Genetic and environmental risk factors for vitiligo and melanoma in Pura Raza Español horses

Abstract

Vitiligo is an acquired, non-contagious disorder, characterised byprogressive patchy loss of skin pigmentation. Vitiligo tends to cover hairand mucous membranes (due to a loss of melanocytes in the affectedareas) [1]. Despite the fact that the phenotype of vitiligo has been readilyrecognised for thousands of years, the underlying pathobiology hasremained largely unknown [2]. Similarly, melanomas are usually pigmentedneoplasm which often present multicentric malignancy in the later stages[3]. They are most commonly found in grey horses and reach a prevalenceof around 80% in horses of 15 years of age or older [4]. Studies in humansindicate that there is a genetic link between melanoma and vitiligo [5,6].Moreover, in horses, the dominant phenotype of greying with age isassociated with a high incidence of melanoma and vitiligo-like skindepigmentation [7].Since the Pura Raza Espa~nol is a mainly grey breed, the animals aresusceptible to vitiligo and melanoma. Since 2012, it has been standardpractice to record a vitiligo score(VS) and melanoma score (MS) in PuraRaza Espa~nol breed registers [8]. This provides the opportunity to estimatethe breed prevalence of these disorders, and to examine potentialenvironmental risk and genetic factors associated with these diseases. Wehypothesised that both VS and MS are prevalent in Pura Raza Espa~nolpopulations worldwide, and that both environmental risk factors andgenetics play a significant role in thedevelopment of these conditions. Thespecific aims of this work were to: 1) measure the breed prevalence ofvitiligo and melanoma in a worldwide population of Pura Raza Espa~nolhorses, including non-grey horses, 2) establish the potential links withinbreeding, age, sex, coat colour and geographic area for the developmentof vitiligo and melanoma in this breed and 3) estimate the heritability andgenetic correlations for VS and MS. A better understanding of how these factors contribute to the development of vitiligo and melanoma is crucialto improve the management and breeding selection of mainly grey horsebreeds.