Polysaccharide Storage Myopathy (PSSM) Disease Explained

Speaker:
Dr. Stephanie Valberg, DVM, PhD, is the Mary Anne McPhail Dressage Chair in Equine Sports Medicine at Michigan State University. Dr. Valberg’s research centers on neuromuscular diseases in horses with a special focus on genetic diseases of skeletal muscle and their nutritional management.
Polysaccharide storage myopathy (PSSM) is a muscle disease that causes horses to develop muscle pain, tying-up and exercise intolerance. To date two forms of PSSM are described: type 1 and type 2. Type 1 PSSM is caused by a genetic mutation in the glycogen synthase 1 gene which causes excessive storage of sugar (glycogen) in skeletal muscle. Clinical trials have shown that horses with type 1 PSSM respond well to low starch, high fat diets and regular exercise. Much less in known about type 2 PSSM since the cause or causes have yet to be determined and clinical trials have not been performed to study diet and exercise responses. Our Equine Neuromuscular Diagnostic Laboratory has received muscle biopsies from hundreds of horses diagnosed with type 2 PSSM based on the microscopic appearance of glycogen in muscle samples. We asked horse owners to provide us with information on how well their horses responded to diet and exercise recommendations. Our goal with the November 14th webinar is to describe the symptoms reported for horses diagnosed with type 2 PSSM by muscle biopsy and to review the information we have analyzed from responses provided by horse owners. This is our chance to thank the owners of type 2 PSSM horses that took the time to answer our questions and share their experiences with other owners.