Test for the splashed white 5 (SW5) and 6 (SW6) white spotting alleles of the MITF gene. It detects the deletions associated with these patterns and with an increased risk of deafness. Complementary to, not a substitute for, clinical and audiological examination.

Applicable breeds: American Paint Horse, Quarter Horse and other spotted breeds. Frequencies: limited data.

• Extensive white spots, with a tendency to a large facial marking, white legs and white belly.\n• Blue eyes or variable ocular depigmentation.\n• Unilateral or bilateral deafness in some carriers.

SW5 was described in 2019 as a ~63 kb deletion spanning exons 6-9 of MITF in a family of American Paint Horses with white spots, blue eyes and deafness (Henkel 2019). SW6 was described in 2020 as an 8.7 kb deletion in MITF in an American Paint Horse foal (Magdesian 2020).

• Do not mate two carriers of white spotting alleles if extensive white is not desired, because of the higher risk of deafness and extreme depigmentation.\n• Consider the combined genotype of the white spotting loci (SW1-8, tobiano, sabino, W) before deciding a cross.\n• In very white foals, assess hearing by means of auditory evoked potentials.\n• A negative result for SW5/SW6 does not rule out other white spotting alleles.

Differential diagnosis with splashed white 1-4 and 7-10, tobiano, sabino and dominant white. Deafness is confirmed with auditory evoked potentials. Iris depigmentation may be accompanied by heterochromia.

1. Henkel 2019, Whole-genome sequencing reveals a large deletion in MITF in horses with white spotting and deafness (PMID 30644113); OMIA:000214-9796.
2. Magdesian 2020, A de novo MITF deletion explains a novel splashed white phenotype (PMID 32242630); OMIA:000214-9796.
3. McFadden 2024, Spotting the pattern: a review on white coat color in the domestic horse (PMID 38338094); OMIA:000214-9796.