I Locus (Intensity)

Affected Genes: MFSD12
Inheritance: Autosomal Recessive
Mutation: chr20:55855086-55855086: C/T
Breed(s): All Breeds
This test will not determine progressive graying/fading
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Testing Summary

The I Locus (Intensity) coat color test evaluates the MFSD12 gene to determine the I locus genotype for the dog. This Mutation has been associated with the extreme dilution of the light, yellow to red pigment (i.e., phaeomelanin) in many breeds, associated with an e/e genotype at the E locus. The phaeomelanin pigment can also be seen in dogs with a dark coat color that express their A locus (Agouti) genotype; for example, a dog with tan (phaeomelanin) points (ky/ky and at/at) or the light base color of hairs on sable/fawn (ky/ky and Ay/-) dogs.

Dogs with I/I and I/i genotypes typically have an unmodified (yellow to red) phaeomelanin pigment. Dogs with an i/i genotype typically have a less intense, cream or white phaeomelanin pigment. However, there are other, unknown genes that influence the final shade of phaeomelanin; genes responsible for the red shade of phaeomelanin are still unknown. Dogs that carry at least one copy of the i Allele can produce light cream or white dogs if bred to another dog that is also light cream or white (i/i) or a Carrier of light cream or white (I/i). The color of the dog’s nose and footpads is still dependent on the B locus; there is no evidence that the I Locus impacts the nose and footpad color.

The I Locus (Intensity) coat color test reliably determines if a dog has one of the following genotypes at the I locus:

I/I

This dog does not carry a copy of the i mutation and has an I locus genotype of I/I which does not result in the lightening of the light, phaeomelanin pigments that produce the dog’s coat color in an e/e dog. This dog will pass one copy of I to 100% of its offspring and cannot produce i/i dogs.

Interpretation: Normal Intensity

I/i

This dog carries one copy of the i mutation and has an I locus genotype of I/i which does not result in the lightening of the light, phaeomelanin pigments that produce the dog’s coat color in an e/e dog. This dog will pass one copy of I to 50% of its offspring and one copy of i to 50% of its offspring. This dog can produce i/i offspring if bred to a dog that is also a carrier of an i mutation (I/i or i/i).

Interpretation: Normal Intensity (carrier)

i/i

This dog carries two copies of the i mutation and has an I locus genotype of i/i which results in the extreme lightening of the light, phaeomelanin pigments that produce the dog’s coat color in e/e dogs. This dog will pass one copy of i to 100% of its offspring. This dog can produce i/i offspring if bred to a dog that is also a carrier of an i mutation (I/i or i/i).

Interpretation: Reduced intensity, likely light shades or white


Detailed Summary

The I Locus (Intensity) corresponds to the MFSD12 gene that is important in determining the shade of the light pigment (phaeomelanin) in dogs. Mutations in this gene modify the expression of the phaeomelanin (reds, yellows and creams) in the hair resulting in an extreme lightening of the coat color of dogs. Canine coat color determination is complex due to interactions of multiple genes responsible for both color and anatomic placement of the color. A dog with two mutant copies of the MFSD12 gene will have an extremely light phaeomelanin that will cause a dog that is e/e at the E locus to have a coat color that is light cream or white.



Testing Tips

Genetic testing of the MFSD12 gene will reliably determine the number of copies of the intensity gene Mutation that a dog carries. Phaeomelanin dilution associated with mutations of the MSFD12 gene is known to be inherited in an Autosomal Recessive manner in dogs. Carrier dogs (I/i) do not display an extreme phaeomelanin dilution, but when bred with another dog that also is a carrier (I/i), there is a 25% chance of having pups with light cream or white coat color (if also e/e at the E Locus). Reliable genetic testing is important for determining breeding practices. Dogs that are not carriers of an i mutation have no increased chance of having pups with a light cream or white coat color.


There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


References

  • Hedan B, Cadieu E, Botherel N, Dufaure de Citres C, Letko A, Rimbault M, Drogmuller C, Jagannathan V, Derriern T, Schmutz S, Leeb T, and Andre C. Identification of a Missense Variant in MFSD12 Involved in Dilution of Phaeomelanin Leading to White or Cream Coat Color in Dogs. 2019 May 21; 10(5), 386. [PubMed: 31117290]