The overall prevalence of SCAs is estimated to be 1–5 per 100,000 people worldwide. Prevalence varies by geographic and ethnic populations. For example, SCA3 (Machado-Joseph disease) is more common in Portugal, Brazil, and parts of Asia, and SCA2 is more frequent in Cuba and parts of India. Some forms of SCA do not become apparent until adulthood.

Spinocerebellar ataxia is caused by inherited gene mutations. While a number of SCA types have been linked to specific gene mutations, not all SCAs have a currently identified genetic cause. A predominant mechanism underlying several SCA types is the abnormal repetition of a segment of DNA, referred to as a trinucleotide repeat expansion. These expanded genetic repeats lead to the production of abnormal proteins by the affected gene, which subsequently impair nerve cell function and result in the progressive neurodegeneration characteristic of SCA.

Most SCAs are inherited in an autosomal dominant pattern, requiring only one copy of the mutated gene from a parent to manifest the disease. Rarely, autosomal recessive or X-linked inherited forms occur (see RareShare Guide on Genetic Inheritance). Over 40 SCA subtypes have been identified, including SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 typically caused by CAG trinucleotide repeat expansions resulting in toxic proteins having segments of glutamine amino acid repeats. Other SCAs may involve point mutations or deletions. One observation in SCAs caused by trinucleotide repeat expansions, is the phenomenon of "anticipation." This refers to a tendency for signs and symptoms to become more severe and appear at an earlier age in successive generations. This progression is directly linked to the expanded repeat mutation's propensity for further expansion when passed down, a phenomenon which is more pronounced when inherited from the male parent. For example, a son may experience an earlier onset and more severe symptoms of SCA than his father due to the fact that the trinucleotide repeats have become longer going from one generation to the next. 

Symptoms of SCA typically begin in mid-adulthood but may vary depending on the subtype. Common features include:

• Progressive loss of coordination and balance (ataxia)

• Gait disturbance and difficulty walking

• Fine motor control problems (hands, speech, eye movements)

• Slurred speech (dysarthria) and trouble swallowing (dysphagia)

• Muscle stiffness, tremor, and peripheral neuropathy

• Visual disturbances (difficulty focusing, involuntary eye movements)

• Cognitive impairment in some subtypes, with possible decline in memory and thinking

SCA2 can be associated with cognitive deficits, including problems with short-term memory, planning, problem-solving, or an overall decline in intellectual function that can progress to dementia. SCA3 is characterized by slowly progressive clumsiness, a staggering or lurching gait, and difficulties with speech and swallowing. SCA7 can involve multiple organ systems including retinal degeneration which can lead to vision loss.

The disease is inherently progressive, with symptoms worsening over time. The rate of this progression is highly variable; some forms may advance slowly over many years, while others can deteriorate rapidly within months. A general expectation across many SCA types is that individuals will require wheelchair assistance within 10 to 20 years of their diagnosis.

Diagnosis of SCA typically includes:

• Clinical evaluation of symptoms with a detailed family history

• Neurological exams focusing on coordination, balance and eye movements.

• Brain imagines (MRI/CT) to identify cerebellar and brain stem atrophy (shrinkage)

• Genetic testing: Confirms the specific subtype (e.g., CAG repeat analysis)

• Electrophysiological tests (EMG/nerve conduction) may be used to assess neuropathy

There is no cure for SCA. Treatment is supportive and symptomatic. This includes:

• Physical therapy to maintain balance and coordination

• Speech therapy to help with dysarthria (weakness in muscles involved in speech) and swallowing

• Occupational therapy to aid daily functioning

• Medications for specific symptoms such as tremor, spasticity, depression or sleep disturbances

• Assistive devices such as wheelchairs, special glasses or communication aids

Researchers are investigating gene therapy, antisense oligonucleotides and other novel approaches.

SCA is progressive and symptoms gradually worsen over time. The rate of progression varies by subtype– SCA1, SCA2 and SCA3 progress relatively quickly, whereas SCA6 tends to progress more slowly. Many patients require mobility aids within 10-20 years of symptom onset. Life expectancy is variable and can be reduced for some types of SCA, especially those with an early onset and multisystem involvement.

1. Klockgether T, Paulson H. (2011). “Milestones in ataxia.” Mov Disord. 26(6):1134-41. doi: 10.1002/mds.23559. PMID: 21626557; PMCID: PMC3105349.

2. Coarelli G, Wirth T, Tranchant C, Koenig M, Durr A, Anheim M. (2023). “The inherited cerebellar ataxias: an update.” J Neurol. 270(1):208-222. doi: 10.1007/s00415-022-11383-6. Epub 2022 Sep 24. PMID: 36152050; PMCID: PMC9510384.

3. National Ataxia Foundation:  Spinocerebellar ataxia.

4. National Organization for Rare Disorders:  Spinocerebellar ataxia.