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

Categories: Muscle phene

Possibly relevant human trait(s) and/or gene(s)s (MIM numbers): 160750 (trait) , 160730 (gene)

Links to MONDO diseases: No links.

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 2018

Species-specific name: myosin heavy chain myopathy

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."

Genetic engineering: Unknown
Have human generated variants been created, e.g. through genetic engineering and gene editing

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."

Prevalence: Gianino et al. (2019): "The E321G MYH1 variant allele frequency was 0.034 ± 0.011 in the general QH population (6.8% of individuals in the breed) and the highest among the reining (0.135 ± 0.040; 24.3% of reiners), working cow (0.085 ± 0.031), and halter (0.080 ± 0.027) performance subgroups. The E321G MYH1 variant was present in cutting (0.044 ± 0.022) and Western Pleasure (0.021 ± 0.015) QHs at lower frequency and was not observed in barrel racing or racing QHs. Knowing that reining and working cow QHs have the highest prevalence of the E321G MYH1 variant and that the variant is more prevalent than the alleles for hereditary equine regional dermal asthenia and hyperkalemic periodic paralysis in the general QH population will guide the use of genetic testing for diagnostic and breeding purposes." Albuquerque et al. (2022) “report of two related QH foals with the E321G MYH1 mutation that had clinical signs of MYHM, with histological confirmation of IMM in one of the foals. This prompted an investigation the aim of which was to determine the allele frequency of the E321G MYH1 variant across QHs using a DNA archive in Brazil. … Of the 299 genotyped QHs, 44 animals (14.7%) were heterozygous (My/N) for the E321G MYH1 variant, and 255 (85.3%) were homozygous for the wild-type allele (N/N), implying an allele frequency of 0.074.”

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 (Horse) (VBO_0001057).
Breeds in which the phene has been documented. For breeds in which a likely causal variant has been documented, see the variant table below

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


By default, variants are sorted chronologically by year of publication, to provide a historical perspective. Readers can re-sort on any column by clicking on the column header. Click it again to sort in a descending order. To create a multiple-field sort, hold down Shift while clicking on the second, third etc relevant column headers.

WARNING! Inclusion of a variant in this table does not automatically mean that it should be used for DNA testing. Anyone contemplating the use of any of these variants for DNA testing should examine critically the relevant evidence (especially in breeds other than the breed in which the variant was first described). If it is decided to proceed, the location and orientation of the variant sequence should be checked very carefully.

Since October 2021, OMIA includes a semiautomated lift-over pipeline to facilitate updates of genomic positions to a recent reference genome position. These changes to genomic positions are not always reflected in the ‘acknowledgements’ or ‘verbal description’ fields in this table.

OMIA Variant ID Breed(s) Variant Phenotype Gene Allele Type of Variant Source of Genetic Variant Reference Sequence Chr. g. or m. c. or n. p. Verbal Description EVA ID Inferred EVA rsID Year Published PubMed ID(s) Acknowledgements
973 Quarter Horse (Horse) Immune-mediated myositis MYH1 missense Naturally occurring variant 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 rs3435577028 2018 29510741

Cite this entry

Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2022). OMIA:002141-9796: Online Mendelian Inheritance in Animals (OMIA) [dataset].


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.

2024 Sperandio, L.M.S., Lago, G.R., Albertino, L.G., Araújo, C.E.T., Ferreira, C., Borges, A.S., Oliveira-Filho, J.P. :
Allele frequency of muscular genetic disorders in bull-catching (vaquejada) quarter horses. J Equine Vet Sci 136:S0737-0806(24)00059-5:105052, 2024. Pubmed reference: 38531516. DOI: 10.1016/j.jevs.2024.105052.
2023 Faccin, M., Landsgaard, K.A., Milliron, S.M., Jennings, A.H., Keith Chaffin, M., Giaretta, P.R., Rech, R.R. :
Myosin heavy-chain myopathy in 2 American quarter horses. Vet Pathol :3009858231204253, 2023. Pubmed reference: 37818977. DOI: 10.1177/03009858231204253.
2022 Aleman, M., Scalco, R., Malvick, J., Grahn, R.A., True, A., Bellone, R.R. :
Prevalence of genetic mutations in horses with muscle disease from a neuromuscular disease laboratory. J Equine Vet Sci 118:104129, 2022. Pubmed reference: 36150530. DOI: 10.1016/j.jevs.2022.104129.
de Albuquerque, A.L., Zanzarini Delfiol, D.J., Andrade, D.G.A., Albertino, L.G., Sonne, L., Borges, A.S., Valberg, S.J., Finno, C.J., Oliveira-Filho, J.P. :
Prevalence of the E321G MYH1 variant in Brazilian Quarter horses. Equine Vet J 54:952-957, 2022. Pubmed reference: 34606642. DOI: 10.1111/evj.13521.
Valberg, S.J., Schultz, A.E., Finno, C.J., Bellone, R.R., Hughes, S.S. :
Prevalence of clinical signs and factors impacting expression of myosin heavy chain myopathy in Quarter Horse-related breeds with the MYH1 E321G mutation. J Vet Intern Med 36:1152-1159, 2022. Pubmed reference: 35426178. DOI: 10.1111/jvim.16417.
2021 Ochala, J., Finno, C.J., Valberg, S.J. :
Myofibre hyper-contractility in horses expressing the myosin heavy chain myopathy mutation, MYH1 E321G. Cells 10:3428, 2021. Pubmed reference: 34943936. DOI: 10.3390/cells10123428.
2019 Gianino, G.M., Valberg, S.J., Perumbakkam, S., Henry, M.L., Gardner, K., Penedo, C., Finno, C.J., Gianino, G.M., Valberg, S.J., Perumbakkam, S., Henry, M.L., Gardner, K., Penedo, C., Finno, C.J. :
Prevalence of the E321G MYH1 variant for immune-mediated myositis and nonexertional rhabdomyolysis in performance subgroups of American Quarter Horses. J Vet Intern Med 33:897-901, 2019. Pubmed reference: 30623495. DOI: 10.1111/jvim.15393.
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
  • Changed by Frank Nicholas on 05 Feb 2019
  • Changed by Frank Nicholas on 15 May 2020
  • Changed by Imke Tammen2 on 08 Oct 2021
  • Changed by Imke Tammen2 on 08 Sep 2022
  • Changed by Imke Tammen2 on 15 Nov 2022