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Inheritance

1

Autosomal recessive HP:0000007

Biallelic PEX12 variants are required. Every patient assigned to complementation group 3 was found to carry variants on both alleles.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:9792857 SUPPORT Human Clinical

"Here we show that all patients from this group carry mutations on both alleles of PEX12."

Establishes biallelic requirement across the whole complementation group.

PMID:20301621 SUPPORT Other

"At conception, each sib of an individual with biallelic ZSD-causing pathogenic variants has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."

GeneReviews Genetic Counseling gives the recurrence risk that follows from the biallelic requirement.

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Discussions and Knowledge Gaps

2

Why does a patient with two apparently severe PEX12 alleles present mildly?

INTERPRETATION pbd3a_internal_aug_reinitiation

Attached to

genetic#PEX12 pathophysiology#Biallelic PEX12 Loss of Function

Genotype predicts phenotype well in complementation group 3 - less PEX12 function, worse disease - with one documented exception that turns out to be informative rather than noise. A compound heterozygote carrying two seemingly null alleles was mildly affected. The explanation was that the expressed allele, a 2-bp deletion eight codons into the reading frame, still produced a functional protein because translation reinitiated at a downstream AUG. The general lesson is that "predicted truncating" is a statement about the reading frame, not about the protein. An early frameshift can be rescued by internal initiation, so severity prediction from variant class alone will occasionally be wrong in the direction of over-calling severity. Curated here because this entry is defined by being the severe end of its locus, and the boundary between 3A and the milder presentations is exactly what such an allele blurs.

Show evidence (2 references)

PMID:9792857 SUPPORT Human Clinical

"However, one patient who presented relatively mild clinical and cellular phenotypes was a compound heterozygote for two seemingly severe mutations on each PEX12 allele."

States the discrepant case that the mechanism explains.

PMID:9792857 SUPPORT In Vitro

"this mutant PEX12 cDNA displayed significant PEX12 activity in a functional complementation assay"

The functional result showing the supposedly null allele retains activity; IN_VITRO because it is a cell-based complementation assay.

Could peroxisomal matrix import be restored therapeutically in a patient?

KNOWLEDGE GAP pbd3a_no_disease_modifying_therapy

Attached to

treatments# pathophysiology#Collapse of Peroxisomal Matrix Protein Import

Every treatment in this entry is symptomatic. Restoring import would mean restoring a membrane translocon in every affected tissue, and the two organs that determine outcome present different obstacles: the brain lesion is a completed malformation of fetal migration, so even perfect postnatal correction could not undo it, while the liver and adrenal disease is progressive and might in principle respond. No approach - gene therapy, read-through of nonsense alleles, chaperone rescue of hypomorphic alleles - has reached patients. The gap is recorded rather than left implicit because the absence of disease-modifying options is the single most important fact about managing this diagnosis.

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Pathophysiology

10

Biallelic PEX12 Loss of Function

Variants on both PEX12 alleles. Truncating alleles that remove the C-terminal zinc-binding domain are the ones associated with the severe presentation.

zinc ion binding GO:0008270 ↓ DECREASED

Downstream

Disrupted PEX2-PEX10-PEX12 Retrotranslocation Channel

Show evidence (2 references)

PMID:14571262 SUPPORT Human Clinical

"Four of the patients have mutations that disrupt the translation frame and/or create an early termination codon in the PEX12 open reading frame predicted to result in truncated protein products, lacking at least the COOH-terminal zinc-binding domain. All these patients display the more severe phenotypes"

Ties loss of the zinc-binding domain to the severe end of the spectrum, which is the presentation this entry curates.

PMID:9632816 SUPPORT In Vitro

"Fibroblasts derived from patients with the peroxisome deficiency Zellweger syndrome of complementation group III (CG-III) were also complemented for peroxisome biogenesis with PEX12."

The complementation experiment that assigned group III to PEX12; IN_VITRO because the result is in cultured patient fibroblasts.

Disrupted PEX2-PEX10-PEX12 Retrotranslocation Channel

PEX12 co-assembles with its paralogues PEX2 and PEX10 into the ubiquitin-ligase retrotranslocation channel of the peroxisomal membrane. Losing PEX12 leaves the channel unable to regulate PEX5 ubiquitination.

ubiquitin-protein transferase activity GO:0004842 ↓ DECREASED

peroxisomal membrane GO:0005778

Downstream

Failure of PEX5 Receptor Recycling

PEX5 delivers PTS1-tagged matrix enzymes and must be ubiquitinated and exported back to the cytosol to be reused. Without a functioning channel it is not returned, so the import cycle stalls after a single round.

Downstream

Collapse of Peroxisomal Matrix Protein Import

Matrix enzymes never reach the organelle. The membrane compartment still forms - the "peroxisomal ghost" - which is the morphological signature distinguishing a biogenesis defect from a single enzyme deficiency.

protein import into peroxisome matrix GO:0016558 ↓ DECREASED peroxisome organization GO:0007031 ↓ DECREASED

peroxisomal matrix GO:0005782

Animal models

Pex2-deficient mouse Mouse recapitulates Reproduces the defining cell-biological lesion, including the ghost membranes.

Downstream

Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids

Plasmalogen Deficiency

Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids

Substrates that only peroxisomes degrade build up systemically: C26:0 and other VLCFA, phytanic and pristanic acid, and C27 bile-acid intermediates. This is the accumulation half of the biochemical signature and the basis of diagnostic testing.

very long-chain fatty acid beta-oxidation GO:0140493 ↓ DECREASED

Downstream

Progressive Hepatic Injury

Adrenocortical Insufficiency

Impaired Neuronal Migration in the Developing Cortex Peroxisomal failure demonstrably disrupts cortical migration, but which accumulating substrate or missing lipid does it is not established.

Plasmalogen Deficiency

Ether phospholipid synthesis begins in the peroxisome, so plasmalogens - major constituents of myelin - and DHA are not made. This is the deficiency half of the signature, and the one most plausibly linked to the white-matter disease.

ether lipid biosynthetic process GO:0008611 ↓ DECREASED

Downstream

Impaired Neuronal Migration in the Developing Cortex

Neuronal precursors fail to reach their laminar destinations during fetal cortical development, producing the perisylvian polymicrogyria and heterotopia that make this a congenital malformation rather than a purely degenerative disease. Because the lesion is formed before birth, it is not reversible by any postnatal intervention.

radial glial cell CL:0000681 neuron CL:0000540

Animal models

Pex2-deficient mouse Mouse recapitulates Reproduces the cortical migration defect that is otherwise inferred from human neuropathology, which is the main reason this model matters for the entry.

Downstream

Severe Neurodevelopmental Impairment

Progressive Hepatic Injury

VLCFA and C27 bile-acid intermediates are directly hepatotoxic, driving cholestasis and fibrosis.

hepatocyte CL:0000182

Adrenocortical Insufficiency

VLCFA accumulation in adrenocortical cells impairs steroidogenesis. Often subclinical at first, which is why GeneReviews asks for ACTH and cortisol measurement by age one even in children who look adrenally well.

cortical cell of adrenal gland CL:0002097

Severe Neurodevelopmental Impairment

Profound hypotonia, intractable neonatal seizures, and absent developmental progress. In the severe form death usually follows within the first year.

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"Infants with severe ZSD are significantly impaired and typically die during the first year of life, usually having made no developmental progress."

GeneReviews states the course of the severe end of the spectrum, which is what PBD3A denotes.

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Pathograph

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

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Phenotypes

13

Digestive 2

Liver Disease FREQUENT Decreased liver function HP:0001410

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"and liver disease that can be severe"

GeneReviews names liver disease in the newborn presentation.

Feeding Difficulties VERY_FREQUENT HP:0011968

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"Affected newborns are hypotonic and feed poorly."

GeneReviews states feeding failure as part of the newborn presentation.

Ear 1

Sensorineural Hearing Loss OCCASIONAL Sensorineural hearing impairment HP:0000407

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"sensory loss (secondary to retinal dystrophy and sensorineural hearing loss)"

PARTIAL for the same reason - the sensory phenotype belongs to the milder end of the spectrum.

Endocrine 1

Adrenal Insufficiency OCCASIONAL HP:0000846

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"progressive peroxisome dysfunction variably manifest as sensory loss (secondary to retinal dystrophy and sensorineural hearing loss), neurologic involvement (ataxia, polyneuropathy, and leukodystrophy), liver dysfunction, adrenal insufficiency, and renal oxalate stones"

PARTIAL because GeneReviews attributes this list to the intermediate/milder end of the spectrum rather than to the severe form curated here; recorded because surveillance is still recommended.

Eye 2

Retinal Dystrophy OCCASIONAL HP:0000556

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"sensory loss (secondary to retinal dystrophy and sensorineural hearing loss)"

PARTIAL for the same reason as the hearing phenotype.

Cataract OCCASIONAL HP:0000518

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"Treatment of manifestations: The focus is on symptomatic therapy and may include gastrostomy to provide adequate calories, hearing aids, cataract removal, glasses to correct refractive errors, supplementation of fat-soluble vitamins, and cholic acid supplementation"

PARTIAL - GeneReviews names cataract removal as a management step, which implies the finding without stating its frequency.

Genitourinary 1

Renal Cortical Cysts FREQUENT Renal cyst HP:0000107

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling"

GeneReviews lists renal cysts among the congenital malformations.

Head and Neck 1

Distinctive Facial Appearance VERY_FREQUENT Abnormal facial shape HP:0001999

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"They have distinctive facies, congenital malformations"

GeneReviews names distinctive facies among the newborn findings.

Musculoskeletal 1

Severe Neonatal Hypotonia VERY_FREQUENT Generalized hypotonia HP:0001290

Severity: SEVERE

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"Affected newborns are hypotonic and feed poorly."

GeneReviews Clinical Characteristics names hypotonia and feeding failure as the newborn presentation.

Nervous System 1

Polymicrogyria FREQUENT HP:0002126

Show evidence (2 references)

PMID:9382874 SUPPORT Other

"The malformation of the cerebral cortex is most severe and reproducibly results in gyral abnormalities centered around the Sylvian fissure with a stereotypic medial pachygyria and lateral polymicrogyria."

Names polymicrogyria and its perisylvian distribution in human Zellweger neuropathology. Graded OTHER because the sentence is background summarising prior human pathology in a paper whose own results are in mice.

PMID:20301621 SUPPORT Other

"neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling"

PARTIAL because GeneReviews names the migration defect generically rather than polymicrogyria specifically; kept alongside the specific quote to place the finding among the congenital malformations of the severe form.

Other 3

Neonatal Seizures from Neuronal Migration Defect FREQUENT HP:0032807

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling"

GeneReviews links the seizures to the migration defect and lists the congenital malformations of the severe form together. The quote stops before "[chondrodysplasia punctata]" because the validator strips bracketed text, so a span crossing it cannot match the cache.

Chondrodysplasia Punctata FREQUENT Epiphyseal stippling HP:0010655

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"renal cysts, and bony stippling"

GeneReviews names the stippling among the congenital malformations. The quote stops short of the sites because "of the patella[e] and the long bones" carries a bracket the validator strips.

Gray Matter Heterotopia FREQUENT HP:0002282

Show evidence (2 references)

PMID:20301621 SUPPORT Other

"neuronal migration defects associated with neonatal-onset seizures, renal cysts, and bony stippling"

PARTIAL because GeneReviews names the migration defect generically rather than heterotopia specifically.

PMID:9382874 SUPPORT Other

"These gyral abnormalities reflect a reduced neuronal population in the cortex and large numbers of subcortical heterotopic neurons."

Names the subcortical heterotopic neurons directly in human Zellweger neuropathology. OTHER for the same reason as the polymicrogyria item - background summarising human pathology in a mouse paper.

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Genetic Associations

1

PEX12

Gene: PEX12 hgnc:8854 relationship_type: CAUSATIVE

Show evidence (1 reference)

PMID:9792857 SUPPORT Human Clinical

"the loss of PEX12 function leads to more-severe cellular and clinical phenotypes"

States the dose-of-function relationship that separates the A and B ends of this locus.

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Medical Actions

4

Supportive and Symptomatic Management

Action: supportive care Ontology label: Supportive Care NCIT:C15747

There is no treatment for the biogenesis defect. Management is entirely symptomatic - gastrostomy feeding, anti-seizure medication, hearing aids, cataract surgery, fat-soluble vitamin and cholic acid supplementation, adrenal replacement. None of it restores peroxisomal import, and the congenital brain malformation is fixed before birth, so no postnatal intervention can address the central lesion.

Mechanism Target:

MODULATES Severe Neurodevelopmental Impairment — Addresses consequences - nutrition, seizures, sensory deficits - without acting on peroxisome biogenesis.

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"Treatment of manifestations: The focus is on symptomatic therapy and may include gastrostomy to provide adequate calories, hearing aids, cataract removal, glasses to correct refractive errors, supplementation of fat-soluble vitamins, and cholic acid supplementation"

GeneReviews Management states that therapy is symptomatic and lists the measures.

Cholic Acid

Action: Pharmacotherapy NCIT:C15986

Agent: cholic acid CHEBI:16359

Oral cholic acid restores feedback inhibition of endogenous bile acid synthesis, so the hepatotoxic C27 intermediates that peroxisome-deficient hepatocytes cannot process stop accumulating. It is the only FDA-approved therapy for Zellweger spectrum disease and the only intervention in this entry that acts on a curated mechanism node rather than on a consequence - which is why it is curated separately from supportive care rather than inside it.

Mechanism Target:

INHIBITS Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids — Suppresses synthesis of the atypical C27 bile-acid intermediates that accumulate because peroxisomal side-chain shortening is blocked. It does not restore peroxisomal import, so the other accumulating substrates are unaffected.

INHIBITS Progressive Hepatic Injury — Removing the hepatotoxic intermediates is what improves the liver chemistry.

Show evidence (1 reference)

PMID:28644367 SUPPORT Human Clinical

"Cholic acid significantly improved urine bile acid metabolite scores (P < 0.0001) and serum aspartate aminotransferase and alanine aminotransferase (P < 0.0001) in patients with SED and ZSD."

The fall in atypical urinary bile acids is the direct readout of the targeted mechanism, and the transaminase fall is the hepatic consequence.

Adrenal Replacement Therapy

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Glucocorticoid replacement once adrenal insufficiency is documented. Curated separately from general supportive care because it depends on active surveillance rather than on symptoms - the deficiency is often silent until stressed.

Mechanism Target:

RESTORES Adrenocortical Insufficiency — Replaces the missing hormone output; it does not correct the VLCFA accumulation that impaired steroidogenesis.

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"adrenal replacement therapy; vitamin D supplementation and consideration of bisphosphonates for osteopenia"

GeneReviews Management names adrenal replacement among the interventions.

Biochemical and Developmental Surveillance

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Structured monitoring rather than symptom-driven follow-up, because several complications are silent until advanced - adrenal insufficiency in particular.

Mechanism Target:

MODULATES Adrenocortical Insufficiency — Detects the deficiency before it presents as crisis; it does not prevent it.

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"ACTH and cortisol levels by age one year and annually thereafter"

GeneReviews Surveillance gives the adrenal monitoring interval.

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Biochemical Markers

3

Very-long-chain fatty acids (Increased)

Context: Plasma C26:0 with the C24/C22 and C26/C22 ratios is the first-line biochemical screen. In the severe form curated here the elevation is unambiguous, unlike the milder end of the spectrum where it can be modest.

Pathograph Readouts

Readout Of Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids Positive Diagnostic

Elevated VLCFA reports the peroxisomal beta-oxidation block directly.

Show evidence (1 reference)

PMID:28677031 SUPPORT Human Clinical

"C26:0-lysoPC in DBS is a sensitive and useful marker for VLCFA accumulation in patients with a ZSD."

Establishes the measured analyte as a readout of VLCFA accumulation arising from the peroxisomal block.

C26:0-lysophosphatidylcholine (Increased)

Context: C26:0-lysoPC in dried blood spots is the assay that makes newborn screening for Zellweger spectrum disease technically feasible, which matters most for the severe form because its window for any intervention is shortest.

Pathograph Readouts

Readout Of Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids Positive Diagnostic

Elevated dried-blood-spot C26:0-lysoPC reports peroxisomal beta-oxidation failure.

Show evidence (1 reference)

PMID:28677031 SUPPORT Human Clinical

"Elevated C26:0-lysoPC levels (>72 nmol/L) were found in 86/91 ZSD DBS"

Quantifies the sensitivity of this readout against the block it reports.

Plasmalogens (Decreased)

Context: Erythrocyte plasmalogens are low because ether lipid synthesis begins in the peroxisome. This is the deficiency half of the signature and moves in the opposite direction to the VLCFA markers, which is what distinguishes a biogenesis defect from an isolated beta-oxidation enzyme defect.

Pathograph Readouts

Readout Of Plasmalogen Deficiency Negative Diagnostic

Reduced erythrocyte plasmalogens report failed peroxisomal ether lipid synthesis.

Show evidence (1 reference)

PMID:9382874 SUPPORT Model Organism

"They display abnormal peroxisomal biochemical parameters, including accumulations of very long chain fatty acids in plasma and deficient erythrocyte plasmalogens."

PARTIAL because the measurement is in the paralogous mouse model rather than in PEX12 patients; it shows both directions of the signature in one animal.

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Diagnosis

2

Plasma Very-Long-Chain Fatty Acid Profile

The first-line biochemical test. Elevated C26:0 with abnormal C24/C22 and C26/C22 ratios points at a peroxisomal disorder before any gene is sequenced.

laboratory procedure NCIT:C25294

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"The diagnosis of ZSD is established in a proband with the suggestive clinical and biochemical findings above by identification of biallelic pathogenic variants in one of the 13 known ZSD-PEX genes."

GeneReviews Diagnosis places biochemical findings ahead of molecular confirmation in the diagnostic sequence.

Molecular Genetic Testing of the ZSD-PEX Genes

Confirmation requires biallelic variants in one of the ZSD-PEX genes; assignment to PEX12 is what makes the entry PBD3 rather than another group.

genetic testing NCIT:C15709

Show evidence (1 reference)

PMID:20301621 SUPPORT Other

"by identification of biallelic pathogenic variants in one of the 13 known ZSD-PEX genes"

States the molecular criterion.

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Animal Models

1

Pex2-deficient mouse

A knockout of PEX2, one of PEX12's two paralogues in the same retrotranslocation channel. It is not a model of PBD3A as such, but it is the model that established what losing that channel does to a mammal.

Species

Mouse

Genotype

PEX2 (Pxmp3) targeted null, homozygous

Publication

PMID:9382874

Pathograph links

Collapse of Peroxisomal Matrix Protein Import recapitulates fidelity: high Reproduces the defining cell-biological lesion, including the ghost membranes.

Limitations: The disrupted gene is PEX2, not PEX12. The two are paralogous subunits of one channel, so the import phenotype is shared, but any PEX12-specific effect - notably its role in stimulating PEX10 ligase activity - is not modelled.

Readouts

Peroxisomal ghost membranes without matrix enzymes

Direction: ALTERED

Interpretation: Membrane compartments form but are empty, the signature of a biogenesis defect.

Show evidence (1 reference)

PMID:9382874 SUPPORT Model Organism

"The PEX2-deficient mice lack normal peroxisomes but do assemble empty peroxisome membrane ghosts."

Direct observation of the ghost phenotype in the model.

Show evidence (1 reference)

PMID:9382874 SUPPORT Model Organism

"They display abnormal peroxisomal biochemical parameters, including accumulations of very long chain fatty acids in plasma and deficient erythrocyte plasmalogens."

Shows both halves of the biochemical signature - accumulation and deficiency - in the model.

Impaired Neuronal Migration in the Developing Cortex recapitulates fidelity: moderate Reproduces the cortical migration defect that is otherwise inferred from human neuropathology, which is the main reason this model matters for the entry.

Limitations: Mice die within hours of birth, so the postnatal white-matter disease and the sensory phenotypes of longer-surviving humans cannot be studied in it. As above, the gene is PEX2.

Readouts

Cortical lamination and white-matter cell density

Direction: ALTERED

Interpretation: Disordered lamination with retained cells in the white matter is the expected signature of arrested radial migration.

Show evidence (1 reference)

PMID:9382874 SUPPORT Model Organism

"In the central nervous system of newborn mutant mice there is disordered lamination in the cerebral cortex and an increased cell density in the underlying white matter, indicating an abnormality of neuronal migration."

The histological result establishing the migration defect in vivo.

{ }

Source YAML

click to show

name: Peroxisome Biogenesis Disorder 3A (Zellweger)
creation_date: "2026-08-27T06:05:00Z"
category: Mendelian
description: >-
  Peroxisome biogenesis disorder 3A is the severe, neonatal-lethal end of the
  PEX12-related Zellweger spectrum - historically complementation group 3 of the
  peroxisome biogenesis disorders, which is where the "3" in the name comes from.
  PEX12 is one of three paralogous RING-finger peroxins, with PEX2 and PEX10, that
  together form the retrotranslocation channel in the peroxisomal membrane. That
  channel exists to recycle PEX5, the receptor that carries matrix enzymes into the
  organelle. When it fails, PEX5 is not returned to the cytosol for another round,
  and matrix protein import collapses.

  The consequence is a peroxisome that is still there but empty. Cells from affected
  patients assemble "peroxisomal ghosts" - membrane compartments with no matrix
  enzymes inside - which is why this is a disorder of biogenesis rather than of any
  single peroxisomal enzyme, and why the biochemical signature is broad: very-long-chain
  fatty acids, phytanic and pristanic acid and C27 bile-acid intermediates accumulate
  because nothing is left to degrade them, while plasmalogens and DHA are missing
  because nothing is left to synthesise them. Both halves damage the developing brain,
  the liver, and the adrenal cortex at once, producing the cerebro-hepato-renal
  presentation Zellweger described.

  Within PEX12 the genotype tracks the phenotype more cleanly than in most of the
  spectrum: alleles that truncate the protein before its C-terminal zinc-binding
  domain give the severe "A" presentation curated here, while alleles retaining
  residual function shift toward the milder end. The KB curates the milder "B" end of
  two other PEX genes - Peroxisome Biogenesis Disorder 1B (PEX1) and 4B (PEX6) - so
  this entry is their severity counterpart at a third locus.
disease_term:
  preferred_term: peroxisome biogenesis disorder 3A (Zellweger)
  term:
    id: MONDO:0013927
    label: peroxisome biogenesis disorder 3A (Zellweger)
synonyms:
- PBD3A
- peroxisome biogenesis disorder, complementation group 3
- PEX12-related Zellweger syndrome
parents:
- Peroxisome Biogenesis Disorder
- Zellweger Spectrum Disorder
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic PEX12 variants are required. Every patient assigned to complementation
    group 3 was found to carry variants on both alleles.
  evidence:
  - reference: PMID:9792857
    reference_title: Phenotype-genotype relationships in complementation group 3 of the
      peroxisome-biogenesis disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we show that all patients from this group carry mutations on both alleles
      of PEX12.
    explanation: Establishes biallelic requirement across the whole complementation group.
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: At conception, each sib of an individual with biallelic ZSD-causing pathogenic
      variants has a 25% chance of being affected, a 50% chance of being an asymptomatic
      carrier, and a 25% chance of being unaffected and not a carrier.
    explanation: GeneReviews Genetic Counseling gives the recurrence risk that follows from
      the biallelic requirement.
pathophysiology:
- name: Biallelic PEX12 Loss of Function
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Variants on both PEX12 alleles. Truncating alleles that remove the C-terminal
    zinc-binding domain are the ones associated with the severe presentation.
  molecular_functions:
  - preferred_term: zinc ion binding
    modifier: DECREASED
    term:
      id: GO:0008270
      label: zinc ion binding
  downstream:
  - target: Disrupted PEX2-PEX10-PEX12 Retrotranslocation Channel
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:14571262
    reference_title: Novel mutations in the PEX12 gene of patients with a peroxisome
      biogenesis disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Four of the patients have mutations that disrupt the translation frame and/or
      create an early termination codon in the PEX12 open reading frame predicted to
      result in truncated protein products, lacking at least the COOH-terminal zinc-binding
      domain. All these patients display the more severe phenotypes
    explanation: Ties loss of the zinc-binding domain to the severe end of the spectrum,
      which is the presentation this entry curates.
  - reference: PMID:9632816
    reference_title: 'PEX12, the pathogenic gene of group III Zellweger syndrome: cDNA
      cloning by functional complementation on a CHO cell mutant, patient analysis, and
      characterization of PEX12p.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Fibroblasts derived from patients with the peroxisome deficiency Zellweger
      syndrome of complementation group III (CG-III) were also complemented for peroxisome
      biogenesis with PEX12.
    explanation: The complementation experiment that assigned group III to PEX12; IN_VITRO
      because the result is in cultured patient fibroblasts.
- name: Disrupted PEX2-PEX10-PEX12 Retrotranslocation Channel
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    PEX12 co-assembles with its paralogues PEX2 and PEX10 into the ubiquitin-ligase
    retrotranslocation channel of the peroxisomal membrane. Losing PEX12 leaves the
    channel unable to regulate PEX5 ubiquitination.
  cellular_components:
  - preferred_term: peroxisomal membrane
    term:
      id: GO:0005778
      label: peroxisomal membrane
  molecular_functions:
  - preferred_term: ubiquitin-protein transferase activity
    modifier: DECREASED
    term:
      id: GO:0004842
      label: ubiquitin-protein transferase activity
  downstream:
  - target: Failure of PEX5 Receptor Recycling
    causal_link_type: DIRECT
- name: Failure of PEX5 Receptor Recycling
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    PEX5 delivers PTS1-tagged matrix enzymes and must be ubiquitinated and exported
    back to the cytosol to be reused. Without a functioning channel it is not returned,
    so the import cycle stalls after a single round.
  downstream:
  - target: Collapse of Peroxisomal Matrix Protein Import
    causal_link_type: DIRECT
- name: Collapse of Peroxisomal Matrix Protein Import
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Matrix enzymes never reach the organelle. The membrane compartment still forms -
    the "peroxisomal ghost" - which is the morphological signature distinguishing a
    biogenesis defect from a single enzyme deficiency.
  biological_processes:
  - preferred_term: protein import into peroxisome matrix
    modifier: DECREASED
    term:
      id: GO:0016558
      label: protein import into peroxisome matrix
  - preferred_term: peroxisome organization
    modifier: DECREASED
    term:
      id: GO:0007031
      label: peroxisome organization
  cellular_components:
  - preferred_term: peroxisomal matrix
    term:
      id: GO:0005782
      label: peroxisomal matrix
  downstream:
  - target: Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids
    causal_link_type: DIRECT
  - target: Plasmalogen Deficiency
    causal_link_type: DIRECT
- name: Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    Substrates that only peroxisomes degrade build up systemically: C26:0 and other
    VLCFA, phytanic and pristanic acid, and C27 bile-acid intermediates. This is the
    accumulation half of the biochemical signature and the basis of diagnostic testing.
  biological_processes:
  - preferred_term: very long-chain fatty acid beta-oxidation
    modifier: DECREASED
    term:
      id: GO:0140493
      label: very long-chain fatty acid beta-oxidation
  downstream:
  - target: Progressive Hepatic Injury
    causal_link_type: DIRECT
  - target: Adrenocortical Insufficiency
    causal_link_type: DIRECT
  - target: Impaired Neuronal Migration in the Developing Cortex
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Peroxisomal failure demonstrably disrupts cortical migration, but which accumulating
      substrate or missing lipid does it is not established.
- name: Plasmalogen Deficiency
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Ether phospholipid synthesis begins in the peroxisome, so plasmalogens - major
    constituents of myelin - and DHA are not made. This is the deficiency half of the
    signature, and the one most plausibly linked to the white-matter disease.
  biological_processes:
  - preferred_term: ether lipid biosynthetic process
    modifier: DECREASED
    term:
      id: GO:0008611
      label: ether lipid biosynthetic process
  downstream:
  - target: Impaired Neuronal Migration in the Developing Cortex
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Impaired Neuronal Migration in the Developing Cortex
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    Neuronal precursors fail to reach their laminar destinations during fetal cortical
    development, producing the perisylvian polymicrogyria and heterotopia that make this
    a congenital malformation rather than a purely degenerative disease. Because the
    lesion is formed before birth, it is not reversible by any postnatal intervention.
  cell_types:
  - preferred_term: radial glial cell
    term:
      id: CL:0000681
      label: radial glial cell
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  downstream:
  - target: Severe Neurodevelopmental Impairment
    causal_link_type: DIRECT
- name: Progressive Hepatic Injury
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    VLCFA and C27 bile-acid intermediates are directly hepatotoxic, driving cholestasis
    and fibrosis.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
- name: Adrenocortical Insufficiency
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    VLCFA accumulation in adrenocortical cells impairs steroidogenesis. Often subclinical
    at first, which is why GeneReviews asks for ACTH and cortisol measurement by age one
    even in children who look adrenally well.
  cell_types:
  - preferred_term: cortical cell of adrenal gland
    term:
      id: CL:0002097
      label: cortical cell of adrenal gland
- name: Severe Neurodevelopmental Impairment
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    Profound hypotonia, intractable neonatal seizures, and absent developmental progress.
    In the severe form death usually follows within the first year.
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Infants with severe ZSD are significantly impaired and typically die during
      the first year of life, usually having made no developmental progress.
    explanation: GeneReviews states the course of the severe end of the spectrum, which
      is what PBD3A denotes.
phenotypes:
- category: Neurologic
  name: Severe Neonatal Hypotonia
  frequency: VERY_FREQUENT
  description: >-
    Profound generalized hypotonia from birth, with poor feeding.
  phenotype_term:
    preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
    severity: SEVERE
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Affected newborns are hypotonic and feed poorly.
    explanation: GeneReviews Clinical Characteristics names hypotonia and feeding failure
      as the newborn presentation.
- category: Neurologic
  name: Neonatal Seizures from Neuronal Migration Defect
  frequency: FREQUENT
  description: >-
    Seizures beginning in the newborn period, arising from the congenital cortical
    malformation rather than from a metabolic decompensation.
  phenotype_term:
    preferred_term: Neonatal seizure
    term:
      id: HP:0032807
      label: Neonatal seizure
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neuronal migration defects associated with neonatal-onset seizures, renal
      cysts, and bony stippling
    explanation: GeneReviews links the seizures to the migration defect and lists the
      congenital malformations of the severe form together. The quote stops before
      "[chondrodysplasia punctata]" because the validator strips bracketed text, so a
      span crossing it cannot match the cache.
- category: Craniofacial
  name: Distinctive Facial Appearance
  frequency: VERY_FREQUENT
  description: >-
    Flat facies with high forehead, large fontanelle and epicanthal folds.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: They have distinctive facies, congenital malformations
    explanation: GeneReviews names distinctive facies among the newborn findings.
- category: Renal
  name: Renal Cortical Cysts
  frequency: FREQUENT
  description: >-
    Bilateral cortical microcysts, present at birth.
  phenotype_term:
    preferred_term: Renal cyst
    term:
      id: HP:0000107
      label: Renal cyst
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neuronal migration defects associated with neonatal-onset seizures, renal
      cysts, and bony stippling
    explanation: GeneReviews lists renal cysts among the congenital malformations.
- category: Skeletal
  name: Chondrodysplasia Punctata
  frequency: FREQUENT
  description: >-
    Stippled calcification of the epiphyses, characteristically at the patella and long
    bones - a radiographic finding that can point at the diagnosis before biochemistry
    returns.
  phenotype_term:
    preferred_term: Epiphyseal stippling
    term:
      id: HP:0010655
      label: Epiphyseal stippling
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: renal cysts, and bony stippling
    explanation: GeneReviews names the stippling among the congenital malformations. The
      quote stops short of the sites because "of the patella[e] and the long bones"
      carries a bracket the validator strips.
- category: Hepatic
  name: Liver Disease
  frequency: FREQUENT
  description: >-
    Cholestasis, fibrosis and coagulopathy; can be severe.
  phenotype_term:
    preferred_term: Decreased liver function
    term:
      id: HP:0001410
      label: Decreased liver function
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: and liver disease that can be severe
    explanation: GeneReviews names liver disease in the newborn presentation.
- category: Endocrine
  name: Adrenal Insufficiency
  frequency: OCCASIONAL
  description: >-
    Impaired cortisol response, often subclinical initially.
  phenotype_term:
    preferred_term: Adrenal insufficiency
    term:
      id: HP:0000846
      label: Adrenal insufficiency
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: progressive peroxisome dysfunction variably manifest as sensory loss (secondary
      to retinal dystrophy and sensorineural hearing loss), neurologic involvement (ataxia,
      polyneuropathy, and leukodystrophy), liver dysfunction, adrenal insufficiency, and
      renal oxalate stones
    explanation: PARTIAL because GeneReviews attributes this list to the intermediate/milder
      end of the spectrum rather than to the severe form curated here; recorded because
      surveillance is still recommended.
- category: Sensory
  name: Sensorineural Hearing Loss
  frequency: OCCASIONAL
  description: >-
    Progressive hearing loss, more often seen in children who survive infancy.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: sensory loss (secondary to retinal dystrophy and sensorineural hearing loss)
    explanation: PARTIAL for the same reason - the sensory phenotype belongs to the
      milder end of the spectrum.
- category: Ophthalmologic
  name: Retinal Dystrophy
  frequency: OCCASIONAL
  description: >-
    Pigmentary retinopathy with progressive visual loss.
  phenotype_term:
    preferred_term: Retinal dystrophy
    term:
      id: HP:0000556
      label: Retinal dystrophy
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: sensory loss (secondary to retinal dystrophy and sensorineural hearing loss)
    explanation: PARTIAL for the same reason as the hearing phenotype.
- category: Neurologic
  name: Polymicrogyria
  frequency: FREQUENT
  description: >-
    Perisylvian polymicrogyria, the MRI-visible result of the arrested cortical migration
    this entry curates as a mechanism node. Present at birth and not reversible.
  phenotype_term:
    preferred_term: Polymicrogyria
    term:
      id: HP:0002126
      label: Polymicrogyria
  evidence:
  - reference: PMID:9382874
    reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice provides
      a model for Zellweger syndrome, a human neuronal migration disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: The malformation of the cerebral cortex is most severe and reproducibly results
      in gyral abnormalities centered around the Sylvian fissure with a stereotypic medial
      pachygyria and lateral polymicrogyria.
    explanation: Names polymicrogyria and its perisylvian distribution in human Zellweger
      neuropathology. Graded OTHER because the sentence is background summarising prior
      human pathology in a paper whose own results are in mice.
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neuronal migration defects associated with neonatal-onset seizures, renal
      cysts, and bony stippling
    explanation: PARTIAL because GeneReviews names the migration defect generically rather
      than polymicrogyria specifically; kept alongside the specific quote to place the
      finding among the congenital malformations of the severe form.
- category: Neurologic
  name: Gray Matter Heterotopia
  frequency: FREQUENT
  description: >-
    Ectopic grey matter, the other structural signature of failed migration. Described
    together with the gyral abnormalities as one co-occurring picture rather than as an
    independent finding, which is why it carries the same frequency as the polymicrogyria.
  phenotype_term:
    preferred_term: Gray matter heterotopia
    term:
      id: HP:0002282
      label: Gray matter heterotopia
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: neuronal migration defects associated with neonatal-onset seizures, renal
      cysts, and bony stippling
    explanation: PARTIAL because GeneReviews names the migration defect generically rather
      than heterotopia specifically.
  - reference: PMID:9382874
    reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice provides
      a model for Zellweger syndrome, a human neuronal migration disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: These gyral abnormalities reflect a reduced neuronal population in the cortex
      and large numbers of subcortical heterotopic neurons.
    explanation: Names the subcortical heterotopic neurons directly in human Zellweger
      neuropathology. OTHER for the same reason as the polymicrogyria item - background
      summarising human pathology in a mouse paper.
- category: Ophthalmologic
  name: Cataract
  frequency: OCCASIONAL
  description: >-
    Congenital cataract in some patients. Curated because the entry already cites its
    treatment - GeneReviews lists cataract removal among the interventions - and an entry
    should not record the operation for a finding it does not record.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: 'Treatment of manifestations: The focus is on symptomatic therapy and may
      include gastrostomy to provide adequate calories, hearing aids, cataract removal,
      glasses to correct refractive errors, supplementation of fat-soluble vitamins, and
      cholic acid supplementation'
    explanation: PARTIAL - GeneReviews names cataract removal as a management step, which
      implies the finding without stating its frequency.
- category: Gastrointestinal
  name: Feeding Difficulties
  frequency: VERY_FREQUENT
  description: >-
    Poor suck and swallow from birth, frequently requiring gastrostomy.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Affected newborns are hypotonic and feed poorly.
    explanation: GeneReviews states feeding failure as part of the newborn presentation.
genetic:
- name: PEX12
  gene_term:
    preferred_term: PEX12
    term:
      id: hgnc:8854
      label: PEX12
  relationship_type: CAUSATIVE
  notes: >-
    The complementation group 3 gene. Genotype-phenotype correlation is unusually
    tractable here: alleles truncating the protein before the C-terminal zinc-binding
    domain give the severe presentation, while alleles preserving residual function
    shift toward the milder end of the spectrum.
  case_fractions:
  - population: Egyptian PEX12 cohort (14 unrelated families)
    case_fraction_percent: 95.0
    cohort_size: 20
    notes: >-
      A founder in-frame deletion accounted for 19 of 20 patients in this series, so the
      allelic spectrum is population-specific rather than universal.
    evidence:
    - reference: PMID:33123925
      reference_title: A founder mutation in PEX12 among Egyptian patients in peroxisomal
        biogenesis disorder.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Herein, we define 20 patients derived from 14 unrelated Egyptian families,
        19 of which show a homozygous PEX12 in-frame (c.1047_1049del p.(Gln349del)) deletion.
      explanation: Gives the founder allele and its share of the cohort.
  evidence:
  - reference: PMID:9792857
    reference_title: Phenotype-genotype relationships in complementation group 3 of the
      peroxisome-biogenesis disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the loss of PEX12 function leads to more-severe cellular and clinical phenotypes
    explanation: States the dose-of-function relationship that separates the A and B ends
      of this locus.
biochemical:
- name: Very-long-chain fatty acids
  presence: Increased
  context: >-
    Plasma C26:0 with the C24/C22 and C26/C22 ratios is the first-line biochemical screen.
    In the severe form curated here the elevation is unambiguous, unlike the milder end of
    the spectrum where it can be modest.
  biomarker_term:
    preferred_term: very long-chain fatty acid
    term:
      id: CHEBI:27283
      label: very long-chain fatty acid
  readouts:
  - target: Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated VLCFA reports the peroxisomal beta-oxidation block directly.
    evidence:
    - reference: PMID:28677031
      reference_title: Evaluation of C26:0-lysophosphatidylcholine and C26:0-carnitine
        as diagnostic markers for Zellweger spectrum disorders.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: C26:0-lysoPC in DBS is a sensitive and useful marker for VLCFA accumulation
        in patients with a ZSD.
      explanation: Establishes the measured analyte as a readout of VLCFA accumulation
        arising from the peroxisomal block.
- name: C26:0-lysophosphatidylcholine
  presence: Increased
  context: >-
    C26:0-lysoPC in dried blood spots is the assay that makes newborn screening for
    Zellweger spectrum disease technically feasible, which matters most for the severe
    form because its window for any intervention is shortest.
  readouts:
  - target: Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated dried-blood-spot C26:0-lysoPC reports peroxisomal beta-oxidation
      failure.
    evidence:
    - reference: PMID:28677031
      reference_title: Evaluation of C26:0-lysophosphatidylcholine and C26:0-carnitine
        as diagnostic markers for Zellweger spectrum disorders.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Elevated C26:0-lysoPC levels (>72 nmol/L) were found in 86/91 ZSD DBS
      explanation: Quantifies the sensitivity of this readout against the block it reports.
- name: Plasmalogens
  presence: Decreased
  biomarker_term:
    preferred_term: ether lipid
    term:
      id: CHEBI:64611
      label: ether lipid
  context: >-
    Erythrocyte plasmalogens are low because ether lipid synthesis begins in the peroxisome.
    This is the deficiency half of the signature and moves in the opposite direction to the
    VLCFA markers, which is what distinguishes a biogenesis defect from an isolated
    beta-oxidation enzyme defect.
  readouts:
  - target: Plasmalogen Deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Reduced erythrocyte plasmalogens report failed peroxisomal ether lipid
      synthesis.
    evidence:
    - reference: PMID:9382874
      reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice provides
        a model for Zellweger syndrome, a human neuronal migration disorder.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: They display abnormal peroxisomal biochemical parameters, including accumulations
        of very long chain fatty acids in plasma and deficient erythrocyte plasmalogens.
      explanation: PARTIAL because the measurement is in the paralogous mouse model rather
        than in PEX12 patients; it shows both directions of the signature in one animal.
diagnosis:
- name: Plasma Very-Long-Chain Fatty Acid Profile
  description: >-
    The first-line biochemical test. Elevated C26:0 with abnormal C24/C22 and C26/C22
    ratios points at a peroxisomal disorder before any gene is sequenced.
  diagnosis_term:
    preferred_term: laboratory procedure
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: The diagnosis of ZSD is established in a proband with the suggestive clinical
      and biochemical findings above by identification of biallelic pathogenic variants
      in one of the 13 known ZSD-PEX genes.
    explanation: GeneReviews Diagnosis places biochemical findings ahead of molecular
      confirmation in the diagnostic sequence.
- name: Molecular Genetic Testing of the ZSD-PEX Genes
  description: >-
    Confirmation requires biallelic variants in one of the ZSD-PEX genes; assignment to
    PEX12 is what makes the entry PBD3 rather than another group.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: by identification of biallelic pathogenic variants in one of the 13 known
      ZSD-PEX genes
    explanation: States the molecular criterion.
treatments:
- name: Supportive and Symptomatic Management
  therapeutic_modality: OTHER
  description: >-
    There is no treatment for the biogenesis defect. Management is entirely symptomatic -
    gastrostomy feeding, anti-seizure medication, hearing aids, cataract surgery,
    fat-soluble vitamin and cholic acid supplementation, adrenal replacement. None of it
    restores peroxisomal import, and the congenital brain malformation is fixed before
    birth, so no postnatal intervention can address the central lesion.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Severe Neurodevelopmental Impairment
    treatment_effect: MODULATES
    description: >-
      Addresses consequences - nutrition, seizures, sensory deficits - without acting on
      peroxisome biogenesis.
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: 'Treatment of manifestations: The focus is on symptomatic therapy and may
      include gastrostomy to provide adequate calories, hearing aids, cataract removal,
      glasses to correct refractive errors, supplementation of fat-soluble vitamins, and
      cholic acid supplementation'
    explanation: GeneReviews Management states that therapy is symptomatic and lists the
      measures.
- name: Cholic Acid
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Oral cholic acid restores feedback inhibition of endogenous bile acid synthesis, so
    the hepatotoxic C27 intermediates that peroxisome-deficient hepatocytes cannot process
    stop accumulating. It is the only FDA-approved therapy for Zellweger spectrum disease
    and the only intervention in this entry that acts on a curated mechanism node rather
    than on a consequence - which is why it is curated separately from supportive care
    rather than inside it.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: cholic acid
      term:
        id: CHEBI:16359
        label: cholic acid
  target_mechanisms:
  - target: Accumulation of Very-Long-Chain and Branched-Chain Fatty Acids
    treatment_effect: INHIBITS
    description: >-
      Suppresses synthesis of the atypical C27 bile-acid intermediates that accumulate
      because peroxisomal side-chain shortening is blocked. It does not restore peroxisomal
      import, so the other accumulating substrates are unaffected.
  - target: Progressive Hepatic Injury
    treatment_effect: INHIBITS
    description: >-
      Removing the hepatotoxic intermediates is what improves the liver chemistry.
  evidence:
  - reference: PMID:28644367
    reference_title: Oral Cholic Acid Is Efficacious and Well Tolerated in Patients With
      Bile Acid Synthesis and Zellweger Spectrum Disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Cholic acid significantly improved urine bile acid metabolite scores (P <
      0.0001) and serum aspartate aminotransferase and alanine aminotransferase (P < 0.0001)
      in patients with SED and ZSD.
    explanation: The fall in atypical urinary bile acids is the direct readout of the
      targeted mechanism, and the transaminase fall is the hepatic consequence.
- name: Adrenal Replacement Therapy
  therapeutic_modality: OTHER
  description: >-
    Glucocorticoid replacement once adrenal insufficiency is documented. Curated
    separately from general supportive care because it depends on active surveillance
    rather than on symptoms - the deficiency is often silent until stressed.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Adrenocortical Insufficiency
    treatment_effect: RESTORES
    description: >-
      Replaces the missing hormone output; it does not correct the VLCFA accumulation
      that impaired steroidogenesis.
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: adrenal replacement therapy; vitamin D supplementation and consideration
      of bisphosphonates for osteopenia
    explanation: GeneReviews Management names adrenal replacement among the interventions.
- name: Biochemical and Developmental Surveillance
  therapeutic_modality: OTHER
  description: >-
    Structured monitoring rather than symptom-driven follow-up, because several
    complications are silent until advanced - adrenal insufficiency in particular.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Adrenocortical Insufficiency
    treatment_effect: MODULATES
    description: >-
      Detects the deficiency before it presents as crisis; it does not prevent it.
  evidence:
  - reference: PMID:20301621
    reference_title: Zellweger Spectrum Disorder.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: ACTH and cortisol levels by age one year and annually thereafter
    explanation: GeneReviews Surveillance gives the adrenal monitoring interval.
animal_models:
- name: Pex2-deficient mouse
  species: Mouse
  genotype: PEX2 (Pxmp3) targeted null, homozygous
  publication: PMID:9382874
  description: >-
    A knockout of PEX2, one of PEX12's two paralogues in the same retrotranslocation
    channel. It is not a model of PBD3A as such, but it is the model that established
    what losing that channel does to a mammal.
  modeled_mechanisms:
  - target: Collapse of Peroxisomal Matrix Protein Import
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the defining cell-biological lesion, including the ghost membranes.
    limitations: >-
      The disrupted gene is PEX2, not PEX12. The two are paralogous subunits of one
      channel, so the import phenotype is shared, but any PEX12-specific effect - notably
      its role in stimulating PEX10 ligase activity - is not modelled.
    readouts:
    - name: Peroxisomal ghost membranes without matrix enzymes
      target: Collapse of Peroxisomal Matrix Protein Import
      direction: ALTERED
      interpretation: Membrane compartments form but are empty, the signature of a
        biogenesis defect.
      evidence:
      - reference: PMID:9382874
        reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice
          provides a model for Zellweger syndrome, a human neuronal migration disorder.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: The PEX2-deficient mice lack normal peroxisomes but do assemble empty
          peroxisome membrane ghosts.
        explanation: Direct observation of the ghost phenotype in the model.
    evidence:
    - reference: PMID:9382874
      reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice
        provides a model for Zellweger syndrome, a human neuronal migration disorder.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: They display abnormal peroxisomal biochemical parameters, including accumulations
        of very long chain fatty acids in plasma and deficient erythrocyte plasmalogens.
      explanation: Shows both halves of the biochemical signature - accumulation and
        deficiency - in the model.
  - target: Impaired Neuronal Migration in the Developing Cortex
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces the cortical migration defect that is otherwise inferred from human
      neuropathology, which is the main reason this model matters for the entry.
    limitations: >-
      Mice die within hours of birth, so the postnatal white-matter disease and the
      sensory phenotypes of longer-surviving humans cannot be studied in it. As above,
      the gene is PEX2.
    readouts:
    - name: Cortical lamination and white-matter cell density
      target: Impaired Neuronal Migration in the Developing Cortex
      direction: ALTERED
      interpretation: Disordered lamination with retained cells in the white matter is
        the expected signature of arrested radial migration.
      evidence:
      - reference: PMID:9382874
        reference_title: Targeted deletion of the PEX2 peroxisome assembly gene in mice
          provides a model for Zellweger syndrome, a human neuronal migration disorder.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: In the central nervous system of newborn mutant mice there is disordered
          lamination in the cerebral cortex and an increased cell density in the underlying
          white matter, indicating an abnormality of neuronal migration.
        explanation: The histological result establishing the migration defect in vivo.
discussions:
- discussion_id: pbd3a_internal_aug_reinitiation
  kind: INTERPRETATION
  attaches_to:
  - genetic#PEX12
  - pathophysiology#Biallelic PEX12 Loss of Function
  prompt: Why does a patient with two apparently severe PEX12 alleles present mildly?
  rationale: >-
    Genotype predicts phenotype well in complementation group 3 - less PEX12 function,
    worse disease - with one documented exception that turns out to be informative rather
    than noise. A compound heterozygote carrying two seemingly null alleles was mildly
    affected. The explanation was that the expressed allele, a 2-bp deletion eight codons
    into the reading frame, still produced a functional protein because translation
    reinitiated at a downstream AUG.

    The general lesson is that "predicted truncating" is a statement about the reading
    frame, not about the protein. An early frameshift can be rescued by internal
    initiation, so severity prediction from variant class alone will occasionally be
    wrong in the direction of over-calling severity. Curated here because this entry is
    defined by being the severe end of its locus, and the boundary between 3A and the
    milder presentations is exactly what such an allele blurs.
  evidence:
  - reference: PMID:9792857
    reference_title: Phenotype-genotype relationships in complementation group 3 of the
      peroxisome-biogenesis disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: However, one patient who presented relatively mild clinical and cellular
      phenotypes was a compound heterozygote for two seemingly severe mutations on each
      PEX12 allele.
    explanation: States the discrepant case that the mechanism explains.
  - reference: PMID:9792857
    reference_title: Phenotype-genotype relationships in complementation group 3 of the
      peroxisome-biogenesis disorders.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: this mutant PEX12 cDNA displayed significant PEX12 activity in a functional
      complementation assay
    explanation: The functional result showing the supposedly null allele retains
      activity; IN_VITRO because it is a cell-based complementation assay.
- discussion_id: pbd3a_no_disease_modifying_therapy
  kind: KNOWLEDGE_GAP
  attaches_to:
  - treatments#
  - pathophysiology#Collapse of Peroxisomal Matrix Protein Import
  prompt: Could peroxisomal matrix import be restored therapeutically in a patient?
  rationale: >-
    Every treatment in this entry is symptomatic. Restoring import would mean restoring
    a membrane translocon in every affected tissue, and the two organs that determine
    outcome present different obstacles: the brain lesion is a completed malformation of
    fetal migration, so even perfect postnatal correction could not undo it, while the
    liver and adrenal disease is progressive and might in principle respond. No approach
    - gene therapy, read-through of nonsense alleles, chaperone rescue of hypomorphic
    alleles - has reached patients. The gap is recorded rather than left implicit
    because the absence of disease-modifying options is the single most important fact
    about managing this diagnosis.
references:
- reference: PMID:20301621
  title: Zellweger Spectrum Disorder.
  tags:
  - GeneReviews
- reference: PMID:9792857
  title: Phenotype-genotype relationships in complementation group 3 of the peroxisome-biogenesis
    disorders.
- reference: PMID:9632816
  title: 'PEX12, the pathogenic gene of group III Zellweger syndrome: cDNA cloning by
    functional complementation on a CHO cell mutant, patient analysis, and characterization
    of PEX12p.'
- reference: PMID:14571262
  title: Novel mutations in the PEX12 gene of patients with a peroxisome biogenesis disorder.
- reference: PMID:33123925
  title: A founder mutation in PEX12 among Egyptian patients in peroxisomal biogenesis
    disorder.
- reference: PMID:9382874
  title: Targeted deletion of the PEX2 peroxisome assembly gene in mice provides a model
    for Zellweger syndrome, a human neuronal migration disorder.
notes: >-
  Scope and naming. "3A" is a complementation-group label, not a severity grade applied
  after the fact: group 3 of the peroxisome biogenesis disorders was defined by cell
  fusion long before PEX12 was cloned, and the A/B suffix then split that group by
  severity. This entry curates the A end. The KB already holds Peroxisome Biogenesis
  Disorder 1B (PEX1) and 4B (PEX6), so the three entries together span two severity
  tiers across three subunits of the same import machinery.

  GeneReviews. The chapter is written for the Zellweger spectrum as a whole rather than
  for PEX12, and it says explicitly that the older phenotype names are now subsumed
  under one continuum. It is mined across all four sections; an earlier version of this
  entry claimed that while leaving Genetic Counseling uncited, which review caught. Evidence items quoting it say which end of the spectrum the
  quoted sentence describes; several phenotypes are graded PARTIAL because the sentence
  supporting them is about the intermediate/milder end while this entry is the severe
  one.

  Animal model. The Pex2-null mouse is curated rather than a PEX12 model because no
  PEX12 mouse is reported in the sources used here. It is the paralogous subunit of the
  same channel, its limitations field says so, and both links are scoped to what the
  shared channel defect explains rather than to PEX12-specific biology.

  Ontology corrections. Ten of the CURIEs the research report suggested were wrong,
  obsolete, or nonexistent, and were corrected against OLS before use. GO:0033539 was
  offered for peroxisomal beta-oxidation but is the mitochondrial acyl-CoA dehydrogenase
  process - the peroxisomal counterpart is GO:0033540 - which would have been a
  mechanistically inverted binding rather than a mislabel. Also wrong: CL:0000601
  (offered as radial glial cell, is cochlear outer hair cell), CL:0001133 (does not
  resolve), CHEBI:143092 (offered as a VLCFA, is a phosphatidylserine species),
  CHEBI:28865 (offered as phytanic acid, is taurocholic acid), CHEBI:36620 (offered as
  cholic acid, is quinolizine), HP:0002656 (offered as chondrodysplasia punctata, is
  epiphyseal dysplasia), HP:0000121 (offered as nephrolithiasis, is nephrocalcinosis),
  HP:0002187 (offered as hypomyelination, is profound intellectual disability), and
  HP:0012825 (offered as a seizure term, is the severity modifier "Mild").

  Bracketed quotes. Two GeneReviews snippets stop short of the sites they describe
  because the sentence embeds "[chondrodysplasia punctata]" and "patella[e]", and the
  reference validator strips bracketed text, so a span crossing a bracket cannot match
  the cache.

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References & Deep Research