Macchiato (splashed white)

The Macchiato coat color was first described in Freiberger horses in 2008. The first recorded foal was born with an unusual coat color phenotype. Compared to the breed standard, the foal had white spots on its coat, a broad white blaze on the head, white-colored legs and abdomen, and blue eyes. Some time later, it was found that the foal was affected by deafness.

White spots develop during embryonic development. Melanoblasts are derived from neural crest cells and subsequently differentiate into mature pigment cells, melanocytes. Abnormalities in melanocyte development lead to the formation of white spots. The causes of the splashed white phenotype may be of two types. Melanocytes may have a problem producing pigment, or partial or complete loss of melanocyte precursor cells may occur during their migration during embryonic development. In addition to coat pigmentation, melanocytes are also essential for proper hearing function. The absence of melanocytes in the vascular structure of the inner ear (stria vascularis) leads to degeneration of the vascular network. As a result of this damage, receptor cells that normally receive acoustic impulses die. Therefore, in addition to changes in phenotype and heterochromic iris, splashed white is also associated with a risk of sensorineural deafness. Research revealed a de novo mutation in the MITF gene (g.21564980T>C). The stallion in which the mutation was found underwent castration, and no offspring from him are known.

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References:

Blatter, M., et al. "Klinische und genetische Befunde bei einem männlichen Freiberger mit der neuen Fellfarbe Macchiato." Schweizer Archiv für Tierheilkunde 155.4 (2013): 229-232.

Hauswirth, R.; Haase, B.; Blatter, M.; Brooks, S. A.; Burger, D.; Drögemüller, C.; Gerber, V.; Henke, D.; Janda, J.; Jude, R.; Magdesian, K. G.; Matthews, J. M.; Poncet, P.-A.; Svansson, V.; Tozaki, T.; Wilkinson-White, L.; Penedo, M. C. T.; Rieder, S.; Leeb, T. Mutations in MITF and PAX3 Cause “Splashed White” and Other White Spotting Phenotypes in Horses. PLoS Genetics 2012, 8 (4), e1002653. https://doi.org/10.1371/journal.pgen.1002653.