Urticaria pigmentosa (UP) is a cutaneous form of mastocytosis that usually occurs sporadically in childhood and generally improves by adolescence. A large number of UP cases have been reported in the literature, but familial cases are rare. In fact, the disease has been reported in fewer than 50 families. Among familial cases, two pairs of dizygotic twins (discordant for UP), four pairs of monozygotic twins (discordant for UP),1,2 and eight pairs of monozygotic twins1,3 and a pair of monozygotic triplets (all having UP) have been described. We describe a ninth set of uniovular twins who were concordant for UP.
Report of Cases.
A pair of 16-year-old twin girls were seen owing to widespread trunk lesions. The lesions were fixed, pink-brown, maculopapular, and round to oval and/or polymorphous; they varied in size from 2 to 10 mm and were distributed over the trunk (Figure) and neck. The palms, soles,
Offidani A, Cellini A, Simonetti O, Bossi G. Urticaria Pigmentosa in Monozygotic Twins. Arch Dermatol. 1994;130(7):935-936. doi:10.1001/archderm.1994.01690070131025