D Locus (Dilute)
The D Locus (Dilute) coat colour test reliably determines if a dog has one of the following genotypes at the D locus:
|D/D||This dog carries two copies of D which does not result in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat colour. The base coat colour of this dog will be primarily determined by the E, K, A, and B genes. The dog will pass on D to 100% of its offspring.Interpretation: Non dilute|
|D/d||This dog carries one copy of D and one copy of d which does not result in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat colour. The base coat color of this dog will be primarily determined by the E, K, A, and B genes. The dog will pass on D to 50% of its offspring and d to 50% of its offspring.Interpretation: Non dilute (Carrier)|
|d/d||This dog carries two copies of d which results in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat colour. However, this variant modifies or "dilutes" the base coat color of the dog that is primarily determined by the E, K, A, and B genes. The dog will pass on d to 100% of its offspring.Interpretation: Dilute|
The D Locus (Dilute) corresponds to a region of the MLPH gene that is important in determining coat colour in dogs. This gene variant modifies the expression of the pigments, eumelanin and phaeomelanin in the hair. A genetic variant within this gene results in a “diluting” or lightening of the coat colour of dogs. Canine coat colour determination is complex due to interactions of multiple genes responsible for both colour and anatomic placement of the colour. A dog with two variant copies of the MLPH gene will have a blue, charcoal, Isabella (lilac) or fawn coat colour depending on the other coat colour genes present in the individual. Disease Association Note: Variants of the D locus are sometimes responsible for a condition called colour dilution Alopecia, black hair follicular dysplasia, or blue Doberman syndrome (depending on the breed) because dilute coat colour can be associated with development of alopecia (hair loss). The clinical presentation of alopecia associated with dilute coat colour is variable within and between breeds; therefore only a portion of individuals carrying two copies of the MLPH gene variant will show hair loss with some breeds being much more likely to develop the condition. Though two copies of the MLPH gene variant are necessary to develop colour 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 colour dilution alopecia is to avoid transmitting the dilute coat colour variant to offspring in susceptible breeds.
Genetic testing of the MLPH gene will reliably determine the number of copies of the colour dilution gene variant that a dog carries. Coat colour dilution associated with this particular MLPH variant is known to be inherited in an Autosomal Recessive manner in dogs. Carrier dogs do not display a dilute colour and are not at risk for Alopecia but when bred with another dog that also is a carrier of the same variant, there is a 25% chance of having pups with diluted coat colour 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 this variant have no increased chance of having pups with diluted coat colour or alopecia.
*Note: Normal results do not exclude inherited mutations not tested in these or other genes that may also contribute to coat colours and traits in dogs.
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.
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