Albinism pathophysiology: Difference between revisions
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* [[Tyrosinase]] converts [[tyrosine]] to [[DOPA]] and then [[dopaquinone]]; subsequenstly, [[dopaquionone]] converts to either [[eumelanin]] or [[pheomelanin]] | * [[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]]) | * [[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== | ==References== | ||
Revision as of 02:39, 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
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