Spastic Paraplegia 81 (SPG81): A Comprehensive Disease Characteristics Report

Disease: Spastic Paraplegia 81 (SPG81) OMIM: #618768 | MONDO: 0032905 | UMLS: C5394033 Causal gene: SELENOI (EPT1) | Inheritance: Autosomal recessive | Category: Mendelian

Summary

Spastic Paraplegia 81 (SPG81) is an ultra-rare, autosomal recessive complicated hereditary spastic paraplegia (HSP) caused by biallelic loss-of-function variants in SELENOI (also known as EPT1 or SELI). SELENOI encodes ethanolamine phosphotransferase 1, the enzyme that catalyzes the final step of the CDP-ethanolamine branch of the Kennedy pathway, converting CDP-ethanolamine and diacylglycerol (or alkyl-acylglycerol) into phosphatidylethanolamine (PE) and its ether-linked form plasmenyl-PE (a plasmalogen). These ethanolamine phospholipids are indispensable membrane constituents, and plasmenyl-PE in particular is critical for myelination and serves as a sacrificial antioxidant in oligodendrocytes.

Loss of SELENOI activity therefore produces a neurodevelopmental disorder characterized by infancy-onset, progressive lower-limb spasticity, delayed motor development with subsequent motor regression, impaired intellectual development, and hypomyelination with brain and cerebellar atrophy. Severely affected individuals additionally develop sensorineural deafness, cortical/ocular visual loss, seizures, microcephaly, and orofacial anomalies (bifid uvula/cleft palate). Mechanistically, a nervous-system–restricted Selenoi-deficient mouse recapitulates the human phenotype—hypomyelination, reactive gliosis, microcephaly, and motor deficits—driven by increased lipid peroxidation and impaired maturation of oligodendrocyte-lineage cells. The disease thus represents a disorder of ether-lipid/plasmalogen homeostasis affecting central nervous system myelination.

SPG81 is exceedingly rare: only about three definitive consanguineous families (from Oman, Israel, and India) have been reported since 2017, plus a fourth candidate family (Korea) carrying a homozygous missense variant of uncertain significance. There is no disease-specific or disease-modifying therapy; management is entirely supportive (antispasticity agents, physical/occupational/speech therapy, seizure control, and sensory/orthopedic support). SELENOI also has pleiotropic roles beyond the CNS—in T-cell activation and Th17 differentiation, adipocyte differentiation, tumorigenesis, embryogenesis, and liver physiology—and emerging data link SELENOI/PE dysregulation to motor-neuron degeneration and TDP-43 pathology in ALS, broadening the disease relevance of this pathway.

Key Findings

Finding 1 — SPG81 is caused by biallelic loss-of-function variants in SELENOI (EPT1), disrupting the Kennedy pathway

SPG81 arises from biallelic (homozygous) loss-of-function variants in SELENOI, the gene encoding ethanolamine phosphotransferase 1 (EPT1). The founding report by Ahmed et al. (2017, Brain) identified a homozygous SELENOI/EPT1 variant in a consanguineous family with complicated autosomal recessive HSP and demonstrated that the variant "dramatically reduces the enzymatic activity of EPT1, thereby hindering the final step in phosphatidylethanolamine synthesis." SELENOI catalyzes the third and final reaction of the CDP-ethanolamine branch of the Kennedy pathway (CDP-ethanolamine + diacylglycerol/alkyl-acylglycerol → PE / plasmanyl-PE).

• Disease identifiers: OMIM #618768; gene SELENOI (HGNC:30396; aliases EPT1, SELI); locus chromosome 2p23.3; NCBI Gene 85465; Ensembl ENSG00000112782; UniProt Q9C0D9.

PMID: 28052917: "associated with mutation in the ethanolaminephosphotransferase 1 (EPT1) gene (now known as SELENOI), responsible for the final step in Kennedy pathway forming phosphatidylethanolamine from CDP-ethanolamine."

PMID: 28052917: "the mutation defined dramatically reduces the enzymatic activity of EPT1, thereby hindering the final step in phosphatidylethanolamine synthesis."

PMID: 27645994: "SELENOI (selenoprotein I, SELI, EPT1)" — confirming gene nomenclature and synonyms.

This finding establishes the causal gene, its enzymatic role, and loss-of-function as the molecular disease mechanism.

Finding 2 — SELENOI-derived plasmenyl-PE is essential for myelination; deficiency causes hypomyelination, lipid peroxidation, and microcephaly

The central mechanistic insight is that SELENOI-derived plasmenyl-PE (a plasmalogen) is essential for myelination, and its deficiency produces the neuropathology of SPG81. Nunes et al. (2024) generated a nervous-system–restricted Selenoi-deficient mouse (necessary because constitutive knockout is embryonic lethal) that faithfully recapitulated HSP features. Brain lipid composition alterations "coincided with motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly," with "increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro." Plasmenyl-PE contains a vinyl-ether bond that "preferentially reacts with oxidants" and thus acts as a sacrificial antioxidant, protecting membranes from peroxidative damage.

PMID: 38582453: "motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly."

PMID: 38582453: "increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro."

PMID: 38582453: "a critical role for SELENOI-derived plasmenyl-PE in myelination that is of paramount importance for neurodevelopment."

PMID: 38582453: "characterized by a vinyl ether bond that preferentially reacts with oxidants, thus serves as a sacrificial antioxidant."

Complementary human/in-vitro work by Horibata et al. (2018) established that EPT1/SELENOI is critical for neural development and maintenance of plasmalogens. Together these define the cellular mechanism: oligodendrocyte dysfunction and oxidative membrane damage → hypomyelination → progressive neurodegeneration.

Finding 3 — SELENOI is a bifunctional selenoprotein with roles beyond the CNS

SELENOI is one of the 25 human selenoproteins and is unusual in being a bifunctional enzyme. Li et al. (2023) describe two distinct biochemical functions—"PE regulation and antioxidant potential"—conferred respectively by its N-terminal CDP-alcohol phosphotransferase domain and its C-terminal selenocysteine (Sec) residue. This dual functionality underlies its involvement in "neurological diseases (especially hereditary spastic paraplegia), T cell activation, tumorigenesis, and adipocyte differentiation." The essentiality of the gene is underscored by embryonic lethality of the constitutive knockout, meaning only partial (hypomorphic) loss of function is compatible with survival, consistent with SPG81 being caused by residual-activity alleles.

PMID: 36963501: "neurological diseases (especially hereditary spastic paraplegia), T cell activation, tumorigenesis, and adipocyte differentiation."

PMID: 36007576: "Deletion of SELENOI in mice is embryonic lethal."

PMID: 40107406: "how Selenoi loss-of-function affects embryogenesis, neurodevelopment, the immune system and liver physiology."

Finding 4 — Clinical phenotype: infancy-onset complicated HSP with spasticity, intellectual disability, and sensory/neuroimaging abnormalities

Across the reported families, SPG81 presents as an infancy-onset complicated HSP. Per OMIM #618768 / MONDO:0032905, it is an "autosomal recessive neurologic disorder with onset in infancy... delayed motor development, progressive spasticity... impaired intellectual development and speech delay," with additional features in some patients including bifid uvula, microcephaly, seizures, and variable ocular anomalies. The most severely affected patient reported had cortical visual loss, sensorineural deafness, and achievement of almost no developmental milestones.

Sarma et al. (2023) summarize the combined phenotypic spectrum: "sensorineural deafness, blindness, cleft palate, delayed motor development, regression of motor skills, impaired intellectual development, poor speech and language acquisition, spasticity, hyperreflexia, white matter abnormalities and cerebral and cerebellar atrophy." Horibata et al. (2018) described a patient with "severe complicated hereditary spastic paraplegia, sensorineural-deafness, blindness, and seizures. Neuroimaging revealed hypomyelination, followed by brain atrophy mainly in the cerebellum and brainstem."

PMID: 29500230: "severe complicated hereditary spastic paraplegia, sensorineural-deafness, blindness, and seizures. Neuroimaging revealed hypomyelination, followed by brain atrophy mainly in the cerebellum and brainstem."

PMID: 36942482: "sensorineural deafness, blindness, cleft palate, delayed motor development, regression of motor skills, impaired intellectual development, poor speech and language acquisition, spasticity, hyperreflexia, white matter abnormalities and cerebral and cerebellar atrophy."

Suggested HPO terms: Spastic paraplegia (HP:0001258), Lower limb spasticity (HP:0002061), Hyperreflexia (HP:0001347), Intellectual disability (HP:0001249), Motor delay (HP:0001270), Developmental regression (HP:0002376), Sensorineural hearing impairment (HP:0000407), Cortical visual impairment (HP:0100704), Seizure (HP:0001250), Microcephaly (HP:0000252), Cerebellar atrophy (HP:0001272), Cerebral atrophy (HP:0002059), Cerebral hypomyelination (HP:0006808), Bifid uvula (HP:0000193), Cleft palate (HP:0000175), Speech delay (HP:0000750).

Finding 5 — Variant spectrum: rare biallelic splice-disrupting/LOF SELENOI variants in consanguineous families

All definitive families are autosomal recessive with homozygous variants. Sarma et al. (2023) noted "only two families reported to date" at the time and identified "a homozygous, synonymous variant in the SELENOI gene (NM_033505.4:c.126G>A:p.(Lys42Lys))" that was found to "disrupt normal splicing and lead to skipping of exon 2, causing in-frame deletion of SELENOI N-terminal 23 amino acids [NM_033505.4:c.57_126del:p.(Tyr20_Lys42del)]." Horibata (2018) identified a novel exon-skipping mutation, and Ahmed (2017) identified a variant that dramatically reduces EPT1 activity. Disease-causing alleles are private/family-specific; SELENOI has ~101 ClinVar submissions dominated by VUS/benign population variants.

PMID: 36942482: "homozygous, synonymous variant in the SELENOI gene (NM_033505.4:c.126G>A:p.(Lys42Lys))."

PMID: 36942482: "disrupt normal splicing and lead to skipping of exon 2, causing in-frame deletion of SELENOI N-terminal 23 amino acids."

PMID: 36942482: "with only two families reported to date."

Finding 6 — Lipidomic biomarker signature: reduced polyunsaturated PE and plasmenyl-PE with compensatory shifts

Horibata et al. (2018) quantified phospholipids by LC-MS/MS in patient fibroblasts and EPT1-knockout HeLa cells, finding markedly reduced in-vitro EPT activity, decreased biosynthesis of ethanolamine glycerophospholipids, reduced polyunsaturated PE species (38:6, 38:4, 40:6, 40:5, 40:4), and significant decreases in most plasmenyl-PE species, while most plasmanyl-PC species increased (a compensatory shift). Ahmed et al. (2017) found in patient blood "alteration to levels of specific phosphatidylethanolamine fatty acyl species in patients," although "in blood EPT1 inactivity may be compensated for, in part, via alternate biochemical pathways"—explaining why blood PE is a poor diagnostic biomarker despite the enzymatic defect. A cellular (fibroblast) EPT activity assay and tissue lipidomics are the most informative biochemical readouts.

PMID: 28052917: "alteration to levels of specific phosphatidylethanolamine fatty acyl species in patients."

PMID: 28052917: "in blood EPT1 inactivity may be compensated for, in part, via alternate biochemical pathways."

Finding 7 — SELENOI-dependent ethanolamine phospholipid synthesis drives T-cell metabolic reprogramming and Th17 differentiation (immune pleiotropy)

Beyond the CNS, SELENOI has immunologic roles. Ma et al. (2021) showed that SELENOI knockout in mouse T cells led to "reduced de novo synthesis of PE and plasmenyl PE during activation and impaired proliferation," with reduced AMPK activation, ATP accumulation, and reduced GPI-anchor synthesis/attachment. Ma et al. (2022) demonstrated that SELENOI KO "skewed differentiation away from pathogenic Th17 cells" toward tolerogenic phenotypes (Foxp3+/IL-10+), and that T-cell-specific KO mice in the EAE autoimmune model showed "diminished clinical symptoms, reduced CNS pathology and decreased T cell infiltration." These immune roles are relevant for understanding the broader biology of the gene, though their contribution to the SPG81 neurologic phenotype is not established.

PMID: 33484950: "reduced de novo synthesis of PE and plasmenyl PE during activation and impaired proliferation."

PMID: 35916034: "skewed differentiation away from pathogenic Th17 cells."

PMID: 35916034: "diminished clinical symptoms, reduced CNS pathology and decreased T cell infiltration."

Finding 8 — Model organisms: constitutive KO embryonic lethal; nervous-system conditional KO recapitulates HSP; cellular models available

The mouse ortholog is Selenoi (Mus musculus, NCBI Taxon 10090). Constitutive/global knockout is embryonic lethal, so faithful modeling required conditional (nervous-system–restricted) knockout, which recapitulates SPG81 features. Cellular models include patient-derived skin fibroblasts and EPT1-KO HeLa cells, both reproducing the lipid defect.

PMID: 38582453: "developed a mouse model of nervous system-restricted SELENOI deficiency that circumvents embryonic lethality caused by constitutive deletion and recapitulates phenotypic features of hereditary spastic paraplegia."

PMID: 36007576: "Deletion of SELENOI in mice is embryonic lethal."

PMID: 40107406: "global and conditional knockout (KO) of the Selenoi gene in mice."

Finding 9 — Epidemiology, prognosis, and management

SPG81 is ultra-rare: fewer than ~10 patients from 3 consanguineous families (Oman, Israel, India) have been published since 2017; prevalence/incidence are not formally estimated (Orphanet lists no point prevalence). Inheritance is autosomal recessive; both sexes are affected; consanguinity is the principal risk factor; there is no known founder allele, and carrier frequency for pathogenic alleles is presumably very low (SELENOI LOF is depleted in gnomAD). Prognosis is poor: infancy onset, progressive course with motor regression, and severe neurodevelopmental disability; the severe end of the spectrum features near-absent developmental milestones, blindness, and deafness. No cure or disease-modifying therapy exists; management is supportive/symptomatic (antispasticity agents such as baclofen/tizanidine, physical/occupational/speech therapy, antiepileptics, sensory aids, nutritional and orthopedic support). Genetic counseling, carrier testing, and prenatal/preimplantation genetic testing are indicated for at-risk consanguineous families once the familial variant is known.

PMID: 36942482: "recently identified, rare autosomal recessive disease, caused by biallelic pathogenic variants in the SELENOI gene."

PMID: 29500230: "severe complicated hereditary spastic paraplegia, sensorineural-deafness, blindness, and seizures."

Finding 10 — Fourth candidate family expands variant spectrum to a homozygous missense VUS (p.Pro266Leu)

Lee et al. (2026, Korea) reported a consanguineous family of six siblings; the index patient and a younger brother carried a homozygous SELENOI c.797C>T (p.Pro266Leu) variant of uncertain significance, interpreted in the context of an SPG81-like phenotype (significant lower-limb weakness, spasticity, developmental delay). Notably, other siblings' phenotypes were explained by different genes (LAMA1 p.Gln1527Ter → Poretti-Boltshauser syndrome; a de novo SATB2 VUS), illustrating intrafamilial genetic heterogeneity. This is the first reported homozygous SELENOI missense candidate variant, contrasting with the splice-affecting/in-frame-deletion alleles of the three prior definitive families.

PMID: 42446524: "We report a family of six siblings born to asymptomatic consanguineous parents, in which three siblings exhibited overlapping spastic paraplegia phenotypes with developmental delay."

Finding 11 — SELENOI/PE dysregulation links to motor-neuron degeneration and TDP-43 pathology in ALS

Isik et al. (2025) found that in human ALS brain, "PE levels were significantly decreased in the disease-affected motor cortex of ALS compared to controls and were inversely associated with disease duration," while PE was unaltered in the disease-unaffected cerebellum. "SELENOI expression was dysregulated only in the motor cortex," the SELENOI–TDP-43 correlation was lost, and "knockdown of SELENOI expression in neuronal cells caused an upregulation of TDP-43 expression." The authors explicitly note that "SELENOI is important in motor neuron development and function, as demonstrated in hereditary spastic paraplegia," linking the SPG81 pathway to broader motor-neuron disease.

PMID: 41002422: "PE levels were significantly decreased in the disease-affected motor cortex of ALS compared to controls and were inversely associated with disease duration."

PMID: 41002422: "SELENOI is important in motor neuron development and function, as demonstrated in hereditary spastic paraplegia."

Mechanistic Model / Interpretation

SPG81 is fundamentally a disorder of ether-lipid (plasmalogen) homeostasis affecting CNS myelination. The causal chain runs from a genetic defect in a single enzymatic step to a progressive neurodevelopmental/neurodegenerative phenotype:

Biallelic LOF SELENOI (EPT1)  [chr 2p23.3]
  │
  ▼
Reduced ethanolamine phosphotransferase activity
(final step of CDP-ethanolamine / Kennedy pathway)
  │
  ▼
↓ Phosphatidylethanolamine (PE)  &  ↓↓ plasmenyl-PE (plasmalogen)
   (compensatory ↑ plasmanyl-PC in some tissues)
  │
  ├──────────────► Loss of "sacrificial antioxidant" (vinyl-ether bond)
  │                          │
  ▼                          ▼
Impaired oligodendrocyte      ↑ Lipid peroxidation in
maturation                    oligodendrocyte-lineage cells
  │                          │
  └──────────┬───────────────┘
     ▼
HYPOMYELINATION + reactive gliosis + microcephaly
     │
     ▼
   Progressive spasticity, motor regression, intellectual
   disability, sensorineural deafness, visual loss, seizures,
   cerebral/cerebellar atrophy

Upstream vs downstream: The upstream trigger is the enzymatic deficiency and consequent depletion of ethanolamine phospholipids (especially plasmenyl-PE). Downstream consequences are oligodendrocyte-lineage lipid peroxidation and maturation failure, producing hypomyelination and, over time, neurodegeneration/atrophy.

Cell types and processes involved: Oligodendrocytes/oligodendrocyte precursor cells (CL:0000128 oligodendrocyte; CL:0002453 oligodendrocyte precursor cell) are the key effector cells; upper motor neurons and corticospinal tract axons (long descending tracts) manifest the classic HSP length-dependent "dying-back" degeneration. Suggested GO terms: phosphatidylethanolamine biosynthetic process (GO:0006646), CDP-ethanolamine pathway (GO:0006657), ether lipid biosynthetic process (GO:0008611), myelination (GO:0042552), oligodendrocyte differentiation (GO:0048709), response to oxidative stress (GO:0006979), ethanolamine phosphotransferase activity (GO:0004307). Cellular components: endoplasmic reticulum membrane (GO:0005789), myelin sheath (GO:0043209).

Anatomical structures (UBERON): brain (UBERON:0000955), cerebellum (UBERON:0002037), brainstem (UBERON:0002298), cerebral white matter (UBERON:0002316), corticospinal tract (UBERON:0005425), spinal cord (UBERON:0002240). Body system: central nervous system (UBERON:0001017). Lateralization is bilateral and symmetric, as typical of HSP.

CHEBI entities: phosphatidylethanolamine (CHEBI:16038), plasmenyl-ethanolamine/plasmalogen (CHEBI:52590), CDP-ethanolamine (CHEBI:57876), selenocysteine (CHEBI:16633).

Evidence Base

Coherence of evidence: Human genetic/clinical reports (28052917, 29500230, 36942482, 42446524) converge on biallelic SELENOI LOF causing complicated HSP. The mouse conditional-KO study (38582453) provides the definitive mechanistic bridge—directly demonstrating that plasmenyl-PE loss causes hypomyelination via oligodendrocyte lipid peroxidation—and no study contradicts this model. The ALS study (41002422) and immune studies (33484950, 35916034) extend the pathway's relevance without challenging the core SPG81 mechanism.

Section-by-Section Data Compilation

1. Disease Information

Complicated autosomal recessive HSP with infancy onset. Identifiers: OMIM #618768; MONDO:0032905; UMLS C5394033; gene SELENOI (HGNC:30396). Synonyms: SPG81; spastic paraplegia 81, autosomal recessive; SELENOI/EPT1-related HSP. Source type: aggregated disease-level resources (OMIM, Orphanet) plus individual case reports; no EHR/registry data.

2. Etiology

Causal factor: genetic (biallelic LOF SELENOI). Genetic risk factor: homozygous pathogenic SELENOI alleles. Environmental risk factor: none identified; consanguinity is the dominant risk factor (all definitive families are consanguineous). Protective factors: none characterized. Gene–environment interactions: none documented. It is a monogenic Mendelian disorder.

3. Phenotypes

See Finding 4 and HPO term list. Onset: infancy (congenital/pediatric). Severity: variable but generally severe; progression: progressive with motor regression. Core features (spasticity, hyperreflexia, motor delay, intellectual disability) appear consistent across families; sensory (deafness, blindness), seizures, microcephaly, and orofacial anomalies are variable. Quality of life is severely impacted, with loss of ambulation and profound developmental disability at the severe end.

4. Genetic/Molecular Information

Causal gene: SELENOI (EPT1), 2p23.3, NM_033505.4. Variant types: splice-disrupting synonymous (c.126G>A → exon 2 skipping → p.Tyr20_Lys42del), exon-skipping, activity-reducing alleles; plus a candidate missense (c.797C>T, p.Pro266Leu, VUS). Classification: pathogenic/likely pathogenic in definitive families; VUS for the missense candidate. Origin: germline. Functional consequence: loss of function (reduced enzyme activity). Allele frequency: private/family-specific; LOF depleted in gnomAD. Modifier/epigenetic/chromosomal: none reported.

5. Environmental Information

No environmental, lifestyle, or infectious contributors. Purely genetic.

6. Mechanism / Pathophysiology

See Mechanistic Model. Pathway: CDP-ethanolamine branch of the Kennedy pathway (KEGG glycerophospholipid metabolism). Cellular processes: oligodendrocyte maturation failure, lipid peroxidation/oxidative stress, myelination defect. Protein dysfunction: loss of enzyme activity. Metabolic changes: ↓PE, ↓plasmenyl-PE. Immune involvement: pathway-level (T-cell PE synthesis, Th17) but not part of the SPG81 clinical picture. Transcriptomic/proteomic profiling of patient CNS tissue is not available.

7. Anatomical Structures Affected

See table in Mechanistic Model. Primary: CNS white matter/myelin, corticospinal tracts, cerebellum, brainstem. Secondary: sensory systems (auditory, visual). Bilateral, symmetric.

8. Temporal Development

Onset: infancy, insidious/chronic. Course: progressive with motor regression; chronic lifelong. No remission. Critical period likely the early postnatal myelination window.

9. Inheritance and Population

Autosomal recessive; consanguinity-driven; both sexes; ultra-rare (~3 definitive families, <10 patients); no founder effect; carrier frequency very low; penetrance appears complete in reported homozygotes; expressivity variable (severity ranges from moderate to profound).

10. Diagnostics

Genetic testing is definitive: WES/WGS or HSP gene panels including SELENOI; single-gene/familial variant testing once identified. Careful splice-variant interpretation is needed (synonymous variants can be pathogenic via splicing). Biochemical: fibroblast EPT activity assay and lipidomics (↓plasmenyl-PE) are supportive; blood PE is unreliable due to compensation. Imaging: MRI shows hypomyelination, cerebral/cerebellar atrophy. Differential diagnosis: other complicated HSPs, hypomyelinating leukodystrophies, peroxisomal plasmalogen-biosynthesis disorders (rhizomelic chondrodysplasia punctata), and other Kennedy-pathway/phospholipid disorders.

11. Outcome/Prognosis

Poor; progressive disability, motor regression, severe neurodevelopmental impairment; severe cases with blindness, deafness, near-absent milestones. No formal survival data. No disease-specific prognostic biomarkers established; earlier/more severe presentation and severe hypomyelination suggest worse outcome.

12. Treatment

No disease-specific/disease-modifying therapy. Supportive: antispasticity agents (baclofen, tizanidine, botulinum toxin), physical/occupational/speech therapy, antiepileptic drugs, hearing/visual aids, nutritional and orthopedic support. No pharmacogenomic, gene, cell, or RNA therapy exists. Theoretical/experimental directions (plasmalogen replacement, antioxidants) are unproven for SPG81. Suggested NCIT terms: Baclofen (C376), Physical Therapy (C15368), Occupational Therapy (C15218), Supportive Care (C15417).

13. Prevention

Primary prevention via genetic counseling for consanguineous families, carrier testing, and prenatal/preimplantation genetic testing once the familial variant is known. No population screening (ultra-rare). No immunization or behavioral prevention applicable.

14. Other Species / Natural Disease

Mouse ortholog Selenoi (NCBI Taxon 10090). No naturally occurring animal disease reported (no OMIA entry). Gene and pathway are evolutionarily conserved. Not zoonotic.

15. Model Organisms

Mouse: constitutive KO embryonic lethal; nervous-system–restricted conditional KO recapitulates HSP (hypomyelination, gliosis, microcephaly, motor deficits); T-cell-specific conditional KO for immune studies. Cellular: patient skin fibroblasts; EPT1-KO HeLa cells reproduce the lipid defect. Phenotype recapitulation of the neural conditional KO is high. Limitation: no model captures the full multi-sensory human phenotype; global-KO lethality prevents whole-organism study.

Limitations and Knowledge Gaps

1. Extreme rarity: Only ~3 definitive families (plus one candidate) exist, limiting genotype–phenotype correlation, penetrance/expressivity estimates, and natural-history data. No prevalence/incidence figures exist.
2. Missense candidate uncertain: The p.Pro266Leu allele (Lee 2026) remains a VUS; functional validation is lacking, and the family showed genetic heterogeneity, so SPG81 causation is not confirmed for that variant.
3. Biomarker limitations: Blood PE is compensated and unreliable; the most sensitive biochemical assays require patient fibroblasts, limiting non-invasive diagnosis.
4. No human CNS omics: Transcriptomic/proteomic/metabolomic profiling of patient brain tissue is unavailable; mechanistic detail derives largely from mouse and cell models.
5. No therapies tested: No preclinical or clinical therapeutic studies specific to SPG81; whether plasmalogen supplementation or antioxidants could help is untested.
6. Citation verification caveats: A few supporting snippets were flagged during curation (e.g., portions of PMID 29500230, 35916034 quotes); the core claims are corroborated across multiple sources, but exact-quote fidelity should be re-verified before database ingestion.

Proposed Follow-up Experiments / Actions

1. Functional validation of p.Pro266Leu: Express the missense variant in an EPT1-null cell system and measure ethanolamine phosphotransferase activity and plasmenyl-PE synthesis to resolve its VUS status.
2. International case aggregation: Use GeneMatcher/Matchmaker Exchange to identify additional families, enabling genotype–phenotype correlation and natural-history characterization.
3. Non-invasive biomarker development: Systematic plasma/CSF lipidomics (plasmalogen panels) across patients and carriers to establish a reliable diagnostic/monitoring biomarker.
4. Therapeutic proof-of-concept in the conditional-KO mouse: Test plasmalogen/ether-lipid precursor supplementation (e.g., alkyl-glycerols) and lipophilic antioxidants for rescue of hypomyelination and motor deficits.
5. iPSC-derived oligodendrocyte/organoid models: Generate patient iPSC-derived oligodendrocytes and cerebral organoids to study human oligodendrocyte maturation, lipid peroxidation, and candidate therapeutics.
6. Cross-disease pathway study: Given the ALS link (PMID 41002422), examine whether modulating SELENOI/PE affects TDP-43 handling in motor neurons—potentially uncovering shared therapeutic targets across SPG81 and motor-neuron disease.

Report compiled from 11 confirmed findings and 14 reviewed papers over a 5-iteration autonomous investigation. Evidence types span human clinical/genetic reports, model-organism (mouse conditional KO) studies, in-vitro/cellular assays, and computational/transcriptomic analyses.

Artifacts

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Reference Validation

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All extracted references resolved successfully.

Term Validation

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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:

• UBERON:0002316 (2 mentions) - the report calls it "Cerebral/cerebellar white matter (myelin)"; UBERON calls it white matter, and lists "neuronal white matter" among its other names

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