ABSTRACT
This chapter discusses genodermatoses characterized by hyperpigmentation. Congenital forms of hyperpigmentation with an increased number of melanocytes include disorders with multiple lentigines and nevocellular or melanocytic nevi. Congenital melanocytic nevi are present at birth or soon after birth. The RASopathies is a group of disorders arising from dysregulation of RAS-MAPK signaling and include neurofibromatosis 1 (NF1), Legius syndrome, LEOPARD syndrome, and Noonan syndrome. Dyschromatosis universalis hereditaria (DUH) is also an autosomal dominant genodermatosis in which, in about 50" of cases, there are hyperpigmented macules on the face. Linear and whorled nevoid hypermelanosis (LWNH) is assumed to reflect an underlying mosaicism or a highly variable genetic defect. The most intriguing differential diagnosis to LWNH is hypomelanosis of Ito (HI) in which the lesions follow the same pattern of distribution and occur at the same age. Incontinentia pigmenti (IP) is a rare genodermatosis that is usually fatal for male fetuses. IP is caused by mutations in the NEMO gene (IKK-gamma).
