If a mare tests positive for PSSM on muscle biopsy but is negative for the GYS1 mutation, which statement about breeding is most accurate?

If a mare tests positive for PSSM on muscle biopsy but is negative for the GYS1 mutation, which statement about breeding is most accurate?

• A. There is no risk of affected foals
• B. PSSM is not inherited
• C. PSSM Type 2 is a genetic disease, so you may end up with an affected foal
• D. Breeding is safe in all cases

Answer: (C)

PSSM can have a genetic basis beyond the GYS1 mutation. If a mare has a biopsy showing PSSM but tests negative for the GYS1 mutation, she likely has PSSM type 2, which is considered to have genetic underpinnings even if the exact mutation isn’t the GYS1 variant. Because there is a genetic component, breeding to another horse with PSSM susceptibility can yield foals that are affected or carry the risk. So, the likelihood of producing an affected foal is real, and breeding is not guaranteed to be risk-free. That’s why the most accurate statement is that PSSM Type 2 is a genetic disease, so you may end up with an affected foal. Options claiming there’s no risk, that PSSM isn’t inherited, or that breeding is safe in all cases don’t fit this genetic reality.

PSSM can have a genetic basis beyond the GYS1 mutation. If a mare has a biopsy showing PSSM but tests negative for the GYS1 mutation, she likely has PSSM type 2, which is considered to have genetic underpinnings even if the exact mutation isn’t the GYS1 variant. Because there is a genetic component, breeding to another horse with PSSM susceptibility can yield foals that are affected or carry the risk. So, the likelihood of producing an affected foal is real, and breeding is not guaranteed to be risk-free.

That’s why the most accurate statement is that PSSM Type 2 is a genetic disease, so you may end up with an affected foal. Options claiming there’s no risk, that PSSM isn’t inherited, or that breeding is safe in all cases don’t fit this genetic reality.