Identification of a novel missense variant in SLC45A2 associated with dilute snowdrop phenotype in Gypsy horses

SLC45A2 mutations are responsible for several dilution phenotypes in horses, including cream, pearl, and sunshine. We sequenced the SLC45A2 gene in a horse that possessed a diluted coat color but tested negative for any known dilution genotypes. We identified a novel homozygous missense mutation in ECA21: SLC45A2:c.305G>A; p.(Arg102Gln) which we have named snowdrop (Csno). The snowdrop dilution is autosomal recessive and dilutes both red and black pigment in the homozygous state, creating a phenotype similar to homozygous cream. We also identified this mutation in the heterozygous state in several relatives, including the sire and dam of the affected horse, where it has no visible effect on phenotype. Based on these data, the snowdrop variant produces a recessive dilution similar to cream, and its discovery confirms that multiple SLC45A2 alleles cause dilute phenotypes in horses.