Because of its strong partnership with the University of California Davis Veterinary Genetics Lab, AQHA is aware of Equine Juvenile Spinocerebellar Ataxia. The disease, which was identified in American Quarter Horse foals in 2020, is inherited as an autosomal recessive trait. A scientific paper describing this gene and the genetic mutation is currently in progress. Genetic testing can determine whether a horse is a carrier of the variant that causes EJSCA. Breeding of two carrier animals has a 25 percent chance of producing an affected foal.

Affected foals developed ataxia, or incoordination, between 1 and 4 weeks of age. Glucose and gamma-glutamyl transferase (GGT) concentrations were commonly elevated in blood tests. Most foals exhibited severely affected hind limbs and less severely affected front limbs. As the disease progressed, these foals would turn the hind limbs to one side, with the front limbs planted on the ground, causing them to appear to walk sideways. Within a few days, the affected foals were unable to stand without assistance and had to be euthanized. Postmortem examinations revealed distinctive lesions in their spinal cords.

Whole genome sequencing was performed on a group of affected and unaffected, but related foals. Analysis of the results led to the identification of the genetic variant that causes EJSCA.

Access more information about testing your horse through Veterinary Genetics Laboratory at UC Davis.

AQHA will publish a story about EJSCA this fall in The American Quarter Horse Journal, and the AQHA Stud Book and Registration Committee will discuss this genetic disease at its meeting during the 2025 AQHA Convention March 28-31 in Las Vegas.