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Association of Idiopathic Epilepsy with a Novel Locus in the Belgian Shepherd
Idiopathic epilepsy in the Belgian shepherd dog is complexly inherited. The objective was to identify novel genomic loci associated with the expression of generalized seizures in the Belgian Tervuren and Sheepdog. Dogs were classified as cases if they met specific seizure criteria and controls if they were over 7 years of age and had no other health disorder. DNA from cases (N=35) and controls (N=58) from dogs predominantly unrelated at the grandparent level, were subjected to a high-density genotyping array consisting of over 170,000 evenly spaced single nucleotide polymorphisms (SNPs). Association analyses were conducted using the software package PLINK. Based on 100,000 permutations and removal of non-informative markers and markers with low call rate, five chromosomal regions reached genome wide significance: chromosomes 5 (p < .034), 7 (p < .015), 24 (p < .0003), 29 (p < .020) and 37 (p < .05). Chromosome 7 showed 4 significant SNPs between 46,094,658 – 49,666,725 bp (CanFam 3.1). A Sequenom iPlex analysis was conducted using 34 dogs representing 17 cases and 17 controls. Sequenom Assay Design Suite was used to multiplex 65 SNPS covering the region between 45.03-48.06MB. Three SNPs demonstrated genome wide significance in three genes: two were intronic SNPs (p = 0.00001 and p = 0.04548) and the third was a missense SNP (p = 0.0061) in a novel gene. The mutation in the novel gene changes the codon from proline to arginine. For the novel gene, a 344 bp region was targeted for resequencing uncovering a second missense SNP within the novel gene. The genome wide analysis confirmed the previously characterized locus found on chromosome 37 and revealed a second locus segregating for epilepsy on chromosome 7. The missense mutation in a novel gene validates the model of a multifactorial genetic regulation of idiopathic epilepsy for the Belgian shepherd while also suggesting the existence of a previously unidentified neurological regulatory gene. Taken together the data support the application of genetic selection to reduce the prevalence of this debilitating disorder.
Keywords: idiopathic epilepsy, canine, genome wide association