Polymorphism Identification in Candidate Genes for Juvenile Idiopathic Epilepsy in the Arabian Horse

As an economically important species, the health of the Arabian horse is paramount for breeders.  Genetic selection for athletic ability, temperament, trainability, and above all, health is vital for the current and future success of the breed.  Here we describe a candidate gene study exploring the basis of Juvenile Idiopathic Epilepsy (JIE) in the Arabian.  The phenotype presents shortly after birth, from 2 days to 6 months of age.  Affected foals are stricken with clusters of classic tonic-clonic seizures, in addition to blindness, lethargic behavior, and a decrease or loss of the menace response. Fatality can occur if seizures cannot be controlled pharmacologically; however, most horses outgrow seizures by 18 months of age and are healthy as adults, perpetuating this deleterious allele if they are used as breeding stock. As JIE is a rare condition in the Arabian horse, few affected individuals are available for study.  Thus, utilization of a candidate gene sequence approach was used to identify mutations in a small sample set.  We targeted two candidate genes, KCNQ2 and KCNQ3, which encode potassium voltage gated channels within the neurons in the brain. We identified a promising SNP in exon 14 of KCNQ3 that may contribute to the disease. Ongoing sample collection to increase statistical power is still underway and future work will verify the association with this SNP.  This approach aims to provide a genetic test to identify affected and carrier individuals to screen breeding stock and reduce the incidence of JIE affected foals.