Pigmentation and melanocyte supply to the epidermis depend on type XVII collagen

Genetic deficiency of type XVII collagen (C17), laminin-332 or type VII collagen causes epidermolysis bullosa (EB). Spontaneous correction of the deficiency, also known as revertant mosaicism, is caused by a second somatic mutation that restores protein expression resulting in clinically healthy (revertant) patches surrounded by fragile (mutant) skin. Interestingly, in some patients, patches of revertant skin show hyperpigmentation. To study the possible role of affected proteins in pigmentation and melanocyte distribution, we investigated clinical documentation and skin biopsy specimens of 13 revertant EB patients having correcting mutations in the COL17A1, LAMB3 or COL7A1 genes. Analysis revealed that lack of C17 led to decreased melanin intensity and melanocyte density in the epidermis when compared with the revertant patches. Reversions of LAMB3 and COL7A1 in keratinocytes did not influence clinical pigmentation or density of melanocytes. We conclude that in human skin, melanocyte supply to the epidermis depends on C17 expression in keratinocytes.