| Domain | Summary | Suggested ontologies / terms | Key evidence / citations |
|---|---|---|---|
| Definition / identifiers | Spinocerebellar ataxia type 15/16 (SCA15/16) is an autosomal-dominant, usually adult-onset, very slowly progressive **pure cerebellar ataxia** linked to **ITPR1**. MONDO: **MONDO:0011694**. Disease knowledge is derived from **aggregated disease-level resources and published family/case series**, not EHR-derived evidence alone. | MONDO:0011694; MeSH/ICD/Orphanet/OMIM should be verified in source databases before KB entry if exact IDs are required. | OpenTargets links **ITPR1** to “spinocerebellar ataxia type 15/16” with evidence support; reviews describe SCA15/16 as a distinct ITPR1-associated ataxia (pqac-00000000, pqac-00000001, pqac-00000012) |
| Gene / variant classes | **Causal gene:** **ITPR1** (inositol 1,4,5-trisphosphate receptor type 1). Reported pathogenic classes include **heterozygous multi-exon/whole-gene deletions** and **heterozygous missense variants** (e.g., **p.Pro1059Leu**, **p.Val494Ile** in reviews). 2023 Dutch cohort found a pathogenic familial deletion involving **ITPR1 exons 1–41** plus part of **SUMF1**. Germline origin is typical. | HGNC: ITPR1; variant classes: CNV deletion, missense; molecular consequence often consistent with loss of function / haploinsufficiency. | Deletions involving exons 1–10, 1–40, 1–44, 1–48 and complete gene are summarized in reviews; 2023 cohort identified a 260.8 kb deletion including **ITPR1 exons 1–41** in two related patients (pqac-00000004, pqac-00000006, pqac-00000007, pqac-00000008, pqac-00000009) |
| Inheritance | **Autosomal dominant**. Penetrance appears **age-dependent** and expressivity **variable**, but precise penetrance estimates are not well established in retrieved evidence. Germline mosaicism is reported for other **ITPR1-associated** phenotypes (especially SCA29-like presentations), but this is not established as a common mechanism for classic SCA15/16. | HPO inheritance term: Autosomal dominant inheritance. | SCA15 is repeatedly described as autosomal dominant; mosaicism evidence in 2023 paper pertains to broader ITPR1-associated ataxia, not classic adult-onset SCA15/16 (pqac-00000001, pqac-00000005, pqac-00000012) |
| Onset / course | Typical onset is **adult**, often **30–50 years**, with reported range **7–66 years**. Course is **chronic**, **insidious**, and **very slowly progressive**; many patients remain ambulatory independently or with a cane **10–40 years after onset**. | HPO: Adult onset; Progressive ataxia; Chronic course. | Reviews summarizing family series report onset range 7–66 years, usual onset 30–50 years, and long-preserved ambulation (pqac-00000001, pqac-00000012) |
| Core phenotypes | Predominant phenotype is a **pure cerebellar syndrome**: gait/limb ataxia, tremor, dysarthria, gaze-evoked nystagmus or other oculomotor abnormalities, and sometimes hyperreflexia without clear pyramidal syndrome. Suggested HPO terms: **Ataxia**, **Gait ataxia**, **Limb ataxia**, **Dysarthria**, **Nystagmus**, **Intention tremor / Action tremor**, **Head tremor**, **Hyperreflexia**. Cognitive function is often reported as preserved in classic SCA15/16; epilepsy is generally not a feature of classic disease. | HPO terms should be mapped during curation; avoid adding exact IDs here unless verified. | Clinical spectrum summarized in reviews; 2023 Dutch familial cases had limb ataxia, vermian atrophy, father with dysarthria, nystagmus, polyneuropathy (pqac-00000001, pqac-00000009, pqac-00000012) |
| Anatomy / cell types | Primary anatomy: **cerebellum**, especially **cerebellar vermis** with milder hemispheric involvement; secondarily cerebellar output pathways may be affected functionally. Primary vulnerable cell type: **Purkinje cell**. Other involved structures in mechanistic models include **inferior olive** and **brainstem/cerebellar circuits**. | UBERON: cerebellum, cerebellar vermis (exact IDs not inserted if uncertain); CL: Purkinje cell, cerebellar neuron (exact IDs should be verified). | MRI commonly shows vermian-predominant cerebellar atrophy; mechanistic mouse work localizes causal dysfunction to cerebellum/brainstem Purkinje-cell circuits (pqac-00000001, pqac-00000009, pqac-00000010, pqac-00000011, pqac-00000012) |
| Mechanism / pathophysiology | Upstream lesion: reduced or altered **IP3R1** function. Core mechanism: **ITPR1 haploinsufficiency** impairs **IP3-mediated Ca2+ release from the endoplasmic reticulum** in Purkinje cells, disrupting intracellular calcium homeostasis, dendritic integration/development, firing patterns, and cerebellar output; downstream consequences include Purkinje-cell dysfunction and cerebellar ataxia, with degeneration over time. Relevant GO processes: **inositol trisphosphate-mediated signaling**, **calcium ion release from endoplasmic reticulum**, **regulation of cytosolic calcium ion concentration**, **Purkinje cell development**, **synaptic signaling**. | GO terms should be finalized by ontology lookup before production use. | Reviews and models converge on abnormal IP3/Ca2+ signaling in Purkinje cells; 2023 CNV paper explicitly supports haploinsufficiency from reduced ITPR1 dosage; conditional cerebellum/brainstem knockout mice show dystonia/ataxia via abnormal Purkinje-cell firing (pqac-00000004, pqac-00000009, pqac-00000010, pqac-00000011, pqac-00000013, pqac-00000015) |
| Diagnostics | Diagnosis relies on **molecular confirmation of ITPR1 pathogenic variant** in a patient with compatible slowly progressive cerebellar ataxia. Testing approaches include **sequence analysis** plus **CNV analysis** because deletions may be missed by SNV-only workflows. Useful methods: **targeted ataxia panel**, **WES/WGS with CNV calling**, **SNP array**, **MLPA/gene dosage analysis** where available. MRI supports diagnosis by showing cerebellar, often vermian-predominant, atrophy. Differential diagnosis includes other dominant ataxias and **ITPR1-related SCA29/Gillespie syndrome**. | MAXO not applicable; HPO/UBERON can annotate MRI and phenotype findings. | 2023 Dutch study recommends adding CNV analysis for at least **ITPR1** in SCA diagnostics; inherited ataxia review emphasizes NGS-based workup after exclusion of acquired causes (pqac-00000008, pqac-00000014) |
| Treatment / management | **No disease-modifying therapy specific to SCA15/16** was identified. Current management is **supportive and rehabilitative**: physical therapy, balance/gait/coordination training, occupational therapy, speech therapy, mobility aids, and standard symptomatic management of tremor or other complications as clinically indicated. General degenerative cerebellar ataxia evidence suggests physiotherapy can modestly improve ataxia severity. | MAXO suggestions: physical therapy, gait training, balance training, occupational therapy, speech therapy, assistive device use. Exact MAXO IDs should be verified before insertion. | No relevant SCA15/16-specific interventional trial surfaced. Meta-analysis in degenerative cerebellar ataxia found physiotherapy reduced SARA by **−1.41** overall, though evidence certainty was low (pqac-00000016, pqac-00000014) |
| Prognosis | Prognosis is generally one of **slow functional decline** rather than shortened survival in classic cases. Ambulation is often preserved for decades, and severe bulbar/fatal complications are not emphasized in classic SCA15/16 reports. Quality-of-life burden is expected from chronic imbalance, tremor, speech impairment, and activity limitation, but disease-specific QoL datasets were not retrieved. | HPO/ICF mapping may be useful for disability annotations. | Long-preserved ambulation and slow progression are consistently reported in reviews; quantitative survival data were not found in retrieved sources (pqac-00000001, pqac-00000012) |
| Epidemiology | Absolute population prevalence/incidence of **SCA15/16** is not well established in retrieved evidence. Reported frequency among dominant ataxia families varies by cohort: about **2.7%** in Australian families, **1.8%** in a cohort of **333 White/Caucasian dominant ataxia families**, and **8.9%** in Central European families; disease appears **rare in Japanese cohorts**. In a 2023 Dutch unsolved ataxia cohort, clinically relevant SCA-gene CNV deletions were found in **3/292 (1%)** high-quality samples, with pathogenic **ITPR1** deletion in **2 related patients**. | Epidemiology fields should note “rare” and “family-series based estimates.” | Frequencies are from review summaries of family cohorts, not population screening; Dutch 2023 CNV study provides recent diagnostic-yield data (pqac-00000001, pqac-00000008, pqac-00000009) |
| Models | Relevant models include **Itpr1 heterozygous/null mice**, **Itpr1 Δ18/Δ18** and **Δ18/wt** mice with reduced IP3R1 levels, and **conditional Wnt1-Cre;Itpr1 flox/flox** cerebellum/brainstem knockout mice. These models recapitulate impaired coordination/ataxia and abnormal Purkinje-cell physiology; conditional knockout also shows dystonia linked to Purkinje-cell firing abnormalities. Computational Purkinje-cell calcium models predict that altered IP3R1 abundance/sensitivity can normalize or disrupt calcium responses. | Model organism: mouse; cell type: Purkinje cell. | Mouse and computational studies support causal links between ITPR1 dosage, Ca2+ signaling, Purkinje firing, and motor phenotype (pqac-00000011, pqac-00000015) |
| Evidence limitations | Evidence base is dominated by **small family series, case reports, and reviews**. Precise **phenotype frequencies, penetrance, survival, carrier frequency, sex ratio, and population prevalence** are poorly quantified. Some recent ITPR1 papers describe **SCA29 or broader ITPR1 syndromes**, which should not be conflated with classic adult-onset SCA15/16. Several exact ontology IDs beyond MONDO were not verified in the retrieved context and should be checked before KB ingestion. | Curation note: separate **SCA15/16** from **SCA29**, **Gillespie syndrome**, and other ITPR1-associated disorders. | Recent evidence improves diagnostic and mechanistic clarity but remains sparse for natural history and treatment-specific outcomes (pqac-00000005, pqac-00000008, pqac-00000014) |


*Table: This table provides a concise knowledge-base style summary of Spinocerebellar Ataxia Type 15/16, covering identifiers, genetics, phenotypes, mechanism, diagnostics, treatment, prognosis, epidemiology, and models. It also flags evidence gaps and separates classic adult-onset SCA15/16 from other ITPR1-associated disorders.*