The Dilution, or D-Locus, corresponds to the gene for melanophilin, MLPH, which is involved in the distribution of pigment. Mutations of the D-Locus result in a ‘dilution’ that affects the eumelanin (black) and phaeomelanin (red/yellow) pigments in the coat. Affected dogs have a diluted or lighter coat coloration and nose, and eye colour may be lightened to blueish, greenish or amber.
The dilution of the eumelanin pigment creates a blue nose and coat colour ranges from silver to almost black (think of a blue, charcoal or silver coat), while the phaeomelanin pigment to appear a pale or cream color. Specifically, chocolate/brown/liver (affected by the B-Locus) dilutes into lilac/light tan/isabella, with noses varying between pink, liver and isabella. Red/yellow/cream (affected by the E-Locus) dilutes into champagne.
Additionally, affected dogs may display a form of hair loss called Colour Dilution Alopecia (CDA). CDA is characterized by patches of thinning or missing hair, manifesting from the age of approximately six months, and may also result in dry, flaky and/or itchy skin.
Inheritance
The D-locus has two alleles: D (dominant) and d (recessive). Dogs that are homozygous or heterozygous for the dominant D allele (DD or Dd) have normal, non-diluted coat colour. On the other hand, dogs that are homozygous for the recessive d allele (dd) exhibit the diluted or lighter coat coloration. There are several different variants of the mutation (d1, d2 and d3), all of which are equally recessive and result in similar diluted phenotypes. In addition, it’s important to note that the D-locus is only one of several genes responsible for coat colour variation in dogs, and the presence of other genes can modify or interact with the dilution effect.
Relevant tests
• H847
• H461
• H897
