D-Locus (dilute/colour dilution)

The D locus (dilute/colour dilution) corresponds to a region of the MLPH gene that is important in the expression of coat colour. This gene variant influences the production of the pigments eumelanin and phaeomelanin in the hair. A genetic change within this gene leads to a "thinning" or lightening of the coat colour in dogs. The determination of coat colour is very complex due to the interactions of several genes that are responsible for both the colour and the anatomical distribution of the colour. A dog with two altered copies of the MLPH gene will have the colours blue, charcoal, isabell or fawn, depending on the other coat colour genes.

Note on disease associations:
Colour thinning is occasionally responsible for a condition known as colour thinning alopecia, black hair follicle dysplasia or blue Doberman syndrome (depending on the breed). The thinned coat colour can be associated with the development of hair loss (allopecia). The severity of alopecia associated with thinned coat colour is highly variable within and between breeds. Only a proportion of dogs carrying two copies of the MLPH gene variant actually show hair loss, with some breeds being much more likely to develop the condition. Although two copies of the MLPH gene variant are necessary to develop colour thinning alopecia, the variable expression of this condition suggests that additional environmental or genetic factors contribute to its development. Affected dogs typically show hair loss beginning at four months to two years of age. The hair may also appear dry and dull. The hair loss is caused by abnormal melanin storage in the hair, resulting in breakage of the hair shaft and lack of normal hair regrowth. Dogs with this condition can also be affected by recurrent bacterial skin infections originating from the hair follicles (folliculitis). Considering that the modifying environmental or genetic factors responsible for alopecia are unknown, the only way to prevent it is to avoid breeding colo