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.
Source: B. A. Valentine, T. H. Flint and K. A. Fischer (2006): Ubiquitin Expression in Muscle from Horses with Polysaccharide Storage Myopathy. In: Vet Pathol 43:270-275 (2006)
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