Evaluation of cardiac phenotype in horses with type 1 polysaccharide storage myopathy.

The research article investigates if horses with type 1 polysaccharide storage myopathy (PSSM1), a genetic disorder causing abnormal glycogen storage, show any signs of heart disease. The study found that although some horses with PSSM1 had slightly elevated levels of a marker for heart muscle damage, there were no significant differences in this or in heart rhythm abnormalities between the affected and unaffected horses.

Background and Objectives

• The focus of this study is on type 1 polysaccharide storage myopathy (PSSM1), a condition in horses that results from a mutation in the gene encoding glycogen synthase (GYS1), leading to abnormal glycogen accumulation in the skeletal muscle.
• Given that several human glycogen storage diseases have a heart disease component, the researchers hypothesized that horses with PSSM1 might also exhibit signs of cardiac abnormalities or disease (a ‘cardiac phenotype’).
• To test this hypothesis, the researchers compared the levels of cardiac troponin I (cTnI), a protein that serves as a marker of heart muscle damage when found in the bloodstream, and the incidence of heart rhythm disturbances in horses with different genetic makeups for PSSM1.

Methodology

• A total of 125 Belgian and Percheron horses were genetically tested for the R309H GYS1 mutation indicative of PSSM1.
• Eight groups of horses that were matched by age, breed, and sex were created, each with a distinct genotype (i.e., whether they had one copy, two copies, or none of the mutated gene).
• Plasma cTnI concentrations were measured and 24-hour Holter ECGs, a type of continuous heart monitor, were used to track and compare heart rhythms across the groups.

Results

• The study found that while some PSSM1-affected horses had slightly increased plasma cTnI concentrations, there were no significant differences between groups.
• There were also no significant differences in the incidence of abnormal heart rhythms, the timing of the electrical signals that control heart rhythm (cardiac conduction intervals), or average heart rate between the groups.

Conclusion

• The researchers did not find any evidence of notable heart muscle injury or abnormal heart rhythms in horses with PSSM1 based on this study.
• They concluded that further research is needed to determine if the function of the heart muscle may be impaired in these horses.