Conference noted::equitation

    I am very disgusted at the number of breeders who are out there
    breeding horses that are HYPP positive or carriers.  HYPP positive
    horses will throw 100% HYPP positive foals.  Carriers have a 50% 
    chance of throwing a positive or carrier foal.   I know for a fact, as
    several people from my barn looked at QH and APHA studs whose owners
    said in passing that they were carriers or positive....but would 
    pay to have the foal tested if they wanted.  
    
    UC/DAvis state the only way to stop the spread of the disease into
    other lines and breeds is to stop the breeding of these animals.
    
    	Comments?
    

    I'm being ignorant here - what is HYPP?  I have not heard of it here in
    the UK.
    
    Please enlighten me
    
    Liz

    I've seen several articles on HYPP in EQUUS, Chronicle of the Horse and
    the Cornell Newsletter, etc. One of them(Cornell Newsletter, I think)
    suggested that the name Impressive is ironic. The stallion was named
    that for his impressive musculature. The article said that HYPP somehow
    caused the heavy muscling because it causes the muscles to work
    "overtime" and become even bunchier than they would normally be in a
    QH.
    
    I'll see if I can find the articles and post the better pieces of info.
    
    J

                                                                Page 1


   *** CURRENT FACTS ABOUT HYPERKALEMIC PERIODIC PARALYSIS (HYPP) DISEASE ***
           (taken w/out permission from UC/Davis memo dated 9/1/93)


     WHAT IS HYPP?
    
     HYPP is a muscular disease that affects both horses and humans.  It
     is caused by a hereditary genetic defect that disrupts a protein
     called a sodium ion channel, a tiny gateway in the membrane of the
     muscle cells.  The genetic defect disrupts the channel's normal
     opening and closing, such that uncontrolled sodium influxes occur. 
     These influxes in turn change the voltage current of muscle cells,
     causing uncontrolled muscle twitching or profound muscle weakness. 
     High levels of potassium in the blood usually are present when the
     disruptions in the ion channel occur.


     WHAT ARE THE EFFECTS OF HYPP?

     Horses w/ HYPP can experience unpredictable attacks of paralysis
     which, in severe cases, can lead to collapse and sudden death.  The
     cause of death usually is cardiac arrest and/or respiratory failure. 
     The disease is characterized by intermittent episodes of muscle
     tremors manifested by generalized or localized shaking, trembling and
     weakness.  Occasionally, episodes are accompanied by respiratory
     noises resulting from paralysis of the muscle of the upper airway
     (larynx & pharynx).  In cases of mild attacks, muscle tremors may be
     so subtle as to be detectable only by an experienced clinician
     performing EMG testing.


     CAN SYMPTOMS OF HYPP VARY IN SEVERITY?

     Clinical signs of HYPP do vary widely among different horses. 
     Homozygous horses are affected more severely that heterozygous
     horses.  Under ideal management practices, the defective gene does not
     appear to have adverse effects, but stress and/or increased potassium
     in the serum can trigger clinical sign of muscle dysfunction.  Why
     some horses manifest severe signs of the disease and other exhibit
     little or no signs is unknown but currently under investigation. 
     Unfortunately, a horse carrying the defective gene but showing minimal
     signs has the same chance of passing the gene to future generations
     as does the affected horse with sever signs.



     WHAT IS THE ORIGIN OF THE GENETIC DEFECT CAUSING HYPP?

     The original genetic defect causing HYPP was a natural mutation that
     occurred as a part of the evolutionary process.  The majority of such
     mutations, which are constantly occurring, are not compatible with
     survival.  However, the genetic mutation causing HYPP produced a
     functional, yet altered, sodium ion channel.  This gene mutation is
     NOT a product of inbreeding.  The gene mutation causing HYPP
     inadvertently became widespread when breeders sought to produce
     horses with heavy musculature.

     IS HYPP LIMITED TO A PARTICULAR BLOODLINE OF HORSES?

     HYPP is associated with horses of heavy musculature, but this does
     not mean that all horses with well developed musculature are
     afflicted with the disease.  The mutant gene causing HYPP presently
     has been identified in the descendants of the horse IMPRESSIVE. 
     RESEARCH HAS NOT YET BEEN PERFORMED ON OTHER BLOODLINES TO ASCERTAIN
     WHETHER THE SAME OR SIMILAR GENETIC MUTATION EXISTING IN OTHER
     BLOODLINES ALSO MAY CAUSE HYPP.  SINCE IMPRESSIVE DESCENDANTS ARE SO
     NUMEROUS, THE GENETIC MUTATION IN THE BLOODLINE IS WIDESPREAD. 
     THEORETICALLY, IT IS POSSIBLE THAT OTHER MUTATIONS CAUSING HYPP IN
     DIFFERENT BLOODLINES MAY BE MORE DIFFICULT TO IDENTIFY BECAUSE THEY
     ARE NOT SO WIDESPREAD.

     HYPP is unique in that it is the first equine disease in which
     breeding and molecular genetics have yielded a specific genetic
     mutation identifiable with a named bloodline.  It is only a matter of
     time before other heritable conditions in various bloodlines
     likewise can be identified.


     (a note from mvb:  I emphasized phrases in this article as it was printed)

     [page 2-4 will be entered as I have time]

    Both horses have been tested for HYPP and have been classified as 
    HYPP negative! I feel much better and can continue my breeding program!

�       <<< Note 1885.5 by STUDIO::BIGELOW "PAINTS; color your corral" >>>
�                        -< The results were negative! >-

�    Both horses have been tested for HYPP and have been classified as 
�    HYPP negative! I feel much better and can continue my breeding program!

Congratulations!  This must be a load off your mind :)

    
    You can say that again!!!!!
    
    
    I would like to encourage anyone w/ horses from the Impressive line
    to get tested.  It only costs $35 for the test.  It is well worth 
    the piece of mind knowing my horses are fit and healthy....and that I
    won't be passing on any defective genes.

    You must be pretty relieved!  How many generations back does Jesse go
    to Impressive?  Are both horses negative/negative?  Is there a
    difference between testing positive on homozygous or heterozygous??
    
    This is an interesting topic!
    
    Karen

    
    Impressive is Jesse great grandfather.  One thing they mentioned in the
    article is that HYPP does not fade away over time, it needs to be bred
    out (ie don't breed any animals w/ the genes) by selectivly breeding 
    (N/N)Impressive lines.   
    
    Homozygous HYPP horses are the severly affect horses.  Their code
    is (H/H).  HYPP is fatal here.  These horses, if bred will throw (H/H)
    horses regardless of the ststus of the other horse. 
    
    Heterozygous HYPP horses may or may not show symptoms, and they are not
    sure why, but are working on it.  Their code is (H/N).   50% chance of
    a (H/N) or a (N/N) horse if bred to a (N/N) parent.
    
    I was afraid my mare could have been a carrier (H/N), as all the
    information lead me to believe that possibility.  I'm glad I did the
    test and know I know for sure that I can continue to breed her.