Polysaccharide Storage Myopathy (PSSM1)
PSSM1, ACDHA Polysaccharide Storage Myopathy Type 1
Polysaccharide Storage Myopathy (PSSM1) is a genetic disorder affecting glycogen storage that leads to chronic episodes of “tying-up”. The disease is caused by a mutation in the enzyme involved in the production of glycogen in muscle. In affected horses, an abnormal form of glycogen usually used as an energy storage source in muscle is improperly made and stored and hence is unable to be utilized following periods of exercise. Symptoms of the disorder can begin around 2 to 3 years of age and include unwillingness to move, muscle damage following exercise, skin twitching, stiffness, sweating, and weakness. Horses that have one or two copies of the mutation should be carefully managed through eliminating high-sugar foods in their diet and consistent exercise to prevent disease onset. Horses with one copy of the mutation seem to have more moderate symptoms while horses with two copies of the mutation are generally more severely affected and can be harder to manage with diet and exercise. One study has also found that horses with both the PSSM1 and MH mutations appear to exhibit more severe clinical symptoms. It is important to note that there are several forms of Polysaccharide Storage Myopathy including a type 2 form of the disease where the responsible mutation has yet to be identified.
Reading Your Results
A. (CLEAR/NORMAL):
These horses have two copies of the normal gene and will neither develop Polysaccharide Storage Myopathy Type 1 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 Polysaccharide Storage Myopathy Type 1 which typically results in chronic episodes of “tying-up” 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 Polysaccharide Storage Myopathy Type 1 which typically results in chronic episodes of “tying-up”.
Additional Details
Inheritances
Autosomal Dominant
Affected gene
GYS1
Chromosome
Ch. 10
Mutation
c.G>A; p.R309H
Publication:
McCue ME, Valberg SJ, Miller MB, et al. Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics. 2008;91(5):458-466. [PubMed: 18358695].
