Coat color genotypes and risk and severity of melanoma in gray quarter horses.
Authors: Teixeira R B C, Rendahl A K, Anderson S M, Mickelson J R, Sigler D, Buchanan B R, Coleman R J, McCue M E
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Melanoma Risk in Gray Quarter Horses Gray Quarter Horses demonstrate substantially lower melanoma prevalence (16%) and severity compared to gray horses of other breeds, despite carrying the STX17 duplication responsible for both greying and melanoma development. Researchers genotyped 335 gray Quarter Horses for variants in three candidate genes (STX17, ASIP, and MC1R) that regulate coat colour and melanoma susceptibility through the melanocortin-1 receptor signalling pathway, recording external melanoma presence and grade alongside age and sex data. Whilst age emerged as a highly significant predictor of both melanoma development (P = 5.28 × 10⁻¹¹) and severity (P = 2.2 × 10⁻¹³), neither the MC1R chestnut allele nor ASIP genotype showed meaningful effects on melanoma risk in this population. The unusually low frequency of STX17 homozygosity in Quarter Horses—the genotype most strongly linked to melanoma in other breeds—likely accounts for their comparatively favourable melanoma profile, though breed-specific genetic background and complex gene interactions may also provide protective effects. For practitioners, this suggests that while age remains the dominant risk factor in gray Quarter Horses, individual genetic variation warrants further investigation as a prognostic tool, and breed-specific data should inform melanoma screening protocols rather than extrapolating from broader gray horse populations.
Read the full abstract on PubMed
Practical Takeaways
- •Gray Quarter Horses have substantially lower melanoma risk and severity than gray horses of other breeds, which may reflect breed-specific genetic protection rather than universal gray horse vulnerability
- •Age remains the strongest predictor of melanoma development and progression in gray horses, suggesting increased clinical vigilance for older animals
- •Genetic screening for STX17 and ASIP genotypes may help identify higher-risk individual Quarter Horses, though MC1R testing alone is not predictive in this breed
Key Findings
- •Melanoma prevalence in gray Quarter Horses (16%) and grade (0.35) was significantly lower than reported in other gray horse breeds
- •Age was strongly associated with both melanoma prevalence (P = 5.28 × 10⁻¹¹) and severity (P = 2.2 × 10⁻¹³)
- •MC1R genotype showed no significant effect on melanoma prevalence or severity in this population
- •Low STX17 homozygosity frequency in Quarter Horses may explain reduced melanoma risk compared to other gray horse breeds