Researchers at the University of California, Davis, School of Veterinary Medicine have identified a genetic cause for the fatal condition equine familial isolated hypoparathyroidism (EFIH) in Thoroughbreds, marking the first genetic variant for hypoparathyroidism identified in any domestic animal species. Additionally, this is the first widely available genetic test for Thoroughbreds.

The study, led by Carrie Finno, DVM, PhD, Dipl. ACVIM, and Gary Magdesian, DVM, CVA, Dipl. ACVIM, ACVECC, ACVCP, was reported in the journal PLoS Genetics. Genetic testing can now be performed at the UC Davis Veterinary Genetics Laboratory to identify horses with the variant and avoid mating carriers that could produce affected foals.

“For Thoroughbred owners and breeders, the loss of a foal has tremendous economic and emotional impacts,” said first author Victor Rivas, who conducted the project as part of his undergraduate training in Finno’s laboratory. “It is important to promote safe and strategic breeding habits by actively breeding horses genetically screened not only for EFIH but for other diseases that may impact quality of life.”

Foals affected with EFIH suffer from low blood calcium concentrations, resulting in involuntary muscle contractions, muscle stiffness that leads to a stiff gait and can progress to an inability to stand, seizures, fevers, and an abnormally fast pulse. Parathyroid hormone is typically produced to increase calcium levels in the body, but in these foals concentrations are low or “inappropriately” normal (i.e., they should be high due to the low calcium). Affected foals die or are euthanized due to poor prognosis. Necropsy results reveal underdeveloped or absent parathyroid glands