title: Coat color genotypes and risk and severity of melanoma in gray quarter horses.
abstract: BACKGROUND
  Both graying and melanoma formation in horses have recently been linked to a duplication in the STX17 gene. This duplication, as well as a mutation in the ASIP gene that increases MC1R pathway signaling, affects melanoma risk and severity in gray horses.
  
  
  OBJECTIVE
  To determine if melanoma susceptibility in gray Quarter Horses (QH) is lower than gray horses from other breeds because of decreased MC1R signaling resulting from a high incidence of the MC1R chestnut coat color allele in the QH population.
  
  
  METHODS
  A total of 335 gray QH with and without dermal melanomas.
  
  
  METHODS
  Blood or hair root samples were collected from all horses for DNA extraction and genotyping for STX17, ASIP, and MC1R genotypes. Age, sex, and external melanoma presence and grade were recorded. The effect of age and genotype on melanoma presence and severity was evaluated by candidate gene association.
  
  
  RESULTS
  Melanoma prevalence (16%) and grade (0.35) in this QH cohort was lower than that reported in other breeds. Age was significantly associated with melanoma prevalence (P = 5.28 × 10(-11)) and severity (P = 2.2 × 10(-13)). No significant effect of MC1R genotype on melanoma prevalence or severity was identified. An effect of ASIP genotype on melanoma risk was not detected. Low STX17 homozygosity precluded evaluation of the gray allele effect.
  
  
  CONCLUSIONS
  Melanoma prevalence and severity is lower in this population of gray QH than what is reported in other breeds. This could be because of the infrequent STX17 homozygosity, a mitigating effect of the MC1R mutation on ASIP potentiation of melanoma, other genes in the MC1R signaling pathway, or differences in breed genetic background.
authors.affiliation: Veterinary Population Medicine, University of Minnesota, St Paul, MN.
authors.forename: R B C
authors.initials: RB
authors.lastname: Teixeira
authors.forename: A K
authors.initials: AK
authors.lastname: Rendahl
authors.forename: S M
authors.initials: SM
authors.lastname: Anderson
authors.forename: J R
authors.initials: JR
authors.lastname: Mickelson
authors.forename: D
authors.initials: D
authors.lastname: Sigler
authors.forename: B R
authors.initials: BR
authors.lastname: Buchanan
authors.forename: R J
authors.initials: RJ
authors.lastname: Coleman
authors.forename: M E
authors.initials: ME
authors.lastname: McCue
mesh_terms: D054366:Agouti Signaling Protein / Q000235:genetics / Q000378:metabolism; D000818:Animals; D005260:Female; D005786:Gene Expression Regulation; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006720:Homozygote; D006734:Horse Diseases / Q000235:genetics*; D006736:Horses; D008297:Male; D008545:Melanoma / Q000235:genetics / Q000662:veterinary*; D009154:Mutation; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D044102:Receptor, Melanocortin, Type 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D054366:Agouti Signaling Protein; D050765:Qa-SNARE Proteins; D044102:Receptor, Melanocortin, Type 1; C515183:a protein, mouse
keywords: ASIP; MC1R; Metastasis; STX17