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“That uveitis is much more common and more likely to cause blindness in Appaloosas compared to other breeds supports a link between uveitis and genetic factors.”

Current Research

While both the research to date and the widespread anecdotal evidence have established the Appaloosa’s significantly greater risk for uveitis and blindness, no one yet knows why the breed suffers disproportionately from this disability.

Fortunately, a researcher at the University of Minnesota’s College of Veterinary Medicine, Mark Rutherford, is now studying the possible genetic links between uveitis and Appaloosas. Here is how the University of Minnesota summarized Dr. Rutherford’s ongoing research project in a “Faculty Research Interests” report posted on the university’s Web site:

  • Spontaneous equine recurrent uveitis (ERU) is the leading cause of equine blindness, resulting from a chronic painful immune-mediated inflammation of the uveal tract in susceptible animals. ERU is thought to be a delayed type hypersensitivity reaction to self or sequestered antigens in the uveal tract. Although ERU affects as much as 10-15% of the equine population, little definitive information can be found with regard to its cause or causes. Appaloosas are eight times more likely to develop uveitis and four times more likely to develop blindness compared to other breeds. That uveitis is much more common and more likely to cause blindness in Appaloosas compared to other breeds supports a link between uveitis and genetic factors.

In this work, we test the hypothesis that Appaloosas suffer a higher incidence of ERU due to breed-specific MHC haplotypes. We are using PCR-sequencing of expressed class I loci to identify alleles and determine allele frequencies in affected and non-affected Appaloosas. The student will be expected to perform PCR using previously collected genomic DNAs, clone PCR products, and sequence alleles. In addition, chi square tests will be performed to determine if a given allele is associated with the occurrence of the disease.

(Source: Faculty Research Interests, University of Minnesota College of Veterinary Medicine, page 11.)

  • The latest research on this subject was reported at the 36th Annual Meeting of the American College of Veterinary Ophthalmologists on October 12-15, 2005. An abstract published in the journal Veterinary Ophthalmology said the purpose of that study was “to investigate whether the equine major histocompatibility complex (MHC) gene region influences the occurrence of uveitis in the Appaloosa horse.” The team of researchers, including Dr. Rutherford, found that “Based on these data, we conclude that a susceptibility allele for ERU in Appaloosas exists in the MHC region.”

(Source: Veterinary Ophthalmology, Volume 8, Issue 6, Page 437-450, November 2005. Abstract available only by paid subscription.)