Genome Sequencing

In 1991, Eliane Marti, Dr. Med. Vet., published a study as a graduate student in Switzerland, showing that chronic hypersensitivity bronchitis (a.k.a. heaves) had a strong hereditary component among Swiss horses. She meticulously defined the

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In 1991, Eliane Marti, Dr. Med. Vet., published a study as a graduate student in Switzerland, showing that chronic hypersensitivity bronchitis (a.k.a. heaves) had a strong hereditary component among Swiss horses. She meticulously defined the clinical signs and studied only those horses maintained in pastures, so as to avoid the more common allergic condition induced by the environment of stabled horses. Leap ahead 14 years. In 2005, Patricia Dranchak, PhD, published a report as a graduate student in Minnesota, demonstrating that recurrent exertional rhabdomy-olysis (RER), a.k.a. tying-up, in Thoroughbred horses is hereditary and probably caused by a dominant gene.


Like Marti, Dranchak conducted a meticulous study to control for environmental variation and to have certainty on the clinical diagnosis. However, the consequences of these studies were different. In 1991, the demonstration of a statistically measurable, inherited component to this important clinical disease was the end of the project. In 2005, we have a gene map for the horse, and the Dranchak study is merely the first step in finding the gene responsible for the hereditary aspect of the disease. Indeed, two co-authors of the Dranchak study, Stephanie Valberg, DVM, PhD, Dipl. ACVIM, professor in the department of veterinary population medicine and director of the Equine Center at the University of Minnesota, and Jim Mickelson, PhD, professor in the department of veterinary biomedical sciences, have been among the leaders developing the horse gene map. Since 1995, their goals have been to use a horse gene map with horse families segregating for RER and find the genetic cause, develop a diagnostic test, and point the way to more effective treatments of RER by veterinarians and farm managers. The pieces for this effort are in place.


Currently, the horse gene map includes over 2,000 genes or genetic markers that can be used in family studies to find genes responsible for disease conditions. We are also in a good position to test candidate genes found to cause similar diseases in humans and mice. This is the approach used to identify the genes responsible for hyperkalemic periodic paralysis (HYPP), severe combined immunodeficiency disease (SCID), and overo lethal white foal syndrome (OLWFS). These tools and successes have led scientists to consider new research approaches. When a graduate student or veterinary scientist begins a research project, the project often begins with identification of the DNA sequence for a target gene.


More recently, scientists have begun to investigate gene expression in connection with horse diseases. When a disease process begins, regardless of whether pathology is caused by heredity, infectious disease, toxins, poor management, or nutritional factors, gene expression changes in some tissues. DNA microarray technology is the approach to investigate gene expression for thousands of genes, if not tens of thousands of genes, simultaneously. The impact on health research is profound and the field has a new name–functional genomics

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Ernest Bailey, MS, PhD, is a professor at the University of Kentucky’s Gluck Equine Research Center, in Lexington. Bailey’s research investigates genetic influences on horses’ innate and adaptive immune systems, which protect animals from infectious diseases. His other interests include the development of the genetic map for horses and investigation of genes involved in the horse health, such as those that might cause contracted tendons, extreme lordosis, and dwarfism.

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