WHAT IS ALBINISM?

Albinism in animals - including humans - is caused by the inheritance of an altered copy of the gene responsible for regulating pigment production. Generally, the presence of a viable allele of this gene is sufficient for pigmentation to occur, so albinism is usually a genetic condition associated with recessive homozygosity, i.e. in both copies of chromosomes, the gene must be altered for albinism to occur.

This implies not only that the mutation must occur - or be inherited - but that it must occur on both copies of chromosomes, those of paternal and maternal origin. So two normally pigmented individuals can have an albino child - if both carry a mutated copy of the gene - but two albinos cannot have a normally pigmented child.

HOW DOES ALBINISM OCCUR?

Albinism is a recessive genetic condition that exists and is documented in virtually all animal species. The genetic cause of albinism is heterogeneous as there are more than 18 genes1 whose recessive mutations are associated with this characteristic loss or decrease in pigmentation. The most frequent cause of albinism in animals, including rodents, is the occurrence of mutations in the tyrosinase gene (one of the 18 genes associated with albinism), which codes for an essential protein in the synthesis of pigment, melanin. Without tyrosinase it is not possible to synthesise pigment, so mutants in the tyrosinase gene manifest albinism, to varying degrees, depending on the residual enzyme activity remaining in the mutated protein. 

The pigment, melanin, is produced in two very specific cell types, melanocytes and retinal pigment epithelium cells, the latter derived from the same optic cup and therefore from the brain, from the central nervous system. Melanocytes derive from the neural crest and, throughout embryonic development, migrate and differentiate to colonise many parts of the body, such as the choroid, cochlea, heart valves, hair bulbs, iris, and skin. Within these pigment cells are specialised lysosome-derived organelles called melanosomes, where most of the proteins involved in melanin biosynthesis accumulate. In adult rodents, melanocytes in the skin accumulate preferentially in the hair bulbs, which is why the skin of these animals, under the fur, has the characteristic pink colour. In humans, on the other hand, melanocytes are distributed both in the hair bulbs and in the epidermis3.

CAN ALBINISM CAUSE PROBLEMS?

Depending on the animal in question, albinism can have certain health consequences, and in others these are minimal. 

For example, in dogs, total or partial blindness and deafness are very common problems, while in rabbits deafness is less common. The most common problem is the sensitivity of the skin and eyes to sunlight, because the lack of melanin means that they cannot process it well and this is particularly troublesome to the eye, which is why it is recommended that dogs wear protective sunglasses and, in the case of rabbits, allow them to exercise in shaded areas or when the sun's rays are as mild as possible. 

As far as the skin is concerned, albino animals are particularly prone to skin cancer due to unprotected exposure to the sun's rays; this is less frequent in medium and long-haired animals because the fur creates a protective layer but, if our pet has short or satin fur, it will be advisable not to expose it to direct sunlight or to put some kind of cotton clothing to block the sun's rays. 

ALBINISM IN RESPONSIBLE BREEDING

As far as responsible pet breeding is concerned, albinism in dogs and cats is forbidden in clubs and, if it occurs, that particular pet cannot be registered and is usually put up for adoption with a strict commitment to neutering. In small pets such as rabbits, guinea pigs, rats or hamsters, albinism is very common and, although it is not a ‘popular’ colour among buyers, it is popular among breeders, being especially interesting in rabbit breeds such as the Teddy Lop or the English Angora, where the REW (albino) specimens are usually the ones with the best fur of all (long and abundant).

THE REW (RED-EYED WHITE), THE HIMALAYAN AND THE BEW (BLUE-EYED WHITE) IN SMALL PETS

In small pets (rabbits, guinea pigs...) we can find three different types of albinism:

• REW (Red-eyed white): This is complete albinism, characterised by white animals with pink eyes and depigmented nails. 

• HIMALAYA: This is partial albinism in which the rabbits are white with fixed coloured body spots and pink eyes. The fixed coloured spots in these animals are the ears, nose, hands, feet and tail, which can be black, chocolate blue and lilac. It is a heat-sensitive colour which, with heat, can fade until the animal is completely white, the best time of year being winter, when the coloured points are strongest and most intense. 

• BEW (Blue-eyed white): An incomplete albinism resulting from the vienna gene, the animal inherits two copies of the vienna gene from its parents and is shown as white with bright blue eyes.
  The REW and BEW colour cannot be crossed with each other, as this would result in animals with ‘violet’ eyes (blue with red reflex), which is not allowed in any breed. 

CONCLUSION

Albinism in animals is a double-edged sword and, if we wish to start in the world of breeding or open the doors of our life to an albino animal, we will always be guided by a specialist breeder and a trusted veterinarian who will advise us on its correct handling, especially in the case of dogs or cats.