D Locus (Dilute)

The Paw Print Genetics D Locus (Dilute) coat color test evaluates three loci (d1, d2, and d3) to determine the D locus genotype for the dog. The d1 mutation is the common mutation that has been associated with color dilution in many breeds, the d2 mutation has been predominantly identified in the Chow Chow, Sloughi, and Thai Ridgeback, and the d3 mutation has been identified in the Pumi, Mudi, Chihuahua, Italian Greyhound, and others. Dogs with D/D and D/d genotypes typically have a non-dilute coat whereas dogs with a d/d genotype typically have a dilute coat. However, the dog’s coat color is also dependent on the dog’s genotypes at many other genes. Dogs that carry at least one copy of d can produce dilute dogs if bred to another dog that is also dilute (d/d) or a carrier of dilute (D/d). Color dilution may also impact the color of the dog’s nose and footpads.

Other Names:Alopecia, Black hair follicular dysplasia (BHFD), Blue Doberman syndrome, Coat color dilution, Color dilution alopecia (CDA), Color mutant alopecia, D locus, d1, d2, d3, Dilution gene
Affected Genes:MLPH
Mutation(s):d1 = G>A, Chr25:48121642 (Common Variant); d2 = G>C, Chr25:48150787 (Chow Chow, Sloughi, Thai Ridgeback, and Others Type); d3 = Chr25:48150749_50insC (Mudi, Pumi, Chihuahua, Italian Greyhound, and Others Type)
Breed(s):All Breeds
This test will not determine progressive graying/fading
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Testing Summary

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

D/D

This dog does not carry any copies of the d1, d2, or d3 mutations and has a D locus genotype of D/D which does not result in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of D to 100% of its offspring and cannot produce d/d dogs.

Interpretation: Non-dilute (does not carry dilute)
D/d1

This dog carries one copy of the d1 Mutation and has a D locus genotype of D/d which does not result in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of D to 50% of its offspring and one copy of d1 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a Carrier of a d mutation (D/d or d/d).

Interpretation: Non-dilute (carries one copy of dilute)
D/d2

This dog carries one copy of the d2 Mutation and has a D locus genotype of D/d which does not result in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of D to 50% of its offspring and one copy of d2 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a Carrier of a d mutation (D/d or d/d).

Interpretation: Non-dilute (carries one copy of dilute)
D/d3

This dog carries one copy of the d3 Mutation and has a D locus genotype of D/d which does not result in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of D to 50% of its offspring and one copy of d3 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a Carrier of a d mutation (D/d or d/d).

Interpretation: Non-dilute (carries one copy of dilute)
d1/d1

This dog carries two copies of the d1 mutation and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d1 to 100% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d2/d2

This dog carries two copies of the d2 mutation and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d2 to 100% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d3/d3

This dog carries two copies of the d3 mutation and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d3 to 100% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d1/d2

This dog carries one copy each of the d1 and d2 mutations and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d1 to 50% of its offspring and one copy of d2 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d1/d3

This dog carries one copy each of the d1 and d3 mutations and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d1 to 50% of its offspring and one copy of d3 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d2/d3

This dog carries one copy each of the d2 and d3 mutations and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog’s coat color. This dog will pass one copy of d2 to 50% of its offspring and one copy of d3 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d2/d1d3

This dog carries one copy each of the d2, d1, and d3 mutations and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog's coat color. This dog will pass one copy of d2 to 50% of its offspring and one copy of d1d3 to 50% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
d1d3/d1d3

This dog carries two copies of the d1 and d3 mutations and has a D locus genotype of d/d which results in the "dilution" or lightening of the pigments that produce the dog's coat color. This dog will pass one copy of d1d3 to 100% of its offspring. This dog can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Dilute (carries two copies of dilute)
D/d1d3 or d1/d3

This dog carries one copy each of the d1 and d3 mutations and has a D locus genotype of either D/d or d/d that cannot be distinguished without additional testing of the parental samples or by examining the coat, nose and footpad color of the dog. The d1 and d3 mutations are known to occur on the same Chromosome, so a dog can inherit both mutations from one parent and will be D/d. If one mutation is inherited from each parent, then the dog is d/d. If the dog is dilute, the D locus will be d/d and this dog will pass one copy of d1 to 50% of its offspring and one copy of d3 to 50% of its offspring. If the dog is not dilute, the D locus will be D/d and this dog will pass one copy of D to 50% of its offspring and one copy of d1d3 to 50% of its offspring. In either case, this dog carries at least one copy of d and can produce d/d offspring if bred to a dog that is also a carrier of a d mutation (D/d or d/d).

Interpretation: Non-dilute or Dilute (carries at least one copy of dilute)

Detailed Summary

The D Locus (Dilute) corresponds to the MLPH gene that is important in determining coat color in dogs. Mutations/variants in this gene modify the expression of the pigments, eumelanin (black and brown) and phaeomelanin (reds, yellows and creams) in the hair resulting in a "dilution" or 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 MLPH gene will have a diluted coat color that may be referred to as blue, charcoal, silver, Isabella (lilac) or fawn (depending on the breed and the base coat color of the dog).

Disease Association Note: Mutations of the D locus are sometimes responsible for a condition called color dilution Alopecia, black hair follicular dysplasia, or blue Doberman syndrome (depending on the breed) because dilute coat color can be associated with development of alopecia (hair loss). The clinical presentation of alopecia associated with dilute coat color is variable within and between breeds; therefore, only a portion of individuals carrying two copies of the MLPH gene Mutation (d/d) will show hair loss with some breeds being much more likely to develop the condition. Though two copies of the MLPH gene mutation (d/d) are necessary to develop color dilution alopecia, the variable presentation of this condition suggests that additional environmental or genetic factors contribute to the development of alopecia. Dogs affected with alopecia typically present with loss of hair between the ages of four months and two years. Hair of affected dogs can also appear dry and dull. The hair loss is caused by abnormal Melanin storage in the hair, which leads to breakage of the hair shaft and the lack of normal regrowth of hair. Dogs with this condition can also be affected with recurrent bacterial skin infections originating in the hair follicles (folliculitis). Given that the modifying environmental or genetic factors responsible for alopecia are unknown, the only way to prevent color dilution alopecia is to avoid transmitting the dilute coat color mutation to offspring in susceptible breeds.

Testing Tips

Genetic testing of the MLPH gene will reliably determine the number of copies of the color dilution gene Mutation that a dog carries. Coat color dilution associated with mutations of the MLPH gene is known to be inherited in an Autosomal Recessive manner in dogs. Carrier dogs (D/d) do not display a dilute color and are not at risk for Alopecia, but when bred with another dog that also is a carrier (D/d), there is a 25% chance of having pups with diluted coat color that may also be susceptible to alopecia in some breeds. Reliable genetic testing is important for determining breeding practices. Dogs that are not carriers of a d mutation have no increased chance of having pups with diluted coat color or alopecia.

Note: In situations where the d and d3 mutations are identified in a dog, the presence of these mutations being located on a single copy of the D Locus cannot be excluded. Therefore, the overall D locus genotype for a dog could be D/d or d/d and cannot be determined without additional testing of parental samples. However, the D locus genotype for a dog in this situation can be inferred without the need for parental testing by evaluating the color of the dog’s coat and nose (see D/d or d/d genotype interpretation above).

Disclaimer:

There may be other causes of this color pattern 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 trait.

References

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