Color Dilution Alopecia
Teri Dickinson, DVM
Alopecia (hair loss) related to dilute coat color is a recognized
condition in dogs. The currently accepted medical terminology for this
condition is Color Dilution Alopecia (CDA). The condition may affect
any dilutely pigmented
dog, regardless of coat color. This condition was previously known as Blue
Balding Syndrome, Blue Doberman Syndrome, Color Mutant Alopecia, Congenital Alopecia,
etc. The term Color Mutant Alopecia arose because dilutes were at one time mutations
from the deep pigment occurring in wild canines. Dilutes are now a regularly
occurring form of pigmentation in many breeds and have been for hundreds of years.
The term mutation is therefore not applicable to dilute individuals. References
to Doberman Pinschers or blue hair coats arose because the condition is common
in blue individuals of this breed, but it is not limited to either blue dogs
or Dobermans. The term congenital means present at birth, but CDA affected dogs
are born with normal hair coats.
The dilute (also known as Maltese) gene also appears in both mice and cats, and
interestingly enough, is not associated with any abnormal coat conditions in
those species.(1) Color Dilution Alopecia (CDA)
has been recognized in dilute individuals of many breeds of dogs including Chow
Chows, Dachshunds, Doberman Pinschers, Great Danes, Irish Setters, Italian Greyhounds,
Standard Poodles, Salukis, Whippets, and Yorkshire
Terriers.((2),(3),(4),(5)) Dilute
individuals carry a recessive genotype of dd and are characterized by blue, bluish-grey,
lavender or flesh-colored noses, lips and eye rims. The coat colors may include
blue, fawn, blue-fawn, bronze, taupe or some variation of these. These dogs are
usually easily distinguished from their deeply (non-dilute) pigmented counterparts.
Deeply pigmented individuals carry a dominant genotype of Dd or DD and have black
or liver noses, lips and eye rims. Coat colors may include black, red, red-fawn,
liver or variations thereof.
CDA is characterized by loss of hair from dilutely pigmented
areas. Coats are normal at birth, and onset of hair loss usually begins between
six months and three years of age. Hair loss usually begins along the dorsal
midline (middle of the back) and often spares the head, tail and limbs. The pattern
seems to vary from breed to breed. It has been
suggested(6) that darker colored (steel blue)
individuals are less likely to be affected, may be less severely affected or
may start to lose hair later in life than lighter colored dogs. This suggests
that the severity of the disease may be related to the amount of dilution present.
Deeply pigmented or white areas of coat are unaffected. In blue dogs with tan
points (Yorkies and Dobermans) the tan areas retain a normal appearance. In piebald
(white spotted) individuals, the white areas are unaffected by the hair loss.
The hair loss may be total or partial and any remaining hairs are usually sparse,
rough and easily broken or removed. The skin in the affected areas is usually
scaly and may occasionally develop bacterial infections. Pruritus (itching) is
usually absent, unless a bacterial infection has set in.
Diagnosis of CDA requires first ruling out other causes of hair loss. Diagnostic
tests should include fungal cultures, skin scrapings to check for parasitic mites,
etc. CDA often closely resembles endocrine (hormone related) hair loss and the
dog should be carefully examined for any other abnormalities, and tested for
normal thyroid function. Presence of dilute pigment and a characteristic course
of disease also aid in making the diagnosis. Microscopic examination of hairs
and\or skin biopsies can be used to confirm the diagnosis.
There is no cure for CDA. Treatment is limited to controlling the scaliness and
any associated pruritus with various
shampoos or topical treatments.
The
cause of CDA is not clearly understood. Microscopic examination of hairs of dilute
individuals reveals that the pigment (melanin) forms large granules (macromelanosomes)
which are rarely found in deeply pigmented hairs. In dilute individuals with
normal appearing coats, these macromelanosomes are not grouped or clumped and
cause no distortion of the cuticle (outer covering) of the hair. Dogs with CDA
have many large groups or clumps of macromelanosomes which tend to distort the
cuticle of the hair. It is hypothesized that this distortion of the cuticle causes
the hairs to break easily, resulting in the short stubby hairs commonly found
in affected individuals. (See Drawing). It is further hypothesized that the rupture
of the hair releases byproducts of pigment formation, which are toxic to the
hair follicles. Regrowth of broken hairs is reduced because of damage to the
follicles caused by these toxins.
Why in some dilute dogs the macromelanosomes are clumped and in others they are
not, is an interesting question at this time. The relationship between dilute
pigment and hair loss is clear, but why are some dilute individuals unaffected?
Weimeraners as a breed are dd, all individuals are dilute, yet the disease is
unreported in this breed. In Dobermans, the dilute individuals comprise only
8-9% of the breed, yet 50-80%6 of the dilute
dogs have CDA. In Italian Greyhounds, many individuals are dilutes, yet the IGCA
health survey reported only 71 affected individuals among the approximately 2200
dogs included in the survey.(7) If half the dogs
included in the survey were dilutes, the incidence of CDA in IG's would be around
7% of the dilute population, as opposed to the 50-80% affected dilute
Dobermans.
A third allele (dl) which is associated with CDA has been proposed.6 While
this is a long way from being proven, it could help explain why some dilute animals
are unaffected. Dogs with a genotype dd would be normal coated dilutes, ddl would
be intermediates (mildly affected?) and dldl would be CDA affected. A genotype
of Ddl should represent
deeply pigmented dogs which were carriers of CDA.
Italian Greyhounds would be an interesting breed to study regarding the heredity
of this condition. IG's have a relatively high incidence of dilutes, and a relatively
low incidence of CDA affected dogs.
Bibliography
1. Brignac, M.M. et al. Microscopy of color mutant alopecia.
Proceedings of the Annual Meeting of the American Academy of Veterinary Dermatology
and the American College of Veterinary Dermatology, 1988:14-15.
2. Muller, G.H. et al. Small animal dermatology.
4th ed. Philadelphia: W.B. Saunders. 1989.
3. Briggs, O.M. et al. Color mutant alopecia in
a blue Italian Greyhound. Journal of the American Animal Hospital Association
1986; 22: 611-14.
4. Miller, W.H., Jr. Alopecia associated with coat
color dilution in two Yorkshire Terriers, a saluki and a mongrel dog.
Journal of the American Animal Hospital Association.
5. O'Neill C.S. Hereditary Skin disease in the
dog and cat. Compendium of Continuing Education 1981; 3: 791-800.
6. Miller, W.H., Jr. Colour dilution alopecia in
Doberman Pinschers with blue or fawn coat colours: A study of the incidence
and histopathology of this disorder. Veterinary Dermatology 1990; 1:
113-122.
7. Slater, M. R. Report of a survey on health problems
in Italian Greyhounds. Italian Greyhound 1994; 36:6 72-74.
Copyright The Italian Greyhound
