Genetic background of the Transylvanian endemic equine recurrent rhabdomyolysis

To investigate the pathophysiology, prevalence and severity of equine exertional rhabdomyolysis in a mountainous region of Transylvania, Romania, this study considered genetic and histological factors. We determined the occurrence and frequency of a mutation in the glycogen synthase gene 1 (GYS1), associated with equine polysaccharide storage myopathy type 1 (PSSM1), in two adjacent populations, one with a significantly high prevalence of the disease (high altitude villages, HV) and the other with a rare prevalence (valley villages, VV). We genotyped GYS1 in 41 animals (HV = 31, VV = 10) and found a significant difference in the appearance of GYS1-positive animals in the HV region. Histological lesions of animals (n = 6) with and without muscle disorders of the two populations were examined. We demonstrated a significant association between the number of rhabdomyolysis episodes and GYS1 mutation (P = 0.03) and positive amylase-resistant PAS staining (P = 0.01). Nevertheless, the correlation between GYS1 mutation and PAS staining was weak (P = 0.06). These studies further confirm the versatile and complex nature of muscle disease in this region.