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HYPP
What is HYPP?
What are the symptoms of HYPP?
HYPP is sometimes confused for…
What causes an attack?
How can horses be tested for HYPP?
Should my horse be tested?
Can horses with HYPP use supplements?
My horse has HYPP
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What is HYPP?
“Hyperkalemic Periodic Paralysis Disease (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
muscle cells. The 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.”1
What are the symptoms of HYPP?
HYPP is characterized by sporadic attacks of muscle shaking or trembling, weakness
and/or collapse. Because the muscles in the upper airway may become paralyzed, an
attack can also be accompanied by loud breathing noises. Occasionally, sudden death
can occur following a severe paralytic attack, presumably from heart failure or
respiratory muscle paralysis.
HYPP is sometimes confused for:
- “Tying-up” – Associated with exercise, horses that “tie-up”
often look stiff after an episode, whereas HYPP horses appear normal.
- Colic – In both HYPP and colic situations, horses may be unable to
stand.
- Seizures – Unlike horses with seizures, HYPP horses are conscious during
attacks, and do not appear to be in pain.
What causes an attack?
Dietary changes, general anesthesia, concurrent illness, exercise restriction, or
stressful events (i.e. long and/or difficult transport) can all trigger a HYPP attack.
How can horses be tested for HYPP?
A blood test to identify the HYPP gene in individual horses is currently available
at the University of California, Davis.2 Of course,
no diagnostic test is 100% accurate, but based on the results thus far this test
is both accurate and reliable.
Should my horse be tested?
The genetic defect that causes HYPP has been linked to descendents of the American
Quarter Horse stallion, Impressive. As of 1998, any foal descending from Impressive
is required to have a statement printed on their registration that recommends testing
for the condition.
It is still unclear if there are other bloodlines that contain different mutations
that lead to HYPP. Research is on-going, however, and more details will be known
over time.
Can horses with HYPP use supplements?
Yes, however all supplements need to be low in potassium. It is important to avoid
electrolytes and molasses, because both contain potassium and may trigger an attack.
Remember that you can find a complete guaranteed analysis of all supplements we
offer on our website, making it easy to see which supplements are appropriate for
a horse with HYPP.
My horse has HYPP:
• How can I prevent an attack?
“ Many horses can be managed with exercise and diet control. Regular exercise
and access to a large paddock or pasture is preferred over stall confinement. Avoid
rapid changes in feed, such as bringing a horse off pasture grass and immediately
switching to alfalfa hay.”3 Because of the
way HYPP affects potassium concentration in the bloodstream, a decrease in potassium
intake helps most affected horses improve. It also may be beneficial to analyze
the contents of your horse’s daily feed, in order to determine the potassium
content.4
• Are there drugs available for this condition?
Many horse owners administer acetazolamide,
a diuretic. Please consult your veterinarian to see if this treatment is appropriate
for your horse.
• My horse has never had an attack. Will he pass the gene on? Does he still
have HYPP?
Because it is a genetic disorder, a horse with the HYPP gene, regardless of how
many attacks he has had, has just as much chance of passing on the gene as his parents
did.
A horse with the HYPP gene is affected for life. Horses do not grow out of this
condition. |
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We gratefully acknowledge the contributions of HYPP expert
Dr. Sharon J. Spier, DVM, Ph.D.,
Associate Professor, Department of Medicine and Epidemiology,
University of California, Davis. As with all medical issues, please contact
your local veterinarian for more information specific to your own horse. |
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1Spier, S. J. "Current Facts about Hyperkalemic Periodic
Paralysis (HYPP) Disease."
2Ibid.
3Spier, S.J. "Test Available for Hyperkalemic Periodic Paralysis in Quarter
Horses."
4Ibid.
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