Albinism pathophysiology
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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 chiasm 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 chiasm and cause monocluar vision
- Monocular vision is manifested as strabismus
- In albinism, macular pigment absent and fovea hypoplasia leads to decreased visual acuity
- Visual acuity ranges froHPS1 gene (HPS1), AP3B1 gene (HPS2), HPS3 gene (HPS3), HPS4 gene (HPS4), HPS5 gene (HPS5), HPS6 gene (HPS6), DTNBP1 gene (HPS7m 20/60 to 20/400 [2][3][4][5]
Genetics
- Genetic mutation in albinism include:[6][7][8]
- Tyrosinase in OCA1; autosomal recessive
- P protein in OCA2;autosomal recessive
- Tyrosinase-related protein 1 (TYRP1)in OCA3; autosomal recessive
- solute carrier family 45, member 2 (SLC45A2) in OCA4; autosomal recessive
- Gene mutation in OCA5 is not identified; autosomal recessive
- SLC24A5 in OCA6; autosomal recessive
- Leucine-rich melanocyte differentiation associated protein (LRMDA) in OCA7; autosomal recessive
- Gene mutation in Hermansky-Pudlak syndrome (HPS) subtypes are as following:
- LYST in Chediak-Higashi syndrome ; autosomal recessive
- GPR143 in ocular albinism 1; x-linked
References
- ↑ "Albinism - StatPearls - NCBI Bookshelf".
- ↑ 2.0 2.1 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Mirzaa G; et al. (1993). "GeneReviews®". PMID 20301683.
- ↑ Marçon CR, Maia M (2019). "Albinism: epidemiology, genetics, cutaneous characterization, psychosocial factors". An Bras Dermatol. 94 (5): 503–520. doi:10.1016/j.abd.2019.09.023. PMC 6857599 Check
|pmc=
value (help). PMID 31777350. - ↑ 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.
- ↑ Grønskov K, Ek J, Brondum-Nielsen K (2007). "Oculocutaneous albinism". Orphanet J Rare Dis. 2: 43. doi:10.1186/1750-1172-2-43. PMC 2211462. PMID 17980020.
- ↑ "Albinism - StatPearls - NCBI Bookshelf".
- ↑ Summers CG (2009). "Albinism: classification, clinical characteristics, and recent findings". Optom Vis Sci. 86 (6): 659–62. doi:10.1097/OPX.0b013e3181a5254c. PMID 19390472.