A glycogen synthase 1 mutation associated with equine polysaccharide storage myopathy and exertional rhabdomyolysis occurs in a variety of UK breeds.

The research article discusses a study conducted to determine if a specific mutation, known as the glycogen synthase (GYS1) mutation, associated with a disease known as polysaccharide storage myopathy (PSSM) and exertional rhabdomyolysis, is present in horses from the UK. The study found that the mutation is indeed present in a variety of UK horse breeds.

Objective and Methodology

The main objective of the study was to investigate whether the GYS1 mutation, previously found in horses with PSSM in the United States, was also present in UK horses showing similar symptoms. An additional objective was to confirm if this mutation is commonly associated with exertional rhabdomyolysis, a muscle disease related to exercise.

• The researchers conducted their study by extracting DNA from 47 samples of muscle or blood from UK horses that had histories of exertional rhabdomyolysis and had been biopsied for diagnosis.
• The percentage of horses testing positive for the GYS1 mutation was compared among different groups categorized by their histopathological characteristics.
• The study also identified the breeds carrying the GYS1 mutation, from a total of 37 horses diagnosed with grade 2 (amylase-resistant) PSSM.

Results

• Out of 47 horse samples, 10 (i.e. 21%) were found to carry the GYS1 mutation. The study confirmed that this mutation was only present in horses with a diagnosis of grade 2 PSSM, and not in horses with normal or other types of myopathy.
• The total prevalence of the GYS1 mutation was found to be high—65%—among horses with grade 2 PSSM.
• A range of breeds, such as Quarter Horse, Appaloosa, Warmblood, Connemara-cross, Cob, Polo Pony and Thoroughbred cross were identified as carrying the mutation.

Conclusions

• The GYS1 mutation is a significant cause of exertional rhabdomyolysis in UK horse breeds. However, it does not account for all forms of PSSM.
• Genotyping—the process of determining differences in the genetic make-up of an individual—is recommended for cases of exertional rhabdomyolysis, either before or in combination with muscle biopsy. However, it is important to note that a significant proportion of horses showing histopathological evidence of PSSM and/or exertional rhabdomyolysis have different diseases.