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Hyperkalemic Periodic Paralysis - HYPP

Hyperkalemic Periodic Paralysis - HYPP

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DNA test
  • DNA test for the Hyperkalemic Periodic Paralysis Disease (HYPP). This DNA test verifies the presence of the recessive HYPP gene.


  • 20 to 30 - hair roots - envelope
  • 5 mL - blood - K3 EDTA tube

Turnaround time

  • 2 to 5  working days

Why test?

  • This genetic test helps breeders to identify horses that carrying the HYPP recessive gene. Informed choices can be made for breeding selections, and prevent the born of affected foals. All offspring of Impressive should be tested for HYPP.
  • Because HYPP is dominant disorder, the effects of it can also be transposed to other breeds of horses when intermixing occurs. This test is important in preserving the inherited health of all horses.
  • Horses with suspicious symptoms of the disease should also be tested.

Results description

 The DNA test verifies the presence of the recessive HYPP gene and presents results as one of the following:

  • nn – Horse tested negative for the gene mutation that causes HYPP. The horse will not pass on the defective gene to its offspring.
  • nH – Horse tested heterozygous for HYPP, both the normal and HYPP alleles were detected. The horse is affected with the HYPP genetic disorder and there is a 50% chance this horse will pass a HYPP allele to its offspring.
  • HHPositive for dominant HYPP gene, indicates the animal carries two inherited copies. Homozygous HYPP horses are genetically bound to pass the gene to 100% of their progeny when bred and all foals will be HYPP horses.

Additional information

Hyperkalemic Periodic paralysis (HYPP) is an inherited disease of the muscle, which is caused by an inherited genetic mutation.

A point mutation in DNA exists in the sodium channel gene, which codes for an abnormal channel to be expressed in skeletal muscle. This mutation is passed on to offspring.

Sodium channels are “pores” in the muscle cell membrane which control contraction of the muscle fibers. When the defective sodium channel gene is present, the channel becomes “leaky” and makes the muscle overly excitable and contract involuntarily.

The channel become “leaky” when potassium levels fluctuate in the blood. This may occur with fasting followed by consumption of a high potassium feed such as alfalfa. Hyperkalemia, which is an excessive amount of potassium in the blood, causes the muscles in the horse to contract more readily than normal. This makes the horse susceptible to sporadic episodes of muscle tremors or paralysis.

Severity of attacks varies from unnoticeable to collapse or sudden death. The cause of death is usually respiratory failure and/or cardiac arrest.

This genetic defect has been identified in offspring of the American Quarter Horse sire, Impressive. To date, confirmed cases of HYPP have been restricted to descendants of this horse. 

HYPP is a dominant disorder meaning both homozygous positive (HH) and heterozygous (nH) horses will be affected. Only homozygous negative (nn) horses are not affected by HYPP.