OMIA 002141-9796 : Myositis, immune-mediated in Equus caballus

Possibly relevant human trait(s) and/or gene(s) (MIM number): 160750

Mendelian trait/disorder: unknown

Considered a defect: yes

Year key variant first reported: 2018

Species-specific symbol: IMM

Inheritance: Finno et al. (2018): "Pedigree analysis supported either an autosomal dominant or autosomal recessive mode of inheritance."

Mapping: Finno et al. (2018): "A genome-wide association (GWA) study . . . on 36 IMM [Quarter Horses] QHs and 54 breed matched unaffected QHs from the same environment using the Equine SNP50 and SNP70 genotyping arrays . . . identified nine SNPs within a ~ 2.87 Mb region on chr11 that were significantly (Punadjusted < 1.4 × 10− 6) associated with the [immune-mediated myositis] IMM phenotype."

Molecular basis: Finno et al. (2018) reported that "Whole genome sequencing of four IMM and four unaffected QHs identified a single segregating nonsynonymous E321G mutation in [a positional candidate gene] MYH1 encoding myosin heavy chain 2X. Genotyping of additional 35 IMM and 22 unaffected QHs confirmed an association (P = 2.9 × 10− 5), and the putative mutation was absent in 175 horses from 21 non-QH breeds."

Clinical features: Finno et al. (2018): "immune-mediated myositis (IMM) [is] . . . characterized by recurrent, rapid-onset muscle atrophy in Quarter Horses (QH)"

Pathology: Finno et al. (2018): "The histopathologic hallmark of IMM is lymphocytic infiltration of myofibers."

Genetic testing: Finno et al. (2018) concluded that their "results suggest that rather than consistently causing a myopathy, homozygosity and, in some cases, heterozygosity for the MYH1 variant predisposed horses to a myopathy under certain environmental triggers." In other words, the jury is still undecided in relation to the utility of genotyping for this variant as a means of selecting against the disorder.

Breed: Quarter Horse.

Associated gene:

Symbol Description Species Chr Location OMIA gene details page Other Links
MYH1 myosin, heavy chain 1, skeletal muscle, adult Equus caballus 11 NC_009154.3 (53350918..53325909) MYH1 Homologene, Ensembl, NCBI gene


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Breed(s) Variant Phenotype Gene Allele Type of Variant Reference Sequence Chr. g. or m. c. or n. p. Verbal Description EVA ID Year Published PubMed ID(s) Acknowledgements
Quarter Horse Immune-mediated myositis MYH1 missense EquCab3.0 11 g.53345548T>C p.E321G The location of this likely causal variant was given as chr11:52,993,878T>C by Finno et al. (2018) in relation to the EquCab2.0 assembly. Applying NCBI's remap gives the EquCab3.0 coordinate as chr11:53,345,548 2018 29510741


Note: the references are listed in reverse chronological order (from the most recent year to the earliest year), and alphabetically by first author within a year.
2018 Durward-Akhurst, S.A., Valberg, S.J. :
Immune-Mediated Muscle Diseases of the Horse. Vet Pathol 55:68-75, 2018. Pubmed reference: 28129093. DOI: 10.1177/0300985816688755.
Finno, C.J., Gianino, G., Perumbakkam, S., Williams, Z.J., Bordbari, M.H., Gardner, K.L., Burns, E., Peng, S., Durward-Akhurst, S.A., Valberg, S.J. :
A missense mutation in MYH1 is associated with susceptibility to immune-mediated myositis in Quarter Horses. Skelet Muscle 8:7, 2018. Pubmed reference: 29510741. DOI: 10.1186/s13395-018-0155-0.
2007 Lewis, S.S., Valberg, S.J., Nielsen, I.L. :
Suspected immune-mediated myositis in horses. J Vet Intern Med 21:495-503, 2007. Pubmed reference: 17552457.

Edit History

  • Created by Frank Nicholas on 09 Mar 2018
  • Changed by Frank Nicholas on 09 Mar 2018