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PubMed1982

Pigment mutations in the mouse which also affect lysosomal functions lead to suppressed natural killer cell activity.

The impact of five pigment mutations in the mouse on natural killer (NK) activity was examined in inbred strains congenic for the respective mutation. Whereas the nature of pigmentation disorder was similar in the five mutant strains (beige, pallid, reduced pigmentation, pale ear, and sepia), all mutations except sepia also led to a significant change in lysosomal enzyme activities in the kidney. A significant reduction in NK activity was observed in the four strains with lysosomal impact, whereas homozygous sepia mice displayed normal NK activity. The pigment mutations analysed are located on different chromosomes and fail to cross-interact negatively with each other in the heterozygous mice. This would indicate that pigment mutations with a parallel impact on lysosomal enzyme activities probably always result in a reduction in natural killer cell activity.

Animals↗
PubMed1993

White mutants in mice shedding light on humans.

In this article we describe the rapid advances made in the molecular genetics of three inherited pigmentation disorders: albinism, piebaldism, and vitiligo, all of which throw light on normal pigment cell function. The focus is on studies in mice, with comparison of data in humans. The critical role of tyrosinase (c-locus or human tyrosinase protein) in normal pigmentation and albinism has been reinforced by the cloning and identification of mutations in tyrosinase and two other melanocyte-specific oxidoreductases structurally related to but functionally different from tyrosinase: the (b) brown-locus protein/gp75/catalase B and dopachrome tautomerase. Each possesses a distinct enzyme activity and yet the three share homology in strategic regions. Most of the point mutations that reduce or abrogate the respective enzyme activities are located in those regions. Tyrosinase-negative albinism is caused only by defects in tyrosinase. A locus for human tyrosinase-positive albinism has been recently mapped to chromosome 15q11.2-->q12, at a gene identified in mice as pink-eyed dilution. On the other hand, several genes encoding proteins critical for the proliferation of melanocytes are known to control the piebald phenotype. So far identified are two membrane-receptor tyrosine kinases, c-Kit and PDGF-R/alpha, and the ligand for c-kit, MGF (mast-cell growth factor, also known as stem-cell factor, c-Kit-ligand, or steel factor). Mutations in W/c-kit (white spotting), Ph/Pdgfr/a (patch), and Sl/MGF (steel), lead to a reduction in receptor kinase activity and failure of melanocytes to thrive and reach the skin during embryogenesis. Finally, mouse mutant models suggest at least two possible causes for vitiligo, a progressive loss of pigmentation that occurs after birth. In one mutant, the Blt (light) mouse, the cyclic death of hair melanocytes may be due to the toxicity of intermediates and byproducts of melanogenesis in the presence of a dysfunctional b-locus protein. In the other model, the "vitiligo mouse," in which the allele vit has been assigned to the microphthalmia (mi) locus, the loss of melanocytes may be caused by defective signal transduction, because in addition to vitiligo mivit/mivit mice have extensive piebaldism.

Albinism↗
PubMed1998

Mutation of the MITF gene in albinism-deafness syndrome (Tietz syndrome).

A mother and her son with albinism and sensorineural deafness compatible with Tietz syndrome (MIM 103500) are reported. An in-frame deletion of the MITF gene that is identical at the molecular level to the mouse mi mutant allele has been found in this family. MITF gene mutations account for 20% of Waardenburg syndrome (WS) type II. These data, together with the wide spectrum of mutant alleles reported in mi mice (which have pigmentary disorders), suggest that MITF could be regarded as a candidate gene in various pigmentation disorders in man.

Adult↗
PubMed2006

The discovery of the human melanocyte.

Around 2200 bc the first written description of a human pigmentation disorder, most likely vitiligo, was recorded, and from that moment the history of research into human pigmentation can be traced. For the following 4000 yr, the origins of human skin colour remained an enigma that was to generate a multitude of misconceptions. Even after European physicians began to dissect and compare dark and light coloured skin to reveal its underlying anatomy, the origins of skin and hair pigmentation were a matter of frequently erroneous speculation. The true source of human pigmentation was only finally revealed with the discovery of the melanocyte in the 19th century. Once tyrosinase was identified to be the key enzyme in pigment formation, attention focused on elucidating the chemical structure of melanin, an enterprise that remains incomplete. The developmental origins of the melanocyte were described from 1940 to 1960, and the concept of the epidermal melanin unit was introduced together with a description of the ultrastructure of the melanosome and melanosome transfer. With these advances came the realization that different skin types exhibit distinct differences at the histological level that relate to varying amounts of eumelanin and pheomelanin produced by the melanocytes. The foundation established over the past 4000 yr is the basis for all current research into this fascinating cell type.

History, 15th Century↗
PubMed1983

[Diagnostic value of electron microscopy in dermatology].

Basing themselves on their personal experience, the authors stress the main indications and the value of electron microscopy in dermatology. In some cases it provides an indispensable adjunct to standard light microscopy (tumor pathology, cutaneous lymphoma, collagenosis, storage diseases, etc). In other cases, it provides greater insight into dermatological affections, such as pigmentation disorders or bullae. Ultrastructural studies should therefore often be included in a thorough morphological examination of a skin biopsy.

Humans↗
PubMed2002

Skin of color: biology, structure, function, and implications for dermatologic disease.

People with skin of color constitute a wide range of racial and ethnic groups-including Africans, African Americans, African Caribbeans, Chinese and Japanese, Native American Navajo Indians, and certain groups of fair-skinned persons (eg, Indians, Pakistanis, Arabs), and Hispanics. It has been predicted that people with skin of color will constitute a majority of the United States and international populations in the 21st century. There is not a wealth of data on racial and ethnic differences in skin and hair structure, physiology, and function. What studies do exist involve small patient populations and often have methodologic flaws. Consequently, few definitive conclusions can be made. The literature does support a racial differential in epidermal melanin content and melanosome dispersion in people of color compared with fair-skinned persons. Other studies have demonstrated differences in hair structure and fibroblast size and structure between black and fair-skinned persons. These differences could at least in part account for the lower incidence of skin cancer in certain people of color compared with fair-skinned persons; a lower incidence and different presentation of photo aging; pigmentation disorders in people with skin of color; and a higher incidence of certain types of alopecia in Africans and African Americans compared with those of other ancestry. However, biologic or genetic factors are not the only ones impacting on these differences in dermatologic disorders. Cultural practices also can have a significant impact. Further studies are needed to help dermatologists optimally treat people with skin of color.

Humans↗
PubMed1988

Pigmented nail streaks may indicate Laugier-Hunziker syndrome.

Laugier-Hunziker syndrome is a rare, benign pigmentation disorder previously described only once in the United States. The syndrome is acquired in early or mid-adult life and is characterized by multiple longitudinal hyperpigmented bands on the nails and pigmented macules of the lips and buccal mucosa. Peutz-Jeghers syndrome and Addison's disease can present with pigment abnormalities similar to those characteristic of Laugier-Hunziker syndrome.

Aged↗