Ataxia is usually caused by damage to a part of the brain known as the cerebellum, but it can also be caused by damage to the spinal cord or other nerves.

The spinal cord is a long bundle of nerves that runs down the spine and connects the brain to all other parts of the body.

The cerebellum is located at the base of the brain and is responsible for controlling:

• walking and sitting balance
• limb co-ordination
• eye movements
• speech

Damage can occur as a result of injury or illness (acquired ataxia) or because the cerebellum or spinal cord degenerates because of an inherited faulty gene (hereditary ataxia).

Sometimes there's no clear reason why the cerebellum and spinal cord become damaged. This is the case for people with idiopathic late-onset cerebellar ataxia (ILOCA).

Acquired ataxia can have a wide range of potential causes, including:

• severe head injury – after a car crash or fall, for example
• bacterial brain infection, such as meningitis or encephalitis (an infection of the brain itself)
• viral infection – some viral infections, such as chickenpox or measles, can spread to the brain, although this is very rare
• conditions that disrupt the supply of blood to the brain, such as a stroke, haemorrhage or a transient ischaemic attack (TIA)
• cerebral palsy – a condition that can occur if the brain develops abnormally or is damaged before, during or shortly after birth
• multiple sclerosis – a long-term condition that damages the nerve fibres of the central nervous system
• sustained long-term alcohol misuse
• an underactive thyroid gland
• vitamin B12 deficiency
• brain tumours and other types of cancer
• certain toxic chemicals, such as mercury and some solvents – these can trigger ataxia if a person is exposed to enough of them
• medications such as benzodiazepines can occasionally trigger ataxia as a side effect

Hereditary ataxia is caused by a faulty gene. Genes are units of DNA that determine a particular characteristic, such as sex or eye colour. A baby receives two copies of every gene – one from their mother and one from their father.

There are two ways that ataxia can be inherited:

• autosomal recessive – Friedreich's ataxia and ataxia-telangiectasia are inherited in this way
• autosomal dominant – episodic ataxia and some cases of spinocerebellar ataxia are inherited in this way

These are described in more detail in the following sections.

Autosomal recessive

When ataxia is autosomal recessive, it means the affected person has inherited the mutated gene from both their mother and their father.

If they only received one mutated gene from either parent, the other normal gene will cancel out the effects of the faulty gene and they will be a carrier of the condition. This means they don't have the condition themselves, but could pass it on to their children if their partner is also a carrier of the faulty gene.

It's estimated around 1 in every 85 people are carriers of the mutated gene that causes Friedreich's ataxia. Fewer people than this are carriers of the mutated gene that causes ataxia-telangiectasia.

If 2 carriers of the mutated gene were to have a baby, there would be a:

• 1 in 4 chance the baby would receive a pair of normal genes
• 1 in 2 chance the baby would receive one normal gene and one mutated gene (be a carrier)
• 1 in 4 chance the baby would receive a pair of mutated genes and develop ataxia

If you have autosomal recessive ataxia and your partner is a carrier, there is a 1 in 2 chance your baby will receive one normal gene and one mutated gene and will be a carrier, and a 1 in 2 chance your baby will receive a pair of mutated genes and develop ataxia.

If you have autosomal recessive ataxia and your partner doesn't and they aren't a carrier, there's no risk of any of your children developing ataxia. This is because your mutated gene will be cancelled out by your partner's normal gene. Your children will be carriers, however.

Autosomal dominant

When ataxia is autosomal dominant, you can develop the condition if you receive a single faulty gene, either from your mother or father. This is because the mutation is strong enough to override the other normal gene.

If you have autosomal dominant ataxia, any children you have will have a 1 in 2 chance of developing ataxia.