What is Hyperkalemic Periodic Paralysis?

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  • Written By: Stephany Seipel
  • Edited By: A. Joseph
  • Last Modified Date: 15 October 2019
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Hyperkalemic periodic paralysis is an inherited genetic disorder that affects both humans and horses. The disease is characterized by muscle weakness and temporary paralysis. Doctors and veterinarians treat the condition through diet and medication.

This disorder occurs because of mutations in the sodium channel genes. Sodium channels are specialized proteins that allow sodium ions to pass through cellular plasma membranes. Sodium and potassium work together in the body to create electrical signals that allow the muscles to contract.

When the body's potassium levels rise and fall, the cells start leaking sodium and potassium into the bloodstream. This causes the muscles to contract involuntarily, creating spasms. Eventually, the muscles lose their ability to contract, and the patient suffers from temporary paralysis.

In horses, this condition is often called Impressive syndrome in honor of a horse named Impressive. Impressive was a champion in the halter classes who was well known for his remarkable muscular structure. His owners often farmed him out to horse breeders who sought to improve their stock.

Impressive had hyperkalemic periodic paralysis, and he passed the disorder down to his many offspring. The condition troubles many Quarter horses, as well as Palominos, Appaloosas and other breeds that were developed with Quarter horse stock. Impressive disease does not skip generations and generally cannot be bred out or diluted.


Hyperkalemic periodic paralysis is autosomal dominant, which means that the patient needs to inherit only one copy of the gene to develop the disease. It affects both male and female horses at equal rates. Human males are more likely to develop the condition than females.

There had been no cure for hyperkalemic periodic paralysis found by early 2011. Horse owners prevent potential attacks by avoiding feed that has high potassium levels. Veterinarians treat the condition by prescribing medications such as acetazolamide, a drug that regulates glucose and potassium levels in the blood.

A human patient is at risk for developing hyperkalemic periodic paralysis if he or she has a parent or grandparent with the disease. A doctor can diagnose the condition by testing the amount of potassium in the patient's body. The doctor might also perform a muscle biopsy or run additional tests to look for other conditions that could be causing the symptoms.

Doctors treat the condition by controlling its symptoms. They prescribe acetazolamide, the same medication that horses use, to prevent episodes from occurring. They might also provide the patient with glucose to lessen the intensity of an attack.


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