Equine cerebellar abiotrophy (CA) is a genetic, neurological condition found almost exclusively in Arabian horses. Results from breeding experiments carried out at the University of California, Davis indicate a recessive mode of inheritance for this condition. This means a horse can "carry" the disease gene but not be affected.
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 are frequently thought to be a consequence of a fall rather than CA.
Signs of CA are variable. Some foals show very severe signs, 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. A small number of horses classified as affected by the genetic test have been reported by owners as showing no signs. CA foals that show signs of the disease 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 signs are consistent with CA.
Research carried out at the Veterinary Genetics Laboratory by Drs. Leah Brault and Cecilia Penedo identified a mutation that is associated with CA. The diagnostic CA test allows identification of horses that are affected or that carry the specific mutation. For horse breeders, identification of carriers is critical for the selection of mating pairs to avoid production of affected foals. Breedings of carrier horses have a 25% chance of producing an affected foal. Breedings between normal and carrier horses will not produce a CA foal, although 50% of the foals are expected to be carriers.
The CA mutation has been found in low frequency in other breeds, such as Danish Sport Horse, Bashkir Curly, Trakehner, and Welsh Pony, that have used Arabian horses as foundation stock. The CA test is recommended for horses that have Arabian ancestors in their pedigree.