Albinism pathophysiology: Difference between revisions
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** Monocular vision is manifested as strabismus | ** Monocular vision is manifested as strabismus | ||
** In albinism, macula pigemnt is absent and fovea hypoplasia leads to decreased visual acuity | ** In albinism, macula pigemnt is absent and fovea hypoplasia leads to decreased visual acuity | ||
** Visual acuity ranges from 20/60 to 20/400 | ** Visual acuity ranges from 20/60 to 20/400 <ref name="pmid20301683"><ref name="pmid31777350">{{cite journal| author=Marçon CR, Maia M| title=Albinism: epidemiology, genetics, cutaneous characterization, psychosocial factors. | journal=An Bras Dermatol | year= 2019 | volume= 94 | issue= 5 | pages= 503-520 | pmid=31777350 | doi=10.1016/j.abd.2019.09.023 | pmc=6857599 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=31777350 }} </ref><ref name="pmid546241">{{cite journal| author=Witkop CJ| title=Albinism: hematologic-storage disease, susceptibility to skin cancer, and optic neuronal defects shared in all types of oculocutaneous and ocular albinism. | journal=Ala J Med Sci | year= 1979 | volume= 16 | issue= 4 | pages= 327-30 | pmid=546241 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=546241 }} </ref><ref name="pmid3288382">{{cite journal| author=King RA, Summers CG| title=Albinism. | journal=Dermatol Clin | year= 1988 | volume= 6 | issue= 2 | pages= 217-28 | pmid=3288382 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3288382 }} </ref> | ||
==References== | ==References== | ||
Revision as of 02:48, 18 August 2021
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Shadan Mehraban, M.D.[2]
Overview
Pathophysiology
Physiology
- Melanocytes are derived from neural crest ectoderm and are found in hair follicles, skin, eyes, and inner ear
- Melanocytes account for 5% to 10% of cells in epidermal basal layers
- Melanocytes contain melanosomes which produce melanin
- Melanin protects skin from ultraviolet; with sun exposure melanin pigment increases in the skin
- Apart from the photo-protective effect of melanin, it has some roles in the development of ocular structures as well as oculoneural pathways
- Melanin converts tyrosine to 2 forms named eumelanin and pheomelanin
- Eumelanin is responsible for black or brown skin color and protects skin from ultraviolet B
- Pheomelanin is responsible for red or blond hair and light-colored, and ruddy skin
- On melanocytes, activation of melanocortin one receptors (MC1R) lead to synthesis of eumelanin over pheomelanin [1][2]
Pathogenesis
- Mutation in Tyrosinase enzyme is responsible for causing albinism
- Tyrosinase converts tyrosine to DOPA and then dopaquinone; subsequenstly, dopaquionone converts to either eumelanin or pheomelanin
- Tyrosinase mutation is seen in oculocutaneous albinism 1 (OCA1) and autosomal-recessive ocular albinism (AROA)
- Lack of melanin increase chances of sun-damage related diseases including actinic keratosis and UV-related malignancies
- Ocular albinism pathway:
- In uterus, melanin is responsible for developement of the fovea, optic nerves, optic tracts, and visual cortex
- Decussation of some optic nerve fibers at optic chiasem are essential for binocular vision
- In people without albinism, about 45% of optic nerve fibers from the temporal part of retina do not cross the optic chiasem to controlateral lateral geniculate nucleus
- In albinism, most of nerve fibers decussate at optic chiasem and cause monocluar vision
- Monocular vision is manifested as strabismus
- In albinism, macula pigemnt is absent and fovea hypoplasia leads to decreased visual acuity
- Visual acuity ranges from 20/60 to 20/400 [3][4]
References
- ↑ "Albinism - StatPearls - NCBI Bookshelf".
- ↑ Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Mirzaa G; et al. (1993). "GeneReviews®". PMID 20301683.
- ↑ Witkop CJ (1979). "Albinism: hematologic-storage disease, susceptibility to skin cancer, and optic neuronal defects shared in all types of oculocutaneous and ocular albinism". Ala J Med Sci. 16 (4): 327–30. PMID 546241.
- ↑ King RA, Summers CG (1988). "Albinism". Dermatol Clin. 6 (2): 217–28. PMID 3288382.