Albinism Totally Explained

Everything about Albinism totally explained

| ICD9 = | ICDO = | OMIM = 203100 | OMIM_mult =,,,,,,,,,,,,,,,,,,,, | MedlinePlus = 001479 | eMedicineSubj = derm | eMedicineTopic = 12 | MeshID = | }} Albinism (from Latin albus, "white"; see ) is a form of hypopigmentary congenital disorder, characterized by a partial (in hypomelanism, also known as hypomelanosis) or total (amelanism or amelanosis) lack of melanin pigment in the eyes, skin and hair (or more rarely the eyes alone). Albinism results from inheritance of recessive alleles. The condition is known to affect mammals (including humans), 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 derogatory ways 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".

Types of human albinism

Albinism is hereditary; it isn't an infectious disease and can't be transmitted through contact, blood transfusions, or other vectors. 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.
   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 don't directly involve the tyrosinase enzyme. In tyrosinase-negative cases, either the tyrosinase enzyme isn't produced or a nonfunctional version is produced. This classification has been rendered obsolete by recent research.
   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.
   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 pigments derived from the diet. Some animals are white or pale due to chromatophore (pigment cell) defects, don't lack melanin production, and have normal eyes; they're 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. Albinism-like conditions may affect other pigments or pigment-production mechanisms in some animals (for example "whiteface", a lack of psittacins that can affect some parrot species.). 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. Of all these conditions, only albinism and melanism affect humans.
   The eyes of an animal with albinism occasionally appear red due to the underlying retinal blood vessels showing through where there isn't 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 doesn't cause mortality 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. Albino axolotls, zebrafish, medaka and frogs are other common laboratory animals. 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.
   About 1 in 17,000 human beings has some type of albinism, although up to 1 in 70 is a carrier of albinism genes.
   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's 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

Oculocutaneous albinism type 1 (OCA1) 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) 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 can't 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. 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 (for example get darker). (An equivalent mutation produces the coat pattern in Siamese cats.) Another variant of OCA1b, called Albinism, yellow mutant type 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. About 1 in 40,000 people have some form of OCA1. 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.

Photophobia, hypersensitivity to bright light and glare.

Foveal hypoplasia, underdevelopment of the fovea, the center of the retina

Optic nerve hypoplasia, underdevelopment of the optic nerve

Abnormal decussation (crossing) of the optic nerve fibers in the optic chiasm

Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus. 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 . 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 doesn't 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. . 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. The resulting sensitivity (photophobia) generally leads to a dislike of and discomfort in bright light, but doesn't prevent people with albinism enjoying the outdoors, especially when using sunglasses and/or brimmed hats.
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 can't be "cured" 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 don't need to take special precautions against skin damage.

Surgical treatment

For the most part, treatment of the eye conditions consists of visual rehabilitation. 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. Nystagmus-damping surgery can also be performed, to reduce the "shaking" of the eyes back and forth. The effectiveness of all these procedures varies greatly and depends on individual circumstances. More importantly, since surgery won't restore a normal RPE or foveae, surgery won't provide fine binocular vision. 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).

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 can't 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. 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 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. Some low-vision clinics provide these aids on trial loan, with instruction in their use.

Sun protection

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 can't afford sunscreen, especially in regions with high exposure to sunlight, as in Africa.
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).

Misconceptions

While some of the very rare albinism disorders that are coupled with deafness and immunodeficiency appear to be linked with inbreeding, In Tanzania in 2008, President Kikwete publicly condemned witchdoctors for killing albinos for their body parts which are thought to bring good luck. 19 albinos had been murdered between March 2007 and April 2008. In Jamaica, people with albinism were historically degraded, and regarded as "cursed". 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 Emperor Seinei of Japan, and Oxford don William Archibald Spooner; actor/comedian Victor Varnado; 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 (a whale off the coast of Australia), Copito de Nieve (a Barcelona Zoo gorilla), Snowdrop (a Bristol Zoo penguin), and the sperm whale Mocha Dick, the inspiration for Herman Melville's novel Moby-Dick.

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