Pigmentary Abnormalities in Animals
Many associations between skin and coat color and developmental anomalies have been recorded in domestic animals. Some of the associations with hypotrichosis are discussed under hereditary alopecia.
Albinism appears to be rare in domestic animals. True albinism is always associated with pink or pale irises and with visual defects and increased risk of solar radiation–induced neoplasms of the skin. It has been noted in Icelandic sheep and in Guernsey, Austrian Murboden, Shorthorn, Brown Swiss, and Charolais cattle. Albinism must be differentiated from extreme white spotting or piebaldism and dominant white. Some animals with extreme piebaldism or dominant white have associated neurologic anomalies or deafness, or suffer death in utero.
Lethal white foal syndrome is one that results from breeding two Overo Paints. In dogs and cats, dominant white or extreme piebaldism can be associated with unilateral or bilateral deafness and sometimes with blue irides or iris heterochromia. White cats with bilateral blue eyes have a 75% chance of deafness. In dogs, deafness may also be associated with merle hair coats and is found in Dalmatians, Sealyham Terriers, harlequin Great Danes, Collies, and white Bull Terriers. Cyclic neutropenia may be found in gray or pale merle Collies. In Rhodesian Ridgebacks, pale coat color is associated with cerebellar degeneration.
In Chédiak-Higashi syndrome of cats and cattle (Herefords, Japanese Black, Brangus), coat color dilution (blue smoke in cats) is associated with neutrophil and platelet abnormalities and shortened life span. This is inherited as an autosomal recessive trait. Male tricolor cats (calico and tortoiseshell) are sterile because the gene for orange is X-linked and recessive, and males have the abnormal XXY genotype.
Pigmentary abnormalities may be acquired, and some of these may be hereditary or familial, as in vitiligo. As a familial disease, vitiligo is best recognized in Arabian horses (Arabian fading syndrome, pinky syndrome); it may also be familial in cattle (Holstein-Friesian), Siamese cats, and in some breeds of dogs (Belgian Tervuren, Rottweiler). Affected animals develop somewhat symmetric macular depigmentation of the skin that occasionally also affects the hair coat and claws or hooves. The onset is usually in young adulthood. Most lesions are on the face, especially the muzzle or planum nasale or around the eyes. Depigmentation may wax and wane. Complete remission may occur but is rare. There is no accompanying systemic or cutaneous pathology. No treatment is available; treatments used in people with vitiligo are unlikely to provide significant cosmetic results in animals.
Lentigo in orange and orange-faced male cats is marked by the development of asymptomatic, pigmented macules. Lesions are first seen on the lips and eyelids at <1 year of age. Other sites include the planum nasale and gingivae. Lentigines are not precancerous and have no medical consequence.
Acquired aurotrichia of Miniature Schnauzers is a familial syndrome in which hair along the dorsal midline changes to golden from the normal black or gray of this breed. The onset is usually in young adulthood. The change may be associated with thinning in the hair coat but no other cutaneous or systemic signs. In most dogs, coat color reverts to normal within 1–2 years.