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Esdaile E, Knickelbein KE, Donnelly CG, Ferneding M, Motta MJ, Story BD, Avila F, Finno CJ, Gilger BC, Sandmeyer L, Thomasy S, Bellone RR. Additional evidence supports GRM6 p.Thr178Met as a cause of congenital stationary night blindness in three horse breeds. Vet Ophthalmol 2024; 27:248-255. [PMID: 37815029 DOI: 10.1111/vop.13151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 09/11/2023] [Accepted: 09/19/2023] [Indexed: 10/11/2023]
Abstract
Congenital stationary night blindness (CSNB) is an ocular disorder characterized by nyctalopia. An autosomal recessive missense mutation in glutamate metabotropic receptor 6 (GRM6 c.533C>T, p.(Thr178Met)), called CSNB2, was previously identified in one Tennessee Walking Horse and predicted to reduce binding affinity of the neurotransmitter glutamate, impacting the retinal rod ON-bipolar cell signaling pathway. Thus, the first aim was to identify the allele frequency (AF) of CSNB2 in breeds with reported cases of CSNB and breeds closely related to the Tennessee Walking Horse. The second aim was to perform ocular examinations in multiple breeds to confirm the link between genotype and CSNB phenotype. In evaluating 3518 horses from 14 breeds, the CSNB2 allele was identified in nine previously unreported breeds. The estimated AF was highest in pacing Standardbreds (0.17) and lowest in American Quarter Horses (0.0010). Complete ophthalmic examinations and electroretinograms (ERG) were performed on 19 horses from three breeds, including one CSNB2 homozygote from each breed. All three CSNB2/CSNB2 horses had an electronegative ERG waveform under scotopic light conditions consistent with CSNB. The remaining 16 horses (seven CSNB2/N and nine N/N) had normal scotopic ERG results. All horses had normal photopic ERGs. This study provides additional evidence that GRM6 c.533C>T homozygosity is likely causal to CSNB in Tennessee Walking Horses, Standardbreds, and Missouri Fox Trotting Horses. Genetic testing is recommended for breeds with the CSNB2 allele to limit the production of affected horses. This study represents the largest across-breed identification of CSNB in the horse and suggests that this disorder is likely underdiagnosed.
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Affiliation(s)
- Elizabeth Esdaile
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Kelly E Knickelbein
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA
| | - Callum G Donnelly
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Michelle Ferneding
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Monica J Motta
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Brett D Story
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Felipe Avila
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Carrie J Finno
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
| | - Brian C Gilger
- Department of Clinical Sciences, North Carolina State University, Raleigh, North Carolina, USA
- Department of Ophthalmology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA
| | - Lynne Sandmeyer
- Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Sara Thomasy
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
- Department of Ophthalmology & Vision Science, School of Medicine, University of California, Davis, Sacramento, California, USA
| | - Rebecca R Bellone
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, California, USA
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Ignacio C, Del Mar LMM, Marta B, Sina Z, Vicent R, Aloma MF. Comparison of two sedation protocols for long electroretinography in horses using the Koijman electrode. BMC Vet Res 2023; 19:106. [PMID: 37537621 PMCID: PMC10401785 DOI: 10.1186/s12917-023-03654-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 07/14/2023] [Indexed: 08/05/2023] Open
Abstract
BACKGROUND In modern times, horses are utilized not only for labour and transportation purposes but also for recreational activities such as competition and pleasure riding. In these various pursuits, the role of vision plays a crucial role. Electroretinography is the most used test to diagnose diseases of the retinal outer segment. There is a wide variety of devices to perform the electroretinography differing one from each other in the corneal electrode and the light stimulation. The Koijman electrode has been tested in dogs but not in horses. The main purpose of this study was to compare electroretinography parameters from horses sedated with detomidine alone or in combination with butorphanol, during a standardized protocol using the Koijman electrode and RETI-port® system. Seven mares were allocated to the detomidine and detomidine plus butorphanol group in a randomised, controlled, crossover study. Friedman and Willcoxon-signed ranked tests were used to compare the electroretinogram parameters. A Student's t-test was used to compare differences in the number of artefacts to valid values ratio obtained under both sedation protocols. RESULTS Dark adaptation peaked after 16 min under scotopic conditions in both groups. No significant differences in electroretinogram parameters between groups were observed. During the mixed rod and cone response evaluation under scotopic conditions, all mares made a movement of the head resulting in a high number of artefacts. The detomidine plus butorphanol group showed a non-significant tendency to have fewer artefacts and a longer duration of sedation compared to the detomidine group. CONCLUSIONS Detomidine alone or combined with butorphanol may be suitable to use Koijman electrode and the RETI-port® to perform a standardized long protocol in horses with some adaptations.
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Affiliation(s)
- Corradini Ignacio
- Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Cardenal Herrera-CEU, CEU Universities, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain
- School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Nr Loughborough, LE12 5RD, England, UK
| | - López-Murcia María Del Mar
- Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Cardenal Herrera-CEU, CEU Universities, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain
| | - Barba Marta
- Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Cardenal Herrera-CEU, CEU Universities, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain
| | - Zebarjadian Sina
- Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Cardenal Herrera-CEU, CEU Universities, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain
| | - Rodilla Vicent
- Departmento de Farmacia, Facultad de Ciencias de la Salud, Instituto de Ciencias Biomédicas, Universidad Cardenal Herrera-CEU, CEU Universities, Santiago Ramón y Cajal, s/n., Alfara del Patriarca, Valencia, 46115, Spain
| | - Mayordomo-Febrer Aloma
- Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Cardenal Herrera-CEU, CEU Universities, Tirant lo Blanc, 7, Alfara del Patriarca, Valencia, 46115, Spain.
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Hack YL, Crabtree EE, Avila F, Sutton RB, Grahn R, Oh A, Gilger B, Bellone RR. 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 2020; 53:316-323. [PMID: 32654228 DOI: 10.1111/evj.13318] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 06/01/2020] [Accepted: 06/25/2020] [Indexed: 11/26/2022]
Abstract
BACKGROUND The 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. OBJECTIVES To identify the genetic cause for CSNB in an affected Tennessee Walking Horse. STUDY DESIGN Case report detailing a whole-genome sequencing (WGS) approach to identify a causal variant. METHODS A 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. RESULTS ERG 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 LIMITATIONS Limited phenotype information for controls and no additional cases with which to replicate this finding. CONCLUSIONS We 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.
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Affiliation(s)
- Yael L Hack
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, California, USA
| | - Elizabeth E Crabtree
- College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Felipe Avila
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, California, USA
| | - Roger B Sutton
- Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, USA
| | - Robert Grahn
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, California, USA
| | - Annie Oh
- College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Brian Gilger
- College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Rebecca R Bellone
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, California, USA.,Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA
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Abstract
Horses perform in a variety of disciplines that are visually demanding, and any disease impacting the eye has the potential to threaten vision and thus the utility of the horse. Advances in equine genetics have enabled the understanding of some inherited ocular disorders and ocular manifestations and are enabling cross-species comparisons. Genetic testing for multiple congenital ocular anomalies, congenital stationary night blindness, equine recurrent uveitis, and squamous cell carcinoma can identify horses with or at risk for disease and thus can assist in clinical management and breeding decisions. This article describes the current knowledge of inherited ocular disorders.
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Affiliation(s)
- Rebecca R Bellone
- Department of Population Health and Reproduction, Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
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Genetic Testing as a Tool to Identify Horses with or at Risk for Ocular Disorders. Vet Clin North Am Equine Pract 2017; 33:627-645. [DOI: 10.1016/j.cveq.2017.08.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Townsend WM. Disease and Surgery of the Equine Lens. Vet Clin North Am Equine Pract 2017; 33:483-497. [PMID: 29103558 DOI: 10.1016/j.cveq.2017.07.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
Abstract
Examination of the lens is critical, particularly when evaluating horses with visual impairment or performing prepurchase examinations. To adequately evaluate the lens, the pupil must be pharmacologically dilated. A cataract is any lens opacity. The size, density, and position of a cataract determine the impact on vision. Cataracts may be congenital or inherited or occur secondary to trauma or equine recurrent uveitis. Surgical removal is the only treatment option for vision impairing cataracts, but careful selection of surgical candidates is critical for successful outcomes.
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Affiliation(s)
- Wendy M Townsend
- Department of Veterinary Clinical Sciences, Purdue University, 625 Harrison Street, West Lafayette, IN 47907-2026, USA.
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Affiliation(s)
- W. M. Townsend
- Department of Veterinary Clinical Sciences; College of Veterinary Medicine; Purdue University; West Lafayette Indiana USA
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Bellone RR, Holl H, Setaluri V, Devi S, Maddodi N, Archer S, Sandmeyer L, Ludwig A, Foerster D, Pruvost M, Reissmann M, Bortfeldt R, Adelson DL, Lim SL, Nelson J, Haase B, Engensteiner M, Leeb T, Forsyth G, Mienaltowski MJ, Mahadevan P, Hofreiter M, Paijmans JLA, Gonzalez-Fortes G, Grahn B, Brooks SA. Evidence for a retroviral insertion in TRPM1 as the cause of congenital stationary night blindness and leopard complex spotting in the horse. PLoS One 2013; 8:e78280. [PMID: 24167615 PMCID: PMC3805535 DOI: 10.1371/journal.pone.0078280] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 09/10/2013] [Indexed: 12/21/2022] Open
Abstract
Leopard complex spotting is a group of white spotting patterns in horses caused by an incompletely dominant gene (LP) where homozygotes (LP/LP) are also affected with congenital stationary night blindness. Previous studies implicated Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1) as the best candidate gene for both CSNB and LP. RNA-Seq data pinpointed a 1378 bp insertion in intron 1 of TRPM1 as the potential cause. This insertion, a long terminal repeat (LTR) of an endogenous retrovirus, was completely associated with LP, testing 511 horses (χ2=1022.00, p<<0.0005), and CSNB, testing 43 horses (χ2=43, p<<0.0005). The LTR was shown to disrupt TRPM1 transcription by premature poly-adenylation. Furthermore, while deleterious transposable element insertions should be quickly selected against the identification of this insertion in three ancient DNA samples suggests it has been maintained in the horse gene pool for at least 17,000 years. This study represents the first description of an LTR insertion being associated with both a pigmentation phenotype and an eye disorder.
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Affiliation(s)
- Rebecca R. Bellone
- Department of Biology, University of Tampa, Tampa, Florida, United States of America
- * E-mail:
| | - Heather Holl
- Department of Animal Science, Cornell University, Ithaca, New York, United States of America
| | - Vijayasaradhi Setaluri
- Department of Dermatology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Sulochana Devi
- Department of Dermatology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Nityanand Maddodi
- Department of Dermatology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin, United States of America
| | | | - Lynne Sandmeyer
- Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Arne Ludwig
- Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
| | - Daniel Foerster
- Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
| | - Melanie Pruvost
- Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
- Epigenomic and Palaeogenomic Group, Institut Jacques Monod, Paris, France
| | - Monika Reissmann
- Department of Breeding Biology and Molecular Genetics, Humboldt University Berlin, Berlin, Germany
| | - Ralf Bortfeldt
- Department of Breeding Biology and Molecular Genetics, Humboldt University Berlin, Berlin, Germany
| | - David L. Adelson
- School of Molecular and Biomedical Science, the University of Adelaide, South Australia, Australia
| | - Sim Lin Lim
- School of Molecular and Biomedical Science, the University of Adelaide, South Australia, Australia
| | - Janelle Nelson
- Department of Biology, University of Tampa, Tampa, Florida, United States of America
| | - Bianca Haase
- Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia
| | | | - Tosso Leeb
- Institute of Genetics, University of Bern, Bern, Switzerland
| | - George Forsyth
- Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Michael J. Mienaltowski
- Department of Molecular Pharmacology & Physiology, College of Medicine, University of South Florida, Tampa, Florida, United States of America
| | - Padmanabhan Mahadevan
- Department of Biology, University of Tampa, Tampa, Florida, United States of America
| | | | | | | | - Bruce Grahn
- Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Samantha A. Brooks
- Department of Animal Science, Cornell University, Ithaca, New York, United States of America
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Church ML, Norman JC. Electroretinogram responses of the normal thoroughbred horse sedated with detomidine hydrochloride. Vet Ophthalmol 2012; 15 Suppl 2:77-83. [PMID: 22498137 DOI: 10.1111/j.1463-5224.2012.01022.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE The main objective was to record electroretinogram (ERG) parameters of normal thoroughbred mares using the HMsERG, a mini-Ganzfeld electroretinographic unit, and a contact lens electrode. The second objective was to determine whether IV detomidine hydrochloride at 0.015 mg/kg is consistently an effective choice for sedation of horses undergoing this ERG protocol. METHODS The study population consisted of 30 normal thoroughbred mares. ERG data were harvested using a protocol that included three different light intensities (10, 3000, and 10,000 mcd s/m(2)) and a 30-Hz flicker at 3000 mcd s/m(2). RESULTS Mean, median, standard deviation, and estimated normal ranges using the 5-95% of the data for a- and b-wave implicit times (IT), amplitudes (AMP), and b/a ratios were reported. Scotopic results at low intensity (10 mcd s/m(2)) had estimated ranges for b-wave IT of 41.8-72.9 ms and AMP of 19.8-173.3 μV. Middle intensity (3000 mcd s/m(2)) a-wave IT was 13.2-14.7 ms with a-wave AMP of 68.4-144 μV; the b-wave IT was 28.7-41.5 ms with b-wave AMP of 105.7-271.5 μV; and the b/a ratio was 0.95-2.71. The high-intensity (10,000 mcd s/m(2)) average recordings showed an a-wave IT of 13-14.9 ms, a-wave AMP of 85.7-186.8 μV; b-wave IT of 26.6-45.4 ms, b-wave AMP of 104.7-250.6 μV; and a b/a wave ratio of 0.7-2.0. The 30-Hz cone flicker showed an IT of 22.8-28.9 ms and AMP of 44.1-117.1 μV. CONCLUSIONS Results of normal thoroughbred ERG responses are reported. The protocol proved to be simple and safe and provided consistent results.
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Affiliation(s)
- Melanie L Church
- Eye Care for Animals, 13034 W Rancho Santa Fe Blvd, Suite 102, Avondale, AZ 85392, USA.
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Ben-Shlomo G, Plummer C, Barrie K, Brooks D. Characterization of the normal dark adaptation curve of the horse. Vet Ophthalmol 2011; 15:42-5. [DOI: 10.1111/j.1463-5224.2011.00923.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Sandmeyer LS, Bellone RR, Archer S, Bauer BS, Nelson J, Forsyth G, Grahn BH. Congenital stationary night blindness is associated with the leopard complex in the Miniature Horse. Vet Ophthalmol 2011; 15:18-22. [PMID: 22051042 DOI: 10.1111/j.1463-5224.2011.00903.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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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Affiliation(s)
- Lynne S Sandmeyer
- Department of Small Animal Clinical Sciences, University of Saskatchewan, Quill Lake, Saskatchewan, Canada.
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Abstract
The objective of this review is to introduce equine clinicians to the rapidly evolving field of clinical genomics with a vision of improving the health and welfare of the domestic horse. For 15 years a consortium of veterinary geneticists and clinicians has worked together under the umbrella of The Horse Genome Project. This group, encompassing 22 laboratories in 12 countries, has made rapid progress, developing several iterations of linkage, physical and comparative gene maps of the horse with increasing levels of detail. In early 2006, the research was greatly facilitated when the US National Human Genome Research Institute of the National Institutes of Health added the horse to the list of mammalian species scheduled for whole genome sequencing. The genome of the domestic horse has now been sequenced and is available to researchers worldwide in publicly accessible databases. This achievement creates the potential for transformative change within the horse industry, particularly in the fields of internal medicine, sports medicine and reproduction. The genome sequence has enabled the development of new genome-wide tools and resources for studying inherited diseases of the horse. To date, researchers have identified 11 mutations causing 10 clinical syndromes in the horse. Testing is commercially available for all but one of these diseases. Future research will probably identify the genetic bases for other equine diseases, produce new diagnostic tests and generate novel therapeutics for some of these conditions. This will enable equine clinicians to play a critical role in ensuring the thoughtful and appropriate application of this knowledge as they assist clients with breeding and clinical decision-making.
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Affiliation(s)
- M M Brosnahan
- Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, New York, USA
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Sandmeyer LS, Breaux CB, Archer S, Grahn BH. Clinical and electroretinographic characteristics of congenital stationary night blindness in the Appaloosa and the association with the leopard complex. Vet Ophthalmol 2007; 10:368-75. [PMID: 17970998 DOI: 10.1111/j.1463-5224.2007.00572.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To determine the prevalence of congenital stationary night blindness (CSNB) in Appaloosa horses in western Canada, investigate the association with the leopard complex of white spotting patterns, and further characterize the clinical and electroretinographic aspects of CSNB in the Appaloosa. ANIMALS STUDIED Three groups of 10 Appaloosas were studied based on coat patterns suggestive of LpLp, Lplp, and lplp genotype. PROCEDURES Neurophthalmic examination, slit-lamp biomicroscopy, indirect ophthalmoscopy, measurement of corneal diameter, streak retinoscopy, scotopic and photopic full-field and flicker ERGs and oscillatory potentials (OPs) were completed bilaterally. RESULTS All horses in the LpLp group were affected by CSNB, while none in the Lplp or lplp groups was affected. The LpLp and Lplp groups had significantly smaller vertical and horizontal corneal diameters than the lplp group had. Median refractive error was zero for all groups. Scotopic ERGs in the LpLp (CSNB-affected) group were consistent with previous descriptions. The CSNB-affected horses had significantly longer photopic a-wave implicit times, greater a-wave amplitudes, and lower b-wave amplitudes than the Lplp and lplp (normal) groups did. No differences were present in photopic flicker amplitude or implicit times. Scotopic flickers in the CSNB-affected horses were markedly reduced in amplitude and abnormal in appearance. No differences were noted in OP implicit times; however, amplitudes of some OPs were reduced in CSNB-affected horses. There were no differences in scotopic and photopic or flicker ERGs or OPs between the normal groups. CONCLUSIONS CSNB was present in one-third of horses studied and there was a significant association between CSNB and the inheritance of two Lp alleles. ERG abnormalities support the hypothesis that CSNB is caused by a defect in neural transmission through the rod pathway involving the inner nuclear layer.
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Affiliation(s)
- Lynne S Sandmeyer
- Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 584.
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