Albinot në Afrikën e Jugut, “ushqim” për shtriganët

Albinot në Afrikën e Jugut, “ushqim” për shtriganët

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  • Postime: 26635
  • Gjinia: Mashkull
ne: 05-07-2011, 14:43:24
Një djalë albino, i cili u zhduk ndërsa kthehej nga shkolla në një qytezë të Afrikës së Jugut, mund të jetë rrëmbyer nga fiset me shtriganë për t’u sakrifikuar. Policia në KwaZulu-Natal ka kërkuar për 14-vjeçarin Sibisuso Nhatave me frikën se trupi i tij mund të jetë përdorur për magjinë e zezë. Albinizmi, një sëmundje gjenetikisht e trashëgueshme që i lind fëmijët pa pigment, shihet në Afrikë si magjike. Praktika është e njohur në këto zona. Në Tanzani, një vajzë albine u rrëmbye nga disa burra që besonin se organet e saj (që iu prenë) do t’i kuronin nga SIDA. Albinët kanë lëkurë shumë të ndjeshme e të zbardhur dhe shikim të dobët. Në një vend ku pjesa më e madhe e popullsisë janë të zinj, ata dallohen fare lehtë. Rreth 12 500 nga 50 milionë njerëzit që jetojnë në Afrikën e Jugut janë albinë. /Panorama

  • Postime: 26635
  • Gjinia: Mashkull
#1 ne: 05-07-2011, 14:46:16
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. While an organism with complete absence of melanin is called an albino an organism with only a diminished amount of melanin is described as albinoid.

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.

here are two main categories of albinism in humans:
In oculocutaneous albinism Types 1-4 with different levels with pigmentation (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 for a Caucasian.
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. Also, ocular albinism is generally sex-linked, therefore males are more likely to be affected. Males are without another X chromosome to mask recessive alleles on the X they inherit.
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.[4] Several have sub-types. Some are easily distinguished by appearance, but in most cases genetic testing is the only way to be certain.
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.

Most albinistic humans appear white or very pale as the melanin pigments responsible for brown, black, and some yellow colorations are not present.
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.[6]
The human eye normally produces enough pigment to color the iris and lend opacity to the eye. 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 as healthy as the rest of the population (but see related disorders below), with growth and development occurring as normal, and albinism by itself does not cause mortality,[7] although the lack of pigment increases the risk of skin cancer and other problems.

Development of the optical system is highly dependent on the presence of melanin, and the reduction or absence of this pigment in albinistic individuals may lead to
Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres[6]
Photophobia and decreased visual acuity due to light scattering within the eye[6]
Reduced visual acuity due to foveal hypoplasia and possibly light-induced retinal damage[6]
Eye conditions common in albinism include:
Nystagmus, irregular rapid movement of the eyes back and forth, or in circular motion.[6]
Refractive errors such as myopia or hyperopia and especially astigmatism[8]
Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus.[6]
Optic nerve hypoplasia, underdevelopment of the optic nerve
Some of the visual problems 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.
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.[9] 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. /Wikipedia