2020 journal article
Whole-genome sequencing identifies missense mutation inGRM6as the likely cause of congenital stationary night blindness in a Tennessee Walking Horse
EQUINE VETERINARY JOURNAL, 53(2), 316–323.
author keywords: horse; congenital stationary night blindness (CSNB); genetics; genomics; Tennessee Walking Horse; GRM6
MeSH headings : Animals; Eye Diseases, Hereditary / genetics; Eye Diseases, Hereditary / veterinary; Genetic Diseases, X-Linked; Horse Diseases / genetics; Horses; Mutation, Missense; Myopia; Night Blindness / genetics; Night Blindness / veterinary; Receptors, Glutamate / genetics; Tennessee
TL;DR:
A likely causal recessive missense variant in metabotropic glutamate receptor 6 (GRM6) is identified, which alters GRM6 binding, and thus signaling from the retinal rod cell to the ON-bipolar cell, impairing vision in low light conditions.
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UN Sustainable Development Goal Categories
3. Good Health and Well-being
(Web of Science)
Source: Web Of Science
Added: August 17, 2020
AbstractBackgroundThe only known genetic cause of congenital stationary night blindness (CSNB) in horses is a 1378 bp insertion in TRPM1. However, an affected Tennessee Walking Horse was found to have no copies of this variant.ObjectivesTo identify the genetic cause for CSNB in an affected Tennessee Walking Horse.Study designCase report detailing a whole‐genome sequencing (WGS) approach to identify a causal variant.MethodsA complete ophthalmic exam, including an electroretinogram (ERG), was performed on suspected CSNB‐affected horse. WGS data were generated from the case and compared with data from seven other breeds (n = 29). One hundred candidate genes were evaluated for coding variants homozygous in the case and absent in all other horses. Protein modelling was used to assess the functional effects of the identified variant. A random cohort of 90 unrelated Tennessee Walking Horses and 273 horses from additional breeds were screened to estimate allele frequency of the GRM6 variant.ResultsERG results were consistent with CSNB. WGS analysis identified a missense mutation in metabotropic glutamate receptor 6 (GRM6) (c.533C>T p.Thr178Met). This single nucleotide polymorphism (SNP) is predicted to be deleterious and protein modelling supports impaired binding of the neurotransmitter glutamate. This variant was not detected in 273 horses from three additional breeds. The estimated allele frequency in Tennessee Walking Horses is 10%.Main limitationsLimited phenotype information for controls and no additional cases with which to replicate this finding.ConclusionsWe identified a likely causal recessive missense variant in GRM6. Based on protein modelling, this variant alters GRM6 binding, and thus signalling from the retinal rod cell to the ON‐bipolar cell, impairing vision in low light conditions. Given the 10% population allele frequency, it is likely that additional affected horses exist in this breed and further work is needed to identify and examine these animals.