HYPP Positive…what does this mean?

We have just learned that Hazy, one of our rescues, is HYPP Positive.

Hyperkalemic periodic paralysis (HYPP) is a muscular disorder caused by an inherited genetic flaw. The flaw is the result of

a gene mutation. Most gene mutations of this type do not propagate because the affected individual does not survive. For some

was a highly sought after sire with his superior conformation, musculature, and excellent show record. Producing over 50,000

offspring he passed on his incredible genes, including in some, the HYPP gene. This particular flawed gene affects the cell membrane

by disrupting the normal opening and closing of the sodium ion channel. These channels are "pores" in the muscle cell membrane

which serve as gateways controlling the flow of sodium and potassium in and out of the cell. This flow controls the muscle fiber

contraction and relaxation. In an affected horse these gateways malfunction and begin to leak, allowing potassium to flow out and

sodium to flow in. Potassium is important for proper function of muscles and nerves. The channel becomes "leaky" when potassium

levels fluctuate in the blood. This may occur with fasting followed by consumption of high potassium feed or hay. Hyperkalemia, which

is an excessive amount of potassium in the blood, causes the muscles in the horse to contract more readily than normal.

HYPP is an autosomal dominant gene meaning that it is not sex related. Both males and females have an equal chance of

inheriting the gene. Because it is a dominant gene it does not become "diluted" and is passed from one generation to the next on an

equally frequent basis. The disease is not infectious or contagious - it is genetic. If a heterozygous individual (N/H), those having one

copy of the gene, is bred to a normal individual, fifty percent of the offspring will be normal (N/N) while the other fifty percent heterozygous

(N/H). If you were to breed two heterozygous individuals to each other, fifty percent would be heterozygous (N/H), twenty-five percent

normal (N/N) and twenty-five percent homozygous (H/H), those carrying two sets of the gene. Less than 1% of the horses tested were

H/H, or homozygous for the gene. As for breeding, a mare who has tested "HYPP H/N", meaning she is heterozygous, or carries one

copy of the HYPP gene, breeding her to a normal sire, or HYPP N/N, will result in 50 percent chance the offspring will carry the HYPP

gene (HYPP H/N) and a 50 percent chance of the foal being normal. Breeding her to a heterozygous sire, or HYPP H/N, will cause only

a 25 percent chance of the offspring being normal (HYPP H/N) and 25 percent chance of the offspring to be homozygous (HYPP H/H, or

carry both copies of the HYPP gene). A carrier of the defect (HYPP H/N) is affected with HYPP. These horses can show clinical signs of

the disease and can pass the gene on to their offspring. Though horses that are homozygous show more severe clinical symptoms,

heterozygotes also obtain the disease because it is a dominant trait.

HYPP attacks vary significantly in duration and severity. Much of it depends upon the individual. Not every horse that tests

positive for the HYPP gene is symptomatic. Some horses possessing the HYPP gene go through their entire life and never experience

an attack. Heterozygous horses (N/H) are more likely to have mild or no attacks at all. Homozygots (H/H), those horses having both

copies of the gene, are more likely to experience attacks with more frequency and of a higher severity, though this is not scientifically

proven. Usually, if a horse is going to experience an attack they will do so by the time they are five years of age but any individual may

experience an attack regardless of age. Genetic predisposition, stresses, and diets all factor into the probability of a horse having an

attack. The least understood factor is genetic predisposition, which is the inherited probability of having an attack. However, it has been

determined that once an individual has suffered an attack, it is highly likely that it will experience another.

HYPP can be very difficult to diagnose by simple observation because of its visual similarities to other equine diseases such

as colic or "tying up." Some signs of an episode are periodic muscle spasms, which look like something crawling under the skin,

trembling, weakness, sweating, leaning on walls or lying down. In the case of a homozygous individual, an attack can be accompanied

by noisy breathing caused by the paralysis of the throat muscle. Some horses may loose complete muscle control and collapse. Death

may occur in rare cases but it is usually attributed to cardiac arrest and or respiratory failure.

It is hard to factor stress into the likelihood of a horse having an attack since the types and levels of stresses differ greatly. Trailering

might cause an episode in one individual while training or even foaling might trigger an attack in another. Hot, humid weather over long

periods of three or more continuous days seems to stress some HYPP horses and can initiate an attack. If horses are stalled provide

plenty of ventilation and a fan for cooling purposes. If the horse is outside be sure the horse has ample access to shaded areas. Always

have plenty of water available for these horses. Horses are creatures of habit and like consistent routines. Every effort should be made

to establish a routine for feeding and training. Try to avoid any sudden changes in routine as it could cause stress. If changes need to

be made they should be done slowly over a period of time. A horse’s physiology depends a lot upon his diet therefore, diet is very

important when dealing with HYPP. You should avoid diets high is potassium levels, since potassium seems to be the main factor in

triggering an attack. By lowering the amount of potassium in the diet, the frequency of attacks can be diminished or eliminated. Most

hays and sweet feeds, which contain molasses, are high in potassium content. Some individuals may need to be placed on a

"complete" feed, that contains the hay and grain rations combined in a pelleted form, which in turn allows for better control of potassium

levels. Other horses can still be fed hay while getting their grain source from high carbohydrate feeds such as oats, corn and barley. Still,

others can be maintained on sweet feeds and hay without experiencing an attack. The ‘total’ dietary potassium level needs to be 1% of

the total amount fed by weight. This is tricky and necessitates an understanding of the levels of potassium in common feeds. Dry grains

such as corn, barley and oats are about 1/2%, and most alfalfa hay is 1.5%. Thus, if you feed equal weighted amounts, you would be at

the ideal 1% level of potassium. Beet pulp is high in fiber and calories and low in potassium (.3%). This is optimal for HYPP horses

though should be supplemented with soy meal, which is higher in phosphorus, for younger horses to balance the high calcium levels

in alfalfa and beet pulp. One major misconception is that HYPP horses should be fed other hays instead of alfalfa. This is misleading

since many other hays contain a higher potassium level than alfalfa - timothy contains 1.8% and orchard grass 2.59%.

Besides diet and stress management, exercise plays a major role in maintaining the HYPP horse. Those affected with the

HYPP gene do better with daily turnout as opposed to stall confinement. Horses experiencing an attack will benefit from light exercise

such as walking or jogging, which increases the adrenaline thus lowering the amount of potassium in the blood and stabilizing the

episode. As stated previously, it is thought that stress, especially in young horses, can trigger an attack. Medication plays an integral part

in HYPP maintenance for some horses, especially those who suffer frequent or severe attacks. Acetazolamide is a mild diuretic that

helps the liver and kidneys shed the excess potassium however it takes approximately 12 hours after being administered to become

effective. Acetazolamide is now approved as a maintenance drug by the AQHA and can be used during competition however, it is still

listed as a substance banned by the ASHA during competition. It is very important to relate the HYPP status of an individual to your

veterinarian before any procedures so that the veterinarian may monitor for any signs of attack during treatment. Some tranquilizers,

such as acepromazine, or those derived from phenothiazine should be avoided because they can trigger an HYPP episode by increasing

the serum potassium level. Those tranqilizers acceptable for use in the HYPP positive horse include Rompun, Torbugesic, and

Dormosadan.

1. Exercise (Use caution as the horse may be uncoordinated).

2. Feed grain high in carbohydrates (corn, oats, or barley) or administer Kayro (light)* corn syrup (approximately 50 cc at 15

minute intervals until tremors subside). You can also dissolve 2 cups of baking soda in water and administer orally.

*NOTE: Do not use dark corn syrup as it contains potassium.

3. Orally administer 3 mg/kg (approximately 6 to 8 tablets) of acetazolamide, which increases the potassium excretion from

the kidney’s and stimulates the release of insulin.

1. Administer 23% calcium gluconate via IV catheter. Most horses will respond to this treatment immediately and rise.

2. In the event the horse does not respond, administer interveiniously 1 L 5% sodium bicarbonate.

3. If there is still no response, administer 3 L 5% dextrose interveiniously, and monitor blood potassium levels.

Each of these treatments will help to lower the potassium level in the blood and also help to stabilize the muscle membranes.

As a preventative you may choose to top dress feed with the light corn syrup and/or baking soda. This is often a cheaper alternative to

medicating daily with acetazolamide though this may not work for every horse – some will require the medication for maintenance of the

symptoms. The AQHA continues to fund research on HYPP and, since initial reports were made, Dr. Sharon Spier, the preeminent

authority on the disease, issued the following statement trying to bring the condition into perspective. "Horses afflicted with HYPP, if

properly managed, can lead productive, useful lives, and bring their owners many hours of pleasure" Anyone who owns a horse with

Impressive in its bloodlines should have the horse tested and be instructed on the proper care and maintenance of a HYPP positive.

Contrary to what many uninformed people believe, HYPP positive horses are maintainable and can lead very happy and prosperous

lives. Many of today’s top horses trace back to Impressive. Some of them possess the HYPP gene but many more do not. With proper

breeding and out-crossing this genetic defect will occur less frequently and one day will possibly become obsolete. Until that day horse

owners should do all in their power to become informed about this disease so that they can make knowledgeable decisions regarding

the health and maintenance of their equine friends.

For additional information and first hand experiences with this genetic defect and its

symptoms and treatments please visit the HYPP Forum at:

http://forums.delphiforums.com/hypp/start

Information provide by a conglomeration of equine experts and advice located under

the yahoo search "Equine HYPP Positive" and the research and articles of Dr. Sharon

Spier, an associate professor in the Department of Medicine and Epidemiology at the

University of California at Davis. She is the Chief of Service in the Equine Field Service.

Her clinical interests are in general equine practice, internal medicine disorders including

diseases of muscle and gastrointestinal disorders. Dr. Spier is the recipient of

the AVMA Council on Research Award in 1994 for excellence in equine research. She

has been involved with research on hyperkalemic periodic paralysis in horses since

1985.

Some, not all, Information found in the following sites:

http://www.netpets.com/horses/healthspa/hypp.html

http://www.neosoft.com/~iaep/pages/nutrition/neutraceuticals/hypp.html

http://www.neosoft.com/~iaep/pages/bulletins/health/hypp.html

Hazy’s diet and exercise level have maintained her to having only infrequent mild attacks.

She will need to be carefully thought out by a prospective new family, but had

been used in LCR’s natural Horsemanship Program last season and quickly became

one of the favorites with her smooth gaits and responsive attitude. With proper knowledge,

feeding and exercising will only be a secondary thought to caring for this well

trained, sound, quiet mare who is so easy to love.