Diluteor Dilutionis used to describe the thinning or lightening of the color intensity. Color Dilute Alopecia (CDA) or color mutant alopecia is a genetic defect also known as "blue dog disease". CDA is a "pigment deficiency syndrome" as it also occurs in Merle.
CDA can only occur in dogs that carry the gene (D locus) for color dilution in homozygous (d/d) form. However, not all paint-diluted dogs will develop CDA. There appear to be other breed-specific genetic factors that are responsible for the outbreak.
Symptoms of CDA
Hair loss, baldness and accompanying skin infections occur from the age of three to six months. Puppies up to six months old often appear healthy and unremarkable. Sometimes the symptoms only appear between the first and second year of life.
The paint-diluted areas themselves are affected by the disease. The veterinarian can already suspect CDA with the clinical symptoms and a hair sample (trichogram).
Responsible for the typical hair loss and all other symptoms is the keratinization of the hair follicles. The storage and transport of the melanosomes is disturbed. Melanin clumps, structural changes and instability of the hair occur. The hair breaks off in the affected areas and hair loss occurs.
The associated keratinization disorder inevitably leads to the most severe skin problems and recurrent inflammation. The first changes in the form of a dull coat, dry, flaky skin and hair loss can be observed from puppyhood. Affected zones are primarily the back of the ears, the entire torso and the limbs. Also typical are red spots between the paws that itch badly. Skin infections, inflammation, and itching are common side effects of CDA. For a definitive diagnosis, however, skin biopsies are needed, which are examined histologically in the laboratory and a genetic test.
How can color mutant alopecia be treated?
There is no known specific therapy that could treat the pigment disorder and clumping. In short: CDA cannot be cured.
Symptomatic therapy can be carried out with mild antiseborrheic and/or antibacterial shampoos. The hair loss is irreversible. The dog usually needs permanent skin care, which should prevent possible recurring skin diseases.
It is possible to treat scaly, dry skin with moisturizing shampoos, sprays and conditioners to prevent further infection.
Since the mode of inheritance of the light color mutation and thus the risk of the disease are known, breeding hygiene measures are very effective and definitely recommended. Affected dogs and their siblings should not be bred from, especially the parents of the affected dogs should not be mated to prevent the disease from spreading further.
The alleles at the D locus are important for breeding
Each dog can produce either eumelanin in black or brown. A mutation at thedilution locus can cause the dilution of these colors in the phenotype to blueor lilac .
The following alleles are known at the D locus:
D- Wild type, dominant, black or brown eumelanind – recessive, color dilution, dilution to blue or lilac
D/D: not affected by color dilutionD/d: carrier of the dilution gened/d: affected by color dilution, diluted coat color
Parents | Offspring |
D/D x D/D | 100% D/D |
D/D x D/d | 50% D/D, 50% D/D |
D/D x d/d | 100% D/d |
D/d x D/d | 25% d/d, 50% d/d, 25% d/d |
d/d x d/d | 50% d/d, 50% d/d |
d/d x d/d | 100% d/d |
Inheritance explained:
If a dog inherits at least one D, it can store pigment normally: D/D or D/d.
D behaves dominantly towards the mutant alleles d. That means: D is above d.
If a dog inherits a mutant allele from each parent, this leads to color dilution: d/d
Good pigmentation is therefore one of the most important criteria when selecting breeding animals, as well as determining their color locus!
In a blue dog, the blue isn't just visible in the coat. The dilution is also noticeable on the nose pigment, lips and eyelid rims. Likewise, the eye color is lighter than in dogs without dilution.
Possible confusion
With dogs in Blue-Merle the brightening comes into play Silver-grey due to the merle phenotype and not due to color dilution. That is why Blue Merle has now been renamed "Black Merle" for some dog breeds. Real blue dogs with merle are called e.g. "Slate-Merle" or "Dilute-Merle< /strong>".
Also not to be confused with dilute are dogs that are characterized by the G locus tend to early graying like Yorkshire Terriers, poodles or bobtails. Also dogs in sable and Agouti where the yellow pigment has been lightened to white look gray with no dilute to be.
Photos: Courtesy of Dr. Filiz Hesselmann, Veterinary Clinic Dr. Apple
Content sources: tieraerztekammer-berlin.decda-hund.jimdofree.com
hunderunden.de (Dr. Filiz Hesselmann)
Additional references
Institute for Genetics, University of Bern: "Colour dilution alopecia (color mutant alopecia) in different breeds", at http://www.genetics.unibe.ch/f...
Kim J-H, Kang KI, Son H-J, Woo G-H, Jean Y-H, Hwang E. -K (2005): Color-dilution alopecia in dogs. Journal of Veterinary Science 6(3), 259-261.
Noli, C., Scarampella, F., Toma, S. (2013): Practical dermatology in dogs and cats. 3. Edition. Schluetersche Verlagsgesellschaft mbH & Co. KG, Hanover.
Peters, S., Koch, H.-J. (2014): Dermatology Atlas Dog. 1st edition. Enke Verlag, Stuttgart.
Rhodes, K.H., Werner, AH. (2018): Small Animal Dermatology. John Wiley & Sons, Hoboken