Hyperkalemic Periodic Paralysis, commonly known as HYPP, has been widely spread throughout the equine industry over the last several years. This heritable disease is caused by a genetic defect that has been found through research to trace back to the great American Quarter Horse stallion, Impressive.
HYPP affects the sodium channels of afflicted horses and overloads the system with high potassium levels that cause episodes which may include: mild muscle twitching that is undetectable to the human eye; noticeable muscle twitching; "crawling" skin, ranging from slight to very noticeable and usually from the back flank area forward; hind quarter paralysis; excessive yawning; and paralysis of the muscles surrounding the heart and/or lungs, causing death due to heart attack or suffocation.
There are three testing statuses for HYPP:
H/H - This status means that a horse carries a double copy of the defective gene and will pass at least one copy of the gene and the disease to 100% of it's offspring.
N/H - This status means that the horse carries one normal gene and one HYPP gene and statistically an N/H horse will pass the gene and the disease to 50% of it's offspring when bred to a N/N or non-Impressive bred horse. N/H to N/H cross will statistically result in 25% N/N progeny, 50% N/H progeny, and 25% H/H progeny.
N/N - This status means that the horse carries two normal genes. It does not have the disease, nor can it be passed on.
NOTE: Not all horses affected with HYPP will show outward signs and will live full productive lives, but as can be seen in our feature stories and on our experience pages, a great many do suffer episodes and some die. How many of the latter are ENOUGH to make breeders and the registries realize that something needs to be done about N/H as well as H/H?
A dominant gene disease requires only ONE PARENT to have and pass on the gene AND the disease. It can be avoided by not breeding diseased animals. HYPP is a dominant gene disease.
A recessive-gene disease requires both parents to pass a copy of the gene for offspring to inherit the disease. These parents are carriers, but do NOT have the disease themselves. The disease can be easily avoided by testing and not breeding carriers to each other. HERDA and OLWS are recessive gene diseases.
HYPP was identified in 1985, and a test was made available for public use in 1992. When the test was made available to the public, breeders were encouraged to test their breeding stock and choose horses who did not carry HYPP to be used as breeding stock. New research shows that not only has the test not been used to cull the disease from the equine industry, but the number of homozygous (H/H) and heterozygous (N/H) have increased! Samples submitted by Quarter Horse owners for HYPP testing in 1992-1996 showed that 1.1% were H/H (homozygous), while 35% were N/H (heterozygous). Testing in 2005 indicated that 2.2% of horses tested were H/H genotype, and 37% were N/H. Keep in mind that these numbers are indications only of the ones actually tested. You can read more detail of testing at http://www.thehorse.com/ViewArticle.aspx?ID=9909&nID=5
While the article listed above from The Horse.com is a very enlightening one, it noted mandatory testing for HYPP with the AQHA beginning in 1988. I believe that date to be 1996, when HYPP was added to the AQHA handbook. That ruling applied only to foals born of Artificial Insemination (AI) or Embryo or Multiple Embryo Transfer (ET or MET). AQHA just started requiring mandatory HYPP testing for all descendants of Impressive effective January 1, 2007.
January 1, 2007 was also the date set by AQHA to no longer allow registry of foals testing H/H. Both rules regarding mandatory testing and denial of registration for H/H tested foals were passed at the 2004 AQHA convention. N/H was not ruled against at that time. While the AQHA mandatory testing rule is good news for the horse industry, it is not good enough. We still need rulings on HYPP from the all of the registries that have Impressive descendants, such as APHA and ApHC, and quite possibly the Arabian Horse Association and the Pinto Horse Association. Additional stock horse registries at risk are the International Buckskin Horse Association and the American Buckskin Horse Association. There are also many part and half blood registries who need to follow suit and pass rulings on both positive statuses and mandatory testing thereof.
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.
In pulling progeny of well known Quarter horse sires for our lists, records indicate that 50% or less of foals sired by each positive stallion, through 2006, are tested with results on record. On average, we've found approximately 60% of the ones tested to be either N/H or H/H. Of those tested through UC Davis laboratory, their newest results are showing approximately 160,000 who are tested to be heterozygous or homozygous for HYPP. Those numbers would show a dramatic increase if all registries required mandatory testing for registry and would make status publicly available as the AQHA does.
HYPP has spread through cross-breeding of affected Quarter horses with horses of other registries, as well as grade (unregistered) horses. This issue, in many ways, effects the entire Equine Industry in the United States. It is time to put human safety and the health of our horses over the desire for trophies, ribbons, money and prizes and eliminate this disease before the possibility becomes beyond our ability to do so.
PLEASE... if you feel strongly about the health of the horses, no matter what breed you have, write to your registries and tell them your feelings! One person can accomplish a little, and many can accomplish ANYTHING!
There has been a lot of talk lately about HYPP Solution. For those who are not aware of it, the HYPP Solution is a liquid developed to mix with semen extender to immobilize HYPP positive sperm cells so that only the negative cells are left to inseminate. After several collections and much lab work, the formula was tweaked so that approximately half of the sperm cells were immobilized. Testing included fresh samples, and cooled and rewarmed samples, over various time periods. After all lab work, several samples of the remaining motile sperm were sent to UC Davis for HYPP testing. Unfortunately, all results showed results of 50/50 with respect to the HYPP gene, so there was no decrease in the positive HYPP cells. In a nutshell, the solution created in the lab did indeed immobilize 50% of the sperm cells, but had no effect on the HYPP affected cells. Dr. Parish is doing a bit more research with the project and when it is completed, he is planning on publishing a paper on it. The HYPP Solution web site (www.hyppsolution.com) will remain up for a period of time and the developer is planning on posting the results on there, but is it not a high priority for him at this time due to the failed results. The last time we checked, the web site, www.hyppsolution.com was no longer available.
Although there is no charge for adding stallion/s to the N/N Stallion galleries and the use of this web site is 100% free of charge to the public, we would appreciate donations of unused QH “bucks” to help towards populating the HYPP lists. If you have done AQHA based research on progeny for Impressive bred stallions or mares and have copies of those records, please feel free to email those lists to us. If you would like to help us in gathering additional horses for our lists, please contact us at bringinglighttohypp@yahoo.com for names of stallions or mares, and the type of list, we need pulled (not all lists give HYPP status). Our goal is accuracy and using the AQHA lists is an extremely accurate way to gather a lot of names. Please feel free to share your horses' status for HYPP and HERDA.
If you have any further questions, please do not hesitate to contact us.
