HYPP: Hyperkalemic periodic paralysis( HYPP) is characterized by sporadic attacks of muscle tremors( shaking or trembling), weakness, and / or collapse. Attacks can also be accompanied by loud breathing noises resulting from paralysis of the muscles of the upper airway. Occasionally, sudden death can occur following a severe paralytic attack, presumably from heart failure or respiratory muscle paralysis.
Manifestation of clinical signs of HYPP depends on many factors including stress, diet, and changes in exercise. Some horses may manifest severe signs of the disease while others exhibit little or no signs.
• Horses with N / N genotype will not have hyperkalemic periodic paralysis and cannot transmit this hyperkalemic periodic paralysis variant to their offspring.
• Horses with N / H genotype can display episodes of hyperkalemic periodic paralysis and are Carriers. They may transmit this hyperkalemic periodic paralysis variant to 50 % of their offspring.
• Horses with H / H genotype can display episodes of hyperkalemic periodic paralysis and typically are more severely affected. They will transmit this hyperkalemic periodic paralysis variant to all of their offspring.
• HYPP carriers are not registerable with the AQHA unless spayed or gelded.
PSSM1: Horses with Type 1 Polysaccharide Storage Myopathy( PSSM1) have a muscle disease characterized by accumulation of abnormal complex sugars( glycogen) in skeletal muscles. The accumulation of abnormal sugars can cause breakdown of muscle fibers( rhabdomyolosis) which leads to muscle pain, weakness, skin twitching, sweating, and reluctance to move.
• Horses with N / N genotype will not have type 1 Polysaccharide Storage Myopathy and cannot transmit the PSSM1 variant to their offspring.
• Horses with N / PSSM1 genotype will have the PSSM1 variant and may show signs of type 1 disease. Horses with this genotype may transmit the PSSM1 variant to 50 % of their offspring.
• Horses with PSSM1 / PSSM1 genotype are homozygous for the PSSM1 variant and may be more severely affected than N / PSSM1 horses. Horses with this genotype will transmit the PSSM1 variant to all of their offspring.
MH: Malignant hyperthermia( MH) is an inherited disease in which affected horses can be triggered by halogenated
anesthetics, succinylcholine, stress, or excitement, which can induce a hyper-metabolic state characterized by symptoms including muscle contracture, elevated temperature, and an irregular heart rhythm.
• Horses with N / N genotype will not have malignant hyperthermia and cannot transmit this malignant hyperthermia variant to their offspring.
• Horses with N / MH genotype will be affected by malignant hyperthermia. They can transmit this malignant hyperthermia variant to their offspring. Matings with N / N genotype will result in a 50 % chance of producing a malignant hyperthermia-affected foal.
• Horses with MH / MH genotype will have malignant hyperthermia.
GBED: Glycogen branching enzyme deficiency( GBED) is a fatal genetic disorder that results from the inability to correctly store glycogen in several organs of the body.
• Horses with N / N genotype will not have glycogen branching enzyme deficiency and cannot transmit this glycogen branching enzyme deficiency variant to their offspring.
• Horses |
with |
N / GED |
genotype |
will |
not |
be |
affected |
by |
glycogen |
branching |
|
enzyme |
deficiency, but are carriers. |
They |
may |
transmit |
this |
GBED variant to 50 % of their |
offspring. |
• Matings between two carriers result in a 25 % chance of producing a
GBED-affected foal.
• Horses with GBED / GBED genotype will have glycogen branching enzyme deficiency, a fatal condition.
MYHM: Myosin-heavy chain myopathy( MYHM) is a muscle disease that results in two distinct clinical disease presentations, immune-mediated myositis( IMM) and nonexertional rhabdomyolysis. Both presentations involve muscle loss or damage and are linked to the same genetic variant.
• Horses with N / N genotype will not have increased susceptibility for a myosin-heavy chain myopathy and cannot transmit the MYHM variant to their offspring.
• Horses with N / My genotype may develop a myosin heavy chain myopathy. They may transmit this MYHM variant to 50 % of their offspring. Matings to horses with the N / N genotype will result in a 50 % chance of producing a foal that may develop myosin-heavy chain myopathy.
• Horses with My / My genotype may develop a more severe form of a myosin-heavy chain myopathy. They will transmit this MYHM variant to all of their offspring.
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INFORMATION: https:// vgl. ucdavis. edu / then SEARCH and / or: CONTACT THE REGISTRAR: qhorse @ aqha. com. au • P: 02 6762 6444
2025 JULY / AUGUST ISSUE