Shirayukihime (Japanese: シラユキヒメ, Hepburn: Shirayukihime; 4 April 1996 – 5 May 2019) was a Japanese Thoroughbredracehorse and broodmare. She competed in 2001, recording no wins in nine starts. She is notable for being a white-coated horse born from a spontaneous KIT gene mutation (designated W14), and for establishing a lineage of white-coated racehorses as a broodmare. Her descendants include Sodashi, the first white horse to win a Japanese Classic, and Hayayakko, the first white horse to win a JRA graded stakes race.
Background
Shirayukihime was a white mare bred in Hayakita (now Abira), Hokkaido, by Northern Farm. She was sired by Sunday Silence and her dam was Wave Wind, a bay mare by the American stallion Topsider. Despite both parents being dark-coated (Sunday Silence was dark bay, Wave Wind was bay), Shirayukihime was born white due to a spontaneous mutation in the KIT gene. The mutation, designated W14, is a 54-base-pair deletion in exon 17 (c.2392_2445del) that causes an 18-amino-acid deletion in the tyrosine kinase domain II of the stem cell factor receptor (SCFR). This disrupts melanocyte precursor cell migration, resulting in a white or spotted coat. The probability of such a spontaneous white mutation occurring is estimated at 1 in 10,000 to 1 in 20,000. Her racing name is derived from the Grimm's Fairy Tales character Snow White. She was owned by Makoto Kaneko and sent into training with Yoshiyuki Goto at the JRA's Miho Training Center.
Racing career
Shirayukihime debuted on February 3, 2001, in a 5-million-yen allowance race on the turf at Kokura Racecourse, finishing eleventh. She ran in eight subsequent races through September 2001, all in the 5-million-yen or 9-million-yen allowance classes. Her best finish was third in a 5-million-yen allowance race over 2000 meters at Fukushima Racecourse on May 13, 2001. This was the first time a white-coated horse finished in the top three in a JRA race. She did not win any of her nine starts and earned ¥1,900,000 in total.
Statistics
The following table details all 9 starts of Shirayukihime's racing career based on official netkeiba and JBIS records.
Following her retirement from racing, Shirayukihime became a broodmare at Northern Farm. Because the W14 white mutation is dominant over other coat colours, approximately 50% of her foals were born white or spotted, following Mendelian inheritance. She was mated with three stallions owned by Makoto Kaneko: Black Hawk, Kurofune, and King Kamehameha. Her broodmare registration was cancelled on February 7, 2017. She died on May 5, 2019.
Amante Bianco (2021, c, white, by Henny Hughes, out of Yukichan) - Haneda Hai (JpnI, 2024)
White coat genetics
The white coat of Shirayukihime and her descendants is caused by the W14 mutation in the KIT gene. This mutation is a 54-base-pair deletion in exon 17 (c.2392_2445del), resulting in an 18-amino-acid deletion in the tyrosine kinase domain II of the stem cell factor receptor (SCFR). Because the mutation occurs in the intracellular domain, it reduces SCFR activity by up to 75%, producing a more severe white phenotype than mutations in the extracellular domain. Horses carrying one copy of W14 may be fully white, spotted (buchi), or have partial white markings. Horses homozygous for W14 are presumed non-viable.
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