PSSM1 test information

PSSM1 is considered a dominant condition, meaning that a single defective copy of the GYS1 gene may already lead to a disturbance of energy metabolism and thereby result in clinical signs of exertional myopathy.

However, the actual impact depends strongly on the horse’s breed background and the way the horse is used.

Breeds that have historically been selected for endurance performance, such as draft horses, are relatively less sensitive due to their muscular composition and may fully compensate for a heterozygous state under appropriate management conditions.

This means that horses with a high proportion of draft horse ancestry may also show a relatively high tolerance toward PSSM1 (more information on PSSM and PSSM1 can be found in the lexicon).

Whether and to what extent a horse carries draft horse genomic background can be determined through breed analysis (link).

Horses with PSSM1 can often be managed successfully through dietary adjustment. Clinically problematic cases are typically those in which a PSSM1 variant is present together with additional MIM variants.