The paper describing the Minnesota studies that have led to a genetic test for EPSM is out. Very interesting findings. For one thing, they have confirmed that Quarter horses with EPSM have the same problem as drafts with EPSM. Comparing the genetic test to muscle biopsy results, about 80% of biopsy positive Quarter horses tested positively. About 47.5% of all breeds with biopsy positive EPSM tested positively. So this genetic change, in the glycogen building enzyme of muscle (glycogen synthase), is a part of the puzzle, but not the whole answer. Like blood testing for muscle enzymes after exercise a positive genetic test confirms EPSM, but a negative one does not rule it out.

I just printed out the article and am looking forward to reading it!

Colleen in Baltimore

I did not read the article yet, so forgive me if the following is addressed there. It would be interesting to know whether those horses who test positive in the gene test are the same who test positive for muscle enzymes afer excercise. In other words, if some EPSM horses test positive for one and not the other, combining the gene test with the muscle enzyme test will increase your negative predictive value when using both tests instead of one (if both are negative it's more certain that a given horse does not have EPSM). What's your opinion on this, Dr Beth?

Good question Karen. From the data presented I can't be exactly sure, but I'm betting that the most likely horse to test positively will be one who is prone to tying up, and then yes, would also be likely to have high muscle enzymes after exercise. So I don't think that both being negative will really help.