Test for the dominant white allele W4 of the KIT gene, characteristic of the Camarillo White Horse breed. It detects the variant associated with white coat with unpigmented skin and eyes. It is complementary to, not a substitute for, clinical examination.

Applicable breed: Camarillo White Horse (United States). Frequencies: limited data; allele linked to a founder lineage.

• Practically complete white coat from birth or early infancy.\n• Pink skin and absence of pigment in the iris (blue eyes).\n• No defined spotting pattern; the white is generalised.

The Camarillo White Horse breed originated in California from a white stallion. In 2007 Haase and colleagues identified in KIT the W4 allele (p.A602V) associated with the dominant white phenotype.

• Avoid crosses between two white animals carrying W alleles, because of the risk of lethal homozygosity.\n• Confirm the specific allele (W4 versus other W alleles) before any breeding decision.\n• Do not confuse with tobiano, sabino or splashed white.\n• A white foal from non-white parents should be investigated for a possible de novo mutation.

In W alleles, white is due to the absence of melanocytes, not to a failure of pigment synthesis. Assess hearing and vision in animals with extensive depigmentation. KIT testing should be interpreted allele by allele, not merely as positive/negative.

1. Haase 2007, Allelic heterogeneity at the equine KIT locus in dominant white (W) horses (PMID 17997609); OMIA:000209-9796.
2. McFadden 2024, Spotting the pattern: a review on white coat color in the domestic horse (PMID 38338094); OMIA:000209-9796.