Phenotype: Equine familial isolated hypoparathyroidism (EFIH) causes involuntary contraction of muscles and seizures in Thoroughbred foals and is invariably fatal. Blood work reveals low calcium, typically high phosphorus, and low or normal parathyroid hormone (PTH) concentrations, suggesting functional hypoparathyroidism.
Mode of Inheritance: Autosomal recessive
Alleles: N = normal, EFIH = equine familial isolated hypoparathyroidism variant
Breeds appropriate for testing: Thoroughbred
Explanation of results:
- Horses with the N/N genotype do not have the genetic variant causing equine familial isolated hypoparathyroidism and cannot transmit the variant to any of their offspring.
- Horses with the N/EFIH genotype carry one copy. They will have normal calcium levels and normal muscle control but can transmit the variant to 50% of their offspring, and if mated to another carrier, there is a 25% chance the foal will have EFIH.
- Horses with the EFIH/EFIH genotype have two copies of the genetic variant causing equine familial isolated hypoparathyroidism and are likely to suffer from EFIH. This condition is fatal.