| Domain | Key evidence | Suggested ontology terms/IDs | Evidence type / maturity |
|---|---|---|---|
| Disease identifiers | Snyder-Robinson syndrome is an ultra-rare X-linked syndromic intellectual disability caused by SMS deficiency; disease mappings in retrieved sources include MONDO:0010664, OMIM:309583, Orphanet:3063. Open Targets links MONDO_0010664 / Orphanet_3063 to SMS (pqac-00000000, pqac-00000004, pqac-00000008) | **Exact IDs:** MONDO:0010664; OMIM:309583; Orphanet:3063. **Term suggestion requiring validation:** “Syndromic X-linked intellectual disability, Snyder type” | Aggregated disease resource + human clinical reports; high confidence for identifiers |
| Causal gene / inheritance | Causal gene is **SMS** (spermine synthase), X-linked recessive; reported disease-causing variants include missense and nonsense changes, with inherited, de novo, and reported maternal mosaic transmission in the broader literature; examples in retrieved evidence include p.Gln148Arg, p.Gly203Asp, p.Pro112Ala, p.Ser302Leu (pqac-00000001, pqac-00000003, pqac-00000004, pqac-00000006, pqac-00000009) | **Exact gene symbol:** SMS. **Term suggestions requiring validation:** HP:0001417 X-linked inheritance; SO terms such as missense_variant, nonsense_variant, splice_region_variant | Human genetic evidence; high confidence for SMS causality, moderate for complete variant spectrum |
| Core biochemical mechanism | SMS catalyzes spermidine → spermine; loss of function lowers spermine and raises spermidine, producing an increased spermidine/spermine ratio, the core biochemical hallmark of SRS (pqac-00000000, pqac-00000006, pqac-00000009, pqac-00000010) | **Exact/near-exact suggestions:** GO:0006598 polyamine biosynthetic process; CHEBI:15746 spermidine; CHEBI:15729 spermine. **Term suggestion requiring validation:** “increased spermidine to spermine ratio” | Human cells + animal models; high confidence |
| Downstream pathophysiology | Evidence supports a causal chain from polyamine imbalance to excessive spermidine catabolism, toxic aldehydes/ROS, lysosomal dysfunction, impaired autophagy-lysosome flux, mitochondrial dysfunction, acetyl-CoA depletion, altered protein acetylation, and tissue injury affecting brain and bone (pqac-00000009, pqac-00000011, pqac-00000013) | **Exact/near-exact GO suggestions:** GO:0006979 response to oxidative stress; GO:0000422 autophagy of mitochondrion/mitophagy (validate fit); GO:0005773 vacuole/lysosomal compartment term suggestion; GO:0005739 mitochondrion; GO:0007015 actin filament organization term suggestion if needed. **All mechanistic ontology mappings should be validated** | Primary mechanistic evidence from Drosophila, patient fibroblasts, and supportive review; moderate-high confidence |
| Neurologic phenotype | Common neurologic features include developmental delay/intellectual disability, hypotonia, seizures/epilepsy, speech impairment, gait abnormalities, learning impairment, anxiety-like behavior and reduced brain volumes in mouse models (pqac-00000000, pqac-00000004, pqac-00000006, pqac-00000010) | **Exact HPO suggestions:** HP:0001249 Intellectual disability; HP:0001252 Hypotonia; HP:0001250 Seizure; HP:0001263 Global developmental delay; HP:0000750 Delayed speech and language development; HP:0001288 Gait disturbance. **Model-only anatomy suggestions requiring validation:** reduced total brain volume | Human clinical + mouse model; high confidence for core human neurologic features |
| Skeletal phenotype | Characteristic skeletal disease includes low bone density/osteoporosis, atraumatic or low-energy fractures, kyphosis/kyphoscoliosis, thin cortex, low bone volume, absent trabecular meshwork, severe mineralization defect, and reduced osteoblast/osteoclast function (pqac-00000002, pqac-00000003) | **Exact/near-exact HPO suggestions:** HP:0000939 Osteoporosis; HP:0002757 Pathological fracture; HP:0002650 Scoliosis; HP:0002808 Kyphosis. **Process/cell suggestions requiring validation:** osteoblast differentiation defect, osteoclast defect | Human clinical + bone histopathology; high confidence |
| Additional/expanded phenotype | Reported additional manifestations include asthenic/thin habitus, facial dysmorphism, long fingers/toes, genital/renal anomalies, respiratory infections, retinal changes, and possible digestive involvement such as jejunal stenosis, feeding intolerance, cholestasis, pancreatic exocrine insufficiency, and failure to thrive in severe cases (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000004, pqac-00000005) | **Exact/near-exact HPO suggestions:** HP:0001508 Failure to thrive; HP:0001511 Intrauterine growth restriction/poor growth term suggestions; HP:0001166 Arachnodactyly term suggestion; HP:0002242 Feeding difficulties; HP:0001394 Cholestasis. **All require phenotype-level validation** | Human case reports/series; moderate confidence for expanded GI phenotype |
| Diagnostic biomarkers / tests | Diagnosis can be made by identifying a pathogenic SMS variant and/or showing decreased or absent spermine synthase activity with elevated spermidine/spermine ratio. One severe report provided markedly abnormal erythrocyte polyamines: spermidine >50 nmoles/8×10^9 erythrocytes (norm 5–11) and spermine 2.58 (norm 3.5–8.5). WES/Sanger are established; DXA/radiography are used for bone disease (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000004, pqac-00000006) | **Exact/near-exact suggestions:** biomarker = elevated spermidine:spermine ratio; assay = SMS enzymatic activity test; genetic test = WES / Sanger confirmation. **LOINC/MAXO/other codes require validation** | Human diagnostic evidence; high confidence |
| Supportive care | Current management is mainly supportive: antiepileptic drugs for seizures, calcium/vitamin D with caution because of ectopic calcification concerns, orthopedic surveillance, nutritional/feeding support, and multidisciplinary genetic care. No disease-modifying standard therapy is established (pqac-00000002, pqac-00000005, pqac-00000011) | **MAXO term suggestions requiring validation:** antiseizure medication therapy; calcium supplementation; vitamin D supplementation; orthopedic monitoring; enteral feeding support; genetic counseling | Human clinical practice from case literature; moderate confidence |
| Experimental therapy: phenylbutyrate (PBA) | PBA improved SRS-related phenotypes in Drosophila and patient fibroblasts by downregulating SAT1, reducing toxic catabolites, restoring acetyl-CoA/protein acetylation, improving mitochondrial and autolysosomal function, and extending fly lifespan. In flies, 2 mM showed benefit, whereas 10 mM was toxic; glycerol-PBA also showed benefit at 0.6 mM (pqac-00000011, pqac-00000013) | **CHEBI / drug suggestion requiring validation:** phenylbutyrate. **MAXO suggestions requiring validation:** experimental small-molecule therapy; metabolite-modulating therapy | Preclinical only (patient cells + fly); moderate confidence, not yet human efficacy |
| Experimental therapy: DFMO | A 2023 EMBO Molecular Medicine study is cited in later reviews as showing DFMO can rebalance aberrant polyamine ratios in SRS, but primary quantitative details were not retrievable in the current tool outputs; therefore translational promise is noted without overclaiming clinical efficacy (pqac-00000012) | **Drug suggestion requiring validation:** difluoromethylornithine / eflornithine. **MAXO suggestion requiring validation:** polyamine-pathway inhibition therapy | Secondary/review-level evidence in current retrieval; low-moderate confidence until primary paper details are confirmed |
| Other experimental approaches | Additional exploratory strategies cited in reviews include direct spermine supplementation, polyamine analogs such as (R,R)-1,12-dimethylspermine, antioxidants/ROS scavengers, and redox-sensitive spermine prodrugs; benefits are partial or preclinical only (pqac-00000011, pqac-00000012, pqac-00000014) | **CHEBI/MAXO suggestions requiring validation:** spermine supplementation; antioxidant therapy; polyamine analog therapy; prodrug therapy | Preclinical / review-supported; low-moderate confidence |
| Model organisms | **Drosophila dSms loss** recapitulates polyamine imbalance, shortened lifespan, locomotor defects, retinal/synaptic degeneration, oxidative stress, lysosomal and mitochondrial dysfunction. **G56S mouse** shows failure to thrive, short stature, reduced bone density, impaired learning, anxiety-like behavior, reduced mobility, heightened fear responses, reduced brain volumes, and impaired mitochondrial oxidative phosphorylation (pqac-00000009, pqac-00000010) | **Exact/near-exact suggestions:** Drosophila melanogaster model; Mus musculus G56S Sms model. **Ontology suggestions requiring validation:** model recapitulates HP:0001249, HP:0001252, HP:0000939; CL terms for neurons, osteoblasts, osteoclasts, fibroblasts | Strong preclinical evidence; high value for mechanism and therapeutic testing |
| Evidence gaps / curation notes | Prevalence, penetrance, founder effects, standardized diagnostic criteria, and long-term prognosis remain poorly quantified because very few families have been reported. Several ontology mappings above are term suggestions and should be validated against HPO/GO/CL/MAXO/LOINC before database ingestion (pqac-00000000, pqac-00000006, pqac-00000012) | **Curation note:** retain exact IDs only for MONDO:0010664, OMIM:309583, Orphanet:3063, SMS, and high-confidence HPO terms; validate all others | Evidence-synthesis note; high confidence for gap statement |


*Table: This table summarizes high-yield evidence and ontology mappings for Snyder-Robinson syndrome across identifiers, mechanism, phenotype, diagnostics, treatment, and models. It is designed as a compact curation aid and flags which ontology terms are exact versus suggestions needing validation.*