Which diagnostic finding distinguishes PSSM Type 1 from PSSM Type 2?

Which diagnostic finding distinguishes PSSM Type 1 from PSSM Type 2?

• A. GYS1 mutation presence
• B. Positive muscle biopsy
• C. Age at onset
• D. History of response to diet

Answer: (A)

The main idea is that PSSM Type 1 is defined by a genetic mutation in the GYS1 gene, while Type 2 does not have this mutation. Detecting the GYS1 mutation provides a definitive genetic distinction: if the mutation is present, the horse is classified as PSSM Type 1; if it’s absent, the classification is Type 2. Muscle biopsy findings can be similar in both forms, so they aren’t reliable on their own for distinguishing them. Age of onset and response to diet can vary and aren’t consistent discriminators, since both types can present similarly and respond to dietary management. Thus, the presence of the GYS1 mutation is the best diagnostic discriminator.

The main idea is that PSSM Type 1 is defined by a genetic mutation in the GYS1 gene, while Type 2 does not have this mutation. Detecting the GYS1 mutation provides a definitive genetic distinction: if the mutation is present, the horse is classified as PSSM Type 1; if it’s absent, the classification is Type 2. Muscle biopsy findings can be similar in both forms, so they aren’t reliable on their own for distinguishing them. Age of onset and response to diet can vary and aren’t consistent discriminators, since both types can present similarly and respond to dietary management. Thus, the presence of the GYS1 mutation is the best diagnostic discriminator.