What is HYPP?

• A. Hyperkalemic Periodic Paralysis
• B. Hypokalemic Periodic Paralysis
• C. Hyperactive Periodic Paralysis
• D. Hyperkalemic Paroxysmal Paralysis

Answer: (A)

HYPP stands for Hyperkalemic Periodic Paralysis. This is a hereditary condition in Quarter Horses (and related lines) where episodes of muscle weakness occur due to elevated potassium levels in the blood. The name reflects two features: high potassium (hyperkalemia) and intermittent weakness (periodic/paroxysmal paralysis). It stems from a genetic mutation affecting muscle cell sodium channels, which makes muscles temporarily unresponsive to nerve signals when potassium is high. Triggers can include stress, fasting, dehydration, or anesthesia. The other options describe either the wrong electrolyte imbalance (low potassium) or use a nonstandard term for this condition. The established, widely used name is Hyperkalemic Periodic Paralysis.