Genetic background of the Transylvanian endemic equine recurrent rhabdomyolysis.

Genetic differences in the glycogen synthase gene 1 (GYS1) are linked to the frequency and severity of equine recurrent rhabdomyolysis in horses from mountainous versus valley regions in Transylvania, Romania.

Research Objective and Background

• The study aimed to understand the causes, prevalence, and severity of exertional rhabdomyolysis (a muscle disease causing muscle breakdown) in horses living in a mountainous area of Transylvania, Romania.
• Equine exertional rhabdomyolysis can be influenced by genetic mutations, especially in the GYS1 gene, which is associated with a condition called polysaccharide storage myopathy type 1 (PSSM1).
• The research compared two neighboring horse populations: one living in high altitude villages (HV) with a high prevalence of the disease, and the other in nearby valley villages (VV) where the disease is rare.

Methodology

• Genotyping: 41 horses were genetically tested for mutations in the GYS1 gene (31 from HV and 10 from VV).
• Histological Analysis: Muscle tissue samples from 6 horses, both with and without muscle disorders, from the two populations were examined under a microscope.

Key Findings

• A significant difference was found in the prevalence of the GYS1 mutation between the two regions, with more GYS1-positive horses in the high-altitude villages (HV).
• There was a significant association between the number of rhabdomyolysis episodes a horse had experienced and the presence of the GYS1 mutation (P = 0.03).
• A positive amylase-resistant periodic acid-Schiff (PAS) staining—an indicator of abnormal polysaccharide accumulation in muscle—was significantly associated with the number of rhabdomyolysis episodes (P = 0.01).
• However, the correlation between having the GYS1 mutation and positive PAS staining was weak (P = 0.06), suggesting other factors may also be contributing to muscle pathology.

Interpretation and Implications

• The study supports that the GYS1 mutation plays an important role in the development and severity of exertional rhabdomyolysis in horses from high-altitude areas.
• The findings indicate complex and multifactorial causes for muscle disease in this Transylvanian region, involving genetic background as well as possibly environmental or other biological factors.
• This research highlights the importance of considering local genetic differences when diagnosing and managing equine rhabdomyolysis.
• Future work could explore additional genetic or environmental contributors to better understand and control this disease in affected horse populations.