Siamese Cats and Temperature-Sensitive Albinism

When most people hear "albino", they probably picture either a very pale-skinned, gray-eyed human, or a white-furred, pink-eyed animal. The Siamese cat is probably the absolute last image that would come to mind if someone were asked to name albino animals. However-- surprisingly-- the Siamese cat actually has a form of albinism, giving it its distinct markings.

Cats and other animals (such as rabbits) who have this genetic trait, called temperature-sensitive albinism, are considered to have "point" coloration by breeders, handlers, and show organizations. The most well-known of point color is the seal-point pattern, seen in the Siamese cat breed, which is a deep, nearly-black shade of chocolate. However, other cat breeds such as the colorpoint shorthair, the Himalayan, and the Birman may have point-markings of any other color or pattern, including tabby and tortoiseshell points.

This uncommon form of albinism results from a mutation carried genetically on the C-locus-- the same locus that also houses the gene for complete albinism. Temperature-sensitive albino cats have a mutated form of tyrosinase, the enzyme responsible for producing melanin, the pigment involved in darkened fur.

Instead of tyrosinase and melanain completely absent, as in animals with true albinism, Siamese cats and other pointed cat breeds have a form of tyrosinas that is able to operate only at below-average body temperatures. Because of this, only the coolest parts of the body-- the feet, tail, and face-- receive properly-processed levels of melanin.

The mutated tyrosinase found in temperature-sensitive albino cats will not act to pigment the eyes, so the eyes of all cats with true point-coloration have blue eyes. This trait can assist with differentiating unusually dark temperature-sensitive albinos from unusually light cats who lack the tyrosinase mutation. The depigmentation, or albinism, of the eye also causes the cats' eyes to flash red when exposed to light, unlike the eyes of pigmented cats, which "glow" green.

The womb of a cat is uniformly warm, so cats with point coloration, including purebred Siamese cats, are born solid white. As specific parts of the body become cooler with exposure to air, the kitten's markings slowly darken in the body's coolest areas. This causes his tail, face, and paws to darken over time to the color he would have expressed had it not been for the mutation. The point-markings of cats can be any color or pattern, including red tabby, cream tabby, dilute tortoiseshell, standard tortoiseshell, blue tabby, blue, chocolate, or lilac.

The longer a cat or kitten with temperature-sensitive albinism is exposed to cold, the darker his markings will get. For this reason, many older colorpoint shorthairs appear to be standard tabbies, and very old Siamese cats may look solid blackish-brown. It was, in fact, a mutation in Siamese cats that overrode the parital albinism and led to the existence of chocolate cats.

Although the Siamese cat and other pointed cat breeds carry a form of albino gene, it is mostly harmless. While some of these cats have compromised vision, there are very few overall dysfunctional traits for temperature-sensitive albinism. Because the tyrosinase mutation only partially causes the absence of melanin, they are not as sensitive to light as other albino animals.

Temperature-sensitive albinism is a common, beautiful, and generally benign mutation, which adds variety to the already glorious spectrum of cats' coat colors and genetics. While many cat breeds exhibit this trait, it maintains an exotic appeal for cat fanciers and breeders because of its unique beauty.