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  Discussion on Research Summary: Night Blindness in Spotted Miniature Horses
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DrO

Posted on Sunday, Nov 6, 2011 - 10:32 am:

Not surprisingly the same genetic mechanism that causes night blindness in spotted leopard Appaloosas causes night blindness in Miniatures.
DrO

Vet Ophthalmol. 2011 Apr 19.
Congenital stationary night blindness is associated with the leopard complex in the miniature horse.

Sandmeyer LS, Bellone RR, Archer S, Bauer BS, Nelson J, Forsyth G, Grahn BH.
Source

Department of Small Animal Clinical Sciences, University of Saskatchewan Department of Biology, University of Tampa Quill Lake, Saskatchewan, Canada Department of Biomedical Sciences, University of Saskatchewan, Canada.
Abstract

Objective
To determine if congenital stationary night blindness (CSNB) exists in the miniature horse in association with leopard complex spotting patterns (LP), and to investigate if CSNB in the miniature horse is associated with three single nucleotide polymorphisms (SNPs) in the region of TRPM1 that are highly associated with CSNB and LP in Appaloosas. Animals studied  Three groups of miniature horses were studied based on coat patterns suggestive of LP/LP (n = 3), LP/lp (n = 4), and lp/lp genotype (n = 4).
Procedures
Horses were categorized based on phenotype as well as pedigree analysis as LP/LP, LP/lp, and lp/lp. Neurophthalmic examination, slit-lamp biomicroscopy, indirect ophthalmoscopy, and scotopic flash electroretinography were performed on all horses. Hair samples were processed for DNA analysis. Three SNPs identified and associated with LP and CSNB in the Appaloosa were investigated for association with LP and CSNB in these Miniature horses. Results  All horses in the LP/LP group were affected by CSNB, while none in the LP/lp or lp/lp groups were affected. All three SNPs were completely associated with LP genotype (χ(2)  = 22, P << 0.0005) and CSNB status (χ(2)  = 11, P < 0.0005).
Conclusions
The Miniature Horse breed is affected by CSNB and it appears to be associated with LP as in the Appaloosa breed. The SNPs tested could be used as a DNA test for CSNB until the causative mutation is determined.
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