| domain | established finding | evidence type/strength | key ontology suggestions |
|---|---|---|---|
| Definition / classification | Mucopolysaccharidosis-plus syndrome (MPSPS) is an ultra-rare autosomal-recessive lysosomal/endolysosomal trafficking disorder with MPS-like glycosaminoglycan accumulation but without deficiency of known lysosomal GAG-degrading enzymes; reviews note debate over whether it is a true MPS subtype or a distinct metabolic disease (pqac-00000003, pqac-00000002) | Human disease review + mechanistic primary study; moderate-strong for disease definition, moderate for classification debate (pqac-00000003, pqac-00000002, pqac-00000005) | Lysosomal storage disease; endolysosomal transport disorder; possible MONDO term search: “mucopolysaccharidosis-plus syndrome”; GO: lysosomal transport, endosome organization |
| VPS33A variants and inheritance | Established severe infantile form is caused by homozygous VPS33A c.1492C>T (p.Arg498Trp / p.R498W); 2024 review additionally reports VPS33A c.599G>C (p.Arg200Pro) in 2 juvenile milder cases. Inheritance is autosomal recessive (pqac-00000003, pqac-00000004) | Human case series/reviews; strong for p.Arg498Trp, moderate for p.Arg200Pro pending broader replication (pqac-00000003, pqac-00000004) | HGNC: VPS33A; SO: missense_variant; inheritance: autosomal recessive inheritance |
| Epidemiology | By 2024, 41 patients had been described; strong founder effect in the Yakut population is reported, with most early cases from Yakutia and a birth incidence estimate of ~1 in 12,100 in Yakuts for p.Arg498Trp. Sex distribution in one 16-patient Yakut cohort was 8 female / 8 male (pqac-00000002, pqac-00000004, pqac-00000010) | Human cohort/review; moderate because numbers are small and literature is rapidly evolving (pqac-00000002, pqac-00000004, pqac-00000010) | Founder effect; rare disease; population of interest: Yakut/Sakha |
| Core phenotypes | Multisystem phenotype includes coarse facial features, short neck/nose, periorbital puffiness, macroglossia, growth deficiency, hepatosplenomegaly, dysostosis multiplex, kyphosis/lordosis, barrel chest, joint contractures/stiffness, clawed fingers, developmental delay/regression, hypotonia, nystagmus, recurrent respiratory infections, congenital heart disease, renal disease/nephrotic syndrome, and hematologic abnormalities including anemia, thrombocytopenia, neutropenia/coagulation defects (pqac-00000000, pqac-00000001, pqac-00000006, pqac-00000009, pqac-00000010) | Human case series and focused review; strong for infantile p.Arg498Trp phenotype (pqac-00000000, pqac-00000001, pqac-00000010) | HPO suggestions: Coarse facial features; Macroglossia; Dysostosis multiplex; Joint contracture; Hepatosplenomegaly; Developmental delay; Hypotonia; Nystagmus; Recurrent respiratory infections; Congenital heart defect; Nephrotic syndrome; Anemia; Thrombocytopenia; Neutropenia |
| Biomarkers / diagnosis | Characteristic laboratory pattern: elevated urinary GAGs, especially heparan sulfate and dermatan sulfate, with very high plasma heparan sulfate; additional reports note increased sialooligosaccharides/sialic acid. A key distinguishing feature is normal activities of known lysosomal enzymes for GAG degradation. Diagnosis is based on MPS-like clinical presentation plus biochemical findings and confirmatory molecular testing for VPS33A; prenatal diagnosis is reported as available (pqac-00000001, pqac-00000004, pqac-00000012) | Human clinical/biochemical evidence; strong for elevated GAGs with normal lysosomal enzyme assays (pqac-00000001, pqac-00000004, pqac-00000012) | HPO: Elevated urinary glycosaminoglycan; Proteinuria; Hypoalbuminemia; Delayed myelination. Diagnostic concepts: urine GAG analysis, plasma HS quantification, VPS33A sequencing |
| Mechanism | VPS33A is a core HOPS/CORVET subunit. p.Arg498Trp is predicted to destabilize VPS33A, reducing full-length VPS33A and other HOPS/CORVET components, causing disordered endolysosomal compartments, abnormal lactosylceramide trafficking, cholesterol/sphingolipid abnormalities, autophagy-endosomal dysfunction, and impaired intracellular handling of GAGs despite normal enzyme activities. Some mechanistic details remain uncertain (pqac-00000005, pqac-00000004, pqac-00000006) | Primary human fibroblast mechanistic study + focused review; strong for VPS33A instability/HOPS-CORVET depletion and trafficking defects, moderate for full causal chain to GAG accumulation (pqac-00000005, pqac-00000004, pqac-00000006) | GO suggestions: endocytic vesicle fusion; lysosomal transport; autophagosome-lysosome fusion; endosome organization. Cellular compartment: lysosome, late endosome, autophagosome |
| Prognosis / natural history | Typical severe p.Arg498Trp disease begins in early infancy with recurrent respiratory problems around 2–6 months and progresses rapidly; most reported patients died from cardiorespiratory failure at about 10–20 months. Juvenile cases linked to p.Arg200Pro appear milder/longer-surviving but remain very limited (pqac-00000000, pqac-00000001, pqac-00000004, pqac-00000010) | Human cohort/review; strong for poor prognosis of infantile founder variant, weak-moderate for variant-specific milder prognosis due to only 2 cases (pqac-00000000, pqac-00000001, pqac-00000004) | HPO suggestions: Infantile onset; Progressive course; Early death |
| Treatment | No approved disease-modifying therapy or relevant clinical trial was identified in retrieved evidence. Current management is supportive/symptomatic: respiratory support, antibiotics, oxygen, vitamins, ACE inhibitors, transfusions, and selected cardiac surgery. Experimental in vitro rescue of patient fibroblast defects has been reported with bortezomib and eliglustat; these findings are preclinical and should not be interpreted as established clinical therapy (pqac-00000001, pqac-00000005, pqac-00000012) | Human supportive-care evidence + preclinical cell data; strong that no specific established therapy exists, weak-moderate for translational promise of bortezomib/eliglustat because evidence is in vitro only (pqac-00000001, pqac-00000005, pqac-00000012) | NCIT-style intervention suggestions: Supportive care; Oxygen therapy; Anti-infective therapy; Blood transfusion; Cardiac surgical procedure; Proteasome inhibitor (experimental); Glucosylceramide synthase inhibitor (experimental) |


*Table: This table condenses the strongest available evidence for key disease-characteristic domains in mucopolysaccharidosis-plus syndrome. It separates established human findings from experimental or still-uncertain observations and suggests ontology mappings useful for knowledge-base curation.*