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Albinism
Classification and external resources
ICD-10 E70.3
ICD-9 270.2
OMIM 203100 103470, 203200, 203280, 203290, 203300, 203310, 256710, 278400, 214450, 214500, 220900, 300500, 300600, 300650, 300700, 600501, 604228, 606574, 606952, 607624, 609227
MedlinePlus 001479
eMedicine derm/12
MeSH D000417

Albinism (from Latin albus, "white"; see extended etymology, also called achromia, achromasia, or achromatosis) is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin. Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. The most common term used for an organism affected by albinism is "albino". Additional clinical adjectives sometimes used to refer to animals are "albinoid" and "albinic".

Albinism is associated with a number of vision defects, such as photophobia, nystagmus and astigmatism. Lack of skin pigmentation makes the organism more susceptible to sunburn and skin cancers.

Contents

Causes and types of albinism

Most forms of albinism are the result of the biological inheritance of genetically recessive alleles (genes) passed from both parents of an individual, though some rare forms are inherited from only one parent. There are other genetic mutations which are proven to be associated with albinism. All alterations, however, lead to changes in melanin production in the body.[1][2]

The chance of offspring with albinism resulting from the pairing of an organism with albinism and one without albinism is low. However, because organisms can be carriers of genes for albinism without exhibiting any traits, albinistic offspring can be produced by two non-albinistic parents. Albinism usually occurs with equal frequency in both genders.[1] An exception to this is ocular albinism, which it is passed on to offspring through X-linked inheritance. Thus, ocular albinism occurs more frequently in males as they do not have a second X chromosome.[3]

There are two of different forms of albinism; a partial lack of the melanin is known as hypomelanism, or hypomelanosis and the total absence of melanin is known as amelanism or amelanosis.

Albinism and related conditions in animals

Snowflake, an albino gorilla
An albino Wistar rat, a strain commonly used for both biomedical and basic research.

Many animals with albinism lack their protective camouflage and are unable to conceal themselves from their predators or prey; the survival rate of animals with albinism in the wild is usually quite low.[4][5] However the novelty of albino animals has occasionally led to their protection by groups such as the Albino Squirrel Preservation Society.

In partial albinism there can be a single patch or patches of skin that lack melanin. Especially in albinistic birds and reptiles, ruddy and yellow hues or other colors may be present on the entire body or in patches (as is common among pigeons), because of the presence of other pigments unaffected by albinism such as porphyrins, pteridines and psittacins, as well as carotenoid pigments derived from the diet.

In some animals albinism-like conditions may affect other pigments or pigment-production mechanisms:

  • "Whiteface" a condition that affect some parrot species is caused by a lack of psittacins.[6]
  • Axanthism is a condition common in reptiles and amphibians, in which xanthophore metabolism is affected rather than synthesis of melanin, resulting in reduction or absence of red and yellow pteridine pigments.[7]
  • Leucism differs from albinism in that the melanin is, at least, partially absent but the eyes retain their usual color. Some leucistic animals are white or pale because of chromatophore (pigment cell) defects, and do not lack melanin.
  • Melanism is the direct opposite of albinism. An unusually high level of melanin pigmentation (and sometimes absence of other types of pigment in species that have more than one) results in an appearance darker than non-melanistic specimens from the same genepool.[8]

Intentionally bred albinistic strains of some animal species are commonly used as model organisms in biomedical study and experimentation, although some researchers have argued that they are not always the best choice.[9] Examples include the BALB/c mouse and Wistar and Sprague Dawley rat strains, while albino rabbits were historically used for Draize toxicity testing.[10] The yellow mutation in fruit flies is their version of albinism.

The incidence of albinism can be artificially increased in fish by exposing the eggs to heavy metals.[11]

The eyes of an albino animal appear red because the colour of the red blood cells in the underlying retinal blood vessels shows through where there is no pigment to obscure it.

Albinism in humans

An albino child sitting with his Tanzanian family.
Albinistic girl from Papua New Guinea

Albinism was formerly categorized as tyrosinase-positive or -negative. In cases of tyrosinase-positive albinism, the enzyme tyrosinase is present. The melanocytes (pigment cells) are unable to produce melanin for any one of a variety of reasons that do not directly involve the tyrosinase enzyme. In tyrosinase-negative cases, either the tyrosinase enzyme is not produced or a nonfunctional version is produced. This classification has been rendered obsolete by recent research.[3]

Most albinistic humans appear white or very pale as melanin pigments are responsible for brown, black, and some yellow colorations.

Because individuals with albinism have skin that partially or entirely lacks the dark pigment melanin, which helps protect the skin from the sun's ultraviolet radiation, their skin can burn more easily from overexposure. (See human skin color).

The human eye is quite large and thus produces enough pigment to lend opacity to the eye, often colouring the iris pale blue. However, there are cases in which the eyes of an albinistic person appear red or purple, depending on the amount of pigment present. Lack of pigment in the eyes also results in problems with vision, related and unrelated to photosensitivity.

The albinistic are generally (but see related disorders below) as healthy as the rest of the population, with growth and development occurring as normal, and albinism by itself does not cause mortality,[1] although the lack of pigment increases the risk of skin cancer and other problems.

About 1 in 17,000 human beings has some type of albinism, although up to 1 in 70 is a carrier of albinism genes.[12]

Classification

There are two main categories of albinism in humans:

  • In oculocutaneous albinism (despite its Latin-derived name meaning "eye-and-skin" albinism), pigment is lacking in the eyes, skin and hair. (The equivalent mutation in non-humans also results in lack of melanin in the fur, scales or feathers.) People with oculocutaneous albinism can have anything from no pigment at all to almost normal levels.
  • In ocular albinism, only the eyes lack pigment. People who have ocular albinism have generally normal skin and hair color, although it is typically lighter than either parent. Many even have a normal eye appearance.

Other conditions include albinism as part of their presentation. These include Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, Griscelli syndrome, Waardenburg syndrome, and Tietz syndrome. These conditions are sometimes classified with albinism.[13] Several have sub-types. Some are easily distinguished by appearance, but in most cases genetic testing is the only way to be certain.

Symptoms and conditions associated with albinism

Genetic testing can confirm albinism and what variety it is, but offers no medical benefits except in the cases of non-OCA disorders (see below) that cause albinism along with other medical problems which may be treatable. The symptoms of albinism can be treated by various methods detailed below.

Eye conditions common in albinism may include:

The visual problems particularly associated with albinism arise from a poorly developed retinal pigment epithelium (RPE) due to the lack of melanin.[citation needed] This degenerate RPE causes foveal hypoplasia (a failure in the development of normal foveae), which results in eccentric fixation and lower visual acuity, and often a minor level of strabismus. Nystagmus is usually seen, as is photophobia or light sensitivity (see below).

The iris is a sphincter formed from pigmented tissue that contracts when the eye is exposed to bright light, to protect the retina by limiting the amount of light passing through the pupil. In low light conditions the iris relaxes to allow more light to enter the eye. In albinistic subjects, the iris does not have enough pigment to block the light, thus the decrease in pupil diameter is only partially successful in reducing the amount of light entering the eye.[citation needed] Additionally, the improper development of the RPE, which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye.[15] The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses and/or brimmed hats.[3]

The lack of pigment also makes the skin unusually sensitive to sunlight and thus susceptible to sunburn.

Surgical treatment

For the most part, treatment of the eye conditions consists of visual rehabilitation.[citation needed] Surgery is possible on the ocular muscles to decrease nystagmus, strabismus and common refractive errors like astigmatism. Strabismus surgery may improve the appearance of the eyes.[citation needed] Nystagmus-damping surgery can also be performed, to reduce the "shaking" of the eyes back and forth.[16] The effectiveness of all these procedures varies greatly and depends on individual circumstances. More importantly, since surgery will not restore a normal RPE or foveae, surgery will not provide fine binocular vision.[citation needed] In the case of esotropia (the "crossed eyes" form of strabismus), surgery may help vision by expanding the visual field (the area that the eyes can see while looking at one point).[citation needed]

Vision aids

Glasses and other vision aids, large-print materials and closed captioning, as well as bright but angled reading lights, can help individuals with albinism, even though their vision cannot be corrected completely. Some albinistic people do well using bifocals (with a strong reading lens), prescription reading glasses, and/or hand-held devices such as magnifiers or monoculars (a very simple telescope).[3] Contact lenses may be colored to block light transmission through the iris. Some use bioptics, glasses which have small telescopes mounted on, in, or behind their regular lenses, so that they can look through either the regular lens or the telescope. Newer designs of bioptics use smaller light-weight lenses. Some US states allow the use of bioptic telescopes for driving motor vehicles. (See also NOAH bulletin "Low Vision Aids".)

Although still disputed among the experts, many ophthalmologists recommend the use of spectacles from early childhood onward to allow the eyes the best development possible.

Misconceptions

While some of the very rare albinism disorders that are coupled with deafness and immunodeficiency, like Chediak-Higashi Syndrome, appear to be linked with inbreeding,[2] the vast majority of sufferers of common albinism are not the product of such unions; the more usual albinism genes are widespread enough that they can easily produce albinistic offspring from parents who are not related.

Culture

Afro-Brazilian albino pride parade during Bahia carnival

In physical terms, humans with albinism commonly have vision problems and need sun protection. But they also face social and cultural challenges (even threats) as the condition is often a source of ridicule, discrimination, or even fear and violence. Cultures around the world have developed many beliefs regarding people with albinism. This folklore ranges from harmless myth to dangerous superstitions that cost human lives. Cultural challenges can be expected to be vastly higher in areas where pale skin and light hair stand out more from the ethnic majority's average phenotype.

In African countries such as Tanzania[17] and Burundi,[18] there has been an unprecedented rise in witchcraft-related killings of albino people in recent years. This is because albino body parts are used in potions sold by witchdoctors. Numerous authenticated incidents have occurred in Africa during the 21st Century.[19][20][21][22] For example, in Tanzania, in September 2009, three men were convicted of killing a 14 year old albino boy and severing his legs in order to sell them for witchcraft purposes.[23]

Other examples: In Zimbabwe, belief that sex with an albinistic woman will cure a man of HIV has led to rapes (and subsequent HIV infection).[24] In Jamaica, the albinistic have long been regarded as "cursed".

Certain ethnic groups and insular areas exhibit heightened susceptibility to albinism, presumably due to genetic factors (reinforced by cultural traditions). These include notably the Native American Kuna and Zuni nations (respectively of Panama and New Mexico); Japan, in which one particular form of albinism is unusually common; and Ukerewe Island, the population of which shows a very high incidence of albinism.[citation needed]

Portrayals of people with albinism in literature and films have historically rarely been positive. This fact is sometimes referred to as the "evil albino" stereotype, or albino bias.[citation needed] While this stereotype is common, in recent years a few more positive roles have also been cast for mock-albino actors and occasionally genuinely albinistic ones.[citation needed]

A number of people with albinism have become famous, including historical figures such as Emperor Seinei of Japan, and Oxford don William Archibald Spooner; actor-comedian Victor Varnado; musicians such as Johnny and Edgar Winter, Salif Keita, Winston "King Yellowman" Foster, Brother Ali, Sivuca, Willie "Piano Red" Perryman; and fashion model Connie Chiu.

There have also been some famed albino animals, including Migaloo, a humpback whale off the coast of Australia; Snowflake, a gorilla from a zoo in Barcelona; Snowdrop, a Bristol Zoo penguin; a pink dolphin in Louisiana[25] and the sperm whale Mocha Dick, the inspiration for Herman Melville's novel Moby-Dick.

References

  1. ^ a b c "Albinism", by Dr. Raymond E. Boissy, Dr. James J. Nordlund, et al., at eMedicine, 22 August 2005. Retrieved 31 March 2007.
  2. ^ a b Online Mendelian Inheritance in Man penise, at Johns Hopkins University (see also Mendelian Inheritance in Man for more information about this source).
  3. ^ a b c d "Facts about Albinism", by Richard King et al.
  4. ^ Ilo Hiler, Albinos. Young Naturalist. The Louise Lindsey Merrick Texas Environment Series, No. 6, pp. 28–31. Texas A&M University Press, College Station (1983)
  5. ^ Dobosz, ByS; Kohlmann, K.; Goryczko, K.; Kuzminski, H. (July 2008). "Growth and vitality in yellow forms of rainbow trout". Journal of Applied Ichthyology 16 (3): 117–20. doi:10.1111/j.1439-0426.2000.00147.x (inactive 2010-02-16). 
  6. ^ "The Parblue Puzzle: Part 4—Common Parblue Varieties: The Cockatiel [Nymphicus hollandicus]" by Clive Hesford, The Genetics of Colour in the Budgerigar and Other Parrots, January 1998
  7. ^ "Amphibian Biology & Physiology: Caudata" at Amphibian Information Resource: An Educational Web Project About Amphibian Species; sourced December 2006, actual authoring/publication date unspecified.
  8. ^ "Feather Colors: What We See" by Dr. Julie Feinstein of the American Museum of Natural History (NY), in Birder's World Magazine online archive; sourced December 2006, actual authoring/publication date unspecified.
  9. ^ Creel D (June 1980). "Inappropriate use of albino animals as models in research". Pharmacology, Biochemistry, and Behavior 12 (6): 969–7. doi:10.1016/0091-3057(80)90461-X. PMID 7403210. 
  10. ^ Draize, J.H., Woodard, G. and Calvery, H.O. (1944) Methods for the study of irritation and toxicity of substances applied topically to the skin and mucous membranes. J. Pharmacol. and Exp. Therapeutics. 82, 377–390.
  11. ^ Brito, Marcelo F. G. de; Caramaschi, ÉRica P. (2005). "An albino armored catfish Schizolecis guntheri (Siluriformes: Loricariidae) from an Atlantic Forest coastal basin". Neotropical Ichthyology 3. doi:10.1590/S1679-62252005000100009. 
  12. ^ "Albinism" by Carol A. Turkington at answers.com
  13. ^ "ILDS - ICD10". http://web.ilds.org/icd10_list.php?VIEW=1&START_CODE=E70.3&START_EXT=14. 
  14. ^ Carden SM, Boissy RE, Schoettker PJ, Good WV (February 1998). "Albinism: modern molecular diagnosis". The British Journal of Ophthalmology 82 (2): 189–95. doi:10.1136/bjo.82.2.189. PMID 9613388. 
  15. ^ a b "Albinism – Review of Optometry Online".
  16. ^ Lee J (May 2002). "Surgical management of nystagmus". Journal of the Royal Society of Medicine 95 (5): 238–41. doi:10.1258/jrsm.95.5.238. PMID 11983764. 
  17. ^ "Africa | Living in fear: Tanzania's albinos". BBC News. 2008-07-21. http://news.bbc.co.uk/1/hi/world/africa/7518049.stm. Retrieved 27 February 2010. 
  18. ^ "Africa | Burundian albino murders denied". BBC News. 2009-05-19. http://news.bbc.co.uk/1/hi/world/africa/8057956.stm. Retrieved 27 February 2010. 
  19. ^ "Africa | Man 'tried to sell' albino wife". BBC News. 2008-11-13. http://news.bbc.co.uk/1/hi/world/africa/7726743.stm. Retrieved 27 February 2010. 
  20. ^ "Africa | Tanzania albinos targeted again". BBC News. 2008-07-27. http://news.bbc.co.uk/1/hi/world/africa/7527729.stm. Retrieved 27 February 2010. 
  21. ^ Ntetema, Vicky (2008-07-24). "Africa | In hiding for exposing Tanzania witchdoctors". BBC News. http://news.bbc.co.uk/1/hi/world/africa/7523796.stm. Retrieved 27 February 2010. 
  22. ^ "Africa | Mothers hacked in albino attacks". BBC News. 2008-11-14. http://news.bbc.co.uk/1/hi/world/africa/7730193.stm. Retrieved 27 February 2010. 
  23. ^ "Death for Tanzania albino killers". BBC News. 2009-09-23. http://news.bbc.co.uk/1/hi/world/africa/8270446.stm. Retrieved 27 February 2010. 
  24. ^ Machipisa, Lewis. "RIGHTS-ZIMBABWE: The Last Minority Group to Find a Voice". Inter Press Service News Agency. IPS-Inter Press Service. http://ipsnews.net/interna.asp?idnews=14122. Retrieved 30 January 2010. 
  25. ^ "Rare Pink Dolphin Seen in Louisiana Lake - Science News | Science & Technology | Technology News". FOXNews.com. 2007-07-03. http://www.foxnews.com/story/0,2933,287938,00.html. Retrieved 27 February 2010. 

See also

External links


Simple English

File:Ministry of Hope Nursery, Lilongwe -
An albino baby girl in an orphanage in Malawi.

Albinism is a condition some people and animals are born with. This condition is caused by a lack of pigment (color) in their hair, eyes, and skin. A person or animal with albinism is sometimes called an albino, but many people prefer to be called a "person with albinism".

People with albinism usually have white or light blonde hair and very fair skin. Their eyes are blue, or rarely pink-ish. People with albinism in reality do have some problems including bad vision and getting sunburn easily. All of these problems are because people with alibinism have little or no pigments in their eyes, skin and hair.[1]

Vision problems in albinism include nystagmus (irregular fast movements of the eyes), strabismus (where the eyes fail to balance) and refractory errors (like being near-sighted or far-sighted).

Albino animals are more easily spotted and thus attacked by predators because they lack the camouflage that the non-albino members of their species have.[needs proof]

Contents

Genetics of albinism

Albinism is a hereditary condition. It is usually inherited in an autosomal recessive pattern; it means, both parents should carry the albinism gene to have a child with albinism.[1]

Famous people with albinism

References

Other websites

Simple English Wiktionary has the word meaning for:
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