Peroxisome Biogenesis Disorder 6B

1. Disease Information

Overview. PBD6B is the milder of two PEX10-linked phenotypes on the Zellweger spectrum: PBD6A (OMIM 614870) is the severe, classically lethal Zellweger syndrome; PBD6B (OMIM 614871) is the intermediate/mild end, corresponding clinically to neonatal adrenoleukodystrophy (NALD) or infantile Refsum disease (IRD)-type presentations, with an extreme mild outlier phenotype of isolated cerebellar ataxia now described.

Identifiers: - OMIM phenotype: 614871 (PBD6B); sibling severe phenotype 614870 (PBD6A) - OMIM gene: *602859 (PEX10) - MONDO: MONDO:0013937 - MedGen: C3553948 - Orphanet: 44 (Zellweger syndrome spectrum — umbrella code; I did not find a PBD6B-specific Orphanet code distinct from this ZSD-spectrum entry) - HGNC: 8851 (PEX10); NCBI Gene: 5192 - Locus: 1p36.32 - ICD-10-CM: E71.510 (Zellweger syndrome) is the billable code found; there is no PEX10/PBD6B-specific ICD-10 code — ZSD as a whole maps to E71.5-series codes (E71.541 "Zellweger-like syndrome" also exists but that is a distinct entity, not a synonym)

Synonyms: Peroxisome biogenesis disorder, complementation group 7, mild form; Zellweger spectrum disorder, PEX10-related, attenuated form; historically "complementation group B" (Japanese fibroblast-fusion nomenclature) vs. "complementation group 7" (US nomenclature) — both refer to the same PEX10 defect (confirmed via Okumoto et al. 1998, PMID:9700193, and Warren et al. 1998, PMID:9683594).

Data derivation: The clinical picture below is derived from aggregated disease-level resources (OMIM, case series, review articles) rather than a single large natural-history cohort specific to PEX10 — PBD6B is documented almost entirely through individual case reports and small family series (Blomqvist et al. 2017, PMID:28784167; Huang et al. 2025, PMID:40267090; Nava et al. 2022, PMID:35038753), supplemented by ZSD-wide reviews that are PEX1-dominated.

2. Etiology

Disease causal factor: Exclusively genetic — biallelic (homozygous or compound heterozygous) loss-of-function or hypomorphic pathogenic variants in PEX10. No environmental, infectious, or purely mechanistic (non-genetic) causal factor has been reported for this entry; I found nothing in the literature search suggesting otherwise.

Genetic risk factors and genotype-phenotype correlation. This is the most substantively documented part of PEX10 biology and is worth stating precisely because it is the mechanistic basis for the PBD6A/PBD6B split:

• Warren, Wolfe & Gould (2000, Human Mutation, PMID:10862081) established the founding genotype-phenotype correlation: nonsense, frameshift, and splice-site mutations correlate with severe Zellweger syndrome (PBD6A), whereas missense mutations retaining partial function — the reported example is a mutation in the C-terminal zinc-binding RING domain (H290Q) — associate with milder NALD-type disease (PBD6B). Notably, the same paper also found some nonsense/frameshift mutations truncating only the C-terminal 1/3–2/3 of the protein retained "nearly normal PEX10 activity" in a complementation assay, underscoring that truncation location, not variant class alone, predicts residual function.
• Subsequent PBD6B-specific missense variants reported: c.530T>G (p.Leu177Arg), homozygous, in an attenuated/late-onset case (Blomqvist et al. 2017, PMID:28784167); a novel splice-acceptor variant c.113-2A>G causing in-frame exon 2 skipping, compound heterozygous with c.890T>C (p.Leu297Pro), in a Han-Chinese family with three affected members classified as PBD6B (Huang et al. 2025, PMID:40267090).
• A structurally distinct extreme-mild outlier phenotype — isolated, later-onset (age 3–8 years) cerebellar ataxia with cerebellar atrophy, without the classic multisystem ZSD picture — has been described in at least 15 patients across 9 families with biallelic PEX10 variants (Nava et al. 2022, PMID:35038753). This is a genotype-phenotype extreme worth flagging separately from "classic" PBD6B/NALD-IRD, since it changes the differential diagnosis (unexplained pediatric/young-adult ataxia) rather than presenting as a recognizable ZSD gestalt.

Modifier genes: None specific to PEX10/PBD6B identified in this search. The general ZSD literature (Klouwer et al. 2015, PMID:26627182) notes only that "although a rough genotype-phenotype correlation exists for several PEX genes, such as PEX1 and PEX26, the severity and progression of the disease is difficult to predict for individual patients" — implying unidentified modifying factors even within an allele class.

Environmental/lifestyle risk or protective factors, gene-environment interaction: None identified. This is a purely Mendelian biochemical disorder; I found no CTD, epidemiological, or GWAS-type literature suggesting environmental modulation of PEX10-related disease risk or severity.

Consanguinity/founder context: Several PBD6B case reports come from consanguineous or genetically isolated families (Han-Chinese family, PMID:40267090; an Assyrian/Iraqi-origin patient, PMID:28784167), consistent with autosomal recessive inheritance generally, but I found no evidence of a defined PEX10 founder allele or population-specific carrier frequency estimate — a Dagestan-family PEX26 report and a Saudi PEX19/PEX26 report turned up in search but concern different genes and should not be conflated with PEX10/PBD6B.

3. Phenotypes

Phenotype data below draws on two evidence tiers that should not be blended uncritically: (A) ZSD-wide severity-tiered descriptions from Klouwer et al. 2015 (PMID:26627182) and the Bose et al. 2022 severity meta-analysis (PMID:35741019, Cells, analyzing 307 patients from 107 studies plus 136 chart-reviewed patients), which are PEX1-dominated; and (B) PEX10/PBD6B-specific case reports, which are the more directly applicable source for this entry but numerically sparse.

Severe end (PBD6A, for contrast — this entry is PBD6B but the spectrum framing matters clinically): - Onset: neonatal - Hepatic dysfunction, profound hypotonia, prolonged jaundice, feeding difficulties, seizures, characteristic craniofacial dysmorphism, retinopathy/cataracts/glaucoma, sensorineural deafness - Brain MRI: neocortical dysplasia (especially perisylvian polymicrogyria — a neuronal migration defect), generalized white matter volume reduction, delayed myelination - Prognosis: "survival is usually not beyond the first year of life" (Klouwer et al. 2015)

PBD6B — intermediate/childhood tier (NALD-like): - Onset: infancy/childhood, delayed developmental milestones as a presenting feature - Ocular: retinitis pigmentosa, cataract, glaucoma, "often leading to early blindness" (Klouwer et al. 2015) - Auditory: sensorineural deafness "almost always present" - Hepatic: hepatomegaly and dysfunction, coagulopathy, elevated transaminases, history of hyperbilirubinemia - Neurologic: some patients develop early-onset progressive leukodystrophy with loss of acquired skills - Prognosis: "most patients die before adolescence" for this tier as a class, though individual course varies

PBD6B — milder/adolescent-adult tier (IRD-like), the tier best documented specifically for PEX10: - Diagnosis can occur in late childhood or adulthood - "Ocular abnormalities and a sensorineural hearing deficit are the most consistent symptoms" (Klouwer et al. 2015) - Primary adrenal insufficiency, "probably underdiagnosed" - Clinical course "usually slowly progressive, although the disease may remain stable for (many) years" - PEX10-specific worked case (Blomqvist et al. 2017, PMID:28784167): an adolescent girl presenting first with sensorineural hearing impairment (age 5), followed in the teen years by sensorimotor polyneuropathy, cognitive delay, impaired gross/fine motor skills, tremor, and muscle weakness — a trajectory the authors explicitly frame as atypically mild for the gene, underscoring the need for peroxisomal screening even without classic Zellweger gestalt. - PEX10-specific outlier phenotype (Nava et al. 2022, PMID:35038753): isolated cerebellar ataxia, onset age 3–8, cerebellar atrophy on MRI in most cases (ataxia was the presenting symptom in 11/14 literature patients), with polyneuropathy and cognitive impairment in roughly two-thirds. The authors recommend metabolic screening (phytanic acid, VLCFA ratios rather than absolute VLCFA levels, which can be misleadingly near-normal in this mild phenotype) for unexplained pediatric ataxia. - Han-Chinese family (Huang et al. 2025, PMID:40267090): three affected relatives with "milder phenotypes," described as "neurological dysfunction, hypotonia, seizures, and various systemic abnormalities" — classified PBD6B.

Severity meta-analysis findings (ZSD-wide, PMID:35741019): seizures, hypotonia, reduced mobility, feeding difficulties, renal cysts, adrenal insufficiency, and hearing/vision loss significantly correlated with severity classification; plasma C26:0 fatty acid levels also differentiated severity tiers.

Quality of life: I found no disease-specific EQ-5D/SF-36/PROMIS data for PBD6B or PEX10-related disease. The Bose group has run a caregiver-reported cross-sectional symptom-prevalence survey for ZSD generally (referenced in search results but not fetched in detail here); a dedicated per-phenotype QoL dataset for the PEX10 subgroup specifically was not located.

Suggested HPO terms (leads only — not verified via OAK/HPO lookup in this session; treat as candidates to check before curation): HP:0001518 (Small for gestational age is not relevant — omit), HP:0001250 (Seizure), HP:0001252 (Hypotonia), HP:0000505 (Visual impairment), HP:0000510 (Retinitis pigmentosa jointly relevant), HP:0000407 (Sensorineural hearing impairment), HP:0001392 (Abnormality of the liver / hepatomegaly-adjacent), HP:0002240 (Hepatomegaly), HP:0000794 (Nephropathy is too broad — renal cortical cysts is HP:0000107), HP:0007281 (Adrenal hypoplasia is not accurate — primary adrenal insufficiency is HP:0000846), HP:0001510-adjacent developmental delay terms, HP:0002066 (Gait ataxia) and HP:0001272 (Cerebellar atrophy) for the ataxia-outlier phenotype, HP:0000965/HP:0007270-type peripheral neuropathy terms. All of these must be re-verified against the current HPO build before use — I am not treating this list as curated.

4. Genetic/Molecular Information

Causal gene: PEX10 (OMIM *602859, HGNC:8851, NCBI Gene 5192), chr1:2,403,964–2,413,797 (1p36.32). Encodes a 326-amino-acid peroxisomal membrane protein (Okumoto et al. 1998, PMID:9700193 describes a 326-aa protein; note Matsumoto/other sources for the related PEX26 gene describe a different, 305-aa protein — these are not interchangeable, reinforcing the gene-identity correction above).

Protein structure and function: PEX10 is a RING-type (C3HC4 zinc finger) E3 ubiquitin ligase embedded in the peroxisomal membrane. It is one of three RING-domain peroxins (PEX2, PEX10, PEX12) that co-assemble into the PEX2-PEX10-PEX12 retrotranslocation channel, whose cryo-EM structure was solved by Feng et al. 2022 (Nature, PMID:35768507): "the three subunits...coassemble in the membrane into a channel with an open 10 Å pore," with the RING zinc-fingers positioned on the cytosolic side to catalyze ubiquitination of the PTS1 import receptor PEX5 as it is extracted (retrotranslocated) from the peroxisomal lumen back to the cytosol. Under normal recycling, monoubiquitination (via the E2 enzyme PEX4) allows PEX5 reuse for another import cycle; when recycling is impaired, PEX10 (with PEX12 stimulating its ligase activity) instead polyubiquitinates PEX5, targeting it for proteasomal degradation.

Pathogenic variant classes reported (PEX10, various complementation-group-7 phenotypes across the PBD6A/6B spectrum): - Homozygous 2-bp deletion, frameshift (Okumoto et al. 1998, PMID:9700193) — severe - Homozygous splice donor-site mutation causing exon skipping vs. compound heterozygous missense + nonsense (two CG7 patients of differing severity; Warren et al. 1998, PMID:9683594) - Missense H290Q in the C-terminal zinc-binding domain — milder NALD phenotype (Warren et al. 2000, PMID:10862081) - c.530T>G (p.Leu177Arg), homozygous — attenuated/late-onset phenotype (Blomqvist et al. 2017, PMID:28784167) - c.113-2A>G (splice acceptor, exon 2 skipping) compound heterozygous with c.890T>C (p.Leu297Pro) — PBD6B, three affected relatives (Huang et al. 2025, PMID:40267090) - c.790C>T (p.Arg264X), a premature termination variant reported in ClinVar/gnomAD-linked material I surfaced via search but did not independently verify against a primary source — flagging this one specifically as unverified for this report (allele frequency cited as 2.5×10⁻⁵ in 237,538 control chromosomes in the search snippet; I could not confirm the originating publication, so treat this figure as a lead only).

Variant classification: ACMG/AMP pathogenic and likely pathogenic classifications exist in ClinVar for numerous PEX10 variants (multiple RCV accessions surfaced in search, e.g., c.790C>T/p.Arg264X, c.1A>G/p.Met1Val, c.711C>T) — I did not systematically enumerate ClinVar's full PEX10 variant table in this session; a dedicated ClinVar query would be needed before curation.

Somatic vs. germline: Exclusively germline — no somatic/oncologic role identified for PEX10 in this search (consistent with its being a housekeeping peroxisomal-import gene rather than a tumor-suppressor/oncogene axis).

Functional consequence: Loss of function (null alleles: nonsense, frameshift, canonical splice-site) → severe phenotype (PBD6A); partial loss of function (missense variants retaining residual retrotranslocation-channel activity) → PBD6B and its ataxia-only extreme. Mechanistically this is loss-of-function/hypomorphic, not gain-of-function or dominant-negative — consistent with recessive inheritance and with the direct biochemical demonstration (Warren et al. 1998) that CG7/PEX10-deficient cells "contain many peroxisomes and import peroxisomal membrane proteins but do not import peroxisomal matrix proteins," i.e., a selective matrix-import defect rather than failure of peroxisome formation per se.

Epigenetic information: None identified specific to PEX10/PBD6B.

Chromosomal abnormalities: None identified as an alternative disease mechanism for PBD6B (contrast: I found an unrelated case report of 1p36.33-p36.32 microdeletion causing pancytopenia, which is a different entity and should not be conflated with PEX10 point-variant disease, since the deletion region only partially overlaps the gene locus and was not reported as PBD6B).

5. Environmental Information

I found no evidence of environmental factors (toxins, radiation, occupational exposure), lifestyle factors, or infectious agents contributing causally to PBD6B. This is consistent with its being a monogenic autosomal recessive enzymopathy/traffic disorder with no known gene-environment interaction literature. This section is genuinely N/A rather than under-researched — the biology (loss of a specific ubiquitin-ligase/retrotranslocation-channel protein) gives no plausible mechanism for environmental modulation, and no CTD/epidemiological hits surfaced.

6. Mechanism / Pathophysiology

Causal chain (numbered, from initiating lesion to clinical manifestation). I want to flag explicitly that steps 1–3 are directly evidenced for PEX10 specifically (Warren et al. 1998, PMID:9683594; Feng et al. 2022, PMID:35768507), while steps 4 onward are inferred by extension from general ZSD/peroxisomal pathophysiology — largely characterized in PEX1-dominant cohorts and in generic peroxisomal-biochemistry literature — rather than demonstrated in PEX10-specific mechanistic studies. I have not found PEX10-specific tissue pathology, transcriptomic, or lipidomic studies; the downstream biology should be read as "expected by shared final-common-pathway logic," not as directly measured in PBD6B patients.

1. Biallelic pathogenic PEX10 variants → reduced or absent functional PEX10 protein (RING-domain E3 ubiquitin ligase) at the peroxisomal membrane. [Direct — Okumoto 1998, Warren 1998]
2. Loss of PEX10 disrupts assembly/function of the PEX2-PEX10-PEX12 retrotranslocation channel, the structure responsible for extracting the ubiquitinated PTS1 receptor PEX5 from the peroxisomal membrane back to the cytosol for reuse. [Direct, structural — Feng et al. 2022, PMID:35768507]
3. Failure of PEX5 recycling (and, via PEX5L as PEX7's obligate co-receptor, secondary failure of PTS2-mediated import) leads to selective failure of peroxisomal matrix protein import while the peroxisomal membrane and membrane-protein trafficking remain comparatively intact — CG7/PEX10-deficient fibroblasts retain morphologically identifiable peroxisomes ("peroxisomal ghosts") that import membrane but not matrix proteins. [Direct — Warren 1998]
4. → Deficient peroxisomal matrix enzyme activities: beta-oxidation of very-long-chain fatty acids (VLCFA), alpha-oxidation of phytanic acid (with downstream pristanic acid accumulation), peroxisomal steps of bile acid synthesis (side-chain oxidation of DHCA/THCA to cholic/chenodeoxycholic acid), and the first two enzymatic steps of ether-phospholipid (plasmalogen) biosynthesis, plus glyoxylate detoxification. [Inferred by extension from general peroxisomal biochemistry — this is the same final common pathway across ZSD complementation groups, not PEX10-specific data]
5. → Biochemical signature: accumulation of VLCFA, phytanic/pristanic acid, and bile acid intermediates (DHCA, THCA) in plasma/urine, with deficiency of plasmalogens (erythrocyte membrane) and mature bile acids. This is the biochemical basis of the diagnostic panel described in Section 10.
6. Branch A — CNS/myelin: VLCFA accumulation incorporates into oligodendrocyte and neuronal membranes, and (by analogy with the better-studied ABCD1/X-ALD pathway) promotes oxidative stress and mitochondrial dysfunction; combined with plasmalogen deficiency (plasmalogens are a major myelin lipid component), this destabilizes myelin → leukodystrophy, and in the severe end of the spectrum disrupts neuronal migration during corticogenesis → neocortical dysplasia/polymicrogyria. [Inferred by extension — the myelin/oxidative-stress mechanism is best evidenced in X-ALD (ABCD1) literature, not PEX10-specific studies; polymicrogyria is a PBD6A-tier (severe) finding and less expected in PBD6B]
7. Branch B — sensory epithelia: plasmalogen deficiency and VLCFA accumulation are proposed to impair photoreceptor/retinal pigment epithelium membrane integrity (→ retinitis pigmentosa/cataract/glaucoma) and cochlear hair-cell function (→ sensorineural hearing loss) — the two most consistently reported PBD6B features. [Inferred/generalized; specific PEX10 cochlear or retinal histopathology was not located in this search]
8. Branch C — liver: failure of peroxisomal bile-acid-intermediate oxidation causes both accumulation of hepatotoxic intermediates (DHCA/THCA) and deficiency of mature bile acids needed for fat/fat-soluble-vitamin absorption → cholestasis, coagulopathy (secondary to vitamin K malabsorption), transaminase elevation, and in more severe cases progressive fibrosis/cirrhosis. [Klouwer et al. 2015 clinical description; general peroxisomal bile-acid biology]
9. Branch D — adrenal cortex: VLCFA/lipid accumulation in adrenocortical cells produces the "striated adrenocortical cell" histopathology described in classic Zellweger syndrome, with reduced steroid biosynthesis → primary adrenal insufficiency, reported in 7/24 ZSD patients (4 asymptomatic) in Berendse et al. 2014 (Orphanet J Rare Dis, PMID for this I located via search snippet as within volume 9/article 133, DOI 10.1186/s13023-014-0133-5 — PMID not independently confirmed in this session). [ZSD-wide, not PEX10-isolated data]
10. Branch E — kidney: renal cortical cysts (reported in ~70% of ZSD cases per search-derived summary; mechanism not detailed in sources retrieved — likely developmental, related to disrupted peroxisomal lipid metabolism during nephrogenesis, but I did not find a mechanistic paper specific to this).
11. Branch F — peripheral nerve/cerebellum (the PEX10-specific mild-end signature): the ataxia/polyneuropathy phenotype described by Nava et al. 2022 and Blomqvist et al. 2017 implies a disproportionate vulnerability of cerebellar and peripheral-nerve tissue to partial (hypomorphic) PEX10 loss relative to liver/adrenal/kidney — this pattern is descriptive, not yet mechanistically explained in the literature I retrieved; I would flag this as an open mechanistic question rather than assert a specific molecular explanation.

Cell types implicated: hepatocyte (liver), oligodendrocyte and cortical/cerebellar neuron (CNS), retinal photoreceptor/RPE (eye), cochlear hair cell (ear), adrenocortical cell (adrenal), renal tubular/cortical epithelium (kidney), Schwann cell/peripheral neuron (the ENU-mouse literature specifically notes "decreased Schwann cell number, defects at the neuromuscular junction," which maps suggestively onto the human polyneuropathy phenotype in mild PEX10 disease).

Suggested GO terms (leads, unverified in this session): GO:0007031 (peroxisome organization), GO:0016558 (protein import into peroxisome matrix), GO:0043574 (peroxisomal transport), GO:0006635 (fatty acid beta-oxidation), GO:0006693 (prostaglandin metabolic process — not directly relevant, omit), GO:0008306 (associative learning — not relevant, omit), a plasmalogen-biosynthesis term (GO:0001516 prostaglandin biosynthetic process is wrong; the correct term is likely GO:0090207 or a related ether-lipid biosynthesis GO ID that I have not verified — do not bind without OAK lookup), GO:0031625 (ubiquitin protein ligase binding) for PEX10's E3 activity. These require verification before curation use.

Suggested CL/UBERON terms (leads, unverified): CL:0000182 (hepatocyte), CL:0000128 (oligodendrocyte), CL:0000540 (neuron), CL:0000646/CL:0002586-type retinal photoreceptor terms, CL:0000499 (stromal cell — too generic, avoid), UBERON:0002107 (liver), UBERON:0000955 (brain), UBERON:0002369 (adrenal gland), UBERON:0002113 (kidney), UBERON:0001846-type cochlea/inner-ear term. Verify all before binding.

7. Anatomical Structures Affected

Organ level (primary): liver, central nervous system (cerebral white matter; cerebellum specifically in the PEX10 mild-outlier phenotype; cortex in severe polymicrogyria), eye (retina, lens, optic structures), ear (cochlea — sensorineural hearing loss), kidney (renal cortex — cysts), adrenal gland (cortex — primary insufficiency).

Secondary/complication-level: peripheral nervous system (polyneuropathy, prominent in the PEX10 mild phenotype specifically), skeletal system (enamel hypoplasia reported as "present in nearly all patients" per Klouwer et al. 2015; classic chondrodysplasia punctata/epiphyseal stippling is a PEX7/RCDP1-defining feature, not a PBD6B-typical one — I want to be explicit that this is a different gene and a different, non-overlapping disorder, even though both are peroxisomal).

Body systems involved: hepatic, neurologic (central and peripheral), ophthalmologic, otologic/auditory, renal, endocrine (adrenal), skeletal (dental enamel), hematologic (coagulopathy, secondary to fat-soluble vitamin malabsorption).

Subcellular level: peroxisomal membrane (site of PEX10 function and the retrotranslocation channel), peroxisomal matrix (site of the resulting import failure), secondarily mitochondria (oxidative stress/dysfunction is implicated by extension from X-ALD biology, not directly demonstrated for PEX10).

Lateralization: Not applicable — this is a systemic/bilateral biochemical disorder, not a laterality-associated condition.

8. Temporal Development

Onset: Highly variable across the PEX10 allelic series — this is the central organizing fact for PBD6B specifically. Null/severe biallelic combinations → neonatal-onset PBD6A (Zellweger syndrome proper, outside this entry's scope but relevant as the severe pole of the same gene). Hypomorphic missense combinations → PBD6B, itself spanning infantile (NALD-like) through late-childhood/adolescent (IRD-like) onset, down to an extreme late-onset (age 3–8) isolated-ataxia presentation (Nava et al. 2022).

Onset pattern: Generally insidious/subacute rather than acute, even in the mildest presentations — e.g., the Blomqvist 2017 case first came to attention via hearing loss at age 5, with polyneuropathy/cognitive/motor decline only becoming apparent through the teenage years.

Progression: "Usually slowly progressive, although the disease may remain stable for (many) years" at the mild end (Klouwer et al. 2015); when progression does occur in the mild/adult tier, it is "mainly related to peripheral neuropathy and pyramidal signs, while cognition remains stable" per the same source — an important prognostic nuance for counseling.

Disease course pattern: Progressive rather than relapsing-remitting; no spontaneous-remission pattern is described anywhere in the literature I retrieved.

Critical periods: Implicit rather than explicitly stated in the sources retrieved — the severe/neonatal tier's neocortical migration defects (polymicrogyria) imply a prenatal critical window, while the mild/PBD6B tier's slow, adult-persisting course suggests no comparable fixed developmental window, consistent with a milder biochemical lesion causing chronic accumulation/deficiency rather than a developmental catastrophe. I am reasoning past directly cited evidence here rather than quoting a specific source.

9. Inheritance and Population

Inheritance pattern: Autosomal recessive. Both PBD6A and PBD6B are allelic (same gene, different variant severity) — this is a point worth surfacing rather than treating them as unrelated diseases, per the dismech convention of keeping related-severity allelic disorders explicit rather than silently lumped or split.

Epidemiology (ZSD-wide, not PEX10-isolated): - Cumulative ZSD incidence commonly cited around 1:50,000 births (Bose et al. 2022, PMID:35741019, cites this figure for context) - US regional newborn-screening-derived estimate: ~1:90,000 (New York, from 1.08 million screenings, per a search-derived summary I could not independently verify against a primary citation this session) - Japan: markedly lower, ~1:500,000 — a striking geographic disparity I found stated in search results but without a primary citation I directly fetched; treat as a lead pending verification - No PEX10/PBD6B-specific incidence figure was found — given the rarity of published PEX10 cases (a handful of families across the literature I retrieved: Chinese, Assyrian/Iraqi, and the Nava et al. 9-family European/mixed ataxia cohort), PBD6B is almost certainly substantially rarer than the ZSD aggregate figure, but I have no quantitative basis to state a number.

Penetrance/expressivity: Functionally complete penetrance is implied (no asymptomatic biallelic carriers reported), but expressivity is highly variable — this is the genotype-phenotype axis already covered in Section 2 (severity tracks variant class/residual function) rather than a separate stochastic-penetrance phenomenon.

Genetic anticipation, germline mosaicism, founder effects: None reported for PEX10/PBD6B in this search.

Consanguinity: Several reported families are consanguineous or from genetically isolated populations, consistent with autosomal recessive disease generally, but no specific consanguinity-attributable-fraction statistic for PEX10 was found.

Carrier frequency: Not established with a verified primary source in this session (the one gnomAD-adjacent figure I surfaced, c.790C>T at AF 2.5×10⁻⁵, is flagged above as unverified).

Population demographics, geographic distribution, sex ratio: No PEX10-specific sex-ratio or ancestry-enrichment data found. Reported case geography spans China, Iraq (Assyrian ancestry), and mixed European cohorts for the ataxia phenotype — this reads as broad geographic distribution rather than a defined high-prevalence population, though the sparse case count makes any such inference weak.

10. Diagnostics

Biochemical testing (plasma/blood, general ZSD panel — Klouwer et al. 2015, quoted directly): "VLCFAs, the peroxisomal bile acid intermediates di- and trihydroxycholestanoic acid (DHCA, THCA), the branched-chain fatty acids phytanic and pristanic acid, and pipecolic acid in plasma, plasmalogen levels in erythrocytes, and C26:0-lysoPC in dried blood spots."

Important caveat specific to mild PEX10 disease: Klouwer et al. explicitly warn that "relatively mild ZSD patients may have (near) normal biochemical tests in plasma and urine" — and Nava et al. 2022 make the same point specifically for PEX10-related ataxia, recommending VLCFA ratios rather than absolute VLCFA levels and phytanic acid measurement as more sensitive in this attenuated phenotype. This is a clinically important point: a normal standard VLCFA panel does not exclude PBD6B.

Urine testing: Bile acids and oxalic acid.

Fibroblast-based testing: When clinical suspicion is high but blood/urine biochemistry is normal, culturing fibroblasts (including at 40°C, a temperature-sensitivity complementation approach historically used to unmask hypomorphic PEX1/PEX6 alleles, per Klouwer et al. 2015) is recommended — I did not find explicit confirmation that the 40°C assay specifically unmasks PEX10 hypomorphs, so I present this as a general ZSD-diagnostic-algorithm step rather than a PEX10-validated technique.

Molecular/genetic testing: Given PEX10's established role, single-gene sequencing, ZSD/peroxisomal gene panels, or exome sequencing are all reasonable approaches; multiple case reports used exome + Sanger confirmation (Huang et al. 2025) or targeted PEX gene screening panels ("The PEX Gene Screen," referenced in search results as a diagnostic approach paper, exact PMID not fetched in this session).

Imaging: Brain MRI for leukodystrophy/polymicrogyria/cerebellar atrophy (the latter specifically relevant to the PEX10 ataxia phenotype per Nava et al. 2022); renal ultrasound for cortical cysts; ophthalmologic exam (retinitis pigmentosa, cataract, glaucoma); audiology (sensorineural hearing loss).

Differential diagnosis: Other ZSD complementation groups (clinically indistinguishable without biochemical/molecular testing); for the isolated-ataxia PEX10 phenotype specifically, the differential is the broader autosomal-recessive-ataxia gene list (Nava et al. 2022 explicitly frame PEX10 as a diagnosis to consider in "unexplained autosomal recessive ataxias"); RCDP1 (PEX7) for any skeletal/rhizomelic features, which — again — should not be expected in PEX10-related disease specifically.

Screening: No dedicated newborn screening program for PBD/ZSD generally exists in most jurisdictions I found evidence for (X-linked ALD newborn screening via C26:0-lysoPC, now on the US RUSP since 2016, is a related but distinct screening target — it detects ABCD1-related disease, not PEX-gene ZSD, though the same analyte can incidentally flag peroxisomal biogenesis disorders). A "Spanish Uniform Newborn Screening Panel" reference surfaced in search results as potentially including peroxisomal markers, but I did not verify its exact scope in this session.

11. Outcome/Prognosis

Prognosis tracks tightly with the genotype-driven severity tier already discussed:

• Severe/PBD6A pole (context only): death typically within the first year of life.
• PBD6B intermediate tier: "most patients die before adolescence" as a class statement (Klouwer et al. 2015), though this generalization is drawn from ZSD-wide (PEX1-dominant) data, and PEX10-specific mortality figures for this tier were not located.
• PBD6B mild tier: patients "can reach adulthood without progression or with long periods of stabilization," with progression (when it occurs) dominated by peripheral neuropathy and pyramidal signs while cognition remains comparatively preserved (Klouwer et al. 2015). This matches the PEX10-specific case reports directly — the Blomqvist 2017 patient and the Nava 2022 ataxia cohort both describe adolescent/adult survival with a slowly accruing neurologic burden rather than early mortality.
• Complications: progressive liver disease, leukodystrophy (both flagged by Klouwer et al. as the drivers of a worse prognosis when they occur even in the milder tiers), primary adrenal insufficiency (treatable if detected), coagulopathy, hearing/vision loss, low bone mineral density (a "Reply: Low bone mineral density is a common feature of Zellweger spectrum disorders" letter surfaced in search — PMID not fetched, flagged as a lead).
• No PEX10/PBD6B-specific survival curve, life-expectancy figure, or prognostic-biomarker study was located in this search beyond the general ZSD severity-correlate list from Bose et al. 2022 (seizures, abnormal EEG, renal cysts, cardiac abnormalities, plasma C26:0 level).

12. Treatment

No curative therapy exists for PBD6B or ZSD generally — Klouwer et al. 2015 state this directly: "Because no curative therapy for patients with a ZSD exists, intervention is supportive and based on symptoms." Management is therefore organ-system-directed:

• Pharmacotherapy — bile acid replacement: Cholic acid (Cholbam®) received FDA approval (announced March 2015 per search-derived regulatory summaries) as the first approved treatment for bile acid synthesis disorders due to single-enzyme defects and "for adjunctive treatment of peroxisomal disorders such as Zellweger spectrum disorders in patients who have liver disease, steatorrhea, or complications from fat-soluble vitamin malabsorption." Approval was based on a long-term single-arm trial plus case reports across 77 bile-acid-synthesis-disorder patients and 34 peroxisomal-disorder patients; cholic acid appeared to decrease hepatic injury and increase height/weight, with 42% of treated peroxisomal-disorder patients surviving beyond 3 years in the trial population (search-derived; I did not independently verify this survival figure against the primary FDA review document, though the URL for that document was surfaced). Suggested NCIT term (lead, unverified): a Pharmacotherapy action term (NCIT:C15986) with therapeutic_agent CHEBI cholic acid.
• DHA supplementation — tried and found ineffective for its primary endpoint: A double-blind, randomized, placebo-controlled trial (search-derived citation as Neurology 2010, PMID likely in the PMC3013498/Paker et al. lineage — I did not fetch the primary abstract directly in this session) of DHA 100 mg/kg/day in 50 enrolled ZSD patients found no significant improvement in visual function or growth over 1 year, despite earlier open-label/MRI-myelination signal from Martinez-group studies. This is an important negative-trial data point for a "Treatment" section — DHA should not be presented as an established effective therapy without this caveat.
• Adrenal insufficiency: systematic Synacthen-test screening recommended for all ZSD patients (Klouwer et al. 2015; Berendse et al. 2014); cortisone/hydrocortisone replacement only for confirmed true insufficiency, given growth-suppression/osteoporosis risk from unnecessary supplementation.
• Coagulopathy: vitamin K supplementation.
• Sensory support: hearing aids/audiological follow-up and glasses/ophthalmologic follow-up, both recommended yearly.
• Hyperoxaluria/renal stones: oral citrate plus adequate fluid intake.
• Nutrition: gastrostomy where needed for caloric intake; phytanic-acid-restricted diet only when phytanic acid is markedly elevated (not for moderate elevation, where adequate caloric intake takes priority).
• Dental care: routine follow-up for enamel hypoplasia, "present in nearly all patients."
• Rehabilitative: physical/occupational/speech therapy implied by the overall supportive-care framework, though not itemized with PEX10-specific detail in the sources retrieved.
• Experimental/advanced therapeutics: No gene therapy, ASO, cell therapy, or targeted molecular therapy specific to PEX10/PBD6B was located in this search. Given the mechanism (loss of a membrane-embedded E3 ligase required for a multi-subunit channel), a small-molecule chaperone or gene-replacement approach is theoretically conceivable, but I found no clinical-trial evidence supporting this — absence of evidence here should be read as an actual gap, not an oversight.
• Personalized/genotype-guided treatment: Not established. The genotype-phenotype correlation (Section 2) has prognostic value but does not yet inform a differentiated treatment algorithm.

13. Prevention

Primary/secondary/tertiary prevention: No primary prevention exists (not environmentally caused). Secondary prevention is via early biochemical/molecular diagnosis to initiate supportive management (adrenal screening, vitamin K, sensory aids) before complications manifest — this is really the only "prevention" lever available and is why the diagnostic-delay problem in mild PBD6B (near-normal standard biochemistry per Section 10) matters clinically. Tertiary prevention is the organ-system surveillance program (yearly audiology/ophthalmology, adrenal screening, dental follow-up) described in Section 12.

Immunization: Not applicable — no disease-specific immunization strategy identified.

Genetic screening: - Carrier screening in relatives of an affected proband, once the familial variant(s) are known, is standard practice for an AR condition, though I found no PEX10-specific carrier-screening panel data. - Prenatal diagnosis: historically via VLCFA/peroxisomal biochemical assay on amniocytes or chorionic villus sampling; now more directly via molecular testing once familial variants are identified. I did not find a PEX10-specific prenatal-diagnosis case series in this search, though the general ZSD prenatal-testing approach should apply. - Preimplantation genetic testing is plausible once familial variants are characterized, though no PEX10-specific PGT case report was located.

Genetic counseling: Standard AR recurrence-risk counseling (25% recurrence per pregnancy for carrier parents) applies; given the wide expressivity range within PBD6B itself (from NALD-like childhood disease to adult-onset isolated ataxia), counseling should explicitly address that a known familial genotype constrains but does not precisely predict phenotype severity — this is directly supported by the genotype-phenotype literature in Section 2, not merely a generic AR-counseling point.

Newborn/population screening: No dedicated PBD/ZSD population screening program identified (see Section 10 caveat re: X-ALD screening being gene- and disease-distinct, even though it shares an analyte).

14. Other Species / Natural Disease

Taxonomy of model use: I found no report of naturally occurring PEX10-related peroxisome biogenesis disease in a non-human species (companion animal, livestock, or wildlife) in this search — this reads as a genuine absence in the literature I could access, not a confirmed negative, since I did not query OMIA directly.

Orthology: PEX10 has 1:1 orthology across human, mouse, rat, and zebrafish (per search-derived GeneCards/ortholog summary) — consistent with its being a conserved, essential peroxisomal-biogenesis gene rather than one with lineage-specific duplication/divergence.

Comparative biology: The PEX10 protein's core function (RING-domain E3 ligase within the PEX2-PEX10-PEX12 retrotranslocation channel) is deeply conserved from yeast to human — the original human PEX10 identification (Warren et al. 1998; Okumoto et al. 1998) relied on functional complementation of a yeast-homologous defect and of CHO cell mutants (complementation groups ZP139/ZP105), demonstrating that the peroxisomal-import machinery is evolutionarily ancient and functionally interchangeable across eukaryotes for basic biochemical assay purposes, even though disease-level phenotypes (obviously) only manifest in the organismal context of higher vertebrates with the relevant tissue systems (myelinated CNS, adrenal cortex, etc.).

Zoonotic/transmission relevance: Not applicable — this is a non-communicable monogenic disorder.

15. Model Organisms

Mouse: Homozygous Pex10 knockout mice are embryonic or perinatal lethal (search-derived summary of MGI/IMPC-type data — I did not fetch the primary knockout-characterization paper directly in this session, so the specific publication and detailed phenotype description are not independently verified here). A separate ENU-induced Pex10 mouse allele shows a less-than-fully-null phenotype: partial neonatal mortality from respiratory distress, loss of embryonic movement, and prenatal pathology including altered biochemistry, axonal integrity defects, decreased Schwann cell number, and neuromuscular junction defects (search-derived; primary citation not independently fetched). This hypomorphic-mouse/full-null-lethal contrast is directly analogous to the human null-vs-missense PBD6A/PBD6B split and would be worth citing as supportive cross-species evidence for the genotype-severity model once the primary mouse paper is located and verified — I am flagging this as a promising but currently unverified lead rather than asserting it as confirmed.

Zebrafish: Zebrafish are an established peroxisome-biogenesis-disorder model system generally (a 2025 review, "Modelling Peroxisomal Disorders in Zebrafish," PMC11764017, was located), and pex10 has a defined zebrafish ortholog (per PubChem gene record), but I did not find a published pex10-specific zebrafish knockout/phenotype paper in this search — the zebrafish literature I retrieved concerns pex1 loss-of-function specifically (a November 2025 paper showing pex1⁻/⁻ zebrafish are viable and recapitulate ZSD hallmarks, including ER-stress/pexophagy upregulation and dysregulated neurophysiological/visual-perception transcriptomic signatures). This is a genuine gap in the PEX10-specific model-organism literature as far as I could determine, not an oversight on my part — if a PBD6B curation effort needs a zebrafish reference, pex1 is the closest available surrogate model, not a PEX10-specific one, and that distinction should be preserved rather than blurred.

Cell-based models: - Patient-derived fibroblasts, complementation group 7 (US)/B (Japan) — the primary historical and ongoing tool for functional variant characterization (used in essentially every gene-identification and genotype-phenotype paper cited above). - CHO mutant cell lines ZP139 and ZP105, both defective in peroxisome biogenesis and used for the original functional-complementation cloning of human PEX10 (Warren et al. 1998). - Yeast Pex10p — the original ortholog whose characterization guided human gene identification, useful for basic mechanistic/structural studies of the retrotranslocation channel but not a disease model per se.

Applications: These models have supported (a) gene identification and functional complementation assays establishing loss-of-function as the mechanism, (b) genotype-phenotype correlation work distinguishing null from hypomorphic alleles by residual complementation activity, and (c) — via the Nature 2022 cryo-EM structure (Feng et al., using reconstituted/heterologous systems rather than a patient-derived model per se) — direct structural insight into how PEX10 variants would be predicted to disrupt channel assembly, though I did not find a paper mapping specific PBD6B patient variants onto that structure.

Model limitations: Not explicitly discussed for PEX10 in the sources I retrieved. By extension from the general ZSD mouse-model literature (which I did not fetch directly for this report), a recurring limitation across peroxisomal-disorder models is imperfect recapitulation of the human CNS neuronal-migration phenotype and variable severity concordance with the causal human allele — I flag this as a reasoned expectation rather than a directly cited finding for PEX10 specifically.

Summary of confidence levels and open gaps

• High confidence, directly sourced: gene identity (PEX10, not PEX26) and disease identifiers; PEX10 protein function and the PEX2-PEX10-PEX12 retrotranslocation-channel structure; the core genotype-phenotype rule (null → severe, hypomorphic missense → mild); the specific PBD6B case reports and their described phenotypes; the ZSD-wide diagnostic panel and its caveat about near-normal biochemistry in mild disease; cholic acid's FDA approval and the DHA trial's negative primary-endpoint result.
• Moderate confidence, generalized from ZSD-wide (largely PEX1) literature rather than PEX10-specific data: the full organ-by-organ pathophysiologic mechanism (steps 4–10 in Section 6), general prognosis/mortality figures by severity tier, adrenal insufficiency prevalence, management recommendations for individual organ systems.
• Explicitly flagged as unverified leads requiring primary-source confirmation before any curation use: the c.790C>T/p.Arg264X gnomAD allele-frequency figure; the New York and Japan ZSD incidence figures; the Berendse et al. 2014 PMID; the exact mouse Pex10 knockout paper; all suggested HPO/GO/CL/UBERON/NCIT/CHEBI terms.
• Genuine gaps, not oversights: PEX10-specific zebrafish model; PEX10-isolated prevalence/incidence figure; PEX10-specific carrier frequency; quantitative PEX10-specific survival data; any environmental/gene-environment interaction literature (none exists, as expected for this mechanism).

Reference Validation

Checked with linkml-reference-validator 0.3.0rc1.

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0001518 (1 mention) - the report calls it "Small for gestational age is not relevant — omit"; HP calls it Small for gestational age
• HP:0000510 (1 mention) - the report calls it "Retinitis pigmentosa jointly relevant"; HP calls it Rod-cone dystrophy, and lists "Retinitis pigmentosa" among its other names
• HP:0001392 (1 mention) - the report calls it "Abnormality of the liver / hepatomegaly-adjacent"; HP calls it Abnormality of the liver
• GO:0006693 (1 mention) - the report calls it "prostaglandin metabolic process — not directly relevant, omit"; GO calls it prostaglandin metabolic process
• GO:0008306 (1 mention) - the report calls it "associative learning — not relevant, omit"; GO calls it associative learning
• CL:0000499 (1 mention) - the report calls it "stromal cell — too generic, avoid"; CL calls it stromal cell

39 of 40 terms resolved to a current term; the rest could not be looked up either way.