>>>> HyPP isn't restricted to just QH's and Paints either, it says Arabians, Appaloosas, Pintos and other stock breeds may be at risk. Any horse that has Impressive in it's bloodlines. Here is the website I got most of my information from, I found it really informative.
Where that website says that "there is now anecdotal evidence (from horses for sale sites and breeders web sites) that HYPP may be crossing over into the Arabian Horse Association,", they did not qualify that statement with the fact that it would have to be HALF Arabians only....NO purebred Arabians would have ANY lineage to the QH Impressive-- the Arabian Horse Assoc. Does not allow ANY crossing to ANY other breed for registered purebred Arabians.
>>>>> And I said any horse with Impressive in it's blood could be at risk. So if a horse, any horse, doesn't have Impressive bloodlines, it obviously isn't at risk. Maybe I didn't state that part clear enough.
There are over 100 purebred Arabians that have the word "Impressive" in their registered name, including some named simply "Impressive", with various spelling differences. They are of NO relation to the AQHA Impressive... but if people see erroneous or incomplete statements such as "there is now HYPP crossing over into Arabs, so avoid bloodlines with Impressive".... do you see where this causes unnecessary and perhaps damaging confusion and the further spread of misinformation?
While there is some good information on the site you referenced, IMO that website also makes some statements that are not 100% accurate, and/or are outdated. It is written by a private individual/indiviudals, not researchers or scientific experts.
IMO other, more technically accurate reference sites are--
The HYPP info page at the Veterinary Genetics Lab at UC Davis--
The HYPP facts page at AQHA--