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# Spinocerebellar ataxias (autosomal dominant ataxias)

A group of inherited diseases in which the [cerebellum](https://durgical.com/en/anatomy/anterior-quadrangular-lobule/) slowly degenerates, causing worsening clumsiness, unsteady walking and slurred speech in adults.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Cerebellum](https://durgical.com/en/anatomy/anterior-quadrangular-lobule/)
- [Vermis](https://durgical.com/en/anatomy/central-lobule/)
- [Pons](https://durgical.com/en/anatomy/pons/)
- [Cerebellar peduncles](https://durgical.com/en/anatomy/superior-cerebellar-peduncle/)
- [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/)
- [Spinal cord](https://durgical.com/en/anatomy/spinal-cord/)
- [Substantia nigra](https://durgical.com/en/anatomy/substantia-nigra/)
- [Putamen](https://durgical.com/en/anatomy/putamen/)

## Why it happens

- [Mendelian inheritance: autosomal dominant, recessive and X-linked](https://durgical.com/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/)
- [Nonclassic inheritance: repeat expansions, mitochondrial genes, imprinting, mosaicism](https://durgical.com/en/general-pathology/nonclassic-inheritance-repeat-expansions-mitochondrial-genes-imprinting-mosaicis/)
- [Functions of the cerebellum](https://durgical.com/en/physiology/functions-of-the-cerebellum/)
- [Trinucleotide repeat expansion disorders](https://durgical.com/en/biochemistry/topics/trinucleotide-repeat-expansion-disorders/)

## What it is

A large group (more than 40 types) of autosomal dominant, progressive neurodegenerative disorders of the cerebellum and its connections in the brainstem and [spinal cord](https://durgical.com/en/anatomy/spinal-cord/). The most common types (SCA1, 2, 3, 6, 7 and 17) are caused by expanded CAG repeats that code for long polyglutamine stretches. They present mainly in adulthood with progressive gait ataxia, dysarthria and eye-movement problems, often with other neurological signs depending on the type.

## Who gets it

Together they affect about 1 to 5 per 100,000 people worldwide, with large regional differences due to founder effects. SCA3 (Machado-Joseph disease) is the most common type worldwide and in Brazil; SCA2 has one of the highest prevalences in the world in Holguín, Cuba; SCA7 clusters are described in Mexico and Venezuela; and SCA10, a pentanucleotide repeat disorder, is described mainly in families of Amerindian ancestry in Mexico and Brazil. Colombian data are limited and families are often identified in specialist centres.

## Causes

- Autosomal dominant inheritance: each child of an affected parent has a 50% risk
- CAG (polyglutamine) repeat expansions: SCA1 (ATXN1), SCA2 (ATXN2), SCA3 (ATXN3), SCA6 (CACNA1A), SCA7 (ATXN7), SCA17 (TBP)
- Non-coding repeat expansions (e.g. SCA10, SCA27B) and conventional point mutations in other types
- Anticipation: longer repeats, earlier onset and faster course in later generations, more marked with paternal transmission in some types

## Risk factors

- Family history of adult-onset ataxia (sometimes hidden by early death, misdiagnosis or non-paternity)
- Ancestry from regions with founder mutations
- Inheriting the expansion from the father (greater repeat instability in some types)

## Pathophysiology

Expanded CAG repeats produce proteins with abnormally long polyglutamine tracts that misfold, form nuclear aggregates and disturb transcription, protein clearance and ion-channel function. Purkinje cells of the cerebellar cortex and neurons of the [pons](https://durgical.com/en/anatomy/pons/), inferior olive, [cerebellar peduncles](https://durgical.com/en/anatomy/superior-cerebellar-peduncle/), spinal cord tracts and, in some types, basal ganglia and [retina](https://durgical.com/en/anatomy/retina/) degenerate. Cerebellar loss causes ataxia and dysarthria; brainstem involvement causes slow saccades and dysphagia; spinal and peripheral involvement causes sensory loss and areflexia. Longer repeats are more toxic, explaining earlier onset.

## Classification

- Polyglutamine SCAs: SCA1, 2, 3, 6, 7, 17 (and dentatorubral-pallidoluysian atrophy)
- Non-coding repeat SCAs: SCA8, 10, 12, 27B, 36 and others
- Conventional mutation SCAs: channel and other gene variants
- Clinical clue types: SCA2 (very slow saccades, neuropathy), SCA3 (bulging eyes, dystonia, spasticity, neuropathy), SCA6 (late-onset, nearly pure cerebellar), SCA7 (retinal degeneration with vision loss)
- Episodic ataxias (EA1, EA2) are related dominant channelopathies with attacks rather than steady progression

## Symptoms and signs

- Slowly progressive unsteady, broad-based gait and frequent falls
- Clumsy hands, intention tremor and dysmetria
- Slurred, scanning speech (dysarthria)
- Nystagmus, slow saccades or double vision
- Swallowing difficulty in later stages
- Type-specific features: neuropathy, spasticity, parkinsonism, dystonia, vision loss (SCA7), cognitive decline, sleep disorders such as REM sleep behaviour disorder

## Red flags

- Ataxia developing over days or weeks, which suggests stroke, infection, toxins or Wernicke encephalopathy rather than a hereditary ataxia
- Choking or recurrent [chest](https://durgical.com/en/anatomy/region/chest/) infections (aspiration)
- Depression or suicidal thoughts, which are frequent in progressive genetic disease
- Rapid visual loss (SCA7) or marked autonomic failure, which suggests multiple system atrophy

## Diagnosis

**Clinical**
Suspected in an adult with slowly progressive cerebellar ataxia and a family history in several generations. Examination shows gait and limb ataxia, dysarthria and eye-movement abnormalities, plus extra-cerebellar signs that point to a type. Acquired causes must be excluded first.

**Tests**
Targeted genetic testing for repeat expansions in the common SCA genes, then broader panels or genome sequencing if negative. Exclude acquired ataxia: vitamin E and B12, thyroid function, alcohol history, celiac antibodies and, where relevant, paraneoplastic antibodies. Pre-symptomatic testing of at-risk relatives is done only with genetic counselling. Nerve conduction studies and eye examination help define the type.

**Imaging**
Brain MRI shows cerebellar atrophy, with or without pontine (olivopontocerebellar) atrophy, and excludes tumours, strokes and demyelination.

## Differential diagnosis

- Friedreich ataxia and other recessive ataxias
- Multiple system atrophy, cerebellar type
- Alcohol-related cerebellar degeneration
- Wernicke encephalopathy and vitamin E or B12 deficiency
- Multiple sclerosis and posterior fossa stroke or tumour
- Paraneoplastic and immune-mediated cerebellar ataxias

## Goal of treatment

No treatment slows most SCAs; care aims to preserve mobility and independence, prevent falls and aspiration, treat associated symptoms and offer genetic counselling to the family.

## Treatment

**Rehabilitation**
Intensive physiotherapy focused on balance and coordination, occupational therapy and walking aids; speech and swallowing therapy.

**Medical**
Symptomatic drugs: dopaminergic drugs for parkinsonism, antispasticity drugs, treatment of neuropathic pain, depression and sleep disorders; carbonic anhydrase inhibitors for some episodic ataxias.

**Conservative**
Genetic counselling for the patient and relatives, including reproductive options and the choice of pre-symptomatic testing.

**Follow-up**
Regular ataxia rating scales, swallowing assessment, nutrition, fall risk and mood screening.

## Complications

- Falls and injuries
- Aspiration pneumonia
- Loss of independent walking and wheelchair dependence
- Depression and cognitive decline in some types
- Blindness in SCA7

## Prognosis

Steadily progressive over years to decades. Survival varies by type: SCA1, 2, 3 and 7 shorten life (often 10 to 20 years after onset in adults, less with juvenile onset), whereas SCA6 progresses slowly with near-normal life expectancy.

## Prevention

- No primary prevention. Genetic counselling and, where available, prenatal or preimplantation testing allow families to make informed reproductive choices.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the inheritance pattern of the spinocerebellar ataxias?

Autosomal dominant.

## What type of mutation causes the most common SCAs, and what phenomenon does it produce across generations?

CAG (polyglutamine) repeat expansions; anticipation, with earlier and more severe disease in later generations.

## Which SCA is the most common worldwide?

SCA3 (Machado-Joseph disease).

## Which SCA type causes progressive visual loss from retinal degeneration?

SCA7.

## Which recessive ataxia is the main differential in young patients?

Friedreich ataxia (GAA repeat in FXN), with areflexia, cardiomyopathy and diabetes.

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## Related conditions

- [Friedreich ataxia](https://durgical.com/en/conditions/friedreich-ataxia/)
- [Multiple system atrophy (MSA)](https://durgical.com/en/conditions/multiple-system-atrophy/)
- [Huntington disease](https://durgical.com/en/conditions/huntington-disease/)
- [Ataxia-telangiectasia](https://durgical.com/en/conditions/ataxia-telangiectasia/)
- [Alcohol use disorder](https://durgical.com/en/conditions/alcohol-use-disorder/)
- [Wernicke encephalopathy (thiamine deficiency)](https://durgical.com/en/conditions/wernicke-encephalopathy/)
- [Multiple sclerosis](https://durgical.com/en/conditions/multiple-sclerosis/)
- [REM sleep behaviour disorder (RBD)](https://durgical.com/en/conditions/rem-sleep-behaviour-disorder/)
- [Restless legs syndrome](https://durgical.com/en/conditions/restless-legs-syndrome/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Spinocerebellar ataxia type 3: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/spinocerebellar-ataxia-type-3/) (MedlinePlus (U.S. National Library of Medicine), 2026).

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Source: https://durgical.com/en/conditions/spinocerebellar-ataxias/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/spinocerebellar-ataxias/