MedGen

Malignant melanoma is a neoplasm of pigment-producing cells called melanocytes that occurs most often in the skin, but may also occur in the eyes, ears, gastrointestinal tract, leptomeninges, and oral and genital mucous membranes (summary by Habif, 2010). For a discussion of genetic heterogeneity of malignant melanoma, see 155600. [from OMIM]

Two types of melanin, the red pheomelanin and the black eumelanin, are present in human skin. Valverde et al. (1995) noted that eumelanin is photoprotective, whereas pheomelanin may contribute to UV-induced skin damage because of its potential to generate free radicals in response to ultraviolet radiation. Individuals with red hair have a predominance of pheomelanin in hair and skin and/or a reduced ability to produce eumelanin, which may explain why they fail to tan and are at risk from ultraviolet radiation. In mammals, the relative proportions of pheomelanin and eumelanin are regulated by melanocyte-stimulating hormone (see 176830), which acts via its receptor (MC1R) on melanocytes to increase the synthesis of eumelanin, and also via the product of the agouti locus (AGTI; 600201), which antagonizes this action. [from OMIM]

Tyrosinase-positive oculocutaneous albinism (OCA, type II; OCA2) is an autosomal recessive disorder in which the biosynthesis of melanin pigment is reduced in skin, hair, and eyes. Although affected infants may appear at birth to have OCA type I, or complete absence of melanin pigment, most patients with OCA type II acquire small amounts of pigment with age. Individuals with OCA type II have the characteristic visual anomalies associated with albinism, including decreased acuity and nystagmus, which are usually less severe than in OCA type I (Lee et al., 1994; King et al., 2001). OCA type II has a highly variable phenotype. The hair of affected individuals may turn darker with age, and pigmented nevi or freckles may be seen. African and African American individuals may have yellow hair and blue-gray or hazel irides. One phenotypic variant, 'brown OCA,' has been described in African and African American populations and is characterized by light brown hair and skin color and gray to tan irides. The hair and irides may turn darker with time and the skin may tan with sun exposure; the ocular features of albinism are present in all variants (King et al., 2001). In addition, previous reports of so-called 'autosomal recessive ocular albinism,' (see, e.g., Witkop et al., 1978 and O'Donnell et al., 1978) with little or no obvious skin involvement, are now considered most likely to be part of the phenotypic spectrum of OCA1 or OCA2 (Lee et al., 1994; King et al., 2001). [from OMIM]