Albinism pathophysiology: Difference between revisions
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* [[Eumelanin]] is responsible for black or brown [[skin]] color and protects [[skin]] from [[ultraviolet]] B | * [[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 s[[kin]] | * [[Pheomelanin]] is responsible for red or blond hair and light-colored, and ruddy s[[kin]] | ||
* On [[melanocytes]], activation of [[melanocortin one receptors]] ([[MC1R]]) lead to synthesis of [[eumelanin]] over [[pheomelanin]] | * On [[melanocytes]], activation of [[melanocortin one receptors]] ([[MC1R]]) lead to synthesis of [[eumelanin]] over [[pheomelanin]] <ref>{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK519018/ |title=Albinism - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref><ref name="pmid20301683">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Mirzaa G | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume= | issue= | pages= | pmid=20301683 | doi= | pmc= | url= }} </ref> | ||
===Pathogenesis=== | ===Pathogenesis=== | ||
* [[Mutation]] in [[Tyrosinase]] [[enzyme]] is responsible for causing [[albinism]] | * [[Mutation]] in [[Tyrosinase]] [[enzyme]] is responsible for causing [[albinism]] | ||
Revision as of 02:41, 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
References
- ↑ "Albinism - StatPearls - NCBI Bookshelf".
- ↑ Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Mirzaa G; et al. (1993). "GeneReviews®". PMID 20301683.