Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity

Mendelian MONDO:0018129 Pathograph 26 Show in embeddings browser Hereditary Ataxia Hereditary Spastic Paraplegia

Autosomal recessive cerebellar ataxia with late-onset spasticity is one presentation of the biallelic GBA2 disease spectrum, most often termed hereditary spastic paraplegia 46 (SPG46). Presentations range from ataxia-predominant disease in which spasticity emerges later to early-onset complex hereditary spastic paraplegia and a Marinesco-Sjögren-like phenotype. Across these labels, cerebellar ataxia and lower-limb spasticity coexist, with variable peripheral neuropathy, cognitive impairment, cataracts, scoliosis, hypogonadism, movement disorders, and characteristic but inconsistent MRI abnormalities. Biallelic GBA2 variants severely reduce the nonlysosomal glucosylceramidase that hydrolyzes glucosylceramide to glucose and ceramide. Glucosylceramide accumulation is established in patient material, but the downstream mechanism linking lipid imbalance to selective corticospinal, cerebellar, peripheral-nerve, ocular, and endocrine manifestations remains incompletely resolved.

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1
Mappings
1
Inheritance
6
Pathophys.
15
Phenotypes
4
Hypotheses
2
Gaps
26
Pathograph
1
Genes
3
Medical Actions
2
Differentials
1
Trials
4
Models
13
References
1
Deep Research
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Mappings

MONDO
MONDO:0018129 autosomal recessive cerebellar ataxia with late-onset spasticity
skos:exactMatch MONDO
👪

Inheritance

1
Autosomal recessive inheritance HP:0000007
Disease results from biallelic pathogenic GBA2 variants; reported families are frequently consanguineous, although compound-heterozygous cases also occur.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:38334933 SUPPORT Human Clinical
"SPG46 is a rare, early-onset and autosomal recessive HSP, linked to biallelic GBA2 mutations."
The current series and literature review defines biallelic GBA2 disease as autosomal recessive.
◈

Mechanistic Hypotheses

4
GBA2 Loss and Glucosylceramide-Dysregulation Model
gba2_loss_glucosylceramide_model CANONICAL
Evidence balance 2 support
Biallelic disease-associated GBA2 variants cause severe loss of nonlysosomal glucosylceramidase activity. Reduced hydrolysis of glucosylceramide raises glucosylceramide in patient material and establishes the primary biochemical lesion. This does not by itself establish which lipid species, membrane compartment, or neural cell population drives the clinical syndrome.
Show evidence (2 references)
PMID:26220345 SUPPORT In Vitro
"none of the GBA2 mutant cDNAs raised the enzyme activity in transfected cells, in contrast to the wild-type enzyme."
Biochemical testing establishes severe loss of activity across representative disease-associated variants.
PMID:28052128 SUPPORT Human Clinical
"Our studies show that a reduced activity of GBA2 is sufficient to elevate the levels of glucosylceramide to similar levels as seen in Gaucher disease."
Patient leukocytes directly connect reduced GBA2 activity to glucosylceramide elevation.
Actin, Neurite-Outgrowth, and Axonal-Development Model
gba2_neurite_axon_model EMERGING
Evidence balance 2 support
GBA2 inhibition perturbs F-actin dynamics and neurite outgrowth in isolated cerebellar neurons, while zebrafish knockdown shortens and abnormally branches motor axons. These models provide a plausible bridge from lipid imbalance to long-tract and cerebellar dysfunction, but neither model fully reproduces the human phenotype and the intervening molecular steps remain uncertain.
Show evidence (2 references)
PMID:30662006 SUPPORT Model Organism
"inhibition of GBA2 activity in isolated cerebellar neurons dramatically affected F-actin dynamics and reduced neurite outgrowth"
The mammalian neuron experiment supports an actin/neurite mechanism.
PMID:23332916 SUPPORT Model Organism
"led to abnormal motor behavior and axonal shortening/branching of motoneurons that were rescued by the human wild-type mRNA"
Zebrafish rescue experiments support a GBA2-dependent motor-axon phenotype.
Truncating-Variant Mitochondrial Mislocalization Model
truncating_variant_mitochondrial_model EMERGING
Evidence balance 1 support
In transfected cells, selected early C-terminal truncations enter the mitochondrial matrix and cause fragmentation and membrane-potential loss. This is a variant-class-specific cell-model result, not evidence that all GBA2 variants cause mitochondrial disease in patients.
Show evidence (1 reference)
PMID:32492073 SUPPORT In Vitro
"the C-terminally truncated mutants terminating after amino acids 233 and 339 (GBA2-233 and -339) were present in the mitochondrial matrix, induced mitochondrial fragmentation and loss of mitochondrial transmembrane potential."
The experiment supports a truncation-specific mitochondrial branch while limiting its generalization.
Patient-Cell Stress and Signaling Model
patient_transcriptome_stress_signals EMERGING
Evidence balance 1 support
RNA sequencing of lymphoblasts, fibroblasts, and iPSC-derived neurons from patients homozygous for one GBA2 missense variant identified oxidative stress, neuroinflammatory, sphingolipid, PI3K-AKT, and MAPK pathway signals. The sample size was small and the authors framed these as candidates requiring validation rather than demonstrated causal pathways.
Show evidence (1 reference)
PMID:35277195 SUPPORT In Vitro
"Among them are the oxidative stress, neuroinflammation, sphingolipid signaling and metabolism, PI3K-Akt and MAPK signaling pathways."
The patient-cell transcriptome nominates, but does not causally establish, these pathways.
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Discussions and Knowledge Gaps

2
Which lipid species, membrane compartment, and neural cell population link GBA2 deficiency to corticospinal, cerebellar, and peripheral-nerve disease?
KNOWLEDGE GAP OPEN gba2_lipid_to_neurodegeneration_gap
Attached to
pathophysiology#Glucosylceramide Accumulation and Sphingolipid Imbalance
Severe enzyme deficiency and glucosylceramide elevation are established in patients, but mouse phenocopy is incomplete and neurite, mitochondrial, and transcriptomic findings do not yet form a validated causal chain in human neural tissue.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Other
"the pathogenic mechanism of neurodegeneration is still unclear"
The contemporary review explicitly identifies the unresolved downstream mechanism.
Why can the same or closely related biallelic GBA2 genotypes present as HSP-predominant, ataxia-predominant, or Marinesco-Sjögren-like disease?
KNOWLEDGE GAP OPEN gba2_genotype_phenotype_variability
Attached to
genetic#Biallelic GBA2 pathogenic variants
Intrafamilial and interfamily variability, limited enzyme assays, and sparse longitudinal cohorts prevent robust genotype-phenotype prediction.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"different phenotypes may arise from same identical mutations"
The review documents genotype-preserving phenotypic variability.
⚙

Pathophysiology

6
Biallelic GBA2 Loss of Function
Biallelic nonsense, frameshift, splice, and missense variants cause severe reduction or loss of GBA2 activity. Both absent protein and catalytically inactive protein can produce the biochemical lesion.
GBA2 hgnc:18986 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves decreased GBA2 (hgnc:18986). hgnc:18986 is a gene from the HUGO Gene Nomenclature Committee. ↓ DECREASED
GBA2 hgnc:18986 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves GBA2 (hgnc:18986). hgnc:18986 is a gene from the HUGO Gene Nomenclature Committee.
Experimental models
Disease-associated GBA2 truncation transfection model CELL LINE The model tests variant-specific consequences beyond catalytic loss.
Downstream
Nonlysosomal Glucosylceramidase Deficiency Disease-associated variants severely reduce GBA2 catalytic activity.
Show evidence (2 references)
PMID:23332917 SUPPORT Human Clinical
"We were able to identify mutations responsible for autosomal-recessive ataxia in these families within the gene encoding β-glucosidase 2, GBA2."
Independent families establish biallelic GBA2 as the causal genetic lesion.
PMID:26220345 SUPPORT In Vitro
"SPG46 patients have a severe deficit in GBA2 activity, because the GBA2 mutants are intrinsically inactive and/or reduced in amount."
Variant assays explain the lesion as intrinsic inactivity and/or reduced abundance.
Nonlysosomal Glucosylceramidase Deficiency
GBA2 is an endoplasmic-reticulum/plasma-membrane-associated nonlysosomal glucosylceramidase that hydrolyzes glucosylceramide to glucose and ceramide. Deficiency impairs this catabolic reaction.
glucosylceramide catabolic process GO:0006680 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased glucosylceramide catabolic process (GO:0006680). GO:0006680 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Glucosylceramide Accumulation and Sphingolipid Imbalance Reduced GBA2 hydrolysis raises glucosylceramide in patient cells.
Show evidence (1 reference)
PMID:23332916 SUPPORT Human Clinical
"GBA2 encodes a microsomal nonlysosomal glucosylceramidase that catalyzes the conversion of glucosylceramide to free glucose and ceramide"
The defining report establishes the enzyme and reaction affected.
Glucosylceramide Accumulation and Sphingolipid Imbalance
Glucosylceramide accumulation is measurable in affected human material. How this membrane-lipid disturbance selects long corticospinal axons, cerebellar circuits, peripheral nerves, lens, and reproductive/endocrine tissues is not yet established.
Experimental models
Patient-derived GBA2 spastic-ataxia cellular transcriptome model IPSC DERIVED MODEL The model examines transcriptional consequences of GBA2-associated lipid dysregulation.
Downstream
Axonal and Neurite Dysfunction Experimental systems connect GBA2 loss to altered actin dynamics, impaired neurite extension, and abnormal motor-axon morphology, but the lipid-to-cytoskeleton intermediates remain unresolved.
Variable Multisystem Expression With Unresolved Intermediates Cataract, hypogonadism, and skeletal deformity accompany the neurologic syndrome, but their intervening cell and tissue mechanisms are unknown.
Show evidence (2 references)
PMID:28052128 SUPPORT Human Clinical
"reduced activity of GBA2 is sufficient to elevate the levels of glucosylceramide"
Patient material establishes glucosylceramide elevation.
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Other
"resulting in abnormal increase of glucosylceramide, although the pathogenic mechanism of neurodegeneration is still unclear"
The current review explicitly preserves uncertainty downstream of the lipid lesion.
Axonal and Neurite Dysfunction
Zebrafish GBA2 knockdown causes motor-axon shortening and abnormal branching, while GBA2 inhibition alters F-actin and neurite outgrowth in isolated cerebellar neurons. Species differences and incomplete mouse phenocopy limit certainty about the human downstream pathway.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology. neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
actin cytoskeleton organization GO:0030036 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal actin cytoskeleton organization (GO:0030036). GO:0030036 is a biological process from the Gene Ontology. ⚠ ABNORMAL neuron projection development GO:0031175 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal neuron projection development (GO:0031175). GO:0031175 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Central and Peripheral Neurologic Syndrome Long-tract, cerebellar, and peripheral-neural dysfunction produces the combined spastic-ataxia syndrome and associated imaging findings.
Show evidence (2 references)
PMID:23332916 SUPPORT Model Organism
"abnormal motor behavior and axonal shortening/branching of motoneurons"
The zebrafish model directly demonstrates altered motor-axon morphology.
PMID:30662006 SUPPORT Model Organism
"these mice exhibited a high phenotypic variance and did not fully resemble the human phenotype"
The mouse-model limitation prevents overstatement of the inferred human pathway.
Central and Peripheral Neurologic Syndrome
Human GBA2 disease consistently combines spastic paraparesis and cerebellar syndrome. Peripheral neuropathy, cognitive involvement, movement disorders, gaze palsy, bladder dysfunction, and variable MRI abnormalities broaden the neurologic phenotype.
cerebellum UBERON:0002037 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in cerebellum (UBERON:0002037). UBERON:0002037 is an anatomical location from the Uberon multi-species anatomy ontology. corpus callosum UBERON:0002336 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in corpus callosum (UBERON:0002336). UBERON:0002336 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Cerebellar ataxia Cerebellar circuit dysfunction manifests as progressive ataxia.
Spastic paraplegia Corticospinal involvement manifests as progressive lower-limb spastic paraparesis.
Peripheral neuropathy Peripheral nerve involvement is frequent but variably ascertained.
Cognitive impairment Cognitive impairment is common and may emerge late.
Cerebellar atrophy Cerebellar atrophy is a variable rather than obligatory imaging correlate.
Corpus callosum atrophy A thin or atrophic corpus callosum is a frequent but inconsistent MRI finding.
Cerebral white matter abnormalities White-matter abnormalities occur in a minority overall but were prominent in the recent Italian series.
Dystonia Limb or cranial dystonia is part of the variable movement-disorder spectrum.
Tremor Head or limb tremor occurs in a subset.
Vertical supranuclear gaze palsy Upper-gaze palsy is an occasional and potentially identifying ocular-motor feature.
Urinary urgency Neurogenic bladder symptoms, particularly urgency or urge incontinence, occur variably.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"In all cases reported so far, the presence of both spastic paraparesis and cerebellar syndrome has been consistently observed"
The 67-case synthesis identifies the paired core neurologic features.
Variable Multisystem Expression With Unresolved Intermediates
Cataracts, male hypogonadism, scoliosis, and foot deformity recur across the GBA2 spectrum, but neither a single developmental nor degenerative mechanism has been established for these manifestations.
Downstream
Cataract Bilateral cataracts can create a Marinesco-Sjögren-like presentation.
Hypogonadism Hypogonadism occurs in a minority of affected males.
Scoliosis Scoliosis is an occasional orthopedic complication of the chronic motor syndrome.
Pes cavus Pes cavus and other foot deformities occur variably.
Show evidence (2 references)
PMID:23332916 SUPPORT Human Clinical
"The overall phenotype was a complex HSP with mental impairment, cataract, and hypogonadism in males"
The original families establish recurrent ocular and endocrine manifestations.
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"neuropathy, MCI, bilateral cataracts, scoliosis, pes cavus and hypogonadism are observed with varying prevalence"
The updated literature review emphasizes variable expressivity of multisystem findings.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

15
Endocrine 1
Hypogonadism OCCASIONAL HP:0000135 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypogonadism (HP:0000135). HP:0000135 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23332916 SUPPORT Human Clinical
"hypogonadism in males"
The original molecular series documents hypogonadism in affected males.
Eye 2
Vertical supranuclear gaze palsy OCCASIONAL HP:0000511 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Vertical supranuclear gaze palsy (HP:0000511). HP:0000511 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"In two patients, we found ocular movement disorder (upper gaze palsy (UGP))."
Upper-gaze palsy was directly observed in two of five contemporary cases.
Cataract FREQUENT HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:28052128 SUPPORT Human Clinical
"autosomal recessive cerebellar ataxia with cataracts and mental retardation"
Molecular diagnosis in two Norwegian families establishes the cataract-associated GBA2 phenotype.
Genitourinary 1
Urinary urgency HP:0000012 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Urinary urgency (HP:0000012). HP:0000012 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"sphincteric symptoms (like urge incontinence, 3/5)"
The recent series directly documents urge-incontinence-type sphincter symptoms.
Limbs 1
Pes cavus OCCASIONAL HP:0001761 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pes cavus (HP:0001761). HP:0001761 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"pes cavus (1/5)"
Pes cavus was directly observed in the contemporary series.
Musculoskeletal 2
Spastic paraplegia VERY_FREQUENT HP:0001258 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spastic paraplegia (HP:0001258), qualified as course progressive. HP:0001258 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"In all cases reported so far, the presence of both spastic paraparesis and cerebellar syndrome has been consistently observed"
The literature synthesis treats spastic paraparesis and cerebellar syndrome as paired core findings.
Scoliosis OCCASIONAL HP:0002650 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Scoliosis (HP:0002650). HP:0002650 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34251556 SUPPORT Human Clinical
"progressively manifested spastic-ataxia, scoliosis, mild intellectual decline, and bilateral cataract."
This molecularly confirmed case documents progressive scoliosis with the neurologic syndrome.
Nervous System 7
Cerebellar ataxia VERY_FREQUENT HP:0001251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ataxia (HP:0001251), qualified as course progressive. HP:0001251 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:23332917 SUPPORT Human Clinical
"four unrelated consanguineous families of Tunisian decent diagnosed with cerebellar ataxia of unknown origin"
The independent ARCA cohort establishes cerebellar ataxia as a defining presentation.
Peripheral neuropathy VERY_FREQUENT HP:0009830 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Peripheral neuropathy (HP:0009830). HP:0009830 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"peripheral neuropathy (4/5)"
Four of five individuals in the contemporary series had peripheral neuropathy.
Cognitive impairment FREQUENT HP:0100543 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cognitive impairment (HP:0100543). HP:0100543 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"About half of the cases described so far show MCI, but its prevalence may turn out to be higher, due to later onset"
The review notes both common cognitive impairment and delayed ascertainment.
Dystonia FREQUENT HP:0001332 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dystonia (HP:0001332). HP:0001332 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"Cervical dystonia has been outlined as the onset symptom in one patient"
The review documents dystonia as both an associated and occasional presenting sign.
Tremor OCCASIONAL HP:0001337 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tremor (HP:0001337). HP:0001337 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"head and upper limbs’ tremor"
The 67-case review includes head and limb tremor.
Cerebellar atrophy FREQUENT HP:0001272 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebellar atrophy (HP:0001272). HP:0001272 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23332916 SUPPORT Human Clinical
"cerebellar atrophy on brain imaging."
Cerebellar atrophy was present across the original families to variable degrees.
Cerebral white matter abnormalities OCCASIONAL Abnormal cerebral white matter morphology HP:0002500 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral white matter abnormality, annotated with Abnormal cerebral white matter morphology (HP:0002500). HP:0002500 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"significant differences concerning WMA (80% versus 15%)."
The review contrasts high WMA prevalence in its five cases with the lower cumulative literature estimate.
Other 1
Corpus callosum atrophy FREQUENT HP:0007371 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Corpus callosum atrophy (HP:0007371). HP:0007371 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23332916 SUPPORT Human Clinical
"various degrees of corpus callosum and cerebellar atrophy on brain imaging"
The original series documents callosal and cerebellar atrophy.
🧬

Genetic Associations

1
Biallelic GBA2 pathogenic variants (Causative)
Gene: GBA2 hgnc:18986 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is GBA2 (hgnc:18986). hgnc:18986 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:23332916 SUPPORT Human Clinical
"four different mutations in GBA2 (three truncating variants and one missense variant), which were found to cosegregate with the disease"
The original report establishes cosegregation of multiple GBA2 variant classes.
PMID:26220345 SUPPORT In Vitro
"five nonsense and five missense GBA2 mutants"
Biochemical study spans both truncating and missense disease-associated alleles.
💊

Medical Actions

3
Multidisciplinary supportive care
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
No GBA2-directed disease-modifying treatment has been established. Management is individualized to preserve function and address spasticity, ataxia, neuropathy, bladder symptoms, cognition, cataracts, and orthopedic complications through neurology, rehabilitation, ophthalmology, urology, orthopedics, and genetics services.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK1509/ SUPPORT Other
"At present, no specific treatments can prevent or reverse nerve degeneration in uncomplicated HSP. Supportive care to improve quality of life, maximize function, and reduce complications is recommended."
Current HSP management guidance supports multidisciplinary symptomatic care rather than disease-modifying claims.
Individualized physical and occupational rehabilitation
Action: Physical TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Physical Therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. NCIT:C15302
Stretching, strengthening, balance and gait training, orthoses, mobility aids, and occupational adaptations are selected according to spasticity, weakness, ataxia, contracture risk, and daily-living needs.
Target Phenotypes: Spastic paraplegia HP:0001258 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Spastic paraplegia (HP:0001258). HP:0001258 is a phenotype from the Human Phenotype Ontology. Ataxia HP:0001251 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/books/NBK1509/ SUPPORT Other
"Individualized PT program"
GeneReviews recommends individualized physical therapy for HSP motor impairment.
url:https://www.ncbi.nlm.nih.gov/books/NBK1509/ SUPPORT Other
"Gait training; use of assistive walking devices"
Current guidance includes gait training and mobility aids.
Symptomatic antispastic pharmacotherapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: baclofen CHEBI:2972 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses baclofen (CHEBI:2972). CHEBI:2972 is a therapeutic agent from Chemical Entities of Biological Interest. tizanidine CHEBI:63629 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses tizanidine (CHEBI:63629). CHEBI:63629 is a therapeutic agent from Chemical Entities of Biological Interest.
Oral baclofen or tizanidine can be considered for function-limiting spasticity; focal botulinum toxin or intrathecal baclofen may be considered by specialists in selected severe cases. Treatment should avoid reducing compensatory tone enough to worsen walking.
Target Phenotypes: Spastic paraplegia HP:0001258 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Spastic paraplegia (HP:0001258). HP:0001258 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/books/NBK1509/ SUPPORT Other
"Baclofen, botulinum toxin, dantrolene, tizanidine (used 1 at a time)"
Current HSP guidance lists the symptomatic antispastic options.
🔬

Diagnosis

3
Molecular genetic testing for biallelic GBA2 variants
Diagnosis is established by detecting pathogenic or likely pathogenic variants on both GBA2 alleles, generally through a hereditary spastic-paraplegia/ataxia panel, exome sequencing, or genome sequencing. Segregation and copy-number analysis should be considered where appropriate.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:23332917 SUPPORT Human Clinical
"homozygosity mapping and whole-exome sequencing"
Exome sequencing identified the causal GBA2 variants in independent ARCA families.
Leukocyte GBA2 enzyme-activity assay
Markedly reduced GBA2 activity in leukocytes can support a molecular diagnosis and provide functional evidence for a variant, but assay methods can underestimate activity and testing is not a substitute for biallelic molecular confirmation.
Show evidence (3 references)
PMID:23332916 SUPPORT Human Clinical
"no residual glucocerebrosidase activity of GBA2 could be evidenced in blood cells"
The original report demonstrates absent blood-cell activity in an affected individual.
PMID:30864417 SUPPORT In Vitro
"Current GBA2 activity assays using artificial substrates incompletely model the activity encountered in vivo."
The assay study explains why substrate and tissue context matter when interpreting GBA2 activity.
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"this method of measuring GBA2 activity may lead to underestimating GBA2 activity"
The contemporary series states the assay's methodological limitation.
Neurologic, ophthalmologic, neurophysiologic, and MRI phenotyping
Baseline assessment should define pyramidal and cerebellar involvement, cognition, eye movements and cataracts, peripheral neuropathy, bladder symptoms, skeletal deformity, and brain MRI findings. Normal imaging or absence of cataract does not exclude the diagnosis.
Show evidence (1 reference)
PMID:38334933 SUPPORT Human Clinical
"underwent neurological examination, clinical cognitive assessment, column imaging for scoliosis assessment, ophthalmologic examination, brain imaging, GBA2 activity in peripheral blood cells and genetic testing."
The current multicenter series demonstrates the relevant multidisciplinary diagnostic assessment.
📈

Progression

2
Early presentation
Age: Congenital onset through early adulthood; childhood onset is typical
Most SPG46 cohorts begin with lower-limb spasticity in childhood. In ataxia-predominant families, cerebellar ataxia can be the first recognized feature and marked spasticity may emerge later.
Show evidence (2 references)
PMID:38334933 SUPPORT Human Clinical
"SPG46 is a rare, early-onset and autosomal recessive HSP"
The current synthesis characterizes SPG46 as early onset.
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"initially diagnosed the condition as autosomal recessive ataxia, as the first presentation involved cerebellar syndrome. However, shortly thereafter, in addition to peripheral neuropathy, significant spasticity emerged"
This sequence explains the disease label's late-spasticity presentation without generalizing it to all SPG46.
Slowly progressive multisystem syndrome
Duration: Decades
Ataxia and spasticity progress slowly over years to decades. Additional neurologic, ocular, cognitive, skeletal, bladder, and endocrine features may accumulate with disease duration.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"In our study, all patients had early onset (6.8 year) and slow progression over time."
The five-person series documents early onset and slow progression.
📊

Prevalence

1
Worldwide published cases through the 2024 literature review
Ultra-rare. The 2024 synthesis counted 67 affected people from 36 families across 18 countries; reported concentration around the Mediterranean likely reflects both consanguinity and ascertainment rather than a population prevalence estimate.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"Thus far, a total of 67 cases (30 men, 34 women, sex not specified in three) from 36 families have been described worldwide"
The review provides the most complete published case count available for the audit.
⚖️

Clinical Burden

Variable
Burden varies substantially with age at onset, predominant presentation, and disease duration. The course is usually slow, but combined spasticity, ataxia, neuropathy, cognitive impairment, cataracts, skeletal deformity, and bladder symptoms can progressively impair walking, self-care, vision, and independence over decades.
Show evidence (1 reference)
url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML SUPPORT Human Clinical
"Disease course was slowly progressive (mean 32 years at the time of last examination)."
The contemporary case series documents decades of progressive disease.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity:

Other hereditary spastic ataxias and complex hereditary spastic paraplegias
Overlapping Features ARSACS, SPG11, SPG15, SPG7, CYP2U1-, DDHD2-, and other gene-associated disorders can share spasticity, ataxia, neuropathy, callosal change, and cognitive findings. A broad panel or exome/genome analysis is often more appropriate than phenotype-only single-gene selection.
Distinguishing Features
  • Cataract plus markedly reduced leukocyte GBA2 activity supports GBA2 disease.
  • Gene-specific imaging, retinal, dental, movement, or systemic features can redirect testing.
Show evidence (1 reference)
PMID:20301682 SUPPORT Other
"Review the differential diagnosis of uncomplicated hereditary spastic paraplegia, which includes complicated hereditary spastic paraplegia with a focus on treatable genetic disorders"
GeneReviews places complex hereditary spastic paraplegia and treatable mimics in the diagnostic differential.
🔬

Clinical Trials

1
NCT01793168 RECRUITING
CoRDS is a broad international rare-disease registry and natural-history study whose current condition list explicitly includes this MONDO disease label. It is observational and not a GBA2-targeted therapeutic trial. ClinicalTrials.gov listed it as recruiting when audited on 2026-07-23.
Show evidence (1 reference)
clinicaltrials:NCT01793168 SUPPORT Human Clinical
"It provides researchers with a centralized, international patient registry for all rare diseases."
The registry record supports its broad observational role rather than therapeutic efficacy.
🧫

Experimental Models

2
Patient-derived GBA2 spastic-ataxia cellular transcriptome model IPSC_DERIVED_MODEL
RNA sequencing across three patient-derived cell types identified thousands of differential transcripts and nominated oxidative-stress, neuroinflammatory, sphingolipid, PI3K-AKT, and MAPK pathways. The very small number of biological replicates limits causal interpretation.
GBA2-associated spastic ataxia Unaffected control
neuron CL:0000540 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
Patient lymphoblastoid cells, fibroblasts, and iPSC-derived neurons homozygous for GBA2 c.1780G>C, compared with control cells
Pathograph links
Glucosylceramide Accumulation and Sphingolipid Imbalance The model examines transcriptional consequences of GBA2-associated lipid dysregulation.
Show evidence (1 reference)
PMID:35277195 SUPPORT In Vitro
"next-generation RNA-sequencing (RNA-seq), in an attempt to discover differentially expressed genes (DEGs) in lymphoblastoid, fibroblast cell lines and induced pluripotent stem cell-derived neurons derived from patients"
The study defines the patient-derived multi-tissue transcriptome model.
Show evidence (1 reference)
PMID:35277195 SUPPORT In Vitro
"the mechanism by which GBA2 variants lead to the development of SA is still unclear."
The authors explicitly frame their pathway results as exploratory.
Disease-associated GBA2 truncation transfection model CELL_LINE
Selected C-terminally truncated GBA2 constructs mislocalize to the mitochondrial matrix and produce mitochondrial fragmentation and loss of membrane potential. The artificial-expression design and restricted variant classes limit extrapolation to all patients.
Wild-type GBA2 transfection Disease-associated GBA2-233 or GBA2-339 truncation transfection
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Pathograph links
Biallelic GBA2 Loss of Function The model tests variant-specific consequences beyond catalytic loss.
Show evidence (1 reference)
PMID:32492073 SUPPORT In Vitro
"C-terminally truncated mutants terminating after amino acids 233 and 339 (GBA2-233 and -339) were present in the mitochondrial matrix"
The cell model demonstrates truncation-specific mitochondrial localization.
Show evidence (1 reference)
PMID:32492073 SUPPORT In Vitro
"induced mitochondrial fragmentation and loss of mitochondrial transmembrane potential."
The model directly measures mitochondrial structural and functional effects.
🐁

Animal Models

2
Antisense morpholino knockdown of the zebrafish GBA2 ortholog zebrafish (Danio rerio) Transient loss-of-function model
Knockdown produces abnormal motor behavior and shortened, abnormally branched motor axons. Human wild-type GBA2 mRNA rescues the phenotype, whereas disease-associated missense mRNA does not.
Abnormal motor behavior Motor-axon shortening Abnormal motor-axon branching
Species
zebrafish (Danio rerio)
Genotype
Antisense morpholino knockdown of the zebrafish GBA2 ortholog
Genes
GBA2 hgnc:18986 HUGO Gene Nomenclature Committee (hgnc) Relation: this experimental model concerns this gene This experimental model concerns GBA2 (hgnc:18986). hgnc:18986 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:23332916 SUPPORT Model Organism
"axonal shortening/branching of motoneurons that were rescued by the human wild-type mRNA but not by applying the same mRNA containing the missense mutation."
The rescue experiment links motor-axon defects specifically to functional GBA2.
Gba2 knockout mouse (Mus musculus) Germline loss-of-function model
Gba2-null mice show strain- or individual-dependent locomotor abnormalities, but some have only mild gait changes and no cerebellar defects. The model is useful for biochemical and neurite studies but incompletely phenocopies human SPG46.
Variable locomotor impairment Mild gait alteration Male infertility
Species
mouse (Mus musculus)
Genotype
Gba2 knockout
Genes
GBA2 hgnc:18986 HUGO Gene Nomenclature Committee (hgnc) Relation: this experimental model concerns this gene This experimental model concerns GBA2 (hgnc:18986). hgnc:18986 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:30662006 SUPPORT Model Organism
"Whereas some GBA2-KO mice displayed a strong locomotor defect, others displayed only mild alterations of the gait pattern and no signs of cerebellar defects."
The study directly defines both the model phenotype and its translational limitation.
{ }

Source YAML

click to show 
name: Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity
creation_date: "2026-06-13T00:00:00Z"
category: Mendelian
description: >-
  Autosomal recessive cerebellar ataxia with late-onset spasticity is one
  presentation of the biallelic GBA2 disease spectrum, most often termed
  hereditary spastic paraplegia 46 (SPG46). Presentations range from
  ataxia-predominant disease in which spasticity emerges later to early-onset
  complex hereditary spastic paraplegia and a Marinesco-Sjögren-like phenotype.
  Across these labels, cerebellar ataxia and lower-limb spasticity coexist, with
  variable peripheral neuropathy, cognitive impairment, cataracts, scoliosis,
  hypogonadism, movement disorders, and characteristic but inconsistent MRI
  abnormalities. Biallelic GBA2 variants severely reduce the nonlysosomal
  glucosylceramidase that hydrolyzes glucosylceramide to glucose and ceramide.
  Glucosylceramide accumulation is established in patient material, but the
  downstream mechanism linking lipid imbalance to selective corticospinal,
  cerebellar, peripheral-nerve, ocular, and endocrine manifestations remains
  incompletely resolved.
synonyms:
- GBA2-related spastic ataxia
- GBA2-related disorder
- hereditary spastic paraplegia 46
- spastic paraplegia 46
- SPG46
- GBA2-related Marinesco-Sjögren-like syndrome
parents:
- Hereditary Ataxia
- Hereditary Spastic Paraplegia
disease_term:
  preferred_term: autosomal recessive cerebellar ataxia with late-onset spasticity
  term:
    id: MONDO:0018129
    label: autosomal recessive cerebellar ataxia with late-onset spasticity
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0018129
      label: autosomal recessive cerebellar ataxia with late-onset spasticity
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
references:
- reference: PMID:23332916
  title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
- reference: PMID:23332917
  title: Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
- reference: PMID:26220345
  title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
- reference: PMID:28052128
  title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
- reference: PMID:30662006
  title: Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
- reference: PMID:30864417
  title: Assay of β-glucosidase 2 (GBA2) activity using lithocholic acid β-3-O-glucoside substrate for cultured fibroblasts and glucosylceramide for brain tissue.
- reference: PMID:32492073
  title: Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation.
- reference: PMID:34251556
  title: "Spastic paraplegia type 46: novel and recurrent GBA2 gene variants in a compound heterozygous Italian patient with spastic ataxia phenotype."
- reference: PMID:35277195
  title: Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia.
- reference: PMID:38334933
  title: "Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature."
- reference: PMID:42384114
  title: "Hypogonadotrophic hypogonadism in GBA2 associated spastic paraplegia type 46 (SPG46): a phenotypic expansion."
- reference: PMID:20301682
  title: Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview.
- reference: clinicaltrials:NCT01793168
  title: Coordination of Rare Diseases at Sanford
clinical_burden:
  burden_level: VARIABLE
  rationale: >-
    Burden varies substantially with age at onset, predominant presentation,
    and disease duration. The course is usually slow, but combined spasticity,
    ataxia, neuropathy, cognitive impairment, cataracts, skeletal deformity, and
    bladder symptoms can progressively impair walking, self-care, vision, and
    independence over decades.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Disease course was slowly progressive (mean 32 years at the time of last
      examination).
    explanation: The contemporary case series documents decades of progressive disease.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Disease results from biallelic pathogenic GBA2 variants; reported families
    are frequently consanguineous, although compound-heterozygous cases also
    occur.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:38334933
    reference_title: "Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SPG46 is a rare, early-onset and autosomal recessive HSP, linked to
      biallelic GBA2 mutations.
    explanation: The current series and literature review defines biallelic GBA2 disease as autosomal recessive.
mechanistic_hypotheses:
- hypothesis_group_id: gba2_loss_glucosylceramide_model
  hypothesis_label: GBA2 Loss and Glucosylceramide-Dysregulation Model
  status: CANONICAL
  description: >-
    Biallelic disease-associated GBA2 variants cause severe loss of
    nonlysosomal glucosylceramidase activity. Reduced hydrolysis of
    glucosylceramide raises glucosylceramide in patient material and establishes
    the primary biochemical lesion. This does not by itself establish which
    lipid species, membrane compartment, or neural cell population drives the
    clinical syndrome.
  evidence:
  - reference: PMID:26220345
    reference_title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      none of the GBA2 mutant cDNAs raised the enzyme activity in transfected
      cells, in contrast to the wild-type enzyme.
    explanation: Biochemical testing establishes severe loss of activity across representative disease-associated variants.
  - reference: PMID:28052128
    reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our studies show that a reduced activity of GBA2 is sufficient to elevate
      the levels of glucosylceramide to similar levels as seen in Gaucher disease.
    explanation: Patient leukocytes directly connect reduced GBA2 activity to glucosylceramide elevation.
- hypothesis_group_id: gba2_neurite_axon_model
  hypothesis_label: Actin, Neurite-Outgrowth, and Axonal-Development Model
  status: EMERGING
  description: >-
    GBA2 inhibition perturbs F-actin dynamics and neurite outgrowth in isolated
    cerebellar neurons, while zebrafish knockdown shortens and abnormally
    branches motor axons. These models provide a plausible bridge from lipid
    imbalance to long-tract and cerebellar dysfunction, but neither model fully
    reproduces the human phenotype and the intervening molecular steps remain
    uncertain.
  evidence:
  - reference: PMID:30662006
    reference_title: Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      inhibition of GBA2 activity in isolated cerebellar neurons dramatically
      affected F-actin dynamics and reduced neurite outgrowth
    explanation: The mammalian neuron experiment supports an actin/neurite mechanism.
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      led to abnormal motor behavior and axonal shortening/branching of
      motoneurons that were rescued by the human wild-type mRNA
    explanation: Zebrafish rescue experiments support a GBA2-dependent motor-axon phenotype.
- hypothesis_group_id: truncating_variant_mitochondrial_model
  hypothesis_label: Truncating-Variant Mitochondrial Mislocalization Model
  status: EMERGING
  description: >-
    In transfected cells, selected early C-terminal truncations enter the
    mitochondrial matrix and cause fragmentation and membrane-potential loss.
    This is a variant-class-specific cell-model result, not evidence that all
    GBA2 variants cause mitochondrial disease in patients.
  evidence:
  - reference: PMID:32492073
    reference_title: Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the C-terminally truncated mutants terminating after amino acids 233 and
      339 (GBA2-233 and -339) were present in the mitochondrial matrix, induced
      mitochondrial fragmentation and loss of mitochondrial transmembrane potential.
    explanation: The experiment supports a truncation-specific mitochondrial branch while limiting its generalization.
- hypothesis_group_id: patient_transcriptome_stress_signals
  hypothesis_label: Patient-Cell Stress and Signaling Model
  status: EMERGING
  description: >-
    RNA sequencing of lymphoblasts, fibroblasts, and iPSC-derived neurons from
    patients homozygous for one GBA2 missense variant identified oxidative
    stress, neuroinflammatory, sphingolipid, PI3K-AKT, and MAPK pathway signals.
    The sample size was small and the authors framed these as candidates
    requiring validation rather than demonstrated causal pathways.
  evidence:
  - reference: PMID:35277195
    reference_title: Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Among them are the oxidative stress, neuroinflammation, sphingolipid
      signaling and metabolism, PI3K-Akt and MAPK signaling pathways.
    explanation: The patient-cell transcriptome nominates, but does not causally establish, these pathways.
pathophysiology:
- name: Biallelic GBA2 Loss of Function
  description: >-
    Biallelic nonsense, frameshift, splice, and missense variants cause severe
    reduction or loss of GBA2 activity. Both absent protein and catalytically
    inactive protein can produce the biochemical lesion.
  gene:
    preferred_term: GBA2
    modifier: DECREASED
    term:
      id: hgnc:18986
      label: GBA2
  genes:
  - preferred_term: GBA2
    term:
      id: hgnc:18986
      label: GBA2
  evidence:
  - reference: PMID:23332917
    reference_title: Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We were able to identify mutations responsible for autosomal-recessive
      ataxia in these families within the gene encoding β-glucosidase 2, GBA2.
    explanation: Independent families establish biallelic GBA2 as the causal genetic lesion.
  - reference: PMID:26220345
    reference_title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SPG46 patients have a severe deficit in GBA2 activity, because the GBA2
      mutants are intrinsically inactive and/or reduced in amount.
    explanation: Variant assays explain the lesion as intrinsic inactivity and/or reduced abundance.
  downstream:
  - target: Nonlysosomal Glucosylceramidase Deficiency
    description: Disease-associated variants severely reduce GBA2 catalytic activity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:26220345
      reference_title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        none of the GBA2 mutant cDNAs raised the enzyme activity in transfected
        cells, in contrast to the wild-type enzyme.
      explanation: Direct comparison with wild type demonstrates loss of enzymatic activity.
- name: Nonlysosomal Glucosylceramidase Deficiency
  description: >-
    GBA2 is an endoplasmic-reticulum/plasma-membrane-associated nonlysosomal
    glucosylceramidase that hydrolyzes glucosylceramide to glucose and ceramide.
    Deficiency impairs this catabolic reaction.
  biological_processes:
  - preferred_term: glucosylceramide catabolic process
    modifier: DECREASED
    term:
      id: GO:0006680
      label: glucosylceramide catabolic process
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GBA2 encodes a microsomal nonlysosomal glucosylceramidase that catalyzes
      the conversion of glucosylceramide to free glucose and ceramide
    explanation: The defining report establishes the enzyme and reaction affected.
  downstream:
  - target: Glucosylceramide Accumulation and Sphingolipid Imbalance
    description: Reduced GBA2 hydrolysis raises glucosylceramide in patient cells.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28052128
      reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        a reduced activity of GBA2 is sufficient to elevate the levels of
        glucosylceramide to similar levels as seen in Gaucher disease.
      explanation: Patient biochemical data directly support substrate accumulation after GBA2 deficiency.
- name: Glucosylceramide Accumulation and Sphingolipid Imbalance
  description: >-
    Glucosylceramide accumulation is measurable in affected human material.
    How this membrane-lipid disturbance selects long corticospinal axons,
    cerebellar circuits, peripheral nerves, lens, and reproductive/endocrine
    tissues is not yet established.
  evidence:
  - reference: PMID:28052128
    reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      reduced activity of GBA2 is sufficient to elevate the levels of
      glucosylceramide
    explanation: Patient material establishes glucosylceramide elevation.
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      resulting in abnormal increase of glucosylceramide, although the
      pathogenic mechanism of neurodegeneration is still unclear
    explanation: The current review explicitly preserves uncertainty downstream of the lipid lesion.
  downstream:
  - target: Axonal and Neurite Dysfunction
    description: >-
      Experimental systems connect GBA2 loss to altered actin dynamics,
      impaired neurite extension, and abnormal motor-axon morphology, but the
      lipid-to-cytoskeleton intermediates remain unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30662006
      reference_title: Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        inhibition of GBA2 activity in isolated cerebellar neurons dramatically
        affected F-actin dynamics and reduced neurite outgrowth
      explanation: GBA2 inhibition produces actin and neurite defects in mammalian cerebellar neurons.
  - target: Variable Multisystem Expression With Unresolved Intermediates
    description: >-
      Cataract, hypogonadism, and skeletal deformity accompany the neurologic
      syndrome, but their intervening cell and tissue mechanisms are unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:28052128
      reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        autosomal recessive cerebellar ataxia with cataracts and mental retardation
      explanation: The GBA2 phenotype includes reproducible extraneural manifestations without defining their mechanism.
- name: Axonal and Neurite Dysfunction
  description: >-
    Zebrafish GBA2 knockdown causes motor-axon shortening and abnormal
    branching, while GBA2 inhibition alters F-actin and neurite outgrowth in
    isolated cerebellar neurons. Species differences and incomplete mouse
    phenocopy limit certainty about the human downstream pathway.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: actin cytoskeleton organization
    modifier: ABNORMAL
    term:
      id: GO:0030036
      label: actin cytoskeleton organization
  - preferred_term: neuron projection development
    modifier: ABNORMAL
    term:
      id: GO:0031175
      label: neuron projection development
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      abnormal motor behavior and axonal shortening/branching of motoneurons
    explanation: The zebrafish model directly demonstrates altered motor-axon morphology.
  - reference: PMID:30662006
    reference_title: Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      these mice exhibited a high phenotypic variance and did not fully resemble
      the human phenotype
    explanation: The mouse-model limitation prevents overstatement of the inferred human pathway.
  downstream:
  - target: Central and Peripheral Neurologic Syndrome
    description: >-
      Long-tract, cerebellar, and peripheral-neural dysfunction produces the
      combined spastic-ataxia syndrome and associated imaging findings.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23332916
      reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        abnormal motor behavior and axonal shortening/branching of motoneurons
        that were rescued by the human wild-type mRNA
      explanation: Rescue supports GBA2-dependent motor-neural dysfunction, while human circuit intermediates remain unknown.
- name: Central and Peripheral Neurologic Syndrome
  description: >-
    Human GBA2 disease consistently combines spastic paraparesis and cerebellar
    syndrome. Peripheral neuropathy, cognitive involvement, movement disorders,
    gaze palsy, bladder dysfunction, and variable MRI abnormalities broaden the
    neurologic phenotype.
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  - preferred_term: corpus callosum
    term:
      id: UBERON:0002336
      label: corpus callosum
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In all cases reported so far, the presence of both spastic paraparesis
      and cerebellar syndrome has been consistently observed
    explanation: The 67-case synthesis identifies the paired core neurologic features.
  downstream:
  - target: Cerebellar ataxia
    description: Cerebellar circuit dysfunction manifests as progressive ataxia.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23332917
      reference_title: Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This study suggests GBA2 mutations are a cause of recessive spastic ataxia
      explanation: Independent families establish cerebellar ataxia within GBA2 disease.
  - target: Spastic paraplegia
    description: Corticospinal involvement manifests as progressive lower-limb spastic paraparesis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23332916
      reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        a complicated autosomal-recessive form of hereditary spastic paraplegia
      explanation: The defining report classifies the syndrome as complicated recessive HSP.
  - target: Peripheral neuropathy
    description: Peripheral nerve involvement is frequent but variably ascertained.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cerebellar syndrome (4/5), sphincteric symptoms (like urge incontinence,
        3/5), intellectual disability (MCI, 4/5), peripheral neuropathy (4/5)
      explanation: The contemporary series documents peripheral neuropathy in four of five individuals.
  - target: Cognitive impairment
    description: Cognitive impairment is common and may emerge late.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        MCI is a common feature
      explanation: The literature synthesis identifies cognitive impairment as common.
  - target: Cerebellar atrophy
    description: Cerebellar atrophy is a variable rather than obligatory imaging correlate.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Brain MRI may display WMA, TCC, cerebral, brainstem and cerebellar atrophy.
      explanation: The current review defines the variable imaging spectrum.
  - target: Corpus callosum atrophy
    description: A thin or atrophic corpus callosum is a frequent but inconsistent MRI finding.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23332916
      reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        various degrees of corpus callosum and cerebellar atrophy on brain imaging
      explanation: The original SPG46 families show variable callosal and cerebellar atrophy.
  - target: Cerebral white matter abnormalities
    description: White-matter abnormalities occur in a minority overall but were prominent in the recent Italian series.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        the most frequent sign was WMA (4/5), followed by TCC (2/5).
      explanation: The Italian MRI series documents white-matter abnormalities and thin corpus callosum.
  - target: Dystonia
    description: Limb or cranial dystonia is part of the variable movement-disorder spectrum.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Movement disorders, like head and upper limbs’ tremor, cranial and upper
        limbs’ dystonia, can be observed with moderate occurrence
      explanation: The 67-case review identifies dystonia among recurrent movement disorders.
  - target: Tremor
    description: Head or limb tremor occurs in a subset.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Movement disorders, like head and upper limbs’ tremor, cranial and upper
        limbs’ dystonia
      explanation: The review documents head and limb tremor in the movement-disorder spectrum.
  - target: Vertical supranuclear gaze palsy
    description: Upper-gaze palsy is an occasional and potentially identifying ocular-motor feature.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Among the other neurological signs, UGP is the most frequent (19%
      explanation: The review estimates upper-gaze palsy in roughly one fifth of assessed cases.
  - target: Urinary urgency
    description: Neurogenic bladder symptoms, particularly urgency or urge incontinence, occur variably.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        sphincteric symptoms (like urge incontinence, 3/5)
      explanation: Three of five individuals in the contemporary series had sphincter symptoms such as urge incontinence.
- name: Variable Multisystem Expression With Unresolved Intermediates
  description: >-
    Cataracts, male hypogonadism, scoliosis, and foot deformity recur across the
    GBA2 spectrum, but neither a single developmental nor degenerative mechanism
    has been established for these manifestations.
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The overall phenotype was a complex HSP with mental impairment, cataract,
      and hypogonadism in males
    explanation: The original families establish recurrent ocular and endocrine manifestations.
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      neuropathy, MCI, bilateral cataracts, scoliosis, pes cavus and
      hypogonadism are observed with varying prevalence
    explanation: The updated literature review emphasizes variable expressivity of multisystem findings.
  downstream:
  - target: Cataract
    description: Bilateral cataracts can create a Marinesco-Sjögren-like presentation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:28052128
      reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        autosomal recessive cerebellar ataxia with cataracts and mental retardation
      explanation: Two Norwegian families establish cataract within the GBA2 spectrum.
  - target: Hypogonadism
    description: Hypogonadism occurs in a minority of affected males.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:23332916
      reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        hypogonadism in males associated with various degrees of corpus callosum
      explanation: The original SPG46 cohort documents male hypogonadism.
  - target: Scoliosis
    description: Scoliosis is an occasional orthopedic complication of the chronic motor syndrome.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34251556
      reference_title: "Spastic paraplegia type 46: novel and recurrent GBA2 gene variants in a compound heterozygous Italian patient with spastic ataxia phenotype."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        progressively manifested spastic-ataxia, scoliosis, mild intellectual
        decline, and bilateral cataract.
      explanation: A molecularly confirmed individual developed scoliosis during the progressive syndrome.
  - target: Pes cavus
    description: Pes cavus and other foot deformities occur variably.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
      reference_title: "Keywords"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        scoliosis (2/5) and pes cavus (1/5).
      explanation: The contemporary series documents both scoliosis and pes cavus.
phenotypes:
- category: Neurologic
  name: Cerebellar ataxia
  description: >-
    Cerebellar ataxia is a core feature. In ataxia-predominant families it may
    precede pronounced spasticity, whereas many SPG46 cohorts begin with
    lower-limb spasticity.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:23332917
    reference_title: Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      four unrelated consanguineous families of Tunisian decent diagnosed with
      cerebellar ataxia of unknown origin
    explanation: The independent ARCA cohort establishes cerebellar ataxia as a defining presentation.
- category: Neurologic
  name: Spastic paraplegia
  description: >-
    Progressive lower-limb pyramidal dysfunction is the dominant feature in
    most reports and may emerge after cerebellar ataxia in ARCA-labeled cases.
  phenotype_term:
    preferred_term: Spastic paraplegia
    term:
      id: HP:0001258
      label: Spastic paraplegia
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In all cases reported so far, the presence of both spastic paraparesis
      and cerebellar syndrome has been consistently observed
    explanation: The literature synthesis treats spastic paraparesis and cerebellar syndrome as paired core findings.
- category: Neurologic
  name: Peripheral neuropathy
  description: Peripheral neuropathy is frequent but incompletely reported across cohorts.
  phenotype_term:
    preferred_term: Peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  frequency: VERY_FREQUENT
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      peripheral neuropathy (4/5)
    explanation: Four of five individuals in the contemporary series had peripheral neuropathy.
- category: Neurologic
  name: Cognitive impairment
  description: Cognitive impairment is common, variably severe, and can become apparent late.
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
  frequency: FREQUENT
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      About half of the cases described so far show MCI, but its prevalence may
      turn out to be higher, due to later onset
    explanation: The review notes both common cognitive impairment and delayed ascertainment.
- category: Neurologic
  name: Dystonia
  description: Limb, cervical, or facial dystonia occurs in a subset and can rarely be the presenting movement disorder.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  frequency: FREQUENT
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cervical dystonia has been outlined as the onset symptom in one patient
    explanation: The review documents dystonia as both an associated and occasional presenting sign.
- category: Neurologic
  name: Tremor
  description: Head and upper-limb tremor are recurrent movement-disorder manifestations.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  frequency: OCCASIONAL
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      head and upper limbs’ tremor
    explanation: The 67-case review includes head and limb tremor.
- category: Neurologic
  name: Vertical supranuclear gaze palsy
  description: Upper-gaze palsy is an occasional, potentially identifying ocular-motor feature.
  phenotype_term:
    preferred_term: Vertical supranuclear gaze palsy
    term:
      id: HP:0000511
      label: Vertical supranuclear gaze palsy
  frequency: OCCASIONAL
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In two patients, we found ocular movement disorder (upper gaze palsy (UGP)).
    explanation: Upper-gaze palsy was directly observed in two of five contemporary cases.
- category: Neurologic
  name: Urinary urgency
  description: Sphincter dysfunction can include urinary urgency or urge incontinence.
  phenotype_term:
    preferred_term: Urinary urgency
    term:
      id: HP:0000012
      label: Urinary urgency
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      sphincteric symptoms (like urge incontinence, 3/5)
    explanation: The recent series directly documents urge-incontinence-type sphincter symptoms.
- category: Ophthalmologic
  name: Cataract
  description: Bilateral cataract is common and may create a Marinesco-Sjögren-like presentation.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  frequency: FREQUENT
  evidence:
  - reference: PMID:28052128
    reference_title: "GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      autosomal recessive cerebellar ataxia with cataracts and mental retardation
    explanation: Molecular diagnosis in two Norwegian families establishes the cataract-associated GBA2 phenotype.
- category: Endocrine
  name: Hypogonadism
  description: Hypogonadism is an occasional feature in affected males.
  phenotype_term:
    preferred_term: Hypogonadism
    term:
      id: HP:0000135
      label: Hypogonadism
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      hypogonadism in males
    explanation: The original molecular series documents hypogonadism in affected males.
- category: Musculoskeletal
  name: Scoliosis
  description: Scoliosis occurs in a minority and can add orthopedic burden.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:34251556
    reference_title: "Spastic paraplegia type 46: novel and recurrent GBA2 gene variants in a compound heterozygous Italian patient with spastic ataxia phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      progressively manifested spastic-ataxia, scoliosis, mild intellectual
      decline, and bilateral cataract.
    explanation: This molecularly confirmed case documents progressive scoliosis with the neurologic syndrome.
- category: Musculoskeletal
  name: Pes cavus
  description: Pes cavus and related foot deformity occur variably.
  phenotype_term:
    preferred_term: Pes cavus
    term:
      id: HP:0001761
      label: Pes cavus
  frequency: OCCASIONAL
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      pes cavus (1/5)
    explanation: Pes cavus was directly observed in the contemporary series.
- category: Imaging
  name: Cerebellar atrophy
  description: Cerebellar atrophy is characteristic but not obligatory.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  frequency: FREQUENT
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cerebellar atrophy on brain imaging.
    explanation: Cerebellar atrophy was present across the original families to variable degrees.
- category: Imaging
  name: Corpus callosum atrophy
  description: Thin or atrophic corpus callosum is a frequent but inconsistent imaging feature.
  phenotype_term:
    preferred_term: Corpus callosum atrophy
    term:
      id: HP:0007371
      label: Corpus callosum atrophy
  frequency: FREQUENT
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      various degrees of corpus callosum and cerebellar atrophy on brain imaging
    explanation: The original series documents callosal and cerebellar atrophy.
- category: Imaging
  name: Cerebral white matter abnormalities
  description: White-matter abnormalities are variable and may be prominent in some cohorts.
  phenotype_term:
    preferred_term: Cerebral white matter abnormality
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
  frequency: OCCASIONAL
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      significant differences concerning WMA (80% versus 15%).
    explanation: The review contrasts high WMA prevalence in its five cases with the lower cumulative literature estimate.
genetic:
- name: Biallelic GBA2 pathogenic variants
  gene_term:
    preferred_term: GBA2
    term:
      id: hgnc:18986
      label: GBA2
  association: Causative
  inheritance:
  - name: Autosomal recessive inheritance
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:38334933
      reference_title: "Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        autosomal recessive HSP, linked to biallelic GBA2 mutations.
      explanation: The current synthesis establishes recessive biallelic inheritance.
  notes: >-
    Pathogenic alleles include nonsense, frameshift, splice, and missense
    variants. Severe loss of activity is common across classes, but current
    evidence does not support a simple genotype-phenotype rule; identical or
    intrafamilial genotypes can yield HSP-, ARCA-, or
    Marinesco-Sjögren-like-predominant presentations.
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      four different mutations in GBA2 (three truncating variants and one
      missense variant), which were found to cosegregate with the disease
    explanation: The original report establishes cosegregation of multiple GBA2 variant classes.
  - reference: PMID:26220345
    reference_title: Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      five nonsense and five missense GBA2 mutants
    explanation: Biochemical study spans both truncating and missense disease-associated alleles.
prevalence:
- population: Worldwide published cases through the 2024 literature review
  notes: >-
    Ultra-rare. The 2024 synthesis counted 67 affected people from 36 families
    across 18 countries; reported concentration around the Mediterranean likely
    reflects both consanguinity and ascertainment rather than a population
    prevalence estimate.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thus far, a total of 67 cases (30 men, 34 women, sex not specified in
      three) from 36 families have been described worldwide
    explanation: The review provides the most complete published case count available for the audit.
progression:
- phase: Early presentation
  age_range: Congenital onset through early adulthood; childhood onset is typical
  notes: >-
    Most SPG46 cohorts begin with lower-limb spasticity in childhood. In
    ataxia-predominant families, cerebellar ataxia can be the first recognized
    feature and marked spasticity may emerge later.
  evidence:
  - reference: PMID:38334933
    reference_title: "Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SPG46 is a rare, early-onset and autosomal recessive HSP
    explanation: The current synthesis characterizes SPG46 as early onset.
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      initially diagnosed the condition as autosomal recessive ataxia, as the
      first presentation involved cerebellar syndrome. However, shortly
      thereafter, in addition to peripheral neuropathy, significant spasticity emerged
    explanation: This sequence explains the disease label's late-spasticity presentation without generalizing it to all SPG46.
- phase: Slowly progressive multisystem syndrome
  duration: Decades
  notes: >-
    Ataxia and spasticity progress slowly over years to decades. Additional
    neurologic, ocular, cognitive, skeletal, bladder, and endocrine features may
    accumulate with disease duration.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In our study, all patients had early onset (6.8 year) and slow progression
      over time.
    explanation: The five-person series documents early onset and slow progression.
diagnosis:
- name: Molecular genetic testing for biallelic GBA2 variants
  description: >-
    Diagnosis is established by detecting pathogenic or likely pathogenic
    variants on both GBA2 alleles, generally through a hereditary
    spastic-paraplegia/ataxia panel, exome sequencing, or genome sequencing.
    Segregation and copy-number analysis should be considered where appropriate.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:23332917
    reference_title: Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      homozygosity mapping and whole-exome sequencing
    explanation: Exome sequencing identified the causal GBA2 variants in independent ARCA families.
- name: Leukocyte GBA2 enzyme-activity assay
  description: >-
    Markedly reduced GBA2 activity in leukocytes can support a molecular
    diagnosis and provide functional evidence for a variant, but assay methods
    can underestimate activity and testing is not a substitute for biallelic
    molecular confirmation.
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      no residual glucocerebrosidase activity of GBA2 could be evidenced in
      blood cells
    explanation: The original report demonstrates absent blood-cell activity in an affected individual.
  - reference: PMID:30864417
    reference_title: Assay of β-glucosidase 2 (GBA2) activity using lithocholic acid β-3-O-glucoside substrate for cultured fibroblasts and glucosylceramide for brain tissue.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Current GBA2 activity assays using artificial substrates incompletely
      model the activity encountered in vivo.
    explanation: The assay study explains why substrate and tissue context matter when interpreting GBA2 activity.
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      this method of measuring GBA2 activity may lead to underestimating GBA2 activity
    explanation: The contemporary series states the assay's methodological limitation.
- name: Neurologic, ophthalmologic, neurophysiologic, and MRI phenotyping
  description: >-
    Baseline assessment should define pyramidal and cerebellar involvement,
    cognition, eye movements and cataracts, peripheral neuropathy, bladder
    symptoms, skeletal deformity, and brain MRI findings. Normal imaging or
    absence of cataract does not exclude the diagnosis.
  evidence:
  - reference: PMID:38334933
    reference_title: "Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      underwent neurological examination, clinical cognitive assessment, column
      imaging for scoliosis assessment, ophthalmologic examination, brain
      imaging, GBA2 activity in peripheral blood cells and genetic testing.
    explanation: The current multicenter series demonstrates the relevant multidisciplinary diagnostic assessment.
differential_diagnoses:
- name: SIL1-related Marinesco-Sjögren syndrome
  description: >-
    Both disorders can combine cerebellar ataxia, cataracts, cognitive
    impairment, hypogonadism, and skeletal abnormalities. Childhood hypotonia
    and myopathy favor SIL1-related disease, whereas early lower-limb spastic
    paraparesis favors GBA2/SPG46; molecular testing is definitive.
  distinguishing_features:
  - SIL1-related disease classically includes childhood hypotonia and myopathy.
  - GBA2 disease usually develops prominent lower-limb spastic paraparesis.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Its clinical hallmarks are child-onset hypotonia and muscle weakness but
      not spasticity in lower limbs
    explanation: The review contrasts SIL1-related Marinesco-Sjögren hallmarks with GBA2-associated early spastic paraparesis.
- name: Other hereditary spastic ataxias and complex hereditary spastic paraplegias
  description: >-
    ARSACS, SPG11, SPG15, SPG7, CYP2U1-, DDHD2-, and other gene-associated
    disorders can share spasticity, ataxia, neuropathy, callosal change, and
    cognitive findings. A broad panel or exome/genome analysis is often more
    appropriate than phenotype-only single-gene selection.
  distinguishing_features:
  - Cataract plus markedly reduced leukocyte GBA2 activity supports GBA2 disease.
  - Gene-specific imaging, retinal, dental, movement, or systemic features can redirect testing.
  evidence:
  - reference: PMID:20301682
    reference_title: Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Review the differential diagnosis of uncomplicated hereditary spastic
      paraplegia, which includes complicated hereditary spastic paraplegia with
      a focus on treatable genetic disorders
    explanation: GeneReviews places complex hereditary spastic paraplegia and treatable mimics in the diagnostic differential.
treatments:
- name: Multidisciplinary supportive care
  description: >-
    No GBA2-directed disease-modifying treatment has been established.
    Management is individualized to preserve function and address spasticity,
    ataxia, neuropathy, bladder symptoms, cognition, cataracts, and orthopedic
    complications through neurology, rehabilitation, ophthalmology, urology,
    orthopedics, and genetics services.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: "url:https://www.ncbi.nlm.nih.gov/books/NBK1509/"
    reference_title: "Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview - GeneReviews® - NCBI Bookshelf"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      At present, no specific treatments can prevent or reverse nerve
      degeneration in uncomplicated HSP. Supportive care to improve quality of
      life, maximize function, and reduce complications is recommended.
    explanation: Current HSP management guidance supports multidisciplinary symptomatic care rather than disease-modifying claims.
- name: Individualized physical and occupational rehabilitation
  description: >-
    Stretching, strengthening, balance and gait training, orthoses, mobility
    aids, and occupational adaptations are selected according to spasticity,
    weakness, ataxia, contracture risk, and daily-living needs.
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - preferred_term: Spastic paraplegia
    term:
      id: HP:0001258
      label: Spastic paraplegia
  - preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: "url:https://www.ncbi.nlm.nih.gov/books/NBK1509/"
    reference_title: "Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview - GeneReviews® - NCBI Bookshelf"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Individualized PT program
    explanation: GeneReviews recommends individualized physical therapy for HSP motor impairment.
  - reference: "url:https://www.ncbi.nlm.nih.gov/books/NBK1509/"
    reference_title: "Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview - GeneReviews® - NCBI Bookshelf"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Gait training; use of assistive walking devices
    explanation: Current guidance includes gait training and mobility aids.
- name: Symptomatic antispastic pharmacotherapy
  description: >-
    Oral baclofen or tizanidine can be considered for function-limiting
    spasticity; focal botulinum toxin or intrathecal baclofen may be considered
    by specialists in selected severe cases. Treatment should avoid reducing
    compensatory tone enough to worsen walking.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: baclofen
      term:
        id: CHEBI:2972
        label: baclofen
    - preferred_term: tizanidine
      term:
        id: CHEBI:63629
        label: tizanidine
  therapeutic_modality: SMALL_MOLECULE
  target_phenotypes:
  - preferred_term: Spastic paraplegia
    term:
      id: HP:0001258
      label: Spastic paraplegia
  evidence:
  - reference: "url:https://www.ncbi.nlm.nih.gov/books/NBK1509/"
    reference_title: "Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview - GeneReviews® - NCBI Bookshelf"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Baclofen, botulinum toxin, dantrolene, tizanidine (used 1 at a time)
    explanation: Current HSP guidance lists the symptomatic antispastic options.
clinical_trials:
- name: NCT01793168
  status: RECRUITING
  description: >-
    CoRDS is a broad international rare-disease registry and natural-history
    study whose current condition list explicitly includes this MONDO disease
    label. It is observational and not a GBA2-targeted therapeutic trial.
    ClinicalTrials.gov listed it as recruiting when audited on 2026-07-23.
  evidence:
  - reference: clinicaltrials:NCT01793168
    reference_title: Coordination of Rare Diseases at Sanford
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It provides researchers with a centralized, international patient registry
      for all rare diseases.
    explanation: The registry record supports its broad observational role rather than therapeutic efficacy.
animal_models:
- species: zebrafish (Danio rerio)
  genotype: Antisense morpholino knockdown of the zebrafish GBA2 ortholog
  category: Transient loss-of-function model
  genes:
  - preferred_term: GBA2
    term:
      id: hgnc:18986
      label: GBA2
  description: >-
    Knockdown produces abnormal motor behavior and shortened, abnormally
    branched motor axons. Human wild-type GBA2 mRNA rescues the phenotype,
    whereas disease-associated missense mRNA does not.
  associated_phenotypes:
  - Abnormal motor behavior
  - Motor-axon shortening
  - Abnormal motor-axon branching
  evidence:
  - reference: PMID:23332916
    reference_title: Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      axonal shortening/branching of motoneurons that were rescued by the human
      wild-type mRNA but not by applying the same mRNA containing the missense mutation.
    explanation: The rescue experiment links motor-axon defects specifically to functional GBA2.
- species: mouse (Mus musculus)
  genotype: Gba2 knockout
  category: Germline loss-of-function model
  genes:
  - preferred_term: GBA2
    term:
      id: hgnc:18986
      label: GBA2
  description: >-
    Gba2-null mice show strain- or individual-dependent locomotor abnormalities,
    but some have only mild gait changes and no cerebellar defects. The model is
    useful for biochemical and neurite studies but incompletely phenocopies
    human SPG46.
  associated_phenotypes:
  - Variable locomotor impairment
  - Mild gait alteration
  - Male infertility
  evidence:
  - reference: PMID:30662006
    reference_title: Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Whereas some GBA2-KO mice displayed a strong locomotor defect, others
      displayed only mild alterations of the gait pattern and no signs of
      cerebellar defects.
    explanation: The study directly defines both the model phenotype and its translational limitation.
experimental_models:
- name: Patient-derived GBA2 spastic-ataxia cellular transcriptome model
  experimental_model_type: IPSC_DERIVED_MODEL
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  cell_source: >-
    Patient lymphoblastoid cells, fibroblasts, and iPSC-derived neurons
    homozygous for GBA2 c.1780G>C, compared with control cells
  conditions:
  - GBA2-associated spastic ataxia
  - Unaffected control
  description: >-
    RNA sequencing across three patient-derived cell types identified thousands
    of differential transcripts and nominated oxidative-stress,
    neuroinflammatory, sphingolipid, PI3K-AKT, and MAPK pathways. The very small
    number of biological replicates limits causal interpretation.
  modeled_mechanisms:
  - target: Glucosylceramide Accumulation and Sphingolipid Imbalance
    description: The model examines transcriptional consequences of GBA2-associated lipid dysregulation.
    evidence:
    - reference: PMID:35277195
      reference_title: Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        next-generation RNA-sequencing (RNA-seq), in an attempt to discover
        differentially expressed genes (DEGs) in lymphoblastoid, fibroblast cell
        lines and induced pluripotent stem cell-derived neurons derived from patients
      explanation: The study defines the patient-derived multi-tissue transcriptome model.
  evidence:
  - reference: PMID:35277195
    reference_title: Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the mechanism by which GBA2 variants lead to the development of SA is still unclear.
    explanation: The authors explicitly frame their pathway results as exploratory.
- name: Disease-associated GBA2 truncation transfection model
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  conditions:
  - Wild-type GBA2 transfection
  - Disease-associated GBA2-233 or GBA2-339 truncation transfection
  description: >-
    Selected C-terminally truncated GBA2 constructs mislocalize to the
    mitochondrial matrix and produce mitochondrial fragmentation and loss of
    membrane potential. The artificial-expression design and restricted variant
    classes limit extrapolation to all patients.
  modeled_mechanisms:
  - target: Biallelic GBA2 Loss of Function
    description: The model tests variant-specific consequences beyond catalytic loss.
    evidence:
    - reference: PMID:32492073
      reference_title: Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        C-terminally truncated mutants terminating after amino acids 233 and 339
        (GBA2-233 and -339) were present in the mitochondrial matrix
      explanation: The cell model demonstrates truncation-specific mitochondrial localization.
  evidence:
  - reference: PMID:32492073
    reference_title: Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      induced mitochondrial fragmentation and loss of mitochondrial transmembrane potential.
    explanation: The model directly measures mitochondrial structural and functional effects.
datasets: []
discussions:
- discussion_id: gba2_lipid_to_neurodegeneration_gap
  prompt: >-
    Which lipid species, membrane compartment, and neural cell population link
    GBA2 deficiency to corticospinal, cerebellar, and peripheral-nerve disease?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Glucosylceramide Accumulation and Sphingolipid Imbalance
  rationale: >-
    Severe enzyme deficiency and glucosylceramide elevation are established in
    patients, but mouse phenocopy is incomplete and neurite, mitochondrial, and
    transcriptomic findings do not yet form a validated causal chain in human
    neural tissue.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      the pathogenic mechanism of neurodegeneration is still unclear
    explanation: The contemporary review explicitly identifies the unresolved downstream mechanism.
- discussion_id: gba2_genotype_phenotype_variability
  prompt: >-
    Why can the same or closely related biallelic GBA2 genotypes present as
    HSP-predominant, ataxia-predominant, or Marinesco-Sjögren-like disease?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - genetic#Biallelic GBA2 pathogenic variants
  rationale: >-
    Intrafamilial and interfamily variability, limited enzyme assays, and sparse
    longitudinal cohorts prevent robust genotype-phenotype prediction.
  evidence:
  - reference: "url:https://www.ebi.ac.uk/europepmc/webservices/rest/PMC11076336/fullTextXML"
    reference_title: "Keywords"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      different phenotypes may arise from same identical mutations
    explanation: The review documents genotype-preserving phenotypic variability.
notes: >-
  This entry represents the MONDO disease term, not only one chronological
  pattern of symptoms. "Late-onset spasticity" describes the
  ataxia-predominant families in which spasticity became prominent after
  cerebellar symptoms; most later reports use SPG46 and describe early-onset
  complex HSP. The HSP-, ARCA-, and Marinesco-Sjögren-like labels are overlapping
  presentations of biallelic GBA2 disease rather than separate established
  molecular disorders. Reduced GBA2 activity and glucosylceramide elevation are
  established. Selective neurodegeneration, mitochondrial fragmentation,
  transcriptomic stress pathways, and systemic manifestations should not be
  collapsed into one proven mechanism. A 2026 report further expands the
  endocrine spectrum with hypogonadotrophic hypogonadism, but its PubMed record
  did not yet contain an abstract at the time of this review.
review_notes: >-
  Full review completed 2026-07-23. Scope was reconciled to the original
  independent GBA2 HSP and ARCA reports and the 2024 synthesis of 67 cases from
  36 families. The entry now distinguishes the MONDO label's
  ataxia-first/late-spasticity presentation from the more common early-onset
  SPG46 presentation and treats HSP, ARCA, and Marinesco-Sjögren-like disease as
  a variable GBA2 spectrum. All causal edges were rebuilt with evidence and
  explicit uncertainty. ClinicalTrials.gov API searches for GBA2, SPG46,
  "spastic paraplegia 46," and the full disease name found no GBA2-specific
  interventional trial; the broad recruiting CoRDS rare-disease registry
  NCT01793168 was retained because its condition list explicitly includes the
  disease. NCBI GEO searches for GBA2 plus spasticity/ataxia, SPG46, and the full
  disease name found no disease-specific accession. The 2022 patient-cell RNA
  sequencing data were reported within the article and supplementary files, so
  the experimental model is represented but datasets remains empty rather than
  inventing a repository accession.
📚

References & Deep Research

References

13
PMID:23332916
Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.
No top-level findings curated for this source.
PMID:23332917
Mutations in GBA2 cause autosomal-recessive cerebellar ataxia with spasticity.
No top-level findings curated for this source.
PMID:26220345
Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46).
No top-level findings curated for this source.
PMID:28052128
GBA2 Mutations Cause a Marinesco-Sjögren-Like Syndrome: Genetic and Biochemical Studies.
No top-level findings curated for this source.
PMID:30662006
Species-specific differences in nonlysosomal glucosylceramidase GBA2 function underlie locomotor dysfunction arising from loss-of-function mutations.
No top-level findings curated for this source.
PMID:30864417
Assay of β-glucosidase 2 (GBA2) activity using lithocholic acid β-3-O-glucoside substrate for cultured fibroblasts and glucosylceramide for brain tissue.
No top-level findings curated for this source.
PMID:32492073
Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation.
No top-level findings curated for this source.
PMID:34251556
Spastic paraplegia type 46: novel and recurrent GBA2 gene variants in a compound heterozygous Italian patient with spastic ataxia phenotype.
No top-level findings curated for this source.
PMID:35277195
Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia.
No top-level findings curated for this source.
PMID:38334933
Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature.
No top-level findings curated for this source.
PMID:42384114
Hypogonadotrophic hypogonadism in GBA2 associated spastic paraplegia type 46 (SPG46): a phenotypic expansion.
No top-level findings curated for this source.
PMID:20301682
Uncomplicated (Pure) Hereditary Spastic Paraplegia Overview.
No top-level findings curated for this source.
clinicaltrials:NCT01793168
Coordination of Rare Diseases at Sanford
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 17 citations 2026-06-13T18:09:37.953439

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

  • Disease Name: Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity
  • MONDO ID: (if available)
  • Category: Mendelian

Research Objectives

Please provide a comprehensive research report on Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

  • What is the disease? Provide a concise overview.
  • What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
  • What are the common synonyms and alternative names?
  • Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

  • Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
  • Risk Factors:

    Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

  • Genetic risk factors (causal variants, susceptibility loci, modifier genes)
  • Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
  • Protective Factors:

    Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

  • Genetic protective factors (protective variants, modifier alleles)
  • Environmental protective factors (diet, lifestyle, exposures that reduce risk)
  • Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

    Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

  • Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

    Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

  • Pathogenic Variants:
  • Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
  • Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
  • Variant type/class (missense, frameshift, nonsense, splice-site, structural)
  • Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
  • Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
  • Functional consequences (loss of function, gain of function, dominant negative)
  • Modifier Genes: Genes that modify disease severity or expression
  • Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

    Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

  • Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

    Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

  • Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

    Search first: CDC databases, WHO, PubMed, NHANES

  • Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

    Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

  • Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

    Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

  • Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

    Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

  • Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

    Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

  • Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

    Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

  • Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

    Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

  • Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

    Search first: PubMed, Gene Ontology, Reactome

  • Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

    Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

  • Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Molecular Profiling (if available):
  • Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
  • Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
  • Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
  • Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
  • Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
  • Advanced Technologies (if applicable):
  • Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
  • Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
  • Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
  • Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

  • Organ Level:
  • Primary organs directly affected
  • Secondary organ involvement (complications, secondary effects)
  • Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

    Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

  • Tissue and Cell Level:
  • Specific tissue types affected (epithelial, connective, muscle, nervous)
  • Specific cell populations targeted (with Cell Ontology terms)

    Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

  • Subcellular Level:
  • Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

    Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

  • Localization:
  • Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
  • Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

  • Onset:
  • Typical age of onset (congenital, pediatric, adult, geriatric)
  • Onset pattern (acute, subacute, chronic, insidious)

    Search first: OMIM, Orphanet, HPO, PubMed

  • Progression:
  • Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
  • Progression rate (rapid, slow, variable)
  • Disease course pattern (episodic, relapsing-remitting, progressive, stable)
  • Disease duration (self-limited, chronic lifelong)

    Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

  • Patterns:
  • Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
  • Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

  • Epidemiology:
  • Prevalence (cases per 100,000 at given time)
  • Incidence (new cases per 100,000 per year)

    Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

  • For Genetic Etiology:
  • Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
  • Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
  • Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
  • Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
  • Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
  • Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
  • Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
  • Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
  • Population Demographics:
  • Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
  • Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
  • Geographic distribution of specific variants
  • Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
  • Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

  • Clinical Tests:
  • Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
  • Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
  • Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
  • Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
  • Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
  • Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
  • Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
  • Genetic Testing:

    Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

  • Overview of recommended genetic testing approach
  • Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
  • Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
  • Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
  • Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
  • Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
  • Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
  • FISH > Search first: ClinVar, cytogenetics databases, PubMed
  • Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
  • Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
  • Omics-Based Diagnostics (if applicable):
  • RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
  • Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
  • Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
  • Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
  • Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
  • Clinical Criteria:
  • Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
  • Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
  • Screening:
  • Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

  • Survival and Mortality:
  • Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
  • Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
  • Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
  • Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
  • Morbidity and Function:
  • Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
  • Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
  • Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
  • Disease Course:
  • Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
  • Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
  • Prediction:
  • Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
  • Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

  • Pharmacotherapy:
  • Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
  • Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
  • Advanced Therapeutics:
  • Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
  • Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
  • RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
  • Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
  • Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
  • Surgical and Interventional:
  • Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
  • Supportive and Rehabilitative:
  • Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
  • Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
  • Experimental:
  • Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
  • Treatment Outcomes:
  • Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
  • Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
  • Treatment Strategy:
  • Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
  • Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
  • Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest MAXO (Medical Action Ontology) terms where applicable.

13. Prevention

  • Prevention Levels:
  • Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
  • Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
  • Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
  • Immunization: Vaccine strategies (if applicable)

    Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

  • Screening and Early Detection:
  • Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
  • Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
  • Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
  • Behavioral Interventions: Lifestyle modifications to reduce risk

    Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

  • Counseling: Genetic counseling (risk assessment, family planning guidance)

    Search first: NSGC resources, ACMG guidelines, GeneReviews

  • Public Health:
  • Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
  • Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
  • Prophylaxis: Preventive medications or procedures

    Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

  • Taxonomy: Species affected (with NCBI Taxon identifiers)

    Search first: NCBI Taxonomy

  • Breed: Specific breeds affected (with VBO identifiers if applicable)

    Search first: VBO (Vertebrate Breed Ontology)

  • Gene: Orthologous genes in other species (with NCBI Gene IDs)

    Search first: NCBI Gene

  • Natural Disease:
  • Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
  • Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
  • Comparative Biology:
  • Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
  • Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
  • Transmission (if applicable):
  • Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
  • Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

  • Model Types:
  • Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
  • Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
  • Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
  • Genetic Models:
  • Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
  • Model Characteristics:
  • Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
  • Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
  • Applications:
  • Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
  • Resources:
  • Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic and clinical claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes from abstracts where possible to support key statements
  • Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, MAXO, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (MAXO terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Comprehensive Research Report: Autosomal Recessive Cerebellar Ataxia With Late-Onset Spasticity (ARCA-LOS)

Executive summary

Autosomal recessive cerebellar ataxia with late-onset spasticity (ARCA-LOS) is a Mendelian neurodegenerative spastic-ataxia phenotype on the ataxia–hereditary spastic paraplegia (HSP) continuum, strongly linked to biallelic loss-of-function or deleterious variants in GBA2 (glucosylceramidase beta 2), a non-lysosomal glucosylceramidase in sphingolipid metabolism. Across case series and mechanistic studies, the disorder is characterized by cerebellar ataxia plus corticospinal tract signs (spasticity, pyramidal weakness) with variable additional findings (neuropathy, cognitive involvement, cataracts, thin corpus callosum/white matter abnormalities, hypogonadism). Recent work (2022–2024) has expanded mechanistic understanding through patient-cell biochemistry, transcriptomics, and larger clinical series with enzymatic assays and imaging descriptions. (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2, martin2013lossoffunction pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3, kakouri2022transcriptomiccharacterizationof pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7)

Evidence map (high-level)

Disease term MONDO ID Primary causal gene Inheritance Core phenotype Notable lab/biochemical findings Key supporting publications Evidence type
Autosomal recessive cerebellar ataxia with late-onset spasticity MONDO_0018129 GBA2 (ENSG00000070610) Autosomal recessive Spastic ataxia with overlap of cerebellar ataxia and spastic paraplegia; gait ataxia, limb spasticity/weakness; variable neuropathy and additional neurologic/extraneurologic features (kakouri2020analyzinggeneexpression pages 1-3, kakouri2022transcriptomiccharacterizationof pages 1-2, OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2) GBA2 is a non-lysosomal glucosylceramidase in sphingolipid metabolism; disease-associated dysfunction linked to altered glucosylceramide/ceramide handling (kakouri2022transcriptomiccharacterizationof pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3) Open Targets disease-target association to GBA2 with literature PMID 23332917; MONDO mapping for the disease term (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2) Human disease ontology / disease-target association
SPG46 (hereditary spastic paraplegia type 46) MONDO_0018129* GBA2 (ENSG00000070610) Autosomal recessive Complex HSP phenotype with spastic paraplegia, cerebellar atrophy/ataxia, mental impairment, cataract, hypogonadism in males; variable corpus callosum and cerebellar atrophy on imaging (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2) Missense example c.1888C>T (p.Arg630Trp) with absent residual GBA2 activity in blood cells in one homozygous subject; GBA2 catalyzes glucosylceramide to glucose + ceramide (martin2013lossoffunction pages 1-2) Martin et al., 2013, Am J Hum Genet 92:238-244, DOI: 10.1016/j.ajhg.2012.11.021; Cioffi et al., 2024, Neurogenetics 25:51-67, DOI: 10.1007/s10048-024-00749-9 (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2) Human genetics, enzyme assay, zebrafish functional model
Spastic ataxia (GBA2-associated; Cypriot family) MONDO_0018129* GBA2 (ENSG00000070610) Autosomal recessive Mixed cerebellar ataxia and spasticity; main features include gait ataxia, spasticity, limb weakness; can include neuropathy, pyramidal/extrapyramidal signs, oculomotor abnormalities, cognitive involvement, seizures, retinopathy, hypogonadism (kakouri2020analyzinggeneexpression pages 1-3) Homozygous c.1780G>C (p.Asp594His) causes marked reduction/abolishment of non-lysosomal glucosylceramidase activity, ~2-fold increased glucosylceramide in patient LCLs, and ~3-fold compensatory increase in lysosomal GBA activity (malekkou2018biochemicalcharacterizationof pages 1-3) Malekkou et al., 2018, Int J Mol Sci 19:3099, DOI: 10.3390/ijms19103099; Kakouri et al., 2020, Int J Mol Sci 21:6722, DOI: 10.3390/ijms21186722 (malekkou2018biochemicalcharacterizationof pages 1-3, kakouri2020analyzinggeneexpression pages 1-3) Human clinical report, patient-derived lymphoblastoid cells, pathway analysis
GBA2-associated spastic ataxia transcriptomic model MONDO_0018129* GBA2 (ENSG00000070610) Autosomal recessive SA tissues/cells from patients with homozygous c.1780G>C used to study disease mechanisms; symptoms framed as overlap between ataxia and spastic paraplegia (kakouri2022transcriptomiccharacterizationof pages 1-2) RNA-seq across LCLs, fibroblasts, and iPSC-derived neurons found 5217 significantly altered genes; implicated oxidative stress, neuroinflammation, sphingolipid signaling/metabolism, PI3K-Akt, and MAPK pathways (kakouri2022transcriptomiccharacterizationof pages 1-2) Kakouri et al., 2022, Cell & Bioscience 12:29, DOI: 10.1186/s13578-022-00754-1 (kakouri2022transcriptomiccharacterizationof pages 1-2) Patient cells, iPSC-derived neurons, transcriptomics
SPG46 / GBA2 literature synthesis MONDO_0018129* GBA2 (ENSG00000070610) Autosomal recessive Review notes ~30 families and 62 patients reported worldwide; phenotypes span complicated HSP, recessive cerebellar ataxia, and Marinesco-Sjögren-like syndrome; notable features include upper gaze palsy and movement disorders (cioffi2024hereditaryspasticparaparesis pages 1-2) GBA2 activity measurable in lymphoblasts/leucocytes; pathogenic mechanism linked to glucosylceramide accumulation and disturbed ganglioside/sphingolipid metabolism (cioffi2024hereditaryspasticparaparesis pages 1-2) Cioffi et al., 2024, Neurogenetics 25:51-67, DOI: 10.1007/s10048-024-00749-9 (cioffi2024hereditaryspasticparaparesis pages 1-2) Human case series and literature review

Table: This table summarizes the disease labels, ontology mapping, causal gene, phenotype, biochemical findings, and supporting studies for GBA2-associated autosomal recessive spastic ataxia/SPG46. It is useful for quickly aligning nomenclature across disease resources and the core human/mechanistic evidence base.

1. Disease information

1.1 Concise overview

“Spastic ataxia (SA)” is commonly used as the umbrella clinical concept for disorders overlapping cerebellar ataxia and spastic paraplegia. A representative definition from recent mechanistic work states: “Spastic ataxia (SA) is a group of rare neurodegenerative diseases, characterized by mixed features of generalized ataxia and spasticity.” (Published 2020-09-14; Int J Mol Sci; URL https://doi.org/10.3390/ijms21186722) (kakouri2020analyzinggeneexpression pages 1-3)

Within this clinical space, ARCA-LOS corresponds to a specific ontology entity in Open Targets: MONDO_0018129 (“autosomal recessive cerebellar ataxia with late-onset spasticity”) with a curated disease–target association to GBA2 supported by PubMed literature (PMID 23332917) (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2).

1.2 Key identifiers

  • MONDO: MONDO_0018129 (Open Targets) (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2)
  • Other identifiers (OMIM/Orphanet/ICD/MeSH): Not retrieved in the documents available in this run; therefore not asserted here.

1.3 Synonyms / alternative names used in the literature

The retrieved literature uses partially overlapping disease labels for GBA2-related disease: * Spastic ataxia (SA) (kakouri2020analyzinggeneexpression pages 1-3, kakouri2022transcriptomiccharacterizationof pages 1-2) * SPG46 / Hereditary spastic paraparesis (paraplegia) type 46 (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2) * “Autosomal recessive cerebellar ataxia with spasticity” (as part of the SPG46/ARCA spectrum) (cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7)

1.4 Evidence source type

The information summarized here is derived from: * Aggregated disease-level resources: Open Targets MONDO mapping and gene association (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2) * Primary human genetics and case series: Martin 2013 (SPG46), Cioffi 2024 (Italian series) (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7) * Patient-derived cell studies: Malekkou 2018 (LCL biochemistry), Kakouri 2022 (RNA-seq on patient-derived cell types) (malekkou2018biochemicalcharacterizationof pages 1-3, kakouri2022transcriptomiccharacterizationof pages 1-2) * Natural history/registry trials and rehabilitation trials in related spastic ataxias: ClinicalTrials.gov records (NCT04297891 chunk 1, NCT05768750 chunk 1, NCT06261424 chunk 3)

2. Etiology

2.1 Primary causal factors

Genetic (Mendelian, autosomal recessive): GBA2 * A core mechanistic/genetic statement from Am J Hum Genet (2013-02-07) reports: “Spastic paraplegia 46 refers to a locus mapped to chromosome 9 that accounts for a complicated autosomal-recessive form of hereditary spastic paraplegia (HSP). With next-generation sequencing in three independent families, we identified four different mutations in GBA2…” (URL https://doi.org/10.1016/j.ajhg.2012.11.021) (martin2013lossoffunction pages 1-2) * A 2024 review/case series similarly states: “SPG46 is a rare, early-onset and autosomal recessive HSP, linked to biallelic GBA2 mutations.” (Published online 2024-02-09; Neurogenetics; URL https://doi.org/10.1007/s10048-024-00749-9) (cioffi2024hereditaryspasticparaparesis pages 1-2)

2.2 Risk factors

For this Mendelian condition, the dominant risk factor is biallelic pathogenic GBA2 variation. Non-genetic risk factors were not identified in the retrieved sources.

2.3 Protective factors / gene–environment interactions

No protective factors or gene–environment interactions were identified in the retrieved sources.

3. Phenotypes (clinical features)

3.1 Core phenotype and variability

A broad clinical description of spastic ataxia notes: “Their main characteristics include gait ataxia, spasticity, and weakness in the limbs.” (Kakouri 2020; Int J Mol Sci; 2020-09-14; https://doi.org/10.3390/ijms21186722) (kakouri2020analyzinggeneexpression pages 1-3)

Additional features reported as potentially present include: “neuropathy, pyramidal and extrapyramidal involvement, oculomotor abnormalities, cognitive involvement, seizures, retinopathy, and hypogonadism” (kakouri2020analyzinggeneexpression pages 1-3).

In GBA2-related SPG46, the phenotype is frequently “complex” HSP. The 2013 report describes the overall phenotype as: “a complex HSP with mental impairment, cataract, and hypogonadism in males associated with various degrees of corpus callosum and cerebellar atrophy on brain imaging.” (martin2013lossoffunction pages 1-2)

3.2 Quantitative phenotype statistics (from a 2024 Italian SPG46 series)

In a multicenter Italian case series (n=5) of SPG46 with biallelic GBA2 variants, key summary statistics included: * Mean onset: 6.8 years * Mean disease duration/progression: 32 years * Mean age at last exam: 38.6 years * Core findings (counts): spasticity 5/5, cerebellar syndrome 4/5, peripheral neuropathy 4/5, bilateral cataracts 4/5; imaging white matter abnormalities 4/5, thin corpus callosum 2/5 (cioffi2024hereditaryspasticparaparesis pages 2-4, cioffi2024hereditaryspasticparaparesis pages 4-7)

3.3 Suggested HPO terms (not exhaustive)

Based on the clinical descriptions in the retrieved sources: * Cerebellar ataxia — HP:0001251 * Spasticity — HP:0001257 * Gait ataxia — HP:0002066 * Pyramidal weakness — HP:0002493 * Peripheral neuropathy — HP:0009830 * Cognitive impairment / intellectual disability — HP:0100543 / HP:0001249 * Cataract — HP:0000518 * Hypogonadism (male) — HP:0000026 * Thin corpus callosum — HP:0002079 * White matter abnormalities — HP:0002500 * Oculomotor abnormality / gaze palsy — HP:0000602

(These HPO identifiers are provided as ontology suggestions; the underlying phenotypes are supported by the cited sources.) (kakouri2020analyzinggeneexpression pages 1-3, martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7)

3.4 Quality-of-life impact

Formal QoL instruments specific to GBA2/SPG46 were not identified in the retrieved papers. However, recent spastic ataxia natural history efforts explicitly incorporate PROMIS domains (“physical function”, “social roles and activities”) to quantify functional impact longitudinally (NCT04297891; first posted 2020-03-06; updated 2022-05-18) (NCT04297891 chunk 2).

4. Genetic / molecular information

4.1 Causal gene

  • Gene: GBA2 (glucosylceramidase beta 2)
  • Role: microsomal/non-lysosomal glucosylceramidase; catalyzes glucosylceramide → glucose + ceramide; also hydrolyzes bile acid 3-O-glucosides (martin2013lossoffunction pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3)

4.2 Pathogenic variants (examples from retrieved primary sources)

Martin et al., 2013 (Am J Hum Genet; 2013-02-07) * Missense variant example: c.1888C>T (p.Arg630Trp) (martin2013lossoffunction pages 1-2)

Cioffi et al., 2024 (Neurogenetics; published online 2024-02-09) * Previously reported variants in their series/literature context: c.472G>A (p.Gly158Arg); c.2063G>A (p.Cys688Thr) (cioffi2024hereditaryspasticparaparesis pages 4-7) * New variants (examples in the excerpt): c.1786G>T (p.Gly596Trp) (homozygous) and truncating variants including p.Gln674 and p.Trp551** as part of compound heterozygous genotypes (cioffi2024hereditaryspasticparaparesis pages 4-7)

Cypriot family (patient-cell functional work) * c.1780G>C (p.Asp594His) identified as causal in a consanguineous family with spastic ataxia and used for downstream mechanistic studies (kakouri2020analyzinggeneexpression pages 1-3, kakouri2022transcriptomiccharacterizationof pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3)

4.3 Variant type/class and functional consequence

Across the retrieved sources, pathogenicity is frequently consistent with loss of function (LoF): * Martin 2013: “three truncating variants and one missense variant” with absent residual GBA2 activity in blood cells for a homozygous missense case; the paper frames the mechanism as “Loss of Function of Glucocerebrosidase GBA2…” (martin2013lossoffunction pages 1-2) * Malekkou 2018: the c.1780G>C variant leads to markedly reduced enzyme activity and substrate accumulation (malekkou2018biochemicalcharacterizationof pages 1-3)

4.4 Population frequency

Detailed allele frequencies from gnomAD/1000G were not present in the retrieved excerpts. However, Martin 2013 reports absence of c.1888C>T in 1,038 control chromosomes and ~6,500 exomes (Exome Variant Server) (martin2013lossoffunction pages 1-2).

4.5 Modifier genes / epigenetics / chromosomal abnormalities

No modifier genes or epigenetic/chromosomal mechanisms were identified in the retrieved sources.

5. Environmental information

No environmental, lifestyle, or infectious triggers were reported in the retrieved sources; this appears primarily a genetic neurodegenerative disorder in the available evidence.

6. Mechanism / pathophysiology

6.1 Primary biochemical mechanism: sphingolipid metabolism disruption

A key mechanistic statement from Malekkou 2018 (2018-10-10; Int J Mol Sci) is: * “The GBA2 gene encodes the non-lysosomal glucosylceramidase (NLGase), an enzyme that catalyzes the conversion of glucosylceramide (GlcCer) to ceramide and glucose.” (https://doi.org/10.3390/ijms19103099) (malekkou2018biochemicalcharacterizationof pages 1-3)

This aligns with Martin 2013’s description that GBA2 “catalyzes the conversion of glucosylceramide to free glucose and ceramide” and emphasizes a lipid/ceramide axis in motor neuron pathology (martin2013lossoffunction pages 1-2).

6.2 Patient-cell biochemical consequences (quantitative)

In lymphoblastoid cell lines from patients homozygous for c.1780G>C (p.Asp594His), Malekkou 2018 reports: * “the mutation strongly reduce NLGase activity both intracellularly and at the plasma membrane level” * “a two-fold increase of GlcCer content” * “the activity of GCase was three-fold higher in LCLs derived from patients compared to controls” * concluding: “loss of function with abolishment of the enzymatic activity and accumulation of GlcCer accompanied by a compensatory increase in GCase.” (malekkou2018biochemicalcharacterizationof pages 1-3)

6.3 Transcriptomic mechanisms (2022; pathway-level)

Kakouri 2022 performed RNA-seq in LCLs, fibroblasts, and iPSC-derived neurons from patients homozygous for c.1780G>C and reports: * “a total of 5217 genes with significantly altered expression” * enriched pathways including “oxidative stress, neuroinflammation, sphingolipid signaling and metabolism, PI3K-Akt and MAPK signaling pathways.” (Published 2022-03-??; Cell & Bioscience; https://doi.org/10.1186/s13578-022-00754-1) (kakouri2022transcriptomiccharacterizationof pages 1-2)

6.4 Neurodevelopmental / neuronal vulnerability and model-organism support

Martin 2013 provides functional model evidence: zebrafish knockdown of the GBA2 ortholog caused abnormal motor behavior and motoneuron axonal defects, rescued by wild-type but not mutant human mRNA (martin2013lossoffunction pages 1-2). This supports a causal chain: GBA2 LoF → altered ceramide/GlcCer handling → neuronal (motoneuron/corticospinal) structural/functional defects → spasticity and ataxia phenotypes (martin2013lossoffunction pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3).

6.5 Suggested ontology terms (GO biological processes; CL cell types)

  • GO:0006665 sphingolipid metabolic process (mechanism supported by GBA2 enzymology and GlcCer accumulation) (martin2013lossoffunction pages 1-2, malekkou2018biochemicalcharacterizationof pages 1-3)
  • GO:0006687 glycosphingolipid metabolic process (malekkou2018biochemicalcharacterizationof pages 1-3)
  • GO:0001525 angiogenesis (not suggested)
  • GO:0006954 inflammatory response / neuroinflammation (supported as an enriched pathway in transcriptomics) (kakouri2022transcriptomiccharacterizationof pages 1-2)
  • GO:0006979 response to oxidative stress (enriched pathway) (kakouri2022transcriptomiccharacterizationof pages 1-2)

Cell types (CL suggestions based on affected systems described): * Purkinje cell — CL:0000121 (cerebellar involvement implied; not directly proven in the excerpts) * Upper motor neuron / corticospinal neuron — (CL term depends on chosen ontology slice; suggested due to HSP hallmark “upper motor neurons”) (cioffi2024hereditaryspasticparaparesis pages 1-2) * Motor neuron — CL:0000100 (supported by zebrafish motoneuron phenotype) (martin2013lossoffunction pages 1-2)

7. Anatomical structures affected

7.1 Organ/system level

The disorder primarily affects the nervous system, especially long motor pathways and cerebellar circuits.

Kakouri 2020 notes the affected structures can include “the cerebellum, the corpus callosum, the pyramidal track, as well as the spinocerebellar tract and/or the sensory tracts of the spinal cord.” (kakouri2020analyzinggeneexpression pages 1-3)

SPG46 imaging in Martin 2013 includes “corpus callosum and cerebellar atrophy” (martin2013lossoffunction pages 1-2). The 2024 series reports frequent white matter abnormalities and thin corpus callosum (cioffi2024hereditaryspasticparaparesis pages 4-7).

7.2 Suggested UBERON terms

  • Cerebellum — UBERON:0002037
  • Corpus callosum — UBERON:0002330
  • Spinal cord — UBERON:0002240
  • Corticospinal tract — (UBERON term varies by resource; suggested due to pyramidal signs/HSP framing)

8. Temporal development

8.1 Onset

There is phenotypic heterogeneity in age at onset across labels (spastic ataxia vs SPG46 series): * Kakouri 2022 states spastic ataxias are “characterized by an early age of onset, usually before the age of 20 years.” (kakouri2022transcriptomiccharacterizationof pages 1-2) * Cioffi 2024 SPG46 series: mean onset 6.8 years with one congenital case (cioffi2024hereditaryspasticparaparesis pages 2-4, cioffi2024hereditaryspasticparaparesis pages 4-7)

Because the target disease label includes “late-onset spasticity,” an important interpretation is that spasticity may appear later than cerebellar features, but the retrieved excerpts did not provide a formal staging model for this timing.

8.2 Progression

The Italian SPG46 cohort had a slowly progressive course with mean disease duration 32 years (cioffi2024hereditaryspasticparaparesis pages 2-4, cioffi2024hereditaryspasticparaparesis pages 4-7).

9. Inheritance and population

9.1 Inheritance

Autosomal recessive inheritance is consistently reported: * “complicated autosomal-recessive form” (Martin 2013) (martin2013lossoffunction pages 1-2) * “autosomal recessive HSP, linked to biallelic GBA2 mutations” (Cioffi 2024) (cioffi2024hereditaryspasticparaparesis pages 1-2)

9.2 Epidemiology / counts

No prevalence/incidence for ARCA-LOS specifically was found in the retrieved sources.

However, Cioffi 2024 provides literature-based counts: * “About thirty families” and “62 patients… described worldwide” (cioffi2024hereditaryspasticparaparesis pages 1-2) * A broader literature summary in the same work notes “67 cases from 36 families” (cioffi2024hereditaryspasticparaparesis pages 4-7)

The same review also notes an apparent higher prevalence in Mediterranean countries (qualitative) (cioffi2024hereditaryspasticparaparesis pages 4-7).

10. Diagnostics

10.1 Clinical evaluation

Diagnosis relies on recognition of combined cerebellar and pyramidal signs (ataxia + spasticity) and evaluation for additional multisystem signs (neuropathy, cataracts, cognitive changes), supported by imaging and genetic testing (kakouri2020analyzinggeneexpression pages 1-3, martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2).

10.2 Imaging

Reported imaging findings across SPG46 include: * corpus callosum involvement / thin corpus callosum * cerebellar atrophy * white matter abnormalities

These are specifically mentioned in Martin 2013 (“corpus callosum and cerebellar atrophy”) and in Cioffi 2024 (WMA and TCC frequencies in their cohort) (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7).

10.3 Biomarkers / enzyme assays (actionable diagnostic adjunct)

A prominent diagnostic biomarker is measured GBA2 enzymatic activity.

Martin 2013 emphasizes feasibility of clinical enzyme measurement: “The missense variant was also found at the homozygous state in a simplex subject in whom no residual glucocerebrosidase activity of GBA2 could be evidenced in blood cells, opening the way to a possible measurement of this enzyme activity in clinical practice.” (martin2013lossoffunction pages 1-2)

Cioffi 2024 provides an explicit leukocyte assay approach and values, including proband activities as low as 0.01 nmol/mg vs control mean 3.9 nmol/mg (ref 2.5–5.3), and stresses diagnostic usefulness of enzyme testing (cioffi2024hereditaryspasticparaparesis pages 2-4, cioffi2024hereditaryspasticparaparesis pages 4-7).

10.4 Genetic testing

The available evidence supports the utility of multi-gene panels/exome sequencing in spastic-ataxia phenotypes (implied by targeted sequencing approaches and exome usage in Martin 2013 and modern cohort screening in Cioffi 2024) (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2).

10.5 Differential diagnosis

The retrieved sources did not provide a structured differential diagnosis list specific to ARCA-LOS; however, they note that spastic ataxia can be caused by many genes (e.g., SACS, FXN, SPG7, POLR3A, NKX6-2, GBA2) (kakouri2020analyzinggeneexpression pages 1-3).

11. Outcome / prognosis

No survival statistics were identified. Available evidence supports chronic, slowly progressive disability in long-duration cohorts (e.g., mean disease duration ~32 years in one SPG46 cohort) (cioffi2024hereditaryspasticparaparesis pages 4-7).

12. Treatment

12.1 Disease-modifying therapy

No established disease-modifying therapy for GBA2-related ARCA-LOS/SPG46 was identified in the retrieved sources.

12.2 Symptomatic/supportive and rehabilitative care (real-world implementations)

Although not specific to GBA2/SPG46, spastic ataxia rehabilitation trials and natural history efforts provide practical implementation templates for similar phenotypes:

Natural history / trial readiness platform * NCT04297891 “Phenotypes, Biomarkers and Pathophysiology in Spastic Ataxias” (first posted 2020-03-06; last update 2022-05-18; start 2020-09-01; primary completion estimated 2024-06) includes standardized ataxia/spasticity scales (SARA, SPRS), PROMIS PROs, biosampling, multi-omics, and multimodal MRI; also includes digital monitoring via mHealth/wearables (NCT04297891 chunk 1, NCT04297891 chunk 2).

Rehabilitation / functional interventions * NCT05768750 (submitted 2023-03-03; start 2022-12-01; estimated completion 2024-12-01) tests a pragmatic 12-week home-based rehabilitation program in ARSACS with balance and spasticity measures (Modified Ashworth Scale) and feasibility/acceptability assessments (NCT05768750 chunk 1, NCT05768750 chunk 2). * NCT06261424 (2024 record) evaluates supervised rehabilitation in spastic ataxias (explicitly ARSACS or SPG7), incorporating objective biomechanical/physiologic endpoints (surface EMG, instrumented gait metrics) and health-economic evaluation (NCT06261424 chunk 3).

These programs are directly relevant to real-world care for spastic-ataxia phenotypes (including GBA2-related disease) because they operationalize measurable outcomes (SARA/SPRS, gait speed, balance tests, spasticity scales) and scalable delivery models (home programs with tele-follow-ups). (NCT05768750 chunk 1, NCT06261424 chunk 3)

12.3 Suggested MAXO terms (examples)

  • Physical therapy — MAXO:0000018 (supportive; supported indirectly via rehabilitation trial designs) (NCT05768750 chunk 1, NCT06261424 chunk 3)
  • Occupational therapy — MAXO term suggested
  • Genetic counseling — MAXO term suggested (autosomal recessive inheritance)

13. Prevention

Primary prevention is not applicable in the usual sense for a recessive genetic disorder; prevention is primarily reproductive and family-risk management: * Carrier testing and cascade testing in affected families (supported by the AR inheritance evidence base) (martin2013lossoffunction pages 1-2, cioffi2024hereditaryspasticparaparesis pages 1-2) * Genetic counseling for recurrence risk and reproductive options

No vaccination or environmental prevention strategies were identified.

14. Other species / natural disease

No naturally occurring non-human disease analogous to ARCA-LOS due to GBA2 was identified in the retrieved sources.

15. Model organisms

15.1 Zebrafish motor neuron model

Martin 2013 provides direct model-organism evidence that reduced GBA2 function causes motor neuron defects, including abnormal motor behavior and motoneuron axonal shortening/branching, and rescue with wild-type human mRNA (martin2013lossoffunction pages 1-2).

15.2 Mouse knockout observations

Malekkou 2018 notes that GBA2-knockout mice can show non-neurologic phenotypes (e.g., male infertility) and do not necessarily reproduce the neurologic phenotype despite brain GlcCer accumulation, highlighting model limitations; in contrast, zebrafish knockdown shows motor neuron defects (malekkou2018biochemicalcharacterizationof pages 1-3).

Recent developments (prioritized 2023–2024)

  1. Large Italian SPG46 case series and literature synthesis (2024): Identification of multiple novel and known GBA2 variants, detailed phenotype frequencies, and a strong emphasis on GBA2 activity assays as clinically useful biomarkers (Published online 2024-02-09; https://doi.org/10.1007/s10048-024-00749-9) (cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7).
  2. Modern mechanistic profiling (2022): RNA-seq across patient-derived tissues/cells implicating oxidative stress, neuroinflammation, and major signaling pathways in GBA2-associated spastic ataxia, offering a framework for biomarker and target discovery (https://doi.org/10.1186/s13578-022-00754-1) (kakouri2022transcriptomiccharacterizationof pages 1-2).
  3. Clinical implementation research (2024): Interventional rehabilitation trials in spastic ataxias with objective gait/EMG endpoints and explicit health-economic evaluation (NCT06261424) (NCT06261424 chunk 3).

Limitations of this report

  • The run did not retrieve OMIM/Orphanet/ICD/MeSH identifiers directly; thus they are not reported.
  • The primary PubMed-indexed paper explicitly titled for “autosomal-recessive cerebellar ataxia with spasticity” due to GBA2 (Open Targets cites PMID 23332917) was not available in full text within the retrieved document set, so the report relies on accessible primary/secondary sources (OpenTargets Search: Autosomal recessive cerebellar ataxia with spasticity,Hereditary spastic paraplegia type 46,SPG46,spastic ataxia-GBA2).

Key references (with URLs and dates where available)

  • Martin E, et al. Am J Hum Genet. 2013-02-07. “Loss of Function of Glucocerebrosidase GBA2…” https://doi.org/10.1016/j.ajhg.2012.11.021 (martin2013lossoffunction pages 1-2)
  • Malekkou A, et al. Int J Mol Sci. 2018-10-10. https://doi.org/10.3390/ijms19103099 (malekkou2018biochemicalcharacterizationof pages 1-3)
  • Kakouri AC, et al. Int J Mol Sci. 2020-09-14. https://doi.org/10.3390/ijms21186722 (kakouri2020analyzinggeneexpression pages 1-3)
  • Kakouri AC, et al. Cell & Bioscience. 2022. https://doi.org/10.1186/s13578-022-00754-1 (kakouri2022transcriptomiccharacterizationof pages 1-2)
  • Cioffi E, et al. Neurogenetics. Published online 2024-02-09. https://doi.org/10.1007/s10048-024-00749-9 (cioffi2024hereditaryspasticparaparesis pages 1-2, cioffi2024hereditaryspasticparaparesis pages 4-7)
  • ClinicalTrials.gov NCT04297891. First posted 2020-03-06; updated 2022-05-18 (NCT04297891 chunk 1, NCT04297891 chunk 2)
  • ClinicalTrials.gov NCT05768750. Submitted 2023-03-03; start 2022-12-01 (NCT05768750 chunk 1)
  • ClinicalTrials.gov NCT06261424. 2024 record (NCT06261424 chunk 3)

References

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  2. (martin2013lossoffunction pages 1-2): Elodie Martin, Rebecca Schüle, Katrien Smets, Agnès Rastetter, Amir Boukhris, José L. Loureiro, Michael A. Gonzalez, Emeline Mundwiller, Tine Deconinck, Marc Wessner, Ludmila Jornea, Andrés Caballero Oteyza, Alexandra Durr, Jean-Jacques Martin, Ludger Schöls, Chokri Mhiri, Foudil Lamari, Stephan Züchner, Peter De Jonghe, Edor Kabashi, Alexis Brice, and Giovanni Stevanin. Loss of function of glucocerebrosidase gba2 is responsible for motor neuron defects in hereditary spastic paraplegia. American journal of human genetics, 92 2:238-44, Feb 2013. URL: https://doi.org/10.1016/j.ajhg.2012.11.021, doi:10.1016/j.ajhg.2012.11.021. This article has 215 citations and is from a highest quality peer-reviewed journal.

  3. (malekkou2018biochemicalcharacterizationof pages 1-3): Anna Malekkou, Maura Samarani, Anthi Drousiotou, Christina Votsi, Sandro Sonnino, Marios Pantzaris, Elena Chiricozzi, Eleni Zamba-Papanicolaou, Massimo Aureli, Nicoletta Loberto, and Kyproula Christodoulou. Biochemical characterization of the gba2 c.1780g>c missense mutation in lymphoblastoid cells from patients with spastic ataxia. Oct 2018. URL: https://doi.org/10.3390/ijms19103099, doi:10.3390/ijms19103099. This article has 13 citations.

  4. (kakouri2022transcriptomiccharacterizationof pages 1-2): Andrea C. Kakouri, Christina Votsi, Anastasis Oulas, Paschalis Nicolaou, Massimo Aureli, Giulia Lunghi, Maura Samarani, Giacomo M. Compagnoni, Sabrina Salani, Alessio Di Fonzo, Thalis Christophides, George A. Tanteles, Eleni Zamba-Papanicolaou, Marios Pantzaris, George M. Spyrou, and Kyproula Christodoulou. Transcriptomic characterization of tissues from patients and subsequent pathway analyses reveal biological pathways that are implicated in spastic ataxia. Cell & Bioscience, Mar 2022. URL: https://doi.org/10.1186/s13578-022-00754-1, doi:10.1186/s13578-022-00754-1. This article has 3 citations and is from a peer-reviewed journal.

  5. (cioffi2024hereditaryspasticparaparesis pages 1-2): Ettore Cioffi, Gianluca Coppola, Olimpia Musumeci, Salvatore Gallone, Gabriella Silvestri, Salvatore Rossi, Fiorella Piemonte, Jessica D’Amico, Alessandra Tessa, Filippo Maria Santorelli, and Carlo Casali. Hereditary spastic paraparesis type 46 (spg46): new gba2 variants in a large italian case series and review of the literature. Neurogenetics, 25:51-67, Feb 2024. URL: https://doi.org/10.1007/s10048-024-00749-9, doi:10.1007/s10048-024-00749-9. This article has 1 citations and is from a peer-reviewed journal.

  6. (cioffi2024hereditaryspasticparaparesis pages 4-7): Ettore Cioffi, Gianluca Coppola, Olimpia Musumeci, Salvatore Gallone, Gabriella Silvestri, Salvatore Rossi, Fiorella Piemonte, Jessica D’Amico, Alessandra Tessa, Filippo Maria Santorelli, and Carlo Casali. Hereditary spastic paraparesis type 46 (spg46): new gba2 variants in a large italian case series and review of the literature. Neurogenetics, 25:51-67, Feb 2024. URL: https://doi.org/10.1007/s10048-024-00749-9, doi:10.1007/s10048-024-00749-9. This article has 1 citations and is from a peer-reviewed journal.

  7. (kakouri2020analyzinggeneexpression pages 1-3): Andrea C. Kakouri, Christina Votsi, Marios Tomazou, George Minadakis, Evangelos Karatzas, Kyproula Christodoulou, and George M. Spyrou. Analyzing gene expression profiles from ataxia and spasticity phenotypes to reveal spastic ataxia related pathways. International Journal of Molecular Sciences, 21:6722, Sep 2020. URL: https://doi.org/10.3390/ijms21186722, doi:10.3390/ijms21186722. This article has 5 citations.

  8. (NCT04297891 chunk 1): Dr. Rebecca Schule. Phenotypes, Biomarkers and Pathophysiology in Spastic Ataxias. Dr. Rebecca Schule. 2020. ClinicalTrials.gov Identifier: NCT04297891

  9. (NCT05768750 chunk 1): Cynthia Gagnon. A Home-based Rehabilitation in ARSACS. Université de Sherbrooke. 2022. ClinicalTrials.gov Identifier: NCT05768750

  10. (NCT06261424 chunk 3): Elise Duchesne. Effects of a Supervised Rehabilitation Program on Disease Severity in Spastic Ataxias. Laval University. 2024. ClinicalTrials.gov Identifier: NCT06261424

  11. (cioffi2024hereditaryspasticparaparesis pages 2-4): Ettore Cioffi, Gianluca Coppola, Olimpia Musumeci, Salvatore Gallone, Gabriella Silvestri, Salvatore Rossi, Fiorella Piemonte, Jessica D’Amico, Alessandra Tessa, Filippo Maria Santorelli, and Carlo Casali. Hereditary spastic paraparesis type 46 (spg46): new gba2 variants in a large italian case series and review of the literature. Neurogenetics, 25:51-67, Feb 2024. URL: https://doi.org/10.1007/s10048-024-00749-9, doi:10.1007/s10048-024-00749-9. This article has 1 citations and is from a peer-reviewed journal.

  12. (NCT04297891 chunk 2): Dr. Rebecca Schule. Phenotypes, Biomarkers and Pathophysiology in Spastic Ataxias. Dr. Rebecca Schule. 2020. ClinicalTrials.gov Identifier: NCT04297891

  13. (NCT05768750 chunk 2): Cynthia Gagnon. A Home-based Rehabilitation in ARSACS. Université de Sherbrooke. 2022. ClinicalTrials.gov Identifier: NCT05768750

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