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Ubiquitin Expression in Muscle from Horses with Polysaccharide Storage Myopathy

Veterinary Diagnostic Laboratory, Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR

Serial sections of formalin-fixed, paraffin-embedded muscle biopsy specimens from 28 Quarter Horse, Paint, and draft-related breeds, aged 0.5–23 years, were treated with periodic acid-Schiff (PAS) stain for glycogen and were immunostained to detect ubiquitin expression. On the basis of findings in PAS-stained sections, a diagnosis of equine polysaccharide storage myopathy (EPSSM) was made in 22 horses aged 2–23 years (mean, 9.4 years); samples from 6 horses aged 0.5–15 years (mean, 7.3 years) had a normal PAS staining pattern, with no relevant lesions. Ubiquitin expression was detected in all but a 2-year-old EPSSM-affected horse and was not detected in the non–EPSSM-affected horses. Ubiquitin expression was greater than the degree of PAS-positive, amylase-resistant material, and ubiquitin was detected in aggregates of amylase-sensitive glycogen as well as in aggregates of amylase-resistant material. Results suggest that glycogen aggregates develop and are ubiquitinated prior to development of amylase-resistant inclusions. Ubiquitin immunostaining may be most useful for confirming the diagnosis of EPSSM in horses with only amylase-sensitive glycogen aggregates and in horses with early amylase-resistant inclusions. However, ubiquitin immunostaining is no more sensitive than is PAS staining for diagnosis of EPSSM.

Key words: Horses; immunohistochemistry; myopathy; polysaccharide storage; ubiquitin.

Request reprints from Dr B A Valentine, Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Magruder 142, Corvallis, OR 97331 (USA). E-mail: Beth.Valentine{at}oregonstate.edu

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