It seems strange to talk and think about diluted coat colours. I get a picture of someone watering the colours down with buckets of water. But the fact is that these colours do actually look like someone has done just that. Dilution genes will cause regular colours like brown and black to become lilac (this is not a purple colour but rather a light greyish-blue), pale brown and grey respectively. Breeders describe these colours as blue, charcoal-grey and lilac.

Dilution alleles

•  D (dilutes or pales eumelanin pigment to blue, and phaeomelanin subtly) = (MLPH)
•    D = not diluted
•    d = diluted pigmentation
•  G (Progressive Greying) = (gene not yet identified) This gene causes gradual greying of black or brown hair and paling of red hair, prior to geriatric age.
•    G = Progressive greying
•    g = wild type, no premature greying

Blue-eyed boys
Blue or charcoal-grey has recently been shown to be caused by the melanophilin gene MLPH. This colour is present from the day the pup is born and is sometimes called ‘born blue’. A clear example of both of these colours diluting is the Blue Dobermann. His upper torso is diluted to slate grey and his undersides are diluted to a paler shade of tan, although the diluted tan colour is quite difficult to see.
Blue is also the name used in breeds such as the Great Dane, Chow and Shar-Pei. “It also occurs occasionally in Newfoundlands, Large Munsterlanders, Australian Shepherds, and other breeds,” says Dr Sheila Schmutz, a canine geneticist.

Black and blue
Different coloured pups can occur in the same litter with some being pitch black to some being completely blue as in the Labrador Retriever. However, both parents will carry the dilution gene and as we have learned before, sometimes gene characteristics will show up and sometimes they won’t, when the trait is recessive. The same can happen with lighter colours.

The Weimaraner
One of the best known examples of a dog with a dilute coat is the Weimaraner. This dog’s coat will always be diluted unlike other breeds where other genes may appear and cause a different colour to show up. Dr Sheila Schmutz says, “The Weimaraner is an example of a brown dog with a diluted coat colour. This dog is most commonly seen as the short-haired variety, but there is also a long-haired variety”.
Although Clarence C Little, author of The Inheritance of Coat Color in Dogs (the man who first investigated coat colours), referred to the Weimaraner as diluted brown, most people call this dog the ‘grey ghost’. Most Weimaraners are b/b at the brown locus and therefore Little was right again!
He also referred to them as ‘d/d’ at the dilute locus. Some slate grey dogs resulted from breeding a Weimaraner coloured dog to a black dog, suggesting this diluter gene is capable of diluting both brown to the Weimaraner pale brown colour and black to a slate grey. Little called this colour blue in a Great Dane/Pointer crossbred pup.

A list of all the breeds that can be affected by dilution
Afghan
Australian Shepherd
Beagle
Boston Terrier
Briard (has both d/d and G/- though)
Chihuahua
Chinese Shar-Pei
Chow Chow
Dobermann  
Great Dane
Greyhound
Italian Greyhound
Labrador Retriever
Large Munsterlander
Miniature Pinscher
Newfoundland (not recognised in all countries)
Poodle (has both d/d and G/- though)
Rhodesian Ridgeback (visible only on their mask which is grey instead of black if d/d)
Weimaraner (all)
Whippet

Elimination
Breeders are very keen to get rid of the dilution gene in the Dobermann and are at the moment actively doing DNA testing.

Different types of dilutions
Progressive greying is the other gene that causes colour changes within a dog’s coat. This type of colour change only happens as the dog grows older and is completely different than the dilution gene and geriatric greying. Since this gene has not yet been discovered it is called G (Progressive greying) for now.
Dogs that could possess the G gene are the Cairn Terrier, Bedlington Terrier, Havanese, Briard, Hungarian Puli, Old English Sheepdog, Bearded Collie, Bouvier des Flanders, Kerry Blue Terrier and others. “The Kerry Blue Terrier illustrates that the muzzle of dogs with a EM allele will not lighten by the same age as the rest of their body. Not all Kerry Blue Terriers lighten to the same extent,” says Dr Schmutz.

Geriatric greying
Many dogs grey as they grow into old age, but don’t seem to grey all over their body. It is most noticeable on their face. This must not be confused with Progressive greying where the dog will lighten all over his body. Another pigment change due to old age could be dark spots in the eyes.

Conditions associated with blue
Skin problems and hair loss seem to be the major issues with blue-coloured dogs. Dr Tosso Leeb and Dr Sheila Schmutz are trying to understand the differences between ‘born blue’ dogs who suffer more with these types of problems than other dogs. “The hair loss and skin problems which occur in blue dogs are called ‘Black Hair Follicular Dysplasia’ in some breeds and ‘Colour Dilution Alopecia’ in other breeds. In the past it may sometimes have been called ‘Blue Dog Syndrome’,” says Dr Sheila Schmutz.
“Colour Dilution Alopecia appears to be the same disorder as Black Hair Follicular Dysplasia but covers a wider range of coat colours. It is also called Blue Dobermann Syndrome, Fawn Irish Setter Syndrome and Blue Dog disease. Blue coat colour appears to be caused by at least two different mutations in the MLPH gene in the 30 breeds we studied. The common mutation causes dilute coat colour in most dogs that are born blue or grey.
“The symptoms of this disorder vary widely among individuals for reasons that are not clear yet. The symptoms seem worst in Large Munsterlanders but Newfoundlands, Dobermanns, Great Danes, Weimaraners, and Italian Greyhounds can all have symptoms. Patchy hair loss on the ears, head and along the spinal column seems to be the most common symptom. Dermatitis, wrinkled skin, and allergic skin reactions may also occur. Some dogs are free of symptoms early in life and then develop them later.
“We have collected DNA samples from blue dogs with and without symptoms to try to understand if the dogs in each group had a different mutation. However, some dogs with the common mutation and some without it had CDA symptoms and others did not. There may be a slightly higher chance that males may suffer more severe symptoms than females,” says Dr Schmutz.

Fawn dilutions
Clarence C Little used a hypothetical allele that he called the C allele to describe dilutions of brown and red. These dilutions are responsible for pale brown and pale red much like the fawn colours you see in the picture of the Chihuahua puppies. This research has not yet been completed so it’s still unknown whether these pale reds and browns are caused by the C allele or a different gene.

Discuss this in our forum

Text: Kerry de Bruyn
Photography: Johann Theron