The complex inheritance of melanoma and coat/skin pigmentation (grey level, vitiligo grade, and speckling grade) in grey horses has been shown to be primarily due to the effects of a 4.6‐kb duplication in intron 6 of the STX17 (syntaxin 17) gene; this constitutes a cis‐acting regulatory mutation that has melanocyte‐specific effects [possibly due to the fact that it affects an enhancer that encodes binding sites for the microphthalmia‐associated transcription factor (MITF), which regulates melanocyte development] [106, 107]. The gene discussed is STX17; the disease is melanoma.