Arabian/Arabian Cross Horse Genetic Tests
Cerebellar Abiotrophy (CA)
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.
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. 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 has 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.
Results reported as:
N/N: Normal. Horse does not possess the mutation associated with CA
N/CA: Carrier. Horse has 1 copy of the mutation associated with CA and is considered to be phenotypically normal and a carrier of the disease gene.
CA/CA: Affected. Horse has 2 copies of the mutation associated with CA and is considered to have the disease.
Brault, L.S., Cooper, C.A., Famula, T.R., Murray, J.D. and Penedo, M.C.T. (2010) Mapping of equine cerebellar abiotrophy to ECA2 and identification of a potential causative mutation affecting expression of MUTYH. Genomics doi:10.1016/j.ygeno.2010.11.006.
Lavender Foal Syndrome (LFS)
Lavender Foal Syndrome (LFS), also known as Coat Color Dilution Lethal, is a fatal autosomal recessive condition of Arabian horses. LFS is found primarily in horses with Egyptian bloodlines but has also been reported in other Arabian breeding groups. The genetic defect results from a mutation in the MYO5A gene that causes neurological dysfunction in newborn foals. Signs of LFS are characterized by seizures, severe hyperextension of limbs, neck and back (opisthotonos), stiff paddling leg movements, involuntary eye movement (nystagmus) and inability to stand or sit upright. LFS foals are typically born with a telltale dilute coat color described as lavender, pale pink or silver, hence the name of the disease. Because birthing of LFS foals is often difficult, the signs can be misinterpreted as resulting from oxygen deprivation during delivery or from a spinal cord injury. LFS foals may have a strong suckle reflex and may be bottle fed but the disease is untreatable and will not improve. Foals will die or have to be euthanized shortly after birth.
The VGL offers a DNA test for LFS to assist veterinarians to make the correct diagnosis and owners to identify affected and carrier horses. The test uses DNA obtained from hair root samples thus avoiding blood sample collection. Breeders can use results from the test as a tool for selection of mating pairs to avoid producing affected foals.
50% N/N, 50% N/LFS
50% N/N, 50% N/LFS
25% N/N, 50% N/LFS, 25% LFS/LFS
Results are reported as:
N/N: Normal - horse does not have the LFS gene.
N/LFS: Carrier - horse carries one copy of the LFS gene.
LFS/LFS: Affected - horse has two copies of the LFS gene.
Brooks SA, N. Gabreski, D. Miller, et al. Whole-genome SNP association in the horse: Identification of a deletion in Myosin Va responsible for Lavender Foal Syndrome. Plos Genetics 2010, 6(4): e1000909.
Gabreski NA, B Haase, CD Armstrong, O Distl, SA Brooks. Investigation of allele frequencies for Lavender foal syndrome in the horse. Animal Genetics 2012 Jan 4. doi: 10.1111/j.1365-2052.2011.02305.x. [Epub ahead of print].
The LFS test is performed under license from Cornell University.