Acid, Bile-Acid Intermediates)
    description: >-
      Loss of DBP activity blocks peroxisomal oxidation of VLCFAs,
      pristanic acid, and bile-acid intermediates.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:33115767
      reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "D-bifunctional protein deficiency impairs the catabolism of very long chain fatty acids, DHCA and THCA, and pristanic acid resulting in accumulation of these metabolites."
      explanation: >-
        This directly links the enzyme defect to accumulation of VLCFAs,
        bile-acid intermediates, and pristanic acid.
- name: Substrate Accumulation (VLCFA, Pristanic Acid, Bile-Acid Intermediates)
  description: >-
    Impaired peroxisomal beta-oxidation causes accumulation of
    very-long-chain fatty acids (C26:0 and abnormal ratios), branched-chain
    pristanic acid, and di-/trihydroxycholestanoic acid bile-acid
    intermediates.
  cellular_components:
  - preferred_term: peroxisome
    term:
      id: GO:0005777
      label: peroxisome
  biological_processes:
  - preferred_term: very long-chain fatty acid beta-oxidation
    term:
      id: GO:0140493
      label: very long-chain fatty acid beta-oxidation
    modifier: DECREASED
  chemical_entities:
  - preferred_term: very long-chain fatty acid
    term:
      id: CHEBI:27283
      label: very long-chain fatty acid
    modifier: INCREASED
  - preferred_term: hexacosanoic acid (C26:0)
    term:
      id: CHEBI:31009
      label: hexacosanoic acid
    modifier: INCREASED
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0)."
    explanation: >-
      This documents the characteristic VLCFA elevations in an affected
      patient.
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The blood bile acid profile showed increased taurocholic acid, glycocholic acid, and taurochenodeoxycholic acid."
    explanation: >-
      This supports accumulation of bile-acid species in affected patients.
  downstream:
  - target: Infantile Neurodegenerative Leukodystrophy
    description: >-
      Accumulated VLCFAs and related metabolites are toxic to myelin and
      developing brain, driving leukodystrophy and progressive
      neurodegeneration.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33045774
      reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The deficiency of this peroxisomal enzyme leads to the accumulation of VLCFAs, causing multisystemic manifestations including the brain, retina, adrenal gland, hearing, and skeletal system."
      explanation: >-
        This links substrate accumulation to multisystem (including CNS)
        disease.
  - target: Craniofacial Dysmorphism
    description: >-
      Severe peroxisomal beta-oxidation dysfunction in early development is
      associated with the Zellweger-like craniofacial dysmorphism seen in
      DBP deficiency.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Infantile Neurodegenerative Leukodystrophy
  description: >-
    Metabolite toxicity produces white-matter disease and progressive
    neurodegeneration affecting myelinating oligodendrocytes, with cortical
    malformation and brain atrophy in severe cases.
  cell_types:
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed and follow-up brain imaging revealed leukodystrophy and brain atrophy."
    explanation: >-
      This documents leukodystrophy and brain atrophy on follow-up imaging.
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cranial MRI revealed bilateral hemispheric and callosal dysplasia, with schizencephaly in the right hemisphere."
    explanation: >-
      This documents cortical/callosal malformation on neuroimaging in a
      severe neonatal case.
  downstream:
  - target: Leukodystrophy
    causal_link_type: DIRECT
  - target: Neonatal Hypotonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Psychomotor Delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Sensorineural Hearing Loss
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Optic Atrophy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
phenotypes:
- category: Neurologic
  name: Neonatal Hypotonia
  description: Hypotonia is a prominent early feature of DBP deficiency.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
    onset:
      onset_category: NEONATAL
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The typical symptoms include hypotonia and seizures."
    explanation: >-
      This directly supports hypotonia as a typical feature.
- category: Neurologic
  name: Seizures
  description: Intractable seizures are a typical neonatal feature.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
    onset:
      onset_category: NEONATAL
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The typical symptoms include hypotonia and seizures."
    explanation: >-
      This directly supports seizures as a typical feature.
- category: Neurologic
  name: Leukodystrophy
  description: Progressive white-matter disease develops in affected infants.
  phenotype_term:
    preferred_term: Leukodystrophy
    term:
      id: HP:0002415
      label: Leukodystrophy
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "follow-up brain imaging revealed leukodystrophy and brain atrophy"
    explanation: >-
      This supports leukodystrophy on neuroimaging.
- category: Developmental
  name: Psychomotor Delay
  description: Affected children show profound psychomotor delay.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
    onset:
      onset_category: INFANTILE
  evidence:
  - reference: PMID:34623748
    reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neonatal hypotonia, seizures, craniofacial dysmorphisms, psychomotor delay, deafness, blindness"
    explanation: >-
      This lists psychomotor delay among the typical features.
- category: Hearing
  name: Sensorineural Hearing Loss
  description: Hearing impairment is part of the multisystem phenotype.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed"
    explanation: >-
      This documents progressive hearing defects in an affected patient.
- category: Ophthalmologic
  name: Optic Atrophy
  description: Optic nerve atrophy and visual loss occur in affected patients.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed"
    explanation: >-
      This documents optic nerve atrophy in an affected patient.
- category: Craniofacial
  name: Craniofacial Dysmorphism
  description: >-
    Zellweger-like craniofacial dysmorphism is characteristic of severe DBP
    deficiency.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This patient showed craniofacial dysmorphism, club foot, and seizures with cyanosis one day after birth."
    explanation: >-
      This documents craniofacial dysmorphism in an affected neonate.
biochemical:
- name: Elevated very-long-chain fatty acids
  presence: INCREASED
  biomarker_term:
    preferred_term: very long-chain fatty acid
    term:
      id: CHEBI:27283
      label: very long-chain fatty acid
  context: >-
    Plasma/fibroblast VLCFA analysis shows elevated C26:0 and abnormal
    C24:0/C22:0 and C26:0/C22:0 ratios, the biochemical hallmark of a
    peroxisomal beta-oxidation defect.
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0)."
    explanation: >-
      This documents the diagnostic VLCFA elevation pattern.
- name: Elevated bile-acid intermediates
  presence: INCREASED
  context: >-
    Accumulation of di- and trihydroxycholestanoic acids (DHCA/THCA) and
    abnormal bile-acid species reflects impaired peroxisomal bile-acid
    synthesis.
  evidence:
  - reference: PMID:33115767
    reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "D-bifunctional protein deficiency impairs the catabolism of very long chain fatty acids, DHCA and THCA, and pristanic acid resulting in accumulation of these metabolites."
    explanation: >-
      This supports accumulation of DHCA/THCA bile-acid intermediates and
      pristanic acid.
genetic:
- name: HSD17B4 pathogenic variants
  gene_term:
    preferred_term: HSD17B4
    term:
      id: hgnc:5213
      label: HSD17B4
  association: >-
    Biallelic HSD17B4 variants cause autosomal recessive DBP deficiency;
    HSD17B4 is located at chromosome 5q23.1.
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:34368026
      reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "D-Bifunctional protein deficiency (D-BPD) is an autosomal recessive disorder caused by peroxisomal β-oxidation defects."
      explanation: >-
        This directly supports autosomal recessive inheritance.
  variants:
  - name: HSD17B4 c.1610A>G (p.His540Arg)
    description: >-
      A homozygous novel missense variant identified by rapid whole-genome
      sequencing, predicted to impair dimerization, with biochemical
      confirmation by VLCFA/bile-acid testing.
    evidence:
    - reference: PMID:33115767
      reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Sequencing revealed a homozygous c.1610A > G (p.His540Arg) variant in HSD17B4."
      explanation: >-
        This documents a disease-causing HSD17B4 missense variant.
  - name: HSD17B4 intron 13 splice variant (exon 14 skipping)
    description: >-
      A polypyrimidine-tract intron 13 variant causing exon 14 skipping and
      a frameshift, with virtually absent enzyme activity, reclassified as
      pathogenic.
    evidence:
    - reference: PMID:34623748
      reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Rapid whole genome sequencing identified two HSD17B4 variants in trans; one likely pathogenic variant and one variant of uncertain significance (VUS) located in the polypyrimidine tract of intron 13."
      explanation: >-
        This documents a pathogenic HSD17B4 splice variant.
  features: >-
    Reported patients carry biallelic HSD17B4 variants, including missense and
    splice-site changes; clinical severity tracks with residual enzyme
    activity. HSD17B4 hypomorphic variants can alternatively cause Perrault
    syndrome (sensorineural hearing loss and ovarian dysgenesis) as an allelic
    phenotype.
  evidence:
  - reference: PMID:33115767
    reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most common features are neonatal hypotonia for D-bifunctional protein deficiency and ovarian dysgenesis in females, sensorineural deafness, and other neurological abnormalities in Perrault syndrome"
    explanation: >-
      This documents the allelic relationship between DBP deficiency and
      Perrault syndrome at the HSD17B4 locus.
has_subtypes:
- name: Type I
  display_name: Type I (complete bifunctional deficiency)
  description: >-
    Combined loss of both 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA
    dehydrogenase activities; the most severe form.
- name: Type II
  display_name: Type II (hydratase-deficient)
  description: >-
    Isolated loss of 2-enoyl-CoA hydratase activity with preserved
    dehydrogenase activity.
- name: Type III
  display_name: Type III (dehydrogenase-deficient)
  description: >-
    Isolated loss of 3-hydroxyacyl-CoA dehydrogenase activity with preserved
    hydratase activity.
treatments:
- name: Multidisciplinary Supportive Care
  description: >-
    Management is supportive and symptom-directed, including antiepileptic
    therapy, feeding and respiratory support, and surveillance for sensory and
    neurologic decline. No disease-modifying therapy is established.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:34368026
    reference_title: "Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supportive care is the main treatment, aiming at controlling symptoms"
    explanation: >-
      This supports supportive, symptom-directed care as the mainstay of
      management.
- name: Dietary Supplementation (DHA and Fat-Soluble Vitamins)
  description: >-
    Docosahexaenoic acid and fat-soluble vitamin supplementation has been
    used; early management of fat-soluble vitamin deficiency is advocated to
    reduce complications.
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  evidence:
  - reference: PMID:33045774
    reference_title: "First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient had type III DBP deficiency; therefore, docosahexaenoic acid and non-soluble vitamins were administered."
    explanation: >-
      This documents DHA and vitamin supplementation in an affected
      patient.
  - reference: PMID:34623748
    reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "advocate for the early management of fat-soluble vitamin deficiencies to reduce complications"
    explanation: >-
      This supports early fat-soluble vitamin management.
differential_diagnoses:
- name: Peroxisomal Acyl-CoA Oxidase Deficiency
  disease_term:
    preferred_term: peroxisomal acyl-CoA oxidase deficiency
    term:
      id: MONDO:0009919
      label: peroxisomal acyl-CoA oxidase deficiency
  description: >-
    ACOX1 deficiency is the immediately upstream peroxisomal beta-oxidation
    defect (the acyl-CoA oxidase step) and shares the downstream VLCFA
    accumulation and infantile leukodystrophy phenotype.
  distinguishing_features:
  - >-
    DBP deficiency affects the HSD17B4 hydratase/dehydrogenase steps and
    additionally impairs pristanic-acid and bile-acid-intermediate
    oxidation; ACOX1 deficiency affects the upstream straight-chain acyl-CoA
    oxidase step.
  evidence:
  - reference: PMID:33115767
    reference_title: "Rapid whole-genome sequencing identifies a homozygous novel variant, His540Arg, in HSD17B4 resulting in D-bifunctional protein deficiency disorder diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HSD17B4 is essential in peroxisomal fatty acid β-oxidation, and mutations in HSD17B4 are associated in multiple autosomal recessive disorders, including D-bifunctional protein deficiency and Perrault syndrome."
    explanation: >-
      This anchors DBP deficiency within the peroxisomal beta-oxidation
      enzyme series, distinguishing it from the ACOX1 step.
- name: Zellweger Spectrum Disorder
  disease_term:
    preferred_term: peroxisome biogenesis disorder
    term:
      id: MONDO:0019234
      label: peroxisome biogenesis disorder
  description: >-
    DBP deficiency is the closest non-biogenesis phenocopy of severe
    Zellweger syndrome, sharing neonatal hypotonia, seizures, craniofacial
    dysmorphism, and VLCFA elevation.
  distinguishing_features:
  - >-
    DBP deficiency is an isolated beta-oxidation enzyme defect with normal
    plasmalogen synthesis and phytanic-acid oxidation, whereas Zellweger
    spectrum disorders are generalized peroxisome biogenesis defects (PEX
    genes) with broader peroxisomal dysfunction.
  evidence:
  - reference: PMID:34623748
    reference_title: "D-bifunctional protein deficiency caused by splicing variants in a neonate with severe peroxisomal dysfunction and persistent hypoglycemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with DBP deficiency resemble those with a severe Zellweger phenotype, with neonatal hypotonia, seizures, craniofacial dysmorphisms, psychomotor delay, deafness, blindness, and death typically within the first 2 years of life, although patients with residual enzyme function can survive longer."
    explanation: >-
      This directly supports the severe Zellweger-phenotype resemblance.
notes: >-
  D-bifunctional protein (DBP, encoded by HSD17B4; also called peroxisomal
  multifunctional enzyme 2 / MFE-2) catalyzes the second and third steps of
  peroxisomal beta-oxidation downstream of ACOX1. This entry was created to
  resolve curation issue 4180: DBP deficiency previously existed in the
  KB only as a differential-diagnosis mention inside
  kb/disorders/Peroxisomal_Acyl-CoA_Oxidase_Deficiency.yaml. It is a genuine
  missing sibling of the ACOX1 entry — same downstream graph (VLCFA accumulation
  -> infantile leukodystrophy), different root-lesion node. HSD17B4 hypomorphic
  variants alternatively cause Perrault syndrome (modeled separately in
  kb/disorders/46_XX_Gonadal_Dysgenesis.yaml). A recent report describes a
  "four-type" subclassification (PMID:34368026); the classical scheme (van
  Grunsven et al.) defines three subtypes (I/II/III), which are recorded in
  has_subtypes above. A dedicated peroxisomal_betaoxidation_defect module that
  ACOX1 and DBP could both conform_to is a possible future structural follow-up.