Hyperkalemic periodic paralysis / HYPP (SCN4A-related) - Horse

What does this test analyse?

This genetic test analyses the SCN4A c.4248C>G variant in horses. The condition is also known as hyperkalemic periodic paralysis, HYPP, hyperkalaemic periodic paralysis, hyperkalemic periodic weakness and an inherited sodium-channel disorder.

What does it mean for the horse?

SCN4A encodes a sodium channel in skeletal muscle. The HYPP variant changes muscle-cell excitability. Affected horses can experience episodes of muscle trembling, weakness, collapse, breathing difficulty and increased potassium. Severity varies, but the genotype is directly important for management, selection and breeding decisions.

HYPP is best known in Quarter Horse-related lines and can also be relevant in related breeds with shared ancestry. The test clarifies whether a horse is clear, carries one copy or carries two copies.

Practical value of this test

• Detects the known SCN4A c.4248C>G variant.
• Distinguishes N/N, N/H and H/H.
• Helps breeders plan matings and limit spread of the HYPP allele.
• Provides owners and veterinarians with clear genetic information when muscle weakness or attack-like episodes occur.

Inheritance and result

HYPP is inherited as autosomal incomplete dominant. One copy can already cause HYPP. Two copies usually create a higher genetic risk and a heavier inherited burden than one copy.