NF1 and neoplasm: Neurofibromatosis type 1 (NF1) is a multi-symptom neurogenetic disorder caused by heterozygous loss-of-function mutations in the neurofibromin 1 (NF1) gene, which encodes neurofibromin, a tumor suppressor that inhibits signaling via the small GTPase rat sarcoma virus (RAS) subfamily of proteins.