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HYPP Hyperkalemic Periodic Paralysis

Name: HYPP Hyperkalemic Periodic Paralysis
Brand: Equigerminal
Price: 43.05 EUR

Test that shows if your horse carries the gene change that causes muscle shaking and weakness in Quarter Horses. Finds...

€43.05 شامل ضريبة القيمة المضافة

About

This test shows whether your horse carries the gene change behind HYPP (Hyperkalemic Periodic Paralysis), an inherited muscle disease. Affected horses have attacks of muscle trembling and weakness that can end in collapse.

It is meant for Quarter Horses, Paint Horses and other horses with Quarter Horse lines, whether used for breeding or offered for sale.

Why test?

Breeding. Knowing the result of both parents tells you what each mating can produce.

Quarter Horse bloodlines. The variant travels with these lines, also into crossbred horses. A horse with this ancestry should be tested even if it looks healthy.

Buying and selling. The result is objective information you can show a buyer.

A horse with attacks. If your horse has unexplained trembling, weakness or collapse, a positive result explains why and changes the management plan.

Clinical signs

Attacks come and go and vary a lot from horse to horse, from barely noticeable to collapse or sudden death. Between attacks the muscles work normally.

Muscle twitching and trembling, sometimes continuous, that can progress to weakness, paralysis and the horse going down
The horse stays conscious and does not seem to be in pain
Spasm of the face muscles, the third eyelid sliding across the eye, drooling, and sweating while body temperature stays normal
Noisy breathing and blue gums as the throat muscles go slack and block the airway; trouble swallowing and a changed whinny
Heavy, well-developed muscling, sometimes very marked
Tiring quickly in work; attacks that can look like colic or staggering, or leave the horse sitting like a dog
In severe attacks, an abnormal heart rhythm and sudden death
Attacks often follow a change of feed, a period without food, a stressful event or a meal rich in potassium

None of these signs is unique to HYPP, and HYPP is not the same as tying up, colic or a seizure. Your veterinarian decides whether a horse is ill, using the history, the examination, blood results and this result.

Transmission

HYPP is dominant. One copy is enough to make a horse susceptible. The gene is not on a sex chromosome, so colts and fillies are affected equally.

What each mating can produce:

n/n x n/n gives 100% n/n
n/n x n/H gives 50% n/n, 50% n/H
n/n x H/H gives 100% n/H
n/H x n/H gives 25% n/n, 50% n/H, 25% H/H
n/H x H/H gives 50% n/H, 50% H/H
H/H x H/H gives 100% H/H

Prevention

There is no cure. The result guides two things.

Breeding. Only a mating between two horses that tested negative is sure to give no affected foals. Breeding from positive horses is not recommended.

Managing a positive horse. The measures reported are:

A diet low in potassium, with grass hay rather than alfalfa
Regular smaller meals instead of large irregular ones, and no sudden changes of feed
Salt available at all times
Daily exercise and turnout instead of long spells in a stable
Telling your veterinarian and anaesthetist the result before any operation, because general anaesthesia can set off an attack

Some medicines that make the horse pass more urine have been reported to make attacks less frequent and less severe. Horses with two copies have been managed with medical and surgical treatment. Your veterinarian sets the diet, monitoring and any treatment.

Results

n/n: negative. No copy of the HYPP variant. Cannot pass it on.

n/H: positive, one copy. The horse is affected, not only a carrier, though it can go a long time without an attack. Can pass the variant on.

H/H: positive, two copies. The most severe form of the disease. Passes the variant to every foal.

Sample

Hair roots: 20 to 40 hairs pulled (not cut) from the mane or tail, with the roots attached. Tape them inside the marked area of the printable sample submission form. Hairs without roots cannot be analysed.

Blood: 5 mL of whole blood in a K3-EDTA tube, collected by a veterinarian. Label the tube with the horse's name and send it with the submission form.

Keep samples dry and at room temperature, and do not freeze them. Do not send hair that is wet, mouldy or soiled with bedding or faeces.

Turnaround

Standard processing: results within 5 to 10 working days of the sample arriving at the laboratory. Shipping is arranged and paid for by the client, and transit time is not included in the 5 to 10 working days.

Samples that fail DNA extraction or amplification are repeated at no extra cost, which may add a few working days. We contact you if a new sample is required.

How it works

🛒 Buy the test: select and buy the test online.

📧 Receive the instructions: after payment is confirmed, you receive the sample collection instructions by e-mail.

📄 Complete the form: print and complete the submission form with the animal’s identification.

✨ Collect the sample: pull 20 to 40 hair roots with the bulb and stick them in the marked area of the form, or ask your veterinarian to collect blood in a K3-EDTA tube.

📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.

📊 Receive the report: the certified report is issued as soon as the analysis is validated.

FAQs

At what age can a horse be tested?
Any age, from newborn foal to adult. The genotype never changes, so one test lasts for life. For young foals, tail hair is usually easiest.

Does a negative result mean my horse cannot have tremors or weakness?
No. This test looks only for HYPP. It does not detect PSSM1, Malignant Hyperthermia or other muscle diseases, and tremors, weakness and collapse have other causes too.

For Professionals

Genetic and clinical detail for veterinarians, geneticists and laboratories.

Gene / locus: SCN4A (sodium voltage-gated channel alpha subunit 4, skeletal muscle), ECA11.
Variant: F1416L (Phe1416Leu), missense. HGVS (EquCab3.0): NC_009154.3:g.15474228C>G; NM_001081761.1:c.4248C>G; NP_001075230.1:p.(Phe1416Leu).
Alternative designations: H allele (OMIA allele symbol); Impressive syndrome, after the founder stallion.
Variant identifiers: rs1148998534 (EVA); OMIA variant 162.
Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
Mechanism: impaired sodium channel inactivation (Cannon et al., 1995). Persistent sodium influx leaves the muscle membrane hyperexcitable. The defect is unmasked by rises in serum potassium, which links episodes to feeding.
Evidence of causality: complete co-segregation of SCN4A with HYPP in families (Rudolph et al., 1992b), followed by identification of the causal variant (Rudolph et al., 1992a). This was the first equine disease with an identified causal variant.
Inheritance: autosomal incomplete dominant (OMIA code AID); homozygotes more severely affected than heterozygotes, described as co-dominant (Naylor et al., 1999).
Penetrance / expressivity: variable; most affected horses show no signs until mature and in training.
Breeds with documented carriers or cases: Quarter Horse (OMIA variant record), Quarter Horse crosses including Appendix Quarter Horses, and American Paint Horses of Quarter Horse descent. All carriers traced to a single founder, the Quarter Horse stallion Impressive, born 1969 (Bowling et al., 1996). The variant spread through selection for heavy muscling. The Appaloosa is not listed because no source was found.
Allele / carrier frequencies: allele frequency by discipline in American Quarter Horses (Tryon et al., 2009; 651 elite performance and 200 control horses): 0% in cutting, working cow, reining and racing; 0.6% in barrel racing; 1.3% in western pleasure; 29.9% in halter; 0.8% in the general Quarter Horse population. Allele frequency 31.8% in halter horses, with no change over time in the random cohort (Brown et al., 2026; 300 performance horses across seven disciplines and 300 random Quarter Horses born 2020 to 2024).
Homozygote phenotype: in Naylor et al. (1999), all 9 H/H horses had respiratory stridor, usually within the first week of life; 5 had dysphagia, 3 ptyalism and 3 weight loss. Six of the 9 died or were euthanised (4 before one year, 1 at 20 months, 1 at five years). Of 35 contemporaneous half siblings, 1 had stridor before weaning and none had dysphagia. On potassium challenge, H/H horses showed ptyalism, third eyelid prolapse, stridor and weakness far more often than n/H horses.
Clinical / diagnostic notes for veterinarians: the DNA test has replaced potassium challenge (false negatives) and electromyography (abnormalities not specific to HYPP). Muscle biopsy is not diagnostic for HYPP but can help exclude other myopathies. Hyperkalaemia has other causes, and serum potassium can be falsely raised by the sample itself. The American Quarter Horse Association treats HYPP as a defect, does not register H/H horses and registers n/H horses.

Key references:

Rudolph JA, Spier SJ, Byrns G, Rojas CV, Bernoco D, Hoffman EP (1992a). Periodic paralysis in Quarter Horses: a sodium channel mutation disseminated by selective breeding. Nat Genet 2:144-147. doi:10.1038/ng1092-144. PMID 1338908.
Rudolph JA, Spier SJ, Byrns G, Hoffman EP (1992b). Linkage of hyperkalaemic periodic paralysis in Quarter Horses to the horse adult skeletal muscle sodium channel gene. Anim Genet 23:241-250.
Cannon SC, Hayward LJ, Beech J, Brown RH Jr (1995). Sodium channel inactivation is impaired in equine hyperkalemic periodic paralysis. J Neurophysiol 73:1892-1899.
Naylor JM, Nickel DD, Trimino G, Card C, Lightfoot K, Adams G (1999). Hyperkalaemic periodic paralysis in homozygous and heterozygous horses: a co-dominant genetic condition. Equine Vet J 31:153-159.
Bowling AT, Byrns G, Spier S (1996). Evidence for a single pedigree source of the hyperkalemic periodic paralysis susceptibility gene in Quarter Horses. Anim Genet 27:279-281.
Tryon RC, Penedo MCT, McCue ME, Valberg SJ, Mickelson JR, Famula TR, Wagner ML, Jackson M, Hamilton MJ, Nooteboom S, Bannasch DL (2009). Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. J Am Vet Med Assoc 234:120-125. doi:10.2460/javma.234.1.120.
Brown BN, Hughes S, Le TM, Tatar NP, Grahn JC, Carrillo-Alvarez M, Bellone RR, Finno CJ (2026). Allele frequencies of 7 inherited disorders in performance and random cohorts of American Quarter Horses (2020-2024). J Am Vet Med Assoc 1-7. doi:10.2460/javma.26.04.0256.