Leucism
A condition causing partial pigmentation loss, not affecting eyes.
Leucism (also spelled leukism) refers to a range of conditions where an animal loses some of its pigmentation, resulting in white, pale, or patchy skin, hair, feathers, scales, or cuticles—but the eyes remain normally colored. This happens because of defects in how pigment cells develop or migrate from the neural crest during growth, leading to a shortage of all pigment types, not just melanin. That’s a key difference from albinism, which is often confused with leucism. In albinism, the pigment cells are still present but produce less melanin, so animals with albinism may show a pale yellow color if they have other pigment cell types.
Partial leucism is more common than a total lack of pigment cells. It creates irregular white patches on an otherwise normally colored animal, a pattern called “pied” or “piebald.” The amount of white versus colored skin can vary widely, even among siblings from the same parents or within the same litter. This effect shows up in horses, cows, cats, dogs, urban crows, ball pythons, and many other species.
Albinism can sometimes cause pink pupils because the lack of melanin in the retinal pigmented epithelium and iris lets underlying blood vessels show through—but not all albinos have pink pupils, and the common belief that they do often leads to albinos being mislabeled as leucistic. Leucism, however, stems from neural crest disorders that don’t affect the retinal pigmented epithelium, since those cells come from the neural tube rather than the neural crest. So most leucistic animals have normally colored eyes.
Notable examples include a leucistic platypus found in 2021 in the Gwydir River near Armidale, New South Wales, Australia, and the Anchorage White Raven, a leucistic common raven known for its trickster behavior, spotted in 2023 and 2024 in Anchorage, Alaska.
Genes that can cause leucism when mutated include c-kit, mitf, and EDNRB. The terms leucistic and leucism come from the stem leuc- plus -ism, via Latin leuco- from Greek λευκός (leukós), meaning white.
- Field
- Biology, Genetics
- Known for
- Partial loss of pigmentation in animals, distinct from albinism
- Related conditions
- Piebaldism, Waardenburg syndrome, vitiligo, Chédiak–Higashi syndrome, flavism, isabellinism, xanthochromism, axanthism, amelanism, melanophilin mutations
Lore & Background
Leucism is often used to describe the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development. This can cause either the entire surface or patches of body surface to lack cells that can make pigment. Since all pigment cell-types differentiate from the same multipotent precursor, leucism can reduce all types of pigment, unlike albinism which only reduces melanin production while melanocytes remain present. In species with other pigment cell-types, such as xanthophores, albinos display a pale yellow color rather than being entirely white.
Reader's Guide
Leucism is significant because it clarifies a common biological distinction often confused with albinism. While albinism involves a reduction in melanin production only, leucism results from a failure of pigment cell development or migration, leading to a broader loss of pigmentation. This distinction is important for understanding animal coloration, genetics, and evolutionary biology. The condition appears across many species, from horses and cats to ravens and platypuses, and its genetic basis involves mutations in genes such as c-kit, mitf, and EDNRB. Notable examples include a leucistic platypus found in the Gwydir River in New South Wales, Australia, and the Anchorage White Raven, a leucistic common raven known for its 'trickster' behavior spotted in Anchorage, Alaska. The term 'leucistic' derives from Greek 'leukós' meaning white. Understanding leucism helps researchers and the public correctly identify and study pigmentary disorders in wildlife and domestic animals.
Did You Know?
- Leucism results from defects in pigment cell differentiation or migration from the neural crest during development.
- Unlike albinism, leucism does not cause pink pupils because the retinal pigmented epithelium derives from the neural tube, not the neural crest.
- Partial leucism, called 'pied' or 'piebald', can vary greatly in the ratio of white to normal-colored skin even among siblings.
More in Genetic disorders with no OMIM 1-24
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