Review of literature

Melanomas are common skin tumours of ageing grey horses. As almost every grey horses will develop such tumours if they live long enough. It was supposed that melanoma development and grey colour are genetically linked. Comparative mappings between human, mouse and horse chromosomes have established the location of the grey locus on the ECA25q. A 4.6 kb intronic duplication in intron 6 of the gene STX17 has also been found to be an active character in the expression of the grey colour phenotype. The main question is how a mutation causing loss of hair pigmentation can also cause melanomas development and a massive production of melanin. Scientists have then emitted the hypothesis that the STX17 duplication would lead to proliferation of dermal melanocytes in skin, therefore predisposing to melanoma development. While,on the other hand, hyperproliferation of melanocytes in the hair follicles may cause premature depletion of stem cells and thus a progressive lowering number of melanocytes able to reach the hair follicles leading to fading away of hair pigmentation