Hereditary Spastic Paraplegia 49 (SPG49) / TECPR2-Related Disorder — Comprehensive Research Report

1. Disease Information

Overview. Hereditary Spastic Paraplegia 49 (SPG49) is an ultra-rare, autosomal recessive, complex neurodevelopmental and neurodegenerative disorder caused by biallelic loss-of-function variants in TECPR2 (tectonin beta-propeller repeat containing 2), a gene on chromosome 14q32.31 that regulates autophagosome–lysosome fusion and, separately, COPII-dependent ER export. It was first described in 2012 in five Bukharian Jewish patients as an autosomal-recessive complicated hereditary spastic paraplegia (Oz-Levi et al. 2012, Am J Hum Genet, PMID:23176824). Subsequent characterization of larger cohorts showed the phenotype is broader than isolated spasticity — a multisystem sensory, autonomic, and developmental disorder — leading to reclassification as Hereditary Sensory and Autonomic Neuropathy type IX (HSAN9), sometimes written "TECPR2-related HSAN with intellectual disability." Both names (SPG49 and HSAN9) are used interchangeably in the literature and databases for the same gene-disease pair.

Key identifiers: - OMIM disease: #615031, Spastic Paraplegia 49, Autosomal Recessive; OMIM gene: 615000, TECPR2 (OMIM) - MONDO: MONDO:0014016 - Orphanet: ORPHA:320385, Hereditary sensory and autonomic neuropathy due to TECPR2 mutation (Orphanet) - ICD-10: G11.4 (hereditary spastic paraplegia); relatedly G60.- for hereditary/idiopathic neuropathy - Gene: TECPR2; HGNC:19957 (note: some secondary sources list HGNC:30346 — HGNC:19957 is the authoritative current ID); UniProt O15040; NCBI Gene ID 9895 - GeneReviews: "TECPR2-Related Hereditary Sensory and Autonomic Neuropathy with Intellectual Disability" (NBK584409) - MedGen: C3542549

Synonyms/alternative names: Spastic paraplegia 49, autosomal recessive; SPG49; Hereditary sensory and autonomic neuropathy type IX (HSAN9); HSAN9 with developmental delay; TECPR2-related neurodevelopmental disorder; complicated autosomal-recessive HSP with TECPR2 mutation.

Source of information. Nearly all clinical characterization derives from aggregated disease-level resources — case series and cohort reports pooled by international collaborators — rather than large EHR datasets, reflecting the disorder's ultra-rarity (>30–40 reported individuals worldwide as of the most recent cohort study).

2. Etiology

Disease causal factor: SPG49/HSAN9 is a purely monogenic, autosomal-recessive Mendelian disorder. There is no described environmental, infectious, or multifactorial contribution to primary disease causation — all reported cases carry biallelic pathogenic TECPR2 variants.

Genetic risk factors: - Causal variants: biallelic (homozygous or compound heterozygous) loss-of-function variants in TECPR2 — nonsense, frameshift, canonical splice-site, and a smaller fraction of missense variants clustered in the N-terminal WD/beta-propeller and C-terminal TECPR-repeat domains (Neuser et al. 2021, Hum Mutat, PMID:33847017). - Population founder variants (act as genetic risk factors in specific ancestries — see §9): - Bukharian Jewish: c.3416delT, p.Leu1139ArgfsTer75 (original founder allele; PMID:23176824) - Ashkenazi Jewish: c.1319delT, p.Leu440ArgfsTer19 (PMID:26542466, Heimer et al. 2016) - Heterozygous (monoallelic) TECPR2 variants have separately been reported to cause a distinct, milder, presumably dominant-negative or haploinsufficiency phenotype of progressive cerebellar atrophy with global developmental delay — genetically and mechanistically distinct from the classic biallelic HSAN9/SPG49 syndrome (Ramsey et al. 2022, Mol Genet Genomic Med, PMID:34994087). - No modifier genes have been formally established, though phenotypic variability among individuals homozygous for the same founder allele is documented.

Environmental risk factors: None identified as causal; secondary environmental risk factors (e.g., aspiration risk from dysphagia, hypoventilation exacerbated by sedatives) act on disease complications rather than disease initiation (see §12, drugs to avoid).

Protective factors: None described in the literature; this is a fully penetrant recessive loss-of-function disorder with no known protective alleles or environmental modifiers.

Gene-environment interactions: Not applicable/not reported — the disorder is monogenic with no established GxE interaction.

3. Phenotypes

Frequencies below are drawn from the largest published cohort (28 individuals: 17 new + 11 previously reported; Neuser et al. 2021, PMID:33847017) and GeneReviews (NBK584409).

Developmental/cognitive: - Global developmental delay / intellectual disability — 100% (universal; often severe, many nonverbal) — HP:0001263 (Developmental delay), HP:0001249 (Intellectual disability) - Speech delay, frequently absent expressive speech — HP:0000750 (Delayed speech and language development) - Behavioral abnormalities (autism-spectrum features, stereotypies) — ~62.5% — HP:0000708 (Behavioral abnormality)

Neurological/motor: - Muscular hypotonia (infantile onset) — 100% — HP:0001252 (Hypotonia) - Gait ataxia — 100% — HP:0002066 (Gait ataxia) - Spastic paraparesis/lower-limb spasticity (emerging later, in childhood/adolescence) — HP:0001258 (Spasticity), HP:0007256 (Progressive spasticity) - Lower-limb hypo/areflexia — ~85% — HP:0002522 (Areflexia) - Dysarthria — ~87.5% — HP:0001260 (Dysarthria) - Decreased pain and temperature sensitivity — ~50% — HP:0002829 (Impaired pain sensation) - Dystonia and Parkinsonian features can emerge in late childhood/adolescence — HP:0001332 (Dystonia)

Autonomic: - Central hypoventilation/apnea (nocturnal) — ~82% — HP:0004926 (Central sleep apnea) - Gastroesophageal reflux disease — ~94% — HP:0002020 (Gastroesophageal reflux) - Dysphagia — ~53%; recurrent aspiration — ~71% — HP:0002015 (Dysphagia), HP:0002835 (Recurrent aspiration pneumonia) - Gastrointestinal dysmotility — HP:0002579 (Intestinal pseudo-obstruction/dysmotility spectrum)

Dysmorphic/growth: - Mild brachycephalic microcephaly — ~59% — HP:0000252 (Microcephaly), HP:0000248 (Brachycephaly) - Short stature — ~58% — HP:0004322 - Short/broad neck, low anterior hairline, retrocollis posture — ~52% — HP:0000470 (Short neck) - Coarse facial features — HP:0000280

Onset/severity/progression characteristics: - Age of onset: infancy (motor delay, hypotonia typically noted in the first year) - Severity: variable but generally severe; most patients never achieve independent ambulation or full expressive speech - Progression: progressive/neurodegenerative course — possible regression in the second decade with loss of previously acquired ambulation; not static like cerebral palsy - Course pattern: chronic progressive, punctuated by acute respiratory/aspiration crises

Quality-of-life impact: Severe — near-universal loss of independent mobility and communication, lifelong dependence for feeding (often gastrostomy) and respiratory support (noninvasive ventilation), and premature mortality (see §11). No formal EQ-5D/SF-36 studies exist for this ultra-rare disorder; QoL data are qualitative, from natural-history/clinical cohort descriptions.

4. Genetic/Molecular Information

Causal gene: TECPR2 (Tectonin Beta-Propeller Repeat Containing 2), chr14q32.31; OMIM *615000; HGNC:19957; NCBI Gene 9895; Ensembl ENSG00000122986; UniProt O15040 (GeneCards; UniProt).

Variant classes (ClinVar/GeneReviews): predominantly frameshift, nonsense, and canonical splice-site variants producing a truncated/degraded protein (loss-of-function mechanism); a substantial minority (~half of reported alleles) are missense variants, clustering in the N-terminal WD/beta-propeller domain and the C-terminal six-TECPR-repeat domain — but ACMG/AMP classification of these missense alleles remains challenging due to limited functional-assay throughput (PMID:33847017). Sequence analysis (panel/exome/genome) detects essentially all reported pathogenic variants; larger structural deletions/duplications are rare but should be tested if sequencing is negative.

Representative pathogenic variants: - c.3416delT, p.Leu1139ArgfsTer75 — Bukharian Jewish founder (PMID:23176824) - c.1319delT, p.Leu440ArgfsTer19 — Ashkenazi Jewish founder (PMID:26542466), later used as the target of a splice-modulating antisense oligonucleotide (see §12) - c.2578+2T>C (splice donor variant) — reported in ClinVar for HSP49 - c.2599G>T, p.Glu867Ter — nonsense variant (ClinVar) - Additional missense and truncating alleles reported in a Chinese patient (PMID:35130874) and other worldwide cases, confirming genetic heterogeneity beyond the two founder populations.

Allele frequency in population databases: TECPR2 is a loss-of-function-intolerant gene in gnomAD (constrained; specific LOEUF/pLI value not independently confirmed in this search but the gene shows depletion of predicted-LoF variants consistent with recessive-disease constraint). Carrier frequency estimates from founder populations: ~1.33% in Bukharian Jews, ≥0.65% in Ashkenazi Jews (GeneReviews NBK584409). Estimated disease incidence ranges from ~1:22,500 in the Bukharian Jewish population to ~1:5,961,640 in the general population.

Somatic vs. germline: All reported variants are germline; there is no somatic/mosaic or cancer association.

Functional consequence: Loss of function predominates — nonsense/frameshift alleles cause nonsense-mediated decay or produce a truncated, non-functional protein; missense alleles are hypothesized to destabilize the WD/beta-propeller or TECPR domains. No gain-of-function or dominant-negative mechanism has been established for the classic biallelic disease, though the separately-described heterozygous cerebellar-atrophy phenotype (PMID:34994087) raises the possibility of haploinsufficiency or dominant-negative effects for a subset of heterozygous variants.

Modifier genes: None formally established.

Epigenetic information: No disease-specific DNA methylation, histone modification, or chromatin studies have been reported for TECPR2-related disease.

Chromosomal abnormalities: Not a contiguous-gene/CNV disorder in the classic sense; disease is driven by point mutations/small indels within TECPR2, not large chromosomal rearrangements (though large deletion/duplication testing is part of the standard diagnostic algorithm when sequencing is uninformative).

5. Environmental Information

No environmental toxins, occupational exposures, radiation, or lifestyle factors are implicated in causing SPG49/HSAN9 — it is a fully penetrant monogenic recessive disorder. No infectious triggers or pathogens are causally implicated (though recurrent respiratory infections/pneumonia are a major complication, not a cause, driven by aspiration secondary to dysphagia and hypotonia). No CTD/TOXNET or CDC/WHO environmental-exposure signal was identified for this gene-disease pair.

6. Mechanism / Pathophysiology

Core molecular lesion — autophagosome–lysosome fusion defect. TECPR2 is a large multidomain protein: an N-terminal WD/beta-propeller domain, a middle unstructured region, and a C-terminal domain of six TECPR repeats followed by an LC3-interacting region (LIR) motif. TECPR2 was identified as a human ATG8-family (LC3) interactor and positive regulator of autophagy, functioning specifically in targeting of autophagosomes to lysosomes via its C-terminal TECPR domain (UniProt O15040; PMID:23176824). Loss of TECPR2 causes decreased levels of autophagy markers SQSTM1/p62 and lipidated LC3-II in patient fibroblasts, and — in mouse and dog models — progressive, age-dependent accumulation of undegraded autophagosomes in neurons.

Second, distinct mechanism — ER exit site (ERES)/COPII secretory defect. TECPR2 also cooperates with the ATG8-family protein LC3C to regulate COPII-dependent ER export: it associates with the COPII coat protein SEC24D, stabilizing SEC24D levels and maintaining functional ER exit sites; TECPR2-deficient patient cells show altered SEC24D abundance and impaired ER export efficiency (Stadel et al. 2015, Mol Cell, PMID:26431026; confirmed and extended by spatial proteomics in Nature Communications 2023). This links TECPR2 loss to a broader secretory-pathway disturbance, not autophagy alone.

Endolysosomal maturation defect (most recent mechanistic advance, 2025). A newly published TECPR2 nonsense knock-in mouse model shows that TECPR2 interacts with the HOPS (homotypic fusion and protein sorting) tethering complex through its middle region and TECPR domain, and that loss of TECPR2 produces a broader dysfunctional endolysosomal system in both neurons and microglia — not merely blocked autophagosome-lysosome fusion. Affected axons accumulate swollen mitochondria, enlarged ER, autophagosomes, glycogen granules, and protein aggregates; microglia adopt a disease-associated phenotype with enlarged lysosomes but reduced capacity to clear neuronal debris, implicating impaired neuroimmune clearance in disease progression ([Cell Death & Disease, 2025, PMID:41173829, DOI:10.1038/s41419-025-08168-w]).

Causal chain (upstream → downstream): 1. Biallelic LoF TECPR2 variants → loss of TECPR domain-mediated autophagosome-lysosome tethering and SEC24D/COPII stabilization (molecular) 2. → Impaired autophagic flux (LC3-II/p62 dysregulation) + impaired ER export/secretory pathway function + impaired HOPS-mediated endolysosomal maturation (cellular) 3. → Progressive accumulation of undegraded autophagosomes, protein aggregates, and organellar damage (swollen mitochondria, enlarged ER) selectively in long axons of sensory/autonomic pathways — particularly the dorsal column nuclei (gracile and cuneate nuclei) and corticospinal tracts (tissue/cellular) 4. → Neuroaxonal dystrophy with axonal spheroid formation, age-dependent neurodegeneration, and secondary microglial dysfunction/disease-associated gliosis that fails to clear debris (tissue) 5. → Clinical phenotype: progressive spastic-ataxic gait disorder, sensory neuropathy, autonomic dysfunction (central hypoventilation, dysmotility), developmental delay, and premature death from respiratory/aspiration complications (organism level)

Suggested ontology terms: - GO (biological process): GO:0000045 (autophagosome assembly), GO:0000422 (autophagy of mitochondrion / mitophagy), GO:0016237 (lysosomal microautophagy) — most specifically GO:0061908 (autophagosome-lysosome fusion, note: verify exact ID against OAK) or the closest reachable macroautophagy child term; GO:0048208 (COPII vesicle coating); GO:0006888 (ER to Golgi vesicle-mediated transport) - GO (cellular component): GO:0005776 (autophagosome), GO:0005764 (lysosome), GO:0070081 (ER exit site — verify against OAK), GO:0030904 (HOPS complex if bindable) - CL (cell type): CL:0000540 (neuron), CL:0000031 (central nervous system neuron — sensory dorsal-column neuron), CL:0000129 (microglial cell) - UBERON: UBERON:0002771 (nucleus gracilis / dorsal column nuclei — verify exact term), UBERON:0002298 (dorsal column of spinal cord), UBERON:0001851 (corticospinal tract)

Immune involvement: Secondary — disease-associated microglial activation with impaired debris clearance (2025 knock-in mouse data), not primary autoimmunity.

Molecular profiling data available: Spatial proteomics of the secretory pathway in TECPR2-deficient cells (Nature Communications 2023); transcriptomic/proteomic/electron-microscopy characterization of the 2025 knock-in mouse model. No published human transcriptomic/GEO datasets specific to patient tissue were identified in this search.

7. Anatomical Structures Affected

Organ level: - Primary: central and peripheral nervous system (brain, spinal cord — especially dorsal columns/gracile and cuneate nuclei, corticospinal tracts, cerebellum), autonomic nervous system - Secondary: respiratory system (recurrent aspiration pneumonia, chronic lung disease from hypoventilation), gastrointestinal tract (dysmotility, reflux) - Body systems: nervous system (primary), respiratory system, digestive system, musculoskeletal system (contractures secondary to spasticity)

Tissue/cell level: - Long-tract sensory and motor axons (corticospinal tract, dorsal column pathways) — the primary site of neuroaxonal dystrophy - Cerebellum — progressive cerebellar atrophy (particularly documented in the heterozygous phenotype, PMID:34994087, and as an MRI feature in some biallelic patients) - Microglia — CNS resident immune cells implicated in the 2025 mechanistic model - Cell Ontology: CL:0000540 (neuron), CL:0000129 (microglial cell), CL:11000015 (or nearest CL term for dorsal column/gracile nucleus neuron)

Subcellular level: autophagosomes (GO:0005776), lysosomes (GO:0005764), ER exit sites/COPII vesicles (GO:0070081), mitochondria (swollen/dysmorphic in affected axons per 2025 model)

Localization/lateralization: Bilateral, symmetric involvement — consistent with a metabolic/degenerative rather than focal-lesion process. Neuroimaging shows thin/dysplastic corpus callosum (~52% in the Neuser 2021 cohort), mild ventriculomegaly, delayed myelination, and cerebral/cerebellar atrophy.

8. Temporal Development

• Onset: Infancy — hypotonia and motor developmental delay are typically the presenting features, with delayed acquisition of independent walking (insidious, not acute onset).
• Progression: Neurodegenerative and progressive rather than static. Course: hypotonia in infancy → spastic-ataxic gait pattern emerging in childhood → possible regression in the second decade with loss of previously achieved independent ambulation → lower-limb spasticity, dystonia, and Parkinsonian features can emerge in late childhood/adolescence.
• Disease stages: no formal staging system exists (unlike cancer); natural-history descriptions divide the course into early developmental-delay phase, a plateau/functional phase, and a later regressive phase.
• Rate: variable but generally described as slowly-to-moderately progressive over years to a decade or more.
• Duration/outcome: chronic, lifelong, generally fatal in childhood/adolescence (see §11).
• Remission: none described — this is a monogenic neurodegenerative disorder without a relapsing-remitting pattern.
• Critical periods: early intervention (physical/occupational/speech therapy, early respiratory and nutritional surveillance) is emphasized in management guidance, though no data show a defined "window" that alters the underlying neurodegenerative trajectory.

9. Inheritance and Population

Epidemiology: - Prevalence: <1 per 1,000,000 (Orphanet ORPHA:320385) — an ultra-rare disease with >30–40 reported affected individuals in the literature to date. - Incidence estimates: ~1:22,500 in the Bukharian Jewish population vs. ~1:5,961,640 in the general population (GeneReviews NBK584409), reflecting the founder-effect concentration of disease in specific communities.

Inheritance pattern: Autosomal recessive for the classic biallelic SPG49/HSAN9 phenotype. A separately reported heterozygous (monoallelic) TECPR2 variant phenotype causes progressive cerebellar atrophy with developmental delay — a milder, likely dominantly-acting or haploinsufficient presentation, genetically distinct from the recessive syndrome (PMID:34994087).

Penetrance: Complete/full penetrance reported for biallelic pathogenic variants (all identified biallelic carriers to date are symptomatic); carriers of a single pathogenic allele in the recessive form are asymptomatic.

Expressivity: Variable — even individuals homozygous for the same founder allele show a range of severity in developmental, respiratory, and orthopedic manifestations.

Genetic anticipation: Not reported/not applicable (not a repeat-expansion disorder).

Germline mosaicism: Not specifically documented in the literature reviewed.

Founder effects (population-specific mutations): - Bukharian Jewish: c.3416delT, p.Leu1139ArgfsTer75 — carrier frequency ~1.33% - Ashkenazi Jewish: c.1319delT, p.Leu440ArgfsTer19 — carrier frequency ≥0.65%

Consanguinity: A substantial contributor — approximately half of affected individuals are born to consanguineous parents (GeneReviews), consistent with an autosomal recessive ultra-rare disease outside the two known founder populations.

Carrier frequency: See founder effects above; carrier screening panels for Ashkenazi and Bukharian Jewish populations increasingly include TECPR2.

Affected populations / geographic distribution: Original description in Bukharian Jewish families (Israel/Central Asian Jewish diaspora); Ashkenazi Jewish founder variant subsequently described; sporadic cases reported worldwide including a Chinese patient (PMID:35130874) and other non-founder populations reported in the 2021 international cohort (PMID:33847017), indicating global but very low-frequency occurrence outside founder populations.

Sex ratio: No sex predilection reported (autosomal gene).

Age distribution: Pediatric-onset disease; the affected population by definition skews toward children and adolescents given reduced life expectancy.

10. Diagnostics

Establishing the diagnosis requires identification of biallelic pathogenic/likely pathogenic TECPR2 variants in an individual with the compatible phenotype (GeneReviews NBK584409).

Molecular/genetic testing approaches: - Targeted founder-variant testing — first-line in Ashkenazi or Bukharian Jewish ancestry (c.1319delT / c.3416delT) - Multigene panels for hereditary spastic paraplegia or hereditary sensory/autonomic neuropathy - Exome or genome sequencing — comprehensive approach for non-founder-population or panel-negative cases; sequence analysis detects an estimated ~100% of reported pathogenic variant types (missense, nonsense, splice-site, small indels) - Deletion/duplication (CNV) analysis — reserved for cases where sequencing is uninformative, since large structural variants are rare in this gene

Neuroimaging (MRI) findings supporting diagnosis: thin/dysplastic corpus callosum (~52%), mild ventriculomegaly, delayed myelination, cerebral and/or cerebellar atrophy, flattening of the pons (particularly noted in the heterozygous cerebellar-atrophy phenotype, PMID:34994087).

Clinical/biochemical testing: No specific validated biomarker or enzyme assay exists; diagnosis is clinical + molecular. Research-grade autophagy-flux assays (LC3-II, p62 immunoblotting in patient fibroblasts) were used investigationally in the original description but are not a standard diagnostic test.

Differential diagnosis (per GeneReviews): - HSAN3 (familial dysautonomia, ELP1/IKBKAP) — usually milder intellectual disability; distinguishing features include alacrima and decreased fungiform tongue papillae - HSAN4 (NTRK1) — painless deformities and anhidrosis with episodic fevers - HSAN5 (NGF) — painless deformities; borderline/mild intellectual disability - Cerebral palsy — excluded by absence of perinatal risk factors and by the progressive course of SPG49/HSAN9 versus the static course of CP - Other complex/AR hereditary spastic paraplegias in the broader SPG differential

Screening: No population newborn-screening program exists (ultra-rare disease); however, targeted carrier screening for the Ashkenazi and Bukharian Jewish founder variants is increasingly incorporated into expanded Jewish genetic disease panels, and prenatal/preimplantation genetic testing is available once familial variants are identified.

11. Outcome/Prognosis

Prognosis is poor. GeneReviews explicitly notes "reduced life expectancy," with deaths occurring in the first or second decade of life in a substantial proportion of reported cases.

Leading causes of mortality: - Asphyxia from aspiration of solid foods - Nocturnal central apnea - Complications of chronic, progressive lung disease (recurrent aspiration pneumonia, respiratory failure)

Morbidity/functional outcomes: - Progressive loss of independent ambulation (many patients regress and lose walking ability in the second decade) - Persistent severe intellectual disability; many individuals remain nonverbal lifelong - Chronic respiratory disease requiring long-term noninvasive ventilation in a majority of patients - Feeding dependence (gastrostomy) common given the high rates of dysphagia (53%) and reflux (94%) - Orthopedic complications (contractures) from progressive spasticity

Recovery potential: None — this is a progressive neurodegenerative disorder; there is no reported spontaneous improvement, and no disease-modifying therapy currently exists to alter the trajectory (see §12).

Prognostic factors: No formal validated prognostic scoring system exists; qualitatively, earlier/more severe respiratory and bulbar (dysphagia) involvement correlates with worse outcomes, consistent with the mortality causes above.

12. Treatment

No curative or disease-modifying therapy is currently approved. Management is entirely supportive and multidisciplinary (GeneReviews NBK584409):

• Respiratory: polysomnography for central hypoventilation/apnea surveillance, noninvasive ventilation, oxygen monitoring — NCIT:C15747 (Supportive Care); relevant NCIT concept for noninvasive ventilation/respiratory support
• Gastroenterology/nutrition: swallow evaluation, feeding adaptations, consideration of gastrostomy, reflux management — NCIT:C15447 (Dietary Intervention); NCIT:C15986 (Pharmacotherapy, for anti-reflux medication such as proton-pump inhibitors)
• Orthopedic/rehabilitative: bracing, physical therapy to prevent contractures — NCIT:C15302 (Physical Therapy), NCIT:C16186 (Orthopedic Surgical Procedure)
• Behavioral: applied behavior analysis for autism-spectrum features — NCIT:C181743 (Behavioral Counseling) or nearest behavioral-intervention term
• Developmental: early intervention services, special education, speech-language pathology — NCIT:C159273 (Speech Therapy)
• Genetic counseling: NCIT:C15240 (Genetic Counseling), given autosomal recessive inheritance and available carrier/prenatal testing

Drugs to avoid: Benzodiazepines and antihistamines are explicitly flagged because they risk decreased consciousness, hypopnea, and CO₂ retention in a population already prone to central hypoventilation.

Experimental/investigational therapy — antisense oligonucleotide (ASO) exon-skipping: A 2022 study developed an ASO exon-skipping strategy targeting the Ashkenazi founder variant TECPR2 c.1319delT (p.Leu440Argfs19), which causes a premature stop codon within exon 8 (Molecular Therapy Nucleic Acids, PMID:35860385): - Patient-derived fibroblasts and iPSC-derived neurons homozygous for this variant were used as disease models, both showing complete absence of TECPR2 protein. - Lead candidate ASO-005-02 achieved ~27 nM potency in patient fibroblasts, inducing skipping of exon 8 to restore an in-frame, partially functional TECPR2ΔEx8 protein that retained the characteristic punctate neuronal localization of wild-type TECPR2 in iPSC-derived neurons. - In vivo testing in cynomolgus monkeys (single 20 mg intrathecal dose) showed an acceptable tolerability profile with broad CNS distribution and confirmed exon-8 skipping across multiple CNS tissues — representing a preclinical proof-of-concept for a precision, genotype-specific splice-modulation therapy* (therapeutic_modality: ANTISENSE_OLIGONUCLEOTIDE; aso_mechanism: SPLICE_MODULATION_EXON_SKIPPING; target_gene: TECPR2 (hgnc — verify correct lowercase HGNC numeric ID); target_exon: exon 8).

This ASO has not, to my knowledge from this search, progressed to a registered human clinical trial (no NCT identifier found); it remains at the primate/preclinical stage as of the most recent identified publication (2022).

No approved gene therapy, cell therapy, small-molecule, or targeted pharmacotherapy exists for the underlying TECPR2 autophagy/secretory defect.

13. Prevention

• Primary prevention: genetic counseling and carrier screening in at-risk populations (Ashkenazi and Bukharian Jewish communities) to inform reproductive decision-making; the disease itself cannot be prevented once biallelic pathogenic genotype is present.
• Secondary prevention: prenatal diagnosis and preimplantation genetic testing (PGT) are available once familial pathogenic variants are identified, allowing at-risk couples to avoid transmission or to prepare for early postnatal management.
• Tertiary prevention (preventing complications in affected individuals): proactive respiratory surveillance (polysomnography, timely initiation of noninvasive ventilation) and aspiration-risk management (swallow studies, feeding modification/gastrostomy) are the most clinically consequential preventive measures, since aspiration and central apnea are the leading causes of death.
• Immunization: no disease-specific vaccine strategy; standard respiratory-pathogen vaccination (influenza, pneumococcal, RSV prophylaxis where age-appropriate) is prudent given the high burden of recurrent aspiration pneumonia, though this is general supportive practice rather than a TECPR2-specific published recommendation.
• Screening programs: no population-based newborn screening exists for this ultra-rare disorder; screening is limited to targeted carrier testing in founder populations.
• Behavioral/public health interventions: not applicable beyond genetic counseling, given the purely monogenic etiology.

14. Other Species / Natural Disease

Naturally occurring TECPR2-related disease in animals — Spanish Water Dog neuroaxonal dystrophy: A naturally occurring, homologous disease was described in Spanish Water Dogs (Canis lupus familiaris, NCBITaxon:9615): four dogs presented with slowly progressive neurological signs (gait abnormalities, behavioral deficits) beginning at 6–11 months of age, segregating in an autosomal recessive pattern. Whole-genome/exome analysis identified a single, perfectly associated non-synonymous canine TECPR2 variant, c.4009C>T (p.R1337W) (Hahn et al. 2015, PLOS ONE, PMID:26555167). Histopathology showed axonal spheroid formation concentrated in the grey matter of cerebral hemispheres, cerebellum, brainstem, and spinal cord sensory pathways — with no iron accumulation — and ultrastructurally the spheroids contained densely packed double-membraned vesicles characterized as autophagosomes, closely mirroring the human disease mechanism. This is catalogued in OMIA as OMIA:001975-9615 (Neuroaxonal dystrophy, TECPR2-related, in dog). Commercial genetic panels (e.g., Paw Print Genetics) now offer this as a breed-specific test, giving it real veterinary screening relevance for Spanish Water Dog breeding programs.

Comparative biology: The dog phenotype (progressive neuroaxonal dystrophy with autophagosome accumulation in sensory/motor long tracts) closely parallels both the human disease and the engineered mouse models, supporting deep evolutionary conservation of TECPR2's role in axonal autophagosome clearance across mammals.

Zoonotic potential/transmission: Not applicable — this is a purely genetic, non-infectious, non-transmissible disorder.

15. Model Organisms

Mouse models (Mus musculus, NCBITaxon:10090; MGI:2144865, Tecpr2):

1. CRISPR-Cas9 Tecpr2⁻/⁻ knockout mouse (Tamim-Yecheskel et al. 2021, Autophagy; also referenced as PMID:33218264 in GeneReviews):
2. Recapitulates behavioral pathology seen in SPG49 patients.
3. Develops age-dependent neuroaxonal dystrophy, predominantly in the gracile (GrN) and cuneate nuclei (CuN) of the medulla oblongata and the dorsal white matter column of the spinal cord — anatomically matching the human dorsal-column sensory pathway involvement.
4. Shows age-dependent accumulation of autophagosomes, consistent with a defect in autophagosome-to-lysosome targeting.

5. Limitation: a knockout (complete null) model may not fully recapitulate the partial loss-of-function seen with some human missense alleles, and mice do not model the severe intellectual disability/speech phenotype central to the human disease (behavioral correlates in rodents are necessarily indirect).

6. TECPR2 nonsense knock-in mouse (2025) (Cell Death & Disease, PMID:41173829):

7. Carries the HSAN9-associated nonsense mutation directly (more genetically faithful than a full knockout).
8. Exhibits gait ataxia, axonal spheroids in sensory medullary regions, and progressive neuronal loss in dorsal column nuclei.
9. Reveals broader endolysosomal dysfunction beyond autophagosome-lysosome fusion, including TECPR2–HOPS complex interaction, organellar damage (swollen mitochondria, enlarged ER) in affected axons, and a maladaptive microglial disease-associated phenotype with enlarged lysosomes but reduced neuronal-debris clearance capacity.
10. This is the most mechanistically comprehensive model to date, integrating proteomics, transcriptomics, and electron microscopy.
11. Applications: studying endolysosomal/autophagy-microglia crosstalk in neurodegeneration; a platform for testing autophagy-enhancing or endolysosomal-targeted small molecules.

Naturally occurring large-animal model: The Spanish Water Dog (see §14) functions as a spontaneous, naturally occurring genetic model complementing the engineered mouse lines, valuable because it arises from an endogenous missense variant (p.R1337W) rather than an engineered null allele.

Cellular models: - Patient-derived dermal fibroblasts — used in the original 2012 description to demonstrate reduced LC3-II/p62 (autophagy flux defect), and subsequently in the 2022 ASO study. - Patient-derived iPSC-derived neurons (homozygous for c.1319delT) — used to confirm absence of TECPR2 protein and to validate ASO-induced exon-skipping and restoration of the characteristic punctate neuronal TECPR2 localization pattern (Molecular Therapy Nucleic Acids, PMID:35860385).

Resources: MGI (Tecpr2, MGI:2144865) for mouse strain/allele information; OMIA:001975-9615 for the canine model.

Summary of Key Ontology-Term Suggestions for KB Curation

Note on curation caveats: Every ontology CURIE above should be verified against the dismech OAK adapters (just validate-terms) before use, since several (exact HGNC numeric ID, exact GO autophagosome-lysosome-fusion child term, exact UBERON dorsal-column-nucleus term) were not independently cross-checked against a live ontology lookup in this research pass and are offered as strong candidates rather than confirmed bindings.

Sources

• Oz-Levi et al. 2012, Am J Hum Genet, PMID:23176824 — original TECPR2/SPG49 description
• OMIM *615000 TECPR2
• GeneReviews: TECPR2-Related HSAN with Intellectual Disability (NBK584409)
• Orphanet ORPHA:320385
• Neuser et al. 2021, Hum Mutat, PMID:33847017 — clinical/neuroimaging/molecular spectrum
• Heimer et al. 2016, PMID:26542466 — Ashkenazi founder variant
• Ramsey et al. 2022, Mol Genet Genomic Med, PMID:34994087 — heterozygous cerebellar atrophy
• Tamim-Yecheskel et al. 2020/2021, Autophagy — Tecpr2 knockout mouse
• 2025, Cell Death & Disease, PMID:41173829 — Tecpr2 knock-in mouse, endolysosomal/microglial mechanism
• Molecular Therapy Nucleic Acids 2022, PMID:35860385 — ASO exon-skipping therapy
• Stadel et al. 2015, Mol Cell, PMID:26431026 — TECPR2/LC3C/COPII ER export
• Nature Communications 2023 — spatial proteomics of TECPR2 secretory pathway disturbance
• Hahn et al. 2015, PLOS ONE, PMID:26555167 — Spanish Water Dog TECPR2 neuroaxonal dystrophy
• Novel Chinese HSP49 case report, PMID:35130874
• UniProt O15040 (TECPR2)
• GeneCards TECPR2
• OMIA:001975-9615 canine model

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.