About PSSM type 1

PSSM type 1, or PSSM1, is a glycogen storage problem that occurs in coldbloods and coldblood infused breeds, such as (but not  limited to) Quarter Horses, Paint Horses, Haflingers, Tinkers, Morgans, draught horses and some warmbloods.

PSSM type 1 is caused by a mutation of the glycogen synthase 1 (GYS1) gene. The glycogen synthase gene enzyme transforms sugars into glycogen, which is subsequently stored in the muscles as an energy source. The mutation renders the glycogen synthase enzyme in skeletal muscles overactive, which causes abnormal storage of glycogen and a disrupted energy metabolism in the compromised muscles during movement. This can cause symptoms like stiffness, lameness, muscle tremors, muscle cramping and/or tying up.