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An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
Black pigment (melanin), a polymer synthesized by melanocytes, protects against solar ultraviolet radiation (UVR). Melanocytes, unlike keratinocytes, do not have desmosomes but have long, branching dendritic projections that transport the melanin they synthesize to the surrounding cells. They originate from the embryonic neural crest. Melanocytes account for 5–10% of cells in the basal layer of the epidermis. Melanin is a polymer that is synthesized from the amino acid tyrosine with the help of a copper-containing enzyme, tyrosinase. Other pigments contribute rarely (e.g. bilirubin in jaundice or pigments derived from drugs such as minocycline or chlorpromazine). Exposure to the sun accelerates melanin synthesis, which explains suntanning. Skin color is mainly due to melanin and blood. The number of melanocytes per unit of body surface area is variable, depending on the site of the body but the density of melanocytes is the same in all humans, irrespective of race. The racial differences in complexion are attributed to the distribution and size of melanosomes, which disperse melanin to the keratinocytes. Melanocytes are completely destroyed in vitiligo. In albinism, melanin synthesis is defective. Localized increase in the synthesis of melanin leads to the development of freckles. Melanocytes in benign proliferation are referred to as nevi, and the malignant ones are known as melanomas.
A Transcriptomic Analysis and shRNA Screen for Intracellular Ion Channels and Transporters Regulating Pigmentation
Published in Bruno Gasnier, Michael X. Zhu, Ion and Molecule Transport in Lysosomes, 2020
Donald C. Koroma, Salwa Y. Hafez, Elena Oancea
Defects in melanosomal function result in albinism, characterized by total or partial lack of pigment in the skin, hair, and eyes. Albinism occurs at a frequency of ~1:20,000 in the US, with significantly higher incidence (>1:1,400) in Africa (Luande, Henschke, and Mohammed 1985). The lack of pigment in albinism causes severe visual impairment and elevated susceptibility to skin cancers. Of the seven types of oculocutaneous albinism identified so far, OCA1–7 (Montoliu et al. 2014), five types (OCA1–4 and OCA6) are caused by mutations in genes encoding putative melanosomal transmembrane proteins. Three of these five transmembrane proteins (OCA2, 4, and 6) have the topology of an ion channel or transporter (predicted by UniProtKB, www.uniprot.org) with unknown function, while the protein encoded by the gene mutated in OCA5 is yet to be identified (Kausar et al. 2013). In addition to mutations in melanocyte-specific genes that lead to albinism, there are other identified mutations that cause diseases associated with hypopigmentation or hyperpigmentation (Chow et al. 2007, Bowman et al. 2019, Wang et al. 2015), suggesting that proteins that are not melanocyte-specific can also regulate pigmentation.
Actions of Dopamine on the Skin and the Skeleton
Published in Nira Ben-Jonathan, Dopamine, 2020
Although there is no cure for albinism, it can be managed depending on the severity of its symptoms. Because the skin is more prone to sunburn, wearing long sleeves and full-length garments is mandatory to protect the skin against UV exposure. These individuals should also use a sunscreen with a high sun protection factor. They are also advised to check for changes on the skin such as a new or a changing mole, an abnormal growth or a lump. Glasses or contact lenses are often used to correct eyesight issues such as near-sightedness, long-sightedness and astigmatism. Sun glasses that filter out UV rays help patients with photophobia or sensitivity to light. Eye exercises may be recommended to deal with squinting and lazy eye.
Clinical albinism score, presence of nystagmus and optic nerves defects are correlated with visual outcome in patients with oculocutaneous albinism
Published in Ophthalmic Genetics, 2021
Alina V. Dumitrescu, Johnny Tran, Wanda Pfeifer, Sajag V. Bhattarai, Andrew Kemerley, Taylor V. Dunn, Kai Wang, Tod E. Scheetz, Arlene Drack
Kruit et al. have previously proposed diagnostic criteria for patients with suspected OCA. Their criteria were developed and applied retrospectively to cohorts of mostly Caucasian/Danish patients. When applied retrospectively to our cohort, overall, 78% of our cases presented here met the Kruit et al. criteria. Of the 13 patients in our cohort who did not meet Kruit et al. criteria, all had at least 3 clinical criteria present and 10 of 13 would have met Kruit et al. criteria if their genetic testing were also positive. These patients may have a phenocopy of albinism, but it is also possible that their genetic testing was not complete. All of our 20 cases with complete, confirmatory albinism genotypes met the Kruit et al. criteria. Fifteen out of the 20 confirmed cases would have met the purely clinical criteria for diagnosis (3 major or 2 major and 2 minor features); however, 5 would have only been diagnosed based on their positive genetic testing. This means that the Kruit et al. criteria for diagnosis, when used without genetic testing may miss up to 25% of albinism cases. As Kruit et al. have noted in their paper, the severity of clinical features of albinism is variable and none of them is enough by itself to establish the diagnosis.
Genotype-phenotype associations in Danish patients with ocular and oculocutaneous albinism
Published in Ophthalmic Genetics, 2021
Line Kessel, Birgit Kjer, Ulrikke Lei, Morten Duno, Karen Grønskov
All participants in this study had previously been given a clinical diagnosis of albinism but in 15 participants we were unable to find a genetic explanation. Next-generation sequencing using an albinism panel was performed but without findings in seven participants. One participant declined genetic testing. One participant had a very fair skin type and nystagmus and had undergone whole genome sequencing because of removal of several melanomas before the age of 25 without finding any genetic explanation for the condition. A family of five demonstrated autosomal dominant inheritance of albinism traits but we were unable to find a genetic cause in any of the known albinism genes. These findings seem to suggest that there are still unknown albinism genes to be discovered or that the genetic techniques currently available do not find all changes in the genome.
A novel iris transillumination grading scale allowing flexible assessment with quantitative image analysis and visual matching
Published in Ophthalmic Genetics, 2018
Chen Wang, Flavia Brancusi, Zaheer M. Valivullah, Michael G. Anderson, Denise Cunningham, Adam Hedberg-Buenz, Bradley Power, Dimitre Simeonov, William A. Gahl, Wadih M. Zein, David R. Adams, Brian Brooks
Albinism is caused by a group of genetic disorders associated with reduced melanin pigment biosynthesis. Oculocutaneous albinism (OCA) results in decreased pigmentation in the hair, skin, and eyes. Most OCA is autosomal recessive and caused by one of four genes: TYR (OCA-1A and OCA-1B, MIM 203100), OCA2 (OCA-2, MIM 203200), TYRP1 (OCA-3, MIM 203290), and SLC45A2 (OCA-4, MIM 606574). Additional rare OCA genes have recently been reported.1–3 A separate group of rare conditions combine OCA-like albinism and involvement of nonpigmented tissues. Examples include the Hermansky–Pudlak syndrome (types 1–9) and Chediak–Higashi syndrome. Ocular albinism (GPR143, MIM 300500) is characterized by X-linked inheritance and hypopigmentation restricted principally to the eye. All types of OCA, as well as OA, are associated with variable nystagmus, foveal hypoplasia, retinal hypopigmentation, abnormal retinal axonal fiber decussation, and iris hypopigmentation. OCA has a substantial breadth of phenotypic heterogeneity confounding subtype diagnosis through phenotype evaluation alone.4 To date, treatment of albinism is largely supportive, including low-vision aids, correction of refractive errors, treatment of amblyopia, and extraocular muscle surgery for strabismus and/or anomalous head posture.