- Written by: Sharalee Worms
MFM P3 
Genetic Testing is Available
MFM is Myofibrillar Myopathy - it is dominant disease
MFM symptoms include exercise intolerance, tying up, pain, stiffness and tremors, heavy sweating, and in severe cases an inability to stand. Another symptom is very dark coffee colored urine. All of these signs often come after exercise and/or high stress.
MFM can be seen clearly on a muscle biopsy.
Horses that carry one copy of either P3 or P4 have a predisposition to develop MFM (also diagnosed as PSSM2). Horses with two copies of the variant (P3/P3 or P4/P4) have stronger symptoms and the symptoms show up when the horses are younger.
Treatment includes a high portein diet and a specific exercise plan.
- Written by: Sharalee Worms
MFM P4 Genetic Testing is Available
MFM is Myofibrillar Myopathy - it is dominant disease
MFM symptoms include exercise intolerance, tying up, pain, stiffness and tremors, heavy sweating, and in severe cases an inability to stand. Another symptom is very dark coffee colored urine. All of these signs often come after exercise and/or high stress.
MFM can be seen clearly on a muscle biopsy.
Horses that carry one copy of either P3 or P4 have a predisposition to develop MFM (also diagnosed as PSSM2). Horses with two copies of the variant (P3/P3 or P4/P4) have stronger symptoms and the symptoms show up when the horses are younger.
Treatment includes a high portein diet and a specific exercise plan.
P3 and P4 are used to signify MFM at this time.*
*Researchers at EquiSeq have identified semidominant alleles of two genes that causes MFM in Thoroughbreds and related breeds. The results are not yet published in a peer-reviewed academic journal. Prior to publication, the variants have been termed P3 and P4.
You can get your horse tested for P4 at Equiseq.com
- Written by: Sharalee Worms
Genetic Testing is AvailableSCID foals have a defect in their immune system - the look normal as foals as long as they receive antibodies from the mares colostrum but will die within six months from infections that they cannot fight.
- Written by: Sharalee Worms
PSSM1 is Polysaccharide Storage Myopathy - it is a dominant disease Genetic Testing is Available
PSSM has many symptoms includung exercise intolerance, tying up, pain, stiffness, and tremors, and sweating profusely. Muscles are often damaged during episodes. Some cannot stand after an episode and death can occur. Many PSSM symptoms are confused for normal horse behavior - eg.s bucking, rolling, biting at the cinch, colic, stretching, camped out stance, Jekyll and Hyde personality.
Treatment starts with eliminating all sugar from the diet and progresses to adding other supplements, including fat. Regular exercise can help manage symptoms.
PSSM1 is seen in Quarter Horses, Paints, Appaloosas and crossbreds of these breeds, as well as Percherons, Belgian Drafts, Selle Francais, Trekpaard, Comtois, and Bretons
PSSM1 is one of the required tests in the 5 panel of tests required by all Quarter Horse breeding stallions.
Some horses that have been described as "hard to start", moody, grumpy, or "just need miles" suffer from PSSM. Symptoms include weird things like flipping in cross ties, being "cinchy, rock hard tense muscles, mysterious lameness, hard to get on a certain lead, bucking when they lope, trouble standing for the farrier, and many other strange symptoms including the major one - tying up - that many horses experience at one time or another, but the PSSM horse is plagued by them.
Genetic Testing is Available
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- How and Where can I test for it? PSSM1 is very easy to test for and you can do it yourself. It involves pulling hair (for detailed instructions click here) and sending the hair sample to a lab that tests for it. If you have a reg AQHA or APHA horse you are intending to breed at some point it is recommended to test through those particular breed registries so that their results will be recorded in your horses file at the registry. For Stallions AQHA requires a 5 panel test before any foals can be registered and they only recognize tests done through their preferred lab.
You can test for PSSM1 through animalgenetics.com
BRIDGE has a pretty good success rate with analysing PSSM1 in pedigrees. There is still the odd horse that tests Positive and comes as a surprise but these are very few and hopefully get fewer the more info we get entered.
BRIDGE is trying to shed light on these bloodlines by asking anyone with a PSSM positive horse to send their info to BRIDGE (email: foals@manitobahorse.com) or contact us through facebook so we can add the bloodlines to our database to help show a clear picture of which horses have the bloodlines which are carrying this. If you prefer to have your info kept private you can still send it to us and we will keep it in our Private Database and use it for research otherwise it will go into the online database available to registered members.
- Written by: Sharalee Worms
Horses that test negative for PSSM1 but have strong PSSM symptoms are tested for PSSM 2, now referred to as MIM.
Previously the only way to test for PSSM2 was with an invasive muscle biopsy, and many still choose to have this test done.
The equine genetic world is advancing rapidly and there is a company pursuing testing for PSSM2 . To date they have found a few different variants which predispose a horse for PSSM2 and a hair test is now publicly available (in the USA) to test for the P2, P3, P4 and PX (RER). They are working on other variants as well and can test for P5/P6, P8 and K1.
Please contact Equiseq.com for more info on testing. If you are outside the USA you can order a test from Equiseq and they will send you a card to send back to them with a dried blood sample. The tests are fairly costly at this point as all new genetic testing is at first but the company's main focus is still on finding and developing tests for more variants. They have your horse's best interest at heart.
Many breeders are still not testing for PSSM2 and most testing is being done because a horse is showing symptoms and the owner is looking for answers. In the future as costs come done breeders will routinely test for all of the PSSM variants.
The symptoms for PSSM 2 are very similar to PSSM 1 and are often more severe. We recommend testing first for PSSM 1 and then if that comes back negative, pursue a PSSM2 diagnosis.
There is more info on the Specific PSSM 2 variants P2, P3, P4, and also on PX in the main menu above Genetic Diseases > PSSM > PSSM2 > and click the variant you wish to see more info on.
BRIDGEquine has many tested PSSM2 horses in the database. We do not have specific source horses yet but can predict fairly well whehter a horse is more likely to be PSSM1 positive or PSSM2 positive. If you are wondering what to test for asking BRIDGE to analyze your pedigree is an excellent way to decide where to start testing.