Genetics and characteristics
Horses display a huge variety of distinct coat color patterns that breeders value and they are often caused by a variant in genes responsible for pigment synthesis. Several genes are known to diminish the intensity of the coloration and cause “dilutions”. One of those dilutions is Pearl dilution characterized by a dilution of the coat, mane, and tail as well as a lightening of the skin, often resembling the champagne dilution. This type of dilution has been previously identified in a few horse breeds including Andalusian, Lusitano, Paint Horse, and Quarter Horse. The cause of the pearl dilution in horses is a single nucleotide change within the MATP gene, also known as the SLC45A2 gene. MATP or SLC45A2 encodes a protein that plays an important role in disrupting the trafficking of pigment molecules to developing melanocytes or pigment-producing cells.
Pearl dilution in horses is inherited as an autosomal recessive trait meaning two copies of the mutated gene are required for a horse to have a pearl coat color. One mutated gene will not change the coat color of black, bay, or chestnut horses, but two mutated genes will cause a chestnut horse to produce a pale, uniform apricot color of body hair, mane, and tail. Pearl is also known to interact with cream dilution and produce what is known as pseudo-double cream dilute horse with pale skin and blue/green eyes. Early detection by genetic testing can help identify carriers of the mutation and help breeders in further selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
Normal coat color |
Horse does not have the gene with the mutation and has a normal coat color. |
Normal coat color - carrier of Pearl dilution |
Horse has one copy of the gene with the mutation and has a normal coat color. |
Pearl dilution |
Horse has two copies of the gene with the mutation and displays a diluted coat color. |
References:
Holl, H. M., Pflug, K. M., Yates, K. M., Hoefs-Martin, K., Shepard, C., Cook, D. G., Lafayette, C., Brooks, S. A. (2019). A candidate gene approach identifies variants in SLC45A2 that explain dilute phenotypes, pearl and sunshine, in compound heterozygote horses. Animal genetics, 50(3), 271–274. https://doi.org/10.1111/age.12790
Sevane, N., Sanz, C. R., Dunner, S. (2019). Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses. Animal genetics, 50(3), 275–278. https://doi.org/10.1111/age.12784
Castle W. E. (1948). The Abc of Color Inheritance in Horses. Genetics, 33(1), 22–35. https://doi.org/10.1093/genetics/33.1.22