Gene Mutation for Muscle Disease Found in Haflingers

Polysaccharide storage myopathy (PSSM) is a hereditary muscular disorder characterized by the excessive accumulation of glycogen and an abnormal polysaccharide in skeletal muscle.

Genetic testing has revealed that many breeds are affected. In a recent study performed at the University of Veterinary Medicine, Vienna, Austria, scientists set out to determine the occurrence and frequency of mutation in the gene coding for skeletal muscle glycogen synthase type 1 (GYS-1) in a herd of Haflingers. Mutation of this specific gene causes type-1 PSSM. Haflingers are a small, hardy breed that originated in Austria and northern Italy.

Of the 50 Haflingers tested, nine of the horses were heterozygous for the mutation, thus the estimated prevalence in this herd was 18%.
Muscle enzyme activity is one way to help diagnose type-1 PSSM. Affected horses often have elevated levels of creatine kinase (CK) and aspartate aminotransferase (AST) following exercise. In this herd of Haflingers, CK and AST levels were significantly higher in horses with the gene mutation.