Niven Abu Ramadan
Niven Abu Ramadan
in Case Study
Dermatologic Manifestations Of Albinism!!

Dermatologic Manifestations Of Albinism!!

The classification of congenital hypopigmentary diseases that result from a defect in the production of pigment (melanin) due to dysfunction of pigment cells (melanocytes) in the skin, the eyes, and/or the ears consists of the following: oculocutaneous albinism types 1-7; ocular albinism; Chediak-Higashi syndrome ; Hermansky-Pudlak syndrome; and Griscelli syndrome. iseases present with a generalized complete or partial loss in pigmentation of the skin and the hair. Mutations in genes that regulate the multistep process of melanin synthesis, distribution of pigment by the melanocyte, and/or melanosome biogenesis are the basis for these diseases. The proteins/gene products (and respective gene) affected in each form of oculocutaneous albinism • Oculocutaneous albinism type 1 - results from mutations in the tyrosinase gene, which maps to band 11q14-3 and is inherited as an autosomal recessive trait. The tyrosinase gene encodes an enzyme that initiates the synthesis of melanin using the substrate tyrosine. Specifically, tyrosinase hydroxylates tyrosine to dihydroxyphenylalanine (DOPA) and subsequently dehydroxylates DOPA to DOPA-oxidase. More than 70 mutations have been identified in tyrosinase that result in the dysfunction or lack of synthesis of this enzyme. Most patients with oculocutaneous albinism type 1 have compound heterozygosity for mutations in the tyrosinase gene. • Oculocutaneous albinism type 2 - results from mutation in the P gene, which maps to band 15q12 and is inherited as an autosomal recessive trait. The P gene encodes a 110-kd protein with 12 putative transmembrane domains localized to the limiting membrane of the pigment granule (ie, melanosome). The function of the P protein in melanin synthesis has yet to be determined. •Oculocutaneous albinism type 3- results from mutation in the tyrosinase-related protein-1 (Tyrp1) gene, which maps to band 9p23 and is inherited as an autosomal recessive trait.The Tyrp1 gene encodes a protein that has been shown to have a dihydroxyindole carboxylic acid (DHICA) oxidase activity in the murine system. DHICA oxidase is a catalytic step downstream from tyrosinase in the biosynthesis of melanin from tyrosine. The function of Tyrp1 in human melanogenesis may be involved as (1) an ionic transporter, (2) a chaperone, and/or (3) a stabilizer of the melanosome complex. •Oculocutaneous albinism type 4 - A membrane-associated transport protein (MATP/SLC24A2).Oculocutaneous albinism type 4 results from mutations in the SLC45A2 gene, formerly called the membrane-associated transporter protein (MATP) gene, which maps to band 5p13.3 and is inherited as an autosomal recessive trait. The SLC45A2 gene encodes a 58-kd protein with 12 predicted transmembrane domains. The function of MATP in melanogenesis is presently unknown. • Oculocutaneous albinism type 5 -Oculocutaneous albinism type 5 results from mutations in an unknown gene, which maps to band 4q24 and is inherited as an autosomal recessive trait. The protein and its function is unknown. • Oculocutaneous albinism type 6 - results from mutations in the SLC24A5 gene, which maps to band 15q21.1 and is inherited as an autosomal recessive trait. The SLC45A5 gene encoded an uncharacterized membrane-associated transport protein and its function is unknown. • Oculocutaneous albinism type 7 - results from mutations in an unknown gene, which maps to band 10q22.2-3 and is inherited as an autosomal recessive trait. The protein is being provisionally labeled as C10orf11 and its function is unknown. !!! Patients should use broad-spectrum sunscreens and should wear appropriate clothing to prevent ultraviolet-induced damage to the skin. Visual impairment can be improved by using corrective lenses.

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