Extracutaneous Melanocytes

Boissy, Raymond E.; Hornyak, Thomas J.

doi:10.1002/9780470987100.ch4

Cited by 25 publications

(33 citation statements)

References 153 publications

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“…Although the number of melanocytes does not differ between eye colors, the melanin pigment quantity, packaging and quality does vary, resulting in a range of different eye shades (Boissy, 1998;Imesch et al, 1997;Prota et al, 1998;Sturm and Frudakis, 2004). The apparently nonmendelian examples of eye color transmission from parents to offspring, combined with the quantitative nature of iris pigmentation indicate that the inheritance of eye color is influenced by several different genes (Badano and Katsanis, 2002;Sturm and Frudakis, 2004).…”

Section: Introductionmentioning

confidence: 99%

Replicated Linkage for Eye Color on 15q Using Comparative Ratings of Sibling Pairs

et al. 2005

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The aim of the study was to perform a genetic linkage analysis for eye color, for comparative data. Similarity in eye color of mono-and dizygotic twins was rated by the twins' mother, their father and/or the twins themselves. For 4748 twin pairs the similarity in eye color was available on a three point scale (''not at all alike''-''somewhat alike''-''completely alike''), absolute eye color on individuals was not assessed. The probability that twins were alike for eye color was calculated as a weighted average of the different responses of all respondents on several different time points. The mean probability of being alike for eye color was 0.98 for MZ twins (2167 pairs), whereas the mean probability for DZ twins was 0.46 (2537 pairs), suggesting very high heritability for eye color. For 294 DZ twin pairs genome-wide marker data were available. The probability of being alike for eye color was regressed on the average amount of IBD sharing. We found a peak LOD-score of 2.9 at chromosome 15q, overlapping with the region recently implicated for absolute ratings of eye color in Australian twins [Zhu,

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Section: Introductionmentioning

confidence: 99%

Replicated Linkage for Eye Color on 15q Using Comparative Ratings of Sibling Pairs

et al. 2005

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“…Ocular melanocytes are occasionally lost, causing photophobia and night blindness. [36] Depigmentation commonly affects visible areas such as the face and hands, which has a significant impact on psychological well-being, especially among people of colour. Studies have shown that individuals with vitiligo are embarrassed by their appearance and usually feel uncomfortable socialising, leading to severe depression in some cases and, on rare occasions, suicide.…”

Section: Vitiligomentioning

confidence: 99%

Biology and genetics of oculocutaneous albinism and vitiligo – common pigmentation disorders in southern Africa

et al. 2013

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The primary pigment that determines human skin, hair and eye colour is melanin, which is synthesised by melanocytes. Melanin protects the skin from ultraviolet (UV) radiation and there is an inverse correlation between the degree of constitutive pigmentation and the risk of sun-induced skin cancers. Besides the life-threatening cancer risk, loss of pigmentation results in premature aging, compromised cutaneous immunity and significant emotional distress to affected individuals. [1][2][3] During embryonic development, melanocyte precursors that arise from the neural crest populate several areas including the interfollicular epidermis and hair follicle bulge in the skin; the uveal tract of the eye; and the stria vascularis, vestibular apparatus and endolymphatic sac of the ear. The development of melanocytes is tightly regulated at the genetic level by a number of genes that control proliferation, survival and migration of precursor cells to the various sites of the body and their differentiation into active melanocytes. A key regulator of this process is the microphthalmia transcription factor (MITF), which has been dubbed the 'master regulator' of the melanocyte, capable of modulating expression of several melanocytespecific proteins.[4] MITF mutations result in Waardenburg syndrome type II.[5] Once the melanocyte has differentiated, MITF regulates expression of genes in response to UV exposure, facilitating the tanning response.Melanocytes produce two forms of melanin, black-brown eumelanin and red-yellow pheomelanin. Skin and hair colour Corresponding author: P Manga (prashiela.manga@nyumc.org)Pigmentation disorders span the genetic spectrum from single-gene autosomal recessive disorders such as oculocutaneous albinism (OCA), the autosomal dominant disorder piebaldism to X-linked ocular albinism and multifactorial vitiligo. OCA connotes a group of disorders that result in hypopigmented skin due to decreased melanin production in melanocytes and loss of visual acuity. There are four non-syndromic forms, OCA1-4, which are classified based on the gene that is mutated (tyrosinase, OCA2, tyrosinase-related protein 1 and SLC45A2, respectively). Despite the fact that multiple genes account for the various forms of OCA, the phenotypes of all four forms result from disruption in the maturation and trafficking of the enzyme tyrosinase. OCA2 is the most prevalent autosomal recessive disorder among southern African blacks, affecting 1/3 900 individuals; while OCA3, although rare, is most prevalent in southern Africa. Another common pigmentation disorder in southern Africa is vitiligo, which affects 1 -2% of people worldwide. Vitiligo is a complex, acquired disorder in which melanocytes are destroyed due to an autoimmune response. The aetiology underlying this disorder is poorly understood, although recent genetic association studies have begun to shed light on the contributing factors. Pigmentation disorders have significant psychosocial implications and co-morbidities, yet therapies are still lacking. Recent progress in...

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“…The iris consists of several layers of which the most important for the appearance of eye color are the anterior layer and its underlying stroma (Robins, 1991;Boissy, 1998). In the brown iris there is an abundance of melanocytes and melanosomes in the anterior layer and stroma.…”

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confidence: 99%

“…It is expected that a relatively small set of major genes contribute to the color variation of these cutaneous tissues within diverse human populations. These pigmentary genes are also expected to be specifically expressed within the melanocyte cell and act to regulate the synthesis, chemical composition, packaging and distribution of the pigment melanin, thus producing the visible differences underlying these traits (Sturm et al, 1998;Sturm et al, 2001).The iris consists of several layers of which the most important for the appearance of eye color are the anterior layer and its underlying stroma (Robins, 1991;Boissy, 1998). In the brown iris there is an abundance of melanocytes and melanosomes in the anterior layer and stroma.…”

mentioning

confidence: 99%

A Genome Scan for Eye Color in 502 Twin Families: Most Variation is due to a QTL on Chromosome 15q

Zhu,

Evans,

Duffy

et al. 2004

Twin Res

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We have rated eye color on a 3-point scale (1 = blue/grey, 2 = hazel/green, 3 = brown) in 502 twin families and carried out a 5-10 cM genome scan (400-757 markers). We analyzed eye color as a threshold trait and performed multipoint sib pair linkage analysis using variance components analysis in Mx. A lod of 19.2 was found at the marker D15S1002, less than 1 cM from OCA2, which has been previously implicated in eye color variation. We estimate that 74% of variance in eye color liability is due to this QTL and a further 18% due to polygenic effects. However, a large shoulder on this peak suggests that other loci affecting eye color may be telomeric of OCA2 and inflating the QTL estimate. No other peaks reached genome-wide significance, although lods > 2 were seen on 5p and 14q and lods >1 were additionally seen on chromosomes 2, 3, 6, 7, 8, 9, 17 and 18. Most of these secondary peaks were reduced or eliminated when we repeated the scan as a two locus analysis with the 15q linkage included, although this does not necessarily exclude them as false positives. We also estimated the interaction between the 15q QTL and the other marker locus but there was only minor evidence for additive × additive epistasis. Elaborating the analysis to the full two-locus model including non-additive main effects and interactions did not strengthen the evidence for epistasis. We conclude that most variation in eye color in Europeans is due to polymorphism in OCA2 but that there may be modifiers at several other loci.Skin, hair and eye colors are some of the most obvious forms of human diversity (Sunderland, 1956), yet the complexities of the genetic mechanisms underlying the differences of these pigmentation phenotypes within individuals remain largely unknown. It is expected that a relatively small set of major genes contribute to the color variation of these cutaneous tissues within diverse human populations. These pigmentary genes are also expected to be specifically expressed within the melanocyte cell and act to regulate the synthesis, chemical composition, packaging and distribution of the pigment melanin, thus producing the visible differences underlying these traits (Sturm et al., 1998;Sturm et al., 2001).The iris consists of several layers of which the most important for the appearance of eye color are the anterior layer and its underlying stroma (Robins, 1991;Boissy, 1998). In the brown iris there is an abundance of melanocytes and melanosomes in the anterior layer and stroma. In individuals with blue eye color, the anterior layer and stroma contain very little melanin. As light traverses these relatively melanin-free layers, the minute protein particles of the iris scatter the short blue wavelengths to the surface. The blue color is heightened because longer wavelengths (yellow and red) are absorbed by the dark background of the pigmented retinal epithelium which also obscures the reddish hue of the adjacent blood vessels. Other colors such as yellow, green and hazel are due to varying amounts of lipid pigment granules in t...

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Extracutaneous Melanocytes

Cited by 25 publications

References 153 publications

Replicated Linkage for Eye Color on 15q Using Comparative Ratings of Sibling Pairs

Replicated Linkage for Eye Color on 15q Using Comparative Ratings of Sibling Pairs

Biology and genetics of oculocutaneous albinism and vitiligo – common pigmentation disorders in southern Africa

A Genome Scan for Eye Color in 502 Twin Families: Most Variation is due to a QTL on Chromosome 15q

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