Test for the mushroom dilution of the MFSD12 gene, specific to the Shetland Pony, which turns a chestnut coat into a uniform sepia tone. Complementary to, not a substitute for, clinical examination.

Applicable breed: Shetland Pony (and suspected in Miniature Horse). Frequencies: limited data; the variant is described in a specific population.

• Dilution of the chestnut coat toward a sepia or greyish-brown tone, without whitening.\n• It does not affect other pigments or the skin.\n• Relatively uniform phenotype in homozygotes.

The mushroom dilution was mapped to chromosome 7, and in 2019 Tanaka and colleagues identified a frameshift mutation in MFSD12, perfectly consistent with the phenotype in Shetland ponies.

• Being recessive, healthy carriers can transmit the allele without showing the phenotype.\n• Avoid pairing two carriers if the mushroom phenotype is not sought.\n• Do not confuse mushroom with silver, cream or champagne.\n• A negative result does not rule out dilutions of other genes.

The dilution affects pheomelanin (red/yellow pigment). MFSD12 has also been associated with pigmentation in other species; the phenotype is exclusively aesthetic.

1. Tanaka 2019, Frameshift variant in MFSD12 explains the mushroom coat color dilution in Shetland Ponies (PMID 31635058); OMIA:002197-9796.