If the horse is registered, he is tested, there is a date that they made rule changes by... just have them look at his papers. More then likely, the horse is HYPP/NN. There are SO many registered impressive horses out there..... if the horse is not negative, then it's your friends choice, but i'd look elsewhere.
It all depends on when the gelding was born and as to what he is registered under. I'm assuming AQHA because he's a quarter horse.
Here's some information I found.
October 17, 2003; letter from AQHA President Steve Stevens:
The next important topic relates to Hyperkalemic Periodic Paralysis (HYPP). The stud book and registration committee has asked the executive committee to obtain input from the membership regarding this important matter that will appear on their agenda at the Reno convention in March 2004. The proposal is as follows:
1. Rule 227 will be amended making foals of calendar year 2006 and after ineligible for registration if they are descendants of the stallion Impressive, AQHA Number 0767246, and found to be HYPP positive (H/H).
2. Additionally, Rule 227 will be amended to provide that foals of 2010 and later that are found to be HYPP (N/H) will only be eligible for registration as geldings or non-breeding mares.
The APHA rule proposals on the table for voluntary testing for HYPP were not passed at their 2007 convention . APHA does not have mandatory testing and will not have voluntary testing unless a new rule is submitted and passed - but the earliest that can take affect is 2009.
The ApHC (Appaloosas) recommends that all descendants of Impressive be tested for HYPP, but will not post the test results on the papers, nor on the web site. Testing is NOT Mandatory.
I think you should get him vet checked these r usually the symptoms: Weakness, especially in the hindquarters, trembling, abnormal perspiring, unusual appearance of the third eyelid (nictitating membrane), collapse, distorted vocalizations. During an attack the horse remains alert. Attacks can occur at rest and during work. The horse appears normal after an attack.
Personally I will never own another QH or any other breed that has been infected with HYPP. She should definitely have him tested if your friend is interested. It would pay in the long run to know if it will have special needs.
Also horses could have the disease and not show any symptoms. It's always better to be safe than sorry. Generally speaking, if a horse doesn't show any symptoms when they're young, theres a greater chance they won't show any symptoms their entire life. But there are always acceptions.
I'm with Vida. I love Vega to death, but I would never want another hypp horse.