Equine polysaccharide storage myopathy

Glycogen spacefilling model

Equine Polysaccharide Storage Myopathy (EPSM or PSSM) is a muscle disease affecting horses. It is characterized by the abnormal accumulation of complex sugars (polysaccharides) in the muscles of affected horses. This condition leads to various clinical signs, primarily related to muscle stiffness, weakness, and pain, which can significantly impact a horse's performance and quality of life.

Causes and Pathophysiology

EPSM is primarily caused by a genetic predisposition in certain horse breeds, including Draft horses, Quarter Horses, and Warmbloods. The disease is linked to a mutation in the GYS1 gene, which plays a crucial role in glycogen synthesis. This mutation leads to the abnormal accumulation of an unusual form of polysaccharide in the muscle cells, which interferes with normal muscle function.

Symptoms

The clinical signs of EPSM can vary widely among affected horses but typically include:

• Muscle stiffness and soreness
• Reluctance to move
• Tying-up (rhabdomyolysis)
• Weakness and muscle wasting
• Recurrent episodes of colic
• Shifting lameness

Diagnosis

Diagnosis of EPSM is based on clinical signs, history, and specific diagnostic tests. Muscle biopsy is the definitive diagnostic test, where samples are examined for the characteristic polysaccharide accumulations. Additionally, genetic testing can identify horses with the GYS1 mutation, aiding in the diagnosis and management of the condition.

Treatment and Management

There is no cure for EPSM, but the condition can be managed effectively with dietary and lifestyle modifications. Key management strategies include:

• High-fat, low-starch diets to provide energy sources that do not exacerbate the condition
• Regular, gentle exercise to promote muscle function and reduce stiffness
• Avoiding stress and situations that may trigger symptoms

Prevention

Preventive measures for EPSM focus on breeding practices. Genetic testing of potential breeding animals can help reduce the incidence of the disease by identifying carriers of the GYS1 mutation.

Conclusion

Equine Polysaccharide Storage Myopathy is a significant health concern in susceptible horse breeds. While it poses challenges to management and care, understanding the genetic basis and implementing appropriate dietary and exercise regimens can help affected horses lead comfortable and productive lives.

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