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Equine veterinary journal2017; 49(6); 739-745; doi: 10.1111/evj.12702

Clinical and histopathological features of myofibrillar myopathy in Warmblood horses.

Abstract: To report a novel exertional myopathy, myofibrillar myopathy (MFM) in Warmblood (WB) horses. Objective: To 1) describe the distinctive clinical and myopathic features of MFM in Warmblood horses and 2) investigate the potential inheritance of MFM in a Warmblood family. Methods: Retrospective selection of MFM cases and prospective evaluation of a Warmblood family. Methods: Retrospectively, muscle biopsies were selected from Warmblood horses diagnosed with MFM and clinical histories obtained (n = 10). Prospectively, muscle biopsies were obtained from controls (n = 8) and a three generation WB family (n = 11). Samples were assessed for histopathology [scored 0-3], fibre types, cytoskeletal and Z disc protein aggregates, electron microscopic alterations (EM) and muscle glycogen concentrations. Results: Myofibrillar myopathy-affected cases experienced exercise intolerance, reluctance to go forward, stiffness and poorly localised lameness. Abnormal aggregates of the cytoskeletal protein desmin were found in up to 120 type 2a and a few type 2x myofibres of MFM cases. Desmin positive fibres did not stain for developmental myosin, α actinin or dystrophin. Scores for internalised myonuclei (score MFM 0.83 ± 0.67, controls 0.22 ± 0.45), anguloid atrophy (MFM 0.95 ± 0.55, controls 0.31 ± 0.37) and total myopathic scores (MFM 5.85 ± 2.10, controls 1.41 ± 2.17) were significantly higher in MFM cases vs. Methods: Focal Z disc degeneration, myofibrillar disruption and accumulation of irregular granular material was evident in MFM cases. Muscle glycogen concentrations were similar between MFM cases and controls. In the Warmblood family, desmin positive aggregates were found in myofibres of the founding dam and in horses from two subsequent generations. Conclusions: Restricted sample size due to limited availability of well phenotyped cases. Conclusions: A distinctive and potentially heritable form of MFM exists in Warmblood horses that present with exercise intolerance and abnormal hindlimb gait. Muscle tissue is characterised by ectopic accumulation of desmin and Z disc and myofibrillar degeneration.
© 2017 EVJ Ltd.
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Publication Date: 2017-06-26 PubMed ID: 28543538PubMed Central: PMC5640499DOI: 10.1111/evj.12702Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research article studies a particular type of exertional myopathy, called myofibrillar myopathy (MFM), in Warmblood horses. It investigates both distinctive characteristics of MFM and its potential inheritance within a family of Warmblood horses.

Methods

The researchers used both retrospective and prospective methods to evaluate MFM in Warmblood horses. Retrospectively, the researchers colleted muscle biopsies from horses already diagnosed with MFM and studied their clinical histories. Prospectively, they collected muscle biopsies from a family of Warmblood horses across three generations. Both sets of biopsies were studied for several factors such as histopathology, fibre types, the presence of protein aggregates in the cytoskeleton and Z disc, alterations visible under electron microscope, and concentrations of muscle glycogen.

Results

Warmblood horses affected with MFM displayed exercise intolerance, stiffness, and reluctance to move forward, along with poorly localized lameness. Analyses of the biopsies revealed several abnormalities:

  • The presence of abnormal aggregates of a protein called desmin in up to 120 type 2a and a few type 2x myofibres.
  • Significantly higher scores for internalized myonuclei, anguloid atrophy and total myopathic scores in MFM cases compared to controls.
  • Evidence of Z disc degeneration, myofibrillar disruption, and accumulation of irregular granular material in MFM cases.

Muscle glycogen concentrations were found to be similar between MFM cases and controls.

In the studied Warmblood family, desmin positive aggregates were found in the muscles of the founding dam and horses from two subsequent generations, suggesting a possibly heritable nature of MFM.

Conclusions

The study concludes that a distinctive, potentially heritable form of MFM exists in Warmblood horses. This myopathy presents with symptoms like exercise intolerance and abnormal hindlimb gait. The affected muscle tissue is characterised by the abnormal accumulation of desmin and degeneration of Z disc and myofibrils. The study’s conclusions are limited by the small sample size.

Cite This Article

APA
Valberg SJ, Nicholson AM, Lewis SS, Reardon RA, Finno CJ. (2017). Clinical and histopathological features of myofibrillar myopathy in Warmblood horses. Equine Vet J, 49(6), 739-745. https://doi.org/10.1111/evj.12702

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 49
Issue: 6
Pages: 739-745

Researcher Affiliations

Valberg, S J
  • McPhail Equine Performance Center, Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, Michigan, USA.
Nicholson, A M
  • Wilhite & Frees Equine Hospital, Peculiar, Missouri, USA.
Lewis, S S
  • Hagyard Equine Medical Institute, Lexington, Kentucky, USA.
Reardon, R A
  • West End Equine Veterinary Services, Inc., Delano, Minnesota, USA.
Finno, C J
  • Department of Population Health and Reproduction, University of California Davis, Davis, California, USA.

MeSH Terms

  • Animals
  • Female
  • Genetic Predisposition to Disease
  • Horse Diseases / genetics
  • Horse Diseases / pathology
  • Horses
  • Male
  • Myopathies, Structural, Congenital / genetics
  • Myopathies, Structural, Congenital / pathology
  • Myopathies, Structural, Congenital / veterinary

Grant Funding

  • K01 OD015134 / NIH HHS
  • L40 TR001136 / NCATS NIH HHS

Conflict of Interest Statement

Authors’ declaration of interests. S. Valberg and her colleagues license the PSSM1 genetic test mentioned in this paper and she receives royalties from the test.

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Citations

This article has been cited 8 times.
  1. Lindsay-McGee V, Massey C, Li YT, Clark EL, Psifidi A, Piercy RJ. Characterisation of phenotypic patterns in equine exercise-associated myopathies. Equine Vet J 2025 Mar;57(2):347-361.
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  2. Valberg SJ, Velez-Irizarry D, Williams ZJ, Henry ML, Iglewski H, Herrick K, Fenger C. Enriched Pathways of Calcium Regulation, Cellular/Oxidative Stress, Inflammation, and Cell Proliferation Characterize Gluteal Muscle of Standardbred Horses between Episodes of Recurrent Exertional Rhabdomyolysis. Genes (Basel) 2022 Oct 14;13(10).
    doi: 10.3390/genes13101853pubmed: 36292738google scholar: lookup
  3. Valberg SJ, Henry ML, Herrick KL, Velez-Irizarry D, Finno CJ, Petersen JL. Absence of myofibrillar myopathy in Quarter Horses with a histopathological diagnosis of type 2 polysaccharide storage myopathy and lack of association with commercial genetic tests. Equine Vet J 2023 Mar;55(2):230-238.
    doi: 10.1111/evj.13574pubmed: 35288976google scholar: lookup
  4. Williams ZJ, Velez-Irizarry D, Gardner K, Valberg SJ. Integrated proteomic and transcriptomic profiling identifies aberrant gene and protein expression in the sarcomere, mitochondrial complex I, and the extracellular matrix in Warmblood horses with myofibrillar myopathy. BMC Genomics 2021 Jun 11;22(1):438.
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  5. Valberg SJ, Finno CJ, Henry ML, Schott M, Velez-Irizarry D, Peng S, McKenzie EC, Petersen JL. Commercial genetic testing for type 2 polysaccharide storage myopathy and myofibrillar myopathy does not correspond to a histopathological diagnosis. Equine Vet J 2021 Jul;53(4):690-700.
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