In NF1, loss of the NF1 tumor suppressor gene that encodes the Ras GTPase-activating protein neurofibromin leads to the development of benign neurofibromas that are located on the skin (cutaneous neurofibromas) or can be deep-seated in large peripheral nerves (plexiform neurofibromas). This evidence concerns the gene NF1 and plexiform neurofibroma.