Introduction

Equine Cerebellar Abiotrophy (CA) is a genetic, neurological condition found almost exclusively in Arabian horses. Results from breeding experiments carried out at UC Davis indicate a recessive mode of inheritance for this condition. This means a horse can "carry" the disease gene but not be affected. However, breedings between two carrier horses will produce an affected foal 25% of the time.

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Detailed Cerebellar Abiotrophy Information

Foals affected with CA appear normal at birth. Around six weeks of age (although sometimes as late as four months), the disease causes the death of neurons in the cerebellum of affected foals, leading to head tremor (intention tremor) and a lack of balance equilibrium (ataxia), among other neurological deficits. Affected horses may show exaggerated action of the forelegs, a wide-based stance, and be unable to rise from a reclining position. They tend to startle easily and often fall due to ataxia. The neurological problems may not be apparent to owners and frequently thought to be a consequence of a fall rather than CA. Symptoms of CA vary in severity. Some foals show very severe symptoms, including the exaggerated gaits and a dramatic lack of balance. Others have little more than the head tremor, which may only manifest itself during goal-directed movement. Regardless of the severity of the symptoms, CA foals are often euthanized or restricted to life as pasture pets, as they are never coordinated enough to be ridden safely. Affected horses are also a danger to themselves because the condition predisposes them to accidents and injury. Veterinarians can perform a series of neurological tests to determine if symptoms are consistent with CA.

The genetic basis of CA is currently under investigation at the Veterinary Genetics Laboratory. While the specific mutation that causes CA is not yet known, we have identified a group of genetic markers adjacent to gene that can be used as a surrogate test (or indirect test) for CA.  When genetic markers lie close to a gene of interest, they often are inherited along with the trait.  The CA test looks for a specific set of alleles that are co-inherited with CA which can be used as a diagnostic tool to identify affected foals and also animals that are potential carriers of the disease.  Breeders who wish to test their horses before breeding may use the CA test in order to avoid breeding two suspected carriers together.

Results of the CA screening test are reported as:

N/N:     Normal. Horse does not possess markers associated with CA.

N/CA:  Carrier (1 copy of the CA gene). Horse has markers associated with CA and is considered to be phenotypically normal and a carrier of the disease gene.

CA/CA: Affected (2 copies of the CA gene). Horse has markers associated with CA and is considered to have the disease.