Test Detail

Test for three dominant white alleles of the KIT gene: W5, W10 and W13. It detects the variants associated with extensive white coats and allows carriers to be identified. It is complementary to, not a substitute for, clinical examination.

Applicable breed: Thoroughbred and Quarter Horse (W5, W10), Miniature Horse, Shetland Pony and Quarter Horse (W13). Frequencies: limited data; W alleles are rare and often arise de novo.

• Extensive or almost complete white coat, with pink skin.\n• There may be residual pigmented patches, especially on the head.\n• Eyes frequently blue or unpigmented.

The W alleles of KIT were described between 2007 and 2011 (Haase and colleagues). W5 and W10 were identified in Thoroughbred and Quarter Horse horses (2009) and W13 in the Miniature Horse, Shetland Pony and Quarter Horse (2011).

• Do not mate two animals carrying different W alleles or the same one: homozygosity is lethal for most alleles.\n• Identify the specific allele, because the risk and the phenotype depend on the variant.\n• Suspect a de novo mutation in a white foal from non-white parents.\n• The combination of a W allele with other spotting alleles increases depigmentation.

The white is due to the absence of melanocytes. Assess hearing and vision. Some W alleles (e.g. W15, W20) are not lethal in homozygosity; the variant must be identified before assuming lethality.

1. Haase 2007, Allelic heterogeneity at the equine KIT locus in dominant white (W) horses (PMID 17997609); OMIA:000209-9796.
2. Haase 2009, Seven novel KIT mutations in horses with white coat colour phenotypes (W5, W10) (PMID 19456317); OMIA:000209-9796.
3. Haase 2011, Five novel KIT mutations in horses with white coat colour phenotypes (W13) (PMID 21554354); OMIA:000209-9796.