Test for the splashed white 1, 2, 3 and 4 alleles, which produce extensive white markings with a large facial marking, white legs and, in some cases, blue eyes and deafness. It detects variants in MITF (SW1, SW3) and PAX3 (SW2, SW4). Complementary to, not a substitute for, clinical and audiological examination.

Applicable breed: American Paint Horse, Quarter Horse, Miniature Horse, Shetland Pony, Icelandic Horse, Appaloosa and others. Frequencies: limited data.

• Very extensive facial marking (broad blaze) and white legs.
• White belly and lower body.
• Blue eyes or heterochromia.
• Unilateral or bilateral deafness in some carriers.

In 2012 Hauswirth and colleagues described SW1 and SW3 in MITF and SW2 in PAX3 as causes of the splashed white pattern; SW4 (PAX3) was added in 2013.

• Avoid mating two carriers of splashed white alleles, because of the greater risk of extreme white and deafness.
• Assess the total load of spotting alleles before mating.
• In very white foals, assess hearing.
• A negative result for SW1-4 does not rule out SW5-10 or other patterns.

Differential diagnosis with tobiano, sabino, dominant white and SW5-10. Deafness is confirmed with auditory evoked potentials. The risk increases with the combination of spotting alleles.

1. Hauswirth 2012, Mutations in MITF and PAX3 cause 'splashed white' and other white spotting phenotypes (SW1, SW2, SW3) (PMID 22511888); OMIA:000214-9796 / OMIA:001688-9796.
2. Hauswirth 2013, Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes (SW4) (PMID 23659293); OMIA:001688-9796.