Albinism in humans

Albinism is a congenital disorder characterized in humans by the complete or partial absence of pigment in the skin, hair and eyes. Albinism is associated with a number of vision defects, such as photophobia, nystagmus, and amblyopia. Lack of skin pigmentation makes for more susceptibility to sunburn and skin cancers. In rare cases such as Chédiak–Higashi syndrome, albinism may be associated with deficiencies in the transportation of melanin granules. This also affects essential granules present in immune cells leading to increased susceptibility to infection.[4]

Albinism
Other namesAchromia, achromasia, achromatosis
A boy with albinism
Pronunciation
  • albino (UK: /ælˈbiːnoʊ/,[1] UK: /ælˈbiːnoʊ/,[2] or US: /ælˈbaɪnoʊ/)[3]
SpecialtyDermatology

Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. It is due to absence or defect of tyrosinase, a copper-containing enzyme involved in the production of melanin. It is the opposite of melanism. Unlike humans, other animals have multiple pigments and for these, albinism is considered to be a hereditary condition characterised by the absence of melanin in particular, in the eyes, skin, hair, scales, feathers or cuticle.[5] While an organism with complete absence of melanin is called an albino, an organism with only a diminished amount of melanin is described as leucistic or albinoid.[6] The term is from the Latin albus, "white".

Signs and symptoms
Girl with albinism from Papua New Guinea

There are two principal types of albinism: oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.

There are different types of oculocutaneous albinism depending on which gene has undergone mutation. With some there is no pigment at all. The other end of the spectrum of albinism is "a form of albinism called rufous oculocutaneous albinism, which usually affects dark-skinned people".[7]

According to the National Organization for Albinism and Hypopigmentation, "With ocular albinism, the color of the iris of the eye may vary from blue to green or even brown, and sometimes darkens with age. However, when an optician examines the eye by shining a light from the side of the eye, the light shines back through the iris since very little pigment is present."[8]

Because individuals with albinism have skin that 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.[9]

The human eye normally produces enough pigment to color the iris blue, green or brown and lend opacity to the eye. In photographs, those with albinism are more likely to demonstrate "red eye", due to the red of the retina being visible through the iris. Lack of pigment in the eyes also results in problems with vision, both related and unrelated to photosensitivity.

Those with albinism 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,[10] although the lack of pigment blocking ultraviolet radiation increases the risk of melanomas (skin cancers) and other problems.

Visual problems
Malian Mandinka singer Salif Keita with albinism

Development of the optical system is highly dependent on the presence of melanin. For this reason, the reduction or absence of this pigment in people with albinism may lead to:

  • Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres[9]
  • Photophobia and decreased visual acuity due to light scattering within the eye (ocular straylight)[9][11] Photophobia is specifically when light enters the eye, unrestricted—with full force. It is painful and causes extreme sensitivity to light.[12]
  • Reduced visual acuity due to foveal hypoplasia and possibly light-induced retinal damage.[9]

Eye conditions common in albinism include:

  • Nystagmus, irregular rapid movement of the eyes back and forth, or in circular motion.[9]
  • Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus.[9]
  • Optic nerve hypoplasia, underdevelopment of the optic nerve.

The improper development of the retinal pigment epithelium (RPE), which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye.[13] The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses or brimmed hats.[14]

Genetics

Oculocutaneous albinism is generally the result of the biological inheritance of genetically recessive alleles (genes) passed from both parents of an individual such as OCA1 and OCA2. A mutation in the human TRP-1 gene may result in the deregulation of melanocyte tyrosinase enzymes, a change that is hypothesized to promote brown versus black melanin synthesis, resulting in a third oculocutaneous albinism (OCA) genotype, ″OCA3″.[15] 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.[10][16] Some of these are associated with increased risk of skin cancer (see list of such genetic variations).

The chance of offspring with albinism resulting from the pairing of an organism with albinism and one without albinism is low. However, because organisms (including humans) 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 sexes.[10] 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 have a single X and Y chromosome, unlike females, whose genetics are characterized by two X chromosomes.[17]

There are two 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.

Enzyme

The enzyme defect responsible for OCA1-type albinism is tyrosine 3-monooxygenase (tyrosinase), which synthesizes melanin from the amino acid tyrosine.

Evolutionary theories

It is suggested that the early hominin evolved in East Africa around 3 million years ago.[18] The dramatic phenotypic change from primate to early hominin is hypothesized to have involved the extreme loss of body hair – except for areas most exposed to UV radiation, such as the head – to allow for more efficient thermoregulation in the early hunter-gatherers. The skin that would have been exposed upon general body hair loss in these early hominins would have most likely been non-pigmented, reflecting the pale skin underlying the hair of our chimpanzee relatives. A positive advantage would have been conferred to early hominids inhabiting the African continent that were capable of producing darker skin – those who first expressed the eumelanin-producing MC1R allele – which protected them from harmful epithelium-damaging ultraviolet rays. Over time, the advantage conferred to those with darker skin may have led to the prevalence of darker skin on the continent. The positive advantage, however, would have had to be strong enough so as to produce a significantly higher reproductive fitness in those who produced more melanin. The cause of a selective pressure strong enough to cause this shift is an area of much debate. Some hypotheses include the existence of significantly lower reproductive fitness in people with less melanin due to lethal skin cancer, lethal kidney disease due to excess vitamin D formation in the skin of people with less melanin, or simply natural selection due to mate preference and sexual selection.[18]

When comparing the prevalence of albinism in Africa to its prevalence in other parts of the world, such as Europe and the United States, the potential evolutionary effects of skin cancer as a selective force due to its effect on these populations may not be insignificant.[18] It would follow, then, that there would be stronger selective forces acting on albino populations in Africa than on albino populations in Europe and the US.[19] In two separate studies in Nigeria, people with albinism were found to be of reproductively significant age more often than not. One study found that 89% of people diagnosed with albinism are between 0 and 30 years of age, while the other found that 77% of albinos were under the age of 20.[19]

Diagnosis

Genetic testing can confirm albinism and what variety it is, but offers no medical benefits except in the cases of non-OCA disorders that cause albinism along with other medical problems which may be treatable. There is no 'cure' for Albinism. The symptoms of albinism can be assisted by various methods.

Management

Since there is no cure for albinism, it is managed through lifestyle adjustments. People with albinism need to take care not to get sunburnt and should have regular healthy skin checks by a dermatologist.

For the most part, treatment of the eye conditions consists of visual rehabilitation. Surgery is possible on the extra-ocular muscles to decrease strabismus.[9] Nystagmus-damping surgery can also be performed, to reduce the "shaking" of the eyes back and forth.[20] The effectiveness of all these procedures varies greatly and depends on individual circumstances.

Glasses, low vision aids, large-print materials, and bright angled reading lights can help individuals with albinism. Some people with albinism do well using bifocals (with a strong reading lens), prescription reading glasses, hand-held devices such as magnifiers or monoculars or wearable devices like eSight and Brainport.[14][21]

The condition may lead to abnormal development of the optic nerve and sunlight may damage the retina of the eye as the iris cannot filter out excess light due to a lack of pigmentation. Photophobia may be ameliorated by the use of sunglasses which filter out ultraviolet light.[22] 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".)

There are a number of national support groups across the globe which come under the umbrella of the World Albinism Alliance.[23]

Epidemiology

Albinism affects people of all ethnic backgrounds; its frequency worldwide is estimated to be approximately one in 17,000. Prevalence of the different forms of albinism varies considerably by population, and is highest overall in people of sub-Saharan African descent.[24] Today, the prevalence of albinism in sub-Saharan Africa is around 1 in 5,000, while in Europe and the US it is 1 in 20,000.[18] Rates as high as 1 in 1,000 have been reported for some populations in Zimbabwe and other parts of Southern Africa.[19]

Certain ethnic groups and populations in isolated areas exhibit heightened susceptibility to albinism, presumably due to genetic factors. These include notably the Native American Kuna, Zuni and Hopi nations (respectively of Panama, New Mexico and Arizona); 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.[25]

Society and culture

In physical terms, humans with albinism commonly have visual problems and need sun protection.

Persecution of people with albinism

Humans with albinism often face social and cultural challenges (even threats), as the condition is often a source of ridicule, discrimination, or even fear and violence. It is especially socially stigmatised in many African societies. A study conducted in Nigeria on albino children stated that "they experienced alienation, avoided social interactions and were less emotionally stable. Furthermore, affected individuals were less likely to complete schooling, find employment, and find partners".[26] Many cultures around the world have developed beliefs regarding people with albinism.

In African countries such as Tanzania[27] and Burundi,[28][29] there has been an unprecedented rise in witchcraft-related killings of people with albinism in recent years, because their body parts are used in potions sold by witchdoctors.[30] Numerous authenticated incidents have occurred in Africa during the 21st century.[31][32][33][34] 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.[35] Again in Tanzania and Burundi in 2010, the murder and dismemberment of a kidnapped albino child was reported from the courts,[28] as part of a continuing problem. The US-based National Geographic Society estimated that in Tanzania a complete set of albino body parts is worth US$75,000.[36][37]

Another harmful and false belief is that sex with an albinistic woman will cure a man of HIV. This has led, for example in Zimbabwe, to rapes (and subsequent HIV infection).[38]

Main article: Albinism in popular culture

Famous people with albinism include historical figures such as Oxford don William Archibald Spooner; actor-comedian Victor Varnado; musicians such as Johnny and Edgar Winter, Salif Keita, Winston "Yellowman" Foster, Brother Ali, Sivuca, Hermeto Pascoal, Willie "Piano Red" Perryman, Kalash Criminel; and fashion models Connie Chiu and Shaun Ross. Emperor Seinei of Japan is thought to have been an albino because he was said to have been born with white hair.

International Albinism Awareness Day

International Albinism Awareness Day was established after a motion was accepted on 18 December 2014 by the United Nations General Assembly, proclaiming that as of 2015, 13 June would be known as International Albinism Awareness Day.[39] This was followed by a mandate created by the United Nations Human Rights Council that appointed Ms. Ikponwosa Ero, who is from Nigeria, as the very first Independent Expert on the enjoyment of human rights by persons with albinism.[40]

See also

References
  1. "albino". Random House Dictionary. 2017. Retrieved 10 November 2017 – via Dictionary.Reference.com.
  2. "British Pronunciation of albino". Macmillan Dictionary. Macmillan Publishers. 2017. Retrieved 10 November 2017.
  3. "American Pronunciation of albino". Macmillan Dictionary. 2017. Retrieved 10 November 2017.
  4. Kaplan, J.; De Domenico, I.; Ward, D. M. (2008). "Chediak-Higashi syndrome". Current Opinion in Hematology. 15 (1): 22–29. doi:10.1097/MOH.0b013e3282f2bcce. PMID 18043242.
  5. "Albinism". Encyclopædia Britannica. Retrieved January 27, 2015.
  6. Tietz, W. (1963). "A Syndrome of Deaf-Mutism Associated with Albinism Showing Dominant Autosomal Inheritance". American Journal of Human Genetics. 15: 259–264. PMC 1932384. PMID 13985019.
  7. "oculocutaneous albinism". Genetics Home Reference. Bethesda, Maryland: U.S. National Library of Medicine, National Institutes of Health. October 2015. Retrieved 10 November 2017. This tertiary source reuses information from other sources but does not name them.
  8. "Information Bulletin - Ocular Albinism". National Organization for Albinism and Hypopigmentation. Archived from the original on 12 March 2017. Retrieved 11 March 2017.
  9. Chen, Harold (2006). Atlas of genetic diagnosis and counseling. Totowa, New Jersey: Humana Press. pp. 37–40. ISBN 978-1-58829-681-8. Retrieved 22 July 2010.
  10. Boissy, Raymond E. (21 July 2016). James, William D.; et al. (eds.). "Dermatologic Manifestations of Albinism". Medscape. eMedicine / WebMD. Retrieved 10 November 2017.
  11. Kruijt, Bastiaan; Franssen, Luuk; Prick, Liesbeth J. J. M.; Van Vliet, Johannes M. J.; Van Den Berg, Thomas J. T. P. (2011). "Ocular Straylight in Albinism". Optometry and Vision Science. 88 (5): E585–92. doi:10.1097/OPX.0b013e318212071e. PMID 21358444.
  12. "How Albinism Affects Vision". LensShopper.com (in Swedish). Retrieved 2017-02-22.
  13. Sowka, Joseph W.; Gurwood, Andrew S.; Kabat, Allan G. (15 April 2009). "Albinism" (PDF). The Handbook of Ocular Disease Management: Supplement to Review of Optometry (11th ed.). New York: Jobson Medical Information. pp. 63A–65A. Archived (PDF) from the original on 24 August 2015. Retrieved 10 November 2017 – via ReviewOfOptometry.com.
  14. King, Richard; Summers, C. Gail; Haefemeyer, James W.; LeRoy, Bonnie (2004). "Facts About Albinism". Albinism.Med.UMN.edu. University of Minnesota. Archived from the original on 25 January 2009. Retrieved 10 November 2017.
  15. Boissy, R. E.; Zhao, H.; Oetting, W. S.; Austin, L. M.; Wildenberg, S. C.; Boissy, Y. L.; Zhao, Y.; Sturm, R. A.; Hearing, V. J.; King, R. A.; Nordlund, J. J. (1996). "Mutation in and lack of expression of tyrosinase-related protein-1 (TRP-1) in melanocytes from an individual with brown oculocutaneous albinism: A new subtype of albinism classified as "OCA3"". American Journal of Human Genetics. 58 (6): 1145–1156. PMC 1915069. PMID 8651291.
  16. Online Mendelian Inheritance in Man, at Johns Hopkins University (see also Mendelian Inheritance in Man for more information about this source).
  17. Haldeman-Englert, Chad (6 November 2017). "Sex-linked recessive". The ADAM Medical Encyclopedia. Bethesda, Maryland / Atlanta, Georgia, US: U.S. National Library of Medicine, National Institutes of Health / Ebix Inc. Retrieved 10 November 2017.
  18. Greaves, M. (2014). "Was skin cancer a selective force for black pigmentation in early hominin evolution?". Proceedings of the Royal Society B: Biological Sciences. 281 (1781): 20132955. doi:10.1098/rspb.2013.2955. PMC 3953838. PMID 24573849.
  19. Hong, E. S.; Zeeb, H.; Repacholi, M. H. (2006). "Albinism in Africa as a public health issue". BMC Public Health. 6: 212. doi:10.1186/1471-2458-6-212. PMC 1584235. PMID 16916463.
  20. 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. PMC 1279676. PMID 11983764.
  21. Pardes, Arielle (2017-07-20). "The Wearables Giving Computer Vision to the Blind". Wired. Condé Nast. Retrieved 8 September 2017.
  22. Anon (2018-03-20). "Albinism causes". www.news-medical.net. News medical. Retrieved 27 July 2018.
  23. Anon (2015-01-07). "World Albinism Alliance". WAA. Retrieved 27 July 2018.
  24. Gronskov, K.; Ek, J.; Brondum-Nielsen, K. (2 November 2007). "Oculocutaneous albinism". Orphanet Journal of Rare Diseases. 2: 43. doi:10.1186/1750-1172-2-43. PMC 2211462. PMID 17980020.
  25. "Ukerewe Albino Society". Southern Africas Children. 2009. Retrieved 21 July 2010.
  26. Magna, P. (January 2014). "Biology and genetics of Oculocutaneous albinism and vitiligo-common pigmentation disorders in Southern Africa". South African Medical Journal. 103 (1): 984–8. doi:10.7196/samj.7046. PMID 24300644.
  27. "Living in fear: Tanzania's albinos". BBC News. British Broadcasting Corporation. 21 July 2008. Retrieved 27 February 2010.
  28. "Burundi albino boy 'dismembered'". BBC News. 24 October 2010.
  29. "Burundian albino murders denied". BBC News. 19 May 2009. Retrieved 27 February 2010.
  30. Vogel, Franck (August 2010). "Zeru, Zeru: Being Albino in Tanzania". Visura Magazine (10). Westford, Vermont: Foto Visura. Retrieved 10 November 2017.
  31. "Man 'tried to sell' albino wife". BBC News. 13 November 2008. Retrieved 27 February 2010.
  32. "Tanzania albinos targeted again". BBC News. 27 July 2008. Retrieved 27 February 2010.
  33. Ntetema, Vicky (24 July 2008). "In hiding for exposing Tanzania witchdoctors". BBC News. Retrieved 27 February 2010.
  34. "Mothers hacked in albino attacks". BBC News. 14 November 2008. Retrieved 27 February 2010.
  35. "Death for Tanzania albino killers". BBC News. 23 September 2009. Retrieved 27 February 2010.
  36. Ingber, Sasha; Martin, Jacquelyn (27 January 2013). "Pictures: Inside the Lives of Albinos in Tanzania". National Geographic News. Washington DC: National Geographic Society. Retrieved 10 November 2017.
  37. Tanzanians with albinism targeted for witchcraft. UNICEF. 30 April 2015. Retrieved 2017-02-22 – via YouTube.
  38. Machipisa, Lewis. "The Last Minority Group to Find a Voice". IPSNews.net. Inter Press Service News Agency. Archived from the original on 21 January 2009. Retrieved 30 January 2010.
  39. "International Albinism Awareness Day".
  40. "Independent Expert on the enjoyment of human rights by persons with albinism". OHCHR.org. Geneva: Office of the High Commissioner for Human Rights, United Nations.
Classification
External resources
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.