| Domain | Established finding | Quantitative/patient evidence | Evidence type/source and date | Confidence/limitations |
|---|---|---|---|---|
| Identifiers / nomenclature | SCAR15 is **Salih ataxia**, an **autosomal recessive spinocerebellar ataxia** distinct from dominant SCA15; OMIM **615705**; MONDO **0014311**; disease gene now standardized as **RUBCN** (former **KIAA0226**; protein previously named **rundataxin**) | Disease entity consistently linked to one recessive syndrome in reported families; Open Targets maps MONDO_0014311 to RUBCN | Human disease report and follow-up case report (2010, 2020); disease-target database mapping (Open Targets) (pqac-00000002, pqac-00000014, pqac-00000001) | High for nomenclature resolution; major caveat is historical confusion with dominant SCA15 and older KIAA0226 nomenclature |
| Gene / variant | Causal mechanism is **biallelic truncating RUBCN loss-of-function**, specifically the Saudi founder frameshift: **NM_014687:c.2624delC, p.A875fs**; older report used another transcript/protein numbering: **2927delC, p.Ala943ValfsX146** | Same underlying deletion reported across both families; parents are carriers in family 2 | Primary human genetics reports (2010, 2020) (pqac-00000010, pqac-00000014) | High; transcript/protein numbering differs between publications and should be normalized during curation |
| Case count / ascertainment | Literature support is extremely small and patient-based | **5 total patients** from **2 unrelated Saudi families**: family 1 = 3 affected sisters; family 2 = 2 affected brothers | Aggregated from primary reports/table (2010, 2020) (pqac-00000002, pqac-00000013, pqac-00000017) | High for known published cases through 2020; ultra-rare disorder, likely under-ascertained |
| Phenotype frequency note | Percentages below are **descriptive only** because n=5 | Example: 3/5 = 60%; 2/5 = 40% | Derived from case table across all 5 patients (pqac-00000013, pqac-00000017) | Very limited inferential value; no population-based denominator |
| Core neurologic phenotype | Childhood-onset cerebellar syndrome with gait ataxia, limb ataxia, and dysarthria | Gait ataxia **5/5 (100%)**; dysarthria **5/5 (100%)**; upper-limb ataxia **4/5 (80%)**; lower-limb ataxia **4/5 (80%)** | Primary human clinical reports (2010, 2020) (pqac-00000002, pqac-00000013, pqac-00000017) | Moderate-high for core syndrome; severity grading is based on very few patients |
| Developmental features | Delayed motor and speech development are common and may precede/overlap with ataxia | Delayed walking **5/5 (100%)**; delayed speech acquisition **5/5 (100%)** | Case table and narrative clinical descriptions (2020 with comparison to 2010 family) (pqac-00000012, pqac-00000013, pqac-00000017) | Moderate-high; ascertainment is through pediatric neurology in consanguineous families |
| Cognition / neurodevelopment | Cognitive involvement ranges from none/borderline to moderate intellectual disability | Cognitive deficit or low IQ documented in **4/5 (80%)**; one patient had no cognitive deficit; family 2 IQs **67** and **72** | Primary patient reports (2010, 2020) (pqac-00000010, pqac-00000012, pqac-00000013) | Moderate; formal psychometrics were incomplete in original family |
| Epilepsy | Infantile epilepsy can occur but is not universal | Epilepsy in **2/5 (40%)**; both onset at **7 months** in family 1; seizure-free after treatment; **0/2** in family 2 | Primary human reports (2010, 2020) (pqac-00000002, pqac-00000010, pqac-00000013) | Moderate; phenotype variability evident even with same founder variant |
| Eye movement abnormalities | Oculomotor abnormalities emerge in some older patients | Nystagmus or saccadic pursuit in **4/5 (80%)** overall; absent in younger family-2 proband at 6.5 y | Primary patient comparison table (2020) (pqac-00000012, pqac-00000013, pqac-00000017) | Moderate; age dependence likely, but longitudinal data are sparse |
| Reflexes / pyramidal signs | Reflex pattern is variable, with lower-limb hyperreflexia in some patients | Lower-limb reflexes enhanced in **3/5 (60%)**, diminished in **1/5 (20%)**, normal in **1/5 (20%)**; plantar responses flexor in **5/5 (100%)** | Human clinical comparison table (2020) (pqac-00000013, pqac-00000017) | Moderate; mixed reflex findings suggest variable corticospinal involvement but no strong proof of pyramidal degeneration |
| Onset / temporal course | Onset is early childhood, usually when learning to walk; course is **slowly progressive** | Initial symptom: unsteadiness at **2, 2, 2.5, 3, and 7 years** across the 5 patients; disability stage reached **3/7** in 3 original patients, **1/7** and **0/7** in younger family-2 siblings at assessment | Primary longitudinal clinical reports (2010, 2020) (pqac-00000002, pqac-00000013, pqac-00000014) | Moderate-high for slow progression; no formal natural history study or survival analysis |
| MRI / neuroimaging | Early MRI can be normal; cerebellar atrophy appears mild and late in some patients | Normal MRI in early scans at **2.5, 6, 8, 9, 16 years** depending on patient; later abnormalities: **mild cerebellar atrophy/prominent folia at 18 y** in one patient and **minimal superior vermian atrophy at 16 y** in another | Human MRI findings from both families (2010, 2020) (pqac-00000010, pqac-00000012, pqac-00000013, pqac-00000014) | High for pattern of delayed/subtle imaging change; limited by tiny sample and irregular follow-up ages |
| Electrophysiology / sensory testing | Large-fiber peripheral neuropathy is not a consistent feature; some auditory/visual pathway abnormalities may occur | Motor/sensory nerve conduction studies **normal in 5/5** when tested; BAER abnormal hearing thresholds in **2/4** tested; VEP abnormal in **1/4** tested | Human neurophysiology table and narratives (2020) (pqac-00000012, pqac-00000013, pqac-00000017) | Moderate; testing not complete in every patient, and BAER/VEP abnormalities were subtle/variable |
| Inheritance / founder effect | Inheritance is **autosomal recessive** with strong evidence of an **Arab/Saudi founder mutation** | Family 2 parents are **first cousins**; identical homozygous haplotype/variant in both families; mutation age estimated at **~1550 years (~62 generations)** | Human segregation, autozygosity, haplotype, and age analysis (2020) (pqac-00000012, pqac-00000014, pqac-00000006) | High for founder effect within reported Saudi cases; carrier frequency/prevalence in broader populations unknown |
| Molecular mechanism — SCAR15-specific evidence | Disease-associated truncation disrupts Rubicon localization/function in endolysosomal trafficking | SCAR15-specific functional conclusion: truncated Rubicon **loses ability to colocalize with Rab7 at late endosomes**, implying defective endosomal trafficking | SCAR15-specific human variant follow-up summarized in 2020 report citing 2013 functional study (pqac-00000011, pqac-00000013) | Moderate; mechanism is disease-specific but based on limited experimental work around a single truncating allele |
| Molecular mechanism — general RUBCN biology (not SCAR15-specific) | Rubicon is a regulator of endosomal maturation, canonical autophagy, and LC3-associated phagocytosis (LAP); interacts with **RAB7**, **UVRAG/BECN1/PIK3C3(VPS34)** complexes | General cell-biology evidence shows inhibitory role in canonical autophagy and required role in LAP; RUBCN-deficient cells can show increased autophagic flux and altered endosome maturation | Mechanistic reviews and broader RUBCN studies (2018, 2023, 2020 kidney model) (pqac-00000007, pqac-00000008) | Moderate for relevance to SCAR15; these data are biologically informative but **not direct proof of pathogenesis in patient neurons** |
| Diagnosis | Recommended practical diagnosis is phenotype recognition plus genomic confirmation of **biallelic RUBCN** variants; WES/autozygosity was effective in published families | In family 2, diagnosis came from **WES + autozygome**; original work used linkage/homozygosity mapping plus candidate sequencing; original screen of **172 non-Friedreich ataxia families** found **no additional KIAA0226 mutations** | Primary reports (2010, 2020) (pqac-00000010, pqac-00000012, pqac-00000014) | High for published diagnostic utility; no SCAR15-specific guideline, and repeat expansion testing still remains important in general ataxia workups |
| Current ataxia diagnostic practice | In broader hereditary ataxia practice, genome-scale testing is increasingly recommended, with attention to repeat expansions | Recent expert/consensus work in ataxia supports WGS/WES/NGS data-sharing approaches because many ataxia cases remain unsolved; not SCAR15-specific | Ataxia practice recommendations and AGI standards (2024-2025) (pqac-00000001) | Moderate relevance; supports real-world implementation context rather than disease-specific evidence |
| Treatment / management | No disease-modifying SCAR15 therapy reported; management is supportive and symptom-directed | Epilepsy in family 1 responded to **vigabatrin ± clonazepam**; no SCAR15-targeted drug, gene therapy, ASO, or registered interventional trial identified | Human case data and trial search context (2010, 2020; no SCAR15-specific trial hit) (pqac-00000010, pqac-00000014) | High for absence of specific therapy in available evidence; supportive rehab use is extrapolated from broader ataxia practice |
| Treatment / broader ataxia trials | Non-SCAR15 ataxia trials exist for symptomatic or rehabilitative approaches, but applicability to SCAR15 is unknown | Examples include riluzole, N-acetyl-L-leucine, VR/rehabilitation, tDCS studies in mixed ataxia cohorts; none are genotype-specific for RUBCN | Clinical trial search results in ataxia field (2024-2025 retrieval context) (pqac-00000000) | Low-moderate relevance to SCAR15; should not be interpreted as evidence of efficacy in SCAR15 |
| Epidemiology | SCAR15 is ultra-rare; published prevalence/incidence not available | Only **2 reported families / 5 patients** in primary literature available here; no population prevalence estimate | Published case literature through 2020 and database mapping (pqac-00000002, pqac-00000014, pqac-00000001) | Low for epidemiologic precision; case-based rarity only |
| Population / demography | Reported families are Saudi/Arab and consanguineous, consistent with founder enrichment | **5/5** reported patients from Saudi Arabia; one family with multiple consanguinity loops, one with first-cousin parents | Primary human reports (2010, 2020) (pqac-00000002, pqac-00000012, pqac-00000014) | Moderate; may reflect ascertainment and founder effect rather than exclusive ancestry distribution |
| Prognosis / outcomes | Functional impairment can remain moderate into adolescence/adulthood, with preserved ambulation but limited running/walking endurance in more affected individuals | Original family patients had disability stage **3/7** (moderate, unable to run, limited walking without aid); family-2 patients were stage **0/7** and **1/7** at 6.5 and 17 y | Human case series comparison (2020) (pqac-00000013, pqac-00000017) | Moderate; no mortality, survival, or adult late-stage outcome data |
| Models / omics | No dedicated SCAR15 animal model or patient omics dataset was identified in the available evidence; mechanistic interpretation relies mainly on cell-biologic RUBCN literature | None specific for Salih ataxia found here | Negative/limited finding from available search and evidence synthesis; general RUBCN biology available (pqac-00000007, pqac-00000008) | Low evidence availability; important knowledge gap for disease modeling and biomarker development |


*Table: This table compiles the highest-yield disease-characteristics evidence for autosomal recessive spinocerebellar ataxia 15 (Salih ataxia), emphasizing the tiny five-patient evidence base. It separates SCAR15-specific findings from broader RUBCN biology so the strength and limits of mechanistic inference are clear.*