Autosomal recessive sca
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autosomal recessive spinocerebellar ataxia types Friedreich AVED
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Autosomal Recessive Spinocerebellar Ataxia (ARCA / SCAR)
"SCA" usually denotes the autosomal dominant spinocerebellar ataxias (SCA1, SCA2, SCA3/Machado-Joseph, etc.), but there is a separate, more heterogeneous group of autosomal recessive cerebellar ataxias (ARCA) — some of which carry the specific label SCAR (SpinoCerebellar Ataxia, Autosomal Recessive; e.g., SCAR10, SCAR20). Friedreich ataxia is the most common recessive ataxia overall, though it isn't numbered as an "SCA."
Major disorders in this group
| Disorder | Gene | Protein / Pathway | Key clinical/biomarker clues |
|---|---|---|---|
| Friedreich ataxia (FA) | FXN | Frataxin - mitochondrial Fe-S biogenesis | Sensory + cerebellar ataxia, areflexia, Babinski sign, square-wave jerks, scoliosis, pes cavus, cardiomyopathy, diabetes |
| CANVAS | RFC1 | Replication factor C subunit 1 | Cerebellar ataxia + sensory polyneuropathy + vestibular areflexia |
| SPG7-related ataxia | SPG7 | Paraplegin (mitochondrial protease) | Ataxia, spastic paraparesis, optic neuropathy |
| Ataxia with vitamin E deficiency (AVED) | TTPA | Alpha-tocopherol transfer protein | Friedreich-like phenotype, but with low serum vitamin E; cardiomyopathy/diabetes far less common than FA |
| ARSACS (Charlevoix-Saguenay) | SACS | Sacsin (mitochondrial fission/localization) | Spastic ataxia, axonal sensorimotor polyneuropathy |
| Ataxia-telangiectasia (A-T) | ATM | DNA double-strand break repair kinase | Ataxia, oculocutaneous telangiectasia, oculomotor apraxia, choreoathetosis, immunodeficiency, radiosensitivity, cancer risk, elevated AFP |
| AOA1 (ataxia with oculomotor apraxia type 1) | APTX | Aprataxin - DNA repair | Ataxia, oculomotor apraxia, polyneuropathy, low serum albumin, high cholesterol |
| AOA2 (non-Friedreich SCAR1) | SETX | Senataxin - DNA repair | Ataxia onset age 11-22, choreoathetosis, dystonic gait, elevated AFP/CK/gamma-globulin |
| SCAN1 (spinocerebellar ataxia with axonal neuropathy) | TDP1 | DNA repair | Ataxia with peripheral axonal neuropathy; a recent 2025 systematic review found a single recurrent variant (c.1478A>G) drives most Middle Eastern cases |
| ANO10-related ataxia (SCAR10) | ANO10 | Anoctamin-10 | Cerebellar ataxia, variable additional features (reviewed via MDSGene 2024) |
| SCAR20 | SNX14 | Sortin nexin-14 | Early-onset ataxia with intellectual disability, macrocephaly |
| Mitochondrial recessive ataxia syndrome (MIRAS) | POLG1 | Mitochondrial DNA polymerase | Sensory ataxia, epilepsy, ophthalmoparesis |
| Ataxia-telangiectasia-like disorder (ATLD) | MRE11 | DNA repair | A-T-like phenotype without telangiectasia/immunodeficiency |
Other recognized recessive/metabolic ataxias
Wilson disease, Refsum disease, Bassen-Kornzweig disease (abetalipoproteinemia), glucose transporter type 1 (GLUT1) deficiency, Niemann-Pick type C, cerebrotendinous xanthomatosis, and a range of syndromic infantile-onset forms (Marinesco-Sjögren, Behr, Brown-Vialetto-Van Laere, Boucher-Neuhauser, Wolfram, Cayman ataxia).
Diagnostic approach
Textbooks emphasize a stepwise work-up: age of onset, associated systemic features (cardiac, endocrine, ophthalmologic, immune), specific biomarkers (AFP, vitamin E, albumin/cholesterol, CK), neuroimaging, and targeted or panel/exome genetic testing, since the phenotypes overlap heavily (many mimic Friedreich ataxia).
Recent literature (surfaced via PubMed, may refine above)
- A 2025 systematic review (PMID 39848142) found genetic homogeneity in Middle Eastern SCAN1 cases, largely attributable to one TDP1 variant.
- A 2024 MDSGene systematic review (PMID 38469933) detailed ANO10-related ataxia (SCAR10) phenotype and a Romani case series.
- These don't contradict the textbook classification above but add population-specific genetic detail.
Sources: Localization in Clinical Neurology, 8e (autosomal recessive ataxia classification list); Bradley and Daroff's Neurology in Clinical Practice, Table 23.7 (Common ARCAs); Harrison's Principles of Internal Medicine 22E (global epidemiology of ataxias).
If you meant a specific subtype (e.g., Friedreich ataxia in depth, ARSACS, or AOA1/AOA2 mechanism and management), let me know and I can go deeper on that one.
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