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To the Editor: Revertant mosaicism occurs when an inherited disease-causing mutation is corrected by a spontaneous genetic event within a somatic cell, followed by expansion of this reverted cell.1 This phenomenon has been recognized as the cause of milder-than-expected clinical phenotypes in patients with primary immunodeficiency syndromes or muscular dystrophy.2 In the skin of patients with the hereditary blistering disease epidermolysis bullosa, revertant mosaicism is manifested as small patches of homogeneously pigmented skin surrounded by skin that blisters easily (Figure 1).For years, the phenomenon of genetic reversion was thought to occur as a single rare event in patients with . . .