In This Issue...

Gauthier, Andre and Taïeb review the current mechanisms thought to underlie vitiligo, focusing on those relevant to non-segmental vitiligo. They discuss the autoimmune, neural and impaired redox theories, each of which has been proposed as a mechanism by which melanocytes are lost in depigmented vitiliginous skin. They suggest that an abnormal and persistent detachment of melanocytes from their typical location at the epidermal:dermal junction in the skin can result from a number of different types of mechanical insults. Melanocytes detached in such a manner are eventually lost via desquamation at the surface of the skin which results in depigmentation of that area. They suggest a new theory (proposing the term melanocytorrhagy) as a critical mechanical defect that leads to progressive melanocyte loss in vitiligo; this theory is consistent with most of the triggers known to elicit vitiligo. Bennett and Lamoreux summarize the rapidly growing number of pigment genes which has virtually exploded in the past decade. Early studies and books (e.g. Silvers, 1979) referred to slightly more than 60 pigment genes just over two decades ago; that number was revised upwards in subsequent years and has just recently passed the ‘100’ century barrier, which promoted this review. Within the time of writing this review, the number has jumped further to 127 at the time of submission, and probably will have gone further by the time you read this. The number of those genes that has been cloned at this point is about 60, which equals the total number of pigment genes known only a few decades ago but now only about half of those known. The authors have done a wonderful job grouping those genes, explaining their levels of action, and detailing why mutations at their loci lead to often dramatic phenotypic changes. This collection of genes has provided the entire scientific community with tools to study questions not only in the pigment field but in virtually all scientific disciplines; its usefulness seems destined to expand even further in the future.

In the featured article in this Issue, Liu et al. report a study which characterizes the physical and structural properties of human hair melanin purified by various extraction, solubilization, digestion and degradation treatments. They found that the morphology and properties of the pigment varied significantly depending on how it was prepared and processed. The chemical extraction of melanins from biological tissues markedly changes their properties whereas enzymatic extraction preserves those properties and is the superior way to prepare and study melanins. The figure shows scanning electron microscope images of melanins prepared from black hair in various manners: (A) by one acid/base extraction method; (B) by a different acid/base extraction method and (C) by enzymatic extraction. The acid/base extractions destroy the proteins associated with the melanosome and alter the molecular structure of the melanin. The authors conclude that melanins prepared in this manner are not biologically relevant and are poor models for studying natural melanins.