Hyperkalemic Periodic Paralysis (HYPP)
HYPP, Impressive Syndrome
Hyperkalemic Periodic Paralysis (HYPP) is a genetic disorder affecting muscle fiber contraction that has been traced back to a horse named Impressive. Symptoms of HYPP can include muscle twitching, respiratory noises, and unpredictable paralysis attacks. Episodes can range in severity from unnoticeable to collapse or even sudden death caused by respiratory failure or cardiac arrest. The mutation responsible for the disease affects pores in the muscle cell membrane that controls muscle fiber contractions. These pores can become “leaky” in the presence of fluctuating potassium levels that can occur with fasting followed by consumption of high potassium feed such as alfalfa. This causes the horse’s muscles to contract more than normal and makes them susceptible to episodes of muscle tremors and paralysis. Horses that have two copies of the mutation are more severely affected than horses with one copy of the mutation. HYPP attacks can be confused with other conditions like “Tying-up” syndrome but can be differentiated. Horses that suffer an HYPP attack typically appear normal following the episode and the attack typically occurs when the horse is at rest as opposed to following exercise. HYPP attacks can also be confused with colic or seizure but the horse is typically conscious and aware of its surroundings and do not appear to be in pain. Long term management of the disease include exercise and diet control that avoid high potassium feeds, feeding several times a day, and frequent access to paddocks or yards for exercise.
Reading Your Results
A. (CLEAR/NORMAL):
These horses have two copies of the normal gene and will neither develop Hyperkalemic Periodic Paralysis nor pass this mutation to their offspring.
B. (CARRIER/NOT AFFECTED):
These horses have one copy of the normal gene and one copy of the mutation associated with this disease. They will develop Hyperkalemic Periodic Paralysis which typically results in muscle twitching, respiratory noises, and unpredictable paralysis attacks and will, if bred, pass the mutation to 50% of its offspring, on average.
C. (AT RISK/AFFECTED):
These horses have two copies of the mutation associated with Hyperkalemic Periodic Paralysis which typically results in muscle twitching, respiratory noises, and unpredictable paralysis attacks.
Additional Details
Inheritances
Autosomal Dominant
Affected gene
SCN4A
Chromosome
Ch. 11
Mutation
c.4248C>G; p.F1416L
Publication:
Rudolph JA, Spier SJ, Byrns G, Rojas CV, Bernoco D, Hoffman EP. Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding. Nat Genet. 1992;2(2):144-147. [PubMed: 1338908].
