Jump to content

Albinism in humans

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 71.198.168.12 (talk) at 06:29, 23 September 2007. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

"Albino" redirects here. For other uses, see Albino (disambiguation).
Albinism in humans

Albinism (from Latin albus; extended etymology), more technically hypomelanism or hypomelanosis, is a form of hypopigmentary congenital disorder, characterized by a lack of melanin pigment in the eyes, skin and hair (or more rarely the eyes alone). Albinism results from inheritance of recessive genes. The condition is known to affect mammals, fish, birds, reptiles, and amphibians. While the most common term for an organism affected by albinism is "albino" (noun and adjective), the word is sometimes used in a derogatory way towards people; more neutral terms are "albinistic" (adjective) and "person with albinism" (noun). Additional clinical adjectives sometimes used to refer to animals are "albinoid" and "albinic". Some say that Albinos are born of the seed of Satan.

Causes

Albinism is a genetic disorder. The principal gene which results in albinism prevents the body from making the usual amounts of the pigment melanin. 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]

Albinism used to be 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]

The chance of offspring with albinism resulting from the pairing of an organism with albinism and one without albinism is low, as discussed in more detail below. 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, because it is passed on to offspring through X-linked inheritance. Thus, males more frequently have ocular albinism.[3]

Because organisms with albinism have skin that lacks (sufficiently or entirely) the dark pigment melanin, which helps protect the skin from ultraviolet radiation coming from the sun, they can sunburn easily from overexposure. (See human skin color for more information). Lack of melanin in the eye also results in problems with vision, related and unrelated to photosensitivity, which are discussed further below.

Most humans and many animals with albinism appear white or very pale; the multiple types of melanin pigment are responsible for brown, black, gray, and some yellow colorations. In some animals, especially 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), due to the presence of other pigments unaffected by albinism such as porphyrins, pteridines and psittacins, as well as carotenoid pigements derived from the diet. Some animals are white or pale due to chromatophore (pigment cell) defects, do not lack melanin production, and have normal eyes; they are referred to as leucistic. 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), is known as melanism, and results in an appearance darker than non-melanistic specimens from the same genepool.[4] Albinism-like conditions may affect other pigments or pigment-production mechanisms in some animals (e.g. "whiteface", a lack of psittacins that can affect some parrot species.).[5] Another is common in reptiles and amphibians: axanthism, in which xanthophore metabolism, instead of synthesis of melanin, is affected, resuling in reduction or absence of red and yellow pteridine pigments.[6] Of all these conditions, only albinism and melanism affect humans.

File:Rodent.gif
An albino Wistar rat, a strain commonly used for both biomedical and basic research.

The eyes of an animal with albinism occasionally appear red due to the underlying retinal blood vessels showing through where there is not enough pigment to cover them. In humans this is rarely the case, as a 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. The albinistic are generally (but see related disorders below) as healthy as the rest of their species, with growth and development occurring as normal, and albinism by itself does not cause mortality[1] (though the lack of pigment is an elevated risk for skin cancer and other problems.) 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. [7] [8] However the novelty of albino animals has occasionally led to their protection by groups such as the Albino Squirrel Preservation Society.

Intentionally-bred albinistic strains of some animal species are commonly used as model organisms in biomedical study and experimentation. Examples include the BALB/c mouse and Wistar and Sprague Dawley rat strains, while albino rabbits were historically used for Draize toxicity testing. [9] Albino axolotls, zebrafish, medaka and frogs are other common laboratory animals.

The incidence of albinism can be artificially increased in fish by exposing the eggs to heavy metals.[10]

Types of human albinism

About 1 in 17,000 human beings has some type of albinism, although up to 1 in 70 is a carrier of albinism genes.[11]

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.)
  • In ocular albinism, only the eyes lack pigment. People with oculocutaneous albinism can have anywhere from no pigment at all to almost-normal levels. People who have ocular albinism have generally normal skin and hair color, and many even have a normal eye appearance.

While there is only one major type of ocular albinism, there are several varieties of oculocutaneous albinism (and disorders which produce the same or similar results), some of which have subtypes. Some are easily distinguished by appearance, but in most cases, genetic testing is the only way to be certain.

Oculocutaneous albinism family

Girl from Honduras with probable OCA1a.
  • Oculocutaneous albinism type 1 (OCA1) (Online Mendelian Inheritance in Man (OMIM): 203100) is the type with (usually) the least amount of pigment. People with this type generally have very pale skin, white to yellow hair (depending on subtype, see below) and light blue eyes; however there are cases in which the irises can appear pink or violet, depending on the amount of blue (non-melanin)[citation needed] pigment present in the irises and the level and direction of light available to the observer. OCA1 is caused by an alteration of the tyrosinase gene, and can occur in two variations. The first is OCA1a, and means that the organism cannot develop pigment at all. The hair is usually white (often translucent) and the skin very pale. Vision usually ranges from 20/200 to 20/400. The second is OCA1b, which has several subtypes itself. Some individuals with OCA1b can tan and also develop pigment in the hair.[3][verification needed] One subtype of OCA1b is called OCA1b TS (temperature sensitive), where the tyrosinase can only function below a certain temperature, which causes the body hair in cooler body regions to develop pigment (i.e. get darker). (An equivalent mutation produces the coat pattern in Siamese cats[citation needed].) Another variant of OCA1b, called Albinism, yellow mutant type (Template:OMIM3) is more common among the Amish than in other populations, and results in blonde hair and the eventual development of skin pigmentation during infancy, though at birth is difficult to distinguish from other types.[2][12] About 1 in 40,000 people have some form of OCA1.[1][2]
  • Oculocutaneous albinism type 2 (OCA2) (Template:OMIM3), the most common type of albinism, is caused by mutation of the P gene. People with OCA2 generally have more pigment and better vision than those with OCA1, but cannot tan like some with OCA1b. A little pigment can develop in freckles or moles.[3] People with OCA2 usually have fair skin but not as pale as OCA1, and pale blonde to golden or reddish-blonde hair, and most commonly blue eyes. Affected people of African descent usually have a different phenotype (appearance): yellow hair, pale skin, and blue, gray or hazel eyes. About 1 in 15,000 people have OCA2.[1][2]
  • Oculocutaneous albinism type 3 (OCA3, or rufous albinism) (Template:OMIM3) has only been partially researched and documented. It is caused by mutation of the tyrosinase-related protein-1 (Tyrp1) gene. Cases have been reported in Africa and New Guinea. Affected individuals typically have red hair, reddish-brown skin and blue or gray eyes. Variants may be the recently-identified minimal pigment type albinism (Template:OMIM3) and rufous oculocutaneous albinism (ROCA or xanthism) (Template:OMIM3). The incidence rate of OCA3 is unknown.[1][2]
  • Oculocutaneous albinism type 4 (OCA4) (Template:OMIM3) is very rare outside of Japan, where OCA4 accounts for 24% of albinism cases. OCA4 can only be distinguished from OCA2 through genetic testing, and is caused by mutation of the membrane-associated transporter protein (MATP) gene.[1][2]
  • Hermansky-Pudlak syndrome (HPS) (Template:OMIM3) is not a type of OCA, technically, but has similar features. HPS has a great range of degrees of pigmentation, from OCA1a-like to almost-normal coloring. Vision usually ranges from 20/60 to 20/200. Apart from the hypopigmentation and impaired vision, people with HPS lack dense bodies in their blood platelets which are responsible for releasing clotting factors. For this reason, HPS patients bruise easily and have a hard time stopping bleeding once it begins (bleeding diathesis, similarly to hemophilia). HPS has seven known forms (HPS-1 through HPS-7), each caused by a different autosomal recessive gene mutation. HPS-1 and HPS-4 may also include pulmonary fibrosis, or scarring of lung tissue that prevents the necessary expansion and contraction during breathing. It is believed that this is due to a buildup of fatty ceroid in the lungs. Colitis, or inflammation in the large intestine, is another symptom of most types of HPS, which may cause diarrhea, nausea, and blood in the stool. HPS is rare generally, but affects 1 in 1800 Puerto Ricans, and is typically fatal by middle age.[1][2]
  • Griscelli syndrome (GS) is similar to CHS in symptoms (and also very rare). It is divided into three types, GS1 (Template:OMIM3), GS2 (Template:OMIM3) and GS3 (Template:OMIM3). Each type is due to a different autosomal recessive gene mutation. Type 1 produces mainly neurological problems in addition to albinism, while type 2 produces mainly immunological issues as well as the hypopigmentation, and type 3 only evidences hypomelanosis without either of the other sorts of problems. People affected by GS differ in appearance from those with OCA, having silvery-grey hair. A fourth and even rarer variant, partial albinism and immunodeficiency syndrome (PAID) (Template:OMIM3), has been identified and requires further study. An additional type called Elejalde syndrome (Template:OMIM3) may exist, but some researchers believe it is actually simply GS1. GS2, because of its immune system effects, results in a very high mortality rate among children and young adults that have it.[1][2]

Ocular albinism family

  • Ocular albinism, type 1 (OA1) (Template:OMIM3), also known as Nettleship-Falls syndrome, is the most common variety of ocular albinism, which affects the eyes but generally not the skin or hair. OA1 is usually associated with nystagmus, and difficult to otherwise detect in females; males show more readily observable symptoms. There are several other identified types of OA, though researchers are not all agreed on the distinctions and classification. Most are caused by a mutation in a gene on the X chromosome, and are X-linked recessive traits.
  • Ocular albinism, type 2 (OA2) (Template:OMIM3), also known as Forsius-Eriksson syndrome or "Åland Island eye disease", mostly only affects males though females are often carriers and can sometimes be symptomatic; it is frequently linked with protanopic dichromacy (a form of color blindness) and with night blindness (nyctalopia).
  • Ocular albinism, type 3 (OA3) (Template:OMIM3), also known as ocular albinism, autosomal recessive (OAR) is a non-X-linked variant, which may be more common among the Amish than in other populations.

The skin color of people affected by OA can be slightly lighter than those of the rest of their families. The eye color can vary greatly, and in some cases only examination of the retina or genetic testing can reveal OA for certain. Some form of OA afflicts 1 in 50,000 people, though certain isolated populations are at greater risk.[1][2]


Other types

Other rare variants of albinism are theorized (by ongoing research as of 2007) to exist, such as

  • Albinism-deafness syndrome (ADFN) (Template:OMIM3, which may actually be closer related to vitiligo); it is predominantly observed among Hopi Native Americans (with an incidence estimated at[citation needed] 1 in 200 individuals)
  • Recessive total albinism with congenital deafness (Template:OMIM3)
  • Albinism black-lock cell-migration disorder syndrome (ABCD) (Template:OMIM3)[2]

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 or may not include:

Albinistic girl from Papua New Guinea

Organisms with albinism usually have impaired vision due to one or more of the listed conditions. While a person with albinism may suffer from common refractive errors like nearsightedness or farsightedness, 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 with pigmented tissue (which makes up the color of the eyes) that contracts to limit the amount of light that can enter through the pupil and relaxes again to allow for better vision in darkness. This mechanism can be observed in humans and mammals (like in cat's eyes) and is needed because too much light is uncomfortable or even painful and decreases vision. In people with albinism, the iris does not have enough pigment to block the light, thus the decrease of pupil diameter is only partially successful in reducing the amount of light that enters 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.[14] The resulting sensitivity (photophobia) generally leads to a dislike of and discomfort in bright light, but does not prevent people with albinism enjoying the outdoors, especially when using sunglasses and/or brimmed hats.[3]

The lack of pigment also makes the skin unusually sensitive to sunlight and thus susceptible to sunburn, so people with albinism should either avoid prolonged exposure to bright sunlight or protect their skin.

Treatment of the symptoms

Albinism is a condition that cannot be "cured" or "treated" per se, but small things can be done to improve the quality of life for those affected. Most importantly to improve vision, protect the eyes from bright lights, and avoid skin damage from sunlight. The extent and success rate of these measures depend on the type of albinism and severity of the symptoms; in particular, people with ocular albinism are likely to have normally-pigmented skin, and thus do not need to take special precautions against skin damage.

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.[15] 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.[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,[who?] many ophthalmologists recommend the use of glasses from early childhood onward to allow the eyes the best development possible.

Optometrists or ophthalmologists who are experienced in working with low vision patients can recommend various optical aids. Clinics may provide these aids on trial loan, and provide instruction in their use. [16] maintains a directory of low vision clinics.

Sun protection

Albinistic man from Niger, with melanomas.

It is vital that people with albinism use sunscreen when exposed to sunlight to prevent premature skin aging or skin cancer. This poses a problem for those who cannot afford sunscreen, especially in regions with high exposure to sunlight, as in Africa. Special sun protective clothing and swimsuits are available and are a good alternative to excessive use of sunscreen.[citation needed]

Use of sunglasses and hats with wide brims can make the glare outside bearable. Other things that can help people with albinism are avoiding sudden changes of the lighting situation (switching the light on in complete darkness), using dimmable switches and adding tint to car windows or blinds to normal windows. Lights should be yellowish rather than blue and not point towards the usual position of a person with albinism (like their seat at a table). When possible, people with albinism generally prefer to have the light on their backs rather than face it.

Misconceptions

While some of the very rare albinism disorders that are coupled with deafness and immunodeficiency 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 that are not related.

A common misconception is that albinistic individuals of a species are sterile; they are in fact fully capable of reproducing. It is also thought by many that people with albinism live short life spans. This is not true in general, but may be a distorted view of a more reasonable fact that people with albinism have a higher risk of skin cancer if they do not use proper skin protection when in the sun. (Some very rare variants of albinism are lethal in and of themselves by adulthood or sooner, but they are so little-known by the general public that they are unlikely to have contributed to this belief.)

Culture

Afro-Brazilian albino pride parade during Bahia carnival
Main article: Albinism in popular culture

While on the physical side, humans with albinism commonly have vision problems and need sun protection, they also face a social challenge, as the condition is often a source of ridicule, discrimination or even fear.[citation needed] Due to albinism's effect on one's outward appearance, cultures around the world have developed many superstitions regarding people with albinism, who are believed by some to have magical powers or to be able to tell the future,[citation needed] a common theme in fiction as well (see Albinism in popular culture for examples). For example, in Zimbabwe, modern folklore posits that sexual intercourse with an albinistic person will cure one of HIV, leading to the rape (and subsequent HIV infection) of women with albinism in that region.[17] In Jamaica, people with albinism were historically degraded, and regarded as "cursed".[citation needed] A long-standing American urban legend is that of alleged "albino colonies" in rural New Jersey.

Portrayals of people with albinism in literature and films are rarely positive. This fact is sometimes referred to as the "evil albino" stereotype, or albino bias. 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.

A number of real people with albinism have become famous, including historical figures such as King Edward the Confessor of England, Emperor Seinei of Japan, and Oxford don William Archibald Spooner; musicians such as Johnny and Edgar Winter, Winston "King Yellowman" Foster, Brother Ali, and Willie "Piano Red" Perryman; even a fashion model, Connie Chiu. There have also been some well-known albino animals, including Migaloo (an Australian whale), Copito de Nieve (a Barcelona Zoo gorilla), and Snowdrop (a Bristol Zoo penguin).

See also

References

  1. ^ a b c d e f g h i j k "Albinism", by Dr. Raymond E. Boissy, Dr. James J. Nordlund, et al., at eMedicine, 22 August 2005; retrieved 31 March 2007
  2. ^ a b c d e f g h i j k l Online Mendelian Inheritance in Man Database, at Johns Hopkins University (see also Mendelian Inheritance in Man for more information about this source).
  3. ^ a b c d e f "Facts about Albinism", by Richard King et al. Cite error: The named reference "Facts_Albinism" was defined multiple times with different content (see the help page).
  4. ^ "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.
  5. ^ "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
  6. ^ "Amphibian Biology & Physiology: Caudata" at Amphibian Information Resource: An Educational Web Project About Amphibian Species; sourced December 2006, actual authoring/publication date unspecified.
  7. ^ 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)
  8. ^ S. Dobosz, K. Kohlmann, K. Goryczko, H. Kuzminski (2000) Growth and vitality in yellow forms of rainbow trout. Journal of Applied Ichthyology. 16, 117–120.
  9. ^ Draize, J.H., Woodard, G. & 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.
  10. ^ de Brito, Marcelo F. G. "An albino armored catfish Schizolecis guntheri (Siluriformes: Loricariidae) from an Atlantic Forest coastal basin" (PDF). Neotropical Ichthyology. 3 (1): 2005. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ "Albinism" by Carol A. Turkington at answers.com
  12. ^ "Ocular Manifestations of Albinism", by Dr. Mohammed O. Peracha, at eMedicine, 13 September 2005; retrieved 31 March 2007
  13. ^ "Albinism: Modern molecular diagnosis"
  14. ^ a b "Albinism - Review of Optometry Online"
  15. ^ by John Lee
  16. ^ "The American Foundation for the Blind".
  17. ^ ipsnews.net
Look up Albino in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Albinism.
Wikisource has the text of the 1911 Encyclopædia Britannica article "Albino".

Albinism in humans

Albinism support organizations

  • Positive Exposure — Non-profit organization founded by photographer Rick Guidotti, "dedicated to celebrating the spirit of difference". Focuses on genetic conditions, especially albinism.
  • Hermansky-Pudlak Syndrome Network (US-based)
  • NOAH — National Organization for Albinism and Hypopigmentation (USA); also has an online support group
  • International Albinism Center (research project based at the University of Minnesota, USA)
  • Albinism Fellowship (UK and Ireland)
  • AFA — Albinism Fellowship of Australia
  • Albino Alliance A support group/forum for people living with albinism in Australia
  • TAF — The Albino Foundation (Nigeria & USA)
  • ALBA — Asociación de Ayuda a Personas con Albinismo [Aid Association to Persons with Albinism] (Spain) Template:Es icon
  • OLA — Organización Latinoamericana de Albinismo [Latin-American Albinism Organization] (Mexico) Template:Es icon

Other

Albinism in animals

Albino Cobra showing binocular markings clearly

Template:Metabolic pathology

Retrieved from "https://en.wikipedia.org/w/index.php?title=Albinism_in_humans&oldid=159752527"