S-Locus (Parti, Piebald, or Random White Spotting)

Description

The S-Locus test looks for the variant associated with piebald, parti and random white spotting in dogs. There is no single basis for the white spotted patterns that occur in animals like cats, dogs and horses. In horses, random white spotting, or deletion of color, is caused by more than half a dozen known genetic factors. In more than 25 different dog breeds, a mutation in a gene called Microphthalmia Associated Transcription Factor (MITF) is associated with piebald spotting.

In many breeds, piebald behaves as a “dosage”-dependent trait. This means that the amount of white a dog shows depends on how many copies of the S-Locus allele the dog has. Dogs like the French Bulldog that have a single copy of the MITF variant (n/S) will show a limited white spotting pattern. Dogs that have two copies of the variant (S/S) will show more white with very little color. In some breeds, dogs that are S/S are completely white, while dogs that are n/S have what is referred to as the mantle. The mantle coloration is seen in several breeds but is perhaps best exemplified by the Great Dane (black with a white chest, throat and feet).

As with horses and other animals, dog breeds with white spotting patterns can be affected by additional mutations in the S-Locus and by other genes that affect where color is deleted and how it is distributed. For example, the Irish spotting pattern (similar to mantle) seen in breeds such as Collies and Shelties is not caused by this mutation.

Possible results

Reference

Efficient mapping of mendelian traits in dogs through genome-wide association.

[PMID: 17906626]