NF1 and neurofibroma: Moreover, in mice, conditional expression of oncogenic NRAS in neural crest-derived tissues leads to development of hyperpigmentation and neurofibromas [42], which are typical manifestations of neurofibromatosis type 1, a disease that sometimes presents with phaeochromocytomas and is caused by loss-of-function mutations in the RAS deactivator NF1 [43], indicating that NRAS mediates at least some of the effects of NF1 loss-of-function that cause neurofibromatosis type 1.