Reasons for performing study: A putative mutation causative of cerebellar abiotrophy (CA), a genetic defect found almost exclusively in Arabian horses, was recently identified. Objectives and hypothesis: To investigate the presence of the CA mutation in breeds other than Arabian and ascertain whether the mutation had been introduced into these breeds by Arabian ancestry. The CA mutation is present in breeds of horses with Arabian ancestry. Methods: Allele-specific PCR was used to genotype 1845 non-Arabian horses for the CA mutation. For those breeds in which at least one carrier was identified, an additional 266 horses were genotyped to determine the frequency of the CA allele. Cerebellar abiotrophy carriers were further genotyped for a haplotype segregating with CA in Arabians. Results: At least one CA carrier was identified in 3 breeds and the frequency of the CA allele calculated: Bashkir Curly Horses (2.8%), Trakehners (0.68%) and Welsh ponies (0.33%). Based on pedigree and haplotype analysis, CA was introduced into these breeds by Arabian ancestry. The Trakehner and Welsh pony carriers were at least half-Arabian, while the Bashkir Curly horses appeared to have had the CA allele introduced by a single Arabian stallion used for developing the breed in the 1960s. Conclusions: The CA mutation is present in breeds of horses that allow crossbreeding with Arabian horses and in breeds that have used Arabians as foundation stock during their development. Potential relevance: Breeds that allow registration of horses with Arabian ancestry should have any Arabian breeding stock tested for the mutation and breeds descended from Arabian ancestry should pursue genetic testing of breeding stock to prevent the occurrence of affected foals.
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