Pathogenically, single postzygotic mutations in the NRAS (neuroblastoma RAS viral oncogene homologue; MIM # 164790; at 1p13.2) proto-oncogene explain the occurrence of single/multiple congenital melanocytic nevi (CMN)s and melanocytic and non-melanocytic nervous system lesions in Neurocutaneous melanocytosis (NCM): these disrupt the RAS/ERK/mTOR/PI3K/akt pathways 1).