EFIH causes critically low calcium and a non-functional parathyroid gland in foals. All known cases so far have been fatal.
Equine familial isolated hypoparathyroidism
Breeds known to be affected
EFIH causes involuntary muscle contractions and seizures in Thoroughbred foals. These foals typically have low calcium and when examined at necropsy they have been found to have little to no parathyroid glands. All foals with this condition have either died or been euthanised due to a poor prognosis.
This disease was first studied in the late 1990s and the causative mutation published by researchers at UC Davis only recently, in 2020. It has been found to occur at low frequency (<2%). However, due to the severity of its symptom’s, carriers should be identified to prevent mating carriers together as this confers a 25% chance of producing an affected foal.
Interpretation of results
n/n: Horse does not carry the mutation associated with EFIH.
n/EFIH: Horse has one copy of the mutation associated with EFIH and will pass this on to approximately half its offspring.
EFIH / EFIH: Horse has two copies of the mutation associated with EFIH and will likely be affected.
Rivas et al. A nonsense variant in Rap Guanine Nucleotide Exchange Factor 5 (RAPGEF5) is associated with equine familial isolated hypoparathyroidism in Thoroughbred foals. PLoS Genetics 2020; 16:e1009028. doi: 10.1371/journal.pgen.1009028