What systems does albinism effect?
http://en.wikipedia.org/wiki/Albinism Albino" redirects here.
For other uses, see Albino (disambiguation). Semi-protected
Albinism Classification and external resources Girl from Honduras
with probable OCA1a-type albinism. 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 DiseasesDB 318
MedlinePlus 001479 eMedicine derm/12 MeSH D000417 Albinism (from
Latin albus, "white"; see extended etymology, also called achromia,
achromasia, or achromatosis; not to be confused with albedo) 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". Albinism is hereditary; it is not an infectious disease
and cannot 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.[1][2] 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] 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 as
they do not have a second X chromosome.[3] Albino Bennett's
Wallaby, Bruny Island, Tasmania, Australia 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, 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. 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 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.[10] 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]
