TESTING

PSSM1

Testing for PSSM1 is simple and inexpensive. The horse owner can send in a hair sample (mane or tail hair with roots intact) to the lab for testing. The DNA is in the root of the hair, so make sure the hairs have  roots on them after pulling. The hair sample is sent in together with a form, that can be downloaded from the lab’s website.  The American western breeds (AQHA, APHA, ApHC) offer PSSM1 as part of their genetic panel test. Check with your registry what rules are in place for having your horse tested in order to have the results be recognized by the registry.

There are several laboratories in Europe that offer testing for PSSM1. For example: Laboklin and Generatio/Center for Animal Genetics in Germany, Animal Genetics UK or the Van Haeringen Institute in The Netherlands. Hair can be sent to a lab in the USA as well (Animal Genetics, UC Davis, Etalon). Often, these labs offer attractive rates, but be aware that the procedures at customs have become quite strict and require extra paperwork. Check their websites for advice.

PSSM2

Until recently, the only way to test for PSSM2 was by means of a biopsy. From an academic perspective, this is still the only full validated diagnostic test, but it also has its limitations, as the biopsy will only provide information on that particular tissue at that particular point in time. In other words: a negative result on a biopsy does not necessarily mean that the horse does not have PSSM2. The procedure itself can trigger a PSSM episode, which might not be in the horse’s best interest.

EquiSeq, a company based in the USA, has identified 6 genes that they associate with PSSM2 symptoms. For the moment, these variants have been named P2, P3, P4, Px, P8 and K1. The issues these variants can cause have been renamed Muscle Integrity Myopathy, to better represent the actual mechanism behind this muscle disease. Research into these variants is still ongoing and has not been fully peer reviewed, but EquiSeq does offer their panel test through their website. In Europe and the UK, the EquiSeq panel is offered exclusively by Generatio/CAG in Germany. Countries from outside of the EU and UK can test through EquiSeq in the USA.

IMM/MYH1

Another affliction that was found while looking for genes causing symptoms of PSSM2 is Immune Mediated Myositis (IMM). This is a genetic defect specific to Quarter Horses and related breeds and can be tested at most commercial laboratories that offer genetic disease testing.