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Impressive’s Flaw
Muscle disease traces to popular sire
  
By
Edward R. Winstead



Featured Article.

Impressive

Impressive certainly lived up to his name. Before his death in 1995, the chestnut quarter horse sired 2,250 foals.

Unfortunately for his offspring, Impressive had a potentially lethal defect in a gene that helps muscle cells operate smoothly. The defect put thousands of Impressive's descendants at risk for a muscular disease known as HYPP, or hyperkalemic periodic paralysis. The same mutation is associated with a variety of symptoms: some carriers show no noticeable effects, while others experience muscle spasms and breathing problems. In severe cases, a horse can have episodes of paralysis and die suddenly.


In the early nineties, researchers identified the gene involved and developed a DNA test that breeders have used to identify carriers of HYPP and reduce the incidence of the disease. With the help of horse pedigrees, a team of geneticists traced the flaw to Impressive. "Had anyone known, Impressive would never have been used as a stud," says James Mickelson, a horse researcher at the University of Minnesota.

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