OMIA:002692-9796 : Night blindness, congenital stationary, GRM6-related in Equus caballus (horse)

Possibly relevant human trait(s) and/or gene(s)s (MIM numbers): 604096 (gene) , 257270 (trait)

Links to MONDO diseases:

Mendelian trait/disorder: yes

Considered a defect: yes

Key variant known: yes

Species-specific symbol: CSNB2

Species-specific description: Hack et al. (2021) reported a Tennessee Walking Horse with congenital stationary night blindness (CSNB) that did not have a the TRPM1 variant known to cause CSNB in horses (see OMIA:001341-9796 : Night blindness, congenital stationary, TRPM1-related in Equus caballus).

Esdaile et al. (2023) "provides additional evidence that GRM6 c.533C>T homozygosity is likely causal to CSNB in Tennessee Walking Horses, Standardbreds, and Missouri Fox Trotting Horses."

Molecular basis: Hack et al. (2021): "WGS [whole genome sequencing] analysis identified a missense mutation in metabotropic glutamate receptor 6 (GRM6) (c.533C>T p.Thr178Met)."

Prevalence: Hack et al. (2021): "This variant [GRM6 c.533C>T] was not detected in 273 horses from three additional breeds. The estimated allele frequency in Tennessee Walking Horses is 10%."

Esdaile et al. (2023) "The CSNB2 allele was present in nine breeds [American Quarter Horse, Racking Horse, Rocky Mountain Horse, American Saddlebred, Spotted Saddle Horse, Standardbred (pacer), Miniature Horse, Missouri Fox Trotting Horse, Morgan], ranging in frequency from 0.0010 in American Quarter Horses (n = 486) to 0.17 in pacing Standardbreds (n = 110 ...). The CSNB2 allele was not detected in trotting Standardbreds (n = 70), Thoroughbreds (n = 1787), Hackney Horses (n = 47), Hackney Ponies (n = 44), and Shetland Ponies (n = 99 ...).

Breeds: American Saddle Horse (Horse) (VBO_0000898), American Trotter (Horse) (VBO_0000899), Miniature Horse (Horse) (VBO_0016848), Missouri Fox Trotting Horse, United States of America (Horse) (VBO_0011833), Morgan (Horse) (VBO_0001022), Quarter Horse (Horse) (VBO_0001057), Racking horse, Rocky Mountain, United States of America (Horse) (VBO_0011836), Spotted Saddle Horse, Tennessee Walking Horse (Horse) (VBO_0001081).
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
GRM6 glutamate receptor, metabotropic 6 Equus caballus 14 NC_009157.3 (2652585..2667335) GRM6 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
1552 American Saddle Horse (Horse) American Trotter (Horse) Miniature Horse (Horse) Missouri Fox Trotting Horse, United States of America (Horse) Morgan (Horse) Quarter Horse (Horse) Racking horse Rocky Mountain, United States of America (Horse) Spotted Saddle Horse Tennessee Walking Horse (Horse) Night blindness, congenital stationary, GRM6-related GRM6 missense Naturally occurring variant EquCab3 14 g.2655618C>T c.533C>T p.(T178M) XM_001916934.4; XP_001916969.3; variant initially reported in Tennessee Walking horse and later reported in other breeds [PMID:37815029] rs1138010744 2021 32654228

Cite this entry

Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2023). OMIA:002692-9796: 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.

2023 Esdaile, E., Knickelbein, K.E., Donnelly, C.G., Ferneding, M., Motta, M.J., Story, B.D., Avila, F., Finno, C.J., Gilger, B.C., Sandmeyer, L., Thomasy, S., Bellone, R.R. :
Additional evidence supports GRM6 p.Thr178Met as a cause of congenital stationary night blindness in three horse breeds. Vet Ophthalmol :, 2023. Pubmed reference: 37815029 . DOI: 10.1111/vop.13151.
2021 Hack, Y.L., Crabtree, E.E., Avila, F., Sutton, R.B., Grahn, R., Oh, A., Gilger, B., Bellone, R.R. :
Whole-genome sequencing identifies missense mutation in GRM6 as the likely cause of congenital stationary night blindness in a Tennessee Walking Horse. Equine Vet J 53:316-323, 2021. Pubmed reference: 32654228 . DOI: 10.1111/evj.13318.

Edit History

  • Created by Imke Tammen2 on 10 May 2023
  • Changed by Imke Tammen2 on 10 May 2023
  • Changed by Imke Tammen2 on 15 Oct 2023