Gaucher disease due to saposin C deficiency is a rare atypical Gaucher disease caused by biallelic PSAP variants that abolish saposin C, the lysosomal sphingolipid activator protein required by glucocerebrosidase (GCase) to degrade glucosylceramide. Although the glucocerebrosidase gene (GBA1) and enzyme are normal, the missing cofactor leads to glucosylceramide accumulation in macrophages, producing a Gaucher-like phenotype with hepatosplenomegaly, thrombocytopenia, and (in some patients) neurological involvement.
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Conditions with similar clinical presentations that must be differentiated from Gaucher Disease Due To Saposin C Deficiency:
name: Gaucher Disease Due To Saposin C Deficiency
creation_date: "2026-06-13T00:00:00Z"
description: >-
Gaucher disease due to saposin C deficiency is a rare atypical Gaucher disease caused by
biallelic PSAP variants that abolish saposin C, the lysosomal sphingolipid activator
protein required by glucocerebrosidase (GCase) to degrade glucosylceramide. Although the
glucocerebrosidase gene (GBA1) and enzyme are normal, the missing cofactor leads to
glucosylceramide accumulation in macrophages, producing a Gaucher-like phenotype with
hepatosplenomegaly, thrombocytopenia, and (in some patients) neurological involvement.
category: Mendelian
disease_term:
preferred_term: Gaucher disease due to saposin C deficiency
term:
id: MONDO:0012517
label: Gaucher disease due to saposin C deficiency
mappings:
mondo_mappings:
- term:
id: MONDO:0012517
label: Gaucher disease due to saposin C deficiency
mapping_predicate: skos:exactMatch
mapping_source: MONDO
mapping_justification: Primary MONDO disease identifier for this saposin C deficiency Gaucher disease entry.
synonyms:
- Atypical Gaucher disease due to saposin C deficiency
- Saposin C deficiency
- Gaucher disease, variant due to SAP-C deficiency
parents:
- Sphingolipidosis
- Lysosomal Storage Disorder
pathophysiology:
- name: Saposin C Deficiency from PSAP Variants
conforms_to: "lysosomal_substrate_accumulation#Lysosomal Hydrolase or Cofactor Deficiency"
description: >-
Saposin C arises from proteolytic cleavage of prosaposin (encoded by PSAP). Biallelic
PSAP variants abolish saposin C, the activator protein that glucocerebrosidase requires
to access and degrade glucosylceramide. Enzyme and GBA1 gene are normal; the defect is
a missing activator cofactor.
gene:
preferred_term: PSAP
term:
id: hgnc:9498
label: PSAP
cell_types:
- preferred_term: macrophage
term:
id: CL:0000235
label: macrophage
evidence:
- reference: PMID:38928321
reference_title: "Deficiency of Glucocerebrosidase Activity beyond Gaucher Disease: PSAP and LIMP-2 Dysfunctions."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Glucocerebrosidase (GCase) is a lysosomal enzyme that catalyzes the breakdown of glucosylceramide in the presence of its activator saposin C (SapC)."
explanation: "Glucocerebrosidase requires the saposin C activator (from PSAP) to degrade glucosylceramide."
- reference: PMID:17919309
reference_title: "Non-neuronopathic Gaucher disease due to saposin C deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Saposin (SAP-) C is required for glucosylceramide degradation, and its deficiency results in a variant form of Gaucher disease."
explanation: "Saposin C deficiency causes a variant form of Gaucher disease."
downstream:
- target: Lysosomal Glucosylceramide Accumulation
description: Without the activator, glucosylceramide cannot be degraded and accumulates.
- name: Lysosomal Glucosylceramide Accumulation
conforms_to: "lysosomal_substrate_accumulation#Lysosomal Substrate Accumulation"
description: >-
Undegraded glucosylceramide accumulates in macrophage lysosomes, producing
lipid-laden storage macrophages (Gaucher-like cells) in the reticuloendothelial system.
cell_types:
- preferred_term: macrophage
term:
id: CL:0000235
label: macrophage
cellular_components:
- preferred_term: lysosome
term:
id: GO:0005764
label: lysosome
biological_processes:
- preferred_term: glucosylceramide catabolic process
modifier: DECREASED
term:
id: GO:0006680
label: glucosylceramide catabolic process
evidence:
- reference: PMID:38928321
reference_title: "Deficiency of Glucocerebrosidase Activity beyond Gaucher Disease: PSAP and LIMP-2 Dysfunctions."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "impairment of GCase activity can be rarely caused by SapC or LIMP-2 deficiencies"
explanation: "Saposin C deficiency impairs glucocerebrosidase function, causing glucosylceramide accumulation."
downstream:
- target: Hepatosplenomegaly
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
intermediate_mechanisms:
- lipid-laden storage macrophages in the reticuloendothelial system
- visceral organ infiltration
description: Glucosylceramide storage in macrophages produces Gaucher-like reticuloendothelial infiltration and hepatosplenomegaly.
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hepatosplenomegaly, kyphosis, and thrombocytopenia"
explanation: This case-family report documents hepatosplenomegaly in PSAP-related Gaucher disease.
- target: Thrombocytopenia
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
intermediate_mechanisms:
- Gaucher-like reticuloendothelial storage
- hypersplenism and marrow involvement
description: Reticuloendothelial and marrow storage disease can reduce circulating platelets.
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hepatosplenomegaly, kyphosis, and thrombocytopenia"
explanation: This case-family report documents thrombocytopenia in PSAP-related Gaucher disease.
phenotypes:
- name: Hepatosplenomegaly
description: Visceral organomegaly from glucosylceramide-laden storage macrophages.
phenotype_term:
preferred_term: Hepatosplenomegaly
term:
id: HP:0001433
label: Hepatosplenomegaly
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hepatosplenomegaly, kyphosis, and thrombocytopenia"
explanation: "Hepatosplenomegaly is a feature of atypical Gaucher disease from PSAP variants."
- name: Thrombocytopenia
description: Thrombocytopenia from hypersplenism and marrow involvement.
phenotype_term:
preferred_term: Thrombocytopenia
term:
id: HP:0001873
label: Thrombocytopenia
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hepatosplenomegaly, kyphosis, and thrombocytopenia"
explanation: "Thrombocytopenia is part of the atypical Gaucher phenotype."
inheritance:
- name: Autosomal recessive
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "A homozygous missense variant c.1076A>C: p.(Glu359Ala) in exon 10 of the PSAP"
explanation: "A homozygous PSAP variant in affected siblings indicates autosomal recessive inheritance."
genetic:
- name: PSAP
association: Biallelic PSAP variants abolishing saposin C
relationship_type: CAUSATIVE
variant_origin: GERMLINE
gene_term:
preferred_term: PSAP
term:
id: hgnc:9498
label: PSAP
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Atypical Gaucher disease is caused by variants in the PSAP gene."
explanation: "PSAP variants cause atypical (saposin C deficiency) Gaucher disease."
diagnosis:
- name: Glucocerebrosidase assay with PSAP sequencing
diagnosis_term:
preferred_term: clinical laboratory procedure
term:
id: MAXO:0000006
label: clinical laboratory procedure
description: >-
A Gaucher-like phenotype with normal glucocerebrosidase (beta-glucosidase) activity is
the key clue; diagnosis is confirmed by PSAP sequencing.
markers: Normal beta-glucosidase activity with a Gaucher-like phenotype and elevated glucosylceramide.
evidence:
- reference: PMID:17919309
reference_title: "Non-neuronopathic Gaucher disease due to saposin C deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Saposin (SAP-) C is required for glucosylceramide degradation, and its deficiency results in a variant form of Gaucher disease."
explanation: "The variant Gaucher phenotype with normal enzyme prompts PSAP/saposin C testing."
- name: PSAP molecular genetic testing
diagnosis_term:
preferred_term: genetic testing
term:
id: MAXO:0000127
label: genetic testing
description: Confirmatory biallelic PSAP sequencing.
evidence:
- reference: PMID:35456468
reference_title: "Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The family was investigated using exome and Sanger sequencing."
explanation: "Molecular sequencing of PSAP confirms the diagnosis."
differential_diagnoses:
- name: Gaucher disease
description: >-
Classic Gaucher disease caused by glucocerebrosidase (GBA1) deficiency, with the same
glucosylceramide storage but a deficient enzyme.
disease_term:
preferred_term: Gaucher disease
term:
id: MONDO:0018150
label: Gaucher disease
distinguishing_features:
- Caused by deficient glucocerebrosidase enzyme activity (GBA1), whereas saposin C deficiency leaves enzyme activity normal.
evidence:
- reference: PMID:38928321
reference_title: "Deficiency of Glucocerebrosidase Activity beyond Gaucher Disease: PSAP and LIMP-2 Dysfunctions."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "GCase deficiency causes Gaucher Disease (GD), which is mainly due to biallelic pathogenetic variants in the GCase-encoding gene, GBA1."
explanation: "Classic Gaucher disease is GBA1 enzyme deficiency, distinct from the saposin C cofactor defect."
treatments:
- name: Supportive Care
description: >-
No saposin-C-specific disease-modifying therapy is established; management is
supportive and symptomatic, drawing on approaches used for classic Gaucher disease.
treatment_term:
preferred_term: Supportive Care
term:
id: NCIT:C15747
label: Supportive Care
definitions:
- name: Clinical case definition of saposin C deficiency Gaucher disease
definition_type: CASE_DEFINITION
description: >-
Gaucher disease due to saposin C deficiency is an atypical Gaucher disease defined by
biallelic PSAP variants abolishing the saposin C activator, with glucosylceramide
accumulation and a Gaucher-like phenotype despite normal glucocerebrosidase enzyme
activity.
scope: Disease-level case definition for saposin C deficiency Gaucher disease.
evidence:
- reference: PMID:17919309
reference_title: "Non-neuronopathic Gaucher disease due to saposin C deficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Saposin (SAP-) C is required for glucosylceramide degradation, and its deficiency results in a variant form of Gaucher disease."
explanation: "Anchors the case definition in saposin C deficiency causing variant Gaucher disease."
Gaucher disease due to saposin C deficiency is an ultra-rare lysosomal disorder in which biallelic pathogenic variants in PSAP (prosaposin) impair production/function of saposin C (SapC), an essential activator/cofactor for lysosomal glucocerebrosidase (GCase). This causes a Gaucher-like phenotype via impaired degradation of glucosylceramide (GlcCer) and related sphingolipids, and can clinically resemble non-neuronopathic (type 1-like) or neuronopathic (type 3-like) Gaucher disease—sometimes despite normal in vitro GCase activity assays (tamargo2012theroleof pages 1-2, rafi1993mutationalanalysisin pages 1-3, motta2014gaucherdiseasedue pages 1-2).
| Disease/Concept | Identifier type | Identifier/value | Notes (inheritance, subtype, comments) | Source |
|---|---|---|---|---|
| Gaucher disease due to saposin C deficiency | MIM/OMIM disease ID | 610539 | Rare PSAP-related Gaucher-like disorder; autosomal recessive; can phenocopy type 1 or type 3 Gaucher disease; standard Orphanet/MONDO/MeSH/ICD identifiers were not found in the evidence (liaqat2022phenotypeexpansionfor pages 1-2, tamargo2012theroleof pages 1-2) | Genes 2022; Mol Genet Metab 2012 |
| Variant Gaucher disease due to saposin C deficiency | Synonym | variant Gaucher disease due to saposin C deficiency | Historical/alternative phrasing for PSAP saposin C deficiency causing Gaucher-like disease (rafi1993mutationalanalysisin pages 1-3, motta2014gaucherdiseasedue pages 1-2) | Somatic Cell Mol Genet 1993; Hum Mol Genet 2014 |
| Atypical Gaucher disease due to PSAP | Synonym | atypical Gaucher disease due to PSAP | Used for PSAP-associated Gaucher spectrum with phenotypic heterogeneity, including visceral and neurologic manifestations (liaqat2022phenotypeexpansionfor pages 5-7, liaqat2022phenotypeexpansionfor pages 1-2) | Genes 2022 |
| PSAP gene | MIM/OMIM gene ID | 176801 | Encodes prosaposin, precursor of saposins A-D; biallelic pathogenic variants can cause saposin C deficiency or broader prosaposin deficiency (liaqat2022phenotypeexpansionfor pages 1-2, motta2014gaucherdiseasedue pages 1-2) | Genes 2022; Hum Mol Genet 2014 |
| GBA gene | MIM/OMIM gene ID | 606463 | Encodes glucocerebrosidase/GCase; canonical Gaucher disease gene; SapC is its essential activator/cofactor (liaqat2022phenotypeexpansionfor pages 1-2, tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2) | Genes 2022; Mol Genet Metab 2012; Hum Mol Genet 2014 |
| Gaucher disease type 1 | MIM/OMIM disease ID | 230800 | Non-neuronopathic Gaucher reference subtype; SapC deficiency may clinically resemble type 1 in some patients (tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2) | Mol Genet Metab 2012; Hum Mol Genet 2014 |
| Gaucher disease type 2 | MIM/OMIM disease ID | 230900 | Acute neuronopathic Gaucher reference subtype; cited in review context for GD classification (pavan2024deficiencyofglucocerebrosidase pages 2-4) | Int J Mol Sci 2024 |
| Gaucher disease type 3 | MIM/OMIM disease ID | 231000 | Chronic neuronopathic Gaucher reference subtype; SapC deficiency often discussed as type 3-like/neuronopathic (tamargo2012theroleof pages 1-2, pavan2024deficiencyofglucocerebrosidase pages 2-4) | Mol Genet Metab 2012; Int J Mol Sci 2024 |
| Prosaposin deficiency | MIM/OMIM disease ID | 611721 | Distinct from isolated SapC deficiency; complete prosaposin deficiency affects all saposins and is typically more severe (tamargo2012theroleof pages 1-2, pavan2024deficiencyofglucocerebrosidase pages 1-2) | Mol Genet Metab 2012; Int J Mol Sci 2024 |
| Saposin C | Molecular concept | Essential activator of GCase | Derived from prosaposin; promotes GCase interaction with anionic lysosomal membranes and stabilizes enzyme activity/protein; deficiency can present despite normal in vitro GCase activity in some assays (tamargo2012theroleof pages 1-2, tamargo2012theroleof pages 5-7, motta2014gaucherdiseasedue pages 1-2) | Mol Genet Metab 2012; Hum Mol Genet 2014 |
| Evidence base | Resource provenance | Aggregated disease literature plus individual case reports | Knowledge derives mainly from case reports/small families and mechanistic studies, not EHR-scale datasets; only a handful of patients have been reported worldwide (liaqat2022phenotypeexpansionfor pages 5-7, tamargo2012theroleof pages 5-7) | Genes 2022; Mol Genet Metab 2012 |
| External identifiers not found in retrieved evidence | Identifier status | Orphanet/MONDO/MeSH/ICD not found | Absence here reflects retrieved evidence only and should not be interpreted as proof that no such identifiers exist in external databases (liaqat2022phenotypeexpansionfor pages 1-2, tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2) | Genes 2022; Mol Genet Metab 2012; Hum Mol Genet 2014 |
Table: This table summarizes the key disease and gene identifiers, core synonyms, and classification facts for Gaucher disease due to saposin C deficiency. It is useful for normalizing nomenclature and linking PSAP-related disease concepts to canonical Gaucher disease subtypes.
Notes on identifiers: Orphanet, MeSH, ICD-10/ICD-11, and MONDO identifiers were not present in the retrieved documents and therefore cannot be reliably populated from this evidence set (tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2).
The evidence base is dominated by single-patient case reports and small families, plus mechanistic in vitro and animal-model studies; it is not derived from EHR-scale aggregated cohorts (tamargo2012theroleof pages 5-7, liaqat2022phenotypeexpansionfor pages 5-7).
No protective genetic or environmental factors were reported in the retrieved evidence.
No PSAP SapC-deficiency-specific gene–environment interaction evidence was found in the retrieved documents.
Across the limited number of reported patients, SapC deficiency can produce type 1-like (visceral/hematologic/bone) disease and/or type 3-like neuronopathic disease. A review of six reported patients described presentations ranging from type 1-like to type 3-like, including adult siblings with mild neurologic deterioration (tamargo2012theroleof pages 5-7, tamargo2012theroleof pages 1-2).
| Phenotype/feature | HPO term suggestion | Typical onset/course | Notes/frequency (if available) | Key evidence |
|---|---|---|---|---|
| Hepatosplenomegaly | HP:0001433 Hepatosplenomegaly | Infantile to childhood; progressive or persistent | Commonly reported visceral feature across cases/families | Seen in classic case summaries and recent reports; 4-month-old PSAP case had hepatosplenomegaly; also reported in Pakistani family and Indian infant (tamargo2012theroleof pages 1-2, pavan2024deficiencyofglucocerebrosidase pages 2-4, liaqat2022phenotypeexpansionfor pages 5-7, li2025prosaposinamultifaceted pages 10-11) |
| Anemia | HP:0001903 Anemia | Infantile/childhood; chronic | Reported in Gaucher-like visceral presentations; not quantified for all cases | Listed among typical GD-like findings in SapC deficiency; present in Indian/Chinese summaries (tamargo2012theroleof pages 1-2, li2025prosaposinamultifaceted pages 10-11) |
| Thrombocytopenia | HP:0001873 Thrombocytopenia | Infantile to childhood; chronic | Recurrent hematologic finding | Reported in Pakistani family and in general SapC-deficiency phenotype descriptions (tamargo2012theroleof pages 1-2, liaqat2022phenotypeexpansionfor pages 5-7, li2025prosaposinamultifaceted pages 10-11) |
| Bone lesions / kyphosis | HP:0002650 Scoliosis/Kyphosis; HP:0002758 Osteolysis or HP:0000930 Generalized osteopenia | Childhood to adult; progressive/variable | Bone lesions are part of GD-like spectrum; kyphosis specifically reported in Pakistani family | Bone disease noted in reviews; kyphosis reported with p.Glu359Ala family (tamargo2012theroleof pages 1-2, liaqat2022phenotypeexpansionfor pages 5-7) |
| Pulmonary hypertension | HP:0002092 Pulmonary hypertension | Variable; likely later complication | Mentioned as part of GD clinical spectrum in SapC-deficiency review, not clearly frequency-defined for SapC cases | Listed among clinical features in 2014 mechanistic paper introduction (motta2014gaucherdiseasedue pages 1-2) |
| Seizures / encephalopathy | HP:0001250 Seizure; HP:0001298 Encephalopathy | Early infantile in severe neuronopathic cases; can be rapidly progressive | Indian infant had encephalopathy and refractory seizures; severe neonatal/infantile presentations reported | 2-month-old infant with encephalopathy and resistant tonic-clonic seizures died by 4 months (li2025prosaposinamultifaceted pages 10-11) |
| Hypotonia | HP:0001252 Hypotonia | Early infantile; progressive in severe cases | Present in severe infantile case; also 4-month-old PSAP_PT had hypotonia | Reported in Indian infant and PSAP_PT with severe neurologic disease (li2025prosaposinamultifaceted pages 10-11, pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Nystagmus | HP:0000639 Nystagmus | Early infantile in severe neuronopathic case | Reported in PSAP_PT suspected as GD2-like | 4-month-old infant had hypotonia, nystagmus, swallowing difficulty (pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Ataxia | HP:0001251 Ataxia | Childhood to adult; progressive neurologic course | Seen in type 3-like / neuronopathic presentations and mouse models | Included in human clinical spectrum and supported by SapC-deficient mouse phenotype (tamargo2012theroleof pages 1-2, sun2010specificsaposinc pages 1-2) |
| Myoclonic epilepsy | HP:0001336 Myoclonic seizures | Childhood/adolescent; progressive neuronopathic course | Reported in GD-like neurologic spectrum due to SapC deficiency | Included in SapC-deficiency clinical overlap with type 3 GD (tamargo2012theroleof pages 1-2) |
| Abnormal horizontal saccades | HP:0000640 Oculomotor apraxia / HP:0000616 Abnormality of eye movement | Childhood/adolescent; neurologic | Characteristic neuronopathic GD-like feature in some reported cases | Listed in review of six reported patients (tamargo2012theroleof pages 1-2) |
| Hearing impairment | HP:0000365 Hearing impairment | Congenital/prelingual or childhood; non-progressive/progressive uncertain | All affected members in Pakistani family had hearing impairment; prelingual profound SNHL highlighted | Strong feature in p.Glu359Ala family (liaqat2022phenotypeexpansionfor pages 5-7) |
| Vestibular dysfunction | HP:0001751 Vestibular areflexia / HP:0001756 Vestibular dysfunction | Childhood; chronic | Reported with hearing impairment in Pakistani family | Present in all affected family members in phenotype-expansion report (liaqat2022phenotypeexpansionfor pages 5-7) |
| GCase activity may be normal in vitro | HP:0012378 Abnormal enzyme/coenzyme activity | Diagnostic caveat; may obscure diagnosis | Important distinguishing feature: SapC deficiency can present despite normal standard GCase assay results | Human SapC-deficient cases can show normal in vitro GCase activity; one case had normal skin fibroblast GCase despite biomarker abnormalities (tamargo2012theroleof pages 1-2, rafi1993mutationalanalysisin pages 1-3, li2025prosaposinamultifaceted pages 11-13) |
| Tissue glucosylceramide accumulation | HP:0011015 Abnormal sphingolipid concentration | Persistent biochemical hallmark | May be demonstrated in spleen/tissue despite normal enzyme assay | Spleen glucosylceramide accumulation documented in variant Gaucher due to SapC deficiency (rafi1993mutationalanalysisin pages 1-3) |
| Plasma chitotriosidase elevation | HP:0034046 Increased circulating chitotriosidase level | Elevated at diagnosis; reflects macrophage activation | Markedly elevated in severe infantile PSAP case | PSAP_PT chitotriosidase 2951.0 nmol/mL/h (pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Plasma glucosylsphingosine (GlcSph) elevation | HP:0034383 Increased circulating glucosylsphingosine | Elevated at diagnosis | Useful GD biomarker in PSAP-related GCase deficiency | PSAP_PT plasma GlcSph 19.0 ng/mL (pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Lyso-Gb3 elevation | HP:0034380 Abnormal globotriaosylsphingosine level | Elevated at diagnosis in reported case | Ancillary lipid biomarker; may assist broader sphingolipid profiling | PSAP_PT Lyso-Gb3 1.98 ng/mL (pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| PPCS elevation | HP:0034385 Abnormal lysosphingolipid profile | Elevated at diagnosis in reported case | Additional plasma biomarker reported in 2024 study | PSAP_PT PPCS 745.9 ng/mL (pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Genetic testing for PSAP variants | HP:0000007 Autosomal recessive inheritance | Confirmatory test; indicated when GD suspected but GBA1 negative or biochemistry atypical | Reported pathogenic variant classes include missense, nonsense, splice-site, start-loss, and deletions | PSAP sequencing/WES/Sanger used across cases; variants include p.E297*, p.Glu359Ala, p.C382G/F, p.L349P, c.1005+1G>A (liaqat2022phenotypeexpansionfor pages 5-7, motta2014gaucherdiseasedue pages 1-2, pavan2024deficiencyofglucocerebrosidase pages 2-4) |
| Negative GBA1 testing should trigger PSAP evaluation | HP:0000007 Autosomal recessive inheritance | Diagnostic workflow recommendation | Particularly important in infantile GD-like disease with elevated biomarkers and low-normal/normal GCase assays | 2024 PSAP_PT was GBA1-negative then diagnosed by PSAP testing; Indian report explicitly advises considering specific activator deficiency when GD is suspected with partially deficient or near-normal GBA activity (pavan2024deficiencyofglucocerebrosidase pages 2-4, li2025prosaposinamultifaceted pages 10-11) |
Table: This table summarizes the reported clinical spectrum and key diagnostic findings for Gaucher disease due to saposin C deficiency caused by PSAP variants. It is useful for distinguishing this ultra-rare activator deficiency from canonical GBA1-related Gaucher disease, especially when enzyme activity is normal or only mildly reduced.
Formal QoL instruments (e.g., EQ-5D/SF-36/PROMIS) were not reported in the retrieved evidence. Severe infantile neuronopathic disease is expected to substantially impair functioning (hypotonia, swallowing difficulty, seizures), while chronic neurologic disease (ataxia) and visceral disease (organomegaly, cytopenias) can impair daily activity and endurance (pavan2024deficiencyofglucocerebrosidase pages 2-4, tamargo2012theroleof pages 1-2).
Evidence-supported PSAP/SapC-domain pathogenic or likely pathogenic variants include: - c.1144T>G (p.Cys382Gly) reported in a variant Gaucher case with glucosylceramide accumulation despite normal measured glucocerebrosidase activity (rafi1993mutationalanalysisin pages 1-3). - SapC lesions summarized in mechanistic work: p.C315S, p.342_348FDKMCSKdel, p.L349P, p.C382G, p.C382F (motta2014gaucherdiseasedue pages 1-2). - A consanguineous family with likely pathogenic c.1076A>C (p.Glu359Ala) in the SapC domain; variant is rare in gnomAD and lies in the SapC GCase-binding region (aa 351–390) (liaqat2022phenotypeexpansionfor pages 5-7). - Severe infantile case: c.889G>T (p.E297*) with nonsense-mediated mRNA decay; GD2-like suspicion clinically (pavan2024deficiencyofglucocerebrosidase pages 2-4).
Variant classes observed: missense, in-frame deletion, nonsense, splice-site; many reported variants affect SapC cysteines/disulfide bonds or otherwise destabilize the SapC fold (tamargo2012theroleof pages 5-7, motta2014gaucherdiseasedue pages 1-2).
No SapC-deficiency-specific modifier gene, epigenetic, or chromosomal abnormality evidence was found in the retrieved documents.
No disease-specific environmental, lifestyle, or infectious contributors were identified in the retrieved evidence; the disorder is primarily genetic (tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2).
Key molecular/cellular processes (GO Biological Process suggestions): - Lysosomal glycosphingolipid catabolic process / sphingolipid metabolic process (supported conceptually by impaired GlcCer breakdown) (pavan2024deficiencyofglucocerebrosidase pages 1-2, pavan2024deficiencyofglucocerebrosidase pages 9-10) - Lysosome organization and membrane-associated catabolism (SapC-mediated membrane interaction/liftase model) (tamargo2012theroleof pages 4-5) - Autophagy (as a degradation route for mutant SapC proteins) (motta2014gaucherdiseasedue pages 1-2) - Neuroinflammatory response / glial activation (microglia, astrocytes activated in SapC-deficient mouse CNS) (sun2010specificsaposinc pages 1-2)
Cell Ontology (CL) suggestions based on evidence: - Macrophage (Gaucher cells; mononuclear phagocyte system involvement) (tamargo2012theroleof pages 1-2, motta2014gaucherdiseasedue pages 1-2) - Microglial cell (activated microglia in SapC-deficient mouse CNS) (sun2010specificsaposinc pages 1-2) - Astrocyte (astrocyte activation in SapC-deficient mouse CNS) (sun2010specificsaposinc pages 1-2) - Purkinje cell (cerebellar Purkinje neuron loss in SapC-deficient mouse model) (sun2010specificsaposinc pages 1-2)
High-citation expert reviews emphasize that SapC functions as a membrane-active cofactor enabling optimal GCase function and that SapC deficiency can yield a Gaucher phenotype even with apparently normal in vitro enzyme assays, which has important diagnostic implications (tamargo2012theroleof pages 1-2, tamargo2012theroleof pages 4-5).
Direct abstract quote (animal model; mechanistic): - Sun et al. report: “The few patients with saposin C deficiency develop a Gaucher disease-like central nervous system (CNS) phenotype attributed to diminished glucosylceramide (GC) cleavage activity by acid β-glucosidase (GCase).” (Human Molecular Genetics; Dec 2010; https://doi.org/10.1093/hmg/ddp531) (sun2010specificsaposinc pages 1-2)
Onset is variable, ranging from infantile severe neurologic disease (including GD2-like presentations) to childhood/adult-onset neurologic deterioration or more type 1-like disease without clear CNS signs in some families (pavan2024deficiencyofglucocerebrosidase pages 2-4, tamargo2012theroleof pages 5-7, liaqat2022phenotypeexpansionfor pages 5-7).
Severe infantile cases may progress rapidly and can be fatal within months (pavan2024deficiencyofglucocerebrosidase pages 2-4). Other cases show chronic neurologic progression (e.g., ataxia) or chronic visceral disease (tamargo2012theroleof pages 5-7, tamargo2012theroleof pages 1-2).
Autosomal recessive inheritance is strongly supported by multiple reports of homozygous/biallelic PSAP variants and occurrence in consanguineous families (tamargo2012theroleof pages 1-2, liaqat2022phenotypeexpansionfor pages 5-7, pavan2024deficiencyofglucocerebrosidase pages 2-4).
No population-level prevalence or incidence estimates were identified in the retrieved literature. Available synthesis notes only a handful of published patients worldwide (e.g., six described in one review; and ~seven reported cases cited in a later family report), consistent with an ultra-rare condition (tamargo2012theroleof pages 5-7, liaqat2022phenotypeexpansionfor pages 5-7).
The likely pathogenic PSAP c.1076A>C (p.Glu359Ala) variant was reported as rare in gnomAD (overall AF 5.3×10−5; South Asian AF 3.6×10−4; no homozygotes in gnomAD per authors) (liaqat2022phenotypeexpansionfor pages 5-7).
Consider PSAP/SapC deficiency when a patient has a Gaucher-like phenotype (hepatosplenomegaly, cytopenias ± bone disease and/or neurologic disease) but: - GBA1 testing is negative, and/or - GCase activity is normal/low-normal on standard assays (diagnostic pitfall), and/or - biomarkers suggest Gaucher-like macrophage activation and glycosphingolipid storage (pavan2024deficiencyofglucocerebrosidase pages 2-4, rafi1993mutationalanalysisin pages 1-3, tamargo2012theroleof pages 1-2).
A 2024 biochemical profiling study reports markedly elevated Gaucher biomarkers in a PSAP case (PSAP_PT): - Chitotriosidase: 2951.0 nmol/mL/h - Plasma glucosylsphingosine (GlcSph): 19.0 ng/mL - Lyso-Gb3: 1.98 ng/mL - PPCS: 745.9 ng/mL with a homozygous truncating PSAP variant (c.889G>T; p.E297*) and severe infantile disease (Jun 2024; https://doi.org/10.3390/ijms25126615) (pavan2024deficiencyofglucocerebrosidase pages 2-4).
A seminal primary report documented glucosylceramide accumulation in spleen despite normal measured glucocerebrosidase activity, supporting “activator deficiency” rather than enzyme deficiency (rafi1993mutationalanalysisin pages 1-3).
Prognosis appears highly variable and genotype/phenotype dependent. A severe infantile PSAP truncating-variant case with GD2-like features died a few months after diagnosis (pavan2024deficiencyofglucocerebrosidase pages 2-4). Milder phenotypes without overt CNS involvement have been reported in families, implying potentially longer survival (liaqat2022phenotypeexpansionfor pages 5-7). Systematic survival statistics are not available in the retrieved evidence.
No controlled clinical trial evidence specific to SapC deficiency treatment was identified in the retrieved documents, and the clinical trials search did not return SapC-deficiency-specific interventional trials.
Mechanistically, SapC deficiency is an activator/cofactor deficiency rather than a primary GCase catalytic deficiency. Expert reviews discuss that increasing SapC levels or restoring SapC–GCase interactions could be therapeutic in principle, and that chemical chaperones can improve folding/trafficking and SapC–enzyme interactions in experimental contexts, but these are not presented as established clinical therapies for SapC deficiency in the retrieved evidence (tamargo2012theroleof pages 5-7, tamargo2012theroleof pages 7-8).
Supportive management is implied by clinical features (e.g., management of cytopenias, organomegaly complications, seizures, swallowing dysfunction), but specific guidelines were not found in the retrieved evidence.
Given autosomal recessive inheritance, prevention is primarily through genetic counseling and prenatal or preimplantation genetic testing in families with known PSAP variants. A PSAP-related infantile case report summary indicates prenatal diagnosis in a subsequent pregnancy identified a carrier fetus who was unaffected postnatally (reported as part of the PSAP infantile case summary in a synthesis) (li2025prosaposinamultifaceted pages 10-11).
Natural SapC-deficiency animal disease was not identified in the retrieved evidence.
A selective SapC-deficient mouse model (knock-in point mutation eliminating SapC) exhibits a CNS-predominant phenotype (hindlimb weakness, progressive ataxia, neurophysiologic impairment, dorsal root ganglion storage cells, Purkinje cell loss, glial activation) with little/no visceral organ storage—highlighting both mechanistic insight and limitations in recapitulating human visceral disease (sun2010specificsaposinc pages 1-2).
Direct abstract quote (mouse model): - “By 1 year, the C−/− mice exhibited weakness of the hind limbs and progressive ataxia.” (Human Molecular Genetics; Dec 2010; https://doi.org/10.1093/hmg/ddp531) (sun2010specificsaposinc pages 1-2)
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