Polysaccharide storage myopathy.

The research paper discusses two types of Polysaccharide Storage Myopathy (PSSM) – a dominant genetic disorder affecting various horse breeds. The study reveals that both types (PSSM1 and PSSM2-ER) respond favorably to a specific diet and regular exercise and provides details about their symptoms, diagnosis, and treatment.

Polysaccharide Storage Myopathy (PSSM)

• Polysaccharide Storage Myopathy (PSSM) is a dominant genetic disorder affecting a significant number of horse breeds. The disease is characterized by excessive accumulation of glycogen (a form of sugar) in the muscle tissues of horses, leading to diverse signs such as Exertional Rhabdomyolysis (ER), a condition causing severe muscle damage triggered by intense exercise.
• The research paper particularly focusses on two types of PSSM: Type 1 (PSSM1) and Type 2 (specifically the ER subtype PSSM2-ER).

Type 1 Polysaccharide Storage Myopathy (PSSM1)

• PSSM1 affects over 20 horse breeds and can exhibit a variety of symptoms, with ER being one of the common ones. It is an autosomal dominant disorder; in other words, only one copy of the affected gene is enough to cause the disease.
• Diagnosis of PSSM1 involves genetic testing or muscle biopsies that demonstrate muscle fibers with abnormally resistant polysaccharides, indicating excess glycogen storage.

Type 2 Polysaccharide Storage Myopathy (PSSM2-ER)

• PSSM2-ER is a subtype of PSSM2 and has been identified as causing ER in Quarter Horses, a specific horse breed. The genetic basis of PSSM2-ER is not well understood yet, leading to diagnosis through muscle biopsy instead of genetic testing.
• Despite the lack of genetic understanding, PSSM2-ER is acknowledged as a glycogen storage disorder, much like PSSM1.

Treatment for PSSM

• Both PSSM1 and PSSM2-ER have shown positive responses to specific dietary changes paired with consistent exercise. A diet low in nonstructural carbohydrates (sugars not bound in plant cell walls) and high in fats seems to be beneficial in managing the symptoms of the PSSM disease.
• However, the researchers mention that further information and more detailed discussion on treating these PSSM forms are presented in the main article.