PSSM1 (Polysaccharide Storage Myopathy 1 Horse)
Polysaccharide storage myopathy (PSSM1) is a degenerative muscle disease caused by a disorder of sugar metabolism. Affected horses show symptoms such as reluctance to move, muscle tremors and tension.
The disease occurs in many breeds. The inheritance is incomplete autosomal dominant.
Genetic Test: available in Shop
- Reluctance to move
- Atactic gait/coordination problems
- Muscle tremors
- Frequent tying up/tension
- Excessive sweating
- Gait changes (cross firing or disunited canter/bunny hopping/rope walking)
- Polysaccharide Storage Myopathy Typ 1 (PSSM1) is a degenerative muscle disease that manifests itself in a disorder of the sugar metabolism of the muscles.
- Excessive activity of the enzyme glycogen synthetase 1 → Abnormal accumulation of glycogen granules in muscle cells.
- Symptoms usually occur during/shortly after physical exercise.
Genotype and Lab Report
Inheritance: incomplete autosomal dominant/semidominant
→ Horses with one or two copies of the variant (n/P1 or P1/P1) are affected. Incomplete or semidominant means that animals with one copy (n/P1) may show milder symptoms and a later age of onset than animals with two copies (P1/P1).
n/n = normal
The horse does not have a copy of P1 and therefore cannot pass it on to any offspring.
n/P1 = affected (heterozygous)
The horse has one copy of P1 and will pass it on to approximately 50% of its offspring. These 50% are at risk of developing PSSM1.
P1/P1 = affected (homozygous)
The horse has two copies of P1 and will pass it on to 100% of its offspring. All offspring will be at risk of developing PSSM1.
Affected horses (n/P1 or P1/P1) should only be bred after careful consideration and with the advice of a genetic expert and veterinarian. Please contact us for consultation and support.
McCue, ME., Valberg, SJ., Lucio, M., Mickelson, JR. :
Glycogen synthase 1 (GYS1) mutation in diverse breeds with polysaccharide storage myopathy. J Vet Intern Med 22:1228-33, 2008. Pubmed reference:18691366. DOI:10.1111/j.1939-1676.2008.0167.x
McCoy, A.M., Schaefer, R., Petersen, J.L., Morrell, P.L., Slamka, M.A., Mickelson, J.R., Valberg, S.J., McCue, M.E. :
Evidence of Positive Selection for a Glycogen Synthase (GYS1) Mutation in Domestic Horse Populations. J Hered :, 2013. Pubmed reference: 24215078. DOI: 10.1093/jhered/est075.
McCue, ME., Valberg, SJ., Miller, MB., Wade, C., Dimauro, S., Akman, HO., Mickelson, JR.: Glycogen synthase (GYS1) mutation causes a novel skeletal muscle glycogenosis. Genomics 91:458-66, 2008. Pubmed reference: 18358695. DOI:10.1016/j.ygeno.2008.01.011.
Further information is available at Online Mendelian Inheritance in Animals.