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Polysaccharide Storage Myopathy 1 (PSSM1)
| Acronym: | PSSM1 |
| Gene: | GYS1 |
| Mutation: | g.19203501C>T |
| Inheritance: | Autosomal Dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Polysaccharide storage myopathy (PSSM) is an inherited glycogen storage disease that affects several breeds of horses. Horses with PSSM accumulate excess glycogen in skeletal muscles which causes muscle atrophy, breakdown of muscle fibers and severe pain that leads to progressive weakness, gait abnormalities and the inability to rise. PSSM is caused by a genetic mutation in glycogen synthase 1 (GYS1) gene which is responsible for converting glucose to glycogen in skeletal muscles. The missense mutation in GYS1 gene causes higher protein activity that results in the excess production of abnormal glycogen that cannot be properly used as an energy source.
PSSM is inherited as an autosomal dominant trait, therefore only one copy of the mutation is needed for a horse to be affected. However, horses homozygous for the mutation are reported to show more severe symptoms. PSSM affects more than 20 breeds such as Quarter horses, Paints, Appaloosas and draft breeds. The disease is incurable, but early detection by genetic testing can help with managing of the symptoms through diet and exercise, as well as with the prevention of further breeding.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
AFFECTED HETEROZYGOTE |
Tested mutation was detected in animal with „affected heterozygote“ result. Animal tested as affected heterozygote has one wild-type and one mutation allele, it is in heterozygous state. It is likely to develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
**Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
McCue, M. E., Valberg, S. J., Miller, M. B., Wade, C., DiMauro, S., Akman, H. O., & Mickelson, J. R. (2008). Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics, 91(5), 458–466. doi:10.1016/j.ygeno.2008.01.011
Stanley, R. L., Mccue, M. E., Valberg, S. J., Mickelson, J. R., Mayhew, I. G., Mcgowan, C., … Piercy, R. J. (2009). A glycogen synthase 1 mutation associated with equine polysaccharide storage myopathy and exertional rhabdomyolysis occurs in a variety of UK breeds. Equine Veterinary Journal, 41(6), 597–601.