By Dr Ananya Mandal, MD
Ataxia is mainly caused by damage to the part of the brain that deals with movement, coordination and balance. The condition is a symptom of an underlying disease rather than a disease in itself.
Normal brain functioning in movement and motion
The cerebellum is located towards the back and lower part of the brain.
The right side of the cerebellum controls movement and coordination in the right side while the left side controls the left side of the body.
The central part of the cerebellum can control complex movements of walking, eye movements and stability of the head and trunk.
Other parts of the cerebellum help to coordinate smaller movements such as speech, eyes and swallowing.
The signals from the limbs and other peripheral organs reach the brain and cerebellum via the nerves in the spinal cord.
It is the spinal cord that carries these signals away from the cerebellum to the limbs and instructs them to function adequately to result in normal co-ordinated movements.
Pathology of ataxias
Ataxias result when there is damage to the cerebellum or the connections in the spinal cord. This damage may be the result of an injury or illness like stroke as is seen in acquired ataxia or due to a degenerative condition affecting the cerebellum and spinal cord as is seen in hereditary ataxias.
In small number of cases no cause may be found. These are classified under idiopathic late onset Cerebellar ataxia (ILOA).
Causes of hereditary ataxia
These types of ataxias result from genetic mutations. Defective genes may be passed on from parents to their offspring.
Sometimes one or both of the parents might be a carrier of the defective gene with no apparent deformity or difficulty. The child inherits the defective gene and may manifest the condition.
It is estimated that around 1 person in every 75 is a carrier of the mutated gene that causes Friedreich’s ataxia and around 1 person in 100 carries the mutated gene that causes ataxia-telangiectasia.
If both parents are carriers of the autosomal dominant defective gene, there is a 25% chance that the baby will have either normal genes or a pair of mutated genes and go on to develop the ataxia.
There is a 50% chance that the baby will have a single abnormal gene and become a carrier without developing ataxia.
If both parents are carriers of the autosomal recessive gene, there is a 50% chance that the baby will receive one normal gene and one mutated gene and become a carrier and a 50% chance that the baby will receive a pair of mutated genes and go on to develop ataxia.
Causes of acquired ataxia
These ataxias usually result due to underlying causes unlike the other two types of ataxias – hereditary and ILOA. Some of the causes of acquired ataxias include:-
Injury to the brain due to severe head injury. This could damage the cerebellum or the spinal cord or the interconnecting links between them. A car crash or a fall may cause this type of damage.
Infection of the brain or encephalitis. After a bacterial infection that affects the brain or a viral infection like chickenpox or measles that can affect the brain, ataxias may result. Ataxias after viral infections are uncommon.
Cerebral palsy may distort a child’s brain growth and development and lead to ataxias.
Ataxias may be seen after a stroke. This may be caused when a vital part of the brain is deprived of blood (ischemic stroke) or a vital part of brain is flooded with blood after a blood vessel rupture (hemorrhagic stroke). After a transient ischemic attack (TIA) ataxia may be seen. This is also called a mini-stroke.
Multiple sclerosis – this condition damages the nerves and may lead to ataxia with time.
Some cancers and diseases of the thyroid gland (underactive thyroids) may also result in ataxia.
Defective immune system disorders like lupus may also cause ataxia.
In children epilepsy or seizures may cause ataxia. Usually an underlying brain development problem may be the cause of ataxia in these children.
Long term alcohol abuse or exposure to toxins and toxic chemicals and heavy metals like mercury, lead, solvents, pesticides etc. may also trigger ataxias.
Some medicines like benzodiazepines used as sleeping aids or tranquillizers may also lead to ataxia as a side effect.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)