PSSM 2

Muscle myopathies occur in all breeds of horses. Over the years some have been identified and a genetic test has been offered by AQHA through UC Davis. Please refer to the current 5 panel. A recent test MYH1 -Myosin Heavy Chain 1 has been proposed as number 6. These all carry a definitive negative or positive for the varaint tested. Remaining in the pool of muscle myopathies is PSSM2, RER and MFM. Dr Valberg, the recognized world expert, now at MSU, has made several very strong statements about a private sector company that first offered a definitive genetic test for the above diseases but has now dialed it back a bit.

The problem continues to be :

1. There is no license needed to offer tests on animals unlike the rigorous approval needed for humans

2. The private company has not established a definitive link between the varaints and the diseases.

3. The company has not disclosed the number of occurances in the healthy population (control group).

4. The company has not passed or even submitted findings for publication/ peer review.

5. The company's test is not all inclusive - cases of PSSM2 without said variants continue.

PSSM2 is much like diabetes 2 in humans in that environmental triggers are involved. I think many tests will be done to establish all of the factors.

These samples are too small to give a valid estimate of the frequency, so it is best to think of these results as scoring presence or absence in a limited sample across breeds.

Cleveland Bay (23) - P2, P3, no P4
Arabian (20) - P2, no P3, P4
Nepal (20) - P2, P3, no P4
Fell Pony (20) - P2, P3, no P4
Mangalarga (25) - P2, P3, no P4
Campolina (24) - P2, no P3, P4
Mangalarga Marchadore (24) - P2, P3, no P4
Konik (19) - P2, no P3, no P4
Caspian Pony (19) - P2, no P3, P4
Turkoman (22) - P2, P3, P4
Kurd (22) - P2, P3, P4
Selle Francois (22) - P2, P3, no P4
Suffolk (29) - P2, P3, no P4
Haflinger (29) - P2, no P3, P4
Akhal Teke (28) - P2, P3, P4
Peruvian Paso (25) - P2, no P3, P4
Exmoor Pony (32) - P2, no P3, no P4
Tennessee Walker (28) - P2, no P3, no P4
Percheron (4) - no P2, P3, no P4
Shetland Pony (24) - P2, P3, P4
Standardbred (24) - P2, no P3, no P4
Norwegian Fjord (12) - no P2, no P3, no P4
Shire (25) - P2, P3, no P4
Highland Pony (24) - P2, no P3, no P4
Icelandic (20) - no P2, no P3, no P4

WHEN A VARAINT IS FOUND IN NUMEROUS BREEDS IT IS AN INDICATION THAT THE VARIANT HAS BEEN WITH THE EQUINE SPECIES BEFORE BREED DEFINITION OCCURRED.

Equiseq

These are Equiseq's Terms of Service (April 2018)

This is their revised test.

In Conclusion (May 2018) - there is no defintive genetic test for PSSM2, MFM, RER. Until peer review is conducted and achieved by the private firm, the variants they are testing cannot be relied on to be predictive or otherwise connected.

To ensure Streaker's customers that Streaker himself has showed no signs of Muscle disease a blood test was performed and both AST & CK were at the low end of normal. .......ul unit of measure

UPDATE FROM EQUISEQ 08/01/2019

How accurate is your test for PSSM2/MFM?

A. Genetic tests score the presence or absence of a genetic variant. Apart from rare cases of human error, the tests are completely accurate. Because some genetic variants are not fully penetrant, some horses that are n/P2, n/P3, or n/P4 will not develop exercise intolerance. This means that the tests are not completely predictive. P2/P2, P3/P3, and P4/P4 horses are much more likely to be affected.

My horse has symptoms of exercise intolerance but tests negative for the P2, P3, and P4 variants (n/n). What does this mean?

A. There are other genetic causes of PSSM2/MFM besides the P2, P3, and P4 variants. Researchers at EquiSeq are working to identify these variants. We are currently reporting results for P5, P6, P8, and K1 to horse owners who are in our research studies

We have new data from a University lab examining the breed distribution of the P2, P3, and P4 variants in an unselected sample of various breeds. Remember that a horse has two copies of every gene, so a sample of 20 horses is actually a sample of 40 genomes.

What else can be said about PSSM2? There has been a decade of GWAS studies that have failed to find a causative variant. These data are, of course, unpublished (it's hard to publish negative results). The people doing this are good at it. Why did this fail? It is either because there are multiple genetic variants with a similar clinical presentation as PSSM2 (just as in human MFM), or that the variants have incomplete penetrance, or both. So without really going deeply into unpublished work, it is still possible to make a broad statement about PSSM2: it is very likely that this disease state is genetically complex, caused by a number of different genetic variants with incomplete penetrance, rather than being caused by a single Mendelian factor.

HOKAHEYFARM