10-09-2009, 11:52 PM
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Impressive was definitely line bred, to Three Bars, but I'm not sure if they've been able to prove that's how he ended up with the genetic mutation that causes HYPP or not. He was definitely the origin of the disease... He sired almost 30 world champion halter horses and to date has around 100,000 descendents...
In the beginning owners of his foals started noticing a wierd muscular twitching type of issue, they were usually mis-diagnosed as tying-up syndrome or colic, it took a pretty long time before they figured out that it was caused by hyperkalemic periodic paralysis.
At the AQHA 2004 convention a motion was passed to set January 1st 2007 as the date after which foals testing homozygous for HYPP would no longer be registerable, with mandatory testing for HYPP for the descendants of Impressive. The Appaloosa association set their date for 2008 I think. I'm thinking the Palomino association also has a rule.
It's kind of a shame that people remember him more for the disease then his show record but I geuss that's the way it is huh? I love Impressive horses by the way... I'm sorry that was off topic, and it didn't answer the questions which was... "did line breeding cause the genetic mutation..." It may very well have played a hand at it...