Ubiquitin expression in muscle from horses with polysaccharide storage myopathy.
Authors: Valentine B A, Flint T H, Fischer K A
Journal: Veterinary pathology
Summary
# Editorial Summary: Ubiquitin Expression in Equine Polysaccharide Storage Myopathy Polysaccharide storage myopathy (EPSSM) is characterised by pathological glycogen accumulation in muscle; this study investigated whether ubiquitin immunostaining could enhance diagnostic accuracy beyond conventional periodic acid-Schiff (PAS) staining. Muscle biopsies from 28 horses (predominantly Quarter Horses, Paints, and draft breeds) were examined using both PAS staining and ubiquitin immunostaining, with 22 horses diagnosed with EPSSM and 6 serving as controls. Ubiquitin was detected in 21 of 22 affected horses but in none of the controls, and notably, ubiquitin expression appeared in both amylase-sensitive and amylase-resistant glycogen aggregates—suggesting the protein marks glycogen deposits before they develop resistance to enzymatic digestion. Although ubiquitin immunostaining may be particularly valuable for confirming EPSSM in early-stage disease (when only loose glycogen aggregates are present) or in borderline cases with minimal amylase-resistant inclusions, it demonstrated no superior sensitivity compared to standard PAS staining for overall diagnostic purposes. For practitioners, this means ubiquitin staining offers confirmatory value in equivocal cases but shouldn't replace PAS staining as the primary diagnostic tool for suspected EPSSM.
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Practical Takeaways
- •Ubiquitin immunostaining can help confirm EPSSM diagnosis when PAS staining shows only early glycogen changes, but standard PAS staining remains sufficient for most cases
- •The presence of ubiquitin in glycogen aggregates indicates the disease process begins before amylase-resistant inclusions form, which may have implications for early detection strategies
- •This diagnostic marker may be most valuable in borderline or atypical cases where muscle biopsy interpretation is uncertain
Key Findings
- •Ubiquitin expression was detected in 21 of 22 EPSSM-affected horses but in none of the 6 non-affected control horses
- •Ubiquitin was present in amylase-sensitive glycogen aggregates before development of amylase-resistant inclusions, suggesting early pathological changes
- •Ubiquitin immunostaining is not more sensitive than PAS staining for EPSSM diagnosis but may confirm diagnosis in early or atypical presentations