The mystery condition PSSM1 explained
Professor Richard Piercy is here to guide us through this complex genetic condition
Equine polysaccharide storage myopathy type 1 (better known as PSSM1) is a genetic condition that causes tying up (muscle cramps) and muscle damage in horses. It’s the result of a mutation in the GYS1 gene, causing too much glycogen (the storage form of sugar) and an abnormal type of polysaccharide (a form of carbohydrate) to be made PSSM1 has a wide range of symptoms and, because of this, researchers and vets tend to think of the disease as a spectrum condition. At one end of the scale, horses with PSSM1 can have serious episodes of tying up and be unable to move. This reaction will generally only come on when the horse is being lightly exercised. While he may seem While veterinary treatment can help to alleviate symptoms of a serious episode of tying up, the condition is generally managed through diet and exercise. There’s no cure for PSSM1, but horses with the condition can lead happy and active lives if managed correctly. A horse with PSSM1 should be exercised every day and given as much turnout perfectly normal at rest, the painful symptoms will appear within a few minutes of being active, causing his muscles to cramp and making it a real struggle for him to move. Tying up like this as a result of PSSM1 often affects young horses and it’s typically first seen when they’re being brought into training. At the other end of the spectrum, If your horse shows signs of tying up and PSSM1 is suspected, your vet can carry out a genetic test to determine whether or not he carries the faulty GYS1 gene. This test can help to distinguish between PSSM1 and other muscle diseases that can also cause tying up. Vets will generally consider a genetic test first in breeds that are most as possible to limit the effects of the condition. Riding only a few days a week and frequently stabling isn’t really an option as it makes symptoms more likely when he’s asked to work. Good-doers with PSSM1 (such as cobs) can usually be managed without needing to give them any extra feed on top of their forage (such as grass and hay). For horses that need additional and stored in the horse’s body. It affects around 30 breeds and in the UK is most common among cobs, Quarterhorses and draught breeds. Signs of the condition generally appear in young horses when they’re first brought into work, but it’s also often diagnosed in horses over the age of seven who’ve been known to struggle with gait abnormalities. horses can have marked muscle wastage and weakness, with the condition actually going unnoticed until the horse is around seven or eight years old. While tying up is a common feature of PSSM1, it’s not always seen and other signs to look out for in your horse include lameness, stiffness and gait abnormalities. commonly known to suffer from PSSM1 (such as cobs and draughts), as this can quickly confirm whether or not a horse carries the gene. This is usually done by taking the DNA from a blood or hair sample (if taken from the root). If your horse’s breed is not commonly known to suffer with PSSM1, your vet might take a muscle biopsy instead. This can be done in
Researchers think the condition originally evolved as a way to help wild horses store their energy when there was little food about. Nowadays, horses are well fed and often under exercised, meaning those with PSSM1 show signs of the disease unless they’re managed correctly. horses of any age, but the key signs of PSSM1 will be most noticeable after the age of five. It’s also not uncommon for vets to do both the genetic test and take a muscle biopsy at the same time. This way, they can establish the likelihood of the horse having the condition, as well as assess how damaged the horse’s muscles might be. calories, a meal that has a higher fat and lower carbohydrate content can be considered, but this should be discussed with your vet first. Research by Professor Piercy and his team has revealed that the condition is caused by a mutation that changes the enzyme’s shape, leaving it permanently active. It’s hoped this discovery will guide medical treatments in the future.