Cerebellar abiotrophy
A foal with head tremors or poor balance has not necessarily been injured in a fall. Cerebellar abiotrophy, or CA, is an inherited condition affecting coordination. Signs vary considerably, and a genetic result needs to be considered alongside examination of the horse.
Recessive inheritance
CA damages brain cells that help coordinate movement
The cerebellum is a part of the brain that helps adjust movement and maintain balance. Equine CA involves nerve cells called Purkinje cells becoming damaged and dying after birth. A horse may still be able to move while struggling to control the accuracy of its movements.
The variant detected by the CA test lies in the TOE1 gene, close to another gene called MUTYH. Early research proposed different explanations, including a change in how cells use MUTYH. Research links the variant to CA, while its exact effect on these genes remains under investigation. Testing helps identify carriers and inform mating decisions without explaining every part of the disease mechanism.
CA coordination problems are often noticed in the first months of life
Many affected foals look normal at birth. Problems are generally recognized within the first six months. Head tremors may be most noticeable during a purposeful movement; other horses lift their legs higher than needed, stand with their feet spread apart or lose their balance.
Ataxia means impaired coordination. It is more than ordinary clumsiness or a training problem. Severely affected horses may fall or struggle to rise. Mild changes, however, can be missed, so a brief observation does not necessarily capture the horse’s full situation.
Horses with the same CA test result can have different coordination problems
Horses with the same copies of the CA variant can have different symptoms or different levels of difficulty. These differences are called variable expression. UC Davis’s clinical resource also reports a small number of horses genetically classified as affected without visible signs. That qualification matters: not every horse with two copies has an identical clinical presentation.
A horse without observed signs cannot be assumed to have tested negative. Nor does that observation establish a percentage chance of remaining symptom-free. Age, examination and follow-up contribute to interpretation, separately from counting the copies detected by a laboratory.
Cerebellar abiotrophy is mainly documented in Arabian horses
CA is mainly documented in Arabians and related horses. The testing laboratory also lists Danish Sport Horses, Trakehners and Welsh Ponies as relevant populations. Finding a variant in a population does not mean all its horses develop the condition.
These findings are not a list of breeds that should automatically be considered affected or clear. Bloodlines and individual information remain important. Findings from a tested group cannot simply be applied as a whole-breed frequency or an individual horse’s probability.
Examining the horse helps distinguish CA from other causes of poor balance
Injury, infection and developmental abnormalities can also disturb balance. The veterinarian investigates when signs began, what they look like and what examination reveals before choosing further investigations. Routine blood results within normal limits do not necessarily rule out cerebellar disease.
Genetic testing contributes to the CA assessment but does not investigate every cause of ataxia. Other examinations may be needed for the alternatives suggested by the case. Examination of the cerebellum after death can confirm characteristic lesions; visual observation alone cannot provide that level of confirmation.
References [2]
The CA DNA test looks for a variant linked to cerebellar abiotrophy
The test looks for the variant associated with CA. N/N, N/CA and CA/CA usually indicate whether the horse has zero, one or two copies of this variant. N denotes a version of the gene without the tested variant; the gene itself is still present.
A horse with one copy of the CA variant is an unaffected carrier: it can pass the variant on, but does not have this form of the disease. With two copies, it has the genetic combination associated with CA, but signs can vary or go unnoticed, as explained above. A result without the variant does not exclude every neurological disorder, and the test cannot precisely predict coordination, severity or suitability for a particular activity.
CA coordination problems can make riding and driving unsafe
There is no treatment that cures CA. The veterinarian therefore assesses the horse’s difficulties: can it move without falling or getting hurt, and can it live in conditions that preserve its welfare? Impaired coordination makes riding or driving clinically affected horses unsafe.
The outlook depends on observed severity and whether the horse can live safely. Severe cases may lead to a decision about euthanasia; other situations require individual assessment. A laboratory result alone, or a video of movement, cannot replace veterinary evaluation of safety and quality of life.
References [2]
Preventing a foal from inheriting two copies of the variant associated with CA
CA has autosomal recessive inheritance: a foal must receive the CA variant from both parents to have the combination associated with the disease. If the mare and stallion each have one copy of this variant, every conception has a 25% chance of a foal with two copies, a 50% chance of an unaffected carrier with one copy and a 25% chance of a foal without the variant. For a foal with two copies, these figures cannot predict whether signs will be visible or how severe they will be.
If one parent has one CA variant copy and a DNA test confirms that the other has none, their foal cannot inherit two copies. Each conception still has a 50% chance of a foal inheriting one copy and becoming an unaffected carrier. These probabilities apply to each pregnancy, without a guaranteed pattern over four births. Keeping reports and selecting partners thoughtfully helps address both health and genetic diversity.
The three possible DNA test results for cerebellar abiotrophy (CA)
One copy of the CA-associated variant: unaffected carrier
The horse has a 50% chance of passing on the variant at each conception without being affected by this recessive form.
On some laboratory reports, affected means that the test found two copies of the CA variant. The word does not establish which signs the horse shows, how severe they are or whether an activity is safe.
Questions about the condition: Cerebellar abiotrophy
Do two CA variant copies always cause the same coordination problems?
No. Signs vary, and a small number of two-copy horses have reportedly shown no visible signs. The test is not a severity score.
Does a fall prove that an injury, rather than CA, caused a horse’s coordination problems?
No. Falling may be a consequence of poor coordination. The history and neurological examination help the veterinarian distinguish possible explanations.
Does a negative CA test rule out every inherited disease that affects coordination?
No. It covers the tested variant. Other inherited or acquired conditions can also cause incoordination.
Scientific sources about the condition: Cerebellar abiotrophy
This article brings together the research and the university and laboratory resources listed below. Numbers after each section link to the references used. Sources consulted in November 2026.
- Cerebellar Abiotrophy (CA): DNA testing and interpretation
UC Davis — Veterinary Genetics Laboratory · Test documentation
- Cerebellar Abiotrophy (CA): clinical signs, diagnosis and prognosis
UC Davis — Center for Equine Health · University resource
- Brault, Famula & Penedo (2011) — Inheritance of cerebellar abiotrophy in Arabians
American Journal of Veterinary Research · Research
- OMIA 000175-9796 — Cerebellar abiotrophy in the horse
The University of Sydney — Online Mendelian Inheritance in Animals · University resource