| Domain | PEX16-specific finding | Evidence strength/type | Suggested ontology identifiers |
|---|---|---|---|
| Identity | Mild **PEX16 deficiency / peroxisome biogenesis disorder 8B (PBD8B)** is the non-neonatal, milder end of the PEX16-related Zellweger-spectrum continuum. **OMIM 614877**; PEX16-related severe PBD8A/Zellweger phenotype is OMIM 614876. (pqac-00000003) | Authoritative disease classification; human disease literature | OMIM:614877; MONDO:0013943 **user supplied—verify against current MONDO release**; MeSH/Orphanet/ICD exact mappings: verify |
| Causal gene | **PEX16**, encoding peroxisomal biogenesis factor 16; gene **OMIM 603360**. (pqac-00000003) | Curated gene–disease and functional evidence | HGNC:8857 **verify current HGNC record**; OMIM:603360; GO:0005777 (peroxisome) |
| Inheritance | Biallelic germline PEX16 variants cause disease through an **autosomal-recessive** mechanism; the reported mild adult had compound-heterozygous variants inherited from the parents. (pqac-00000000, pqac-00000001) | Strong human segregation plus functional evidence | HP:0000007 (autosomal recessive inheritance) |
| Cardinal phenotype | A slowly progressive **spastic-ataxia/leukodystrophy phenotype** may begin in childhood with toe walking and falls and evolve into marked lower-limb spasticity, cerebellar ataxia/dysarthria, tremor, dystonia, white-matter abnormalities, and wheelchair dependence; cognition may remain substantially preserved. (pqac-00000000, pqac-00000001) | PEX16-specific human case evidence; very small sample | HP:0001257 (spasticity); HP:0001251 (ataxia); HP:0001260 (dysarthria); HP:0001332 (dystonia); HP:0002415 (leukodystrophy); HP:0002352 (white-matter abnormality) |
| Other possible manifestations | Across PEX16-related disease, reported ocular findings include cataract, optic atrophy, and abnormal retinal pigmentation; atypical cases require surveillance for hearing, vision, liver, adrenal, renal, skeletal, and neurologic complications. (pqac-00000003, pqac-00000006) | PEX16 ocular summary plus broader ZSD natural-history protocol; frequencies unknown | HP:0000518 (cataract); HP:0000648 (optic atrophy); HP:0007703 (abnormal retinal pigmentation); additional exact terms: verify |
| Biochemical caveat | Plasma VLCFAs may be **normal or only mildly abnormal** in mild PEX16 disease; normal VLCFAs therefore do not exclude PBD8B. Broader testing includes C26:0/C26:1 and C24:0/C22:0 and C26:0/C22:0 ratios, phytanic/pristanic acids, erythrocyte plasmalogens, pipecolic acid, and DHCA/THCA. (pqac-00000000, pqac-00000008) | Direct PEX16 case observation plus expert diagnostic review | HP:0032312 (abnormal very-long-chain fatty-acid level)—exact applicability may be absent in mild disease; CHEBI identifiers for individual analytes: verify |
| Molecular mechanism | PEX16 is an integral peroxisomal membrane biogenesis factor and PEX3 docking component. Biallelic dysfunction disrupts early membrane assembly and protein trafficking, producing fewer, enlarged, or absent functional peroxisomes and downstream impairment of VLCFA/branched-chain fatty-acid oxidation, ether-lipid synthesis, bile-acid metabolism, and redox homeostasis. (pqac-00000001, pqac-00000017, pqac-00000018) | Human patient-cell evidence supported by fly and mouse functional studies; some downstream tissue links remain inferred | GO:0007031 (peroxisome organization); GO:0016558 (protein import into peroxisome matrix); GO:0033540 (fatty-acid beta-oxidation using acyl-CoA oxidase); GO:0005777 (peroxisome); GO:0005783 (endoplasmic reticulum) |
| Diagnostic approach | Confirm with biallelic PEX16 variants using a peroxisomal-disorder/leukodystrophy panel, exome, or genome sequencing, with deletion/duplication analysis as needed. Pair genetics with multianalyte peroxisomal biochemistry and, when results are equivocal, cultured-fibroblast assays of catalase localization, peroxisome number/morphology, VLCFA oxidation, and plasmalogen synthesis. (pqac-00000000, pqac-00000008, pqac-00000009) | Expert-review/technical-standard approach plus PEX16 patient-cell validation | NCIT:C15709 (genetic testing); NCIT:C101295 (whole-exome sequencing)—verify current NCIT labels; LOINC assay identifiers: laboratory-specific/verify |
| Treatment status | No approved PEX16-specific disease-modifying treatment is established. Management is multidisciplinary and supportive: physical/occupational/speech therapy, mobility and spasticity management, hearing/vision support, nutritional or gastrostomy support when needed, seizure treatment, and surveillance of liver, adrenal, renal, bone, dental, and neurologic status. (pqac-00000009, pqac-00000011) | Expert consensus extrapolated from Zellweger-spectrum care; no PEX16-specific response rates | NCIT:C15329 (supportive care); NCIT intervention identifiers for individual therapies: verify |
| Prognosis | PBD8B can permit survival into adulthood but is generally chronic and neurologically progressive; one individual progressed from childhood gait disturbance to wheelchair dependence while retaining near-normal cognition at age 41. Gene-specific survival rates, life expectancy, and validated prognostic biomarkers are unavailable. (pqac-00000000, pqac-00000001) | Direct longitudinal history from one adult plus major evidence gaps | HP:0003676 (progressive disorder); survival/prognosis ontology mapping: verify |
| Model evidence | Pex16-null Drosophila show reduced peroxisomes, locomotor impairment, bang sensitivity, and markedly shortened lifespan; human reference PEX16 rescues organelle and behavioral phenotypes, whereas variant rescue distinguishes severe from hypomorphic alleles. Hepatocyte-specific Pex16-knockout mice lack hepatic peroxisomes and show enlarged liver, hepatocyte proliferation, altered serum lipids/bile acids, and resistance to diet-induced steatosis. (pqac-00000014, pqac-00000015, pqac-00000018) | Strong experimental loss-of-function/rescue evidence; organismal models do not fully reproduce mild human neurologic disease | NCBI Taxon:7227 (Drosophila melanogaster); NCBI Taxon:10090 (Mus musculus); CL:0000182 (hepatocyte) |
| Current research/registries | The recruiting longitudinal PBD natural-history study **NCT01668186** targets 244 participants with annual multisystem, imaging, biochemical, and genotype–phenotype follow-up; the recruiting ZSD retinopathy study **NCT06190626** targets 30 participants. Neither provides PEX16-specific outcomes yet. (pqac-00000006, pqac-00000013) | Active observational research; no efficacy inference | ClinicalTrials.gov:NCT01668186; ClinicalTrials.gov:NCT06190626 |
| Key evidence gaps | No reliable PEX16/PBD8B prevalence, incidence, penetrance estimate, sex ratio, carrier frequency, founder effect, protective allele, environmental modifier, validated quality-of-life measure, genotype-specific treatment response, natural veterinary counterpart, or proven epigenomic/single-cell/spatial signature has been established. | Absence of adequate PEX16-specific cohorts; do not infer from aggregate ZSD data | Ontology mappings unavailable or not applicable; mark as **unknown** rather than negative where systematic study is lacking |


*Table: Compact knowledge-base summary of mild PEX16 deficiency/PBD8B, integrating human, cellular, animal-model, diagnostic, and clinical-management evidence. Unverified or unavailable ontology mappings and major evidence gaps are explicitly identified.*