PSSM 2

PSSM 2, in Germany sometimes also called muscle integrity myopathy (MiM), is a collective term for various neuromuscular disorders that show similar symptoms but do not have the typical GYS1 gene defect associated with PSSM 1. Horses benefit from supplements of

PSSM 2 currently includes gene mutations at 6 risk alleles: P2, P3, P4, Px, P8 and K1. Research suggests that further risk alleles may exist.
The severity of symptoms depends on which mutation occurs, whether several genes are affected and whether the mutation is homozygous or heterozygous. These changes disrupt the structure of the muscle fibres, making the muscle "fragile". This often leads to muscle tension, gait irregularities, reluctance to move, recurring intermittent lameness and behavioural changes, up to and including painful muscle breakdown (e.g. visible as grooves or muscle indentations). Symptoms usually occur in episodes and typically do not appear until around 8 years of age. Episodes can be triggered, for example, by surgery, injury-related rest periods, vaccinations or other physically demanding phases, especially in combination with a low-protein diet.

Due to the gene defect, the body uses more protein to "improvise" the functional structure of the muscle. Affected horses therefore benefit from a ration with an increased content of small intestine digestible protein. As the amino acid quality of the protein should be as high as possible, amino acid supplements such as marstall Amino-Muskel are recommended.

Grain-free and low-sugar feeding has become established practice for PSSM 2, but is not strictly necessary. Supplements of omega-3-rich linseed oil are, however, advisable. Horses also need a slightly increased supply of magnesium, sodium chloride (salt), and generous amounts of vitamin E (>2000 mg vitamin E/day). Antioxidants such as vitamin E and C are particularly important for horses with P8, but also support horses with the other gene defects. Trace elements such as zinc, manganese, copper and, above all, selenium (1.8 mg/day) should be fed to cover requirements, but not in excess.

See also Polysaccharide storage myopathy and PSSM 1