| Domain / phenotype | Evidence / frequency and temporal characteristics | Suggested HPO term | Functional / QoL consequence |
|---|---|---|---|
| Cerebellar ataxia / gait ataxia | Core phenotype. Discovery family: late truncal ataxia emerging after years of cognitive-affective symptoms; adult-onset, slowly progressive (pqac-00000013). Multicenter cohort: mean age at onset 40.0 ± 13.8 years, range 17–74; age at onset highly variable (pqac-00000017, pqac-00000019). Australian 2024 series: ataxia in 3/3, onset ages 32, 57, 61; summary of all reported patients in that series: gait ataxia 8/9 (pqac-00000012, pqac-00000003). | HP:0001251 | Progressive imbalance, falls, loss of independent mobility; disease-specific QoL metrics not reported in collected SCA48 sources. |
| Dysarthria | Common motor cerebellar sign. Australian 2024 series: dysarthria 3/3; presenting symptom in 2/3 (pqac-00000012, pqac-00000010). Qualitative reports across families describe adult-onset progressive speech impairment (pqac-00000015). | HP:0001260 | Reduced speech intelligibility and communication; no SCA48-specific QoL scale reported. |
| Cerebellar cognitive-affective syndrome / cognitive impairment | Hallmark non-motor feature. Discovery family: 6 fully affected patients showed cognitive-affective syndrome; 3 presymptomatic carriers already had focal cerebellar atrophy before ataxia (pqac-00000013). Multicenter cohort: cognitive impairment in 54% of STUB1 variant carriers, predominantly frontal syndrome (pqac-00000019, pqac-00000006). Australian 2024 series: cognitive impairment 2/3 (pqac-00000012). | HP:0100543 | Executive dysfunction, memory/language deficits, impaired daily planning and judgment; no standardized SCA48 QoL outcome reported. |
| Psychiatric / behavioral symptoms | Frequently reported qualitatively: depression, anxiety, behavioral changes, psychiatric dysfunction (pqac-00000012, pqac-00000015). Large Dutch family had prominent behavioral changes with cognitive decline (pqac-00000007). In the 9-patient summary from the Australian report, psychiatric symptoms were 6/9 (pqac-00000003). | HP:0000708 | Major impact on social/occupational functioning and caregiver burden; no disease-specific QoL metrics available. |
| Tremor | Increasingly recognized feature. Australian 2024 series: tremor 3/3, with rest tremor in 2 and action tremor in 1; summary frequency 3/9 in prior aggregate comparison cited in the same report (pqac-00000010, pqac-00000003). Can precede or accompany ataxia (rest tremor was presenting symptom in 1/3) (pqac-00000012). | HP:0001337 | Impairs handwriting, feeding, and fine motor tasks; no SCA48-specific QoL metric reported. |
| Dysmetria / limb incoordination | Discovery and later case reports describe complete motor cerebellar syndrome with dysmetria (pqac-00000013). Australian 2024 series: dysmetria 2/3 (pqac-00000012). | HP:0001310 | Fine motor inaccuracy affecting reaching, dressing, and utensil use; no formal QoL data reported. |
| Oculomotor abnormalities | Qualitative recurrent feature: oculomotor abnormalities and dysmetric saccades reported in SCA48 literature summarized in 2024 series (pqac-00000012). In that series, ocular abnormalities occurred in 1/3 and impaired upward gaze in 1 patient (pqac-00000012). | HP:0000508 | Visual tracking difficulties may worsen gait/balance and reading; QoL metrics unavailable. |
| Pyramidal signs / hypertonia / pathologic reflexes | Positive pyramidal tract signs described as part of phenotypic spectrum (pqac-00000015). Australian 2024 series: pathologic reflexes 2/3, hypertonia 2/3, extensor plantar responses reported in individual cases (pqac-00000012, pqac-00000009). | HP:0002495 | Adds stiffness and gait disability to cerebellar syndrome; no formal SCA48 QoL data reported. |
| Parkinsonism / bradykinesia / rigidity | Recognized less-common but recurrent feature. Dutch pedigree: gait disturbance could present as ataxia or parkinsonism (pqac-00000007). Australian 2024 series: bradykinesia 1/3, cogwheel rigidity 1/3, parkinsonian rest tremor in 2/3 (pqac-00000012, pqac-00000003). | HP:0001300 | Slowness and rigidity worsen mobility and upper-limb function; QoL metrics unavailable. |
| Chorea / dystonia / hyperkinetic features | Reported as rarer clinical features in qualitative summaries (pqac-00000012, pqac-00000015). Dystonic head posturing documented in one 2024 Australian case (pqac-00000012). | HP:0002072 / HP:0001332 | May complicate diagnosis and interfere with speech/posture; no SCA48-specific QoL data. |
| Peripheral neuropathy / sensory loss / areflexia | Rarer but documented. Australian 2024 series: one patient had length-dependent sensorimotor axonal peripheral neuropathy on nerve conduction study with sensory loss, absent ankle jerks, pes cavus/hammer toes, and Romberg sign (1/3) (pqac-00000012). Qualitative summaries mention peripheral neuropathies (pqac-00000012). | HP:0009830 | Sensory loss and neuropathy worsen gait instability and distal weakness; QoL metrics unavailable. |
| Dysphagia | Qualitative feature in disease summaries; explicitly present in 1/3 Australian patients and among presenting symptoms in 1/3 (pqac-00000012). | HP:0002015 | Risk for choking, nutrition problems, and aspiration burden; no SCA48-specific swallowing QoL measure reported. |
| Bladder dysfunction | Reported in one Australian patient as urinary urgency/incontinence during progression (1/3) (pqac-00000012). | HP:0000020 | Can reduce independence and increase caregiver burden; QoL metrics unavailable. |
| Cerebellar atrophy on MRI | Highly consistent biomarker-level phenotype. Discovery pedigree: vermian and hemispheric atrophy; presymptomatic focal vermian/paravermian and lobules VI–VII atrophy before ataxia (pqac-00000013). Australian 2024 series: cerebellar atrophy 3/3, often diffuse (pqac-00000012). Umano 2022 de novo case: prominent pan-cerebellar atrophy (pqac-00000011). | HP:0001272 | Correlates with progressive motor/cognitive disability; no direct MRI-QoL linkage quantified in collected SCA48 studies. |
| Purkinje cell loss / cerebellar degeneration (pathology) | Neuropathology: massive Purkinje cell loss in vermis and major loss in hemispheres reported in heterozygous STUB1 patient(s) (pqac-00000019, pqac-00000006). Additional reports found subtotal Purkinje cell loss, molecular layer atrophy, p62-positive inclusions, and thalamic/brainstem degeneration (pqac-00000008). Temporal pattern inferred as downstream pathology of progressive disease. | HP:0007366 | Likely substrate of worsening coordination and cognition; patient-reported QoL metrics not available. |


*Table: This table summarizes ontology-ready clinical phenotypes for spinocerebellar ataxia 48 using only collected evidence. It distinguishes exact frequencies from qualitative reports and notes where disease-specific quality-of-life data are unavailable.*