Spinocerebellar Ataxias

What are spinocerebellar ataxias?

Spinocerebellar ataxias (SCAs) are rare disorders that cause problems with movement, coordination, and balance. This loss of muscle control is called ataxia.

Many different types of SCA are possible. Some symptoms are common to all SCAs, but some SCAs have unique symptoms. Symptoms of SCAs get worse over time, sometimes slowly and sometimes quickly (within months). People with SCA often live long lives, but some types of SCA can affect how long someone lives.

People with SCA often have damage to cells in the part of the brain that controls muscle movement and balance, called the cerebellum. When cells in the cerebellum die because of this damage, it’s called cerebellar degeneration. SCAs can also affect cells in other parts of the brain and nervous system.

Repeated sections of DNA (kind of like repeated words in a sentence) cause some types of SCA, but other kinds of gene changes can also cause SCA. These variants (also called mutations) in a group of specific genes cause SCAs. Variants in different genes cause different types of SCA.

Symptoms of SCA

Most people with SCA start having symptoms in middle adulthood, but some people can have symptoms in childhood.

Some SCA symptoms are common to most types of SCA:

Unsteady walking and problems with balance
Weak or clumsy movements of the hands, arms, or legs
Slow or slurred speech
Trouble seeing clearly and moving the eyes
Shaking when trying to use the hands
Muscle weakness or twitching (myoclonus)

Some symptoms may develop later or only in certain types of SCA:

Numbness, tingling, or nerve pain in the hands or feet
Trouble swallowing (dysphagia), which can lead to choking or food going down the wrong way into the lungs
Problems with thinking, remembering, and concentrating
Stiffness or movements a person can’t control
Problems with walking or speech
Loss of the ability to do daily activities over time

Types of SCA

More than 40 different types of SCA can happen, each caused by changes (variants) in genes that are passed down in families. The most common types of SCA are Machado-Joseph disease (SCA3), SCA1, SCA2, and SCA6. These types of SCA are all inherited in an autosomal dominant pattern. That means only one parent needs to pass on a variant to a child in order for the child to get the disorder. SCAs are very rare, affecting only 1-5 people in 100,000 worldwide, although rates vary by ethnic background and where a person lives.

Machado-Joseph disease (SCA3)

Machado-Joseph disease (also called SCA3) is the most common type of SCA. Repeated sections of DNA in the Ataxin-3 gene (ATXN3) cause Machado-Joseph disease. People with Machado-Joseph disease may have these symptoms:

Clumsiness in the arms and legs that gets worse over time
Tight or stiff leg muscles
Muscle twisting that can cause unusual postures (dystonia)
Sleep disorders
Problems with bladder control, breathing, digestion, heart rate, and blood pressure

People can have three different types of Machado-Joseph disease, named for when a person first has symptoms. The three types are:

Type I: Symptoms begin between ages 10 and 30 and often include very stiff muscles with abnormal movements.
Type II: In this most common type of SCA3, symptoms begin between ages 20 and 50. It causes various symptoms—including noticeable problems with balance, stiff and jerky walking, and weak reflexes.
Type III: Symptoms start between ages 30 and 50. It can cause muscle twitching, weakness, muscle weakening and thinning, and abnormal sensations—such as numbness, tingling, cramps, and pain in the hands and feet.

SCA1

Repeated sections of DNA in the Ataxin-1 gene (ATXN1) cause SCA1. People with SCA1 have weakness and paralysis in their eye and eyelid muscles. Symptoms usually start between ages 30 and 40. People with SCA1 may have these symptoms:

Loss of muscle control, coordination, and balance in their arms and legs
Slurred or slow speech (dysarthria)
Trouble moving the eyes normally
Muscle stiffness
Overactive muscle reflexes

SCA2

Repeated sections of DNA in the Ataxin-2 gene (ATXN2) cause SCA2, also known as olivopontocerebellar atrophy. People with this condition have trouble with vision and eye movements. SCA2 can damage the retina, the light-sensing part of the eye. SCA2 symptoms can start in infancy or in adulthood. People with SCA2 may have these symptoms:

Muscle weakening and thinning (atrophy)
Slurred or slow speech (dysarthria)
Trouble swallowing (dysphagia)
Movement disorders
Problems with short-term memory, thinking, planning, concentrating, and problem solving (in some people)

SCA6

Repeated sections of DNA in the CACNA1A gene cause SCA6. It usually begins between ages 40 and 60. People with SCA6 often have these symptoms:

Trouble walking
Slurred or slow speech (dysarthria)
Vision and eye movement problems
Mild problems with thinking and memory (in some people)
Muscle stiffness
Overactive reflexes

Who is more likely to get spinocerebellar ataxias?

SCAs are inherited in an autosomal dominant pattern. In these cases, a person only needs to inherit one copy of the affected gene from either parent to have the disease.

When a parent has SCA, each of their children has a 50/50 chance of inheriting SCA, too. If a child inherits the variant that causes a type of SCA from one of their parents, they will eventually develop symptoms of the disease. A child who doesn’t inherit the variant that causes SCA won’t develop the disease and can’t pass it to future generations. Genetic testing can help a person understand their risk of developing SCA.

Many types of SCAs are genetic disorders called expanded repeat diseases. Expanded repeat diseases happen when parts of a person’s DNA code repeats itself many times—sort of like adding extra words in a sentence, making it hard to read. This stops the gene from working the way it should or causes proteins to clump together. People with some types of SCA have repeats in genes that make important brain proteins.

The number of DNA repeats a person has can be different, even among people in the same family who have SCA. The more DNA repeats a person with SCA has, the earlier in life their symptoms will begin. Their symptoms may also be worse.

In some families, each generation may develop symptoms earlier and have worse symptoms due to the repeats getting longer when they are passed from parent to child. This phenomenon is called "genetic anticipation." The repeats are more likely to be longer if a male parent passes down the gene variant.

If you think someone in your family may have SCA or that you might be a carrier, let your medical team know and they may refer you for genetic testing.

How are spinocerebellar ataxias diagnosed and treated?

Diagnosing SCA

Doctors may suspect SCA after neurological tests and taking a person’s family history, but diagnosing SCA requires a genetic test. When screening for SCA, a doctor may ask detailed questions about:

Family members who show (or showed) symptoms of SCA
How old relatives were when they symptoms began and how fast their symptoms got worse over time

A doctor may also look at brain, CT (computed tomography), and MRI (magnetic resonance imaging) scans to look for loss of brain tissue that can happen in some people with SCA. Other types of specialized brain scans can show how the brain is working. Doctors can use other tests, such as sleep studies, to look for problems with breathing, movement, or sleep quality that could be related to SCA.

People who are at risk for SCA (for example, those who have a parent with SCA) but don’t have any symptoms can still have genetic testing. This will help them determine whether their DNA has a gene variant that causes SCA and whether they might get SCA later in life.

Genetic testing is a personal choice to learn the benefits and risks of knowing information that current treatments can’t change. Some people find it helpful to know what’s causing their symptoms or to plan for the future. Others may find the same information stressful, especially since SCA doesn’t have a cure yet. A genetic counselor can help people and their families think through these complex issues.

Learn more about neurological diagnostic tests and procedures.

Treating SCA

Currently, SCAs don’t have a cure. People with SCA often receive medicines, therapy, or assistive devices to manage symptoms and help with movement, speech, and everyday tasks.

Physical aids and assistive devices

Canes, walkers, or wheelchairs can make walking and balance safer for people with SCA. Eye surgery can help for a short time, but eye problems usually get worse over time. Special glasses can help with blurred or double vision. Computer devices like tablets can help people with SCA communicate if they have troubling speaking.

Medicines

In some cases, medicines used for people with Parkinson's disease can help people with SCA who have movement problems and tremors (shaking), but this treatment doesn’t usually work very well. Some medicines such as muscle relaxers or botulinum toxin (commonly known as Botox) can calm overactive muscles and treat muscle stiffness. These treatments can also cause unwanted side effects like sleepiness or trouble swallowing.

Depending on the type of SCA a person has, other medicines can treat symptoms such as daytime sleepiness, bladder problems, muscle cramping, or speech and swallowing problems.

Rehabilitation therapy

Rehabilitation therapy can help people with SCA do daily tasks. Types of therapy include:

Speech therapy to help with problems speaking and swallowing
Physical therapy and exercise to help help with walking problems and to maintain muscle strength
Occupational therapy to help with daily tasks like eating and bathing

What are the latest updates on spinocerebellar ataxias?

The National Institutes of Health (NIH), which includes NINDS, is the leading federal funder of research on the brain and nervous system, including disorders such as SCAs. NIH supports new research to better understand, diagnose, and treat SCAs.

Several NIH-funded studies are currently looking for new ways to diagnose and treat SCAs. NIH-funded research is testing whether AI (artificial intelligence) methods can improve SCA diagnosis, which may help people get treatment sooner. Other NIH-funded research is testing the safety of deep brain stimulation in people with SCA1 and SCA3. This treatment sends targeted electrical signals to brain regions that control movement and currently helps treat Parkinson’s disease.

Gene variants that cause SCA1, SCA8, and Machado-Joseph disease make proteins that are harmful to brain cells. NIH-funded research is testing ways to lower amounts of these harmful proteins.

Other research is testing medicines that target repeated sections of DNA to treat multiple types of SCA. This research may also guide treatments for other health conditions with repeated sections of DNA. Multiple studies are developing better ways to deliver medicines to the brain, which will help treat conditions like SCAs.

Researchers don’t fully understand the exact ways that gene variants cause some types of SCA. Current NIH-funded research is trying to identify the underlying causes of SCA1, SCA2, SCA6, SCA7, SCA12, SCA17, SCA47, and Machado-Joseph disease. This information will help researchers better understand SCAs and may lead to future SCA treatments.

NIH also supported an international research study to find early signs of SCA and improve the tests doctors use to measure SCA symptoms.

For more information on research about SCAs, check NIH RePORTER, a searchable database of current and past research projects funded by NIH and other federal agencies. RePORTER also has links to publications and resources from these projects.

For research articles and summaries on SCAs, search PubMed, which contains citations from medical journals and other sites.

How can I or my loved one help improve care for people with spinocerebellar ataxias?

Consider participating in a clinical trial so clinicians and scientists can learn more about SCAs and related disorders. Clinical research with human study participants helps researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of participants are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities. This helps make sure that study results apply to as many people as possible and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research, visit the NINDS Clinical Trials site and NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with SCAs at ClinicalTrials.gov, a searchable database of current and past clinical studies and research results.

Where can I find more information about spinocerebellar ataxias?

Information may be available from the following sources: