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Leucism

From Wikipedia, the free encyclopedia
Leucisticwhite lionsowe their colouring to a recessive allele. Note the eyes and lips remain the normal colour. Studies have shown that the reduced pigment comes from a mutation in the gene fortyrosinase,the same as causes Type Ioculocutaneous albinismin humans.[1]
All-white dominant white horse with pink skin, brown eyes, and white hooves.
Thiswhite horseowes its coloring to a dominant allele (dominant white).
A leucisticrock dove.Both the eyes and legs are still of the normal colour.

Leucism(/ˈluːsɪzəm,-kɪz-/)[2][3][4]is a wide variety of conditions that result in partial loss ofpigmentationin ananimal—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes.[4]It is occasionally spelledleukism.Some genetic conditions that result in a "leucistic" appearance includepiebaldism,Waardenburg syndrome,vitiligo,Chédiak–Higashi syndrome,flavism,isabellinism,xanthochromism,axanthism,amelanism,andmelanophilinmutations. Pale patches of skin, feathers, or fur (often referred to as "depigmentation") can also result from injury.[5]

Details

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(video) Awhite tigerat Tobu Zoo, inSaitama,Japan.This phenotype is due to a mutation in the same gene that results in Type IVoculocutaneous albinismin humans.[6]

Leucismis often used to describe thephenotypethat results from defects inpigment celldifferentiation and/or migration from theneural crestto skin, hair, or feathers duringdevelopment.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 makepigment.

Since all pigment cell-types differentiate from the samemultipotentprecursor cell-type, leucism can cause the reduction in all types of pigment. This is in contrast toalbinism,for which leucism is often mistaken. Albinism results in the reduction ofmelaninproduction only, though themelanocyte(ormelanophore) is still present. Thus in species that have other pigment cell-types, for examplexanthophores,albinos are not entirely white, but instead display a pale yellow color.

More common than a complete absence of pigment cells is localized or incompletehypopigmentation,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 inhorses,cows,cats,dogs,the urbancrow[7]and theball Python[8]but is also found in many other species.

Due to the lack of melanin production in both theretinalpigmented epithelium (RPE) andiris,those affected byalbinismsometimes 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.[9]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 theneural crest.Instead, an out-pouching of theneural tubegenerates theoptic cupthat, in turn, forms theretina.As these cells are from an independent developmental origin, they are typically unaffected by the genetic cause of leucism.

Notable examples

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Genetics

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Genesthat, whenmutated,can cause leucism includec-kit,[11]mitf[12]andEDNRB.[13]

Etymology

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The termsleucisticandleucismare derived from the stemleuc-+-ism,from Latinleuco-in turn derived fromGreekleukosmeaningwhite.

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See also

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References

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  1. ^Cho, Yun Sung; Hu, Li; Hou, Haolong; Lee, Hang; Xu, Jiaohui; Kwon, Soowhan; Oh, Sukhun; Kim, Hak-Min; Jho, Sungwoong; Kim, Sangsoo; Shin, Young-Ah (2013-09-17)."The tiger genome and comparative analysis with lion and snow leopard genomes".Nature Communications.4(1): 2433.Bibcode:2013NatCo...4.2433C.doi:10.1038/ncomms3433.ISSN2041-1723.PMC3778509.PMID24045858.
  2. ^"leucistic".Oxford Dictionaries.Oxford University Press.Archived fromthe originalon August 10, 2012.RetrievedJanuary 9,2016.
  3. ^Merriam-Webster,Merriam-Webster's Unabridged Dictionary,Merriam-Webster, archived fromthe originalon 2020-05-25,retrieved2015-11-12.
  4. ^ab"leucism".The American Heritage Dictionary of the English Language(5th ed.). HarperCollins.
  5. ^"Depigmentation of Skin: Symptoms, Signs, Causes & Treatment".MedicineNet.Retrieved2020-06-23.
  6. ^chemport.cas.orghttps://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%252BC3sXotlGksbg%253D&md5=1ee737efa06deefbbb993e3412a921a0.Retrieved2020-06-23.{{cite web}}:Missing or empty|title=(help)
  7. ^White crowsatCornell University.
  8. ^Piebald ball Python sat Constrictors (archived 9 October 2006, fromthe original,accessed 18–22 July 2006).
  9. ^"Oculocutaneous Albinism".NORD (National Organization for Rare Disorders).Retrieved2020-06-23.
  10. ^Rare white platypus in Gwydir River near Armidale is leucistic, researchers find,James Paras,ABC News Online,2023-11-03
  11. ^Coat color, dominant whiteArchived2009-01-30 at theWayback Machineat Online Mendelian Inheritance in Animals.
  12. ^An L1 element intronic insertion in the black-eyed white (Mitf[mi-bw]) gene: the loss of a single Mitf isoform responsible for the pigmentary defect and inner ear deafnessat Human Molecular Genetics.
  13. ^Waardenburg syndromeat Atlas of Genetics and Cytogenetics in Oncology and Haematology (archived 26 December 2005, fromthe original,accessed 18–22 July 2006).
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  • Media related toLeucismat Wikimedia Commons
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