Genes linked to vitiligo in horses possibly tied to melanoma susceptibility – study

Phenotypic classification of vitiligo-like depigmentation - grade 0 to 1.
Phenotypic classification of vitiligo-like depigmentation, grade 0 to 1.

Researchers who identified the genes most likely responsible for the skin disorder vitiligo, which mostly affects grey horses, believe some may be tied with the greater risk of melanoma seen among these lighter-coloured animals.

Vitiligo is an autoimmune disease characterized by the loss of skin pigmentation. In horses, it results in patchy depigmentation of the skin around the eyes, muzzle and anus.

Vitiligo-like depigmentation occurs mostly in grey horses, with 26% to 67% showing evidence of the condition. In non-grey horses, its prevalence is between 0.8% and 3.5%.

In humans, it has been established that multiple genes are involved in the condition. Indeed, up to 322 genes related to vitiligo in humans have been addressed in 202 scientific articles. However, in horses, the underlying candidate genes remain unknown.

Thomas Druml and his fellow researchers set out to identify genes potentially involved in the disease in horses based on genetic data from 152 Lipizzaner selected for their grey coat colour, and 104 solid-coloured Noriker horses (an Austrian draught breed), who were used as controls.

All of the horses were visually checked for vitiligo, with 33 of the Lipizzaner horses (21.7%) showing evidence of the condition. None of the Noriker horses showed vitiligo-like characteristics.

The researchers, reporting in the journal BMC Veterinary Research, identified several candidate genes on four chromosomes (ECA1, ECA13, ECA17, ECA20) seemingly involved in vitiligo development in grey horses.

Four of the genes, PHF11, SETDB2, CARHSP1 and LITAFD, are associated with the innate immune system, while the others, RCBTB1, LITAFD, NUBPL, PTP4A1, play a role in tumor suppression and metastasis (the process by which cancer cells spread).

Phenotypic classification of vitiligo-like depigmentation, grade 2 and 3.
Phenotypic classification of vitiligo-like depigmentation, grade 2 and 3.

In addition to the higher incidence of vitiligo-like depigmentation, grey horses carrying the coat colour STX17 gene mutation also showed a higher incidence of melanoma, which ranges from 46.1% to 50% in grey Lipizzaners.

Given the complex nature of vitiligo, the highlighted genes need further verification by expression studies and replication studies across breeds, the research team said.

“The current study indicates a relationship between this depigmentation phenotype and melanoma in grey horses and represents a research question that needs further investigation,” they said.

The authors noted that several vitiligo susceptibility genes in humans, particularly those expressed in pigment-producing melanocytes, have been detected to be involved in susceptibility to malignant melanoma.

The study team comprised Druml, Gottfried Brem and Gertrud Grilz-Seger, with the University of Veterinary Medicine Vienna; Brandon Velie, with the University of Sydney; Gabriella Lindgren, with the Swedish University of Agricultural Sciences; Michaela Horna, with the Slovak University of Agriculture; and Anne Ricard, with the University of Paris-Saclay.

Druml, T., Brem, G., Velie, B. et al. Equine vitiligo-like depigmentation in grey horses is related to genes involved in immune response and tumor metastasis. BMC Vet Res 17, 336 (2021).

The study, published under a Creative Commons License, can be read here

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