Leucism () is a wide variety of conditions that result in the partial loss of pigmentation in an

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes. It is occasionally spelled ''leukism''. Some genetic conditions that result in a "leucistic" appearance include piebaldism, Waardenburg syndrome, vitiligo, Chédiak–Higashi syndrome, flavism, isabellinism, xanthochromism, axanthism, amelanism, and Melanophilin mutations. Pale patches of skin, feathers, or fur (often referred to as " depigmentation") can also result from injury.

Details

''Leucism'' is often used to describe the phenotype that results from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells that can make pigment. Since all pigment cell-types differentiate from the same multipotent precursor cell-type, leucism can cause the reduction in all types of pigment. This is in contrast to

albinism Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino. Varied use and interpretation of the term ...

, for which leucism is often mistaken. Albinism results in the reduction of melanin production only, though the

melanocyte Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart. ...

(or melanophore) is still present. Thus in species that have other pigment cell-types, for example xanthophores, albinos are not entirely white, but instead display a pale yellow color. More common than a complete absence of pigment cells is localized or incomplete hypopigmentation, resulting in irregular patches of white on an animal that otherwise has normal coloring and patterning. This partial leucism is known as a "pied" or " piebald" effect; and the ratio of white to normal-colured skin can vary considerably not only between generations, but between different offspring from the same parents, and even between members of the same litter. This is notable in horses, cows,

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, dogs, the urban crow and the ball python but is also found in many other species. Due to the lack of melanin production in both the retinal pigmented epithelium (RPE) and iris, those affected by

sometimes have pink pupil due to the underlying blood vessels showing through. However, this is not always the case and many albino animals do not have pink pupils. The common belief that all albinos have pink pupils results in many albinos being incorrectly labeled as 'leucistic'. The neural crest disorders that cause leucism do not result in pink pupils and therefore most leucistic animals have normally colored eyes. This is because the melanocytes of the RPE do not derive from the neural crest. Instead, an out-pouching of the neural tube generates the optic cup that, in turn, forms the retina. As these cells are from an independent developmental origin, they are typically unaffected by the genetic cause of leucism.

Genetics

Gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s that, when

mutated In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitos ...

, can cause leucism include '' c-kit'', '' mitf'' and '' EDNRB.Waardenburg syndrome
at Atlas of Genetics and Cytogenetics in Oncology and Haematology (archived 26 December 2005, fro

accessed 18–22 July 2006).

Etymology

The terms ''leucistic'' and ''leucism'' are derived from the stem '' leuc-'' + ''

-ism ''-ism'' is a suffix in many English words, originally derived from the Ancient Greek suffix ('), and reaching English through the Latin , and the French . It means "taking side with" or "imitation of", and is often used to describe philosoph ...

'', from Latin ''leuco-'' in turn derived from Greek ''leukos'' meaning ''white''.

Gallery

File:Leucistic Texas Rat Snake.jpg, Leucistic Texas rat snake ('' Elaphe obsoleta'') File:Common Grackle Leucistic.jpg, Leucistic common grackle ('' Quiscalus quiscula'') File:Paon blanc Madère 2008.jpg, Leucistic Indian peacock (''

Pavo cristatus The Indian peafowl (''Pavo cristatus''), also known as the common peafowl, and blue peafowl, is a peafowl species native to the Indian subcontinent. It has been introduced to many other countries. Male peafowl are referred to as peacocks, and ...

'')

References

External links