Monozygotic twins discordant for cutaneous mastocytosis

Cutaneous mastocytosis (CM) may be transmitted as an autosomal dominant trait.1In 1938, Dommartin2published a thesis on CM in twins in which he reviewed previous cases of monozygotic twins who were concordant for the disease. Then, he described one case in which only one of a pair of dizygotic twins was affected. In all of the literature we found descriptions of two pairs of dizygotic twins discordant for CM, eight pairs for monozygotic twins both of whom had the disease,3,4and three pairs of monozygotic twins discordant for the disease.3Moreover, a set of monozygotic triplets, all of whom were affected with CM, has been described.5We report a fourth instance of discordance for CM in monozygotic twins and review some possible explanations for this occurrence. Report of a Case Four-year-old male twins were seen because of fixed skin lesions, present in one boy,