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 biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

—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 Vitiligo is a disorder that causes the skin to lose its color. Specific causes are unknown but studies suggest a link to immune system changes. Signs and symptoms The only sign of vitiligo is the presence of pale patchy areas of depigmen ...

, Chédiak–Higashi syndrome, flavism, isabellinism, xanthochromism, axanthism,

amelanism Amelanism (also known as amelanosis) is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and ...

, and Melanophilin mutations. Pale patches of skin, feathers, or fur (often referred to as "

depigmentation Depigmentation is the lightening of the skin or loss of pigment. Depigmentation of the skin can be caused by a number of local and systemic conditions. The pigment loss can be partial (injury to the skin) or complete (caused by vitiligo). It can b ...

") can also result from injury.

Details

''Leucism'' is often used to describe the

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (biology), morphology or physical form and structure, its Developmental biology, developmental proc ...

that results from defects in pigment cell differentiation and/or migration from the

neural crest Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...

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 A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

. 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 Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

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 hear ...

(or melanophore) is still present. Thus in species that have other pigment cell-types, for example

xanthophores Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, ...

, 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 A piebald or pied animal is one that has a pattern of unpigmented spots (white) on a pigmented background of hair, feathers or scales. Thus a piebald black and white dog is a black dog with white spots. The animal's skin under the white backgro ...

" 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

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

s, cows, cats, 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

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...

l 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

. Instead, an out-pouching of the neural tube generates the optic cup that, in turn, forms the

. 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, can cause leucism include '' c-kit'', ''

mitf Microphthalmia-associated transcription factor also known as class E basic helix-loop-helix protein 32 or bHLHe32 is a protein that in humans is encoded by the ''MITF'' gene. MITF is a basic helix-loop-helix leucine zipper transcription fact ...

'' 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 philo ...

'', 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'')

References

External links