Cerebellar Abiotrophy

Carrier

Your horse has ONE cerebellar abiotrophy gene mutation. 

This means that your horse does not have the disease but is a carrier of one cerebellar abiotrophy gene mutation. 

Horses with just one gene mutation are clinically unaffected and can live normal lives without any limitations on performance.

Breeding implications

If you breed your horse with a mate that does not have the cerebellar abiotrophy mutation, there is:

  • A 50% chance the foal will not have the mutation.
  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.

If you choose to breed your horse with another horse that also has one mutation, there is:

  • A 25% chance the foal will not have this mutation.
  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.
  • A 25% chance the foal will have cerebellar abiotrophy.

If you breed your horse with a mate that is affected with this disease, there is:

  • A 50% chance the foal will have one gene mutation and be disease free, like your horse.
  • A 50% chance the foal will have the disease.
What is cerebellar abiotrophy?

Cerebellar abiotrophy is the most reported brain disease in horses. This condition is caused by the loss of brain cells (called Purkinje cells) in the cerebellum (the part of the brain that controls a horse’s sensory perception and the ability to coordinate physical movements). 

It’s estimated that up to 9 percent of Arabian Horses carry this gene mutation.

What are the symptoms?
  • Head tremors; manifested by high-frequency jerking of the head.
  • Stiff or excessively high-stepping gait from the shoulder.
  • Difficulty getting up, backing up, in tight turns.
  • Affected horses are prone to falling and running into things
  • Poor depth perception
  • Uncontrolled movements.

Symptoms may be confused with other causes of severe locomotion problems, e.g., a head injury or wobblers syndrome, because the disease affects the neurons that control balance. 

There is no cure for cerebellar abiotrophy, but it’s not contagious, and there are ways to prevent it through responsible breeding practices. 

How is it inherited?

Cerebellar abiotrophy is a recessive condition, which means your horse must have two copies of the diseased gene to be affected. However, as your horse has only one copy of the disease gene, it is called a carrier, without having the disease.

Genomic Details

Cerebellar abiotrophy is caused by a mutation in the TOE1 gene that is on chromosome 18. This gene is thought to be involved in the development of Purkinje neurons, which help to coordinate movement in the part of the brain called the cerebellum. When these Purkinje neurons do not form, the horse has coordination and movement problems. The mutation that causes cerebellar abiotrophy is a switch in one of the four base pairs that make up a DNA molecule. Guanine (G) is replaced by Adenine (A) changing the protein of the TOE1 gene. 

Therefore, a horse’s genetic result for cerebellar abiotrophy can be one of three possibilities:

  • G/G: Normal. Does not have the disease. Does not have the mutation.
  • G/A: Carrier. Does not have the disease. Carries one gene mutation from one parent. This might be passed to the foal.
  • A/A: Affected. Has the genetic disease. The horse has inherited a gene mutation from each parent. One mutation will be passed to their foal.