Polysaccharide storage myopathy or PSSM is a muscle disease that occurs primarily in horses with Quarter Horse bloodlines such as Quarter Horses, Paint Horses, and Appaloosas. PSSM also occurs in other breeds including Drafts, Draft crossbreeds, and Warmbloods. The primary clinical sign of this disease is muscle cramping or tying-up; however, clinical signs may vary with different breeds and severity. There are several different abbreviations used to describe polysaccharide storage myopathy including PSSM, EPSM and EPSSM. Tying-up also occurs in other breeds of horses such as Thoroughbreds and Standardbreds, but this form of tying-up has a different cause.